185 The Canadian MineraLogist Vol. 32, pp. 185-188(1994) THEMn ISOTYPEOF ANDORITE . AND UCHUCCHACUAITE HTIIFANG Lru axo LUKE L.Y. CHANG Depamtrcntof Geology,University of MaryIand"College Park Maryland20742, U.S.A. ';. CHARLES R. KNOWLES Idaho Geological Suney, Moscow, Idaha 83843, U.S.A. Alsrnasr Phaserelations in the systemAgrS-MnS-SbrS3 were studiedbetween 300' and 500"C using evacuatedand sealedglass capsules.Two ternaryphases, Ag2Mn Sb6S12(Ag2S.2MnS.3Sb2S3) and Ag1.a1Mn .r2sb5.65sl2 (Ag2S'4MnS'4Sb2S3) are stable in the system,and both form equilibrium assemblageswith stibnite and alabandite.The phaseAg2Mn2Sb6S12 is a Mn isotype of andorite,with a 12.19(l),, 19.58(1)and c 4.00(l) A. The limits of Pb-for-Mnsubstitution along the join andoriteand its Mn isotype,Agr@br-fln )rSb6S12,are 0.40 ) x ) 0.95. Uchucchacuaiteis readily synthesizedfrom its reportedcomposition AgMnPir;Sb5S;;.tt iris an ina,ili6-rype structue and calculatedunit-cell dimensioni a 13.08(1),b 19.466), andc 4.27Q) A. Uchucchacuaiteforms a completesolid-solution series with andorite,whereas the solid-solutionis incompletebetween uchucchacuaiteand the Mn isotypeof andorite. Keywords:andorite, Mn isotype,uchucchacuaite, solid-solution series. Sovruanr Les relationsde phasesdans le systbmeAgrS-MnS-Sb2S3 ont fait l'objet d'6tudesentre 300oet 500'C par synthdsesdans des ampoulesde verre 6vacudeset scelldes.Deux phasesternaires, Ag2Mn2Sb6S12 (Ag2S'2MnS'3Sb2S3) et Ag1.a1Mn2.s2Sb5.65S12(Ag2S.4MnS.4Sb2S3) sont stablesdans le systlme;les deux d6finissentdes assemblagesi 1'6quilibre avecstibine et alabandite.La compositionAg2Mn2Sb6S12 serait I'isofype manganiferede l'andorite; sesparambtres rdticulaires sonta 1.2.79(l),, 19.58(1)and c 4.00(1)A. La substitutionentre andorite et son isof'?e -anganifdre,Agr@bt-,Mn )2Sb6S12 est partielle: 0.40 ):r > 0.95. I1 est facile de synth6tiserI'uchucchacud'te i partir d'un m6langeayant la compositionattribu6e i cetie espice, AgMnPb3Sb5Sl2.Cette phase p^ossbde une structuresemblable i celle de l'andorite, et sesparamdtres dticulaires sont a 13.08(1),b 19.46(1)and c 4.27(1.)A. L'uchucchacual'teforme une solutionsolide compldte avec l'andorite, tandis qu'avec l'isorype manganilbrede I'andorite, elle est incompldte (Traduit par la R6daction) Mots-cl6s:andorite, isotype manganifbre, uchucchacuaite, solution solide. INTRODUCTIoN andoritesolid-solution in the system,and proposed a miscibility gap betweenfizelyite and andoriteat Andorite is consideredto be a relatively common about 400'C in their hydrothermalexperiments. A sulfosaltof silver, and in somedeposits, it forms the Sn isotypeof andoritewas synthesized,and found to chiefsilver ore (Chace1948). Its compositiongener- form a completesolid-solution series with andorite ally deviatesfrom the ideal formula, Ag2Pb2Sb6Sr2,(Chang1987). as demonstratedby Nuffield (1945), Mozgova et al. Andorite-like phasesalso were synthesizedwith (1983),and Mo61oet al. (1.989)because of substi- manganese(Chang 1982),but their characterization tution between2Pb2+ and Ag1+ + Sb3+or between and phaserelations with andoritehave not beenestab- 3Pb2+and 2Sb3++ I. In the systemAgzS- lished. Recently, a Mn-bearing andorite-typemineral, PbS-Sb2S3,andorite displays an extensiverange of uchucchacuaite,was reported from a telescoped solid solution at temperaturesbetween 300' and depositat Uchuc-Chacua,Peru (Modlo et al. 1984). 500'C (Hoda & Chang 1975).The compositionsof Uchucchacuaite has an ideal composition ramdohrite and fizelyite all fall into this range. AgMnPb3Sb5Sr2illustrating a complexscheme of Bortnikov et al. (1980) observedthe formation of replacementof Ag + Sb by Pb + Mn. 186 THE CANADIAN MINERALOGIST The purposeof this study is to examinethe phase the samebulk compositiontreated by the two methods relationsin the systemAg2S-MnS-Sb2S3 and between were found to be identical. A total of sixty-five com- andoriteand uchucchacuaite. positionswere preparedfor the determinationof phase relations in the systemAg2S-MnS-Sb2S3 and for the E:enrutvnlrrar PnocBpunss synthesisof uchucchacuaite.For the deterrninationof Mn = Pb substitution,twenty compositionsat a Starting compositionswere preparedfrom reagent- 5 mole Vointerval were preparedfor eachof the three gradelead, manganese, antimony, silver and sulfur; all joins underconsideration. have 9999Voor better purity, as specifiedby the sup- The quenchedphases were examinedby X-ray pliers' information. Synthesisand heat treatmentwere powder diffraction and reflected-light microscopy. made in muff1efurnaces using the conventionaltech- Chemicalcompositions of selectedsamples were nique of sealed,evacuated glass capsules(Kullerud obtained by electron-microprobeanalysis. The probe & Yoder 1959).Two to five months were used for was operatedat a referencebeam-current of 0.1 pA equilibrium experimentsin the temperaturerange and 15 kV. The beam diameter was maintainedat 300'-500'C. As a test of the attainmentof equi- I pm at all times. A referencestandard of synthetic librium, some sampleswere heatedto complete PbS was used for sulfur, and ptue metals were used melting (-800'C), quenched,ground under acetone, for all other elements.The data were correctedfor resealedin a new evacuatedglass capsule, and backgroundand drift, and the matrix effects were annealedat the desired temperaturefor the same correctedusing a ZAF computerprogram. Cell dimen- period of time as experimentswith samplesprepared sions were computedwith a least-squaresrefinement from raw starting materials.The final assemblagesof prognm (Benoit1987). lUlnS AA A AA A ftc. l. Phaserelations in the systemAgrS-MnS-Sb2S, at 400'C. Symbols used in the diagrams,solid triangle, half-filled circle and solid circle, representthree-phase, two- phase,and one-phaseassemblages, respectively. Dashed lines mark the region of andoritesolid-solution in the systemAgrS-PbS-SbrSr. TIIE Mn ISOTYPEOF ANDORITE AND UCHUCCHACUAITE 187 PHASERELATTONS nr rrrE TABLE1. X-RAY POWDER-DIFFRACIIONDATA FOR PHASES A ANDB Svsreu AgrS-MnS-Sb2S3 PbeA Phue B d*-d*&QL[) Phaserelations in the systemAgrS-MnS-Sb2S3 5 210 were studiedin the temperaturerange 300o-500oc. 5.83 5.81 5 130 5.80 5 240 A liquid forms from compositionshaving between 3.89 3.EE 10 3.57 3.54 25 12r 3.s7 50 18 and43 moleVo SbrS3 and between 58 and 80 mole 3.s0 40 7o Sb2S3along the join AgrS-Sb2S3at 500'C and 3.34 3.34 50 250 3.35 50 are presentin equilibrium assemblageswith AgrS, 3.30 @ AgSbS2,Sb2S3 and MnS in the ternary system.The 3.21 2i 3|{) 3.2t m systembecomes completely solidified at 450'C. 3.15 3.15 30 410 I 2.881I Jtl Figure I illustrates the phaserelations in the system Ln6 1., 30 2.883 100 at 400'C. Ag3SbS3and AgSbS, are stablealong the 2.E73 430 join Ag2S-Sb2S3,whereas MnrSb2S6 exists along 2.791 2.792 100 32! 2.788 40 ( 2.67E\ 440 the join MnS-Sb2Q.Both Ag3SbS3and AgSbS, are 2.6'ts tl 10 2.680 60 well-characterizedphases (Keighin & Honea 1969), 2.@ lJl but the structural analysis of Mn3Sb2Suhas not 2.565 30 been done.The sevenmost intensereflections of 2.489 2fr 2408 Mn3Sb2S6 in A are 2.303(100),1.849(80), td G)l 2.?42 ,ix 15 351 3.424(75), 2.686(50),2.37 5 (50), 2.056(35),and 2.214 to 2.537(35).A comparisonwith )(RD datafor Pb3Sb2S6 2.168 @ @DF n-266) and Sn3Sb2S6(PDF 30-1368) did not 2.r38 ,.i0, 10 )ll result in a match.Neither stephanite(Ag5SbS) nor an 2,M4 ,.* 531 2.046 70 phase (MnSb2Sa)(Harris i 2.Q31 25 unnamed 1989) was 2.W7 2A observedin the system. 1.975 Lq12 D 54r Two ternary phaseswere found, designatedas 1.966 4T PhaseA and PhaseB for convenience.Phase A has a 1.955 t.r$ 10 6Q 1.952 60 compositionAgrMnrSbuS,, (AgrS.2MnS.3Sb2S3), 1.933 1.936 10 1.10.0 1.847 1.E70 n 621 1.855 80 a compositionalequivalent to andorite,and it has a '7ro 1.822 1.820 10 small range of solid solution extending to 1.805 Ag2.eeMnl.saSbo.oeSrz.Phase B has a composition Agt.o,Mnr.rrSb5.65Sr2(Ag2S.4MnS.4Sb2$). Electron- microprobeanalysis of thesesynthetic phases gave Ag2.2sMn1.3sSb6S12for Phase A and Agr.aeMn2.ru Sb6S,2for PhaseB, which illustrates a fair match betweenthe compositionsprepared from raw starting materials and the compositions after heat treatment. X-ray powder-diffraction data for PhaseA (Table 1) can be indexedon the basisof the unit cell of andorite. Mn-bearing sulfosalt mineral, is not a stablephase in whichyields a I2.79(l), D 19.58(t)and c 4.00(1)A. the systemat temperaturesbetween 300' and 500"C. As tabulatedin Table 1, PhaseB has severalmajor reflectionsthat matchthose of PhaseA. but it also has Snurusts oF UcHUCCHAcUATTEANDEXTENT many distinct onesthat cannotbe accountedfor if an oF Mn ._--Pb Sussrrrul'IoN andoriteunit-cell is used for indexing. Both PhaseA and PhaseB form equilibrium assemblageswith Uchucchacuaiteis readily synthesizedfrom its stibnite and alabandite,and bulk compositions reportedcompositiono AgMnPbrSbrS 12 (Ag2S'2MnS' betweenPhase A and PhaseB produceddistinct two- 6PbS'5Sb2S3)(vlo€lo et aI.1984) in the temperature phaseassemblages. range300'-500'C. AgMnPb3SbsSuhas an andorite- At400'C, AgSbS2can take only 17.5mole 7oMnS, type structure,and calculatedcell;dimensions are c and the rangeof solid solutiontoward MnS is lessthan 13.04(1),b 1,9.46(l)and c 4.2i7(l)A. Cell dimensions 5 mole 7o AgSbS2,although MnS and AgSbS, are of uchucchacuaiteare a L2.67, b 19.32,and c 4.38 A isostructural.This is in contrastto the extensiverange Mo0lo et al.1984). of 70 mole 7o PbS in AgSbS2 in the system The extent of Mn = Pb substitution in the tlree Ag2S-PbS-Sb2S3(Hoda & Chang1975). andorite-fypephases was studiedat 400'C. Along the Experimentsat 300'C were conductedwith a join andorite(.r = l) - uchucchacuaite(.r = 0), there is LiCl-NH4Cl flux. Resultsobtained show no major a complete solid-solution series Ag1*"Mn1-, changein phaserelations as comparedwith those at Pb3-"Sb5+xS12.Electron-microprobe analysis was 400'C. Samsonite(AgsMn2SbaSl), the only known performedon the compositionsof two membersof 188 this series.Results are Ag,.rrMno35Pb2.3eSbr.rrS,,for RSFEREwcES x = 0.65 and Ag1.25Mne.s0Pb2.70Sb5i5Sfor x = 0.25, p BENoIr, P.