Canadian Mineralogist Vol. 30, pp.327-333(1992)
MoSSBAUERsPEcrRoscoPY oF THEAs-Au GHALGoGENIDES PETZITE,FISCHESSERITE AND UYTENBOGAARDTITE
FRIEDRICH E. WAGNER Physik-DepartmentEIS, TechnischeUniversittit Milnchen, D-8046 Garching, Germany
JERZY A. SAWICKI AECL Research,Cholk RiverLaboratories, Chalk River, Ontario KOJ IJO
JOSEPHFRIEDL Physik-DepartmentEt|, TechnischeUniversitdt Milnchen, D-8M6 Garching,Germany
JOSEPHA. MANDARINO Departmentof Mineralogy'Royal OntarioMuseum, Toronto, OntarioM5S 2C6
DONALD C. HARRIS ologicalSurvey of Canada,601 Booth Street,Ottawa, Ontario KIA OE8
ABSTRACT
1974u M
SOMMAIRE leTAu Nous avons 6tudi6les spectresde Mrissbauerdes rayons ,y (77.3 keV) de I'isotope g6n€r€sd 4,2 K et mesur6s sur des 6chantillonsnaturels er synthetiquesde Ag3AuTe2Oetzite), et des 6chantillonssynthdtiques de AgsAuSe2 (fischesserite)et Ag3AuS2(uytenbogaardiite). Touiies compos6sfont preuve d'un gradient intensedans le champ ilectrique auiour diinuclEus des atomesd'or, et en fait le plus intensequi ait 6t6 d6couvertdans une espdceaurifbre. D'aprbs les d€placementsisombres et les interactions6lectriques quadrupolaires, et en particulier la similarit6 de ces parambtresdans le Ag3AuS2avec ceux de Au2S, I'or dans ces composdsAgAuX2 serait monovalent. (Traduit par la R6daction)
Mors-cl^s:min&aux r6fractairesde I'or, or invisible, or incorpor6 dans le r6seau,chalcog€nures de Ag-Au' petzite' l97Au, . fischesserite,uytenbogaardtite, spectroscopieMcissbauer d6placementisombre, interaction 6lectrique quadrupolaire,mine de Hollinger, Timmins, gisementde Hemlo, Ontario.
INTRoDUcTToN commonly is refractory to conventional techniques of extraction (cyanidization), a better under- Gold occurs in nature as well-defined minerals standingof themineralogicalcharacteristicsofgold great practical (native goId, i.e,, metallic gold or gold alloys with and gold-bearing minerals is of used iilu"r, and compounds, mainly with Te, Bi or Sb), significance. Mdssbauer spectroscopy can be and as a dilute impuiity within sufides (mainiy to characterize the nature of gold in such materials arsenopyrite and pyrite) (Wilson 1982, Harris (Wagner et al. 1986,1988, 1989, Friedl el al. l99l). 1990). ilecanse goid locked up within sulfides In this context, it is of interest to understand the 327
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Mdssbauerspectra of gold in well-definedminerals shift increasewith the valence state of gold and of gold. As part of a systematicsurvey of gold with the covalencyof the bonds betweenthe gold minerals by ter4u Mdssbauerspectroscopy, in the and its ligands. For the linear, two-fold-coor- present work we report on a study of petzite, dinated Au+ compoundsas well as for the planar fischesseriteand uytenbogaardtite.These minerals four-fold-coordinated Au3+ compounds, distinc- are silver-gold chalcogenideswith the general tive approximatelylinear correlationsbetween the formula Ag3AuX2, whereX standsfor Te, Se, and electric quadrupole splitting and the isomer shift S, respectively(Priride 1988a, b, c). have been found (Bartunik et u|.1970, Faltens & Petzite (Ag3AuTe) is the widely occurring Shirley 1970). Using these correlations, one can natural silver-gold telluride known since 1845.At determine the valence state of gold in such temperaturesbelow 320oC,it has a cubic structure compoundsfrom the observedvalues of the isomer (Frueh 1959, Cabri 1965, Chamid et al. 1978), shift and the quadrupole splitting. For bonding comparablewith that of garnet. The spacegroup situationsthat deviate from the two-fold linear or is 14fi2. The rare mineral fischesserite(Ag3AuSe2) four-fold planar coordination, however, a distinc- was first describedin l97l (Johan et al. l97l); tion between Au+ and Au3* on the basis of below 270oC, it has a cubic 1432crystal structure, Mdssbauerspectroscopy may be difficult, the more similar to that of petzite.The very rarely occurring so sinceone normally cannot determinethe sign of mineral uytenbogaardtite(Ag3AuSr) is an analog the electric quadrupole interaction, which is of petzite and fischesserite.Messien et al. (1966) expectedto be negativefor linear Au+ and positive reported the low-temperature form of Ag3AuS2 for planar Au3* compounds(Parish 1982, 1984). (stablebelow 185'C) to be cubic,but Graf (1968), Smit er ol. (1970) and Barron et al. (1978) Iater EXPERIMENTAL demonstrated that the symmetry of the room- temperature modification is actually tetragonal, Mcissbauerspectra of petzitehave been measured P4r22 or P4,. The observedreflections show that for two natural and three syntheticspecimens. One the space group is primitive and that the only of the natural specimensis a S-mm-thick slab of possible elementsof non-unit translational sym- rock from the Golden Spectreproperty, Hemlo, metry area 4, or a 4, axis. Despitethese differences, Ontario. The specimencontains small inclusionsof the crystal structures of the three minerals are petzite, intergrown with hessite (Ag2Te) and closely related. The packing of anions is ap- chalcopyrite (CuFeS), highly disseminated in proximately body-centered:gold is coordinatedby quartz and K-feldspar. It also contains a large two, silver by four chalcogenatoms distributed in amount of native gold. The second natural a tetrahedron. Gold atoms are located on the l,/8, specirnenconsists of single-crystalpieces with a l/8, l/8, e/c., positionsin the cubic (or almost total volume of about l0 mm3, which were cubic) unit-cell, which contains eight gold atoms. extractedfrom ore of the Hollinger mine, Timmins, Eachgold atom hastwo closeTe, Seor S neighbors Ontario. This specimen was obtained from the ("dumbbell") locatedalong the body diagonal,and Royal Ontario Museum, where it is registeredas six Ag atoms as next-nearestneighbors. Because of M13740. It containsa very small amount of visible this linear two-fold coordination, the environmenr native gold. Unfortunately, we could not obtain of gold in theseminerals is very different from that, natural specimens containing fischesserite and for instance,of the gold-silver ditellurides,in which uytenbogaardtite in quantities measurable by there is a six-fold coordination of Te atoms to the Mdssbauerspectroscopy. gold. Also, the distancebetween Au and its nearest A synthetic specimen of petzite was obtained neighbors,2.61 Ain perzite (Chamid et al. 1978), from the Royal Ontario Museum, where it is is markedly shorter than any bond length in the registeredas R395. The specimensproduced in the gold ditellurides (Tunell & Pauling 1952, Pertlik course of this work were made by fusing the 1984a,b, c). elementsin the required stoichiometricamounts in The information about the chemicalstate of gold evacuatedand sealedquartz tubes. In the caseof obtained by Mdssbauerspectroscopy stems mainly Ag3AuTe2and Ag3AuSe2,the chargeswere melted from the electric quadrupoleinteraction and from at 1000'C for 12 hours. After grinding and sealing the isomer shift of the Mdssbauer pattern. The again, the specimenswere annealedat 900oC for former splits the Mdssbauerline of leTAuinto a Z hoursand then cooledfrom 900oCto 700'C for doublet whoseseparation, the quadrupolesplitting 6 days. Two specimensof Ag3AuS2were prepared (QS), dependson both the symmetryand the degree by heating to 1200"C for 12 hours. The first of of covalencyof the bonds betweenthe gold atoms them was prepared with the exact stoichiometric and their ligands.The isomershift (IS) is a measure proportions of the elements, whereas in the of the electrondensity at the gold nuclei. Both the preparation of the second one, excesssulfur was electron density at the gold nuclei and the isomer included. The temperatureof the synthesisseems
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TABI! I . [JNfI€En DATAOBTAINED FOn THEA&ArX2 6-T€, Se,S) COiVIPOIJNBSTUOIED of the gold-silver alloys derivedfrom IN THE PRESENTWORT compositions the M6ssbauerspectra. reTPt leTAu cc rPq!{D sPAcE a 6) o (A) V (A3) REFEFENCE The l8-h-halfJife sources for the cm.P Mdssbauermeasurements were prepared by irradia- le6Pt A&ArTez | 4192 10.3860{4) . 1120 chamlt et a/. (1978) tion of about 200 mg of enriched metal in a cublc I 0.338(4) I 105 lhb work, F395 neutron flux of 2 x l0l3 n/s.cm2for one day. The A&A€A t432 e.e57(3) 890 Johe etaL (1971) cublo 9.974(1) 992 lhle el|(, synlh. 10000C Mdssbauer y-rays were detected with a planar yielded rates of A&4r9, P412or P41 9.64 9.81 919 Banon etal. (1978)a intrinsic Ge detector, which count tetragonal 9.71(1) 9,S0(4) s25 lhls mfi, lynlh. 500oC uD to 2 x 105/sin the window of the single-channel analyzerset on the 77.3 keY line. The absorbersof "Thg rolocn@g rof6r to lho @nl crystalloodphlc wo& on the res@tlvo mln€mls. ilho €ll ed06 ol on€ ot &o s@m€ns O@balo ss@h) Ere q@ted; oxperlnonhJ 0106 synthetic specimenswere fine powders distributed @€ @l Olvon h ths @10ren€. uniformly over an area of 2 cm2,The absorber thicknesswas betweenabout 60 and 200 mg/cm2. The gold content of the petzite-bearingslab of rock to havebeen too high, as in both casesa significant was not determined, but was sufficient for amount of sulfur did not react. Thus, the third measurement of a Mcissbauer spectrum. All specimenof Ag3AuS2was prepared at 500'C for measurementswere performed with both the source 100 hours and then cooled to room temperature and the absorber cooled to 4.2 K in a liquid He during 20 hours. This procedurealso was used to bath cryostat. The spectrawere least-squares-fitted preparea sampleof petzite.The chemicalcomposi- with superpositionsof Lorentzian lines. All line tion of the specimenswas determinedby electron- positions and isomer shifts are given with respect leTAu microprobe analysis, which showed significant to the source,i.e., to in Pt metal. In order fractions of native gold in petzite and in the to convert them to shifts relative to metallic gold, uytenbogaardtitesynthesized at high temperatures. 1.23 mm/s must be added to the given values. The indexing of the X-ray powder-diffraction photographsyielded good agreementof the unit- RESULTS cell parameterswith the published structural data (Table l). The results of electron-microprobe The leTAu Mcissbauerspectra of some of the analysisofthe native gold inclusionspresent in the specimensare shown in Figure l, and the relevant specimensare in fair agreementwith the calculated Mdssbauerparameters are compiled in Table 2.
N N
o E E o a Esg.o a o F roo FT F o o t g 3 6 6
-lsdd VelocltY (nnls) Yeloclty (ns/4 Frc, 1. leTAuMcissbauer specrra of petzite (AggAuTe2),fischesserite (Ag3AuSe, and uytenbogaardtite(Ag3AuS).
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gold-silver alloy componentsgiven in Table 2 refer to the areas of the respectivecomponents in the lS (nds) OS (hd8) W (ffi8) Rl(%) Mdssbauerspectra. The relative amountsof petzite Pstsns A&A!To2 and gold-silver alloy may be different from these f-factors of Tlmmlns,Onl. +r.19(2) 4.56(5) 1.85(4) 92(21 values becausethe Lamb-Mdssbauer (M13740) -0.68(16) 1.88(40) 8(2) Alz&2a the two componentsmay differ somewhat.In the H€mb,Onl. r1.14(4) 4.80(7) r.7e(8) 31(1) course of this work, no efforts were made to -0.7 412') 2.20{5) 69(1} ,!rza!o,a measurethe ratio of thesef-factors. Synthetlc +1.1 8(4) 4.58(7) r.90(5) 75121 AU gold-silver (R395) -0.7s(9) - 2.o1t2ot z5(2t *jrta The composition of the alloys ObServed-in the spectra can be estimated using an Synthollc +1 ,12(1 ) 4.so(4) r.68(0) zo(r) &+ (r000oc/12h) "0.59(1 I - 2.30(2) Bo(r) AvT2t{Jaempirical linear relationship between the content of iSOmerShift Synlhetlo +1,12(3) 4.52(6) 2.14(4t s6(r) Au+ silver, x, in Au1s'-"Ag" allOySand the (500oc/100h) -0.81 (4) " z.3a(s) ,r4(r) AleAea ISof theM6ssbauerline(Huray etal. 1976),which can be written as Fbd€srlte Ag3AuSo2 xlat.9ol = 44.(Islmm/sl + 1.23). given been Stnihatic +1.20(1) 4.96(3) 1.9412') 1OO The compositions in Table 2 have (r000oo/12 h) derived from this relation and the observedisomer shifts. Note that the composition of the metallic Uytenbogurdtno &3Arq phasein both the petziteand the uytenbogaardtite Synlh9ilc +1.s7(2) 5.38(4) r.94(4) 79(1) samplesis always much richer in gold than the 0200ocn2 h) "0.63(6) 2.05(17) 21(1) ar744€% nominal Au/Ag ratio in thesespecimens (AuAg:). Synlh€llc +1.60(2) 5.42(5) 1.96(0) 64(1) (t200oc/J2 h) -0.64(3) 2.s8(8) 36(1) AuToAg@ This seemsto be a systematicdeviation, the alloy phasebeing alwaysabout AurAg whateverthe total Synthetic +1.6s(1) 5.36(3) r .96(2) 100 (500ocn00 h) amount of gold presentin the metallic form. The excess silver is presumably bound in a silver 'lS ls tho bomor thftit @lattuoto lho su@ ot Au In Pt mlal, OS b lho ol@fic qladrupolo 8pfildfq, W ttre F$rHM lire width, and Rl lhs clsdve Inlonsily ot lhg rstpgctlve @mponsnt8. telluride such as hessite(AgrTe), which is invisible Fiolres In brackeb Indlcate u!€nalnty l. last dlgn(g) reponed. to Mdssbauerspectroscopy.
Fischesserite Petzite The leTAu spectrum of synthetic Ag3AuSq The spectra of the five different. specimensof exhibits a symmetrical quadrupole doublet and petziteexhibit two well-separatedabsorption lines. shows no trace of a gold-silver alloy. The The different intensitiesof the two resonant lines Mdssbauerparameters of this doublet arevery close can be attributed to the presenceof different to those of petzite (Table 2). amounts of native gold (electrum)in the different specimens. The right-hand peak is always at Uytenbogaardtite virtually the sameposition, + 3.48 + 0.03 mm/s, and has nearly the natural linewidth. The left-hand The M0ssbauer spectrum of the synthetic peakis alwaysmore intense'aiitlSfghtly broadened, Ag3AuS2sample prepared at 500'C is symmetrical which indicatesthat it is composedof the left peak and shows no traces of impurities, whereas the of a quadrupoledoublet attributable to petziteand specimens prepared at 1200'C contain some a peak due to impurities of a gold-silver alloy. The gold-silver alloy. Fits in analogy to those for the left-hand peak of petzite should be at the same petzite spectrayield the resultsgiven in Table 2. placein all cases,whereas the position of the alloy peak may vary with the Au/Ag ratio, sinceAu-Ag DtscussloN alloys have a more positive isomer shift (Huray e/ al. 1976)than pure gold with its resonanceline at The common feature of the M6ssbauerspectra -1.23 mm/s. These considerationsleave only the of the three compounds-.investigatedis a rather disposition of lines as shown in Figure I for the large quadrupole splitting (QS = 4.5-5.4 mm/s). consistentfitting of all of the petzite spectra.The Large magnitudes of the quadrupole splitting, Timmins specimen(M13740) yielded the spectrum which is a measureof the gradient in the electric with the weakestline for the gold-silver alloy. We field at the Au nuclei, are in accordancewith the therefore consider the Mdssbauer parameters of linear two-fold coordination of the gold atoms petzite obtained for this sample (IS : +1.19 expectedfrom the similarity of the cell edgesin all mm,/s, QS : 4.56 mm/s) as the most reliable that three compounds,although a determinationof the can presentlybe given. atomic position so far has been made only for The relative intensities (RI) of the petzite and petzite.The similarity of the M6ssbauerparameters
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Au (I)
Au (III) an E E
(5
_l-
= o- u(CN)28r2 aJ) KAu(CN)2[t2 lrl -I a o- e, o.-No3Au03 o s(%Hs)AAu(Nia a
uFa
101 L IS0MERSHIFT (mm/s)
Fla. 2. Plot of the magnitudeof the electricquadrupole splitting- versas the isomer shift (relativeto gold in a platinum matrix) for Au+ and Aur* compounds'as well as the gold minerals studied in the presentwork.
of all three compounds in the Ag3AuX2 series compounds(Parish 1984). In the present case, confirms that the coordination of gold is very however, only the magnitudesof the quadrupole similar in all threecases. On the basisof the known, interaction can be determinedfrom the Mdssbauer approximately linear relation betweenIS and QS spectraof powder absorbers.Even oriented single- in covalentauric and aurous compounds(Bartunik crystal specimens,which normally allow the sign et al, 197O,Parish 1982,1984), of which a part is of the quadrupole interaction to be determined shown in Figure 2, one finds the investigated (Prosseret ol. 1975),would not be helpful in the compoundsto be betweenthe Au+ and the Au3+ present case, where the cubic (Ag3AuTe2 and regions. In both valence states, the IS and QS Ag3AuSq), or at least nearly cubic (Ag3AuS2) increaseas the gold-ligand bonds become more symmetry would preclude a net alignment of the covalent,and greater electron density is placed on tensors of the gradient in the electric field in the the gold atom. An unambiguous distinction absorber,and hencethe determinationof the sign betweenAu+ and Au3* could be made if the sign of the electric quadrupole interaction. However, of the gradient in the electric field could be the linear coordination of the gold betweenits two determined,since the gradientsare expectedto be nearest tellurium neighbors in Ag3AuTq @rueh negative in the Au* and positive in the Au3* 1959),together with its position in the plot of the
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quadrupolesplittings versusthe isomer shifts (Fig. quadrupole splitting allows petzite to be easily 2), strongly support the notion that gold in petzite distinguished from the ditelluride minerals is monovalent. From the similarity of the calaverite, sylvanite and krennerite. Notably, the Mdssbauerparameters of petzite, fischesseriteand Mdssbaueranalyses can be made on rather large uytenbogaardtite,one then concludesthat the same pieces of rock without separation of the gold is true for the oxidation state of the gold in the mineral, as long as the overall content of gold in latter two minerals. This view is supported by the the sampleexceeds about 100ppm. similarity of Mdssbauer parametersof Ag3AuS2 with those of the Au+ compound Au2S (Faltens& AcKNowLEDGEMENTS Shirley 1970), which has the Cu2O type structure (064, Pn3m) (Hirsch et al. 1966),in which the gold This work has been jointly funded by the is linearly coordinated to two neighboring sulfur DeutscheForschungsgemeinschaft and AECL Re- atoms at a distanceof 2.L7 A. Figure 2 showsthat search. Helpful comments by Louis J. Cabri, Au2Salso falls betweenthe Au+ and Au3+ regions Robert F. Martin and an anonymous referee are on the QS yersrs IS plot and is remarkably close acknowledged. to Ag3AuS2,which indicatesvery similar bonding situationsand gold-sulfur distances. RsFpRENcss The Au-Te distances are 2.61 A in petzite (Chamid et al. 1978).Because of the smaller size BARroN,M.D., Krnr"r,C., Bunrr, E.A.J. & OrN,I.S. of the unit cell, the distancesbetween Au and Se (1978):Uytenbogaardtite, a new silver-gold sulfide. in fischesseriteare expectedto be smaller than the Can.Mineral. 16, 651-657. Au-Te distancesin petzite. This may be the reason for the larger quadrupolesplitting. The quadrupole Banrumr, H.D., Porzrl, W., Mossneunn,R.L, & splitting along the seriesAg3AuTe2 - Ag3AuSq - KarNoL,G. (1970): Resonanceabsorption of y-radiation Ag3AuS2 increases with on Au(I) and Au(III) compounds.Z. decreasing unit-cell Physik 240, l-16. volume, and hencewith decreasinggold-chalcogen distance. It is tempting to attribute this to Caanr,L.J. (1965):Phase relations in the Au-Ag-Te increasingcovalency, with the Au-S bond beingthe systemand their mineralogicalsignificance. Econ. most covalent.It is, however,difficult to decideto Geol.60,1569-1606. what extentthe increasingcovalency is attributable to the nature of the ligands and to what extent it CHeuro,S., PouEoeNsrava,E.A., SrtntooNov,E,M. is attributable to the decreasingbond-length of the & Brrov, N.V. (1978):Refinement of the structure gold-ligand bond. of petziteAuAg3Te2. Sov. Phys. Crystallogr.23, -269(Kristallo grafiya The differencein isomer shifts betweenpure Au 267 23, 483-486). (IS : -1.23 Ag3AuX2(IS - metal mm/s) and rhe Falrgrs, M.O. & SurnLEy,D.A. (1970):Mcissbauer + I .2-1.6mm,/s) shows that thedensity of electrons spectroscopyof gold compounds.J. Chem.Phys. at the Au nucleusin the Ag3AuX, compounds is 53,4249-42&. larger than that of Au metal. The observed magnitudeof the isomershift in petzite(IS = + 1.2 Fnrppr,J., WacNrn,F.E., Sewrcrr,J.A., Hannrs, mm/s) is only slightly smaller than in gold-silver D.C., MaxrenrNo,J.A. & MenroN,P. (1991): ditellurides(IS = + 1.4-1.7 mm/s) (Wagneret ol. le7Au,57Fe, and l2lsb Mdssbauerstudy of gold 1986,1988). The explanationof the smallervalues minerals and ores. Hyperfine Interoctions 69, of the isomershift, and thus smallercharge-transfer 945-948. from tellurium to gold atoms, may rest in the fact FrurH, A.J., Jn. (1959):The crystallographyof that in the ditellurides, gold the atoms are bonded petzite,Ag3AuTe2. Am. Mineral. 44,693-701. to six fairly close tellurium atoms, whereas in petzite the gold has only two close neighbors. In Gnar, R.B. (1968):The systemAg3AuSx-Ag2S. Am. addition, whereasmost of the other phasesin the Mineral.53,496-500. systemAg-Au-Te have metallic bonding, conduc- tivity data suggest that covalent bonding is of Hannrs,D.C. (1990):The mineralogyof gold and its considerablesignificance in petzite (Rucklidge & relevanceto gold recoveries.Miner. Deposita Stumpfl 1968). 2S(suppl.),53-S7. HrnscH,H., Dr CucNac, A., Geon, M.-C. & CoNcrusroNs Pounaorcn,J. (1966):Cristallographie du sulfure aureux.C. R. Acad. Sci.Paris 2638, 1328-1330. The electricquadrupole interactions observed in Ag3AuX, compoundsare the largest so far found Hunav, P.G., KrnrHlrNr, T.J., OnrNsuarN,F.E., in any gold mineral. In particular, its large THousoN,J.O. & TuNc, C.M. (1976): leTAu
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isomer-shift studiesof charge-densityperturbations (1988c): Silver-gold-tellurium.In Temary in Au-basedalloys. P&ys. Rev. Bl4,4776-4781. Alloys. 1. Ag-Al-Au to Ag-Cu-P (G. Petzow & G. Effenberg, eds.). Verlag Chemie, Weinheim, JoHen, 2., Prcor, P., Prnnnot, R. & Kvetx, M. Germany (250-269). (1971): La fischesserite, Ag3AuSe2, premier s6l6niure d'or isotype de la petzite. Bull. Soc. Fr. Pnossen,H., WecNrn, F.8., WonrueNN,G., Kelvtus, Mindral. C ristallogr. 94, 381-384. G.M. & WAppl-txc,R. (1975): M PanrsH,R.V. (1982): Gold and Mdssbauerspectros- RucrLrnce, J. & Sruveru, E.F. (1968):Changes in the copy. Gold Bull. 15, 5l-63. composition of petzite (Ag3AuTe) during analysis by electron probe. Neues Jahrb. Mineral. (1984): Gold-197 Mcissbauer spectroscopy in Monatsh.,6l-68. the characterization of gold compounds. /n Mrlssbauer Spectroscopy Applied to Inorganic Surr, T.J.M., VrNenae,E., WIensMa'J. & Wtrcrns' Chemistry,I (G.J. Long, ed.). Plenum Press,New G.A. (1970): Phase transitions in silver gold York (577-617). chalcogenides.J. Solid State Chem. 2,309-312. Prnrlrr, F. (1984a): Kristallchemie natihlicher Tel- Tuxru-, G. & PeurrNa, L. (1952\: The atomic luride. I. Verfeinerung der Kristallstruktur des arrangement and bonds of the gold - silver Sylvanits, AuAgTe2. TschermaksMineral, Petrcgr. ditellurides. Acta Crystallogr. 5, 375-381. Mitt. 33,203-212. We,cNsn,F,E., ManroN, P. & RscNanp,J.-R. (1986): (1984b): Crystal chemistry of natural tellurides. Mdssbauer study of the chemical state of gold in II. Redetermination of the crystal structure of gold ores. In Gold 100. Proc. Intern. Conf. on = krennerite, (Au1-rAgr)Te2 with x 0.2. Tscher- Gold. 2. Extr. Metall. of Gold (435-443\. maks Mineral. Petrogr. Mitt. 33,253-262. & - (1988): rqAu Mtlssbauer (1984c): Kristallchemie natihlicher Telluride. study of gold ores, mattes, roaster products and III. Die Kristallstruktur des Minerals Calaverit. gold minerals. Hyperfine Interactions 41, 85l-854. AuTe2. Z. Kristallogr. 169, 227-236. P.M. & MantoN, P. (1989):A leTAu PnrNcE, A. (1988a): Silver-gold-sulfur. In Ternary Swasu, Mdssbauer study of the roasting of refractory gold Alloys. l. Ag-Al-Au to Ag-Cu-P (G. Petzow & HyperJine Interactions 46' 68l-688. G. Effenberg, eds.). Verlag Chemie, Weinheim, ores. Germany (214-219). WnsoN, W.E. (1982): The gold-containingminerals: (1988b): Silver-gold-selenium. In Ternary a review. Mineral. Rec. 13,389-400. Alloys.s. 1. Ag-Al-AuAs-Al-Au to As-Cu-PAg-Cu-P (G. Petzow & G. Effenberg, eds.). Verlag Chemie, Weinheim, Received Apfl 8, 1991, revised manuscript accepted Germany (221-223). September 9, 199L Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/30/2/327/4005996/327_30_2_cm.pdf by guest on 24 September 2021