Document LJGJNxrNqkJxRpREg4GmYj6Qw

STATE OF MONTANA M O N TA N A BUREAU OF MINES AND GEOLOGY S. L. Groff, Director SPECIAL PUBLICATION 74 ELEVENTH INDUSTRIAL MINERALS FORUM Robeit L. Bite Department of Geology and Mineralogy Ohio Stats University 125 South Oral Drive Columbus, Ohio 43210 Lawrence E. Mannion Stauffer Chemical Company 1415 South 47 Street Richmond, California 94804 Patti L. Broughton Saskatchewan Geological Survey 1914 Hamilton Regina, Saskatchewan Canada S4P 3P5 Wylie N. Hamilton Alberta Rerearch Council 11315 87 Avenue Edmonton, Alberta Canada T6G 2C2 Milton E. Halter Alberta Research Council Petroleum Plaza 9915 108 Street South Tower Ed mon Ion, Alberta Canada T6G 2C2 Onth> E- Donn Subsurface Geological Laboratory Saskatchewan Department of Mineral Resources 201 Dewdney Avenue Eart Regina, Saskatchewan Canada 54N 4G3 lames A. Rhodes Stauffer Chemical Company 1415 South 47 Street Richmond, California 94804 Richard A_ Sheppard U.S. Geological Survey Federal Center Denver, Colorado 80225 William B. Beatty Building No. 44 Stanford Research Institute 333 Ravenswood Avenue Menlo Park, California 94025 Piter M. Peterson Raw Materials Development Division Burlington Northern, Inc, 509 Midland Bank Building BsUings, Montana 59101 Richard H. Olson 14618 West Sixth Avenue Suite 202 Golden, Colorado 80401 Alfred L Bush U-S. Geological Survey Federal Center Denver, Colorado 80225 Wilbert R. Danner Department of Geological Sciences University of British Columbia Vancouver 8 British Columbia Canada V6T1W5 M O NTANA COLLEGE OF M INERAL SCIENCE AND TECHNOLOGY Butte, Montana 1976 CPC-BCALTRSCPT00001094 THE GEOLOGY OF MONTANA TALC DEPOSITS Richard f t Olson* ABSTRACT Tale depona in the ftecambrian rock* o f Rjuthwestem Montana (Beaverhead and Madison Counties) arc unique wRIito the U.S. to th a t lame bodies of tremollts-free talc ore tan be Qpanqrit mined. All known deposite are in pie-Beitk n dolomite mat. The ctfeto I* suspected to be mciasomutfc, the sQioeeiis component having beep contributed by an intrusive body o f fteectnbiiBn granite gneias. frecarofernn defoitnEtion was extreme and s chare cteaized fey Multiple periods of folding and the flowsge of less competent rocks, rather than by fault'mg. Post-PiCumbrian folding ha* been negligible; the characteristic Lsrarnide sttu chare is block faulting along notthweit trends. The talc Is thought to have been formed to Precartbrkn time; the high-unglc block fault* have i rigniftasnes with regard to the formation of the talc but do tend to complicate mining operations, Tieroolrte-frec ta k ore bodies that have horizontal widths of more than 2D0 feet, vertical depth of several hundred feet, and strike kngthj of a mus* ss W mile are known to the Ruby and Gravelly Range*. Where dokMafte i* intorbedded with tremoUte-frcc talc in the Gravelly Kaigc the stale o f this relationship permits the use of ooflVCuittonal open-pit raining methods with subsequent upgrading by hamj-sottfag techniques. Underground mining has beso used in the past, but all cut rent Montana tak>xnintog operations at on the surface. The hand-sotted crude ore, some of which is shipped overseas, is f inely ground or micronlzcd to ro ll m bit and fluid-energy mills, The product* are diitribuled nationwide and abroad. TALC-MINING INDUSTRY The talc-raining industry, Eke that of many other industrial mineral commodities, has a complex and Varied structure. This is necessitated by th e fact that products made from stich ores have a multitude of uses; literally hundreds o f products, most o f them manufactured from roughly similar res, are currently a t the market. Talc, which has the composition 3MgO'4SiOt *H, O, is a valid mineral species and has long been recognized a such by mineralogists. The term "talc" , however, to talc miners, talc processors, talc salesmen, and talc consumers, covers a m ultitude of sins and when so used ay pertain to material that contains little or none of the mineral talc. Among such persons, the term "talc" raay be freely applied to any talc-like rock or mixture u f such rocks that can be used to manufacture products acceptable to a customer. sr Talc may be regarded as the pure end member of 4 series, soapstone being the impure end member o f that 3Crhs. Soapstone is a rock name, not a mineral name, and soapstone is generally composed predominantly o f ^ p u re talc containing relatively. minor amounts of CkrtuulUil, Sold bo, Oolondo. chlorite, mica, ami various amphjbole and pyroxene minerals. Treiualiti',which has a theoretical chemical compo sition 2CaO'5MgO'8Si03 tHj O, is, more commonly than not, the major component in "talc" ores, at the expense of the mineral talc Itself, which may be o f only miner volumetric importance. This relationship may hold throughout large talc-mirung districts, e,g., the New York and Califontia-Nevada districts. Other talc-like minerals (i.e., chemically or physi cally sinuhi) that may constitute various proportions of " talc" ores arc anthophyflite, antlgorite, chlorite, pyrophyllite, and serpentine. The mechanics o f the formation o f talc bodies and tite inherent compositions of the rocks from which such bodies have been formed dictate that some impurities will be present, even if one of the "talc-ilke" minerals are present; such indigenous impurities Include caldte, dolomite, tragnerite, and quartz. By " indigenous" is meant those materials that will be generated in situ by incomplete alteration to the mineral talc, i.e,, the reconstitution of rite pre-existing parent material with out any appreciable addition o f extraneous material. VSi;J*J CPC-BCALTRSCPT00001095 100 KUEVETH INDUSTRIAL MINERALS FORUM Many other Impurities may also he introduced and modified during epigenetic process! of mincralirattoa; the most common o f these are caleite, dolomite, graphite, hematite, limoniie, magnetite, pyrite, pyrolurite, quartz, and various sulfate, " Steatite" is a much-abused name, which means, unfortunately, different things to different people. It was originally a mtaeralogical name used to denote massive talc o r falcse rode. It has subsequently been used to designate a grade o f talc ore th a t am be used to manufacture electronic insulators, thereby having pri marily physical connotat ion rather than mlneralogical and chemical connotations. At one tne the term was even synonymous with soapstone, but the present meanings of these two terms agre far apart. In order to qualify as steatite-grade today, talc ore must contain less than 1.5% CaO, less than 1.5% Fej 0 $ , less than 4.0% A ljO j, and only minute quantities o f "other im purities', and It must be suitable for the manufacture of high-frequency electrical insulators. Virtually all o f this country's reserves of steatite-grade talc ore are in southwestern Montana. That grade o f tale is present in several other districts, but those bodies are compara tively small, and most must be mined in conjunction with the lower-grade ores, the market for whose products dictates the rate at which the steatite-grade ores nay be economically mined. The te im '" stcatite'` will not be employed in this taper in the discussion o f Montana's talc deposits. The term "talc" will be used in the mineralogies! sense for cures that are predominantly composed o f that mineral alone and contain little o r none o f the " talc-like" minerals. For those ores that contain measurable amounts of tremolite or other "talc-Hke" minerals, the term " talcrock" will be used. This usage is not an attem pt to establish aomendatural rules but merely a desire to accentuate the difference in purity between Montana tale ores and the ores from the other five major talcmining districts o f North America. High-purity talc ores, which can be mined as such without extracting other, lower grade ores and which can be used for the manufacture of high-purity talc products, are at present known in the United States only in southwesternmost North Carolina and southwestern Montana. Those in North Carolina are mined under ground; only In Montana may such ores be mined by open-pit methods at relatively tow cost. t i l e wxjliit Unit fetcmmtr scquR isicd w iib Ment&Aa's talc. depoaii* r a d th e ir Recriopy w hejt P 2 r , Ine., by w hom b e w as em ployed* p u rch ased S o u th ern Caftifornl* Mineral* C om pany, w h ic h v i i th e n , a* ITfcaer f t n o w , me o f th e tw o xs**3<h producer* of M ontana tale o m end ibcir product* It w ould so t be to all cf thorn I t i z mptojrce w ho w ittingly hared thelx know ledge, b u t Ivi, Jo h n V- B u rk , O tto P + Rohlfa, W*H*r W, W*id, and t , H. W ood In P& rtkulsj w orked In tke field w ith the w itter and their help a n d c o n trib u io na a n d good com pany are heiewttfe specificstily acknowledged- I>prtoc h it te n o re wftts Ftttsnr th e wjtitest km bad. th e pdvtisg a n d tits ple&auro of w o tking w ith Dr R u d o lp h M* H b g b sig an d Mr* C. F Joy* cortsuhajkia, b o th o f whom free ly ab ated th e reaujt o f th eir cmxdderabliK p rio r experience in th e M o n ta n a ta lc riid r i f t and m ade n u m ero u s extrem ely h elp fu l suggestions acid c o s irib utioeuu .A lte w M k with- F ilter the w riter w ai ptttfleged to p a r tld p s te In t b e imswtrvtei&n o f tw o P h ,P . disecrialkm fi a t Pcniaryb a ld a Sialte Univaxalty. Dia. Jo h n M- C axihas an d Aagelio F* OkoEBia xtudted th e esn iia l and ao atih tra parts o f th e R u b y Range, wwpectiYely* particularly th o se specific area* th a t eem to bar th e greatest potential for the discovery of co rntnerdal talc deposit*. T heir w ork w u a general area) stu d y encompajMfng m ainly stratigraphy. trueture* and general geology; it we* newer Intended that, they, by ibemfebea* solve th e rid d le o f ta le ganeabL T heir excejttimt ooriixibutiort (Ofcuxria, 1 9 1 1 ; Osyiha.ii,, I i7 3 > , however, serve a t t h e firm background u p o n w h ich *H f u tu re w ork o n tb e talc deposit* o i the R u b y f n g e w dl be based, Pfizer, lue-, deserves credit and sincere thank* for Ha generous support of t n * tw o Investigation. Mesata. F 4 Slevtrw , Jam es D , Mukry&n* a n d D onald F , K ennedy o f C yprus Industrial Mineral* C om pany have also Stared their knowledge over th i veers and have extended the courtesy o f conducting th e w riter on viatts to their nslnes and mill i Montana. Severa) geotogfertii o f th e 0 ,2 . Geological Survey* p a r t i e s laxly Mr. K e n n e th L. ^Wler an d Ms. K aren Shaw* have th ro u g h years of dedicated effort and detailed mapping im uch o f it tti.ll unpublished) co n trib u te d t o th e lw > v lrd ii o f tike extrem ely com plicated pre-Reltian stratigraphy and structure of the south* w estern past of tb e R uby Rang*, particularly tu tb e Christensen Ranch T ^-m late quadrangle. A partlcuJbwfy slgutfleant map (Jam es, Wler, a n d Shaw* 1969> was opei) <B*a p rim arily in oMe* to enhance th e know ledge o f p o ten tial talc-bearing areas fo r those econom ic, geologists th en involved jfri th e sesJrch f u r new ta lc m ines In th e R u b y Range* F o r m any m eat Lufornuitivc Kind con stru ctiv e suggestions, a s w ell a s the b en efits o f num ero u s pleasant field t ic u r c o iia , th e w rite r 1 fondly indebted to Mr. Wler an d M i .Shaw* Mr. W alter K , Sht-och, form erly I'r&tiderrt a n d Owner of S o u th ern C ahfoiuia MiocirmU Com pany, an d Mr* Ja m e s i>. Muirymii of Cyproa Industrial M inerals C om pany have kindly atppliod background isfonm atlon on the h isto ry o f th e grow th and devalopmeiit of the Mbotana talc industry, which it incorporated brio th is paper. Messrs, T o m MeOov<tt* and B e n n ett O w en o f DiDorx, M ontana, have been, involved in the prospecting fo r and tb* mining and proaaaiAns o f M ontana talc for m ora th a n fo u r drf-psdei betw een th e m . T h e y havs sirre d th eir eonsdd- arable have showed the w riter several depotita of wfalek be had n o t b een aw are, kutve p o in te d o u t feature th a t be h ad n u t been* an d have desoribed som e th a t h a d been deitroyed or mined out. Little o f th e Investigation* docum ented tn th b paper could have been nmde w ithout the cooperation of ranchers in the ajaa, partkrtilaily F red W. ( ''B uster^) Brow n and A ri C hrtrtensro of D illon, Montana* Botii o f th em fim* genPcTnen not only allowed access to ail o f their large land holding b u t aho accom panied th e w riter on many field trip and pointed o ut fi-PVAial features th a t w ould otbfijvri*e have gone uuktioivn to him* Mr. R aym ond Olson served ** a m ost capable field eadjtantr lu J974 an d made many itignJIicuti and maantugfu) contributiom to th is study* I i f J i * ' | I > \ , I \ f I * | \ j I { | CPC-BCALTRSCPT00001096 TOT C E O tO Q T O F MO S T ANA TA LC DEPO SITS--B , a OLSON 101 TALC VS. TEEMOUTE CONTROVERSY Rightly or wrongly, in recent governmental inves tigations into health and safety n a tte rs tremolite has been likened to asbestos. The results o f a symposium on the health hazards o f respirable dust in the mining and milling o f talc and "talc-like" ores, convened by the UJS. Bureau o f Mines in Washington, D.C., on May 8, 1973, have recently been published (Goodwin, 1974). This and other such investigations have led many consumers to switch. From products manufactured from tremolitic ores to those manufactured from high-purity talc ores, such as those mined in Montana. The production o f talc ore in Montana has more than doubled in the peiod 1969-1974, gad much o f that sharp and relatively sudden increase must be attributed to that factor. While "the jury is still out" on this controversial matter, the Montana talc-mining industry stands to benefit at the expense o f all the other districts, with the possible exception of North Carolina. USES Talc products, whether manufactured from highpurity talc ores, troolitic ores, or other types of "talc-like" ores, are numerous and have myriad uses and applications. These are well docum ental in the literature, particularly by Johnstone and Johnstone (1961), Cooper and Hartwell (1970), Olson (1970), Wells (1972), Patton (1973), and Roe (1975). The natural color of Montana tabs ores ranges from white or very pale green at the lightest to dark green, greenish gray, or even black at the darkest. In most o f these ores, except for the darkest ones or the ones containing graphite, the color (whiteness) improves noticeably upon fine grinding {particularly in the 5snicron size). Blending o f darker ores w ith some of the lightest ores can extend the life o f ore bodies. Darker ores may be used in place of lighter ores if color is not a particularly important product specification, The ceramics, paint, and paper industries consume more than half the dollar value o f tale products currently sold In the United States, and it is in these three industries that virtually aQ o f Montana's talc products are used. It is the development o f high-quality pigment-grade products that has enhanced the rapid growth of Montana's talc industry in recent years, and these product hues have been brought about by the development of extremely fine grinding or "mieronizing" techniques in "jet" or fluid-energy mills. Many rtf the Montana talc products currently sold by both present producers will have mom titan 50% of their weight in the --4 micron size, and almost all o f them Will have considerably more than 50% of th en weight in the --10 micron slate. OTHER NORTH AMERICAN TALC DISTRICTS Before embarking upon a description o f Montana's talc deposits, it would be well to briefly describe the other five major talc-mining districts o f North America and to cite similarities and differences, so that the reader wiH then have a background for comparison. The geological settings of talc deposits In the United States and Canada are as varied and diverse as would be expected for any naturally occurring mineral tDmmodity, but there are some broad similarities. First, 1a*c is invariably a secondary mineral formed in situ from pre-existing or introduced material or both- Second, commercial bodies are generally tabular and concordant (at least in the overall sense, If not everywhere locally), ^ in8 "molded" after the shape o f the parent material, whteft is generally a sedimentary or meta sedimentary rock unit, Third, most o f the talc ore bodies occur within Preeambmn rock units; the few that do n o t are ^ ro<;k units no younger than Early Paleozoic age. Finally, in almost every deposit where genesis can either be firmly established or confidently inferred, the time of the talc formation is Ptecambria as well- The reasons for th b almost total restriction of talc to the Precambrian in both space and time are unclear. It may be easier to understand in the case of ultranafk rocks, for they may be much more abundant in the Frecambrian than in younger rocks. It is somewhat more difficult to understand with regard to dolomitie rocks, for they are certainly much more common in the Cambrian and younger systems than in the Preeambmn. It m y be that deep burial and the consequent conditions o f dynamic irsetamarphism could have attained sufficient intensities only during the Precambrian; such a theory would perhaps explain the formation of talc in Montana and New York, for instance, but would probably not be applicable to some of the other districts, which have undergone deep burial but do not show conditions o f pi ,.-3 i CPC-BCALTRSCPT00001097 JTLEVENTK iN D trsT B IA I. MINERALS F O E U il extreme dynamic metamorphism and isoclinal structure, such as are common, for instance, in Montana and New York. It seems safe to say, however, that even though conditions o f dynamic metamorphism have not neces sarily been attained in all six districts, or at least cannot definitely be proved, conditions o f burfal beneath miles of rock cover have been attained in every district. The answers to w hat conditions lave effected the origin of talc m ay well have to await sohtUcai by workers in academia, for few economic geologists have the time and the resources to devote to such problems. Until such questions are answered a should suffice to say that if one wants to find talc in commercial quantities then one should restrict the search to Precambrian and possibly Early Paleozoic sequences in geosyndinai areas; in other words, stick to "elephant country" ! The six major tale-mining districts in the United States and Canada are: New York, Vermont-Quebec, N orth CaroiLmi-Georgia-Alabama, Texas, CalifornkNera da, and Montana (Fig. 10*1). The history, geol ogy, and several other aspects of the first five districts will be treated briefly below; Montana wfll then be described and discussed in detail. NEW YORK talc in the United States by the U.S, Geological Survey (ChhJester so l others, 1964) Indicated that New York then had almost 75 percent o f this country's `"measured and indicated" talc ore and about 4 0 percent o f its "inferred talc ore. All of the known talc and talc-rock lies within a narrow belt, which probably averages only 500 feet in width and is only about 8 miles long. The bedrock complex o f the Gouverneur mining district consists exclusively of metamorphic rocks of PreCumbrian age (the Grenville Series), but two specific types, namely, gneiss and marble, dominate. The gneiss is the older unit and Is about 3,000 feet thick; the marble Is the younger unit and has a maximum known thickness of about 2,000 feet. Thin sheets and lenses o f amphibolite occur within both the marble and' the gneiss but are minor in total volume. Brown and Engel (1956) subdivided the marble sequence into fifteen units, of which only Unit #13, the " talc unit" , is known to contain commercial deposits o f talc, tremolite, or zinc minerals. Unpublished geological investigations indicate that the composition of most o f the marble in the district is relatively simple and probably docs not and did not differ greatly along strike. The " talc unit" , a dolomitlc marble, shows evidence o f being only 250 feet thick in its least contorted areas; greater thickness maybe due to structural flowsge. Talc was first produced and milled in the United States in northern New York in 1876 between the towns o f Fowler and Animat in $t. Lawrence County, Before the turn of the century this operation became known as the International Pulp Company, which changed its name to the International Talc Company in 1944, and was acquired by the R. T. Vanderbilt Company in 1974. The Gouvemeur Talc Company, a Vanderbilt subsidiary from the beginning, began opera tions near the zinc-mining town of Balmat in 1948. M o t to their acquisition o f International Talc Company in 1974, Gouverneur shared with them in the New York talc district's annual production on an approx imately 50-50 basis. The New York talc district has long been and stai may barely be the most important in the United States in terms of total annual production. It is most peculiar that this district, although dominant in pro duction for the last century, and even more dominant in terms o f proved and potential ore reserves, k the smallest in area o f aH six talc-mining districts in North America. All of the known commercial talc and talc-rock occurs within the Balmat-Edwards or Gouverneur mining district. A comprehensive study of The zinc and the talc ores occur within the same stratigraphic unit, but not together except at a few localities. Locally, the siliceous dolomite o f Unit #13 has been converted to tremolite under conditions of dynamic metamorphhmor metasomatism; subsequently, tele, anlhophyllite, and serpentine have locally been formed from the tremolds. In the northeasternmost part of the district, anthophyllite may locally be the major constituent o f the ores. New York talc ores are commonly more than half tremolite. Tremolitk ores have been proven b y under ground workings to down dip depths o f at least 1,100 feet and by wire drilling (generally in the search for commercial zinc deposits) to dewndip depths o f more than 3,000 feet. Mineable bodies o f almost tremolitefree talc (pbty or "scaly" variety) have been discovered and recently exploited in mines near Talcvlile; these, however, are near the hanging-wall contact and are difficult to mine by themselves, so their scale of production tends to be directly related to that of the tremolitic ore being produced at the same tim e. Field mapping by U-S. Geological Survey workers has indicated that the tremolite and talc and associated minerals were formed prior to i .0 x 1G9 years ago. fI I i i I t l I i 1r CPC-BCALTRSCPT00001098 T H E G K O L O O Y o r M O N T A N A TAt,C U P O S t T S - R , H, OLS0N 103 CPC-BCALTRSCPT00001099 UN E LK V NTH IH liU ST H IA L MTH7.RAI.S FORUM The zones o f eoimserdal laic-rock locally pinch and swell, but they are on the whole conformable to the dotom itie marble layers. The region?.] dip is about 45" to the northwest, and departures are only locally significant. Tight and contorted cross-folds superimposed upon the main talc belt have locally resulted in the thickening o f th e talc-rock sequence by at least 50 percent. All o f the rocks are complexly folded, and metainGipbL-sm to the amphibolite fad es is common, if indeed not ubiquitous. Both open-pit and underground mining methods are employed, A large crushing facility is installed within one underground mine. The deposits of the New York talc-mining district may well constitute the largest reserves o f tremoUtictype ore in the world, for nothing described in the literature a t the present time is o f rirniar magnitude. In th e late !9<50's the total production o f the New York taio-mining district was on th e order of 225,000 tons annually. Although the most resent production figures issued by the LF.S. Bureau of Mines group New York's production w ith that of several other states, it can be safely inferred that New York now producing on the order o f 250.000 tons annually. New York talc ores are milled as is, i.e., without any beneficial ion of any sort. Milling Is accomplished in ball mills and in fluid-energy ("jet") mills and the product is then air-classified. VERMONT QUEBEC The district that Is commonly known as the Vermont Laic-mining district runs through the central part o f th a t state but also extends southward into Massachusetts and northward M o Quebec. Bodies o f ultra mafic rock have been intruded into a sequence of phylllte, schist, gneiss, greenstone, and amphibolite rocks; the uHramafic bodies have been locally serpentinized and partly converted into talc. These talc-rock deposits are commonly associated w ith dunite, peridotite, and serpentinite, which were probably the parent rock. These ultraijafic rocks "form part of a belt more than 2,000 miles long, which extends from Alabama to Newfoundland" (ChJdester and others, 1951). The talc-rock itself is more o f a talc-carbonate complex, which locally grades into a carbonate complex rich in magnesite. The talo-rock is dark, g a y to dark gray, has a schistose structure, and is relatively high in t o n content. The mineral talc itself is minor in all the known deposits. The ultraxnafic bodies are as much as 1 mSe in width and as much as 3% miles in length (Crudest and others, 1951). The commercial bodies, which occur hi those ultramafic bodies known as the "verde antique" type, are zoned around re s of serpentinite. The talecontaining zone (" steatite zone") forms the outer shell or zone of the body; between it and the serpentinrte core is the "grit zone'*, which. Is commonly several feet to several tens of feet thick. "Grit" is the miner's term for rock that is composed of talc and carbonate minerals only, Although there are few masses o f high-purity talc in the Vemimit-Quebec district Large enough to mine as such, trcmolitc is not known, and talc itself is the only laic-like mineral contained within the ultramafie bodies. The major problem hindering the production o f pure talc is the fineness o f Its physical admixture w ith its contained impurities, In northern Vermont, entire ultiamafic bodies have been converted into grit and have widths on the order of 100feet or so;in southern Vermont one similar body has a width of about 175 feet, In the state of Vermont alone at least 145 occurrences are known. In an area having a strike length o f about 150 miles and a width ranging from 5 to 25 mites, Homoelinai folding is the regional structure; isoclinal folding is thought to be uncommon, for little repetition by folding has been noted. Few workers have attempted to date either the host rocks of the Vermont Me-bring district or the time of steatization, but studies by Christman (1959) and Christman and Secor (1961) suggested that the age of the parent rocks is Early Paleozoic, probably Ordovician. Open-pit ruining has been done in the past, but in recent years all production has come from underpound workings, some of which extend to vertical depths of more than 1,000 feet. The ore reserve situation in the Vennont-Quebec district has never been seriously investigated by anyone who would be at liberty to disdose the results o f such a study-Proved ore reserves probably do not exist, for these producers seldom block out tonnage far ahead o f the producing faces. Judging from the geographical distribu tion of the known bodies in Vermont atone, however, the reserves o f tale-rock must be extremely large. Producers have historically had the choice of grinding the talc-rock as mined and processing it for F 1 | ] 1 j ! CPC-BCALTRSCPT00001100 THE GSO LOGY OF MONTANA TALC DEPO SITS-K, H. OLSON 10& relatively low priced dusting compounds and fillers o Several talc occurrences and ore deposits are of bensficiating the taknrock by flotation or other known between Murphy in western N orth Carolina means in order to derive high-value products containing and Dadeville in eastern Alabama. Compared with those major amounts of the mineral talc. If one wants to of the other major talc-mining districts, these are manufacture the most profitable product line in this relatively smalt deposits, but some o f them axe im district, he is faced with the necessity o f employing wet- portant in th at they are of high quality and serve processing benefication techniques*The Eastern Magnesia specialized consumer needs, Talc Company, lrtc. (now Engelhard Minerals ami Chemicals Corporation) has been using wet-benefiesation. NORTH CAROLINA methods on ores near Johnson* Vermont, since 1937. The ore is subjected to froth flotation, then dewatered The Murphy Calc district is about 85 miles long, la a rotary vacuum drum filter. The filter cake Is then extending from southwesternmost North Carolina Into dried, pulverized, and air-classified; Hanab (1955) has northern Georgia. Although talc is found in sedimentary described this operation in delaiL Eastern Magnesia rocks and also associated with ultramafic bodies in Talc Company, Inc., established another, much more North Carolina, it is only those in sedimentary r o d s 1 modern froth flotation plant at West Windsor, Vermont, that are o f commercial interest at present. The host in 1964; since 1972 this operation has been know as rock for these ore bodies is the Murphy Marble, which Windsor Minerals, Ino., a wholly owned subsidiary of is generally more dotoraitic than ealdtic. Although the the Johnson & Johnson Company. Trauffer (1964) has marble has been reported to he as thick as 400 feet or described this operation in detail. so, such thickness may be caused by structural defor- rrEtion and therefore may be totally anomalous. The The U. Bureau o f Mines noted production of Murphy Marble in the vicinity o f Murphy, North 251,087 tons o f "talc, soapstone, and pyrophyllite" in Carolina, has been divided into as many as eleven f Vermont in 1973. zones, only one of which (about 45 feet thick) is known to contain commercial talc deposits. Little QUEBEC information is available about the geology o f the marble belt and its talc zone in areas away from mining activity, Deposits ill the serpentine belt of the Eastern Townships of Quebec have been described as being probably because climatic conditions cause outcrops to be few and far between. altered from peridotite. These deposits are simitar to those in Vermont and have been described by previous workers as " soapstone" . Baker Tale Limited in Highwaier, Quebec, used to mine such ore and dry-grind it for low-grade low-value filers and dusting compounds. In the 1late 1960's wet-procsssing methods were intro duced, particularly froth flotation and high-intensity wet magnetic separation; consequently, products now being manufactured from the same ores are being sold to the paint, cosmetic, and paper industries at consid erably higher unit values. Despite the relatively small size o f the North Carolina talc deposits, the operations can be profitable because the purity and the color of the talc are extremely high and the products can compete w ith those manufactured from Montana talc ores m the only pure talc products of high color in North America that can be produced without the use o f wet benefldatlon methods. Tremoltte is minor; indeed, even talc formed after (rejnolite, which is common in most other districts, is rare here. NORTH CAR OLINA G EGRGIA-A LAIIAMA Although several deposits of talc and soapstone ate known in the Appalachian Mountain province between Vermont and western North CarpHna, none of them have such a history o f past or present production, nor in the w riter's opinion the future potential, to even suggest the possibility of their becoming major talcraining districts. These occurrences in Massachusetts, Connecticut, Rhode Island, New Jersey, Pennsylvania, Maryland, and Virginia were described by Chidcsier and others (1964). The talc seems to have originated by "relatively simple metasomatic processes" (Chid ester and others, 1964). Although the white talc-bearing zone in the Murphy area Is dokwnitic marble, which is locally "slightly sandy", Van Horn (1948) did not believe that the parent material contained sufficient magnesia and silica to permit the talc to form by dynamic jTBtarnorpiusin alone. Owens (1968), however, on the basis o f a petrologic study of diamond drill cores, felt fla t the talc is of nsrtamorphic origin. The age o f the Murphy Marble has not yet been definitely determined. The general consensus, however, is that it is either latest Precambrfan o r Chmbro-Ordovirian, "f !v ; K Jf 1L ip . -'b i J CPC-BCALTRSCPT00001101 IftS EUVKHTH INISTRIAJ, MINERALS FORUM Both open-pit and underground mining methods iwv been employed in the past, but recently the trend fas been toward deeper underground mining. The developmental costs of shaft-sinking to relatively small sie bodies are among the highest such costs known to 0 writer, further testifying to the superior quality of these carbonate-derived ores. Production figures for North Carolina talc are tomped together with those for pyrophyllil e and soap stone by the IJ.S. Bureau o f Mines in the Minerals Yearbook, making it difficult to determine tha levels of talc production, but in recent years the total production o f all three has ranged from 80,000 to 100,000 tons annually. Because North Carolina ha* in recent years been the only domestic producer of pyrophyllHe, it is likely that North Carolina** talc production is less than 50,0D0 tons annually. North Carolina is st present the only domestic producer of talc crayons or welders pencils, a relatively minor but w arem dy lucrative product line, operations have historically been tempered by the presence o f adverse surtida! staining; mining operations are now conducted underground. The principal product lines have been crayons and finely ground products of both dark and light colors, but at the present time only the latter are being produced. The U.S. Bureau of Mines stated (Minerals Yearbook) that the production of '`talc, soapstone., and pyrophyllite" I Georgia in 1973 am ounted'to 38,000 tons. ALABAMA Pure white talc is mined near Wuiterboro in Talladega County, Alabama; as far as is known, all o f this production goes to cosmetic and pharmaceutical uses. The parent rock is a carbonate sequence of probable Cansbro-Oriovidan age, which underlies the area, but the geological relationships are far from clear (McMurray and Bowles, 1941). . Work being conducted by the North Carolina Stale Minerals Research Laboratory on the possibilities of beneficlating talc-rock from those deposits associated with wltraroafic rocks is reportedly encouraging. Further advances in the wet benefication of talc-rock ores would increase the prospects that such deposits, which are similar to those in Vermont, would become of economic interest. GEORGIA A few occurrences o f talc are known in the Canton area in northern Georgia, which is the soutlrwestemmost part of the Murphy Marble Belt, but Georgia's principal tak deposits are in Murray County. Individual talc deposits may be teas o f feet wide and several thousand feet long and may extend for several bundled feet downdip (Crudest and others, 1964). Fur cron and others (1947), in the m ost dots Lied investigation to date, cond ud ed that the tele has been formed by the alteration o f dolomltic portions of the Cohutta Schist of Precamb riart age; earlier workers, however, believed that it has been derived from peridotite. Needham (1972) thought that the soapstone and other talcose rocks o f Murray County were formed by serpentmization, followed by metasomatism and metamoiphism. Chidester and others (1964) stated that ultra mafic bodies are not rare in Georgia, but no talc is known to be associated with them. Talc in Murray County was discovered about 1872 and mining was begun shortly thereafter. Open-pit Talc and anthophyllite asbestos deposits, first noted in 1873, are present in Tallapoosa and Chambers Counties, Alabama, where they are associated with ultramific bodies (Neathery, 1968). The talc content ranges from 3 to 26 percent, probably averaging 20 percent for the better deposits,and anntttlproduction is about 5,000 tons (Neathery, 1970). Neathery and others (1967) have described ftotation-concentratio n feasibility studies, which show that "good-grade talc concentrates** can be made from these ores, b u t the economics of such an operation are yet to be proved. TEXAS Texas has two talc districts - the Llano district in the central part of the state and the Alla moore district northwest o f Van Horn in the westernmost part of the stats. The latter district, the more recently put into production, is now the only one of importance and is the only one that will be discussed here. The Allamoore district extends about 20 miks east-west and is as nmcli as 5 nudes wide. Its ore deposits are in the Allamoore Formation, o f Precambrian age, which consists of "thousands of feet" o f carbonate rocks, volcanic rocks, and phyUite (King and Flawn, 1953). The talc is associated with dolomite, but it may be observed to intergrade with phyllitejn certain parts o f the district. The talc-rock deposits are large tabular masses, which pinch and swell to widths as great as 3TO feet and may be several thousand feet long. The strata, which are ill the lower plate below a large overthiust fault 1 [ i CPC-BCALTRSCPT00001102 TIES G E O LO O T O F MONTANA TA LC UETOSlTS--S - H. OLSON 107 (the upper plate having been almost entirely eroded), ate vertical or dip steeply to the south. No ore body of which the writer is aware has ever been "bottomedout" b y either drilling or mining. Large iron-oxidestained "horses" o f either carbonate rock or volcanic rock are fairly common but are generally easily elim inated b y the use o f selective mining methods. Talc is commonly found "from the grass roots down", and the soil cover is generally less than I foot thick. Caliche is abundant in the uppermost 5 feet or so o f these dark ore bodies but seldom causes any problems at greater depths. Petrographic and X-ray studies of the ores indicate that tremolEte is not present t any significant degree but dolomite Is so finely admixed with the talc as to make it extremely unlikely that pure talc can ever be produced from the known ore bodies by present betefidation techniques. There is little Indication of a hydrother mal origin for these ores. The talc ore (ceramictype) is generally strongly foliated, the Individual foliae ranging from paper-thin to as thick as V* inch. This dark Texas crude ore looks little like talc ore when one first visits the district, even to the trained observer. Hie first impression is to Identify tl as black shale or perlite or some other non-ialc-bearing rock. Despite its dark or even blade color and its "non-talc look" , however, this talc-rock is a superior ceramic erode ore and has superior pressing qualities and excellent firing characteristics. Flawn (1958) described the district In a stage of infancy, ami King and Flawn (1953) described in detail the overall geology o f the district and the surrounding areas. A more recent detailed study has been financed by the Texas Bureau o f Economic Geology, but the results have not yet been compiled and made available. AD o f the production has been from large open pits, w ith the exception of minor amounts o f lightcotored (generally pink to white) talc, which have been mined in small underground workings and then finely ground into filler and extender products. Almost afl of the ore produced is shipped out of the district to the east, and even into Mexico, as crude unprocessed ore for use in the ceramic industry, particularly for the manufacture o f wall tile. Mining costs are probably the lowest anywhere for talc ores, Flawn (1958) gave the " costs o f mining, transportation, and loading into cars" as ranging from S i-75 to 3.00 per ton, and it is unlikely th at these costs hay subsequently increased more than would be expected from inflation and increased labor and equip ment costs. It is by far the youngest of all the major talc mining districts o f North America, for production commenced in 1952. The U.5, Bureau of Mines credited Texas with the production o f 232,514 tons o f ore in 1973. CALIFORN1A-N1VA DA Of the major talc-mining districts o f North . America, the one that combines the largest area with the greatest number of productive comnwrcial deposits is the one fn southeastern California, which barely extends northward into Nevada. It is about 200 miles long and has an average width o f 30 intics hut is locally as much as 75 miles wide. Engel and Wright (I960) divided this long "belt" Into three separate areas, each of which contains a slightly different characteristic type of deposit. This district is too large and its geology too complicated to be satisfactorily summarized within the scope o f this paper, in general, however, all the deposits have been formed by the "metamorphism and hydrothermal replacement of siliceous and sillcated magnesian marbles and limestones" (Engel and Wright, I960). The deposits come in ail sizes. The WesternAcme mine complex near Teeopa in San Bernardino County, California, is more than 5,000 feet long (although locally severely complicated by cross-faulting) and as mush as SO feet wide and has been mined downdip for at least 350 feet. The deposits in the southern two areas occur In Frees mbiian sedimentary rocks, were probably formed in Preeambrian time, and are spa felly associated with a thick diabase sill intruded near the base o f a widespread carbonate member. In the northernmost o f the three areas, which has not been historically as important a producer as have the other two areas, deposits occur in Lower Paleozoic formations and are thought to have been formed by replacement processes, probably in Cretaceous or Tertiary time. There are two main types of ore in this district: the " hard" ore of the miners is tremolitlc, and the "soft" ore is talc schist. Many deposits contain both types, but their distribution is erratic and unpre dictable, Most of the ore is markedly trem olitk, but there are some relatively small bodies of high-grade talc. The problem with these high-purity tele bodies, however, is that they generally cannot be mined by themselves, but must be extracted along with the tremolitic ores; therefore, the production of high-grade talc in CaliforniaNevada today generally has to be a function o f the production of tm nolitic ores to supply the market for their products. h .U4 - ,i CPC-BCALTRSCPT00001103 lOfi ELEVENTH IND U STR IA L NUMERALS FO R U M Most o f the mtiling in the California-Kevada district has been done underground, relatively little mechanization is involved, and limbering costs are high. A small proportion o f the district's production has been obtained by open-pit mining methods, but most such operations are decidedly sporadic. In no other talc-mining district anywhere sa North America are the mines so far from rail transpor tation as those in the Califomia-Ncrada district, but It serves mainly 2 special local market, especially southern California, and seemingly can meet and beat the current potential competition from other districts. Mills and Other processing facilities re not located at or near the mines but in the Los Angeles area 01 at various points along th e tw o railroad lines serving the Los Angeles area. Haulage routes to either a processing facility or the railroad are on the order of SO miles or more. Soapstone was mined from small deposits along the foothills of the western Sierra Nevada in the mid-ISOO's, but the current California-Nsvaria talc mining district was established during World War I, when the area around Darwin In Inyo County, California, supplied block-grade steatite talc to compensate for the temporary elimination of foreign supplies. California production slacked off in the post-war period b u t was rejuvenated during World War II; since that time, however, California has not been a significant factor in the supply of steatite-grade talc. In the mid-1930's the use of California trem olale ores for the manufacture of wall tile began to come into its own, and th e ceramic industry became the major market, as it is today. The talc content of sudi ores is not critical, and a consider able amount of carbonate material can be tolerated, indeed may even be desirable. HISTORY OF THE MONTANA TALC INDUSTRY T he only prior significant description of Montana talc deposits in the literature is that of Perry (1948). This excellent work, however, was compiled and pub lished in the very early days of the Montana talc industry, In the almost thirty years since its publication that industry has undergone a period of amazing growth and development; therefore it is thought appropriate to present here some o f the available background on the history of that period. Much o f th e credit for the growth and develop ment o f the Montana talc industry belongs to two fine gentlemen who recognized, among other things, the unique quality o f its ores and by their intelligent foresightedness, hard work, and perseverance paved the m y fo r the current prominent position of Montana is N orth America's talc picture. Mr. Henry Mulryan (deceased, formerly President of Sierra Talc Company) and Mr. Walter K. Skeoch of Honolulu, Hawaii (formerly President o f Southern California Minerals Company) began their involvement with Montana talc in the 1940'$ and are hereby acknowledged as the pioneers of th a t Industry. Mr. Skeoch and one of Mr, Mulryan' sons have been so kind as to supply invaluable back ground inform ation regarding the history o f their contributions. The following information concerning his p i t in the growth and development of the Montana talc industry has been supplied by Mr, Walter K. Skeoch. . . "During the summer of 1942, the ecEHnetaUicr division of the O.S. Bureau o f Miner alked me to mvest^ate and, if possible, develop a rnwil outcrop of talc near Ennis, Montana, Samples from the Johnny Gulch o u tu ap and from a small exploratory pit were sent to several `steatite ceramic' manu facturers who were then trying to find an American sour for Mock talc. They indited ibis was necessary for the supply of spacers or divider* used te radio filament lamps. They were dependent on imported material called 'Wondifstono' from Africa, which was satisfactory for gas lite tubes but could w>t withstand the high-intensity shock required for o rb products, The samples were interesting but almost at! had Cine hair cracks when sawed into shape. The open pit proved latonioui, so a shaft was sunk Mid exploratory drifts driven. The market was for 2 " x 2 s* x S " blocks and we wore offered to IQtf per pound for bluets sawed to sixe and delivered to railhead. The Vermont talc suppliers could supply such products, hat the iron content was too high. The manufacturers refused to buy the ground materh.110 we wore obliged to cancel our lea when the owner, t Mi. Clark, would not sell the property. Siena Tate was later ssccessfinl in parcnasing the property sow known as the Yellowstone Mine, Front that cxperieii we learned o f an outcrop o f talc southeast o f LUion, Montana. No work had been done upon this property, and w purchased the mineral rights from 4 rancher, Mr, Clyde Smith, The original purchase of 40 acres was located in Axes Canyon. Originally we explored underground by vertical shaft and laterals and later by open-cut methods. This property, the Sindth-DEUon Mine, produced a very pure talc that was much in demand as a steatite ceramic materMl The . U.S. Government stockpiled forty carloads o f it for emergency use. The property was worked coraUnuntmly from 1943 until five late 1960's, after the sale of Southern California Minerals Company to Pfizer, Inc. A second 40 acres was purchased from Mr, Smith about I960 but did not prow productive. Our Ogden, Utah, mill was completed in 1944. At first only a Raymond roller mill was installed, then later a high speed Raymond hammer mEI; stifl liter Fins Pigments Corpo ration produced the extremely low-raieran talc `399' at this facility. It I CPC-BCALTRSCPT00001104 THK GEOLOGY O F MONTANA TALC DEPOSITS--it, It, OLSON 108 The Barrette,* Montana, crushing plant was instailed la 1943. The intention was to blend the Montana tales at Ogden, Utah, "with mads whiter Caitforitla ore -- this w a done successfully ioi the paint and paper trade. Then better tale was developed from the Stone Crede chums (Treasure State Mine) purchased from Mr, Claude Brown in 1952. U t Barrati mill uraj eampfcted in December 1954 with a targe Raymond roller mlB, a highspeed Raymond trammer mill, od a large Xidwefl talli for H nc Pigment Corporation. A t that time, star ling In 194? and Lasting until 1965, Fine Pigmenti Corporation was owned 60% by Tri State Minerali Company fa divdo of Southern California Minerals Company) and 40% by Whittaker, a irk and Pamela Company, the o f New York City, Tri State Minerals Company purchased the W.CJJ. interest ta 1965. The Ogden mill was closed and most o f th at equipment was moved to Barretts, but some o f the equipment was moved to a new modern mill built at Dunn Siding. California (on the Union Pacific) in 1964-65 by goatheM California Mineral* Company. Several other talc daini* la Montana were pnrahased during the period 1946-1966. The largest, and the only one of these mined, i* the Keystone-Regal, east o f B ilo n , Montana, purchased In 1947, The property wal explored by a vertical draft 110 feet deep and 100-foot long tunnel* driven hi all four directions --eff m fa/et This may be the largest body o f talc on recoid. The quality ceB eitt, b u t not o f such a good color as arc the Stone Credit grades (Treasure Chest Mine). The odor on all die Montana grades was w ry much improved by the installation o f sorting belts and vibralingscreen ring devices and magnetic separators. An electric lotting falde was installed bat w discorded, u the mattimi mainte nance w ork required wa* to great." In February 1966 Mr. Walter K. Skeoch sold Southern California Minerals Company to Pfizer, Inc. of New York City. Its Montana talc mines and mill haw been operated since then by the Minerals, Pigments, sad Metals Division o f that firm. Mr, Henry T . ("Joe" ) Mulryan is President of Cyprus Industrial Minerals Company, the successor of S ena Talc Company. His brother, Mr. lames D, Mubyart, to Western Area Production Manager of Cyprus Industrial Minerals Company and is In charge of that finti's Montana talc operations, based mi Three Forks, Montana, and has supplied the following information concerning, among other things, his father's f a rt in the development and growth o f the Montana talc industry. "Tbs originai name o f the Yellowstone Mine was the Mountain Talc Mint). Sierra Talc, largely through iny father' effort*, acquired the property in 1948, Tbe mine was renamed the Yellowstone Mine a t th at time sad the story behind this b that Henry Mulryan and Otis Booth, both, of S ta n . Talc, drivlojj to Montana to Look over the property after haring acquired I I One commented to th e other that duce they bad t*0* bought the mine, they ought to figure out seme sort of a aure for it. A bout that time, there was occasion fot a *Sb*Ud B a rretts on C to o n W est T ri-m inuta quadran gle panic-type stop la the ear they were driving, and a bottle of Yellowstone whiskey, which had been under the front seat, rolled o u t and hit the passenger eti the foot. They felt that this must have been an omen o f some sort, and the mine was named Yellowitemi Mane. I t is therefore named for the Yellowstone whiskey, in spite of tine fact it is only about 50 miles h a m Wert Yellowstone, Montana. Cyprus took over tile mine in late 1964 when tin ? acquired Sierra Talc. Tire Beaverhead Mine was discovered by a group including Bennett Owen and Bob Dutton. This property was nothing more than a prospect and was purchased by Sierra on a lease option in the early 1959'. Mere again, Cyprei took over this property in 1964 when they acquired Sierra Tale, 11 Yeltewatoire Mine began with Mr. I_ F, Tmiisch's operations as a small underground glory-holing type o f operattonThe talc Wat beta mined primarily in the Week lava area where there was a high percentage of manganese dendrite. This material was being w ed in the electronic industry fur tire manufacture of non-fired ceramic, pieces, such w insulator time* for Mgh-freqseney electronic tubes. In the late 1940's, when Sierra look over, there was some extensive underground Work, primarily to tty to dehneste the deposit and ta find out whether open f i t mining was fteasihle rad also to grit some larger samples than we hsd had in the past to work with, in our lab to dotermini! what could be done with the talc. In the early 1950'* tire mine wjn opened u p as an, open p it and there has been no underground weak since. A t the Beaverhead Mine the previous owners bod done very little. If anything, other tiswt asseasment work. In tire mid1950's, when Sierra took over, some exploratory underground work was done. In the early 1960's aaseuaneat work was beta* doiwiu the form of stripping, with the idea of eventually opening up the deposit. By the late 196i's the mine waa opened up for opea-pii operations and all underground work cessed. This mine operates mt a seasonal bash normally because o f tire altitude and weather conditions at that altitude. A t the Yelkjwrtone Mine all of the tele shipped front the mine hand sorted. The Oral sorting shod was iiutalkd in either tire 1st* 1940's or early 1950't In this shed tire waste is picked from the tale by tile sartsn. A new sorting died Wo* built in 1958-59 and the reason for tills w as to reprove the facilities as wed as to increase the capacity. In 1971 w e installed a p it sorter, t i we cal! it, Into which the lower-yield material is fed and the talc is picked from the waste. Basically, this is the fnocesdng hMory of the Yritowrtone Mine at the mine rite. At tire Bewreitewd Mine there were no facilities o f this type untB 1974, at winch time wb put in a ptiot-sfea pit sorter, which differ from tire Yellowstone pit so rt in B ut bcridaOy the need to pick watte Is lower at tire Beaverhead than it 1* at the Yellowstone; therefore, the process more resembles the sorting shed at the Utter than it dons tire pit sorter. Certain difficulties with tire Beaverhead ore required, however, that it be washed pilar to texting; tire rteorert point at which this could reasonably be done was Alder, Montana. In the late 1969's or early 1970's wash plant was inatelleti at Alder, a id the crushed ore was run through a hag washer and the waste was then picked from the wwhed material This system has remained barically unchanged since it wo* installed, except that occasionally we have found that (he need to wash the ore bus decreased with materials from certain areas o f the pit, ,'1f1J CPC-BCALTRSCPT00001105 TWCTigBBlfttMMMI c 110 ELEVENTH INDUSTRIAL MINERALS FORUM T he Three Forks, Montana, grinding piast was built In 1960-61 with one toller mill and one Double. Ejglity efejht ihild-eneiEy m ill A svcsmd such fiujri-tiBaigy mill w ai added In 1963, A pellet system wm added, In 1970, and we have undergone a major expanaen in 1973-74 in which we have added a third such fluid energy mill, storage dlus, etc., p in pneumatic conveying systems. We have also added a Stadman mill for th e preparattofi of feed for the ijajd-eneigy mills. The Grand U ta J , Nebraska, grinding plant was hunt, I believe, in 1952 with only one r o t e jisIJL We put in the first fluid-energy mill, which was a single mil) rather than a double min, in 1955, The second ope w?.a Installed about 1958. T he plant was generally remodelled In 1962 and the two single fluid-energy mills were replaced by one Double Eightyeight, and taiprovements were made in the packaging system. A second r o t e mill was added la 1969. T h e basic difference: Id the two fluM-erwgy plants is the fact tin t Three Forks has a pelletizing system, and a more sophisticated materials handling system, whereas Grand Island has only the basic necessities o f such an operation. The flow sheet at Grand island would be basically a tontte-nnlosding and storage area, a jaw crusher, one o f two roller mills, a l t e r of which can feed a packet bin or a feed bin foi the fluM-eoergy ffiSb, which in turn feed a second packaging system. A t Three Forks we have esBMtrtslly the same system through th e jaw crusher, but then we split to either a r o t e mill nr a Stedsrsn cage mill Basically, the Stedman mill feeds the fluid-energy circahr, and the r o t e ml3 feeds the packer bin. T he fluid-energy mill! t e n feed stbs from which umterial cam be redsim ed to go t e r into Ore second paefcea Mn drectly or into the pcltetfctag feed system, from which ft then gees to a third packaging station. Finished product* are then loaded out as is airy normal operation. The sals In Europe o f our fluid-energy-miII product from plants In the United States reached the point where we could justify the buildlug of a plant in Europe. G ent. Belginm, was the site jefectcd. This plant was constructed in 1965-66 and m i basically comparable to the original Three Forks setup. We have installed a pellet mill and a second fliiid-es-wgy mUl plus silos and pneumatic conveying since the plant w as built. Use product* rnide In Europe a nmsttfaetwetl in large part from crude ore from the Yellowstone Mine; this has been the basic a w material used In the Belgium operation. Periodically we accumulate between 15,000 and 20,000 tons s i crude ore tM make angle shipments o f this sire a t needed in order to keep the Gent plant supplied with mill feed. As indicated above, we orfelnaHy used only Yellowstone crude in Europe, h u t as the Beaverhead crude became avsflabt we began to ship small quantities of it to Europe, When we established s working agreemCBt with a tote producer in Asn&alb, we began shipping crude talc from th a t country to Gent for grinding. The baste supplies of ores used a t Gent, however, are still those front Montana. Generally speaking, we started at the Montana operations to the steatite tote business for the cerastes market. Later, we began to produce material for the control of pitch in paper-pulp milts. This h is become the predominant market for our Three Forks pleat, the ceramic and paunt Industrie* being secondary. We have abo began recently io move into the synthetic ru b b and plastics industries w ith our Montana talc I*mind*. Over the years the shMts in our product line have by and huge been gradual" GEOLOGY OF MONTANA TALC The geology o f Montana talc deposits has been described extensively in only one prior publication (Perry, 1948) but has been described briefly in three other publications (Heinrich, 1960; Heinrich, and Rabbltt, 1960; ChMertei and others, 1964). High-purity la k deposits in southwestern Montana are totally restricted to dolomltic marble of the proBeltian sequence of "Cherry Creek-type rocks" . The talc occurs m generally conformable lenses and stringers within the marble, If they are anywhere discordant, it Is commonly a t relatively low angles. Talc is invariably localized within a narrow stratigraphic range. Structural control, in the strictest sense, has not been recognized, but there is an apparent restriction of talc mineralization to th at part o f the marble that is spatially dose to large bodies of the Oilkm Granite Gneiss. The complete restriction of th e talc mineralization to the marble only must indicate t o t the aqueous solutions that contributed to the deposition of talc were amenable to doing so in the dolomite only. Winkler (1974) gave the following reaction; 3 dolomite + 4 quartz +1 H30 1 talc + 3 calcite + 3 C0 T t b seems to be the most likely reaction to account for the formation o f Montana talc deposits; Inasmuch as the host dolomite is not notably siliceous adjacent to the talc, it is likely t o t most of the silica required was metasomatieally introduced, probably along with t o water. In the Ruby Range the Dillon Granite Gneiss may have been emplaced before the talc was formed, but if this be the case, then the close spatial relationship between the talc and th e granite gneiss suggests the probability of a relationship that must be explained in some manner. Garihan (1973) has noted that finergrained dolomite and. thin-bedded marble "are notably barren of talc" and his studies suggest t o t high-parity talc has invariably been formed as a replacement of pure coarsely crystalline dolomite marble. Furthermore, he concluded t o t "with the exception of one occur rence, talc miners Illation in marble above the main mass of Dillon Gneiss is confined to one stratigraphic i . i i ! CPC-BCALTRSCPT00001106 '" t h e g u o l g y o f Mo n t a n a t a l c d e p o s i t s --h h . o l s o n hi ijnrtf the Regal marble". The Regal (Keystone) Mine and the Treasure Mines all occur within the Regal marble 0* OarMan {19? 3), who further concluded that "In general, talc is associated w ith tight folds, Fractures, marble breccia zones, bedding planes and faults" and that all o f these factors, along w ith texture and compositional and chemical factors, are important in localizing the formation of th e talc* Both Okuma (1971) and Carihan (1973) believed that the talc is genetically associated with the north northwest to northwest high-angle fault system. The writer disagrees, on the basis o f his study o f producing mines during the late 196Q*js, in which no evidence was found of differing composition, mineralogy, texture, e tc , ia areas proximal to such fault surfaces. It would m m that if those faults have been a factor in the formation o f the talc, such changes and lateral variations would be readily recognized within the ore bodies ~* unless, o f course, th ey have been masked by subsequent retrograde metomorphism. It is peculiar that although tremolite has been noted by many workers near high-purity talc m south western Montana, all o f the ores mined at present and in th e part are and have been, to the writer's knowledge, totally free o f detectable tremolite. Most chemical analyses o f Montana talc ores express CaO as being present only in "trace" amounts, rath er than as a definitive quantitative value. Of dozens of such samples collected by the writer and subjected to X-ray diffraction analysis, not a siogle one has shown a detectable am ount o f tremolite. The purity of Montana talc ores is shown in Table 10*1, as modified from Chid ester and other# (1964). In the discussions o f file Individual Montana talc mines, deposits, and prospects, the terra "talc-zone" will be used to denote that stratigraphic zone th a t Is susceptible to the formation o f talc. All o f this zone may be converted to talc, or none o f it, or an y part between these two extremes; In large areas o f numerous talc occurrences and considerable future tale potential, such as the area o f the southern Ruby Range between Timber G ulch and Stone Creek and the area between Johnny Gulch and Cherry Creek along the eastern flank o f the Gravelly Range, overlying soil cover Is either completely,absent or extremely thin. It would be most unusual over much o f these areas to find sot's (particularly in the low ground beneath timber stands) that are more than 1 foot thick. Indeed, at the Regal (Keystone) Mine, sod cover over the talc and dolomite bedrock is generally completely absent. In the high country north o f Gordon Peak in the Ruby Range and in the central part T-.W ''I 1 yi i U\ Table 10-1. --Chemical anrtyfet o f tile re horn the DSkMt-Ensli district* Montai, Bcwto Group mine* Kstoenye mtneSt Stea tite^ Smii-lM&ou mine SD-l3 Sl>24 5D-3& SD-S Sweet Trees* me m ine1 Y ellmo willsPtio n e Stea tite' -1 8 ........................ il 3 314 5 -e 57.72 U3 .48 U4 30.72 Trace Trace 594 58.46 1.90 .84 JO 31.78 Trace Trace 6.22 6295 ,27 .71 <05 31.13 2 M ,14 5.03 Nil 62.06 JO ,67 <M 31.12 .01 m .18 5 . Ml SL78 SI J$ <05 31.06 ,02 .08 .17 5.17 Nt 62.37 JO .63 <05 31.32 .01 m .10 490 Ml 61J JO .10 .20 3L7 V, t . * VV 5.6 60.40 191 27 M 30.81 .14 M 5.15 62.65 .31 1.51 Trace 30.23 .05 .15 .08 4.87 ,27 62.73 .10 1.45 < .0 5 30.32 .01 .03 .27 5.14 M *AtmJy*t unknown. Datajftom S. W._StockdaJe, Amrarkrni Chemef Chip. fAnalysis by Raymond G, Osbrarne laboratories, Inc. . ,, ..... , ... , _ , a M s a n white to pale-green opaque to translucent fine-grained to dense talc rode with interraked K detttes and vernier s o f May t a l i Contain! scattered tiny flake* of grapMle and a few dendrites of manganese oxide. Analysa by Leonard Shapiro, *Whno to pstogreen or seam-colored massive talc rock, predominantly fine grained but with variable proportion o f disseminated "SKlfettji-rizsd tolia or plates o f talc. Analysis by Leonard Stopiro. "Piiip jcsJe intermixture of types 5D-I and SD-2. ATMlyii by Leonard Shapiro. "Material representative of whiter and dens parts o f sample SD-I- Analysis by Leonard Shapiro. fAnelyrt* by A. J, MacArihur, Sierra Talc and Ctey Co. "Dense pategrten tala. Analysis by Leonard Shapiro, j * i `\ Vf i ) CPC-BCALTRSCPT00001107 112 ttnEYXNTH OTOUSTRTAL H O i m U FORUM of H itt range to th e north o f Stone Creek thicker soils are developed however, particularly ia stands of timber. It is in such areas that a geochemical approach to ore-finding, should such prove feasible, would prove invaluable for the discovery of concealed talc deposits the normal system o f " float -prospe cting" doei not work well In such areas. Over large areas o f the northwestenunost part of the southwestern flank o f the Ruby Range the bedrock has been sharply pedimented and major parts o f large acreages have bedrock actually exposed or have "bedrock-at-the-grassroots" . The area between Carter Creek and the divide between Hoffman Creek and Winnipeg Creek, from the Regal (Keystone) Mine northwesterly to the floor o f the Beaverhead Valley is an excellent example. Along the southwest edge of the Ruby Range, thick. aOovial terrace deposits conceal vast areas of bedrock that could contain talc, but It is unlikely th at methods will ever be found to assess whether or not talc deposits may be present there a t depth, Gohsg downhill to the northwest from the range divide, one comes into the pedimented area, then into the terraced area, and finally into the alluvial fill o f the Beaverhead Valley. The crucial reason that we have not attained a better and more nearly complete understanding o f the geology erf Montana talc deposits is that no geologist has ever "lived with** a Montana talc deposit or mine from the time o f its discovery through its develop mental stages and on into its period o f mining activity, Any field geologist who has attem pted to decipher geological relationships in tranches dug long ago in talcose rocks knows what an exercise In frustration it can be! The talc exploration geologist should be afforded the opportunity to n ap and sampfe while the bulldozer is there. Talc producers generally feel that talc mines ran be operated without geological control or advice. Until daily geological studies are made upon such deposits, it stands to reason that they will continue to remain enigmas! ORIGIN OF TALC IN MONTANA Commercial talc ores in Montana have formed only in dolomitic marble of pre-Beltian age. Although M e in other districts has formed through the alteration of ultramafic rocks, no such origin is known to the writer for any commercial deposit in Montana. Garitoo (1973) has recognized that many marble layers in the Ruby Range that have been host to the formation o f talc deposits are not cuartzosc nor do they contain interbeds of metaquartzite; therefore, he believed that the Mica needed for the formation o f the talc had to be introduced. The writer has made several siroilai observations and fully agrees w ith Garihan's conclusion. Garihan (1973) also slated that `The talc was derived chiefly from low-grade regional metamorpliisra of dolomitic marbles, through th e action of hydrothermal solutions containing silica and perhaps magnesia" , Retrograde rastaraorphism o f tremolite to form talc, so common and Important hi other districts, is thought n o t to have been a factor to the Ruby Range because tremolite is not known to be present in Montana talc ores. Okuma (1971) thought that some of the talc in the Ruby Range may have been formed as the result of th e replacement o f serpentine and tremolite, The writer does not dispute this possibility but stresses that all o f the known commercial talc bodies have been formed from dolomitic marble only. It seems very unlikely that such ore bodies have been invariably completely altered to tele, leaving no contained tremDlite or serpentine remaining whatsoever; many such, ore bodte*, however, do contain large "horses'* o f unaltered dolomite, which are either mined around or thrown to waste. All o f the pre-Gheiry Creek rocks and the " Cherry Creek-type rocks" and most of the rock types o f the Dillon Granite Gneiss have been subjected to upper amphibolite grades o f regional metamorphism, a longlived metamorpMc event f pre-Beltian tim e, which included the development of intense isoclinal defor mation. It is unlikely that the talc was formed during the period of upper amphibolite regional metanaotphiim, but it could well lave been formed during the period o f regional meta morphism of greenschist grade, which post-dated the amphibolite period and predated the intrusion o f the diabase dikes. If the age o f the dikes is Precambrian, w hich although not absolutely proved is very likely, than the talc was almost certainly formed in PreCambrian tim e. This age of formation seems most likely, for were the talc to have been formed in Cambrian or later time it would be extremely unlikely that no talc at all would have been formed in the thick dolomite units of th e Cambro-Ordovician Systems in the northern third of the Ruby Range (Tysdal, 1970). Garban (1973) noted that tale has not been, found in those Paleozoic dolomite strata in the northern third 1 , I 1 ' ' 1 ( >* i l j s ( [ ' j j 1 j j j CPC-BCALTRSCPT00001108 THE G EO LO G Y O F MONTANA TA LC D E PO SIT S--B. K, OLSON 113 of the range, yet talc has been formed in the pre-BeJtian dolomites at m any localities very near the Paleozoic outcrops. This, plus the fact that the Fakozuic rocks are completely unmetamorphosed, led him to conclude that th e age o f the talc mineralization was Frecambmn. Oleoma (1971) also thought that the most likely age of the talc mineralization was ProCambrian. Although the writ has n o firm proof one way or the other, he concurs fully w ith this age assignment for the formation of the talc, Okuma (1971) stated that "The talc bodes result from the replacement o f dole mbit- marbles by aqueous solutions rich in silica" and he fo rth stressed th a t. " Areas o f retrograde metamorphism may be of special significance in talc prospecting" . Van Horn (1945) has studied in detail the talc deposits of the Murphy Marble Belt in southwesternmost N orth Caro Baa. It is interesting that the geology -of this district is similar in many ways to th at o f Montana and that many o f Iris conclusions concerning the genesis o f the Murphy talc ores are also appropriate for th e genesis o f Montana talc ores. Van Horn thought that simple dynamic metamorphism could not, by itself, h aw accounted for the formation of the Murphy talc o r because o f the lack o f silica and magnesia in the original marbie, but he believed that such nsetamorphism might have formed zones o f weakness in the marble. The subsequent introduction of h o t aqueous solutions may haw partly silictfied the dolomite and at about the same t o e , or possibly somewhat later, may have formed talc bodies in such zones o f weakness. The writer believes that the mechanism o f for mation o f Montana, talc bodies was probably extremely similar to that postulated by Van Horn (1948) for the Murphy, North Carolina, talc ores. The dynamic metamorphism of the earlier upper amphibolite period may have formed zones o f weakness and allowed the intro duction o f siliceous material (probably from the Dillon Granite Gneiss) and possibly some magnesia also (proba bly rcmobilized from amphibolite and other ulii mafic rocks). After this jnetasonaatie event had afforded the opportunity for the introduction of all th e constituents necessary for the formation of the talc, It is thought that the talc Itself couM have been formed during the retro grade meiamorphism; he., the event of greenschM grade that Okuma (1971) and Garihan (1973) judged to have been widespread over both o f then areas. This theory of origin can neither be proved nor disproved at this t o e ; the final solution must await detailed studies o f paiagsnesis by workers who cart follow the mining o f these talc ore bodies over sufficiently lengthy periods of time. GEOGRAPHICAL DISTRIBUTION OF MONTANA TALC All commercial Montana talc deposits of which (he writer is aware are contained within pre-Beltian metasedimentary strata, They are also geographically restricted to a relatively small area in southwesterninoat Montana (Fig, 10-2) bounded b y the Beaverhead-Jci'ferson, Madison, and R ed Rock Rivers; more specifically to parts o f the R uby Range, the Greenhorn Range, and tlie Gravelly Range, Taic occurrences are known hi adjacent ranges, especially in the Tobacco Root Mountains, but these have; not yet produced any w e. The talc has invariably been developed within dolomite marble o f pre-Beltsm age. These marble and associated metasedimentary strata are known as the Cherry Creek Group and were originally studied and described b y Peale (189b) south o f Ennis, Montana. The Pony Series, as described by Tinsley and others (1933) in the Tobacco Root Mountainsf is not known to occur w ith the dolornitie marble of the Cherry Creek in any area where the latter contains commercial talc deposits. The DOlon Granite Gneiss is younger than the dolomitic marble b u t still pre-Beltian in age. Ross and others (1955) have mapped the unit which all o f the known commercial talc occurs as "Pre-Boh gneiss, schist, and rotated " rocks" and it constitutes significant portions of an area about 180 miles long in an east-west direction (R ed Lodge to Baornck) and 85 miles wide (Three Forks to the idaho-Montana line near Upper Red Rock Lake), The unit is a conspicuous and predominant one over this area o f 15,000 square miles and totally makes up single homogeneous blocks of several hundred square miles each. The dolomitic marble, however, is not an. integral part o f this unit over its entire extent. As known today, admittedly from fragmental and incomplete informa incm, the doiomitic marble is probably significant only in the Ruby Range, the Greenhorn Range, the Gravelly Range, the Tobacco Root Mountains, and possibly in part o f the Madison Range. Perry (1948) has described several talc deposits In th e Ruby Range, the Gravelly Range, and the Greenhorn Range, and Ms work is o f interest in that it describes the Montana talc-mining district and its deposits in their early productive stages. Much mining md prospecting have been accomplished since then, however, and it is one of the purposes of this paper to update Perry's work, -:i 'I'7 'i -4 ! - -3ji I .y - --i .3 t CPC-BCALTRSCPT00001109 ELEVENTH INDUSTRIAL MINERALS TORUM The two ranges that contain all o f the large Montana talc deposits, namely the Ruby and Gravelly Ranges, will be the ones dealt with at most length m this paper. They have the most obvious present potential and may well have the best future potential. The other areas and ranges mentioned above are, at the present time, stHJ strictly wildcat areas. The areal geology o f the Greenhorn Range has never been published. The Ruby Range has bee described in reconnaissance fashion by Klepper (1950), The entire Ruby Rpige has been mapped in recent years by student investigators, but the results o f this work have not yet been published. Tysdal (1970) mapped the northern third of the Ruby Range, which 1 ! i 10-2. -Index map of fiosrthwwtini JHontan- } \ CPC-BCALTRSCPT00001110 !& % >: THE G EO LO G Y OF MONTANA T A LC U ZPO SITS--A . 1, O LSO N consists for the most part o f Paleozoic strata, Garihan (1973) in the central part of the Ruby Range and Okim (1971) in the southern part, In a joint study that was subsidized by Pfizer, Inc., mapped aj! of that range that has, in the writer's opinion, any significant chance o f containing commercial talc deposits, Mann (1954, 1960} mapped much o f the Gravelly Range, including significant amounts of pre-Beltian rocks, b u t did not differentiate them into separate units, Hadley (1969a, 1969b) mapped key areas along the eastern flank of the Gravelly Range, which give considerable insight into the tale potential of that ta , Student investigators are currently working in and mapping portions o f the Gravelly Range, b u t it will be some tim e before that work is reported. It is difficult to discard a stratigraphic name such aS "Cherry Creek" , because of its longevity and wide spread usage,but the writer chooses not to use it without qualification (except at t o type area), fo i there is no way to be certain that one is always referring to sequences of the same age when widely scattered outcrops of pre-B eltian doiomitic marble are being considered. T he Cherry Creek Group, as defined by Peak (1896) south o f Ennis, Montana, consists o f more than 7,000 feet of interlanitaated gneiss, mica schist, marble, crystalline limestone, and quartzite, Heinrich and R abbitt (I9 6 0 ) restudied the type area and charac terized the Cherry Creek Group as containing the following major classes o f rock types; 1. Marble, calc-schist, and lime-silica te gneiss 2. Quartzite and quartz schist 3. Fhyflite 4. Mica schist 5. Kyanite schist and kyanite-stauiolite schist 6. SiUiuBftite schist and gneiss 7. Magnetite schist and related rocks ( "iron form ation'') 8. Anyphibok gneiss, schist, and amphibolite 9. Quartz-feldspar gneiss, granitic gneiss, btotite, and injection gneiss The marble layers form the thickest and the most persistent of th e units within the group at this locality, md Individual marble layers ay much as 1,500 feet thick have been noted. Quartzite units as thick as 6S0 feet have also been noted. The " total minimum thickness o f the Cherry Greek group in its type area is estimated to be about 30,000 feet" (Heinrich and Rabbitt, 1960). Heinrich (i9 6 0 ) studied the Cherry Creek G roup in the Ruby Range and reported the following as the characteristic rock types: L Marble and calcium*rmgJ$ium-sUicate gneiss 2. Quartzite and conglomeratic quartzite 3. Muscovite and biotile schist, some prnetiferous 4. Biotlte gneiss, some containing various amounts of garnet 5. SUiirrwmte schist and gneiss, some gamedfeious 6. Hypersthcne-magnetite schist 7. Pyroxene schist and gneiss 8. Chlorite schist 9. Corundum schist 10. Hornblende gneiss, amphibolite, and schist 11. Anthophyllitie gneiss and schist The marble units are the most conspicuous; individual units as thick as 1,6QQ feet have been noted, b u t such thicknesses may not be original. They may have resulted from flowage that occurred during the epochs o f intense folding in Precambrian time. In the Tobacco Root Mountains, Tansley and others (1933) described the Cherey Creek Group as consisting o f " quartzites, limestones, schists, and gneisses whose sedimentary origin is unquestionable, whereas the Pony group possesses features common to both sedimentary and igneous rocks. No limestone or true quartzite occur s in the Pony group". "Cherry Creek-type rocks" wfll be discussed and described below in detail; the use o f the foregoing terminology will allude to the bet that the term Cherry Creek Group, as used in the past for occurrences outside the type locality area, should not necessarily imply stratigraphic correlation or tin equivalence. Therefore, except for the type locality in the Gravelly Range, the term " Cherry Creek-type rock#' will be used in this paper to denote a series of pre-Behian strata o f unquestionable sedimentary origin, characterized by marble and quartzite and coniainuig abundant schist and minor gneiss, with no implication whatsoever that any o f the geographically isolated sequences can be correlated stratigiaphically w ith any other. GEOLOGY OF THE RUBY RANGE T he R uby Range is elongate in the general direction o f N . 40 E., being about 30 miles long and having a width of 10 to 15 miles. Altitudes along the base o f the range are generally 6,000 feet or so above '*1 i 4 -* CPC-BCALTRSCPT00001111 l i e XLEYBNTV in d u s t r ia l m in e r a l s f o r u m sea level; the highest peak* are la the northern third and stated that most of these rocks are coarse grained of th e range, R uby Peak at 9,391 feet above sea level being the liighest point la the range. The Ruby Range may b e divided into several geological blocks, each having certain unifying characteristics. and banded. He believed that the discontinuous nature o f some o f the amphibolite bodies indicates their origin as mafic sills and provides evidence for an intrusive origin. Okima mapped this group as being confined to the southeasternmost pert o f hi* area and described it !'? A generalised geological map (Fig. 10-3) has been as being composed of metasedimentiay, meta-igneous, compiled b y the writer from his own field work and and ndgimtUic units. from unpublished n a p s b y James, Wier, and Shaw (19& ), Tysdai (1970), O ktarn (1971), and Garihan Garihan (1973) described "a belt two kilometers (1973). These four unpublished maps cover the entire wide between Sage and Mormon G eeks" o f pre-Cherry R uby Range except for a very small triangular segment G eek rocks along th e central part o f th e eastern flank at its southeasternmost extremity. Six geological units of the range, but the area that is so exposed is too small are shown on Figure 10-3; three of PrtCambrian age, one to allow the establishment o f firm and reliable relation- "mixed" Piecambrian-Paleoroic, one almost entirely drips to other lithologic sequences in the range. Dus i Paleozoic, and one Tertiary-Quaternary. The second group o f pre-Cherry G eek rocks includes gneiss, schist, oldest unit is that one along the southwestern flank amphibolite, and migmatite --b u t no marble or meta- o f the range that contains " Cherry Geek-type rocks". quartzite, Virtually all of th e known dohmdtlc marble in the range is within the boundaries o f this unit; those that ate not are contained within the undifferentiated PieCambrian portions o f the "mixed" PieeanibrianFalcozoie unit. The granite gneiss unit along the south eastern flank o f the range is the one that previous workers have called the "Dillon Granite Gneiss" . The Heinrich (1960) described rocks o f th e "preCbeny G eek group" in the Ruby Range as "gnehsie, banded, and coarse-grained" and noted the absence of distinctive laterally persistent units. Schist was noted as markedly subordinate to gneiss, distribution o f this unit on Figure 30-3 has been delineated so as to exclude all known marble units. "CHERRY OTHER-TYPE ROCKS" H ie "mixed" iberambiian-Pulcostoic unit has been estab lished because it covers an area where the relationships between th e intensely folded Preeambrian units and the liornodinal Paleozoic formations have been complicated by Laramide block faulting, resulting in a mosaic-like complex of the two very different sequences. The Paleozoic block consists almost entirely o f CamhrianPennsylvanian formations, but has some scattered and relatively minor outcrops o f Cretaceous, Tertiary, and Particular attention was paid to th e '`Cherry Geektype rocks?' by both Okuma (1971) and Garihan (1973) because a good deal o f their attention was devoted toward talc occurrences, and sU o f the known commer cial deposits of talc in th e Ruby Range, and all of Montana for that matter, are found within th e bound aries o f dolomitio marble units o f the "Cherry Creektype rocks" . Quaternary units, A Ttetwry-Quateniaty block is shown along th e central portion o f the eastern flank o f the range where units o f such ages are so widespread that Okuma (1971) listed the following as the distinctive ioek types o f his "Cherry Geek Group" : they can readily be Aown* even on th e scale o f Figure 10-3. 1. Marble ROCK UNITS 2. Quartzite 3. Caidtim-magnesium schist and quartzite PRE-CHBRitY CREEK ROCKS 4. Amphibolite and hornblende gneiss 5. Mica schist Both Okuma (1971) and Garihan (1973) recognized the presence o f rocks pre-dating "Cherry Geek-type rocks" along tire southern margin and the eastern 6. Silliroanite schist and sillimanite gneiss 7. Magnetite schist (iron Formation) 8. Other rock types (not mapped separately) margin, respectively, o f th e Ruby Range, Gkuma listed the main rock types o f this group as: The marble layers are conspicuous and invaluable as structural marker units and have been mapped as Bjuie-garnet-quarl z-feidspfir gneiss B iot ite-garnet gneiss 30 to several hundred feet thick. They arc generally well-bedded, Individual layers ranging from 6 inches to Amphibolite and hornblende gneiss 4 feet in thickness. The dolomite generally crops out CPC-BCALTRSCPT00001112 THK GROWN Y OF MONTANA TAM? StBFaSITS--B. I t OLSON 117 45f5r 1152 15 Teriiary - Quaternary P A L \ Paleozoic Fault-block mosaic of undifferentiated Precambricm and Paleozoic rocks CC ] Cherry Creek- type rocks GG } Dillon Granite Gneiss P C.... I Pre-Cherry Creek rocks 10-3. -GenuUzed gee!ogle m*p of Ruby HaagBtTcNanf and MadiKtn Cbunlieg, CPC-BCALTRSCPT00001113 1 18 fcLCVBHTH INDUSTRIAL MINERALS FOR DM better than its endoartg units, but is further sharply delineated by dense growths of greasewood and the presence of a light-orange lichen, which seemingly grows only upon the dolomite rock. The dolomite is generally w hite to light gray in fresh color. ActinoBte and tremolite occur locally in the marble, but generally only near contacts with the ultramafic rocks; both minerals are unknown within commercial talc bodies. Garnets are also locally -developed, within the marble. Quartzite layers range from 15 to 180 feet in thickness, and although they are decidedly subordinate in volume compared to the marble, they do make excellent structural marker units. AmphibolHe and hornblende gneiss are decidedly Important voiuraettitally, and these units range from 6 inches to 1,500 feet in thickness. Most o f the "Cherry Cheek Group" is of sedimentary origin, according to Okuma (1971), but the amphibolite bodies probably t r a e originally Igneous dikes and sills. Gnriten (1973) stated that In the southern part o f the Ruby Range the rocks of the "Cherry Creek Group" trend uniformly northeasterly, b u t in the central part of the range, especially along Stone Greek, they bend easterly and then southeasterly, and them continue in a general easterly direction into the Greenhorn Range in the vicinity o f Ruby Dam. He recognized the following lithologic subdivisions of the `^Cherry Ckeek Group" ; !. Marble 2. Caloeate rook 3. Metaquartzite 4. Sitllmairite schist 5. Biotite gneiss a t schist 6. Chlorite schist and related rocks 7. Actinoiite schist 8. "Iron Formation" 9. Amphibolite and related rocks 10, Anthophyllite gneiss and related rocks and further specified that this order of listing does not la any way connote stratigraphic succession. He mapped marble layers 100 feet to approximately 1,500 feet thick and noted the presence of b o th calsttlc and dolomitic marble; the ealdtlc variety is finer .grained than the dolomitic variety, which is only locally fine p a in e d and sugary textured as is the calcific marble. Garite n (1973) stated that the marble commonly grades into cale-sflicate rock and dkspridte marble, which is much more common than tremolitie marble. The calcsilicate rock, a relatively minor rock type, may or may not contain carbonate and if relatively rare in the central part of the range; it is much more widespread, however, in the southern part, where it has been used as marker beds for napping. Sillimanite schist constitutes only 8 percent of Garihan's measured section along Stone G eek on the western flank o f the range. This rock type Is easily eroded, and several valleys, such as Mine Gulch, have been cut front it. It can be mapped locally by the micaceous soil funned upon it. Amphibolite constitutes more than 20 percent o f the thickness of the "Cherry G eek Group" according to Gariban (1973) and1 is thus one of its more important lithologic units. He recognized one such unit as being about 1)300 feet thick and stated that some of these units can be traced "for several kilometers" laterally. Anthophyllilfc amphibolite Is common. Antbophyliite is also found In the gneiss and schist, as is cunurungtomte; the two minerals are Indistinguishable in the field but were not found together in thin section. Garthan (1973) also noted the occurrence of cordierite-anthophyllite gneiss, which is associated w ith amphibolite. There seen little doubt that these m&tamorphic unit! originally formed a sedimentary sequence, Heinrich (1960) made a petrographic study of some oF the marble in the " Cherry G eek Group" of the Ruby Range and by the use of staining techniques he found that dolomilic marble is about twice as abundant as calcitic marble. The Carter Creek iron deposit, which bridges the Beaverhead-Madkon County line southeast o f Dillon, is in " Cherry Geek-type rocks" . A detailed geological map of this deposit has been published (James and Wier, 1972). DILLON GRANOT GNEISS The Dillon Gra nitc G neks o f southwestern Montana has been described by Heinrich (1953, I960). The major rode types In the Dillon Granite Gneiss in the southern part o f the Ruby Range, according to Okuma (1971) are; 1. Reddish-brown quartz feldspar gneiss 2. Foliated, light-colored pegmatitic gneiss 3. Coarse-grained bkrtrte-fsldspar-quartz gneiss 4. Olive-gray granite gneiss 5. Eptioie-ridi gneiss The Dillon. Granite Gneiss is generally conformable with those metasedimentftry rocks th at it has intruded (here the "Cherry Creek-type rocks" ), 1111(1 anX MOS* cutting relationships are generally minor in degree and angularity. Okuma (1971) favored a magmatic origin but recognized that th s is not the only plausible genetic model. CPC-BCALTRSCPT00001114 TH E GEOLOGY OF MONTAKA TALC DEPOSITS--. H. OLSON 11 In the central part of the Ruby Range, Garihan (1973) recognized three major rode types in the Billon Granite Gneiss: Biotiie-Iiombknds-garnat gneiss Pegrnatitic Dillon Granite Gneiss Chloritic DilJe n Granite Gneiss Heinrich (1960) described these ultramsfie intrusive bodies as 'hinmetamorphosed" and noted that th ey are cut by the younger diabase bodies and also by the master faults of the Ruby Range (northwest system). GJUNFUIXTES tad stated that the Dillon Granite Gneiss is concordant with the "Cherry Creek-type rocks''. All of those workers who have published major contributions upon the pre-Bdtian rocks of the Ruby Range view the Dillon Granite Gneiss as a large tabular intrusive body, of baiholithic proportion, which is In regional concor dance w ith its enclosing rocks. Other alternatives, however, must be considered, such as gra nitbat ion and the regional metamorphisra of sedimentary sequences. Garihan (1973) provided detailed petrographic descrip tions o f the various types of rocks within th e Dillon Granite Gneiss in his area. Gramilite rocks have been recognized by Garihan (1973) only in the northern part of the Mine Gulch 7id-minute quadrangle. I s the field they are difficult to distinguish from amphibolite, and their outcrops are generally poor, but they have been recognized as granulites after thin-sedion study. They are common to terrenes underlain by the Dillon Granite Gneiss, less common in those underlain by the "Cherry Creek Group", and are o f interest because o f their proximity to at least two talc-bearing marble units. DIABASE DIKES Heinrich (1960) described " non-foltrted pegma tites, which commonly are zoned" , which transgress the pain o f the country rock that includes them. These pegmatite bodies are not abundant, and al though Heinrich judged them to be genetically related to the Dillon Granite Gneiss, he recognized th at they may be much younger, possibly even o f laram ide age. Unfortunately they are not known to comp into contact anywhere with rocks younger than Dillon Granite Gneiss, and thus can be dated only as post-Dillon and probably pre-Tobacco Root batholith in age, ULTRAMAF1C ROCKS Ultrarnafic rock units, which Okuma (1971) re ferred to as peridot he, intrude th e pre-Cherry Creek rocks, the "Cherry Creek Group" , and the Dillon Granite Gneiss jji the southwestern part o f the Ruby feege. They are fifteen feet to several hundred feet wide. Similarly, hr the centra! part o f the R uby Range, Garihan (1973) described the pre-Cherry Creek rooks, hr "Cherry Creek Group" , and the Dillon Granite Gneiss as all playing host to ultrarnafic bodies. For most part, he stated, the ultrarnafic' bodies are concordant, l.e., parallel to the regional foliation, but they are locally discordant. The three major types o f ultrarnafrc rocks are metaperidotite, metapyroxenite, SKpentinite. Garihan (1973) thought that the ^traraafic rocks were probably introduced at least M tnrly as the implex isoclinal folding and upper Amphibolite metamorphic event. Diabase dikes, with preferred orientation in the north-northwest octant, are common along the southern two thirds of the Western flank of the R uby Range, Okuma (1971) described them as ranging from 5 to 500 feet to width and extending as much as 5 miles. They commonly occupy long and relatively narrow distinctly depressed swales, which are generally free of all vegetation except grass and contain few o r no outcrops. Their intrusion has had little or no effect upon the older country rocks, except for the marble, which may locally have had small amounts o f serpentine developed, These dikes have not been subjected to th e high-grade amphibolite nets morphic event, but have teen metamorphosed to tire greenschist facies. Okuma (1971) speculated about the age o f these diabase dikes -- as to whether they are of ftecambrem, Fnleozoie, or Tertiary age -- and concluded that they are probably Rretmbriau. Girihan (1973) stated that such diabase dikes are also common in the central part o f th e Ruby Range and that they may be as wide as 100 feet and as long as 1 mile, possibly more. They are easily recognized and traced upon aerial photographs. They generafly cut the foliation of the enclosing pre-Beltian rocks at high angles and are not folded as are those older rocks. They are vertical or subvertical, as judged by the linear nature o f their traces over extremely rugged topography, and they are decidedly Less metamor phosed (generally only to the greenschist fades stage) than the enclosing rocks. Their lack of folding and foliation suggests that they were emplaced later than the phases o f shearing and rearystalHzatioii th at are associated with the ultrarnafic rocks and the other K.j 'i Ki y, ':?1 1; CPC-BCALTRSCPT00001115 ISO ELEVENTH m m JS T B iA I MINERALS FORUM older pre-Beltian rocks. The mapping by Garjhan (1973) strata, completely absent From the Ruby Range, are and Tysdal (1970) suggests that these dikes haw no known in the Pioneer Mountains to th e west; this was intrusive relatlojisMp whatsoever with the Paleozoic probably the source.- strata o f the northern third of the Ruby Range, despite their locally close proximity to those strata. If this TERtlARY-QlIATERNARV inference is correct, the diabase dikes are o f Pre- i? ' carabrian age and are possibly the youngest Pre Cambrian la te Tertiary and Quaternary strata are present in unit in the range, : the Ruby Range, especially In Its northern third along the lowermost flanks. T A large diabase dike cuts what may well be the -i. largest single talc deposit in the Ruby Range, the Regal su. (Keystone) Mine In sec- 2, T. 8 S-, R- 7 W-, Madison METMORPHTSM County. This dike ts more than 200 feet wide at the AH pre-Cherry Creek rocks, the " Cherry Creek mine and, with two other similar bodies along approx Group" , and most o f the rock types o f the M fon imately the same strike, can be traced for about 4 miles Granite Gneiss have been subjected to upper amphibolite 1: in a north to north-northwest direction. It Is probably grades o f meiamorphism, according ta Garihan (1973), *. vertical, or at least veiy close to vertical, as deduced "as part o f a prolonged pre-ileltian episode which > from its almost linear trace over rugged topographic Included Isoclinal deformation and subsequent intrusion relief. of baric dikes" . He thought that th available informa tion strongly suggests that the pre-Cherry Creek rooks f Heinrich (1960) described one diabase dike in may d ite back to 3.1 x 10* years ago and that the Axes Canyon near the southwestemmost extremity of Dillon Granite Gneiss is on the order of 1.6 X 10* years i- the R uby Range as being 600 feet wide and 6 miles old. He further inferred a second regional metamorphism long. He stated that these bodies are generally intruded of greerischist grade of an undetermined (but certainly along faults, particularly the master fault set o f the Precambrian) absolute age. range (north to northwest system). Okuma (1971) also agreed that the Pre Cambrian CNDIFFESENnATEP PRECAMBRIAN rocks o f the Ruby Range have beat subjected to regional metamorphism of the upper amphibolite facies and Tysdal (1970) has mapped large a r m o f Pre further observed that garnet is ubiquitous in r o d s of enmbriau rocks in the northern third o f the R uby the Ruby Range. He saw no clear evidence to suggest Range but has not differentiated them into separate multiple metamorphisni, Le., multiple inetairioiphism lithologic units or groups. He mentioned "meiadolomite1* of the highest rank achieved (upper amphibolite fades). i. as o n e o f the five dominant rock types, however, so it Ilk study o f thin sections indicated that the later is likely that "Cherry Creek-type rocks" are present. retrograde .metamorphism of the greenscliist fades was widespread and that the formation o f the talc may PALEOZOIC well be related to this later met morphism. STRUCTURAL GEOLOGY Tysdal (1970) described the Prccarnbriaii-Canibrian unconformity In the northern third of the Ruby Range as a nearly planar contact, and he mapped and measured Cambrian, Devonian, Mississippian, and Pennsylvanian formations that have an aggregate thickness of about 5,300 feet, of which approximately 1,500 feet (mostly Cambrian and Devonian) is dolomite or markedly dolomltic. No talc Is known to have been formed in these younger dolomite beds. CRLTACKO OS-TERTIARY Tysdal (1970, p. 94) asserted that the Beaverhead Formation, of Cretaceous-Tertiary age, contains quar tzite clasts th at have been eroded from Beltran rocks. Belt According to Okuma (1971) "the southwestern portion o f the Ruby Range has remained relatively stable since Its intense deformation in late Free&mbrian time" . Almost throughout his area the foliation is " Invariably parallel to the formations!, contacts of the different rock types". Isoclinal folds are characterized by parallel or near-parallel limbs, and Okuma recognized three phases o f Preeambrian folding, The prominent northwest- and north-northwest-trending master faults, which arc readily recognized locally by the abrupt juxtaposition of radically different rock types, have essentially no topographic expression whatsoever, despite then large displacements. The Elk Creek Fault, trending N. 40e W., displaces the "Cherry Creek G roup" - Dillon CPC-BCALTRSCPT00001116 T H E G EO LOGY OF M ONTANA T A L C DEPOSITS--II. BL OLSON 181 Granite Gneiss contact a horizontal distance of 2 miles; the Red Canyon Fault displaces it about 1 mile. Qkunja (1971) thought that the age o f the high-angle faulting could be Latamide; if the strikes o f the diabase dikes indicate Rrecamferian lines o f weakness, however, then these faults could have originated in fteeaaib ik n time and been reactivated in the Tertiary, Gkurria suggested th at the pre-Cherry Creek rocks, the "Cherry Greek Group" , and the Dillon Granite Gneiss were deformed contemporaneously. According to him, Precambiiaii structural deformation " was primarily by # combination of flexural-flow, slip or shear along sehirtosity, and plastic flow" . Those investigating in detail the pre-Bahian rocks of the Ruby Range recopiize either two, three, or four phases of folding in Frecatnbrian time. Tight isoclinal folding is common in such rocks throughout this area, The master northwesttrending faults, which are postfoWjrng In age, are superimposed throughout the range at approximately right angles to the strike of the Precambrian foliation. This faulting is probably much more pervasive and important in scale than is presently recognized; the faults can be easily recognized where they cut the Precambrian-Palcozoic unconformity, but they m ay be extremely difficult to trace where areally confined to the Precambriaa sequences. The rangebounding faults in the central part of the eastern flank o f the range have an overall trend o f about N. 50 E,, but In th e northern part o f the eastern flank they trend north-northwest. The age o f tins high-angle faulting is difficult to ascertain. Garthan (1973) thought that the northwest-trending faults may have been initiated to Ptecarobrian tim e, if one considers that the diabase dikes represent th e establishment o f weakness surfaces in the north-northwest octant in Prccanibrian tune. He favored the theory of recurrent movement on these faults in Precambriaa, Laranude, and posrt-Laramide times; the writer agrees th at this is most plan able. Tyadai (1970) described the Ruby Range as being on the western edge o f the foreland o f the Rocky Mountains in a structural setting that is characterized by: a) high-angfe faults cutting basement rocks.. b) extensive exposures o f ftecarhbriart tneta- rnorphic rocks in the cores o f m ountain uplifts. c) relatively thin cover of Paleozoic and Mesozoic sedimentary rocks. The Paleozoic and Mesozoic strata in the Ruby Range had an aggregate thickness o f about 10,000 feet or less during deformation in the la te Cretaceous-early Tertiary, according to Tysdal (1970). Major normal faults border the western, northern, and modi of the eastern shies of the range in Tyadafs area* He showed seven major fault blocks within the range, all delineated by en echelon northwart-trendtag high-angle faults; all except one of these faults are downthrow on the southwestern side and upthrow on the northeastern side. These basement blocks have been idled to the northeast and plunge to the northwest. Tysdal (1970) described the northwest to north-northwest master faults to Iris area as having throws of 6,000 to 7,000 feet and stated that they generally truncate the northeast-trending faults, which are relatively minor In magnitude and importance. He has mapped broad anticlinal folds involving Cambrian formations, referring to them as flexural flow folds, but these structures are totally different th an the tight isoclinal folds developed in the piC-Bcltian rocks. He has also mapped synclinal folds, whose limbs locally become vertical and overturned. These anticlinal and synclinal folds are closely associated with the northwest to north-northwest rrartef faults and were m ost likely formed as a consequence o f then proximity to those major faults. ACTIVE TALC MIMES IN THE RUBY RANGE TREASURE CHEST MINE T he Treasure Chert Mine, near the head of the Left P o rk o f Stone Cheek to the north-centra] part o f the R uby Range, is owned by Pfizer, Inc. It is and has long been th e most important producer in that range. The Treasure State Mine, which has not produced any talc ore for more than a decade, lies a few hundred feet downhill and to the west o f the Treasure Chest Mine. The two are believed to be faulted-off segments of what was once a single ore body, and the writer has named the structure that separates them as the Treasure Fault (Fig. 10-4), The Treasure Chert Mine lies midway on the south hillslope of the Left Fork of Stone Creek in the NWli sec. 14, T. 1 S., R, 6 W., Madison County,Montana (Mine Gulch 7H-imraite quadrangle). This large tabular ore body has a strike length of about 1,000 feet (o f which 700 feet o f strike length on the western end has the greatest commercial potential) and horizontal width as great as 120 feet, and has been mined to a vertical depth of about 250 feet. Its strike ranges from east to N, 60s E.,, and the dip averages 55* northerly. The actual local strike must be determined by close scrutiny o f the outcrops, for an intricate system o f right-lateral faults has Imparted an overall trend to the entire ore body of somewhat south of east. ifi V! 3t ..'- `M 1 J CPC-BCALTRSCPT00001117 R.5 W R.6 . .W 3.7 .W ] ELEVENTH INDUSTRIAL MINERALS FORUM CPC-BCALTRSCPT00001118 , R.9 R.9 .W T H E OJSOUOGY O F M O NTANA T A IC d e p o s i t s - . h . o l s o n 123 The Treasure Chert Mine is unusual among talc deposits in the Ruby Range In that throughout parts of its lateral extant a thick dolomitic marble unit has been completely converted to talc. The footwall is dark biotite schist, called "The Blackwall" by miners, and the hanging wall is Dillon Granite Gneiss, which is generally cWorttic. The footwall schist is locally gamrtiferpus and extensively serpentinfeed and chlouti/.ed. The extensive alteration lias resulted in a crumbly and relatively incoherent mass, which renders much of this schist susceptible to widespread are! unpredictable sloughing into the pit. The presents o f numerous but generally unmappable undutatoiy fault surfaces Is indicated by the abundance o f slickensides on fresh surfaces. The alteration and the faulting, plus the fact that th e talc generally has been formed and is therefore mined right up to the vein-schist contact, all combine to constitute an extremely difficult safety problem. Several slides o f schist footwall blocks have occurred during periods of mining activity; as the pit goes deeper, attaining a satisfactory amount of stability of the steep footwall will become an increasingly difficult problem. The hanging wall is a medium- to coarse-grained variety o f Dillon Granite Gneiss, which contains Motte and garnet. Individual beds are well layered, and the gneiss is concordant w ith both the tale-containing marble and the footwall schist. it Is generally uniform within each individual Faultblock. Geological relationships observed during the writer's investigations of this mine suggest that the alteration o f dolomitic marble to talc within the ''talczone" occurred first, and that subsequent high-angle block faulting jostled individual fault blocks around so that rocks of different lithology were directlyjuxtaposed. The presence of the right-lateral faults went unrecognized for many years during the early operation of this open pit. This is understandable, for little if any structure can be observed within the " talc-zone" ,which reacts plastically to deformative forces. A further com plication is that lithologic contacts must generally be observed during the mining operations; even only a few days after they have been originally unearthed, and ceilairily at the and o f the mining season, such relation ships have generally become totally obscured by the movement of mining machinery, by slumping, or by concealment under waste material. During the planetab k-and-alidade mapping performed by the writer in 1969 it was even necessary to call upon earth-moving machines equipped w ith ripper teeth in Order to locate lithologic contacts within the pit floor, so pervasive and obscuring were the huge ammurts o f dust generated by the mining activity. The extent o f the faulting cannot be accurately mapped nor truly understood until one works in the footwaD schist or the hanging-wall granite gneiss in areas dose to the `Talc-zone" itself. The Treasure Chest Mine is situated along the nose o f the major broad structural arch o f the Ruby Range as mapped by Garihan (1973, H te I). In the prierai vidnty o f the mine the strata generally strike cast to N. 60 E. and although the dips may range from 25 northerly to vertical, the common range is 4S" to 65" northerly. Along w ith this regional dip, the major structural features include a strongly developed en echelon set o f high-angle to vertical right-lateral faults striking N. 20 W, These faults may be as closely spaced horizontally as 100 feet or so, but the spacing h generally ' wider than this. The southwestern block has moved rd ativ d y upward along each one of the faults th a t has been recognized to date. The Treasure Fault is the most important of these within the mine area; it has displaced the Treasure ore body in rightlaleial direction ISO to 200 feet. Present evidence within th e mate area does not conclusively indicate whether the formation o f the talc preceded or post dated the faulting. The writer's w ork in the late 1960's suggested that the talc was formed prior to the faulting, hut this conclusion is still improved. The character of the "lalo-zoac" was nowhere observed to change appreciably, near or adjacent to the fault surfaces, and The westernmost block of the Treasure Chest Mine, between the Treasure and Pit Faults, (tee Garihan, 1973, Fig. 42, p, ISO) has not over the years contained appreciable amounts of the highest-grade talc are. Q dorttic material and white quartz veinlets have been locally so abundant that no ore whatsoever could he recovered from this portion o f the "talc-zone" , and it has thus either gone to w is e or has been left. The area between the Pit Fault and the westernmost exposure of the Dolomite Fault has contained the best ore mined on this property. During the late 196G's the " talc-zone" between the footwall schist and the hanging-wall gneiss was composed entirely of the highest-grade talc over a horizontal width of 120 feet (true vein width o f about 95 feet). From the Dolomite Fault eastward, the quality of the ore within th e "talc-zone" becomes lower and lower, and the talc is contaminated by large "horses" of dolomite and dolomitic talc as well as by large " knobs" of silidfied material. Where these contaminants are present in large masses they can easily be mined around and left or can be sorted out and sent to waste by the use o f mining machinery , but inasmuch as handsorting methods are not employed at this n in e, much material containing appreciable! quantities o f pure talc v `.s 'M ; *r, J CPC-BCALTRSCPT00001119 124 ELEVENTH INDUSTRIAL MINERALS FORUM is throw n to waste from areas where eofttandnatfa by waste is intim ate and on a small seal. In recent years efforts have been made to extend the Treasure Chest Mine to the east, but present exposures indicate that these attem pts have met with little success. Much high-grade talc is present in the easternmost reaches of th e present mine area, but its recovery will require the use o f sorting methods rather than large earthmoving machinery alone, which is the present method of operation. In th e mid-1960's the waste;ore ratio was on the order o f 3:1 or 4:1, but It is now on the order of 15:1 and will soon be at least as great as 20; 1. Present mining costs may be approaching the point that would justify considering tire alternative of underground mining. Even if th e operating costs of the latter were greater, the improved safety th a t would result from eliminating the high-standing dangerous "Btackwall" might help to offset them . In addition to the recent targe increases in the v a st store ratio, it is now nece&aiy to transport waste greater and greater distances from the mine area. T he highest grade tale from lhe Treasure Chest Mine m ust rank w ith the purest grades o f talc known throughout the world. Large blocks have been mined (consisting of several thousand tons each) that are either w hite or pale greenish and are homogeneously crypto crystalline and massive pure talc. Garihan (1973) has petrographically identifie! minor amounts of apatite, chlorite, graphite, limonite, and rutila in the talc o r e of this mine, but these impurities have not commonly been abundant enough to render the talc unsuitable for the mill. Talc that is darker green than usual is termed "#2 ore" b y the m inas, but compositionai differences between It and th e lighter-colored f*#l ore" are slight; it is the color that is the Important difference. All o f the marble that ha* been observed within the mine area b y th e writer is dolomitic, not caldtic. The Treasure Chest Mr does not have enough recorded history to indicate whether the "talc-zoue" is thinning or thickening w ith depth, Le., are we within the upper half or th e lower half of a lenticular body? The most easterly o f th e right-lateral high-angle to vertical faults that has been recognized within the mine area lies about 400 feet east o f the easternmost recognizable part of the Dolomite F ault. If the ore body or indeed even the *`talc-2one" is present east of this unnamed fault, and if the pattern o f right-lateral displacement only persists, th en the talc would have to be uphill from and southeast o f the present mine area. Efforts to locate such an easterly extension by bulldozing and drilling have thus far been, to the writer's best knowl edge, unsuccessful. Talc ore from the Treasure Chest Mine Is trucked 30 miles or so to the Pfizer mill at Barretts Siding on the Union Pacific Railroad about 8 miles southwest of Dillon, _ TREASURE STATE MINE The Treasure State Mine was in operation long before the presence o f tale ore in the Treasure Chest Mine area was even known. Shortly after the latter mine was opened, the Treasure State Mine was closed; it la s been inactive ever since, although much highgrade pure talc ore obviously remains in this lower deposit, ft is situated in the NW& se a 14, T. 7 S., R. 6 W., Madso n County (Mine Gulch 7kSminute quadrangle), downhill and to the west across the Treasure Fault from the Treasure Chest Mine. The Treasure State Mine is obviously a faultedoff extension of the same ore body as that which produces at the Treasure Chest Mine. Its offset has been right lateral, the stir direction o f relative movement as is shown along all of the known faults within the Treasure Chest Mir area. The geology of the two mines k almost identical. Talc in the Treasure State Mine has been proved to have a strike length o f at least 400 feet and a horizontal width o f 75 to 100 feet and has te e n mined down dip to a depth o f about 200 feet, The writer did not have the opportunity to observe this mine during its operation, but it is likely that blocks o f high-purity talc without dolomitic or siliceous "horses" were not as large here as those in the Treasure Chest Mine. This grade factor plus the greater length and width o f the latter deposit were probably the principal reasons that the Treasure State Mine was abandoned in favor o f the Treasure Chest Mine; never theless, it is certainly true that much recoverable oregrade talc remains in the Treasure State Mine, awaiting the day when its cost of recovery will become competfitlve with then-present sources. In (be last days o f its operation this mine was certainly "high-graded" ; before it can be reactivated some o f the sins of the past must be redeemed and paid for. As in the "tale-zone" of the Treasure Chest Mine, talc in the Treasure State Mine may locally extend from the footwall schist to the hanging-wall granite gneiss. Garihan (1973), however, lias described some interesting relationships irs this mine that are not well shown in the Treasure Chest Mine. He described a four fold division of rock types from south (footwall) to north (hanging wall): schist, pale-green talc, a dark blue* green talcose-roek -one with gneiss foliation, and finally less-altered varieties o f M lo n Granite Gneiss. j I j > , j 1 * { i I | j l I ; I CPC-BCALTRSCPT00001120 T H E GEOI/OGY O F M ONTANA TA LC D EPO SITS--ft. Ht OLSON 128 He furth er described the talccwe-rock rone as being "probably highly altered Dillon Gneiss'1. The presence of a "transitional zone" between the "talc-zone" and the hanging wall in the Treasure Chest Mine has been locally noted by the writer, but it is either not nearly as well developed there as In the Treasure State Mine or else it may be present but a lade of exposures does not allow its widespread recognition In this active mining area, Any westward extension of the talc of the Treasure State Mine is presently enigmatic. Poorly developed evidence suggests that It might be faulted uphill b y a totally anomalous left-lateral fault, but such 'possibility would have to be proved with the bulldozer or th e drHI. It is extremely unlikely, however, that the present westernmost exposures of this ore body are identical with its actual westernmost extent. Both the Treasure Chert Mine and the Treasure State Mine ate owned by the Minerals, Pigments and Metals Division of Pfizer, Inc., which obtained them through the acquisition of the assets of Southern California Minerals Company in 1966, BEAVERHEAD MINE T h e Beaverhead Mine, owned and operated by Cyprus Industrial Mineral Company, lies southeast of the Treasure Chest and Treasure State Mines and over the crest of an east-west ridge, from them. Present operations are within the NW54 $M sec. 14, T, 7 S,, I t & W,,, Madison County (Mine Gulch ?&-minute quadrangle). The mine lies high on a steep hiMope north o f the head o f the Middle Fork o f Stone Creek, oi% 2,ODD feet or so southeast of Pfizer's Treasure Chest Mine. T he geology o f this mine is similar to that o f the Pfizer mines to the north, except for the strong possibility that the strata of tire Beaverhead Mine hive been overturned w ith respect to the strata of tire Pfizer mines. At the Beaverhead Mine we have essentially a angle body o f talc that has at h ast 800 feet o f strike length, and is offset by relatively minor lateral faults, it ranges In horizontal width from 25 to 100 feet (probably averaging near 75 feet), and Juts locally been dned to a vertical depth o f 150 feet, The strata dip homoclinally north 35 to 70s ; the average dip Is probably close to 45. The strike ranges from east to slightly north of cast. T he footwall is dolomitic, and the hanging wall b imposed o f schist and gneiss. This relationship is exactly the opposite to that of the Treasure Mines; coupled'with the fact that the dips are about the same, this suggests the possibility that the Beaverhead Mine may be on the same isoclinal foM as the Treasure Mines but on the opposite limb. Field mapping by Garihan (1973) and the writer, however, has not been able to prove or disprove this possibility. As contrasted with the Treasure Mimes, the " talc-zone*' of the Beaverhead Mine is only locally a ingle homogeneous talc body from tire footwall to the hanging wall; almost every where it contains numerous large "horses" o f non-talc rock, especially dolomite that las not been altered to talc. Seemingly the dolomite is more abundant in the lower half {southern part) o f the " talc-zone" than in the upper half (northern part), and the purest talc occurs along the hanging-wall contact. The footwall o f the "talc-rone" is well-layered granite gneiss, which is very similar to that which. Forms the hanging wall o f both Treasure Mines, Between this gneiss and the talc ore is a dolomitic zone, suggesting that fo r some reason the "talc-zone" was not entirely converted to talc ore, as it was at places in th e Treasure ' M in, The hanging-wall rock adjacent to the " talc-zone" 1* biotlte schist, which is in turn overlain by welMayered granite gneiss, which has been locally cldoritizcd. Garihan (1973) stated that |fr# hanging-wall country rock Is similar to the footwall material of the Treasure Orest, and the writer fully agrees. In this mine, in b o th o f tire Treasure Mines, and in the Smith-Mlon Mine there is the suggestion that the best talc Iks along the contact of th e "tele-zone" with bio rite dust, suggesting th at this sharp contact may have represented a pronounced permeability barrier and thus may have locally chan nelized a id impounded the mineralizing solutions. The present exposures of the Beaverhead Mine probably constitute its full possible extent, for it is likely that the western and eauern extremities are "pinch-outs" rather than faults. If the Treasure Fault extends this far south, the Beaverhead Mine probably lies entirely cast o f i t Several small high-angle to vertical northwest-trending right-lateral faults are present within the mine area, but their offsets seem to be even Iks than those o f analogous faults hi the Treasure Chest Mine. All o f these faults th at have been recognized in the Beaverhead Mine have their southwestern side throw n upwards, as is also true of all those In the Treasure Mines. Whereas topography is the friend o f the raiser at th e Treasure Mines, where the talc is dipping in the same direction as the hillslope, topography is the firm enemy o f the miner at the Beaverhead Mine. Stripping .1 `S "IK* ;* CPC-BCALTRSCPT00001121 l e Kr.EVXNTn INDUSTRIAL. MINERALS FORUM ratios, a t present probably similar to those at the Treasure Chest Mine, will become pronouncedly greater and at a faster rate for similar rates of production than they will at the Treasure Mines. The Beaverhead Mine has yielded most of its production in less than the last decade. Gaiifuai (1973) noted that the mine area tripled in rise during the period 1968-73, and s massive 1974-75 stripping operation has increased th e mine arm, even further. Ore produced from the Beaverhead Mine if trucked southeast down the Cottonwood Road to the Ruby drainage and thence to a small washing plant at the terminus o f a Burlington N orthern spur a t Alder, Montano. From this plant it may go to Belgium for processing there for European markets, o r to Cyprus' domestic mill! in Grand Wand, Nebraska, or Three Forks, Montana. 450 feet long (approximately along strike) and 50 to 100 feet wide, and the vertical depth is 20 to 30 feet. Berry (1948) described a shaft 60 feet deep and 300 feet of drifts off: the bottom of the shaft, all o f which are in talc, but these workings have been inaccessible for many years. The Regal Mine is of particular interest geomorphologieally. it is a true " pedlmented" talc deposit, fox over several acres bedrock talc appears in large out crops right i t the surface without any grass or sod cover whatsoever. Talc-marble contacts are abrupt and have been locally faulted, as shown by numerous small lateral offsets. Talc float is locally so abundant th at one's boot can hardly be placed upon the ground surface without touching some of It, REGAL (KEYSTONE) MINE The Regal (Keystone) Mine s situated alongside the Sweetwater Road in th e NW14 NEJ4 and NEVi NWW sec. 2, T. 8 SL, R, 7 W., Madison County (Christensen Ranch 714-iiiinute quadrangle). It is owned by Pfizer, Inc., having been acquired b y them In 1966 along with all other assets of Southern California Minerals Company. Okuma (1971) described the mine as occurring dose to the core o f a tightly refolded syreform. The ore body Is complex in that there axe many large lenses o f talc enclosed within a la rp body o f dolom ite marble; this relationship has been further complicated by wide spread faulting. Except for intrusive diabase, rock types other tiran talc and marble are rare upon this fairly large property. H ie marble strikes N. 45a ., to S. 80 E. and dips 30 to 75 north; although the structural geology in the area around the mine is extremely complex, this uniform attitude holds throughout the exposed extent o f talc on the surface. A diabase dike more than 200 feet wide, seemingly vertical to subvertical, cuts the foliation o f the marble almost at right angles along the western edge o f the best exposures of the talc. Okuma (1971) has observed that at many places where the diabase has intruded the marble, no talc has been formed along the contact, but rather the dolomitic marble has been contact-metamorphosed to calotte and fine-grained serpentine. A conjugate fracture set may be observed along the north wail of the open pit on the southern ride of the Regal Mine area; these fractures are vertical or subvertical and strike N, 60 W. and N. 30 ., the former being apparently better developed. The bedrock Faults that displace talc-marble contacts so spectacularly at many places on the ground surface have the same azimuth traces as the aforementioned fractures, and similarly the northwesterly ones are better developed; however, the existing exposed relationships do not allow even a well-educated guess as to the relative directions of movement along these presumably minor faults. The Regal Mine could well be the largest single mass of talc in the entire Ruby Range, Unfortunately, its operation has thus far been controlled strictly by sales conskicretions; Le., the talc at the surface makes relatively poor products (mainly because of the dark color) and consequently low sales and profit figures do not result in the generation o f sufficient funds to explore its potential at depth. This is a common failing in the industrial-minerals field and is certainly not restricted to talc alone! As the Regal tale ores ire known now, it is true th at the color is bad, owing to the presence of graphite and Ihmmite (altered from contained pyrtte), but the character o f the talc at depth is almost completely unknown. SAUERBIER MINE Bedrock talc is exposed at the Regal Mine along more than 750 feet of strike length and over a horizontal width o f more than 300 feel perpendicular to strike, A small open-pit mine has been developed along the southern margin o f the Regal taic deposit. It Is about The Sauerbier Mine is the newest talc mine in the Ruby Range, having been established upon almost virgin ground in 1973. It is situated in the NWkS NW14 sec, 25, T. 8 S., R, 7 W., Madison County (Elk Gulch 714-minute quadrangle). It lies just south of a major j1 ; j j | f ! J ^ ^ j * j j | ** j , j | ; 1 CPC-BCALTRSCPT00001122 T H R G RO t C O Y O F M O N T A .N A T A I .C D E f-O S T S --R . H , O I O N 127 fault zone developed along the southwestern edge of the flats south of the Sweetwater Road; the Carter Creek Fault may connect with this zone. It is unlikely that any large commercial talc ore bodies will he found east o f this property, for it is seemingly the easternmost extent o f the marble in this general vicinity. The talc has been developed within a marble zone, which strikes N. 35* E. and dips from vertical to an estimated 70 southeast. Downhill northward from the mine toward the valley of Sweetwater Creek, shallower southeast dips (as flat as 30* or so) may be locally observed. The east and southeast dips to sec, 7.5 contrast with west and northwest dips in sec. 26 and over much of the Owen-McGovem Prospect and Indicate the degree of local structural complexity, which is probably due to the proximity o f the aforementioned major fault zone. The talc Is more sporadic and erratic in its distribution within this "talc-zone" than to that o f any other Montana talc deposit of which the writer is aware. Hand sorting lias been necessary at this mine from the beginning, and unless pronounced changes in the geological relation ships are encountered, it will probably always be so. The American Talc Company, of Summit, New Jersey, has mined this property under lease from Mr. Karl L. Sauerbier o f Alder, Montana. The handsorted ore is trucked along the Sweetwater-Ruby Road to Alder, where it is stockpiled on concrete pads for shipment by rail to mills in South Plainfield, New Jersey, and Alpine, Alabama. INACTIVE TA LC MINES IN THE RUBY RANGE AMERICAN OiEM ET MIME B0Z0-20B0 MINI The American Chemet Mir is situated in the m * sec. 12, T, 8 S., R, 7 W,, Madison County (Christensen Ranch 7;4-minute quadrangle). It was once operated by the American Chemet Corporation of Chicago, Illinois. The workings consist of three open pits and several minor bulldozer trenches. The talc is contained within "a complexly folded northeast'trending belt o f marble" (Okuma, 1971), winch is Isolated within large expanses of Dillon Granite Gneiss extending both northwest and southeast. BANNING-JONES MINE A talc deposit in the SW& sec. 13, T. 8 S., R. 8 W., Beaverhead County (Dillon East 714-mtoute quadrangle) was leased by the State of Montana In 1964 to Messrs. Wallace Banning and Lester Jones, both o f Dillon, Montana (Geach, 1972). It is situated within the same belt o f marble as is the Smith-Dillon Mine, which lies along strike from It about I mile to the southwest. Talc lias formed within a marble zone as much as 100 feet wide, but the wider* zone of talc known (without included marble bodies) is only about 10 feet wide, and few such dolomite-free talc bodies are more than 5 feet wide. The talc is exposedmn b o th sides of a major north-flowing gully and has seemingly been displaced at least 100 feet laterally by a right-lateral fault, which has determined the course of he gully. Small amounts of talc were in; oed here, hand sorted, and tracked to Sheridan, Montana, where they Were purchased by American Chemet Corporation. The Bozo-Zobo Mine ties in the NEtl sec. 19, T. 8 S., R. 7 W.} Beaverhead County (DiUon East 714minute quadrangle) on the northern wall o f Axes Canyon near its head. The strata here strike N. 50 B. and dtp 80 northwest. The best exposures are in a large open cut near the southwest edge o f the property, where the talc is 25 to 30 feet wide and has been mined to an esti mated maximum depth o f 50 feet or so, Seemingly less than half o f the mineralized zone was converted into talc, as shown- in this cut, rendering selective mining difficult and hand sorting probably absolutely necessary. The occurrence o f talc at several different levels along the north wall o f Axes Canyon may indicate either the presence of several veins or the repetition o f a single vein by tight isoclinal folding or faulting, but this puzzle will be solved only by careful mapping, aided by the results o f the previous drflltog program. Manganese oxides have locally stained the laic so intensely as to render it useless. The Bozo-Zobo Mine lies roughly along strike from a similar prospect in the SW% NW14 sec. 19, which is described elsewhere in this article. The two may represent the same stratigraphic zone and therefore a potential strike length of talc o f 3,000 feet or so, but such a possibility, o f course, would have to be proved by detailed mapping of this relatively small area. The property was drilled by R, T. Vanderbilt Company to 1962-63 under the direction of Mr. 1. R. Morcttj; four core holes and at least 23 rotary drill holes were sunk during the course o f that exploration program. } * CPC-BCALTRSCPT00001123 S8 KLKVKKTH INDUSTRIAL MINERALS rO R U H American Chemet Corporation o f Chicago, Illinois reportedly shipped approximately 8,000 tons o f ore from this property in the mid-196Q's. SMnifDlLLON MINE The Smitli-DiUon Mine, topographically the lowest tale mine lit the Ruby Range, Is situated almost at the mouth o f Axes Canyon near the southwestern corner of the range in the WH sec. 23 T. 8 S.r R. 8 W., Beaver head County (Ashbough Canyon 754-irajnite quadrangle). Although th is mine was an important producer of highgrade ore in the early days of the Montana tale district, it has been inactive for several years now. Originally an underground operation, it was open-pitted in its last days. The marble unit in which the talc occurs is about 1,300 feet thick according to Okuma (1971). The regional strike is N, 30* to 40 E, and the dip is & f to 70 northwest. Although ad of the talc occurs in dokanitie marble, relatively little of the "talc-zone" has been converted into talc. Marble ribs, locally veined with white quartz, are common within the talc bodies and have long created a problem in the mining of this deposit. Okoina (1971) also noted the presence o f small thm folded " stringers" o f talc within the marble of the "talc-zone" . The feotwall in the mine area is dark mica schist* which is extensively slickenrided, as in the footwails o f the two Treasure Mines. It is probable that the tale exposed in shallow diggings at the Crown Mine, about 700 feet to the northeast, represents the same zone as that at the SmithDdkm Mine* b u t to the writer's best knowledge this has yet to be proved by exploration. The presence o f abundant talc float over the concealed area between these two properties, however, suggests that they may represent the same ore zone and that there may be a fair degree of lateral continuity of talc mineralization. Although it is obvious that talc would have to be mined much more selectively upon this property than upon other Pfizer properties --indeed, hand-sorting may even b e an absolute necessity here -- much of the talc o n the Smith-DlUon and adjacent properties is pure and o f good light color. Mining rights on this and adjacent properties are owned by the Minerals, Pigments and Metals Division of H im , Inc., which, obtained them through their aequisit ion in 1966 o f the assets of Southern California Minerals Company, SWEETWATER MINE Numerous workings along the Sweetwater Road about 16 miles southeast o fDillon ar e collectively known as th e Sweetwater Mine (Okuma, 1971). These workings are situated in the EM sec. 13 and NEW see. 24, T. 8 S., R. 7 W., Madison County (Christensen Ranch 7 14-minute quadrangle). The tale, as proved thus far by the open-pit mining, occurs over a strike length of a to u t 750 feet and has an average horizontal width o f about 50 feet; ft has been rained to down-dip depths o f about 125 feet in the open pit, and according to Perry (1948), to depths of more than 200 feet underground. The talc has been abruptly truncated at the northern end of the pit by an easi-west fault, which dips 55 to 60 south. Leftlateral displacement along this fault is on the order of 70 feet. The talc lies completely within a marble unit, which is about 460 feet wide, strikes N, 20 to 30 B. and dips 50 northwest (Okuma 1971). The marble is a relatively thin unit completely isolated within a large mass of Dillon Granite Gneiss, rinnlar to the situation at the American Chejnet Mine only a mile or so to the north. Okun (1971) cited convincing evidence that, in this particular deposit at least, the talc has definitely formed from dolo.mitk marble and not by the alteration of ultramafic rooks. TALC PROSPECTS IN THE RUBY RANGE BENNETT OWEN CLAIM The B ennett Owen Claim is located near the head of Cottonwood Creek in the NWli sec. 12, T. 7 S., R. 6 Vf., Madison County (Mine Gulch 7-minute quad rangle). T he strata here strike N. 70 E. and dip 55 north. Talc is shewn in place by bulldozer cuts over a strike length o f at least 80 feet and a width of St least 20 feet. Although the exposed ta b is everywhere dark green, it powders surprisingly to white or near-white colors. Garihan (1973) described this as the largest body of uniformly dark green,low-purity talc known to him in the central part of the Ruby Range. His petrographic work has shown the presence of opaque minerals and minor chlorite in the talc. The footwtU rode is dolomitic marble and the hanging-wall rock is either dolomitic marble or reddish Dillon Granite Gneiss, depending upon the location; therefore, the geology is similar to that ( | ? ti 1 j { f j 4t i * j j I j | I ! I f j CPC-BCALTRSCPT00001124 T H E G EO LOGY O F MONTANA TALC DEPO SIT S - i i , EL OLSON 129 of th e Treasure and Beaverhead Mines a rnfle or so to the southwest. CRESCENT PROSPECT The Crescent Prospect was acquired by Pfizer* Inc,, when they obtained the assets of Southem California Minerals Company in 1966, It has not been mined, chiefly because of its graphite content and the presence of dark staining throughout the talc. This deposit fa situated in the SW34 sec. 1, T. 9 S .,R . 3 W., Beaverhead County (Aahbough Canyon 7)4-mInute quadrangle). The talc occurs within marble layers 10 to 15 feet thick, which have been intruded by pegmatite and granite gneiss bodies. The marble strikes northeasterly, dips northwest at 50 or so, and is locally so decomposed that It fa friable. Perry (194S ) described talc float as having in extent o f 0 0 to 1,000 feet along strike. A shaft and some small workings have proved the talc to a depth o f at least 20 feet. GEM CLAIM Two small bulldozer cuts in the SEli sec. 34, T. 6 S,, R . 6 W,, Madison County (Beaverhead Rock SE 7H-nunute quadrangle) have exposed small bodies of dark-green talc, which are not o f economic interest, as exposed, because of their small size and dark color. These showings are on the Gem Claim, which fa owned by Pfizer, Inc. OWEN-McGOVERN PROSPECT SECTION 11,T. 7 S ..R . 6 W. Bulldozer cuts in the S3i sec. 11, T. 7 S., R, 6W ., Madison County (Mine Gulch 754-rntnute quadrangle) just north of the heft Fork o f Stone Creek have exposed several showings of talc. The strata in tlifa area strike roughly east-west and dip 50 to 60" north. These talc bodies, which are developed within dolomitlc marble, are as thick as 10 feet and have lengths of as much, as B0 feet. Minor amounts o f the talc are o f the lightcolored variety sought for commercial uses, but most of it fa somewhat darker; furthermore, the common presence of Iimonite arid graphite renders that talc which is exposed of minimal economic interest. SECTION 13,T. 7 S .,R . 6W . Cyprus Industrial Minerals Company has cut I small prospect pit into the same marble unit as that o f th e Treasure Mines, This pit fa located about 4,000 feet southeast o f the Treasure Cheat Mine and is in. the WA sec, 13, T. 7 S,, R, 6 W-, Madison County (Mine Gulch 734-minnte quadrangle). The relationships o f the talc bodies are poorly exposed, this being an old pit, but the largest talc body fa less than 5 feet wide. The strike fa roughly east-west and the dip fa 50 to 60 north. Graphite is locally present, and m ost o f the talc is dark green, but minor quantities have the light-green commercial color. SPRING CREEKPROSPECT The Owen-McGovern Prospect fa covered by the Badger #t*S mining claims in the SE3S sec. 23 and the m see. 26, T. S S , R. 7 W., Madison County (Elk Gulch 734-minute quadrangle). Although the geology o f these deposits fa n o t yet satisfactorily understood, it is apparent that they are a continuation of the talc at the Sauerbkr Mine, which fa to the northeast. Several bodies of dolomitic marble are present upon this property, and all o f the known talc occurs within such rock, There fa no talc deposit in Montana known to the writer whose geological relationships are so difficult to decipher as this one! The dolomite bodies have been intruded by pegmatite, amphibolite, and diabase dikes. The soil and tree cover are thick and exposures are rare. The regional strike of the strata fa Nr 20" B, and the dip ranges from 50" to 80 northwest. Okuma (1971) Sated that this property has "now been thoroughly investigated" , but the writer strongly disagrees. No detailed geological map has ever been made of this complex area, and the relatively minor amount o f exca vations and drilling cannot rule out th e possibility of ore bodies within this large area. Talc in doiomitic marble is exposed along the north side o f Spring Creek In the SE3i SE54 sec. 32, T. 6 S-, R. 6 W., Madison County (Beaverhead Rock SE 734-aimttfi quadrangle), This same zone o f talc extend* (seemhgly continuously) southweslward into the NE)i sea 5,T, 7 S,, R. 63V. and northeastward into the central part of sec. 33, T. 6 S., R. 6 W., where it seemingly extends underneath the Cambrian strata. This zone, which extends for about 6,000 feet In a northeasterly direction, shows the longest single strike length o f talc known to the writer in the Ruby Range or anywhere else in Montana. Talc widths of more than 20 feet and continuous lengths of 100 feet or mote are exposed in the old workings along the north ride o f Spring Creek. The marble unit, which contains all o f the known talc showings on this property, strike* N, 50 E .s dips 60 to 70 northwest, and has a horizontal width of about 1,500 feet over most of its strike length; Garihan (1973) called this unit the "Regal Marble" , the same doiomitic marble unit as that which contains the Regal (Keystone) Mine, and he slated that it may be traced to the south from this prospect for a distance o f about 10 miles. 1 CPC-BCALTRSCPT00001125 ISO E L E V IN T H IN D U STR IA L M IN ERA LS E O R tlM Muck o f the talc exposed upon the Spring Creek Prospect is darker than that now being used (except for that of the Regal Mine), and this deposit contains more different colors o f talc than any known to the writer in Montana; nevertheless, the presence of some suitable-colored talc phis the extremely large size of this prospect make it worthy of a serious exploration effort. WHITNEY CLAIMS The Whitney Claims were acquired by Pfizer, Inc., when it obtained the assets of Southern California Minerals Company in 1966, They lie to the north of the Treasure Mines on the steep hillsbpe north of the Left Fork o f Stone Creek in and around the SW14 sec. 2, T. 7 S . L 6 W., Madison County (Mine Gulch 7tminute quadrangle). As at the nearby Treasure Mines of Pfizer and the Beaverhead Mine of Cyprus, the strike is roughly eastwest and the dip is to the north or northwest, in this area about 50 or so. The talc is entirely enclosed within d o b m itic marble, and much o f it is light green and crypto crystalline, as are th e best commercial talc ores elsewhere in the Ruby Range. Us quality and desir ability, however, are downgraded by the presence of pyriie and limonite, b y the intense hearing to which it has been subjected, and by the presence of bodies of quartz and dolomite within the talc bodies. Southwest o f the main Whitney Claim, some small cuts in the SEK sec. 3, T. 7 S., R. 6 W., Madison Cbunty (Mine Gulch fki-minute quadrangle) hnie exposed small quantities o f green graphitic iac in fractures within dobm itic marble. This talc body to as much as 15 feet thick. O ther cuts below the timber line have exposed additional talc occurrences, one of which is more than 20 feet wide. These tale bodies, which arc In the western most exposure o f the marble o f the Whitney Claims, are contaminated by the presence o f marble "horses" and locally abundant graphite. MISCELLANEOUS PROSPECTS IN THE CENTRAL RUBY RANGE Garihan (1973) has noted the occurrence of talc bodies in dolomite in the SWA sec. 1 7 ,T .7 S .,R .6 W., and the presence of talc float in the SWK sec. 18, T7 S,, R . 5 W., and in theSWK sec. 11, T. 7 S-, R. 6 W,, all in Madison County and all on the Mine Gulch 714-minute quadrangle. These do not seem to be of interest in themselves as exposed, but they may well indicate areas worthy o f further investigation. MISCELLANEOUS PROSPECTS IN THE SOUTHWESTERN RUBY RANGE Tale occurrences are numerous throughout the southwestern part of the Ruby Range, especially upon the Benson Ranch which, to Hie writer's best knowl edge, has never been thoroughly prospected or studied. The writer has never done any field work o n the Benson Ranch, but from oral descriptions given by others, it is obvious that it would take souk lime for any worker to even visit, let alone inspect and study these occur rences, None o f the prospects described below are on the Benson Ranch, Talc in place is exposed fairly continuously for about 1,350 feet o f strike length along the crest of the northern wall of Axes Canyon in see. 19, T. 8 S., R. 7W ., Beaverhead County (Ashbough Canyon and Dillon East 714-minute quadrangles). The strata here strike N . 55 E, and dip 55 northwest. Most of this talc is in the SWTi NWJ4 sec. 19, This talc, for th e most part, Is much darker than any currently being mined in Montana, indeed some o f it is black -- but the large size o f this showing would seem to render it worthy of further exploration. Several talc prospects in the southwestern part of the Ruby Range, discovered and developed by Messrs, Tom McGovern and Bennett Owen o f Dillon, Montana, are now under lease to I. M. Huber Corporation of Atlanta, Georgia. The remaining properties discussed In this section all belong to this group. Talc in place may be traced fairly continuously over a strike length of about 900 feet in th e W}4 NE& see. 35, T. 8 S., R. 8 W., Beaverhead County (Ashbough Canyon 714-mimite quadrangle). The strata strike N. 55 R at this locality and dip 70 north to vertical. A t least three dearly separate stratigraphic zones contain talc, and solid widths o f at least 10 feet have been locally proved by shallow irenclres. The talc is light green and at depth could probably be as good as most o f that which is now being mined in Montana, assuming that impurities such as pyrite and graphite were absent. Bulldozer cuts have exposed talc in place at two localities in the NW'4 NWVa sec, 36, T, g S , R. 8 W,, Beaverhead County (Ashbough Canyon 7%-rnimite quad rangle). The talc exposed to generally dark green. Mining rights are owned by the State of Montana. The Valley View Prospect, in the SWH sec. 25, T. 8 S., R. 8 W., Beaverhead County (Ashbough Canyon 714-minute quadrangle) is, with the exception of the i i -I I t ii i r i CPC-BCALTRSCPT00001126 T H E G E O L O Q V O F M O N T A N A T A L C D E P O S IT S --R . H. O L S O N 131 Regal (Keystone) Mine, the largest body of dark talc known to the wiiter in the southwestern part oT the Ruby Range. Bulldozer excavations have exposed a probable horizontal width of talc of about 90 feet, and the talc may be traced for at least 150 feet along strike. The strata at this locality strike N. 50 E. and dip 55 northwest. Green talc, somewhat resembling that of the Regal (Keystone) Mine, occurs in place along a ridge crest for several hundred feel and has horizontal widths of 5 to 30 feet in the SEW SEW NEW sec. 26, T. 8 S., R. 8 W,, Beaverhead County (Ashbough Canyon 7W-minute quad rangle). The enclosing dolomile strata are essentially vertical. This showing and other isolated outcrops to the southwest and northeast make up a total strike length of at least 1,200 feet in sec. 26 and adjacent sec. 25. This talc is megascopicaUy very similar to that of the Valley View Prospect. In sec. 1 and 2 , T. 9 S., R. 8 W., Beaverhead County (Ashbough Canyon 7W-nunute quadrangle) a well-developed zone o f talcose rocks may be traced for 5,000 feet along strike (east northeast) from the Brown Ranch Road along the base of the range in the SEW SWW sec. 2 on into the SEW NWW sec. 1. Talc ore, per se, has never been observed upon the surface by the writer, but the extent of the talcose development in rocks in place certainly warrants further exploration of this large and long zone. Talc float of high purity and light-green color has been traced continuously along relatively horizontal land over more th an 600 feet of strike length to the south west o f Hanson Spring in the SWW SWW sec. 3, T. 8 S., R. 7 W., Madison County (Christensen Ranch 7Wminute quadrangle). The horizontal width o f the talc zone perpendicular to the strike is locally as much as 325 feet. The strata here strike N. 30 E. and dip 70 to 75 northwest. Outcrops are rare, but the host rock can clearly be observed to be dolomitic marble. Darker talc crops out in higher stratigraphic positions to the northwest over a stratigraphic thickness o f about 200 feet and along strike lengths of at least 300 feet. in the writer's opinion, one of tire most attractive talc exploration targets in Montana occupies an estimated 480 acres in sec. 10 and an estimated 220 acres in sec, 11, T. 8 S., R. 7 W., Madison County (Christensen Ranch 7!d-minute quadrangle). Along the northern boundary of this area, talc is exposed both in place and as abundant float in several separate stratigraphic zones over about 7,000 feet of strike length before being truncated on the eastern end by the Carter Creek Fault. In the SWW NEW sec. 10, abundant talc float has been traced along a 650*foot strike length and over at least 170 feet of horizontal width in an area where the enclosing dolomite strata strike N. 50 E. and dip 80 northwest. High-purity talc lying in a gentle swale on the Gopher #1-3 mining claims in the SWW NWW sec. 2, T. 8 S,, R. 7 W., Madison County (Christensen Ranch 7W-minute quadrangle) probably represents a southwestward extension of the talc of the Regal Mine, owned by Pfizer, Inc. The light-colored talc float, which may be traced over about 200 feet of strike length and a horizontal width of 100 feet, is probably the equal in quality of any talc being mined in the Ruby Range. Talc float is abundant along both sides of a ridge of dolomitic marble that extends from the NEW sec. 15 on Into the SWW sec. 11, T. 8 S., R- 7 W., Madison County (Christensen Ranch 7W-minute quadrangle). Sporadic talc float has been detected by brief recon naissance studies over a strike length o f 4,000 feet or so; but a puzzling riddle lies in the fact that there are so few outcrops of talc compared to the large abundance of float. Most of the talc observed is green, somewhat darker than the grades that are being mined in Montana. This long ridge of dolomitic marble has the structure of a synform, its axis striking N. 30 E. and dips averaging 50 or so on both the northwest and south east limbs. The dolomite strata seemingly wrap around the southwestern nose of the ridge, giving structural closure there, but on the northeastern end the dolomite is truncated by the Carter Cheek Fault. A large thick band of dolomitic marble north of Gordon Peak in sec. 21 and 22, T. 8 S-, R. 7 W., Beaver head and Madison Counties (Christensen R anch 7Wminute quadrangle) contains several talc prospects in dolomite strata, which strike east-west and dip 40 to 65" north. This large belt of predominantly dolomitic rock averages about 2,500 feet in width over almost 3 miles of strike length. One talc zone in the NEW NEW NEW sec. 21 extends for about 500 feet along strike. GENERAL GEOLOGY OF THE GRAVELLY RANGE The name "Cherry Creek" was first used by Peale (1896) for rocks in an area 15 to 20 miles south o f Ennis, Montana, along the base of the eastern flank of the Gravelly Range. He stated that "The Cherry Creek 1.I (*4,1 xA CPC-BCALTRSCPT00001127 is* ELEVENTH 1NDU3TKIAI, MINERALS EORUM beds consist of a series o f marbles, or crystalline lime stones, a ad interlaminated mica-schists, quartzites, and gnsis&es" and that `"They are all highly inclined and are perfectly conformable to one another occupying an area o f 30 to 40 square miles.'' H e i r total thickness, according to Peak, "is certainly not less than several thousand feet" and to his columnar section he showed a thickness of 7,000 feet or more for the "Cherry Creek" portion o f the Precambrian section. The most detailed study of the type area o f the Cherry Creek Group has been made by Heinrich and R a b b it (i9 6 0 ). In general the grade of the metamorphism increases slightly as one goes northward, but it is puzzling how rocks o f different mctamorphlc grades can exist together in the same area, e.g., phyllite, mica schist, and kyanite schist along the Cherry Creek drainage. Heinrich and Rabbitt (I960) recognized the folew ktg major classes of rocks in the type area of the Cherry Creek Group: reported one dolomitfc marble as nearly 4 0 0 0 feet thick, but later workers and the writer believe that much of this thickness is likely due to structural flowage during folding and to repetitions caused by tight folding. Heinrich and Rabbitt also noted the relatively rare presence of tremolitic marble in the area, but the pres produced thus far from the Johnny Gulch area have characteristically contained no detectable tremolite, J; may be readily seen from a comparison with the rock types mapped, as "Cherry Creek-type rocks" in the Ruby Range by Okuma (1971) and Garihan (1973) that the sequences there and In the Gravelly Range are very much alike. One o f the most striking differences involves the amphibolite rocks, for Heinrich and Rabbitt (1960) stated that " dark-colored amphibole gneisses axe much less common In the Cherry Creek area than some other pre-Belt ian areas, as for example, in the Ruby Mountains." They estimated the total minimum thickness of the Cherry Creek Group in its type area as about 30,000 feet. J , Marble, calc-schist, and lime-silicate gneiss 2. Quartzite and quartz schist 3. Phyllite 4. Mica schist 5. Kyanite schist and kyam teslaurollte schist 6. Silllrnanitc schist and gneiss 1. Magnetite schist and toted rocks (" iron formation") 8, Amphibole gneiss, schist, and amphibolite 9. Quartz-feldspar gneiss, granitic gneiss, biotite, and injection gneiss The marble layers are the thickest and the most laterally persistent o f these rock types. Heinrich and Rabbitt Hadley (J969a, 1969b) hat mapped the geology of tw o key 15-minute quadrangles in the area o f the producing talc mines o f the Gravelly Range and has shown in detail, within that restricted area, the distribu tion of the dolomitic marble o f the type Cherry Creek Group. Mann (1954, 1960) has described the general geology of that part of the Gravelly Range that Is of interest for its talc potential. Most of his attention was devoted to the Paleozoic and Mesozoic Systems; rock types within the C h ary Creek Group were not differentiated. GEOLOGY OF TALC IN THE GRAVELLY RANGE There ate three known areas of significant talc mineralization is the Gravelly Range: the Yellowstone Mine in sec. 4, T. 9 5 , R. 1 W., the Johnny Gulch Prospect in sec. 34, T . 8 S., R . 1 W., and sec. 3, T, 9 S., R. I W., and the Tri-State Prospect in sec. 5, T , S S., R. I W., all in Madison County. Several other occurrences o f talc axe known in the Gravelly Range, but only these three will be discussed at length here, Hogberg (1963) generalized that in the Gravelly Range the lens-shaped talc bodies "n a y he as much as 100 feet wide, tjOQO Feet long, ISO feet deep, and are generally concordant with the regional structure" . All of the talc that is known In the Gravelly Range occurs within dolomitic marble units and is generally concor dant with the metamoiphic foliation. The largest single mass erf marble in the Graveliy Range is that one situated between Johnny Gulch and Cherry Creek, which form s an area about 5 miles long: and H i miles wide, roughly parallels the strike of the strata, and contains all o f the currently known commer cial talc deposits In the area. The nature o f the Formation of talc in the Gravelly Range is similar to th at in the Ruby Range, as are the mineralogy and the chemistry of the ores. In addition, the general geology o f the two areas is very similar, the starting materials for the talc are everywhere the same, and the structural evolution of the two areas is also similar. For reasons unknown, however, the relation ships of the talc ore bodies to their enclosing rocks is markedly different in the two ranges. In the Ruby S -j ! j * i ! ' f r * J CPC-BCALTRSCPT00001128 T H E OKOLOGY O F MONTANA T A L C D E P O S IT S - . H. OLSON 133 Range, for instance, it is not uncommon for an entire wide zone o f dolomite between other, non carbonate rock types to have been converted almost completely into talc containing few or no "horses" of foreign rock. Even where the entire "talc-zone" has not been converted to talc, it Is common in the Ruby Range to have large thick tabular masses o f talc "intcrbedded" with other rock types within the "talc-zone". This relationship has been nowhere observed in the Gravelly Range, where there is invariably an intimate and small-scale inter calation o f talc with dolomite and where there are few bodies o f pure talc more than 5 feet thick containing no foreign rock types. The behaviour of the talc in the Gravelly Range Is markedly digitate on a small Kale; the behaviour of the talc in the Ruby Range is generally. tabular and in much larger bodies. Even where the behaviour of talc in the Ruby Range could be described as digitate, it would be more subtly so and on a much larger scale than in the Gravelly Range, Throughout this a m the removal of the talc by either powered shovel or front-end loader is made easier by the profusion of post-talc fracturing and shearing, which is strongly developed and closely spaced as shown in all o f the existing workings. Therefore, if past history Is to be a reliable guide, we can generalize that although ore bodies ran be mined in the Ruby Range with large mining machinery but without hand sorting, the ore bodies in the Gravelly Range will continue to be mined with similar equipment but the resulting mill feed will necessarily continue to be subjected to hand sorting. Current investigations by graduate students o f the University of Indiana will shed new light upon the intricate problems of the type Cherry Creek sequence, especially with re p rd to mefsmorphic events. The major difference between the Cherry Creek sequences o f the Ruby Range and those o f the Gravelly Range lies in the maximum degree o f metamorphism undergone in Precambrian tune -- upper amphibolite grades having been reached in the areas of talc mineralization in the Ruby Range, whereas in some areas o f talc mineraliza tion in the GraveDy Range it may be that only greenschist grades were attained. In the Ruby Range a widespread regional metamoiphic event of greenschist grade was experienced after the higher-grade events; therefore, it is possible that the talc in both ranges formed during periods o f similar intensity of Precambrian metamor phism (i.e., greenschist pads), whether or n o t con temporaneously. TALC MINES AND DEPOSITS IN THE GRAVELLY RANGE YELLOWSTONE MINE The Yellowstone Mine, In the SH sec. 4, T. 9 S., R. 1 W,, Madison County (Cameron 15-miqute quad rangle) is the primary Montana source of talc ore for Cyprus Industrial Minerals Company ami has been So for more than tw enty years (Fig. 10-5). The mineralized area, according to Perry (1948), is at least 2,OCX) feet long at a northeast direction and about 800 feet wide. Within this area there are several large bodies of talc within the main d o b mite mass, but these large talc-bearing bodies enclose abundant dolomite "horses". The writer was allowed to study the geology o f tbs Yellowstone Mine in the summer of 1974, There we several workings, both underground and open pit, within thi3 large mineralized area. Many of these workings, inducting all of the underground ones, have been inactive for many years. The main pit, which is also the deepest one, has been developed along an sitauth o f M. 20 W. for the most part -- a direction dtet is n o t exactly parallel to the foliation o f the strata but Is fairly dose to being so. Such a relationship is common throughout the mine area, Le.t a slight direc tional variance is common between the strike o f the dolomite foliation and the longest dimension o f the talc ore bodies. The strike of the strata within the main mine area ranges from north to H. SO0 E. and dips range from vertical to 50 east. The main pit is now about 2,500 feet long, averages about 200 feet wide, and has been mined to down-dip depths o f ISO to 200 feet. Unlike the producing talc ore bodies o f the Ruby Range, talc at the Yellowstone Mine does not form large enough individual bodies to permit the mining of high-purity talc ore by the use o f machinery alone; all of the ore now exposed within the area of the Yellow stone Mine must be hand sorted in order to derive suitable mill-feed material, in one area o f the Treasure Chest Mine (Ruby Range), the entire dolomite unit (^talc-zone"), about 120 feet wide horizontally, had been converted into commercial talc of the highest grades. In the Yellowstone Mine, thicknesses o f more than 5 Feet o f high-purity talc without included dolomite are uncommon. Talc was noted to be abundant in one local area of the main pit of the Yellowstone Mine, but not a single thickness of more than 1 foot o f pure Sh 1 I I CPC-BCALTRSCPT00001129 1S4 E U iV K /m i IWHUSTRIAI. MlNKRALS FORUM 10-5, --Tale mines and proijrects, Qravdly Range, Madison County. CPC-BCALTRSCPT00001130 TH B GEOLOGY O F MONTANA T A L C D E fO S tT S --H. H. OLSON 135 talc was observed. The talc is commonly seen to " make" in a gray fine- to medium-crystalline dolomite, which is generally thin bedded (laminae or foliae commonly less than 6 inches thick). Although most o f the talcdolomite contacts seem to follow primaiy features, there are indications that many o f them may represent fractures or faults o f extremely small displacement. It is more common for the contacts o f the small bodies of hlgh-purity talc to cross-cut the dolomite foliation at low angles than for them to be concordant, although In the lowermost levels o f the main pit such cioas-cutting relationships were observed to form a t angles of 30 or more. Shear surfaces developed at such angles to the foliation may have locally exerted n control upon the attitude and shape of individual talc bodies. Most of the talc at the Yellowstone Mine Is green or fight p a y (almost the color o f the enclosing dolomite), not pale green to white, as is much of the talc in the Ruby Range. All of the ore at the Yellowstone Mine is taken to sorting facilities where workers remove either the waste from the ore or the ore from the waste, depending upon grade. The high-grade ore is taken to an old enclosed and permanent hand-sorting facility along the north hillslope o f Johnny Gulch, where the waste is picked out and the talc is discharged from the end of the conveyor belts into holding bins. The lower-grade ore is taken to a portable hand-sorting facility In one of the upper pits, where the talc Is picked out and the waste is discharged o ff the end of the conveyor belt. This portable facility was placed in operation In 1972 and w in result in a much longer life for this mine. The towest-grade material, not regarded aa waste, is taken to large stockpiles north of the mining area. These stockpiles, called "bone piles" by the miners, consist of material that is too tow in grade to justify hand sorting at present b u t which may prove to be susceptible to ftotation-beueficktion processes in the ihture. If such methods of bencficiation ever prove feasible, these "bone piles" would constitute an immense supply of highpurity Montana talc ore. All o f the hand sorting or `'picking" at th e Yellowstone Mine is done upon dry rock, unlike the Pfizer operations, where hand sorting at their B anatts mill is performed upon wet rock. that war with governmental support (U.S. Bureau of Mines) in an effort to locate a replacement source for such denied material, which bad formerly been readily obtainable from Italy. These underground workings proved one talc lens to extend to a depth o f about 80 feet and another talc outcrop was traced at that tme through a vertical distance o f 150 feet. Seemingly the " block talc" (a to known as " lava talc" or " carving talc") occurred only In the deeply weathered siderite zone, from the surface- down to a depth o f no more than 45 feet or so. Ankerite and black manganese dioxide were a to abundant within this intensely weathered zone. The "block talc" graded downward into ceramic grades of talc, which In turn were underlain by hard unaltered dotomite. Hogberg (1963) ha* described th e history o f the exploration and development o f the Yellowstone Mine. Tri-State Minerals Company leased the property in 1942 and began exploratory work under the direction of Mr. L. F. Teutsch. The Sierra Talc Company of South Pasadena, California, purchased the land from Mr. Lewis Clark, the original discoverer, in January 1949 and then went from underground prospecting to open-pit mining. Hogberg (1963) gave the Yellowstone Mine "approximately 75 years of reserves based upon an annual production rate of about 20,000 tons o f cleaned talc" . Initial construction on the Three Forks, Montana, mill was completed to 1961 a t a cost o f about $400,000; the expansion, which was completed in 1974, is reported to have coat about 2,500,000, JOHNNY GULCH PROSPECT Those talc occurrences in sec, 34, T. 8 S,, R. 1 W., and sec. 3, T. 9 S., R, W,, Madison County (Cameron 15-minute quadrangle), which have been intermittently prospected over the years, are here referred to as the Johnny Gulch Prospect. These occurrences He within the same thick dotomite unit aa do those of the Yellow stone Mine less than a mile to the southwest, but unless isoclinal folding has afforded an incredible coincidence they are not to equivalent strata. The hand-sorted ore from the Yellowstone Mine h trucked either to Alder, Montana, for shipment to Cyprus' processing facilities in Belgium or Grand Island, Nebraska, or to their mill at Three Porks, Montana, During World War 11, the Yellowstone Mine area became extremely important because the U.S- was shut off from foreign sources o f "block talc" or "lava talc". Underground exploratory work was performed during Talc has been mined from deep, strike tranches and is exposed in shallow bulldozer scrapings over a strike length of about 1,500 fe e t The foliation o f the dolomite strikes on the average N . 25 E. and dips 75 to 80 northwest. In the area o f the main pit in sec. 3, where talc was mined to depths estimated at 30 to 40 feet over a total strike length o f 425 feet, talc in place is sporadic over a horizontal w idth o f as much as 275 feet. 9 n Zr CPC-BCALTRSCPT00001131 XUKVBNTK M 0B5TRJAL MINERALS FORUM T he talc forms more o r less concordant lenses with digitate outlines and most are less than 6 inches thick. The talc is generally darker than that in the Yellowstone Mine. In the 1960's the American Chemei Corporation of Chicago, Illinois, mined talc on this property in the SWK NWK sec. 3. TRI-STATE PROSPECT During World War II, th e Tri-State Minerals Com pany prospected by pits and a 25-foot shaft a talc fens 5 feet thick and several tens of feet tong in the NEK SEK sec. 5, T, 8 S , R . 1 W., Madison County (Cameron 15-nrimite quadrangle). This property "was abandoned because of tow grade and lade o f quantity" (Perry, 1943). MINOR OCCURRENCES SOUTH OF YELLOWSTONE MINE A small talc prospect has been opened in the SEK NEK sec. 8 , T. 9 SL, R. 1 W., Madison County (Cameron 15-mirtute quadrangle) about 1 mile southwest of the Yellowstone Mine. Dark tale is here associated with weathered and altered marble. Several small nearly vertical talc bodies are known in the NWK NWK sec. 9, T. 9 S , H I W ., Madison County (Cameron lS-minute quadrangle), and the pat tern of the dispersion of the talc float indicated to Hogberg (1963) that the aggregate thickness n a y be 100 feet. This area, unlike i s others described in the Gravelly. Range, is complicated by a local cover of Tertiary volcanic rocks. GEOLOGY AND TALC DEPOSITS OF THE GREENHORN RANGE The Greenhorn Range lies between the Ruby Range on the west and the Gravelly Range on die east. A belt o f " Cherry Creek-type rocks" extends from the east-central part of the Ruby Range eastward into the Greenhorn Range in the vicinity of Ruby Dam. Little is known o f the overall geology of this range, but several tale occurrences are known within it. TALC RIDGE MINE The most notable tele deposit in the Greenhorn Range is the Talc Ridge Mane, along Little Willow Creek on the western flank of the range in the SWK NEK sec, 30, T, 8 S-, R. 3 W., Madison County (Home Park Ranch 7K-minute quadrangle). This deposit was recently leased by American Talc Company of Summit, New Jersey, and has been mined by them during the period 1973-75, The ore is trucked to Adder, Montana, where It is stockpiled o n concrete pads for shipment by rail to processing facilities in South Plainfield, New Jersey, and Alpine, Alabama. The writer has not seen this deposit since American Talc Company began recent naning operations; the following description Is based upon a brief visit to the property in 1969, All o f the observe! talc is contained within dolomitfc marble units. The " talc-stone" is not completely converted to talc but contains abundant intercalated carbonate rock. The strata strike N. 45 E. and dip 25 to 4fT northwest. Smell pits on the property suggest that small-scale high-angle to vertical faulting is wide spread and well developed and would severely complicate the conduct o f large-scale open-pit mining operations. Left-lateral fault displacements were noted, but their magnitudes could not be determined. Individual veins of high-purity white talc are as much as 2 0 feet wide, Footwall and hanging-wall rocks are either dolomite, granite gneiss, or mica schist; locally the rock type of the footwall o f one talc vein will be similar to that o f the hanging wall o f an adjacent talc vein and vice versa, suggesting that some o f the talc veins may be repeated by isoclinal folding. Although on a large stale the talc is generally concordant with the foliation o f the dolomitic marble, the contacts of the talc bodies are locally strongly discordant over relatively small distances, The American Chemet Corporation o f Chicago, Illinois, once held a lease upon this property, at which time the existence o f the uppermost talc vein was seemingly unknown. WILLOW CREEK PROSPECT The WUow Creek Prospect, in the WWK NEK sec. 31, T. 8 S., R, 3 W,, Madison County (Home Park Ranch 7W-mimitc quadrangle) is covered by the Willow Creek #1 and # 2 mining claims. Exposures in a small trench on this property indicate that the strata strike N. 40" E. and dip about 30 northwest. No talc thicknesses in excess of 10 feet were observed, and despite the presence on the property of a small stockpile o f tale in 1969, no appreciable lateral extension of the talc had then been proved. The geology is extremely similar to that o f the nearby M e Ridge Mine, which lies less than 1 mile north of this prospect. It is extremely unllcely that this deposit could be an extension of the | j | . J . ( *' j j j j j I j < 1 CPC-BCALTRSCPT00001132 TH E -GEOLOGY OF MONT AHA TA LQ D E,FU 3iT$-K. FJ. OLSON 137 one s t the Talc Ridge Mine, but it may represent s struc tural repetition o f the same strata by isoclinal folding, OTHER DEPOSITS Perry (1948) reportal the presence of a talc deposit "southwest o f Virginia City on Idaho Creek" along the western flank o f the Greenhorn Range, No locality infor mation is given, and the writer has not visited this reported occurrence. Although Perry described the talc as "good" in hand specimens, he further stated that "as a whole the deposit is said to be small and the average material Impure" , Many questions concerning the geology o f the PreCambrian strata to the Greenhorn Range, partieularly the relationships of its "Cherry Creek-type rockf* and its bearing on the origin o f tale in Montana, may bf answered by the ongoing investigations of Dr, Richard B. Berg o f the Montana Bureau of Mines and Geology, who is currently mapping and studying the relation ships of the dolomiiic marble and associated pre-Bcltian rocks within the Ruby Dam and adjacent T'/i-mimrte quadrangles. g e o l o g y a n d t a l c d e p o s it s o f THE TOBACCO ROOT MOUNTAINS The Tobacco Root Mounts! lie north of the Ruby, Greenhorn, and Gravelly Ranges and contain the northernmost significant exposures of pre-Beltian rocks in this area of southwestern Montana, Tansley, Schafer, and Hart (1933) have described a sequence o f melasedimentary rocks in the southern and southwestern parts of the Tobacco Root Mountains, which they refer to as the " Cherry Creek Series'*. The lithologic types that they recognized in this series are quartzite, limestone, schist, and gneiss, whose sedimen tary origin is unquestionable, and they noted the high garnet content In many of its members,The major differ ence that they brought out in comparing the Tobacco Root sequence to that of the type section at Cherry Creek along the eastern flank o f the Gravelly' Range is the p e a t abundance o f garnet rock in the Tobacco Root region, a rock th a t w rare near Cherry Creek They divided th e " Cherry Creek Series" into three divisions, of which the limestone occurs In the medial division. The thicknesses of th e limestone units range from 1,500 feet, where they have been thickened by intense folding, to complete "pinch-outs" where stretched out on the limbs o f folds. In certain areas, units that were once calcareous have been replaced by abundant garnet and hornblende and lesser amounts of tremolite, actinoliie, epidote, and quartz, suggesting widespread contact metamorphisro. This relationship is further complicated by the local development of a m ore intense metamorphism imposed upon these rocks in proximity to the Tobacco Root Batholith, o f Laramide age. There is the strong possibility that limestone members have been repeated in overturned tight isoclinal folds of the type that is well known in th e Ruby Range to the south, Reid (1957, 1959, 1963) has studied and mapped J&ige exposures of the "Pony" and " Cherry Creek" metamorphic rocks over large areas in the northern Tobacco Root Mountains, Despite the detailed lithologic descriptions fa these texts, no differentiation o f indi vidual lithologic types within these two major me lamorphic rode groups was made in his mapping. Within hfa n a p area in the north end of the Tobacco Root Mountains (Reid, 1957), the only marble found Is caleiUe rather than dotomitlc. Gfllmeister (1971) described a coarse, dominantly caldtic marble, which has restricted occurrence along the southwestern part of the Tobacco R oot Mountains, The thickness of this marble unit ranges from 0 to 1,000 feet. He has named this unit the "Occidental Marble" after the Occidental Mine on the ridge between the North and South Forks of Indian Creek. Burger (1967) has described the bedrock geology of the Sheridan District along the western flank o f the Tobacco Root Mountains. He described both marble and calc-silicate rocks, the latter being relatively unarm mon. Thicknesses o f marble units range from 100 to 800 feet and average 300 feet. Hess (1967) noted the presence o f b o th calcitk and dolondtic marble in the central and southern Tobacco Root Mountains and further contributed toward an eventually better understanding of local Pre Cambrian geology by pleading against the dogmatic usage o f such stratigraphic terms as "Cherry Creek" and "Pony" when one is unable to prove stratigraphic equivalence from place to place. He suggested that a " single, long-lasting metamorphism took place in the Tobacco Root Moun tains between 1550 and 1700 million years ago" , accompanied by the development of isoclinal folding along northeast-trending axes and the intrusion o f ultramaffc and mafic rocks. This is a similar history to that described in the central and southern parts of the Ruby Range by Carihan (1973) and Okuma (1971), respectively. ^ : b *=, j ; CPC-BCALTRSCPT00001133 isb ELKVBNTH IN D U ST R IA L M INERALS FORUM Cordus (1973) cited evidence which suggests that the maihte in the southern part of the Tobacco Root Mountains was im pute siliceous dolomite prior to metirnojphism- He further described the conti nuity o f at least one o f the marble layers for more than 30 in lts along strike and described it as uni formly dotomitic. Perry (1948) described a small talc occurrence in marble of "Cherry Creek-type ro d " along Granite Creek about 2 miles north o f Virginia City, Montana. Small stringers o f high-grade talc are present with in a marble unit 65 feet thick, but commercial talc cannot be extracted from this deposit under current conditions. Levandowsld (1956) described thicknesses of marble units in the Sheridan-Alder area along the southwestern flank o f the Tobacco Root Mountains as ranging from only a few feet to as much as 1,700 feet. He described two talc deposits as haring maximum known widths of 25 feet and lengths o f 55 feet, Both of these talc bodies have been developed within marble and am spatially associated with garnet sctast and granite gneiss. Although the Tobacco Root Mountains have dolonritic marble similar to that found in the Ruby Range to the south, and the conditions o f regional metamorphism and granitic intrusive activity are simitar in both areas, relatively few talc occurrences are known tn the Tobacco Root Mountains, It is not yet dear whether this discrepancy might be due to tack of attention and prospecting or to actual paucity o f talc there. The range has been studied for several decades by graduate students of the University of Indiana, which maintains a summer field camp near WMtehaB, at the northeastern corner o f the range. These investigations, both past and ongoing, will con tribute to a better understanding o f the detailed geolo^? of th e Tobacco Root Mountains and may well help to result in the discovery o f new talc deposits - but only tim e will teB. OTHER ASSOCIATED MINERAL DEPOSITS Several oth er mineral commodities are closely associated spatially or stratigraphically with Montana talc deposits, the m ost important being graphite, sdiinrnnie, iron formation, kyanite, and manganese. GRAPHITE High-grade crystalline graphite has been mined from deposits in the Axes Canyon area of the Ruby Range southeast o f Dillon (Perry, 1948; Ford, 1954). The graphite occurs in veins and veiniets in gneiss anti pegmatite as well as being disseminated in smaller masses a id flakes in those same host rocks. Ford (1954) sug gested th at the deposition o f graphite occurred after the emplacement o f th e pegmatite and after the period of regional metaraorphlsm. Despite their dose spatial association, the graphite was obviously deposited tong after th e dolomitic- marble in the " Cherry Creek-type rocks" was iei.iystrite.ed. SILLIMANITE SIBimanite deposits in the central and southern parts o f the R uby Range have been described by Heinrich (1950). The most common types o f occur rence and the ones having the greatest economic potential are biotite-ssllimanite schist Mid biotitc-gametsfliiinanite gneiss. The sjUimanite also occurs in peg matite and locally at a massive rock, the latter type commonly being found as residual cobbles and boulders. There seems to be some relationship between the abundance of pegmatite and the abundance o f the sillimanite; furthermore, sfllimanite " pods" are com monly developed along pegmatite contacts. The most pomlsirg deposit, situated on the Art Christensen Ranch near th e Sweetwater Road east o f Dillon, is a silvery biotitc-mmcorite schist, which contains differing amounts of siBImanite. Locally, there is also the possibility of placer sillimanite deposits. All of the sillimanite occurrences are in rocks th at are closely associated, both spatially and stratigrapWcally, with the dolomitic marble that contains all o f the known corrtmereiri talc deposits. IRON FORMATION A unit of banded "iron formation" (magnetite schist) as much as 1,000 feet wide and 2 miles tong is present to the west o f and across the Carter Creek Fault from the Regal (Keystone) talc mine in the southwestern part of the Ruby Range. Mapping by James and Wiex (1972) shows the complexity of this small local area. Similar bands o f "tron* formation" are present in the type area o f the Cherry Creek Group along the base o f the east err. flank of the Gravelly Range south of Ennis. In both of these mountain ranges, the iron is closely associated CPC-BCALTRSCPT00001134 THE GaoLOY OF MOHTAM TALC I>EPOBITS-H. H. OLSON IW both spatially and stiaiigraphically with the dolomitic marble that contains all of the known conunerdal talc bodies. KYANITE Kyanite gneiss and schist and kyanite pegmatite and veins have bees described by Heinrich and Rabbitt (1960) in the type area o f the Cherry G eek Group along the base of the eastern flank of th e Gravelly Range south o f Ennis, b u t only the layers of kyanite gneiss and schist seem to have any potential economic significance. Although these kyanite occurrences are not far from the talc deposits to the south in Johnny Gulch, it must be noted th at their nsetamorphic grade k consid erably higher than that of the Johnny Gulch area, and it is possible th at structural events lave placed these two areas in much doser juxtaposition than they were originally. MANGANESE Manganese oxide miserais have been widely devel oped in the pre-Beltian marble o f the Ruby Range and the Gravelly Range. Such mineralization, as described by Heinrich (i960) in the southwestemmost part of the Ruby Range, "is generally low-grade but highly variable" . This impregnation and subsequent alteration la s ween locally so intense that the marble may be converted to a crumbly, porous, and commonly inco herent rock. The manganese, minerals have formed hi the same marble that contains all of the known commer cial talc bodies, but even though both the manganese and the talc must have formed in Piecam h rfan time, the possibility of any genetic relationship is unknown. PROSPECTING HINTS In most mining districts, whether they produce metals or industrial minerals, the original discoveries are made by prospectors and miners; geologists come along later and refine the details This is certainly true o f the Montana trio-mining district, for the writer is aware of only a single talc occurrence that has been discovered by a geologist. This situation will obviously change in tim e to come as future trie deposits-are sought on the fringes o f the now-known "elephant country" and as more sophisticated tech niques are developed to find burled deposits, but for the time bring, the Montana talc prospector must be given full ami well-deserved credit for his most significant contributions to the development o f the Montana talc industry. Guidelines for tak prospecting nay be presented here based on present knowledge, but the main problem with applying them dogmatically is that it is still not certain whether they are truly diagnostic for areas o f trie mineralization only, or whether they might Include features th a t could be present or even abundant in barren areas as well. Their diagnostic reliability, by and large, must await more thorough gmlogicai studies in larger areas away from known areas o f mineralization. r The only certain criterion known at this time is that oil of Montana's known commercial trie ore bodies occur within dolomitic marble of the pte-BcItian se quence o f `'Cherry Creek-type rocks" . Therefore, there seem? little to be gained by searching for trie in other lithologic units or formations. From his work in the southern part o f the Ruby Range, Okurna (1971) has formult! guidelines for prospecting for trie, and these are quoted verbatim; " a) All the commerai talc deposits are intimately associated with the marble units. Dolomitic marbles seem to be a prerequisite for th e formation of high quality talc in the Ruby Range. b) The talc generally occurs in areas o f structural weakness, such areas being marked by faulting, brecciation, silicification and, in many cases, recrystallization. c) The trie deposits are related to the presence o f intrusive rocks, probably o f granitic or other composition, from which they obtained their supply of hydrothermal solutions. To some degree the nearness to Dfllon Granite Gneiss especially of the olive-pay variety may be a useful guideline for prospecting, d) Areas o f retrograde metamorphism may be o f special significance in talc prospecting." GarIlian (1973) tes likewise developed similar guidelines, derived from his work in the central part of the Ruby Range, and these are also quoted verbatim: " 1) lo o k In areas of structural complexity in the vicinity of known mines, both along the trend of the marble host and in adjacent coarse %K i- CPC-BCALTRSCPT00001135 140 ELEVENTH IN D U STR IA L M IN ERA LS FO R U M dolomites; the deposits tend to occur in groups spatially. Isolated occurrences are unusual. All the marbles should be walked out, with an eye out for float chips on the ground o r stringers o f talc in outcrop. This is considerably easier than mapping all lithologies, 2) Look in areas where non-carbonate rocks have been chioritized and talclfied. This is certainly the case in the vicinity of the Treasure mines, where the Dillon Gneiss has been ehksritized extensively. Elsewhere, however, rocks such as the Dillon Gneiss are not altered near known talc deposits, so that this is at bed: a secondary criterion, 3) Bulldoze and drill prospects to evaluate the talc body in the third dimension. 4) Rely on prospector's scratching*; they usually mean something!" To these valuable guidelines the writer will add here some from his own experience. Occurrences of bedrock tale should not be ignored amply because they are relatively thin. In the first place, one might be looking at the edge or the top of what might continue downward or laterally into a much larger body. In the second place, It must be remembered that the form or shape o f Montana talc bodies may be markedly digitate and that only an extremely thin apophysis of a large ore body may have been exposed by erosion at the time one comes across It. Tale ore bodies characteris tics Dy swell and pinch, thinning on the limbs of folds and thickening on the crests and in the troughs of folds. This plasticity, plus the natural lenticular habit, renders this caution against cavalier treatment of such occur rences advisable here. but this method of course cart aid in locating only those talc bodies that have already been breached by erosion. With practice one may develop the ability to discern the presepce of talc float chips as small as %* or so from the standing position; when one has thus determined that talc is indeed present and then gets down on hands and knees, the distribution of float chips smaller than a matebhead may be readily traced. The aid o f digging and burrowing animals, evidence free for the taking, should be utilized wherever posable. Badgers digging their burrows commonly throw out talc fragments in areas where such would not otherwise be exposed on the surface, so never pass by a badger hole in pre-Beltian dolomite country without inspecting its spoils pOe! Ants will commonly build their abodes o f the coarsest rock chips available, and the writer has seen many such anthills composed of an abnormally high percentage o f talc chips; therefore, anihills in pre-BeltIan dolomite country should also be inspected, even though (unlike badger and gopher holes) Mich debris would represent only surfidal material. In areas of talc mineralization still undisturbed by mining, the writer has observed that one o f more o f the following associated features will be presort; a) Doiomitic marble is exceptionally coarse grained. b) Doiomitic marble is exceptionally closely foliated, individual foliae being commonly 1 inch thick or ' less. c) Silidfication is common, not as veins but as irregular masses, adjacent to and near the talc. d) Large calcite rhombs, I inch or more on a side, are locally developed. The time-honored technique of tracing float chips o f talc uphill to their source will continue to be useful, e) Pervasive "soaking" of dobrrutic marble by iron oxides or manganese oxides. POSSIBLE FUTURE TRENDS IN THE MONTANA TALC INDUSTRY It Is likely, in the writer's opinion, that solid, thick; homogeneous talc ore bodies without included waste rock (e.g., Treasure Chest Mine) will not continue to be the source o f such ores in Montana for a much longer period of tim e. More and more, 1 think drat talc ores wilt be procured from deposits such as the Yellow stone Mine, winch are characterized by the digitate interfingering of talc with included waste rock on a relatively small scale. This will require sorting, of course, either by manual labor or possibly by some mechanical or phuiodectrical means yet to be perfected, but the grade o f talc fed into the mill in the future should not suffer as compared with today's mill feed. This will be most advantageous from a conserva tion standpoint, for it is an unfortunate but nevertheless true fact that many thousand tons o f high-grade talc ore has been thrown onto the dumps o f Montana talc mines because operators did not want to bear the expense of setting up sorting methods. Tliis reluctance I 1 [ CPC-BCALTRSCPT00001136 T H E f.E O L O G V OF MONTANA T A U 3 D S P O S tT S --II. M, OXSON to establish such installations may have been due to budgetary reasons or to competition For investment dollars with other divisions within large companies -- whatever the reason, it has been and still is a dolefully wasteful procedure and should be stopped! Whether or not a sorting method can be installed at any given time la not as important as the Fact that many operators have been reluctant to even go to the added expense of separately stockpiling such "middling" fractions For later sorting or other upgrading processes. A case in point may be found in Stone Creek in the Ruby Range, where many thousand tons o f high-grade talc lie irre trievably lost because they arc now hopelessly mixed with abundant waste rock in those large dumps. It becomes increasingly more difficult to locate new sources of Montana talc ore; such waste should not be allowed to continue! O f the two talc-grinding mills in Montana at the present time, one is served b y only tw o mines and the Other obtains virtually all of its feed from only one mine. Future milling operations in the Montana talc industry may n o t be so fortunate; it seems likely to the writer that such operations will instead be served by numerous mines. This may not only become necessary, but it may slso become desirable IF it affords the oppor tunity for carefully performed and intelligently directed blending o f ores from numerous sources. Underground operations have beer, pursued at the Yellowstone Mine in the Gravelly Range and at the Smith-Dihon Mine in the Ruby Range, but all present operations are open pit. The reluctance o f present opera tors to adopt underground mining methods in the face of open-pit competition is fully understandable, but it should be understood by them and by others contem plating new entries into the Montana talc Industry that the profit margin In such operations can probably withstand the increased costs o f underground mining, particularly when such advantages as year-round opera tion, increased selectivity In extraction, and other factors inherent in underground mining are considered. There fore, it may weil be that future exploration for Montana talc deposits will not be confined to areas where only open pitting is feasible -- as has generally been the case in the past REFERENCES BROWN, X. S., and ENGEL, A. 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