UBC Theses and Dissertations

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UBC Theses and Dissertations

Some studies of gold and its associated minerals Davis, Edwin Philip 1939

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SOME STUDIES OF GOLD AND ITS ASSOCIATED MINERALS by E.P. Davis. A paper submitted to the Department of Geology and Geography of the University of British Columbia, in partial fulfillment of the requirements for the degree of Master of Arts. - 2 •T x ^ & ACKH0W1EDGBHBNTS. This research was carried out in the laboratories of the Department of Geology at the University of British Columbia, under the supervision of Dr. H. V. Warren, whose assistance and encouragement was appreciated greatly by the writer. Thanks are also extended to Mr. W. H. White, who collaborated in the work of examining the Chelan tailings, and to Mr. J. Donnan for his excellent workman-ship in mounting and polishing some very d i f f i c u l t telluride sp ecimens. TAB 15 OF CONTENTS  Part 1. STUDIES OF SECTIONS M P TAILINGS CHELAN DIVISION .GHOWE SOUND COMPANY? Holden. Washington. XiOCB-ijXon •••••••••»••••••••••»••»••••»••»••••»»•••• 1 • General Geology 1« Mineralogy of the Ore . . . . . . . . 1. Paragenesis 4. Illustrations 6. 7. Distribution of Gold in Rougher Tailings 8. Table 1 9. Table 2 10. Summary and Conclusions 11. LOCATION: The Holden gold-copper property is in the Chelan range on Railroad Greek and about fifty-two miles north west of the town of Chelan, Washington. The topography near the mine consists of a series of more or less parallel high h i l l s , some rising to more than eight thousand feet, with narrow creeks in bet\Yeen. GENERAL GEOLOGY. In this deposit the ore occurs in metamorphosed sed-iments, probably, pre Cambrian, and consists of an irregular lense. The ore i t s e l f appears to be of Mesozoic Age. It is intruded by Mesozoic acid and intermediate intrusions, and the end products that have formed, have appeared as small dykes. There was considerable s i l i f i c a t i o n with the deposition of the ore.With one exception no major faulting has taken place. Minor movements, however, are numerous. o The strike of the ore body is S. 35 E., and i t dips o o 3. W. between 65 and 75 . Mineralogy of the Ore: The Chelan is a contact type of deposit. The percentage composition of the ore is approximately: 35 % Quartz 5 % Pyrite 25 % Sphalerite 1 5 ^ Ghaloopyrite 20 % Pyrrhotite. The principal shlphides in order of relative abund- \ ance are;- Sphalerite, Pyrrhotite, Chalcopyrite, and pyrite. \ Six representative sections were examined. A general • idea of the mineralogical relations ws ascertained. PYRITE; | It occurs as irregular fragments varying in size from j several mms. to one or two microns. Generally, i t is f a i r l y well; crystallized but is also fractured and corroded with quartz. : j SP HALERITE: ) This is the most abundant of the sulphides. It is in intimate contact with the chalcopyrite and pyrhotite. Some irregularities in the outline of the sphalerite indicate that i t tended to crystallize f i r s t . CHALCOPYRITE: This comprises about Jazgnty per cent of the sulphides / ; ' / . ' n ( '•' present. It has smoothly rounded boundaries. ,. ,/ * v' / • . . PYRRHOTITE: -This represents about fifteen_per cent of the sulphides. The regular contacts of the sphalerite, chalcopyrite, and pyrrhotite, denote them to he of contemporaneous deposition. The gangue is composed of quartz and sericite. The quartz is of two ages. The original material being clear, while the second generation, or recrystallized quartz, is dark and veins the earlier mineral. Gold uas found to be disseminated through the original quartz. Assays run on rejects from the polished sections showed that the sulphides also carried a minor amount. The gold was very fine, the sizes being less than a micron. None was seen in association with the sulphide minerals. . ASSAYS. 245 cross cut 04 oz./Ton. 550 stope Trace 700 " , 243 chute Trace 243 " Trace 700 " , 248 chute 01 Oz/Ton. 4, PARAGEMESIS. A study of the above sections showed two probable periods of mineralizations. Emanations from the granite high in s i l i c a and sulphur dioxide f i r s t made their way along the fractured contact zone. Pyrite was probably the fi r s t mineral to crystall-ize—as shown by the good crystal outline of some and also by the fracturing and Erosion of other crystals. Gold precipitated with the quartz and became finely dessiminated through i t , a typical high temperature occurrence. later there was fracturing of the original zone material and what appeared to be in the section another later generation of quartz, is in reality , a recrystallization of the original quartz; and this process of solution and recrystalliaation parallelled the deposition .of the sulphides. Thus, as the mineralization solution was injected, the sulphides came in contact with gold already present, which may account for i t s being associated with the chalcopyrite, sphalerite and pyrrhotite. 6 ILLUSTRATION I . This shows the pyrite veined with pyrrhotite, sphalerite and quartz. The sulphides, veining the pyrite, are obvious-ly later. Mag. x 154 ILLUSTRATION 2. This photo micrograph clearly shows the or-iginal and reorystall-ized quartz. Note the chalcopyrite crystal surrounded by the re-crystallized quartz. Mag. x 154 7 ILLUSTRATION 3. This i l l u s t r a t e s c l e a r l y , by t h e i r smoothly rounded boundaries, the contem-poraneous deposition of the c h a l c o p y r i t e , p y r r -h o t i t e and s p h a l e r i t e . S e r i c i t e i s a l s o present. i g . x 154 ILLUSTRATION 4. x 2430 This photo micrograph shows the gold i n i s l a n d s thru the o r i g i n a l quartz. The average s i z e of the gold p a r t -i c l e s i s about .4 microns. DISTRIBUTION OF GOLD IN.ROUGHER TAILINGS FROM GHELAN DIVISION • HOIS SOUND COMPANY,HOLDEN. WASH. , After flotation of a copper concentrate the rougher tailings from the Chelan mill s t i l l carry appreciable amount of gold. A sample of these tailings was received by the Dept. of Geology, University of B.C., for investigation of the mineralogical association and distribution of the gold. Briefly, the method 'was to screen&size a large sample down to /200 mesh, size the -200 material into seven products with the Haultain 'Infra-sizer 1, and to 'pan' a l l the products. Four mineral products were taken from the Panner. In the tables these are designated: Tip, Pyrite, Middling and Tail; and the mineralogical compositions are as follows: Tip -,- free gold, galena, plus some pyrite. Pyrite- at least 99^ pure pyrite. Mid. -Sphalerite, any chalcopyrite present, or pyrrhotite, plus up to 30^ pyrite, and a small amount of siliceous material. Tail - Siliceous material containing under 1% sulphur. Finally, a l l the products were weighed and assayed using one, two, three, or four assay ton charges, depend-ing on the amount of material available and the importance of the assay. TPrgw these weights and assays the following tables have been constructed: 2 ° TAB IE #1 - SIZE DISTRIBUTION OF GOLD. PRODUCT SIZE 0z. Aft./ton Content Mg9 Au. DISTRIBUTION % m*% Au 1 Head _Samp_lB . 0.024 "'"4720"* iW.b~ 100.0 - ^3 5 : 0.032 .020 0.4 0.4 /65 0.047 1.338 4.1 6,9 /lOO 0.050 1.048 12.0 21.5 - /l50 0.060 1.770 16.8 36.4 /200 0.020. .725 20.9 15,0 I-S #1 #2 #3 : ' / l * f A fu-jt.tJ s' ; t 0.025 0.015 0.010 .143 .334 .150 3.3 12.7 8.6, 2.9' 6.8 3.1 #4 #5 0.010 0.007 .101 .049 . 5.8 4.0 3.1 1,0 ;#s #7 0.005 0.0.10 .035 .151 2.9 8. 5 0.8 3.1 4.864 100.0 ioo 4o •Note* W eight loss i n screening -'Inf rasizing 1.5 % - 1.9 Weij in ;ht-Corrected Table # 1 . Assayed head - 0.024 Oz. Au. per ton. Calculated head - 0.028 Oz. Au. per ton. Calculations are based on the latter as this is regarded as more nearly correct ( see E. & M. Jour. Vol. 138 pp.353) _ £ A B ! g _ § > - TOfflRALOGIOAL PISTRIBTTPTOJcbF am-.rt 10. I Content JOT A u . Oz/ ton % . A u . DISTRIBUTION IN PRODUCTS _T0TAL DISTRIBUTION TO. % A n -i-35 0 .032 0 . 0 2 0 •0.4 0.4 65_EEED_ _ _ _ _ .047»-Tip 194.5 Mid.- ,29 : T a i l : .017 ^338 .200" .010 .123  .333 0.014 .4 99.6 100.0 59.2. 330 36.4 98,6 .0006" „ 0 1 6 4 .1 ." 6^9 ~4.1~ .2 2.6 10,. M E D _ _ ' • r i p - ' P y r i t e Mid. T a i l _ i.050 ' 214.0 2,335 ,350 ,019 50 JTSED .060 _ l s P £ 8 _ .330~ .160 .120 _ 1.770 .007 .3 1.6 98.1 100.0 . 31.5 15,3 11.4 37.3 95.5 12.0 .0008' . 036 . . .20 11.8 21.J5 6.8' 3.2 2.5 8,0 •''•'. T i P . P y r i t e Mid . Ss . i l ' 14.68 .233 .197 .030 .500 .160 .257 .820 1,737 ,120 2.5 4 .5 93.0 100.0 28 i 2 9.0 14,5 46.2 JL6.8 _ .92 .4 . .7 15.7 10.3 3.2 5.3 17.0 |:oo K E D _ T i p , P y r i t e •Mid. T a i l —•020 2.92 .020 .035 .021 ~ T i p Pyr i t e Mid; T a i l J L ° 2 5 5.82 .020 .035 .010 5.725 . 015~ .072 .123 .617 .827 .143_ . 010 .049 ,069 ,013 .014 10.0 9.6 80.4 100.0 2.0 10.0 16.9 85.0 113.9 20. 9_ _ .003 2.1 2.0 16,8 15_,0 .3 1.5 2.6 12.7 ,141 ".03 6.9 - _ „ „ 3.3 .001 42.8 34.3 1.4 33,9 48.2 .... 1-2 23.3 9.1 .7 100,0- $8.5 2._9_ ~ .2 1.0 1.4 a 3 Tip Pyr i t e Mid. T a i l ,.015 .25 .010 0020 .013 _.334-.005 ,02E ;04oo ;228  .300 12.7_ _ .012-1.5 1,1 10.1 _6 |8 ' .1" .6 .8 4.7 ;o£ 12.1 8.9 79..0 100.0 1.5 18.1 12.0 .68.4 96.0 \'J3 EEED_ Tip Pyr i t e Ifid, T a i l 2.20' . .023 .035 .007 _.150 .005 .025 .025 .095 8_j_6 ~ .0013 .6 A . 1 . r .5 .5 1.9 .150 .016 7.3 4.8 , 87.9 L100.0 3,3 16.7 16.7 r .63.3, ioo.o 7.6 |i?.#4,FEED Tip P y r i t e Mid. T a i l .010 1.46 .017 .026 .006 .101 .005 . O i l .046 .04,7 .109 .017 6,4 17.3 76.3 100.0 4 .9 10.9 45.5 46.5  107.8 5.8 .001 • .4 1.0 4.4 2.1 .1 .2 .9 1 . 0 E5_HSED Tip LI P y r i t e 'Mid . T a i l .007 .87 .06 .013 .005 i M 9 _ .005 .010 . 015 .027 .057 - - 4.0 10.2 ,0006 .1 2.5 20040 .2 .3 16.3 30.6 .6 .3 81,2 55.2 3.2 .6 100.0 116.4 - AP05 2.10 .007 .027 .004 .010" .035. .005 .005 .015 .01?  .042 .151 .05 14.3 .0015 .1 1.4 .14.3 .04 .1 11.1 42.8 .3 .3 87.5 47.6 2.5 .4 100.00 119,0 - - 8.5 3.1 T i p P y r i t e H i d . •:'' T a i l TOTALS 4'. 8 4 0 100.0 99.5 11. i.. SUMMARY AND. CONCLUSIONS. I . . SIZE DISTRIBUTION OF GOLD: Inspection of Table #1 indicates that about 80$ of the gold is in the /200 mesh material which constitutes about 52%> by weight. 2. MINERALOGICAL DISTRIBUTION OF GOLD: The middling products average about 25% pyrite and 5% siliceous impurities, and the tabulation below is slightly corrected for these figures: Mineralogi-oal.af^ooia'tlbnV~%~ total Wt77l° total Au7~^~Au. • « o e Free gold......... Pjm \i © <a •-• « « • • « * « * « • • « • • Sphalerite,pyrrhotite,chal Siliceous gangue.«..... /35 mesh & $7Infrasizer products were not panned - © ' 22 © 2 , 100.00 -8.5 n 13.3 . 1.56 5.3 ' • 9 11.7 o 2»21 77.7 0 . 49.4 96,6 0, 63s 8.5 3„4 100. a. 100.0 Mineralogically the gold tends to favor the sphalerite and/or pyrrhotite, probably the latter. The inference is that sections of the. mine rich in pyrrhotite would be richer in gold. About 50%' of the gold is associated with the gangue. In view of the fact that the finest pure gangue carries at least .005..Oa. Au / ton, we can say that at least 20% of the gold occurs as finely-disseminated particles throughout the ore-body. Such an occurrence of disseminated gold, which does not notably favor any particular mineral, is typical of the high-temperature, contact-metamorphic ore-body. 3. It was not possible to demonstrate that the loss of free gold in the flotation circuit is due to refactory coatings. True, the gold - particles do appear rather dark colored but are similar, in appearance to gold particles from other deposits. A chemical test of gold concentrate indicated about one part in ten million ^ pf manganese, but this might have come from other sources, such as tramp iron. 4. The fact that 'tips' gave no test for copper indicates that native copper is not present in the rougher tailings. TELLURIDES. * ) TABLE OF CONTENTS. Part.2„ Acknowledgements . i . Bibliography .»•.•••».•»»»••»•»••»»••»»••*. • i i . Introduction 1. Summary of ^ Available Information ............. 2. Table of Etch Reactions 15. Examination of Labelled Specimens 16. Cripple Greek Tellurides ....................... 20. Examination of X-rayed Specimens .. .......... " 22. Illustrations 25. Examination of WiIke Specimens ............... 26. Identification of Tellurides by selective iridescent filming ................. 28, Filming Media .................................. 29. Results of Filming 31. Conclusions 32. Appendix 33. i i BIBLIOGRAPHY. American Mineralogist., Economic Geology... » > e • « .....Volume 10 11 16 •i 1 7 20 Volume 2 " 4 6 " 10 " 15 " 33 The Occurrence of Telluride Minerals at Kalgoorlie. .F.L S t i l l w e l l . Erzmikraskopische Bestimmungstafeln ......H..Schaeiderholm und P. Ramdohr. Microscopic Determination of the Ore Minerals TELLURIDES Introduction: This work was undertaken in an endeavour to find a possible way of more accurately identifying the gold-bearing tellurides. As these minerals rarely occur as single specimens, but usually as intergrowths of several tellurides, i t was necessary to study as many members of the family as possible. A large number of specimens were collected which were supposedly identified. On checking these specimens, by etch tests, witji those of the present authorities, Schneiderholm und Ramdohr, Short and St i l l w e l l , i t was found that these vrorkers dis-. y agreed among themselves and also that specimens acquired by us were incorrectly labelled. Accordingly a l l available information on the char-acteristics of this family was procured, a summarj'' of which is included in this paper* 2. Summary of Available Information Concerning Tellurides. HSSSITE; % 2 T e Isometric. * Crystals sometimes highly modified and distorted; also massive compa ct or fine-grained; rarely coarse'..granular* Cleavage: Indistinct. Fracture: Even -- somewhat sectile. Hardness: 2.5 - 3. Spec. Gr: 8.45 - 8.89 Color : between lead and steel gray. Color in section HHCU HOI KCN20^ Feglo 20^ HgClg(Sat) KOH(Sat) Galena white P P P P P N When isolated in areas of quartz or carbonate, i t s color is distinctly creamy white, but in cohtrastwwith creamy white sylvanite, krenneritef, or calaverite, there is a bluish tint while in contact altaite i t s color becomes purplish gray, OCCURRENCE; Hessite occurs both as a primary and secondary telluride. It is associated with Petzite and other tellurides, gold and sulph-ides. It may be in rounded areas without crystalline form or as ragged inclusions. PET2ITE: (AgAu)^ Te. Isometric. Massive fine to comp act. Fradture: Subconchoidal. Slightly sectile to b r i t t l e . Hardness: 2.5-3. Spec. Or: 8.7 - 9.02. Color : Steel or iron gray to iron black.,.often tarnishin Color in section HNOg HCJL KCN20/° FeCl?20# HggJLg(Sat) KOH(Sat) Grayish white P N. N P P N . y Petzite may be identified by i t s characteristic gold etch pattern, ' its Triangular cleavage pits and its' isotropism. Hessite shows none of these properties. — -fn contrast to Hessite i t shows a faint bluish tinge on well-polished surfaces. It is more br i t t l e than Hessite. .OCCURRENCE: Similar to and associated with Hessite. ALTAITIS: PbTe CleavageJ Fracture: Sectile. Hardness: Spec, Gr: Color : Isoraetric. Cubic. Subconchoidal. 3. 8.16. Tin white'with a yellowish tinge, tarnishing to bronze yellow. Color in.sect ion HNO . HC1 KCN20^ FeCl?20^. HgOlo(Sat) KOH(Sat) White P.E-. P N P R N Altaite readily distinguished from other tellurides in polished section by it s white color, cubical cleavage and its etch-ing with Hydrochloric acid. It is closely similar to Naumannite(Ag£,Pb)Se, the distin ction being dependent on a micro-chemical test for Selenium. ' OSDURKENGE.: iCt is primary and is associated with other tellurides, free gold and the usual sulphide minerals. TETRADYMITE: Bi 2(TeS) 3 Rhombohedral. Cleavage.* Basal perfect. Laminae flexible - not very sectile. Hardness: 1.5-3 - soils paper. Spec, Gr: 7.2 - 7.6. . Lustre : Metallic splendent. Color : Pale steel gray. Color in section HNO HC1 KCN20/= FeClgSofo HgCl (Sat) KOH(Sat) et ching Galena white P.E. N N Available informati on concerned only atomic structure. RIQK&RDITE:) Gu Te • ) 4 3 ) FSISSITE. ) Gu Te 5 3 Both massive. Hardness: 3.5 - and - 3,0 Spec, Gr: 7,5 and 6,0 Colors : Deep purple and dark bluish black — black. Color in section HNCU H61 KCN20> FeCl.,20^ HgCl 2(3at) KOH(Sat) - Purple P.B. P P P P P These show no difference. The color may be bluish gray or even blue as well as purplel The details of etching are similar to Ghalcocite. OCCURRENCE: 1$ is secondary and it s association is similar to other tellurides. GAIAVBRITE: (Au%) Te Massive indistinctly crystalline - B r i t t l e . Hardness: 2.5 Spec. Gr: 9.045 Color Pale bronze yellow. Calaverite has a much higher per cent of gold than sylvanite. s how any cleavage as opposed to Krennerite. Calaverite is gener-a l l y allot riomorphicl OCCURRENCE: A primary telluride and is most commonly associated with Coloradoite. It dissociates" at a shallow level into second-ary Sylvanite, Petzite, and free Gold. Other associates are the tellurium minerals and sulphides. Colftr in section imO„ HC1 KCN 20% FeGl^f, Creamy white P*E* N N P P It is anisotropic and shows fine etch lines. It does not 8, NAGYAGITE*: Au|b 1 4 Sb3 Te ? S 1 7 (?) Orthorhombic. Cleavage* (B) Perfect. Thin laminae flexible. Hardness: 1-1.5, Spec. Gr: 6.8 - 7.2. Lustre : Metallic Splendent'. Streai and Color: Blackish—lead gray. Color in section HHP HC1 KCN20% FeCl 20j£ HgCl.(Sat) K0H(Sat) -3 White P N N N N Its identification is assisted by the peculiar uneve surface and polish. It is anisotropic. OCCURRENCE: N n Same as other tellurides. KRENNERITE; (Aulg)Te 2 (?) Orthorhombic. Cleavage: One direction (G) perfect, Fracture: Subconchoidal to uneven. Brittle. •Spec. Gr: Color : 3 .3 . Silver white to brass yellow. Color iiL_§e_qtioii HNO HC1 KCN 20$ FeCl Creamy white P.E, N 3fiH& H E CI (Sat) JtOH^Sa^ •N Krennerite has perfect cleavage, develops etch lines and may be silver white. OCCURRENCE: It has not been recognized in any association suggestive of secondary origin and its,associations are similar, to Sylvanite. an.* 'SYLVANITE: (AuAg) Te Monoclinic Hardness: Spec. Gr: Color : Color in section HNCL Creamy White P.E Cleavage: one direction perfect (b). Fracture: uneven 1,5 - 2 B r i t t l e . 7.9 - 8i3.' Pure steel gray to silver white inclining to yellowish. HC1 KCN 20% F e C l o 2 0 % . HgClo(sat) KOH(Sat) N H P N ;N Sylvanite:sometimes shows lamellar twinning and bireflection. It 13 d i f f i c u l t to t e l l from Krennerite but where i t i s able to show good -cleavagej the mineral is- described as Krennerite where i t .is not clearly Sylvanite. Sylvanite does not develop fine etch l i nes. , ' • OCCTJRRENCE": In primary associations with Galaverite;, Petzite, Hessite, Altaite,Nagyagite, Seligmannite,Gold, and Sulphide minerals. GOLORADOITE: HgTe Cleavage: Hardness: Spec. Gr; Color : One direction 2.5 8.07 Iron black. /// etching Color in section HNOg, HG1 ICON 20$ FeCl 320$ HgCl2(Sat) KOH(Sat) Grayish white N N N This is one of the hardest and more bri t t l e tellurides. Its color in polished section varies from grayish white to brownish white or white. Etched surfaces treated with FeCl and cleaned with 3 HC1 show strong anisotropism. OCCURRENCE: It occurs in veins with Gala verite-, and also with Krennerite, Sylvanite, Petzite and Altaite. In comparison with other tellurides, i t is conspicuously an associate of primary free gold. 12. MELONITE: NiTe \ 2 Cleavages One perfect. In indistinct granular and foliated particles, Color : Reddish white. Lustre : Metallic, Hardness; 1-1,5. Spec. Gr: 7,3, et chins Color in Section HHP. HOI KCN20$ FeCl?20# Hp;Cl2 (Sat) KQH(Sat) Creamy pink •• pinP.E, li N P N N This is the hardest telluride, and the most b r i t t l e . These with i t s creamy pink color, make i t easily recognized. OCCURRENCE: Whether primary or secondary is not known. Associations similar to other tellurides. 13 ANTAMOKITE: AuAg Telluride. available inf ormation.-ETCH TESTS, etching Color in section HNO3 HCl KCN20$ Grayish white P N N FeCl320$ HgClg(Sat) KOH(Sat) P P N STDTZITE: Ag^Te (?) t A rare silver telluride. Negative to standard etching tests. Hardness low. Associated with other tellurides. . Follows edges of Hessite vein and transgresses i t in part. Kalgoorlie, Australia, etching Color in section HNO, HCl KCN 20% FeCl320$ Milg-CSafc.) K0H(Sat) Grayish v/hite N N N N >' N • N 14. TELLURIUM: Tg Rhombohedral. In prismatic crystals. Commonly columnar to fine granular massive. Perfect prismatic cleavage. "Hardness: 2 - 2.5. Spec. Gr: 6.2 Lustre : Metallic. Color and strealfc: , Tin white. Color in section HNO o White . P.E. etching SOI KCN 20$ feCl 320i' ^gCl 9 :(Sat). KOH(Sat) N N N N N - 3 rsive. ' Cleavage: one direction perfect, Color : Gray. Spec. Gr: 7.32. No available information. ORMBTITE.: • . ". BigTe S Similar to Grunlingite. No available information. 15. ' HNO, HCl ,:, i A-C/V , .. H.CI,... .... •ip. F.L.S. fTLS FI---J. Ge^. Altaite White PS PI P PI ti H II P PI | N N H N Isotropic Antaraokite Grayish white p H N p ; P B Cala verite Creamy PB PES P 11 H II N 11 11 p P i P 11 N ii P N P Aniaotropio Coloradoite Grayish " P PS P H PS N . N H N p 11 PI p N 11 H N N Hesaite Galena " P PI P P PS H E PS P p PI ; p P PS H N N Isotropic and Anisotropic Krennerite Creamy PE PES N H H H p PI N H P N Anisotropic llolonite Cream PB PES N PS n N N H p P3 H. H II N togyagite White P PI P H 11 N N N N II H 11 N H K N N Aniootropia Petzite Grayish " P N PI N PI N PS N H p P T V ra II H Isotropic Rickardite Purple PE P3 P P II P P II P P N V PS N P P N Sylvanite Creamy PB PI P N IT If N N N P P Nr 51 • ii N 11 N 11 Anisotropic Stutzite Grayish " H N H M H H N H ' Anisotropic Tellurium White PE PS P N P N H It N II W PS . N': P N ii H 11 II N Anisotropic Tetradymite Galena PE PS P II N N H . M ' P P N ii N H N Anisotropic PI pi Legend: FLS FL Stillwell. . NIS NI4 Short. Germ.. . . . , H . Schneiderholm und, Rhamdohr. P Pos it i ve N Negat i ve. PE Positive with effervescence. PI......Positive with iridescence. . PES Positive with effervesoence and.etains. PS Positive with stains. I 16. Examination of Labelled Specimens, Section #1. This specimen was acquired from a reputable scientific house and was marked Altaite. Upon examination, the polished section was found to contain three intergrown tellurides, the properties and etch reactions of which were as follows: (a) Position of mineral in the section log - 53 el and 22.1 color : creamy white Hardness: B -Anisotropic : Light to dark No visible cleavage. MP-3 HOI KCN _FeCl 3 HgCl^ KOH P N N P.stains N N This mineral is believed to be Sylvanite but no twinning lamellae- were seen. (b) log - 51.0 and 24.0 color : creamy white hardness : B Anisotropic : Light to dark. This mineral was in intimate smooth contact with (a). HNO HCl KCN FeCl HgCl9 KOH P N N N N N This mineral is probably Nagyagite8 17. (c) log - 49.5 and 13,5 color : Gi-ayish white, hardness: A. Isotropic. In contact with (a), HMO H61 KCN FeCl HE01„ KOH _ ? _ __ g_ — b — g _ — P N N P. stains P N This was considered to be Petzite but lacks the charac-teri s t i c triangular cleavage pits described by other workers. It should be intergrown with Hessite. Section #2.. This specimen was acquired from the same source as / / l . It was labelled Sylvanite. The results of tests were: log: 40.4 color: Creamy white. Hardness: C / Anisotropic slightly. HNO _HCl . KCN FeCl 3 HgCl^ KOH P ' N N N; N P stains, This mineral does not check with the etch test reactions any known telluride nor does i t show lamellar twinning. Identifi-cation by this means is impossible. 18 This telluride was received from the aaiae source as $1 and $2. It was marked Gala, verite. log 53 and 15. color : creamy white. hardness: 0, Anisotropism strong, . Habit; Long acicular crystals. HNO HOI KCN FeCl HgCl KOH Pwith eff. N N N P dark N stain As these etch reactions do not correspond, to any given in the proceeding table identification was impossible. Section #4, This ws.s also received with the previous specimens. It was labelled Petzite. It was found to contain an intergrowth of two tellurides. log 53.1 and 15. (a) Color : Creamy white. Hardness B Anisotropic. 19.; . -HPi. JSPJL _FeG2. JHgCl. „ KOH p• . • N N p stains N N From the etch tests this would appear to be Sylvanite, but i t shows no twinning.. (b) Color : Greyish white. Hardness: A Isotropic. MO _H81__ _K0JL JteCJU F^ m KOH 3 •-> 6 P eff, N N P darkens This may be Petzite but does not show the cleavage pits described by Short and Sti l l w e l l . Also, according to them, i t should be intergrown with Hessite. ' These etch tests were a l l checked independently by Mess s. W.H.. White and E. Schmidt. From this work i t was realized that some other means of identification must be found. In order to flro^tM'sipilt was necessary to get as many specimens of each mineral as possible. 20. CRIPPLE GREEK TELLURIDES. Sorne samples from Cripple Creek, Colorado, were collected by Dr. H.V. Warren,. These were mounted in bakelite and poliished. The set included some high grade concentrates which were treated similarly. The following is the result of microscopic examination and etching: Section #1. Log 15 and 52 Two tellurides were present. (a) Color : Grayish white. Hardness! A Anisotropism doubtful. .HNO HCl;:. KCN FeCl HgCl 6KpH_ P N N P P N Due to the fact that Petzite may be either positive or negative with, H61, this probably is i t . Apparently the reaction varies with the direction in which the seStion is cut. Spec. #2. Log 43 and 14.75. Color : Creamy white. Hardness: C* Anisotropic. MO Mi_ _ICJL; Fe01„ _HgCl„ KOH 3 o . <J P stains N ' N p P • From its etch tests, this.is Calaverite. . M,N,Short states that i t is Negative to KOH but both Stillwell and Schneiderholm and Ramdohr state that i t is possible. : Other sections from this suite were examined but due to the wide difference in etch reactions, the results were considered of no value, The positions of the minerals were logged with the large scale toward the lamp and the small scale on the left hand side of the microscope stage. The number on the section faces the operator. -Through the efforts of Dr. H.V.Warren arrangements ?;ere made with the Washington Geophysical Laboratory, that they should send us some specimens. These wefe three in number, and consisted of X-rayed specimens. The X-ray examination of minerals is sup-posed to be the last word in accurady, and the identification by this method considered definite. However, after mounting and polishing, and making a micro-scopic examination of the three spedimens, i t was' found that one of them contained two intergrown tellurides and also free gold. Results of Etch Tests on X-rayed Specimens, Section #1. Specimens marked Calaverite. Color : creamy white Hardness : C Anisotropic. H N O 3 HCl KCN. FeCl 3 H E CI., KOH P N N Pdarkens N N This agreed with Short. Both Stillwell and Schneiderholm und Ramdohr make Calaverite positive with KOH. Section #2. Specimen marked Sylvanite. Color J creamy white Hardness : C-Anisotropic. HNO„ HCl KCN FeCl ? HgCl 2 KOH P N N P N P 23. This specimen .showed the distinct lamellar twinning described in the literature as being distinctive of Sylvanite. However, none of the reference works give a positive reaction with KOH. Illustration 1. Section $3,. Specimen marked Krennerite. Color : Creamy white Hardness : C Anisotropic. (a) HNOo HCl KCN FeGU HgClo KOH P N K N N N From the color in section, hardness and anisotropism, this is assumed to be Krennerite. However, i t gives the etGh reactions for Nagyagite. (b) Color : Grayish whit8 Hardness : A Isotropic. HMO^  HG1 KCN FeClg HgClo KOH P N P P N N The identification of this is doubtful as i t does not check with any given reactions. It is thought to be Petzite. This section also Eontained free gold. Illustration 2. A l l these tests were checked independently by Dr. Warren. From the results , i t may be seen that the etch reactions are of doubtful value in determining the members of the telluride family, assuming X-ray analysis to be correct*, Mag. x 154 Examination of Wilke Sections A number of specimens were obtained from Wilke in California. These were a l l identified.v/iAfter mounting and polishing, the check etch tests were as follows! Section ^1. Sp ecimen marked Sylvanite. Color : Creamy white Hardness : C Anisotropic. HNO^  HCl KCN FeCl 3 HgCl^ KOH P N N. P N N This agreed with the work of others but did not show the twinning of the Washington specimen. Also, i t was not positive to KOH. Section Specimen marked Tetradymite. Color : Galena white Hardness : B Anisotropic. HNO. HG1 KCN FeCl HgCl„ KOH 3 3 * P P N P N N This agreed with the reactions given by M.N. Short. It shows perfect nasal cleavage. It is undoubtedly Tetradymite. Section $ 3. Specimen marked Altaite. This contains two tellurides intergrown. The Altaite was white while the other a much darker-almost brownish mineral-was unidentifiable. Color J White Hardness : B Doubtfully Isotropic HHQ3 HCl KCN FeCl HgCl KOH 3 ^ P P N P N N This is believed to be Altaite,,. According to Stillwell, the stain with FeCl persists after buffing which was a noticeable 3 feature of this mineral,, SS5ii°iLJ^ i.« Specimen marked Nagyagite, Color : White Hardness : B Anisotropism doubtful. MP-3 HCl KCN FeClg HgCl^ N . • N N N This agreed with the tests of other workers. KOH N Section" Specimen marked Calaverite, Color : CrSamy white Hardness : C Anisotropic, HNO3 HCl KCN FeCl 3 HgCl^ K 0 H P N N P N P This agreed with Stillwell and Schne'iderholm und Ramdohr, but Short atates i t negative to KOH, It is probably correctly iden-t i f i e d . From the results of this series of etch tests, i t can be seen that, with regard to the tellijride family, very l i t t l e con-fidence may be placed in these reactions. In the writer's opinion, much pi the discrepancy is due to'crystal orientation. Unfortun-ately, in the specimens used, cleavage has not been sufficiently discernible to prove this assertion. It may be proved at a later date. Identification of Tellurides  by Selective Iridescent Filming. Attention was drawn to this method of identification by the success of A.M. Gaudin, and his assistants, at the Montana School of Mines, in the filming of the Silver Sulphide minerals. Gaudin, A.M.,...Economic Geology, Volume 33, No. 2, Page 145. The method of selective iridescent filming consists in creating on the surface of minerals transparent films of such thickness that light interference takes place between beams reflected from the top and from the bottom of the film; the selective character of this filming arises from the fact that films of different thick-ness and different optical prop erties are formed on different minerals, thus giving different colors. Aside from the composition of the filming medium, two other important factors affect the color obtained^1 nanraly the length of filming time, which should be, controlled with a stop watch, and the temperature of reaction; The color obtained on the same mineral is not always exactly the same; this happens i f the mineral is chemically anisotropic, because the film thickness is not the same on the crystals cut in different orientations. In addition, minor differencesiinocoiLor may occur because of local differences in stirring of the bath, or because of other details such as macrostructure of the specimens. Differentiation by selective iridescent filming does not have to depend on minor color differences; i t depends on sharply contrasting colors, each perhap s of several shades, obtained by filming foraa precisely controlled length of time at a definite temperature. In i t s application, the method of iridescent filming has consisted so far in oxidizing the surfaces of the minerals by im-mersion in a liquid bath. FILMING MEDIA. The f i r s t filming solution used on the tellurides was the standard chromium Tri-oxide—Hydrochloric acid bath. This was made up of one part of Chromium tri-oaide dissolved in five parts-/ of water, two parts of this solution being mixed with three parts| of concentrated Hydrochloric acid and then diluted 2:1 with water. This solution was found unsatisfactory. A faint film of fourth order colors was formed on one or two minerals while others were not oxidized a i a l l . It was then attempted to film the minerals by adjusting the amounts of the various reagents in the above solution, but the results were negligible. Other solutions were investigated. A two per cent solution of 30° iodine in Methanol, plus an equal volume of Hydrochloric acid was tried. This gave no results. Other liquids composed of salts of iron in nitrate and nitrite solutions were tried. They gave fair results, but difficulty was found in controlling them. The writer has noticed that nearly a l l the tellurides react with Nitric acid, and most of them film with Ferric chloride; so that some solution may eventually be evolved which contains these reagents. Further work is to be done next year. Finally, the standard silver filming solution, used by Gaudin, was tried. This solution is composed of one part two per cent iodine-methyl alcohol solution and one part concentrated Sulphuric acid by volume. Also a solution containing Potassium Permanganate, in-stead of lodinss-, was tried but was found unsatisfactory. The first solution gave fair l y good results over a limited range of minerals. 31. Results of filming with • tStandard!Filming:l»56Iution. Solution used: Standard Silver Filming Solution. Time : 10 seconds. Temperature : 22° C. Only the minerals of which the writer was reasonably certain were used for filming. PETZITE: First order, orange to purple. CALAVERITE: Tan to pale purple. SYLVANITE: Light tan to pale pink and purple—lighter tan than Calaverite. KRENNERITE: Second order blue to pink. Dominantly pink. Various times and temperatures were tried, but the filming with this solution seemed most effective at the ten second immersion period. Also, the -solution i t s e l f and the acetone used for washing tended to attack the bakelite mounts of the minerals, making longer immersion dangerous to the sp ecimens themselves. CONCLUSION. Several of the tellurides may be distinguished directly, in polished section, by their physical characteristics, Tetrady-mite and Rickardite in particular, the former by its hardness and basal clea vage, the latter by its purple color. However, the majority varying as they do between crea.m, gray, and white, and with many sim-i l a r i t i e s in behaviour to etching, need at present a very complicated method of attack. In the writer's opinion, the solution of the problem lies in filming, as the foregoing results seem to indicate. It is his inten-tion to continue this work next year in an endeavour to formulate a solution which wi l l differentiate completely and easily between any of the telluride family. "... 3a,' '•;::v -'f- APPENDIX. Development of Etch Cleavages. Of the reagents commonly used in routine minera-graphic tests, only nitric acid yields definite etch patterns on Calaverite, Krennerite, and Sylvanite. Three strengths of acid WQ-re. used: l i l , :|:2 , and concentrated HNO ., The time of etch-ing is an important factor, one minute being used for the 1:1 acid and forty seconds for both the other concentrations. For a comparative study of these three tellurides, specimens of known crystal orientations must be used. The results obtained on each specimen by each concentration of acid are totally different, , The,sections used by.the writer were cut in a random direction.but .upon comparison with the illustrations shown in "Etch Tests on Calaverite, Krennerite, and Sylvanite" by M.N. Short, the reactions showed striking similarity when treated with 1:1 HNOg. Calaverite. - • ' . W h e n etched with 1:1 acid, upon washing and drying the specimen, the surface breaks up into irregular areas, each consist-ing of a flake a few microns thick. The curled edges give a some-: what' shingled effect. With 3:2 acid, a distinct parallel etch structure is developed. With concentrated acid a more, uniform etch cleavage is developed, consisting of fine parallel line, across the surface of the? specimen.: Krennerite. . ' Did not check with Short, probably due to the crystal orientation. Sylvanite. With 1:1 acid etchings, takes the form of short discon- -tinuous:cracks which give the surface a vernicular appearance. With 3:2 acid, two etch directions are clearly brought out and seem to be of BqualEiimportance. With concentrated acid tests, two cleavages at right angles are shown. Parts of the section do not react. SUMMARY. . Etch Tests On Calaverite Krennerite and Sylvanite.......M.N. Short. Ameri can Mineralogist '-Vol.. 22. ' $ 5 . The results of etching the three tellurides are not as simple and conclusive as had been hoped for. The variations in results when different "strengths of acid and different times of etching are employed cal l for control of both factors. On the other hand, the etch patterns are not capricious; each figure illustrates several experiments performed under the same conditions, and the conclusion ls } justified that, under the same conditions, a given specimen w i l l yield the same etch patterns. G alaverite and krennerite give similar patterns, but krennerite will give two etch-cleavages at right angles in certain tions whereas-calaverite apparently w i l l give an etch-cleagage in 35. only one, direction. Both krennerite and calaverite flake, and many specimens of both minerals develop circular areas that may represent spherical inclusions when etched with 1:1 HNO j Etch-cleavage in one direction indicates, but does not prove calaverite. Sylvanite gives an etch-cleavage similar to that of krennerite but the cleavages develop while the drop is on the specimen and the surface does not flake when washedgand dried. In conclusion, etching witheboth 1:1 and concentrated nitric acid w i l l usually lead to a decision whether an anisotropic gold and silver telluride is sylvanite or one of the other two minerals, salaverite and krennerite. It. is d i f f i c u l t to distin-guish calaverite from krennerite by etching with nitric acid in some cases, but i f two etch-cleavages at right angles are developed the mineral is probably .krennerite. 


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