Carwdian MineralogistVol. 16, pp. 651-657 (1978)

ABsrRAcr

Uytenbogaardtite, Aga,AuSz, occurs with acanthite,electrum and quartz in specimens from TambangSawah, Benkoelen district, Sumatra, Indonesia, theComstock lode, Storey County, Nevada, U.S.A.and Smeinogorski (Schlangenberg), Altai, U.S.S.R.The mineral is tetragonal, P4r22 or l4r a 9.76,c 9.784. (Comstock lode), a 9.68, c 9.81A CfambangSawah), Z - 8; D(calc) - 8.34 g/cm3 (Comstocklode), 8.45 g/cma Clambang Sawah). The strongestX-ray powder diffraction lines are 2.71(L0) (2O3),2.60(9) (321), 2.124(7\ (421). Measured composi-tions lie close to Ag"AuS:, although uytenbogaard-tite from the Comstock lode contatns up to 4 wt.Vo Cu. These data indicate that uytenbogaardtiteis identical with synthetic low-temperature AgaAuSs.Pleoctrroisrn in reflected light is: grey-white togrey-white with a brownish tint (air), brownish grey-white to brownish pink (oil). Measured reflectivitier(RVo at specific wavelengths) are: 33.2-34.6(470 nm), 30.3-34.6 (546 nm), 31.1-35.2 (589 nm),30.5-33.3 (650 nm). The polishing hardness issliehtb below that for acanthite; ZI[N15 is about 20.The name is in honor of Willem Uytenbogaardt,Professor of geology at tie Technical University,Delft. The Netherlands.

SorvnvrernB

On trouve l'uytenbogaardtite, AggAuSr, accompa-gn6e d'acanthite, 6lectrum et quartz, dans des 6chan-tillons de Tambang Sawah, disrict de Benkoelen,Sumatra (Indon6sie), dans la veine Comstock, comt6de Storey, Nevada (E.U), et b Smeinogorsk (Schlan-

*Current address: Department of the GeophysicalSciences, The University of Chicago, 5734 SouthEllis Avenue, Chicago, Illinois 60637, U.S.A.

UYTENBOGAARDTITE, A NEW SILVER.GOLD SULFIDE

M. D. BARTON{'Department ol Geological Sciences, Vireinia Polytechnic lttstitute and State University,

Blacksburg, Virsinia 24061, U.S-4.

C. KIEF"TNetherlands Organization for the Advancernent of Pure Research (ZWO)' Amsterdam'

The Netherlands

E. A. J. BURKEInstitute lor the Earth Sciences, Free Uniyersity, Amsterdam 11, The Netherlands

I. S. OENGeoloeical Institute, University of Arnsterdam, Amsterdam, The Netherlands

genberg), Altai (J.R.S.S.). C'est un min6ral t6trago'ia, ri'zz ou.P41, a 9.76, c 9.784. (Comstock);

a 9.68, c 9.814 Cfambang Sawah); Z - 8; D(calc)8.34 (Comstock), 8.45 (Iambang Sawah). I-es raiesde diffraction-X les plus lntenses sont 2.71(10)(203), 2.60(9) (321) et 2.l2LQ) (421). ks compG'sitions obtenues par analyse sont proches deAg:AuSz, quoique l'ufienbogaardtite de Comstockcontienne jusqu'i 4Vo (wids) de cuivre. Ces donn6esmontrent que I'uytenbogaardtite et la forme basse-temp6rature de Ag*AuSz sont identiques. En lu-midre r6fl6chie, le min6ral est pl6ochroique, de gris-

blanc d gris-blanc teint6 de brun dans l'air, et d'ungris-blanc brunitre au rose brundtre dans l'huile. I*sr6flectivit6s mesur6es (en VoR b certaines longueursd'ondo donn6es) sont les suivantes: 33.2'34.6 (470

nm), 30.3-34.6 (546 nm)' 3l.l-35.2 (589 nm), 30.5-33.3 (650 nm). La duret6 au polissage, 7IlN15, estapproximativement 20, soit un peu moins que pourl'acanthite. Ce min6ral est d6di6 au ProfesseurWillem Uytenbogaardt, de l'Universit6 Techniquedo Delft (Pays Bas).

(Traduit Par la R6daction)

INt'noPucrtoN

Two ternary comPounds, AgsAuS, and

AgAuS, are kngwn at low temperatures in the

system Ag-Au-S. Neither phase has been re-ported to occur in nature, although they mightbe expected in certain gold-silver deposits. Ex-

amination of several acanthite (Ag'$ + elec-trum (Au,Ag) assemblages has led to the dis-covery of natural AgaAuSz, uytenbogaardtite,from the Comstock lode, Storey Counfy, Ne-vada, U.S.A. and Smeinogorski (Schlangenberg),

Altai, U.S.S.R. Simultaneously, in the course of

an investigation of the gold-silver ores fromthe Tertiary yolcanic belt of Sumatra, Indonesia,

651

652 THE CANADIAN MINERALOGIST

uytenbogaardtite was found in a sample fromTambang Sawah, Benkoelen district. At all threelocalities, uytenbogaardtite occurs as small blebsup to 100 pm across and as rims intimatelyassociated with acanthite, electrgm, quartz andother minerals.

The name (pronounced y0feNnO.Cen-DAIT) is for Willem Uytenbogaardt, Professorof mineralogy and petrology at the Free Uni-versity in Amsterdam from 1960 to 1976, dedi-cated promoter of guantitative ore microscopyin his function as chairman of the I.M.A. Com-mission on Ore Microscopy from 1962 to 1970,and now Professor of geology at the TechnicalUniversity in Delft, The Netherlands.

Both the mineral and the name have beenapproved by the Commission on New Mineralsand Mineral Names of the International Min-eralogical Association. Type material will bepreserved in the collections of the Free Univer-sity in Amsterdam, the University of Amsterdamand the United States National MuseumIN.M.N.H. 105328 (Comstock lode) andN.M.N.H. B239 (Smeinogorski)1.

Prtystcer- eNn Oprrcel PRopERTIEs

In polished section uytenbogaardtite showsweak to distinct reflection pleochroism. In airthe color varies from grey-white to grey-whitewith a brownish tint. In oil imrnersion thepleochroism is more distincl brownish grey-white to brownish pint; in contrast, acanthiteis distinctly blue. The anisotropy is strong inboth air and in oil, but without distinct coior..The reflectance is slightly higher than that foracanthite and was measured with a Leitz MpVmicroscope photometer at four standard wave-lengths. The instrument was equipped with aKnott 9592A photomultiplier tube, a Veril8-200 continuous-band interference filter anda l6:L objective of O.40 N.A. A tungsten car-bide, WC-6, provided by Messrs. Carl Zeiss(Oberdochen), was used as a standard. Thereflectance values, measured on a grain withmaximum bireflectance, are given in Table 1.

Light (i.e., heat) etching is extremely strong,even stronger than for acanthite. The Comstock-

TABLE 'I. REFLECTANCE VALUES FOR UYTENBOGAARDTITE*

Ennx xmin

TABLE 2. REPRESENTATIVE mntVSfS Or UYTET'|gOOAARDTIru*

Cu 5 ToTAL

Aq-AuS^ (Jdea l ) 55 .34' J Z

Comstock lode 56 . l5 5 . 85 6 . 5

Smeinogorsk i 56 .0n t 7 I. 54 .6

Tambang Sawah 54.553.256.7

10 .97 100 .00

11 .2 99 .312.3 98.412.4 99.9I 0 .4 98 .81 0 . 3 r 0 0 . 1I0 .8 100 .7I I .3 99.2l I . 7 1 0 0 . 0l l . 0 1 0 0 . 3

2 0 R

27 .327 . 4J a . +

32.735 .333 .435 . 132.6

2 . 23 . 0J - b

in weight pef cent

lode material develops a completely differentsurface in several tens of seconds under moder-ate illumination. This surface suggests photo-induced decomposition; it requires a fresh polishfor its removal. Tambang Sawah and Smeino-gorski uytenbogaardtites, in contrast, seem tobe relativelv stable.

Microindentation hardness (VHN), measuredwith a Leitz Durimet-Pol hardness tester apply-ing the minimum load of 15 e and an indenta-tion time of 15 seconds, is about 20, whichcorresponds to a Mohs hardness of about 2.Because of the small grain-size and the low hard-ness only one indentation could be made. Thepolishins hardness is lower than that for acan-thite. Uytenbogaardtite is considerably more

O AgsAuSa

A Comstock lodo

I Tombong Soroh

I Snelnogonhl

molo Z S

mob % Au

Frc. 1. Selected analyses from the Comstock lode,Tambang Sawah, and Smeinogorski specimensplotted in tle triangular diagram Ag-Au-S.

/ 40

470 nm546589650

34.6%34.635. 233.3

33.2/"30 .33 t . l30.5

* measured on material from Tambang Sawah

UYTENBOGAARDTITE. A SILVER-GOLD SULFIDE 653

brittle than acanthite. On probing with a sharp-ened steel needle uytenbogaardtite broke upinto small pieces, whereas associated acanthitetended to smear. Synthetic AgsAuS, is reason-ably easy to grind to a powder.

CnsMlcel CovtPosrrroN

Electron-microprobe analyses were obtainedindependently in three laboratories. Despite tleuse of different operating conditions, differentstandards and different correction schemes, theresults obtained are comparable.

Analyses of material from the three localitiesdemonstrate

'that uytenbogaardtite is close to

ideal AggAuSa. Neither the Ag/Au nor the(Ag + Au)/S ratios (atomic) show any sys-tematic departure from the expected values of3/1 and 2/1. Analyses selected from the morethan 70 done are given in Table 2 and plottedin Figure 1. The only additional elements de-tected occur in the Comstocklode material,where up to 4 wt. Eo coppet is present alongwith traces of selenium and tellurium.

In spite of inaccuracies introduced by thesmall grain-size and instability under the elec-tron beam, possibly due to diffusion processessimilar to those described by Rucklidge &Stumpfl (1968) for petzite, AgrAuTer, analyseswere reproducible. During long exposures ofa single spot to the beam a detectable shift ofthe sold to silver ratio occurs in which the ex-cited area of sulfide becomes more silver-rich.

CnvsrenocnePnY

Owing to the small grain-size and the multi-granular nature of uytenbogaardtite, neitherpowder smear-mounts nor single-crystal methodscould be used. X-ray powder data obtained usinga Straumanis-type Debye-Scherrer camera (Tam-bang Sawah specimen; Mn-filtered FeKcu radia-tion) and a Gandolfi camera (Comstock lodespecimen; Ni-filtered CuKa radiation) indicatethat the new mineral is identical with the tetra-gonal low-temperature form of syntheticAs,AuS, (Graf 1968; PDF 20-461). The X-raydata and cell edges (calculated by least-squaresmethods) are given in Table 3.

For the Debye-Scherrer camera exposure,uytenbogaardtite was powdered under the micro-scope with a tungsten carbide microdrill andtaken into droplets of rubber solution. For theGandolfi camera exposure, it was gouged froma polished section with a sharpened steel needleand picked up on a glass fibre coated with sili-

TABLE 3. X-MY P0l,,lDER DIFFRACTION DATA FORUYTENBoGMRDTITE AND SYNTHETIC AglAus2

Synthetic Ag3AuS2*

hkl dobs dca. lc I

Uytenbogaardtite

A A T" o b s - c a l c A d T

" o b s - c a l c '

I I 0 6 .98 6 .894 B210 4 .38 4 .360 6220 3.46 3.447 2300 3 .2+ 3 .250 331 0 3 .09 3 .083 6222 2.809 2.825 6203 2.731 2.724 10321 2.609 2.609 9331 2.236 2.238 3421 2.124 2.129 8422 1.992 I .994 5520 t .807 1.81 1 5521 1 .780 1 .781 4

" l i l s.7sa (A) 9 .85

6.94 6 .845 44.33 4.329 33 .47 3 .422 |

: .0 : 3 .061 ;2.802 2.807 32 , 7 1 2 2 . 7 1 0 1 02.591 2 .590 92 .226 2 .222 I2 . 1 1 2 2 . 1 1 4 41 . 9 8 0 1 . 9 8 0 2r 7aa l 798 l

1 . 7 6 8g . o a r

9 . 8 1

B.45 g/cn3

4.365

3.2533.0862 . 8 r 92 .7112..609

2 .13 2 . r 30

r . a r 1 . 8 1 2

9 .78

8.34 g/m3

4.40

3-.243 . 0 92.822 . 7 12.60

t 0

;:

densities 8.29 glw3

'Powder data and cell edges frcn Graf (1968)r only those data

that correspond to observed lines ln the natural material aregiven here. Graf's intensities are ten tires those given here.

cone grease. In both cases' owing to small grainsize and intimate intergrowth with acanthite orelectrum (or both), a1l patterns contained linesof acanthite or electrum. The small amounts ofmaterial used vielded rather diffuse diffractionlines. For dnxr, Eteartet than 3A, backgroundfrom the rubber solution was significant. Inneither case could a correction for film shrink-age be made because of the absence of backreflections.

Messien et al. (1966) reported low-tempera-ture Ag'AuSr to be cubic, a 9.724, but Graf(1968) later demonstrated that the symmetry isactually tetragonal. Observed reflections showthat the space group is primitive and that theonly possible non-unit translational symmetryelements are a 4r- or a 4raxis. As there are noobserved reflections of the tvpe 00/ it is notpossible to ascertain if a four-fold screw axis ispresent; however, as Messien et al. (1966) in'dicate the presence of a 4t axis, the probablespace group is either P4r22 or P4r.

OccURRENcE ANo PenecsNssts

Uvtenbogaardtite occurs with acanthite, elec-trum and q:uafiz at the three localities, all hy-drothermal precious-metal deposits. The Tam-bang Sawah and Comstock lode deposits closelyresemble each other and the late-stage uyten-bogaardtite parageneses are similar. The Smeino-gorski deposit is of a different type; there,uytenbogaardtite may be supergene. All threeassemblages, however, contain typical low-tem-perature gold-silver parageneses.

Hydrothermally-altered Tertiarv andesiticrocks are the hosts for the gold- and silver-bearing quartz veins of Tambang Sawah and

654 THE CANADIAN MINERALOGIST

the Comstock lode. Hypogene minerals commonto both deposits include quartz, chalcedony,kaolinite, calcite, rhodochrosite, adularia, sphal-erite, galena, acanthite, pyrargyrite and electrum;opal, inesite and rhodonite occur only at Tam-bang Sawah. and pyrite, chalcopyrite and Ag-

ffi-

bearing sulfosalts (besides pyrargyrite) are re-ported only from the Comstock lode. The oxida-tion zone at Tambang Sawah consists of a massof quartz and manganese oxides, whereas thecementation zone is enriched in acanthite. Avariety of supergene sulfides and sulfosalts are

\ -i.,.;d'.it'ffil:

t,

UYTENBOGAARDTITE. A SILVER-GOI.D SULFIDE 655

reported from the Comstock lode (Bastin 1922,van Bemmelen 1949, Bonham 1969).

The uytenbogaardtite-bearing samples fromTambang Sawah and the Comstosk lode aresimilar in texture and paragenesis. The samplefrom Tambang Sawah is composed of an inequi-granular quartz aggregate enclosing small vugspartly filled either with manganese oxides anda chloritic mineral or with acanthite and achloritic mineral. Locally there is brecciationand recementation with chloritic-sericitic ma-terial. The sample shows the usual black coatingof manganese-bearing rocks exposed at thesurface, but not the expected veining with man-ganese oxides or acanthite.

Textural relations in the acanthite-filled Yugssuggest an overlapping order of deposition ofquattz, galena, sphalerite, acanthite, electrumand uvtenbogaardtite. There is a gradation in-ward from anhedral quartz to prismatic qtattzcrystals that protrude into the vugs. Inclusionsof acanthite in the prismatic quartz crystalsdemonstrate the overlapping deposition ofacanthite and vug-filling quartz. The acanthiteaggregates in the vugs enclose and partly replacea few corroded and veined grains of galena andsphalerite. Electrum generally occurs as veryfine grains, partly interstitial to and partly en-closed in the acanthite grains. Occasionally, ag-gregates of electrum form the central filling ofa vug and enclose corroded and rounded grainsof acanthite. The acanthite adjoining suchaggregates of late electrurn shows replacementby irregular, locally vein-like spots of uvtenbo-gaardtite less than 100 pm across (Fig. 2a, b).In places the acanthite has apparently recrys-tallized into a fine-grained aggregate of acan-thite with interstitial uytenbogaardtite grains(Fig. 2c). The dispersed fine-grained electrumis locally associated with a few small grains ofuytenbogaardtite in the surrounding acanthite.Microprobe analyses indicate that the silvercontent of the electrum (about 43 wL 7o) issimilar to that in the hypogene electrum fromthe Salida and Mangani deposits in the sameAu-Ag ore province (Kieft & Oen 1973,1977).

Manganese oxides appear only where acan-thite is almost completely replaced. Other vugsare filled with chloritic material or aggregatesof several manganese oxides, or both, commonlywith concentric banded textures. Electron micro-probe analvses indicate that the manganeseoxides enclosing electrum contain between 4and 20 wt. 7o silver. The dissolution of acan-thite and replacement by a chloritic mineral andmanganese oxides is presumably related to alate change in the physico-chemical environ-ment.

Massive acanthite fills the interstices betweeneuhedral quartz crystals (about 1 mm) at oneend of the Comstock lode specimen (N M.N'H'105328). The remainder of the specimen iscomposed of an ejquigranular aggregate ofquartz with minor acanthite.

The textural relationships indiqate that quartz,the earliest mineral, is followed by sphalerite,chalcopyrite, pearceite, electrum and acanthite.The acanthite encloses irregular masses of chal-copyrite, sphalerite, pearceite and electrum-Covellite replaces some of the chalcopyrite,whereas the electrum blebs are almost univer-sally surrounded by 5-10 g,m rims of uytenbo-gaardtite (Fig. 3). No other phases are observedin contact with the uytenbogaardtite apart fromacanthite and electrum. The mole fraction ofsilver in the electrum is about 0.45 adjacent tothe uvtenbogaardtite and is up to 0.7 in thecentres of the larger grains. The acanthite con-tains about 0.5 wt. Vo copper as well as tracesof selenium.

The deposits of the Smeinogorski area consistof veins in hydrothermally altered, sfionglyfolded slates, sandstones and carbonates ofDevonian and Carboniferous age that have beenintruded by.Hercynian-age granites. Most of therich precious-metal ore is thought to be super-sene (Emmons 1937).

The uytenbogaardtite specimen from Smeino'gorski (N.M.N.H.8239) is a yellow-stained ag-

Frc. 3. Uytenbogaardtite rims (grey with blackspots) around electrum (white) and enclosed byacanthite (uniform grey). The spotting of theuytenbogaardtite is due to the extremely rapidand pronounced photo-etching. The bar is 20pm long.

656 THE CANADIAN MINERALOGIST

Frc. 4. Intergrowth of acanthite and electrum havinga bulk Ag:Au ratio of 3:l (expanded-beam mi-croprobe analysis). Enclosing material is electrum(white). The bar is 10 pm long. Oil immersion.

gregate of anhedral to euhedral quartz crystals,partly coated on one Surface by asanthite, elec-trum, chlorargyrite and minor naumannite. Theacanthite, naumannite and chlorargyrite sur-round masses of electrum up to 1 cm in max-imum dimension. Euhedral quartz crystals areinterspersed. Uvtenbogaardtite occurs in contactwith the outer edge of the electrum and as in-clusions in the electrum. Extremely fine-grainedintergrowths of acanthite and electrum havinga bulk AglAu ratio of 3/1 (determined by ex-panded-beam electron-microprobe analysis) areinterpreted to be breakdown products of uyten-bogaardtite @ig. ). The presence of chloragyritesupports a supergene origin for at least part ofthe observed assemblage.

Stenrr-ttY

Experimental work on the system AgaAuSz -Ag,S by Graf (1968) iudicates that only below113'C can AgaAuSa (uytenbogaardtite) coexistwith AgzS (acanthite). Low AggAuS, is stablewith gold-bearing argentite solid solution from113" to 185oC where it inverts to high AgaAuSz,part of the solid solution. Figure 5 (Barton1978) shows some of the electrum compositionscoexisting with uytenbogaardtite and acanthite.Observed electrum compositions are not com-patible with these experimentally determinedtielines. One possible explanation is that theuytenbogaardtite-bearing assemblages reflect dis-

log fr" .-- t o

Fro. 5. Log fugacity of sulfur versas 1000/T ("K)plot (Barton 1978) showing stability of the metal-saturated phases in the system Ag-Au-S. Ab-breviations: low-temperature AgAuS m, uytei-bogaardtite a, (Ag,Au):S solid solution I, acan-thite a, solid sulfur S, liquid sulfur S, silver Ag.The dashed lines are isopleths showing mole frac-tion Ag in coexisting electrum.

eguilibrium during cooling of a high-tempera-ture, gold-bearing argentite * electrum assem-blage. On cooling the argentite would have ex-solved uytenbogaardtite leaving the original sil-ver-rich electrum with acanthite * uytenbo-saardtite.

The variation in AglAu ratio in the electrumfrom the Comstock lode suggests that the uyten-bogaardtite is breaking down to acanthite *gold-rich electrum or that it is reacting withsilver-rich electrum to yield assemblages morecompatible with the phase diagram. Althoughthe occurrence of uytenbogaardtite as rimsaround the electrum blebs in the Comstock-lodespecimen might suggest that acanthite and elec-trum reacted to give uytenbogaardtite, this isunlikely given the electrum composition(s) andthe experimentally determined phase relations.

Barton (1978) has estimated the standard freeenergy of formation of low-temperature AgsAuSzas a linear funstion of temperature: AG" =4O75O + 22.OT (calories; T - oK). The es-timated error is -f 1500 calories.

AcrNowLeocEMENTs

The authors are greatly indebted to Mr. H. A.van Egmond of the Free University of Amster-dam for the painstaking and inventive polishingof the new mineral, and for devising the tung-sten carbide microdrill. The help of Dr. A. H.van der Veen of Billiton Research Co. of Arn-hem" and of Mr. R. H. Verschure of the Labo-ratory of Isotope Geology at Amsterdam withthe X-ray work is acknowledged. M.D.B. ac-

Ag T"c

200 300

tooolr

UYTENBOGAARDTITE. A SILYER-GOLD SULFIDE 6 7

knowledges the assistance of Mr. L. B. Wigginsof the U.S. Geological Survey and Mr. S. H.Loh of V.P.I. & S.U. with the microprobeanalyses, and the helpful comments of Dr. J. R.Craig of V.P.I. & S.U., Dr. J. R. Goldsmith ofthe University of Chicago and Drs. P. B. Barton,J. R. Clark and G. K. Czamanske of the U.S.Geological Survey. Mr. J. S. White of the U.S.National Museum provided the material fromthe Comstock lode and Smeinogorski. Dr. A. T.Anderson of the University of Chicago assistedwith some of the photography. Microprobe fa-cilities were provided by the U.S. GeologicalSurvey (Reston, Virginia), V.PJ. & S.U., andWACOM, a working group for analfiical geo-chemistry subsidized by the Netherlands Or-ganization for the Advancement of Pure Re-search. M.D.B. was partially supported by anNSF graduate fellowship and by a McCormickfellowship ([Jniversity of Chicago).

RennnnNcss

BARroN, M. D. (1978): The Ag-Au-S System.M.S. thesis, Virginia Polytechnie Inst. and StateUniv., Blacksburg, Va.

BAsrtr{, E. S. (1922): Bonanza ores of the Com-stock lode, Virginia City, Nevada. U.S. Geol. Received May 1978; revised manuscript acceptedSurv, Bull. 785,41-63. tuly 1978,

veN BeMrvrsLE\ R. W. (1949): The Geology olIndonesia. fr. Economic Geology, GovernmentPrinting Office, The Hague.

BoNHAM, H. F. (1969): Geology and mineral de'posits of Washoe and Storey Counties, Nevada.Nev. Bur. Mines Bull, 20.

EMMoNs, W. H. (1937): Gold Deposits ol theWorld. McGraw-Hill, New York.

Gnen, R. B. (1968): The system AggAuSg-AgaS.Amer. Mineral. 53, 496-500.

Krrrt, C. & OsN, I. S. (1973): Ore minerals in thetelluride-bearing gold-silver ores of Salida, In-donesia. with special reference to the distributionof selenium. Mineral. Deposita 8,312-320.

& _ (L977): Ore mineral paragenesesin Mn-Sn-Ag-Au-Se-bearing veins of Mangani,Sumatra. Indonesia. /a Problems of Ore Depos!tion,4th IAGOD Symp. (Varna 1974) 2, 295'302.

MsssrEN, P., Barwrn, M. & Tevrr.mBn, B. (1966):Structure cristalline du sulfure mixte d'argent etd'or. Soc. Roy. Sci. Lidee Bull. 56,727-733,

RucKLTDGE, I. & Srtnvrpn", E. F. (1968): Changesin the composition of petzite (AgsAuTez) duringanalysis by electron probe. Naaes lahrb, Mineral.Monatsh., 6I-68,