tive of exsolution (e.g., Harris & Owens 1972), and,. Springer ... Owens (1979) reported the synthesis of end- .... B-Cu2@e,Zn)SnSn contains stannite in iron-rich.
Canadian Minerologkt Yol. 27, pp. 689-697(1989)
A REINVESTIGATION OF THE STANNITE (CurFeSnSn) - KESTERITE (GulnSns4l PSEUDOBINARY SYSTEM STEPHEN A. KISSIN Deryrtmentof Geologlt,LakeheadUniversity,ThunderBay, OntarioP7B sEI
ABSTRACT The pseudobinary system stannite (Cu2FeSnS/ kesterite (Cu2ZnSnSf was investigatedin the temperature range from 5@ to 8@'C using synthaic starting materials and molten NaCl-KCl eutectic fluxes in evacuated,sealed silica tubes. A solvus separating stannite and ferrokesterite-kesterite intersects the liquidus, indicating that no solid solution [B-Cu2(Fe,Zn)SnSa]extendsenthely acrossthe system. An inJlection in the boundaries of the miscibility gap implies that an unquenchable hightemperature phase, presumably cubic Cu2(Fe,Zn)SnSa, exists. Below the inflection at ca. 7M"C, the two-phase region slopes toward the iron end-member composition. Thus, exsolution lamellae of ferrokesterite-kesteritein stannite should efst, and the compositions of eoexisting stannite and ferrokesterite-kesterite define a temperature. The phase a-Cu2(Fe,Zn)SnSais shown not to be a pseudobinary phase, and although encountered in this study, it is not likely an equilibrium reaction-product. The experimentallydeterminedsubsolidusphase-boundaries do not correspond well to those implied by natural assemblages.The reasonsfor the ldck of agreementare unclear, but at present, a stannite-kesterite geothermometer cannot be considered to be experimentally calibrated. Keywords: phase relations, stannite, kesterite, ferrokesterite, geothennometer.
SouuannE Le systime pseudobinairestannite (Cu2FeSnSj - kestel rire (Cu2ZnSnS) a fait I'objet d'une 6tude entre.s00 et 8@oC de matdriaux synth€tiquesplac€s dans un-baln NaCl-KCl eutectique dans des contenants de silice scelldg et 6vacu6s. Un solvus entre stannite et ferrokesteritekesteriterecoupele liquidus, ce qui indique I'absenced'une solution solide continue 0-Cuz(Fe,Zn)SnSa.Une inflection deslimites de la lacune de miscibilit6 serait due i une phase de haute temp6rature non-trempable, probablement l'a forme cubique de Cu2(Fe,Zn)SnSa.En dessousde l,inflection, d 7@oC envfuon, le champ de stabilitd de deux phases coexistantestend vers le pOle ferrifbre. D* lamelles d'exsolulion de ferrokesterite-kesterite seraient donc possiblesdansla stannite,et la composition desdeuxphases d€finirait donc une teinp€rature.Ia phasea-Cu2fe,Zn)SnSa n'es1pas pseudobinaire;quoiqu'elle apparalt ici, elle serait un produit m6tastable.Les chemps de stabilit6 subsolidus indiquds par l6.sexp6riencesne correspondentpas trds.bien avec ceux qui sont d6duits desassemblagesnaturels, ibuldes raisons qui ne sont pas claires. Le gdothermombtre
fond6surl'equilibrestannite-kesterite n'estdonctoujours pascalibr6. (Iraduit par la Rddaction) Mots-cl&:relationsdephases,sta:rnile,kesterite,ferrokesterite,g6othermombtre. INTRoDUCTIoN Phase relations along the pseudobinary join Cu2FeSnSn-Cu2ZnSnSo are of interest in relation to the occurrenceof stannite and kesterite, the mineralogical counterparts of the end members. Intergrowths of the two minerals exhibit textures suggestive of exsolution(e.g., Harris & Owens 1972),and, Springer (1972) proposed that such relationships could serveas a geothermometer. Moh (1960)reported, without further details, that a.Completesolid-solution characterizesthe system. He later indicated that the solid $olution is complete above700oC(Moh 1975).Franz(1971)reportedon synthese$of various structural modifications of the iron end-member.In a study on the systemstannitestrhalerite, Bernhardt (1972) nferred that transformlrtion.from cubic to tetragonal symmetry in stanrite occurs at 706C, as indicated by DTA experiments, a result confirmed in a high-temperature X-ray-diffraction study by Bente (1974). The only complete study of the join Cu2FeSnSa-Cu2ZnSnSa was attempted by Springer {1972), w.ho einployed dry synthesesand molten 'halide flux experiments in sealed, evacuatedsilica tubes, as well as DTA experiments. Although both erfd-membersmelted congruently, he found that intermediate members melted incongruently to products that depart from binary compositions. At high temperatures, he found that a complete solidsolution extends across the system as a phase he called B-Cur@e;Zn)SnSa.At 680oc, he found the iron end-memberto invert to a different structure, a-Cu2(Fe,Zn)SnSa.From this temperature a two"phaseloop opens with decreasingtemperature and increasing zinc content. Moh (1975) accepted Springer's work but offered somemodifications. He equatedSpringer's680oCa-0 transition to fhe 706o transition of Bernhardt and suggestedthat the high-
689
690
THE CANADIAN MINERALOGIST
kesterite, or both, which are believed to be at temperature form should be designated as oCu2@e,Zn)SnSa,and the low-temperature form, as equilibrium. The materials synthesizedat 800oC were used as B-Cu2(Fe,Zn)SnSa. Work on the systemwas begun anew becauseof starting materials for experiments at 700, 600 and 500 t 2"C. The experimentslasted four daysat 6@ the obvious disagreement between the trform [or the p-form of Moh 1975] and 700oC, and eight days at 500oC. In all cases, Cu2(Fe,Zn)SnSa and the structure of natural stannite. Also, Kissin molten halide fluxes were employed. The products & Owens (1979) reported the synthesisof end- were X-rayed with CoKtNr, znttt, G., Pocct,L., Srnn, G., & TaNBltt,G. (in press): A Mdssbauer studY of the pseudobinarysystem. Cu2FeSnSa-Cu2ZnSnSa Periodico Mineral. im pseuH.-J. (1972):Untersuchungen BTnNHARDT, dobiniiren System Stannin - Kupferkies. Neues Jahrb. Mineral., Monatsh., 553-556. Covezzs,M., Consnt,F. & Tawerrt,G. (1986):Stannite group minerals:investigationson stanniteand kesterite. Rend, Soc. Ital. Mineral. Petrol. 41, 2t7-222. FraNz, E.-D. (1971): Kubischer Zinnkies und tetragonalerZnnkies mit Kupferkiesstruktur.Neaes Jahrb, Mineral., Monatsh., 218-223. Her,r,,S.R.& Srrwanr, J.M. (1973):The crystalstructure refinement of chalcopyrite, CuFeS2.Acta Crystallogr.B,29,579-585. Szwairsrr, J.T. & Strwent, J.M. (1978): Kesterite, Cu2(Zn,Fe)SnSa,and stannite, structurally similar but distinct Cu2(Fe,Zn)SnS4, minerals.Can. Mineral. 16, l3l-137. Hannrs, D.C. & OwENs,D.R. (1972):A stannitekesteriteexsolution from British Columbia. Cor. Minerat.ll, 531-534. Krssru,S.A. & Ownts,D.R. (1979):Newdataon stannite and relatedtin sulfide minerals.Can. Mineral. t7 , 125-135. (1989):Therelativesof stannitein the &light of new data. Can. Mineral. n,673'688. T.L., TnoNeve,N.V. KovauexrEr,V.A., EvsrIcveBva, & Vval'sov, L.N. (1979):KuramiteCu3FeSnSa a new mineral of the stannite group. Zap, Vses. l0E, 564-569(in Russ.). Mineral. Obshchestva an Mon, G.H. (1960):ExperimentelleUntersuchungen Zinnkiesen und analogen GermaniumVerbindungen.NeuesJahrb, Mineral., Abh,94, tt25-tt46. (1975):Tin-containingmineral systems.II, in the CuPhase e relationsand mineralassemblages Fe-Zn-Sn-S system.Chem.Erde 34, l-61. Prrnur, w. (19?3):Tin sulphidesfrom the depositof Brunswick Tin Mines, Limited. Can. Mineral. 12, 46-54. PrerzscH,C. & FnrrzscH,E. (1984): Neue UnterdesStannins. suchungenzur Hoch-temperaturphase i Chem.Erde 43, ll7-127.
Bnrrn, K. (1974):Untersuchungen im pseudobiniiren Rucrroce, J.C. & Gaspannnt,E.L. (1969):Specifications of a computerprograrnfor processingelectron System Stannin (Cu2FeSnSf Briartit microprobe analytical data (EMPADRYII), Dep. (Cu2FeGeS).Neues Jahrb. Mineral., Monatsh,, Geol., Univ. Toronto, Toronto, Ont., 8-13.
THE STANNITE _ KESTERITE SYSTEM
SrnrNcnn,G. (1972): The pseudobinarysystem CurFeSnSo-Cu2ZnSnSo and its mineralogical significance.Can. Mineral. 11, 535-541. Srewanr,J.M., Knucrn,C.J., AruuoN,H.L., DrcrrNsou, C.H. & Harl, S.R. (1972):The X-RAy system of crystallographicprogramsfor any computer having a PIDGIN FORTRAN compiler. Uziv. Marylond Computer Center Tech. Rep, TR'-192.
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tra obtainedwith a Si(L0 del:exr:or. X-Ray Spectrom, 5, t6-28. WaNc, N. (1982): A contribution to the stannite problem.,Iz Ore Genesis- The Stateof the Art (G.C.Amstutz,A. El Goresy,G. Frenzel,C. Kluth, G. Moh, A. Wauschkuhn& R.A. Zimmermann, eds.).Springer-Verlag, Berlin.
Srarnau, P.J. (1976):A comparativestudy of tech- ReceivedJanuary4, 1989,revisedmanwcript accepted niquesfor quantitative analysisof the X-ray specJuly 8, 1989.
