Canadion Mineralogist Vol. 25, pp,229-236 (1987)

STANNOIDITE-BEARINGTIN ORE: MINERALOGY,TEXTURE AND PHYSICOCHEMICALENVIRONMENT OF FORMATION

MASAAKI SHMIZU Department of Petrologt and Mineral Deposits, University Mt6eum, University of Tokyo, Tokyo II3, Japan

NAOTATSU SHIKAZONO GeologicalInstitute, Facahyof Science,University of Tokyo, Tokyo 113,Jopan

(Ramdohr ABSTRACT had been called hexastannite 194, 19ffi) and yellow stannite [-tvy 1967).The chemical for- mula Cur(Fe,Zn)2SnSg had been originally Stannoidite-bearingtin ores fron Japanesevein-type as- tin (Kato depositshave been studied. The stannoidite commonly co- signed 1969)1 however, the formula existswitl chalcopyrite, bornite and sphalerite; the atomic Cur@e,Zn)rSn2st2 was later proposed (Springer Fe/Zn ratio of the sphalerite is low, in the range 0.@2 - 1972,Boorman&Abbott 1967,Petruk 193). Mdss- 0.015. Basedon iron content of sphalerite and the mineral bauer, chemicalanalysis and crystal-structurestudies assemblage,the probable range in sulfur fugacity and tem- confirm the chemical formula as Cu{Fel*@d+, perature for the stannoidite-bearing tin ore is estimatedto za2+)Snt+So (Yamanaka& Kato 1976,fudoh & be lf - - 1fr16atm. and 2@ 300.C. This estima.tedranee Takeuchi 1976).Some analytical data on stannoidite is different from that for the srannite-bearingtin or" oi- have been obtained (e.g., Petruk 1973, Kissin & mated by Shinizu & Shikazono (1985). Tungsten-free tin ore deposits seemto have formed at a higher fugacity of Owens 1979), but details of the natural ocsurrence sulfur or lowo temperaturethan tungsten-beaxingdeposits of the nrineral and its physicochemicalenvironment of rin. of formation have not been clarified. In this paper, the compositional relations of coex- Keywords: stannoidite, sphalerite, tennantit€, tetrahedrite, isting stannoidite, sphalerite and tennantite- stannite, Japan, vein-typetin deposits,Fe-Zn partition- tetrahedrite-seriesminerals are reported. Based on ing, sqlfur fugacity, temperature. thesedala, the sulfur fugacity of stannoidite-bearing tin ore is estimated. Considering the complementary Sonauarnn work on stannite-bearingtin ores from Japaneseore deposits(Shimizu & Shikazono 1985),a comparison On a 6tudi6le minerai d'6tain A $annoidite desgisements betweenenvironmental conditions of thesetwo tlpes d'&ain en veines du Japon. La stannoidite coexiste cou- of tin sulfides is made. ramment avec chalcopyrite, bornite et sphaldrite, Le rap- port atomique Fe/Zn de la sphaldrite est bas, entre 0.002 et 0.015. Vu la teneur en fer de la sphaldrite et l,associa- Satvrpr.aPnnpenanron enn tion desmin6raux, on propose une fugacitd de soufre pour ANALnTcAL PnocsouRE ce minerai entre 10-6 et 1016 atmosphereset une temp6- rature de formation entre 2@ et 3@oC. Ces valeurs diffb- The samples used for this study belong to the rent desr6sultats obtenus par ghimizu s1ghikazono (1985) UniveirsityMuseum of the University of Tokyo; some pour le minerai d'6tain e stannite. Les gisements d'6tain were collected by the present authors. Locations of danslesquels letung$eue est abs€ntindiqueraielrt une fuga- tle samples studied are shown in Figure 1. citd de soufre plus dlevdeou une temperafire plus basse que les gisements d'&ain i tungstOne. The chemical composition of coexisting stannoi- dite, sphalerite and tennantite-teFahedrite-series (Iraduit par la Rddaction) minerals was determinedusing a JEOL 733 electron- microprobe analyzerat the OceanResearch Institute Mots-clds: stantroidite, sphaldrite, tennantite, tetraedrite, of the University of Tokyo. The acceleratingvoltage stannite, Japon, gisementsd'6tain en veines, r6parti- used was 25 kV, and the following standards were tion de Fe et de Zn, fugacit€ de soufre, temp6rature. usedfor analysis:natural chalcopyrite(Cu), synthetic Zno.oFeo.+S(Zn, Fe, S), synthetic CdS (Cd), syn- thetic MnS (Mn), synthetic SnS (Sn), synthetic INr,nooucloN Ag3As$ (Ag, As) and synthetic Cu1sFe1.sZne., Sb4SE(Sb). The characteristic X-ray intensities for Stannoidite is a common tin-bearing mineral in eachpoint were mea$uredtwice for a fixed interval Japinese tin ore deposits, and was frst described of five seconds.The averagedvalues were corrected from the Konjo deposit by Kato (1969). The mineral for dead time and background. Quantitative correc- 229

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I f tions for atomic number, absdrption and fluores- i C'- cence effects were also perfopmed based on the lli method proposedby Sweatmah& Long (1969).

TEXTURES AND ASSEMBLAGES oF STANNOI TlN Onns

Two characteristictextures stannoidite-bearing ores are observedunder the (Figs.2,3). Where relict cassiterite such as observedin the ores from the Konjo and deposits,stau- noidite usually includesstanni and stannite in turn includesaggregates of ercins(Fie.2). This texture, which was pointed out by Kato (1969),sug- geststhe following sequenceof tin minerals: cassiterite (early) stannite-stannoi- dite (late). On the other hand, where occursat the margin of somestannoidite suchas observed in the samplesfrom the Tada, idani. Omodani Fro. l. Map of Japan, showing samplelocations' and Fukoku deposits, showsa replace- ment or reaction texture (Fig. ), as mentionedby Lee et sl. (1974). In this case, is invariably absent. This texture suggests following sequence of precipitation: stannoidite wsonite. The sequence of of tin minerals inferred from the two types textures mentioned aboveis consideredto be e*stannite-stan- noidite-mawsonite. This i a trend of increas- ing of metaVsulfur, Fd* and Cu/Sn ratios in the tin sulfides. The mineral assemblages are presentedin Table l. The common opaque that coexist with stannoiditeare bornite, sphalerite, tennantite-tetrahedrite-series and roquesite. This assembl4gegenerally not include stannite. Stannoidite is rarely with galena, wit- tichenite, arsenopyrite and It is notewor- thy that stannoidite does not coexist with pyrite, except in the tin ores from the deposit. Thes'e ores contain stannite together stannoidite. On the other hand, stannite coexistswith pyrite. From the textures observed, idite, bornite, chalcopyrite, sphalerite and te! seriesminerals seemto have foj nearly contem- poraneously.

CHEMICAL CosxsrNc Sr ^q,NnTENNANTTTE- MNERAT.S

Scanning patterns and analytical data 0- 100um obtained by analyzerreveal that most stannoidite grains compositionally Frc. 2. Photomicrograph of stannoidite-stannite- cassiterite-bearingsample from the Konjo ore deposit' homogeneous.Reprqentative composruons Okayama Prefecture, Japan (Sd stannoidite' St stan- and atomic proportions of mineral coexisting nite, Cp chalcopyrite, Cas cassiterite). with sphalerite and te-series

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minerals are given in Table 2. It seemsclear from the analytical data on stannoidite that this mineral is represented by the stoichiometry CqFe!*@d+,Zn)Sn2S12, which is in agreement with the results by Yamanaka & Kato (1976) and Kudoh & Takeuchi (197A. There is a wide range in extent of Fe and Zn sub- stitution in stannoidite (DFe/Zn between 2.03 and 14.4), as summarizedin Table 3. The stannoidite from tlre Tada deposit is the richest in Zn (5,2AwtJ/o Zn,9.09 wt.rlo Fe) and has the approximate formula CurFgZnSn2Sp; that from the Konjo deposit is the richestin Fe (11.90wt.Vo Fe, 1.69fi.90 Zn) and has the.formula CurFq(Fee.rrZns.1e)Sn2Sp.From the FeP*/Znzt ratio of stannoidite,a continuoussolid- solution is inferred to exist betweenCusFqZnSn2Sp and CurFerFeSn2Sl2,as already pointed out by Petruk (1973). Iron and manganesecontents of sphaleritecoex- isting with stannoiditeare in the rangefrom 0.lZ to 1.93wt.9o, and from 0.02to 0.16wt.Vo, respectively (Table 2). The cadmium content of sphalerite, from 0.17 to 0.25 wt,0/0,is generallyhigher than iron and manganese.TheFe/Zn ratio of sphaleritecoexist- ing with stanniteor stannoiditeis listed in Table 4. Note that the iron content of sphalerite is very low, comparedwith that of sphaleritecoexisting with stan- nite (Shiml'u & Shikazono 1985). Chemical analytical data on tennantite- tetrahedrite-seliesminelals indicate that the As con- tent is generallyhigher than the Sb conten! thus they can be called tennantite, but someare rich in Sb and 0 100um Ag, and can be called Ag-bearing tetrahedrite. - Representative chemical compositions of coexist- Frc. 3. Photomicrograph of stannoidite-mawsonite- ing stannoidite and sphalerite (Table 2) and ranges bornite-bearing sample from the Tada ore deposit, in the atomic Fe+ /Zrf+ ratio of coexistingstannoi- Hyogo Prefecture, Japan (Sd stannoidite, Mw dite, sphalerite and tennantite-tetrahedrite-series mawsonite, Bn bornite, Cp chalcopyrite, Gn galena,Ag minerals from Japanesevein-type tin deposits are Ag-mineral, gang. gangue minspal). summarized in Table 5 and Figure 4l The atomic Fe* /h2+ rado of stannoidite was calculated from the EFe/Zn ratio obtained by electron-microprobe in which (FeS).' denotes the FeS component in ana)yzerand is based on the r.1u1ie6hip: (F&* / sphalerite. The equilibrium constant for reaction (1) tA{(EFe/20-2}. Zil2+)stmoraite= The Fe+ /Zn2+ is expressed as ratio of stannoidite is positively correlated q/ith that of sphalerite and tennantite-tetrahedrite-series minerals (Fig. a). K = df,.s./(S) (2)

The freeenergy of reaction(1) is expressedas DNcussroN

As describedabove, stannoidite commonly coex- AGr: - RT ln K: -RT ln ta*s./(S)l (3) ists with sphalerite (sp), chalcopyrite and bornite. Therefore, the following chemical reaction can be usedto estimatethe fugacity of sulfur [/(S)] of for- Therefore, sulfur fugacity (in logarithmic units) is mation of the mineral assemblage. expressedas

g) 5CuFeS2: CusFeSr+ 4@eS),o+ 52 (1) loe/(SJ = -# -log df,6

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UIBIE 1. IM{[[O*i AIID RWRESEI{U{IIVE MINBIIL ASSEIiIBT'$ OF SAI.IPLES

Ore D6p. C!, (rt.t I!) sd Sp Bo llem !&, St Go OtbeF

tida + (.0.02) s s +

0bsLtai + ((0.021 s eq-Etndals (1)

eodel- s ((0.05) t{q, tp(e) , AP(o) '

lUrsobe t +Rq

Fukolor * ((0.04) RS' l.ld

AsbLo s (a0.01) Py, cv(r), DJ(1)

setoda s ((0.05) flt, rf,(e), sc(o)

!(uro + (<0.19) t + + + Rq, AP(e,

fanjo s(<0.34) s + +

Cb dElccpjfr{te, Sd stamjdlte, S? e[*Dl"dfta, rfl bct}lts, [b8n teryE serf€ rdMl, ur mite, St stamite' ar 9a1s, Fq rcquesite, Io asstr'lEfte, ng Et1re silve, ld mtiLdit€, Py pfdtte' Cv oallire, DJ djr! EftEfc*toit€, !{i rclfmite, sc stE€LLte. s c.olrm, + les (m' (e) @ly (1) late stage.

BBX,E 2. REPREiEITIACTVECStsfi(AL O&{PGIIICEG, O!'@($lttrG SBNIOIIITE (Ed) Ar'{D (ep)

w@PEacm M€25(sd)d2l

@e EP. G as !€h&E &a MO lc b s 0.00 1.98 r2.04 && d 39.27 0.04 8.95 4.64 0.08 0.01 99.8 7.93 0.01 0.93 0.ol [.26 d1 39.? 0.8 11.5 4.5 15.5 28.8 100.8 0.08 2.50 0.86 Ep 0.24 0.01 o.t7 69.32 0.62 0.16 0.00 33.43 99.95 o.oq 0.00 o.0o o.97 9,00 o.0t 0.00 lf.7? M&!t 3d 38.8? 0.03 9.0: 4.51 0.03 0.03 19.23 28.67 1OO.4O 8.05 0.00 2.1! 0.91 0.00 0.01 Ml d 38.95 0.03 9.34 4.10 0.03 0.00 t9.24 tOl.O6 7.99 0.00 2.4 0.82 0.00 0.oo 0.01 0.99 0.00 0.00 0.oo 0.99 a 0.63 0.00 0.!2 53.90 0.47 0.04 0.00 32.37 99.81 0.01 0.00 ** sd2 38.0 9.8 3.5 0.! 0.0 D.3 T.1 99.8 7.89 0.?0 o.0l 0. ol u.9{ ar :2. e 15.8 30.5 9t.6 7.96 0.02 2.60 0.63 1.80 q.01 sp2 o.a 0.3 66.0 0.6 0.t 100.2 0.00 0.01 0.98 0.00 o.0l d 38.81 0.06 10.2s 2.91, 0.01 0.06 19.06 29,:8 100.34 7.94 0.01 2.{0 0.00 g1 lt.g 0.2 18.3 28.5 rot.8 8.19 0.02 2.18 0.58 0. 03 0.8? 64.79 0,25 o.07 0,00 32.31 99.65 0.ga 0.oo 0.02 0.97 0.00 0.00 0.00 0.99 d 38.59 0.03 L0.99 2.91 0.10 0.03 18.63 28.1? 99.45 8.Og 0.00 ?.60 0.38 0.01 0.01 2.08 u.6s Bp 2.43 0.00 1.93 63.9 0.?1 0.03 o.m 32.97 101.03 o.Oa 0.00 0.03 0.94 0.01 0.00 0.00 0.99

&6 d 38.88 0,01 f!.02 2.24 0.31 0.03 :,9.03 29.03 100.55 7.96 0,00 2.57 0.45 0.04 0.01 2.O9 t!.90

ko ad 38.65 0.06 0.0? 0.02 L1.1L 29.62 99.24 7.95 0.01 2.35 9.42 0.01 0.00

gr 3g.: 9.4 A.2 99.r s.u o.o2 2.26 0.85 L.76 13.34

a3 :g.3 :,8.9 29.3 99.8 7.94 2.69 0.33 2.08 u.95 d 39.06 0.0{ [.98 1.59 tt.02 29.06 100.63 8.Ol o.0I 2.70 0.3{ 0.03 zl.z o.t 12.5 !.2 16.3 31.2 99.7 7.9 0,or ?.88 0. 24 72.54 "a4 r (ato & lujl.ki (1969), 2 Sd@ (1984), 3 Kjstn S oFrE (ut79) , 4 Kato (1969) . Data &talred tv nlcc'Frcbe.

The free energy AGr of reaction (l) as a function eram(Fig. 5). As in Fieure 5, sphalerite of temperaturesan be derived from the thermochem- coexisting with stannoidite clntains a mole fraction ical data on chalcopyrite-bornite-pyrite-Sz Gas) of FeSin a range from 0.ffi2 lto 0.011. The temper- equilibrium (Schneeberg 1973) and FeS-pyrite-S2 ature of formation of a stan$oidite-bearing assem- (gas) equilibrium @arton & Skinner 1979). The blage cannot be stimated pr4isely. However, fluid- activity coefficient of FeS in sphalerite is assumed inclusion studies of the J4panese vein-type tin tobe2,4, from ttre experimentaldata by Barton & depositsconsidered here (e.C., Imai 1973)suggest feulmin (1960. The relationshipbetween tempera- that stannoidite-bearing assehblagesformed in the ture and FeScontent of sphaleritein equilibrium with temperaturerange 20 - 300oC. Accepting this tem- bornite and bhalcopyrite was obtained on the basis perature range, the probafole /(S) region for of equation (4). Isopleths for FeS content of stannoidite-bearing assembl{ges is estimated, as sphalerite in equilibrium with chalcopyrite and bor- shown in Figure 5. nite were drawn on a log /(S, - temperature dia- Lee et al. (1975)conductedlan experimental study I I Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/25/2/229/3445999/229.pdf by guest on 30 September 2021 STANNOIDITE.BEARING TIN ORE 233

TABLE3. Ef,(}flC 'TEIZN RATTOOF STANNDIDIIE

Iocation or Ore D€p. Range (l{o. of aely€is) Ref,erence (s) €sten USSR l.70 - 3.s4 (5) Botava et al. (1978) etc. 9 veir-t)rpe dep. in Japd* 2.O3 - L4.4 (60l

l'lowt. Pl€sant, Ceada 2.O3 - (?) Petnl< (1.973)

Kidd Creek, Caada 2.2r (1) Kissin & Of,ens (L979) St. !4ichael-'s ltouni 3.37 - 4.96 (8) U@re ! H@ie (L984)

tada z.v5 - z-cJ (9) 3.00 (1) r€b & hrjiki (1969) Otmidel- 2.27 - 2.37 (3) otrpdai 2.33 - 2.91 (e) Akercbe 3.L4 - 3.29 (2) shioza{a (1984) 3.24 (1) Y@aaka & Kato (L976) 4. L3 (].) Kaeo E Fujiti (1969) nrkoku 2.34 - 4.L3 (s) 3.2L (1) Kato & Eujil

II\BLE 4. Felzn RAIIIO OF gPmLmrE F"oM Erl+.BEARrltG VENWIPE D@GI*' IN &iPA}I studies have not been carried out) might be large, probably more than 10.5 log/(S). Unfortunately, Sphal.erlte r st@iait€ we cannot estimate/(S) and temperature from the Ole Dop. Ferlh assemblagebecause a relevantexperimental study has Tada 0.002 - 0.007 not beencarried out at a temperaturebelow 300"C,

hdst 0.004 - 0.0L1 and no information is available on the thermochem- ical mixing-properties *enobs 0.005 - o.00s of the stannoidite solid- solution; however,note that theoreticallyit would hbku 0.015 be possibleto estimateboth/(S, and temperature Sphaldito + €tamoldito a stenlte based on the mawsonite-stannoidite-bornite- Ashto 0.036 - 0.041 chalcopyrite-sphalerite assemblage if reliable

Sphalerite t slannlte (Sh161zu & ShLl

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BFLE5. ASO{TCEE,?+/',bp+rAErOCE'@KrSrrrlx3SBNt,l)rDXXE (Sd), SlBr,StrE (Sp) ll{)$E[GNEB- EIRI|EEDRTIffiIES MINERIiL(IgN)

G€ hp.. Sal (avg! !o. .atFts) glr (av93 rc. galt€ts) l€s (av93 rc. !s!*i6) tda 0.0L - 0.14 (0.081 9) 0.002- 0.00? (0.00{: 8) Sse[t I Otelil&L 0.09 - 0.t{ (0.t2r 7, .baal 0.09 - 0.19 (0.r4: 5l I ; oEdad o.tt - 0.32 (0.22: 9) 0.004- 0.0L1 (0.007,8, | 5 0.22 - 0.24 (O.23t 2l IF &sobo' 0.38 - 0.43 (0.{lr 2l 0.00s- 0.008 (0.006t3) ,E o.r2 - 0.23 (o.lsr 5i | rlbb 0.:.:. - 0.72 (0.46, 9, o.ots (o.ors: r) | 3 0.94 - 1.61 (1.:.4r 4D I &hio 0.5S - 1.19 (0.87! 3) 0.036 - O.O,l1 (0.039: 2l I 0.3{ - 3.97 (L.25: 4l

sotoda 1.06 - 1.d3 (1.21, 9) abasl &668t Ito@ 1.31 - l.{l (1.3S. 6) l.t3 - 3.02 (1.90:rrl

!o.Jo 2.Ol - 2.10 (2.05! 6) &6t 1.52 - 4.3A (2.71. 7l * griozm (1984)

!(n

N c N l N o tL lo'n'o AI€NOtsE {- lFUKot0 I loMo. T TOANI

01231 01231 (Fe?' t znz' )sp x1o2 ( Fe2' lZn2' )t"nn-t"t|.

Frc.A. F&+ /Zfr+ of sphalerite (left) and of tennantite-tetrahedrite-series mineral (right) as a function ofFe2+ /Zn2+ in stannoidite (atomic proprortions).

Cu-Ag-Au; Zndominant) mineralization, and tung- High content of indium in chalcopyrite, shown in sten is not recoverd from these deposits.On the Table 1, probably indicatesa high temperatureof other hand, the Akenobe, Ikuno and Ashio deposits formation. Sphalerite rarely appears where the are characterized by polymetallic (Cu-Zn-Pb-Sn- F&+ /Znz+ rado of the coexisting stannoidite W-Ag-Au-Bi) mineralization, and tungsten is reco- exceedsapproximately 1. These differences imply veredfrom thesedeposits . T:heFe/Znratio of coex- that the tungsten-bearing deposits formed under isting sta:rnoidite, sphaleriteand tennantite from the lower /(S) or higher temperature conditions (or tungsten-bearingpolymetallic depositsis higher than both) than tungsten-freedeposits. in those from the tungsten-freepolymetallic deposits. More detailedinvestigations will be needd to clar-

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Xp."g=0O01

0005 00r N LN

ql o rlo

Stonnite region 1985)

TemDeroture 200 250 300 350'C

FIc.5. Ternperature- log/(S) diagram for stannoidite-bearingores from Japanese vein-typedeposits.

ify the factors that lead to different/(S) and tem- existing minerals from the Mount Pleasant tin perature conditions for different types of tin-bearing deposit.Can, Mineral. 9, l6Gl79, hydrothermal deposits. Boreve,M,M., BSRMAN,Yu.S. & Saloounsxeve,S.M' (1978):First find of stannoiditein gold-silverores AcKNowLEDGEMENTS of the easternUSSR. Dokl. Akad. Nauk SSSRMl, 202-204(in Russ.). The authors are grateful to Prof. H. Shimazaki of the University of Tokyo for helpful discussions. Irraar,H. (1973):Geology and fluid inclusion of the Dr. A. Kato of the National ScienceMuseum and Ashio ore deposit. lst Abstr. General Research (B) (No. (in Mr. G. Matsuo of Nihon-Chikagakusha Co. permit- Assemblage $A707), 12-13 Japanese). ted the use of the from sample the Konjo deposit Kero, A. (1969):Stannoidite, Cus(Fe,Zn)2SnS6, a new and one from the Fukoku deposit,respectively. The stannite-like mineral from the Konjo mine, authors acknowledgethe helpful commentsof the OkayamaPrefecture, Iapan. Bull. Nat. Sci.Mus. two referees. This study was partly supported by a Tokyo 12, 165-172. Grant-in-Aid for Scientific ResearchNo. 6054058 and 61740469from the Ministry of Education of - & Furm, Y. (1969):The occurrenceof stannoi- Japan and by the funds from Co-operative dite from the xenothermal ore deposits of the Programme (No. 85136) provided by the Ocean Akenobe,Ikuno, and Tada mines,Hyogo Prefec- ResearchInstitute, the University of Tokyo. ture, and the Fukoku mine, Kyoto Prefecture, Japan.Mineral. J. 5, 417433.

REFERENcES KrssrN,S.A. & OwtNs,D.R. (1979):New dataon stan- nite and relatedtin sulfide minerals,Can. Mineral. BanroN,P.8., Jn. & SxrNNBn,B.J. (1979): Sulfide 17,125-135. mineral stabilities.In Geochemistryof Hydrother- mal Ore Deposits(2nd edition; H.L. Barnes,ed.). Kuoon,Y. & Texeucsr,Y. (1976):The superstructure Wiley-Interscience,New York. of stannoidite.Z. Krist. lM, 145-160.

& Towr'lnt, P., III (1966):Phase relations Ler, M.S., Terexoucnt,S. & Irraar,H. (1974):Occur- involving sphaleritein the Fe-Zn-S system.Ecoz. renceand paragenesisof the cu-Fe-sn-S minerals, Geol,61,815-849. with reference to stannite, stannoidite and mawsonite.J. Mineral. Soc.Japan tl, Spec.Issue BoonueN,R.S. & Asporr, D. (1967):Indium in co- 2, 155-164(in Japanese).

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-, - & -(1975): Synthesesof stannoi- Smnaru,M. & SsrazoNo, N. (1985):Iron and zinc dite and mawsoniteand tleir genesisin ore deposits. partitioning between coexisting stannite and Econ. Geol. 70. 834-843. sphalerite:a possibleindicator oftemperature and sulfur fugacity.Minerol. Deposita20, 3t+320. LEw, C. (1967):Contribution i la min€ralogiedes sul- fures de cuivre du type Cu3XS4.Bur. Rech. Gdol, Surozawe,T. (1984):Mineralizstion of the Akenobe Minidres,M6m.54. Tin-PolymetallicDeposits, Hyogo Prefecture,Cen- tral Japan.M.S. thesis,Univ. Tokyo, Tokyo, Japan. Moons, F. & Howre, R.A. (1984):Tin-bearing sul- phidesfrom St. Michael'sMount and Cligga Head, SpnrNcsn,G. (1972)z The pseudobinary system Cornwall.Mineral. Mag. 48, 389-396. Cu2FeSnSa-CurZnSnSaand its mineralogicalsig- nificance.Can. Mineral. 11, 535-541. PBrnur,W. (1973):Tin sulphidesfrom the depositof BrunswickTin MinesLtd. Can. Mineral. 12,4G54. SwBervau,T.R. & LoNc,J.V.P. (1969):Quantitative electronprobe microanalysis of rock-forming Rauoonn, P, (1944\: Zum Zinnkiesproblem./D&. minerals. J. Petrology 10, 332-379, Preuss,Akad. Wiss., Math.-Natur, Kl. 4' 1-30. Yauarara, T. & Kero, A. (1976):Mdssbauer effect (1960):Die Erzmineralien und ihre Verwach- study of s1Feand llesn in stannite,stannoidite and sungm (3rd edition). Akademie-Verlag,Berlin. mawsonite.Amer. Minerql. 61, 260-265. ScrNsBsenc,E.P. (1973): Sulfur fugacity measure- ments with the electrochemical cell ReceivedJanuary 29, 1986,revised monuscrtpt accepted AglAgIlAg2**S,fs,. Econ.Geol.68' 507-517' August 25, 1986,

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