Carwdian Mineralogist Vol. 16, pp. 651-657 (1978) UYTENBOGAARDTITE,A NEW SILVER.GOLDSULFIDE M. D. BARTON{' Department ol Geological Sciences,Vireinia Polytechnic lttstitute and State University, Blacksburg,Virsinia 24061, U.S-4. C. KIEF"T NetherlandsOrganization for the Advancernentof Pure Research(ZWO)' Amsterdam' The Netherlands E. A. J. BURKE Institute lor the Earth Sciences,Free Uniyersity, Amsterdam 11, The Netherlands I. S. OEN GeoloeicalInstitute, University of Arnsterdam,Amsterdam, The Netherlands ABsrRAcr genberg), Altai (J.R.S.S.). C'est un min6ral t6trago' ia, ri'zz ou.P41, a 9.76, c 9.784. (Comstock); - D(calc) Uytenbogaardtite, Aga,AuSz,occurs with acanthite, a 9.68, c 9.814 Cfambang Sawah); Z 8; (Iambang I-es raies electrum and quartz in specimens from Tambang 8.34 (Comstock), 8.45 Sawah). plus 2.71(10) Sawah, Benkoelen district, Sumatra, Indonesia, the de diffraction-X les lntenses sont (421). compG' Comstock lode, Storey County, Nevada, U.S.A. (203), 2.60(9) (321) et 2.l2LQ) ks par proches de and Smeinogorski (Schlangenberg), Altai, U.S.S.R. sitions obtenues analyse sont quoique de Comstock The mineral is tetragonal, P4r22 or l4r a 9.76, Ag:AuSz, l'ufienbogaardtite jusqu'i (wids) Ces donn6es c 9.784. (Comstocklode), a 9.68, c 9.81A Cfambang contienne 4Vo de cuivre. basse- Sawah), Z - 8; D(calc) - 8.34 g/cm3 (Comstock montrent que I'uytenbogaardtite et la forme En lu- lode), 8.45 g/cma Sawah). The strongest temp6rature de Ag*AuSz sont identiques. Clambang pl6ochroique, de gris- X-ray powder diffraction lines are 2.71(L0) (2O3), midre r6fl6chie, le min6ral est gris-blanc l'air, et d'un 2.60(9) (321), 2.124(7\ (421). Measured composi- blanc d teint6 de brun dans dans l'huile. I*s tions lie close to Ag"AuS:, although uytenbogaard- gris-blanc brunitre au rose brundtre (en certaines longueurs tite from the Comstock lode contatns up to 4 wt. r6flectivit6s mesur6es VoR b 33.2'34.6 (470 Vo Cu. These data indicate that uytenbogaardtite d'ondo donn6es) sont les suivantes: (589 30.5- is identical with synthetic low-temperature AgaAuSs. nm), 30.3-34.6 (546 nm)' 3l.l-35.2 nm), Pleoctrroisrn in reflected light is: grey-white to 33.3 (650 nm). La duret6 au polissage, 7IlN15, est que pour grey-white with a brownish tint (air), brownish grey- approximativement 20, soit un peu moins white to brownish pink (oil). Measured reflectivitier l'acanthite. Ce min6ral est d6di6 au Professeur (RVo at specific wavelengths) are: 33.2-34.6 Willem Uytenbogaardt, de l'Universit6 Technique (470 nm), 30.3-34.6 (546 nm), 31.1-35.2 (589 nm), do Delft (Pays Bas). 30.5-33.3 (650 nm). The polishing hardness is (Traduit Par la R6daction) sliehtb below that for acanthite; ZI[N15 is about 20. The name is in honor of Willem Uytenbogaardt, INt'noPucrtoN Professor of geology at tie Technical University, Delft. The Netherlands. Two ternary comPounds, AgsAuS, and AgAuS, are kngwn at low temperatures in the Ag-Au-S. Neither phase has been re- SorvnvrernB system ported to occur in nature, although they might gold-silver deposits. Ex- On trouve l'uytenbogaardtite, AggAuSr, accompa- be expected in certain (Ag'$ gn6e d'acanthite, 6lectrum et quartz, dans des 6chan- amination of several acanthite + elec- tillons de Tambang Sawah, disrict de Benkoelen, trum (Au,Ag) assemblages has led to the dis- Sumatra (Indon6sie), dans la veine Comstock, comt6 covery of natural AgaAuSz, uytenbogaardtite, de Storey, Nevada (E.U), et b Smeinogorsk (Schlan- from the Comstock lode, Storey Counfy, Ne- vada, U.S.A. and Smeinogorski (Schlangenberg), of *Current address: Department of the Geophysical Altai, U.S.S.R. Simultaneously, in the course Sciences, The University of Chicago, 5734 South an investigation of the gold-silver ores from Ellis Avenue, Chicago, Illinois 60637, U.S.A. the Tertiary yolcanic belt of Sumatra, Indonesia, 651 652 THE CANADIAN MINERALOGIST uytenbogaardtite was found in a sample from TABLE2. REPRESENTATIVEmntVSfS Or UYTET'|gOOAARDTIru* Tambang Sawah, Benkoelen district. At all three localities, uytenbogaardtite occurs as small blebs Cu 5 ToTAL up to 100 pm across and as rims intimately (Jdeal associatedwith acanthite, electrgm, quartz and Aq-AuS^'JZ ) 55.34 10.97 100.00 other minerals. Comstocklode 56.l 20R 2.2 11.2 99.3 (pronounced y0feNnO.Cen- 55.8 27.3 3.0 12.3 98.4 The name 56.5 27.4 J-b 12.4 99.9 DAIT) is for Willem Uytenbogaardt, Professor Smeinogorski 56.0 Ja.+ I 0.4 98.8 n t7 I 32.7 10.3 r00.1 of mineralogy and petrology at the Free Uni- . 54.6 35.3 I0.8 100.7 versity in Amsterdam TambangSawah 54.5 33.4 I I .3 99.2 from 1960 to 1976, dedi- 53.2 35.1 lI.7 100.0 cated promoter of guantitative ore microscopy 56.7 32.6 ll.0 100.3 in his function as chairman of the I.M.A. Com- in pef mission on Ore Microscopyfrom 1962 to 1970, weight cent and now Professor of geology at the Technical lode material develops a completely different University in Delft, The Netherlands. surface in several tens of secondsunder moder- Both the mineral and the name have been ate illumination. This surface suggestsphoto- approved by the Commission on New Minerals induced decomposition;it requires a fresh polish and Mineral Names of the International Min- for its removal. Tambang Sawah and Smeino- eralogical Association. Type material will be gorski uytenbogaardtites, in contrast, seem to preserved in the collections of the Free Univer- be relativelv stable. sity in Amsterdam, the University of Amsterdam Microindentation hardness(VHN), measured and the United States National Museum with a Leitz Durimet-Pol hardnesstester apply- (Comstock IN.M.N.H. 105328 lode) and ing the minimum load of 15 e and an indenta- N.M.N.H. B239 (Smeinogorski)1. tion time of 15 seconds,is about 20, which corresponds to a Mohs hardness of about 2. Becauseof the small grain-sizeand the low hard- Prtystcer- eNn Oprrcel PRopERTIEs ness only one indentation could be made. The polishins hardness is lower than that for acan- In polished section uytenbogaardtite shows thite. Uytenbogaardtite is considerably more weak to distinct reflection pleochroism. In air the color varies from grey-white to grey-white with a brownish tint. In oil imrnersion the pleochroism is more distincl brownish grey- white to brownish pint; in contrast, acanthite is distinctly blue. The anisotropy is strong in O AgsAuSa both air and in oil, but without distinct coior.. The reflectance is slightly higher than that for A Comstocklodo acanthite and was measured with a Leitz MpV microscope photometer at four standard wave- I TombongSoroh lengths. The instrument was equipped with a Knott 9592A photomultiplier tube, a Veril I Snelnogonhl 8-200 continuous-band interference filter and a 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. The reflectance values, measured on a grain with maximum bireflectance, are given in Table 1. / 40 Light (i.e., heat) etching is extremely strong, even stronger than for acanthite.The Comstock- 'I. TABLE REFLECTANCEVALUES FOR UYTENBOGAARDTITE* moloZ S Ennx xmin 470 nm 34.6% 33.2/" 546 34.6 30.3 mob % Au 589 35.2 3t.l 650 33.3 30.5 Frc. 1. Selectedanalyses from the Comstock lode, * Tambang Sawah, and Smeinogorski specimens measuredon material from TambangSawah plotted in tle triangular diagram Ag-Au-S. UYTENBOGAARDTITE. A SILVER-GOLD SULFIDE 653 On probing with a sharp- TABLE3. X-MY P0l,,lDERDIFFRACTION DATA FOR brittle than acanthite. UYTENBoGMRDTITEANDSYNTHETIC AglAus2 ened steel needle uytenbogaardtite broke up into small pieces, whereas associatedacanthite Synthetic Ag3AuS2* Uytenbogaardtite tended to smear. Synthetic AgsAuS, is reason- dca.lc I AAT -calc AdT -calc ' ably easy to grind to a powder. hkl dobs "obs "obs I I 0 6.98 6.894 B 6.94 6.845 4 210 4.38 4.360 6 4.33 4.329 3 4.40 4.365 220 3.46 3.447 2 3.47 3.422 | CnsMlcel CovtPosrrroN 300 3.2+ 3.250 3 3-.24 3.253 310 3.09 3.083 6 :.0: 3.061 ; 3.09 3.086 222 2.809 2.825 6 2.802 2.807 3 2.82 2.8r9 203 2.731 2.724 10 2,712 2.710 10 2.71 2.711t0 Electron-microprobe analyses were obtained 321 2.609 2.609 9 2.591 2.590 9 2.60 2..609 331 2.236 2.238 3 2.226 2.222 I independently in three laboratories. Despite tle 421 2.124 2.129 8 2.112 2.114 4 2.13 2.r30; use of different operating conditions, different 422 1.992 I .994 5 1.980 1.980 2 : 520 t .807 1.811 5 r 7aa l 798 l r.ar 1.812 standards and different correction schemes,the 521 1.780 1.781 4 1.768 s.7s g.oa r results obtained are comparable. " lil from the three localities a (A) 9.85 9.81 9.78 Analyses of'that material demonstrate uytenbogaardtite is close to densities 8.29 glw3 B.45 g/cn3 8.34g/m3 ideal AggAuSa. Neither the Ag/Au nor the 'Powder data and cell edgesfrcn Graf (1968)r only those data (Ag + Au)/S ratios (atomic) show any sys- that correspondto observedlines ln the natural material are tematic departure from the expected values of given here. Graf's intensities are ten tires those given here.