Document nmdwXzq01bdXqn0ndBw7OGzDz

[I AMKKK'A^ INSTinn: )>[- A Mi MI-: tAI.U'Ki'.KVYl. CNi VI M Technical Publication No. 2285 CUs H, Miami Technoloiy, November 194? K\:imiii;ition and Valuation of Chrysolili* Asbestos Deposits Occurring in Massive Serpentine llv Mu'iiaki. J. Mksski..* Mkmhkr AIMK i.\V Y->rk Merin,;. M.if.-h to47* I'm critical shortage oi a-bc.-tos liber in tlir world today brings to tin- foreground the question of locating ami developing new deposits. The object of this paper is to di-ce." sonic of the more important factors which 'I1011I1I he con-idi-rcd in the examina tion and ralunlion of a nev\ a-besto- enterprise. Some of the more important uses of as liestos tiher are for textiles, heat insulators, building materials, filters ami a series of other uses. The properties of this mineral, such as fibrous structure, color, strength. -ilhincsS and flexibility, coupled with re sistance to lire, certain chemical action and decay make its application unitiue for cer tain industrial uses which consume over sco.cco tons annually. l'ho.se same unique properties which make this mineral so valuable also make a deposit one of the most difficult to appraise accurately, because of the many undeter minable and varying factors which must he considered before a deposit can properly lie termed commercial. The majority of the asbestos fiber today, having the above mentioned propel ties, is sold liv grades which are basis! on fiber length. Present day fiber prices vary over a wide range from to $225 for crude fibers and Sjoo to S20.C0 per ton for milled (trades. Tor valua tion purposes a careful study should he made of existing fiber prices and markets. KVAMlXArtnN UK Dkihsms t In carrying out prospecting anti examina tion of a deposit, considerable caution is required to gel the necessary information in the form that will have the most value for-the final determination. There are two main classes of asbestos fibers, chrysolite and the amphiboles, the chrysotile being, l>y far. tlie most important Imth in abundance and uses. This paper will stress mainly chrysotile deposits, how ever. the amphiboles have many important ii-cs. especially amosite and croctdalitc. Their valuation presents special problems as other factors may be involved, espe cially as they arc not graded according to any well defined and adopted standard but usually according to the use for which they are being supplied. Most chrysotile deposits occur in two main types of rock, (t) mainly in basic igneous, such as dunite and peridotite, (2) to a lesser extent in sedimentary rocks, such as dolomite and limestone. All of these re quire a certain degree of melamorphism to lie favorable to asbestos formation. Ap proximately 00 pet of the asbestos deposits are derived from serpentinization of dunite or peridotite. whereby the magnesiumsilicate olivine was altered to hydrous mag nesium-silicate serpentine. I'nder certain favorable geological conditions, this ser n-cvtvn! .it tin- -iTicr of thr Ajt:' 7, 1047; revision Aun. is. 1047. * <u*t:i*r.il Vermont Asbestos of TV Ruln-mut 0>.. Hvlu Park. V*. pentine takes a fibrous form having a defi nite crystal structure, probably due to molecular rearrangement, anil is known as chrysotile. The fiber veins arc usually ir iVijivnyhl. 1947. hy ths Am-ri' .ill Instilun* ..i Mount: wist Mt.-tal'iirRical hnyinoTS Ini* Ptintc.l m I! ASARCO ALV 0006158  i\\ir\iiM. niKssmii.i \siiimos pii'usiis is \i\ssivi sikpimim regularly I ;~t ril >n I o I ill l lu- rock m;v--. some being conlitiunii'only a few feet lilul "tiler; may continue up t" hundred- of Irrl. known its the ilii'dl ami open \ein respec Ri ot ISill. I .\ IA l Hi <V>1.\|\1 n lit rim, I'uost'l.r'l I\c. AM) I'.NAMIVA 1 Io\ The first requisite is ("establish the exact properties ami quality of the liher, fulluweil I'll'. I fllKYsOTII I \S|I1ST"S vi tv smmivii cm ur asiiistos wii sui t out . lively. I ln \ vary in width I'nnn 1 .r.t to ;i in . Iml at lime' veins up to 5 in. have been ioiind. In tlie-e deposits asbestos is commonly found in two main forms, "cross tiher" l I'ifi 11 where the libers are normal to the vein and "'lip tiher" where the fiber' lie in the same miii more or less parallel with the vein wall', both of commercial value, though ero" fiber is ti-tially preferable and Ini' more evleu-iw tt-c-. The serpent:! i/ed area- which lontain asbestos usually lake the form of large mas ~ive < llipso-d.ii I .od't s or -.mII defined sills or ham!', wiiv h bec.iit'i of s,-or, gat ion were e-pecially favorable to win dcwlopmcin and may coi.:a::i any.'In re from iii'ignili cant quantity up to ic pci by weight of asbestos fiber Tin- liber content and liber length \arv oou-ideruhly between one de posit and am-ibor. a- well as within the same deposit hy a chemical analysis which may indicate what known fiber it resembles, and if it has any special properties, such as freedom from iron, which would give it a premium value. This should then be followed liv svstematic examination to determine how much liber the various mineralized areas contain and of what different lengths and proportions. 1. A careful geological study of the area. noting all contacts, barren intrusions, fiber areas and degree of serpentinizalion. and so forth, followed bv a proper geological map. I'stially because of the nature of the basic rocks, asbestos deposits show considerable outcrops which can be easily blasted open for examination. It might be well to indi tioti that some experimental work with geophysical methods has been tried in asbestos deposits using magnatometer and electrical induced-current methods. While ihe-e were helpful in outlining -erpentine ASARCO ALV 0006159 r i MICHAEL ). MKSSKJ. 3 areas, they did not conclusively prove the presence of asbestos fiber. 2. If a mineralized area has favorable indurations from visual inspection it should the presence of any slip liber. However, care should be taken in measuring the vein width that is continuous, as frequently broken or divided veins occur and what Fin 2 -ClIKYsoTH.K ASllf.SToS VI.IN' snow INC I1KOKI N VEIN'S. be divided into definite areas for prospect may seem like a 1 o-iti. vein is in reality two, ing purposes and 100-ft square is a con 4-in. veins (Fig 2). Where possible photo venient unit. This can later lie divided into graphs should be taken of the area exposed 10-ft strips for logging all surface indica as these may later be enlarged and the liber tions. Surface prospecting, depending on veins measured. I have found photograph' the overburden present, usually takes the very useful in this work as they lake into form of bla-tiiig open the outcrop-, small consideration all the rock exposed. There open rut-, trenching and test pits, followed is a human tendency when sampling, to by diamond drilling to prove depth. Ill take only the rock that contains liber. From certain location- a tunnel and cross cuts this, an approximate liber content may be may be advisable, since in addition to calculated for each area (Fig i>. expo-ing fiber indication-, it will yield a From each exposed area a representative good -ample of ore for te-t purposes. Where -ample of the ore should be taken, varying the deposit i- not cxpo-cd on surface, con- in quantity from one to a thousand tons, ] volitional methods of underground pros- depending on the zone of inllueiice which l peeling arc u-ually applied, the area will have, the information de-ired. j ICach favorable area should lie carefully ami the facilities available for tc-ling it. measured and all veins over '.is in. in The term "representative sample'' a~ u-ed | width, should be logged taking into account here require- some comment. It should be iI--. . t ASARCO ALV 0006160 KVAI.UATING CIIRYSOTII.E ASBESTOS DEPOSITS IN MASSIVE SERPENTINE taken in such a manner as will not cause a concentration ami distort the results, as all the rock will have to he mined, milled and paid for. unless it is low (trade and of mt.AH Fie. 3-- C It R vsot i i.r aaiikstos suowim. kimmN-itocK si'Ki errnr. sufficient size to he left in place depending on the mining method. For example, a part of an area may contain 1.5 pet of fiber with veins over 1 in., while another part may contain a pet liher with most of the veins under 1 1 in. I'olh areas separately, would he (traded as poor on*, hut together, the value of the ore would he raised to economic or medium (trade ore with the addition o| in. liher as a sweetener. IlMMuMl IH'H.I.IXO As in mo-t other deposits the extension of surface induations must he proved in depth hv diamoml drilling. Standard prac tice now >eens to he tile use of 11 s ill, diam eter core with .I.Y tools. The drilling t" start usually coii-i-is of a few split holes followed later hy a carefully laid out pro gram so that each hole will he assigned a definite zone of influence and vivid as much new information as possible. Holes are usu ally laid out on ico-ft renters, depending on conditions and information desired. Angle holes are often used lo establish the outhounds of the deposit. A check made of three operating mines indicated that a foot of hole was required lo prove anywhere from 200 to a 50 tons of ore, which means that the zone of influence assigned to a hole is being somewhat standardized. To a large extent this will depend on the nature of the deposit. The cores should he carefully logged, show ing the geology and all liher veins over 'as in. in width. The core is usually read in sections of 5 ft and the veins in each section are care fully measured. From this, the liher content can he fairly clo-ely estimated. The terms good ore (over 5 pet liher content), medium ore 1 t to 5 pet content) and poor ore to to A pet content) are used to designate sections of the core. However, there living no ac cepted standard, these terms are somewhat elastic and should he defined in each reiHirt, since some mining companies use other classifications. It is considered good practice to take the core from two or three different holes and have them crushed up and the fiber recov ered to serve as a check against the original readings and a plus or minus factor may he determined. The other cores tire always saved and used for future reference. The sludge from the drilling should he collected, examined and correlated to the core readings, especially in areas where core is badly broken up and may have de stroy'd the fiber Veins. In sjiji fiber deposits, it is not possible to measure the veins and readings are usu ally done hy visual inspection as compared to some known core, the fiber content of which has been confirmed by test-mill re sults. In such deposits test samples are an absolute necessity to obtain the fiber ronteul and the fiber length. The cost of ilia- ASARCO ALV 0006161 M1CI1AI.1. 1. MI.sM.I. drilling usually iarV> front S'.;o up l" per loni. 11..-11\.. i); i Samit)Pnnr Tim Miil In new <lepo-.ilv. the lest samples are not always of the size the engineers may want them to he, but are determined to a large extent, by the capital available tor explora tion. While some estimate of the praties that may be expecteil can be obtaine<l from the liber length measured during surface and core readings, the exactness w ill de] <eml to a large extent on past experience of the observer. As a guide, the following liber lengths when milled usually will give grades in the following groups: 11 c to 1in., group 6 and 7; 1 >, to 1in., group 4 and 5; 11 in. and over, group .7. If a deposit is in the vicinity of an exist ing asbestos mill, tile samples should be sent there to determine the liber content and the classification of different grades of liber for each sample. In such a case, mill efficiency would have to be considered be cause a certain destruction of the liber length in the milling process is inevitable. Furthermore, some loss in the mill tailings and fan exhausts has to be taken into ac count and this is usually 0.5 to t pci of the total liber content and usually consists of the shorter, group 7. libers. However, for new deposits that cannot Use any surround ing facilities, a pilot test mill is almost a neces-ity, not only ior le-ting the samples, but it may obviate \erv useful modifica tion# nece-.-ary for a mill to treat the par ticular type of ore e/V.i lelltly. Asbesto- milling practice is based on crushing the ..re. drying, tiherizing in hammer mil!- to ir-e the liber, then screen ing and a-pirating the tree liber ttliis usu ally in two or three -imilar stages!, then cleaning the liber and da-dfying it in l routine! type grader-. The difficulty of the problem of clas-ifyiug the liber in order to get the most economic \ allies out of tinore, may be realized when it is considered that lon.iug iroin the drpo-it. x.triou# length- of fiber in various proportions are found and i; i- i:<-ary to make standard grades of predetermined tests. Alter a deposit has been worked for some time, the mill is adjusted to produce certain standard grades favorable to the particular deposit, however to a large extent, this is governed by market demands. A flow sheet of a typical pilot test mill would consist of: a 6 by iS in. jaw crusher; horizontal iS in. by i(j ft rotary dryer; 4 by 10 ft shaking screen with air suction; verti cal or horizontal-type libcri/.er; shaking screen with aspirator; fan and collector; a cleaning screen, a rotary grading trommel and a Quebec Standard Testing Machine. The cost of such a unit, including {tower, would be around Sjo.oco. Representative samples of the liber pro duced from the ore samples should be tested in the Quebec Standard Testing Machine to obtain the grades of liber. It is always advisable in new deposits to send samples of the liber to various manufacturers for test purposes. Asbestos liber, following Canadian prac tice, which is now considered world stand ard, is divided inlo nine main groups and each group is subdivided in grades, giving a total of approximately 25 standard grades of liber, each having a different test and value. ('rude fibers lluind processed)- - (roup 1--Crude No. 1. 3j-in. staple an<l longer. (Iroup 2--Crude No. 2. aN-in. staple and longer up to :lj-in. Mill l ibers (nuiehine processed> - (roup .; Textile spinning libers (lesi- ing over o--S--0--2). (roup 4--Shingle libers (testing below o--S--6-- 2 and including o--1.5-- 0-5--,v'Group 5--Paper liber- 1 testing below o--1.5--9.5--5-0 and including o-- o--S--S). ASARCO ALV 0006162 IViMWiX'. i lIKi.Mi! II I VsM.M'ih .* t.r<-ui i> W.i-tc stucco. jr ftl er : testing hi low e o- > S ai:.i \ i r o c : ;: . (in-up; .-hott' ti-tinge c- s 11 ami below -. (-n-up S .'ami weighing nii-r g- lb per cubic font ami under 7.; tl>. (ir-rnp t-and ami gravel. weighing over 75 II- pi-r cubic foul. The testing machine consists <>1 a nt-.-t ] four rectangular sincns held in a frame on a lalile w hit li i- actuateil liy an eccentric. The tup -erven has 'e-in. openings, the second 4-mcsli. the third 10-me-h ami the fourth is a pan. though at pre-ent, a i.-mesh i- nfteii used. Tor a te~t a pound -ample is pul mi the tup screen and the machine run l'ur tun minutes at .too rpm. The amount ui tilier remaining on each screen is linn weighed ami recorded in ounce- which determine* the test. I'tBt.K V.\i t'AiiuN or Di.rosir Tiber prices are those that would be ubtained in a cumpetilive market. but as thiis not usually known at such an early stage, it is advisable to u.-e for calculating pur poses. the Canadian prices in effect at the time, less about S to to pet for a safety factor. However, some mines in Africa and Russia do not u-u tin- -landard Canadian test designation but have their own standard- and priie-. In such ca-e- their standard- -hm:M lie clearly defined anil preferably t r.ui-p'-i d in term- of the Cana dian -tandard. both of which, are funda mentally ba-i-1 :! liber length. 15y avcrag:,.g the -urface readings, tin- core hole- ami ore u--1 -ample n-ult- from the vari-'U- ana- examined, the average tiher o-nti nt for the drpo-it maybe obtained. holloaing the -ante procedure for e-li mated grade- of liber and calculating thiin term- of average per ton value, then bv combining the two and knowing the I in.--ilde ore I.-unave, an average value per : f .-re ".a;. ' 1 e-:.d- -1 - . : 1 ; -it (live; . a : t v. b.w . av. v.dm per ton of on t::. a r pn : t da\ im. ditions would be approximately -?i..'S to $1.50 to be worth consideration, however other factor- may be involved which may vary these figure.-. 1'roin this il is evident that in an ashestndepo-it two important variables are pres ent, the liber content and liber length, and in most case- one helps to compensate for the other. Olltl.K C.I.M.K.VI. T.Vi I11KS TO 11 h Cnxsiiis nu> in V.vt.t ation 1. Proximity of liber to market, to de termine it favorable or unfavorable freight hucrenlia! -hmtld be emi-idered. Tariff- mi import-, depending mi country in which drpo-it i- located. v Mill efficiency. Asbestos ore varies so much from one deposit to another that milling practice has to be mm lifted to suit each particular ore. Such factors as moisture content, hardness of rock, harshness or softness of tilier have to be considered be sides the overall efficiency which is based on lihcr recovery. Asbestos ore. unless concentrated in rela tively rich small pockets which can Inworked economically by hand for crude fillers, usually has a relatively low per-ton ore value and ha- to be worked in fairly large tonnages with low mining and milling eo-ts. I>eposits with a liln-r content of 1.5 to 2 pet are being worked but in tnosi de posit-. about 5 to 7 pci i- considered average. 4. Certain low-grade areas may have to he "excluded unli--. they can lie worked together with other better grade areas to bring them within the economic limits. \fter a careful estimate of the milling, crushing, drying and milling costs are made, knowing tile average ore value, the commercial po-sibilitir- of a deposit can he c-stabli-hvd, -' ASARCO ALV 0006163