Canadian Mineralogist Yol. 2.4,pp. 385-397(1986) COMPOSITIONAL TRENDS IN TETRAHEDRITE NEIL E. JOHNSON, JAMES R. CRAIG AND J. DONALD RIMSTIDT Departmentof GeologicalScimca, WrginiaPolyechnic Institute and Stote University, Blacksburg, Wrginia 24061, U,S.A, ABSTRACT louin (Johnson& Jeanloz1983) est pr6f€rable d tout moddle ionique, Available mmpositional data for l27t samplesof natural tetrahedrite and 295 of synthetic tetrahedrite were (Traduit par la R6daction) s1amingd.They show: compositional rangesof four to ten Cu, zero to six Ag, and a total of two (Fe, Zn, Hg) atoms, Mots-cl&:t€1la€drite. synth€tique et naturelle,zone de BriI- completesubstitution (up to four atems) amongAs, Sb and louin, substitutionsAg-Fe-Zn-Hg-Cd-As-Te-Bi. Te, and a total of 13 atoms of S per formula unit. Data on contentsof Pb, Bi and Cd in natural samplesare insuffi- cient to define their compositional ranges,and virtually no INrnooucrroN data exist on other substitutions, involving Co, Ni, Mn and Au. A generalized formula (Cu,Ag)6Cua@e,Zn,Cu,Hg, In the most recenttlorough studiesof the chemical Cd)2(Sb,As,Bi,Te)a(S,Se)13is proposed on the basis of compo$ition and physical propertiesofnatural tetra- thesecompositions. The cell rlimensisn is a linear function hedrite, Charlat & L6vy (1974, lms,1976) propo- of chemicalelements in the formula errceptinAg-rich tetra- sed,on the basisof a suiteof 54 samplesfrom selec- hedrite, where it increaseswith Ag content, up to four Ag ted localities worldwide, the general formula atoms per formula unit, and then decreases.Ag and As (CuAg) Zn,Cu,Hg,Cd)2(Sb,As)aS Subse- have a low tolerance for each other in the structure, to(Fe, 13. and quent studies have confumed that Se plots of Fe versus Ag, Zn versus Ag, and Hg versus Cl substitutesfor suggestthat incorporation of Ag'is controlled by several S (Johan & Kvadek 1971,Brodin et al. 1979),and, factors. For the purpose of explaining compositional vari- Bi + Te sub$titute for As + Sb (Oen & Kieft 1976, ations in tetrahedrite, the simple Brillouin zone model of Mozgova et al. 1979). Other studies report the pre- 6eading (Jotrnson& Jeanloz1983) is superiorto any ionic senceof Pb, Co, Ni, Au and Mn (Schroll & Azer model. Ibrahim 1958,Bishopel al. 1977,Pattrick 198, Basu et al. 1981, 1984a). Keywords: syothetic and natural tetrahedrite, Brillouin The tetrahedrite structure, as descdbed by zone, Ag-F e-Zn-Hg-Cd-As-Te-Bi substitution. Wuensch (l9g), can be written as:.rYMl6rrrM26 lrr\XrvY?l4vrz, where Ml representsCu or Ag, M2 SoNaMarns representsCu, Fe, Zt,Hg or Cd, Xstands for Sb, As, Bi or Te, and Y and Z could be either S or Se. On a examinEles donn6esd.isponibles sur la composi- Although the existence of the six-co-ordinated Z tion de 12716chantillons de t6tra€drite naturelle et 295 sp€- anion in the structure (the l3th S atom) has been cimens de t6traddrite slnth€tique. Ces donndesindiquent: generally accepted, there has been some resistance des domainesde composition pouvant aller de quatrei dix @elov&Pobedimsftayn1969, Kaplunnik et al. 1980, atomes de Cu et de z6ro i six Ag, un total de deux atomes Babushkine/ a/. 1984)to this in favor of a l2-S-atom Zn, Hg), (usqu'i quatre @e, substitutibn compl&te ato- model. Furthermore, the distribution of mes) entre As, Sb, et Te, et par the two 13 atomes de S du total (M) unitd formulaire. Les donn6essur la teneur des 6chantil- metal sitesin the crystal structuredoes not match lons naturels en Pb, Bi et Cd sont insuffisantes pour d6fi- that of meta! atoms in thegeneral chernicalformula nir leurs domainesde composition: quant aux donndessur above. Severalauthors (Godonikov & Il'yasheva les autres substitutions, impliquant Co, Ni, Mn et Au, elles 1973,Johnson & Jeanloz1983, Miller & Craig 1983, sont pratiquement inexistantes. On propose ici la formule Pattrick & HaII 1983)have collected compositional gdn6ralis6e(Cu,Ag)6Cua(Fe,Zn, Cu,Hg,Cd)2(Sb,As, Bi,Te)a data from published sourcs in order to review tetra- (S,Se)13qui est fondde sur ls donndessusmentionndes. La hedrite chemistry or to illustrate a point germaneto maille dimension ds 14 est fonction lin6aire des €ldments their research.Because the chemical composition of chimiques qui entrent dans la formule, saufpour €chanfil- a mineral reflects the underlying cry$tal chemistry, lons riches en Ag, of elle augmente la avec teneur en Ag, provide de z6ro i quafe Ag par unit€ formulaire, aprds quoi elle a large base of analytical data may infor- diminue. Dans la structure, Ag et As ont I'un pour I'autre mation on crystallochemical relationships. This peu de tol€rance; les courbes de Fe, Zn et Hg, en fonction report is a comprehensivecompilation and analysis de Ag, Ag et Cu, respectivement, portent e penser que that clarifies soruereported relationships, unearths I'introduction d'Ag ddpend de plusieurs fdcteurs. Pour otler onesthat exist in tetrahedrite-group minerals, expliquer les variations de composition dans la tdtra6drite, and thereby servesas a guide for future research.To le moddle simple de la liaison chimique par zone de Bril- minimize confusion, the use of varietal names of 385 386 TI# CANADIAN MINtsRALOGIST t€trah€drite-s€riesm€mb€rs (tsnnantite, freihrgite, schwatzite,elc) has beenavoidd; su(h m€mbersare described as As-rich tetrahedrite, Ag-rich tetrahe- drite, Itrg-rich tetrah€drite, elc. TLredata base for this paper consisb of reported compositionsof l27l samplesof natural tetrahedrite from various oredeposia atrd 295 of syntletic tetra- hedrite. The data were not critically evaluatedexcept 80 to remove clearly inaccurate analytisal data {e.8., totals qualling 9390, 30 weight 9o Fe). The follow- ing informa.tion is consider€dfor each composition: o50 o Cu, Ag, Fe,Zt, Hg, Cd, As, Sb, Bi, S, Fb, Te, Mn and Se contents in qeieht 90, and the length of the ! 'ro d unit'csll edreea (fi A;, where given. Data on other reported substitutions are sufficiently rare and their reported inportance is sufficiently small that they 30 can be ignored. The weight percentagewas convertd to number of atoms basedon 29 atoms per formula e0 unit. Two additional variableswere considereddur- ing the processing:BZ, the number of valenceelec- trons per unit cell, and CHR, the net ionic charge t0 per formula unit (after Johnson& Jeanloz1983). The results were then ploued as functions of each other 0 or as functions of their frequency. A complete list- { 5 6 7 I I l0 ll l? 13 !{ 15 16 Artm ing of all the data may be obtained from the authors, and will be included in the Ph.D. dissertation of the Ftc. l. Number of (S, per anions Se) forrnul,a unit. first author. E2 I 0.0 0.5 1.0 2.0 e.5 1.0 3.3 1'0 ,1.5 0.0 0.5 1.0 l.s 2.0 2.s 1.0 t.5 c.0 Sb Ato0r! Sb Atdftt Ftc.2a. Number of As atoms yersannumber of Sb atoms ftc. 2b. Number of As atoms versasnumber of Sb atoms for samplesof natural tetrahedrite. Dashedline is ideal for samplesof synthetic tetrahedrite. Dashed line is as solid-solution. in Figure 2a. COMPOSITIONAL TRENDS IN TETRAHBDRITE 387 Rssur-TS IAE|.! I. PUBLISIIEDS()URCES OT OATAUSEO III ftIS PAPER,II{CLIJDIIG NUfiBEROF SAI'IPT€SAIID IXEIR ORTGI{ (TAI'RAL ORSYNHFIIC) S and Se contents tbulgqln8 et ql. (1975) Itl Llco d rl. (192) 35S go Ar!n. (192) Itl ilsske & Sllnrer (1971) 14S Recalculatingweight valuesto the mean atomic Araya et rl. (l9Z) 17il lhfu6n ( 1984) 4tt Abaey (1975) 3t{ ntllor A cn'lg (1983) 32 l 9o S indicates that the hypothesis of 12 S atoms per Arer lbrrhlo (1958) 7N ilorulc & Kublcr (1972) 14 tl Brsu or ql. (t981) 5N lilougovoot al. (1979) 184 tl formula unit can be rejectedat the 9,9010confidence &ru ot .1. (1984r) 5t{ llozgov! ot !1. (1980) 28N Edsu ot !1. (1984b) 12! iipoeto3 (1983) 1l{ level. By far the largest number ofreported tetrahe- BlEh (1981) ltl ilalk (1975) 4tl Bl3hopot rl. (l9Z) IN N$h (1975) 8N drite compositions(8590) have 13 S atoms per for- BoldyEva & BorcdlyeY (1974) 2N lrnHn Gszg) 25[ Brodln * 61. (1979) 3N illshlsll ot !1. (1971) 5l{ mula unit (Fie. 1), effectivelyending the debateas qurkhsd-86@nn (1984) 6N llorgorodovr ot !1. (1978) 41 t{ Cdh & Hrl (1979) 5l{ &tr st al. (1973) IN to whether tetrahedrite contains 12 or 13 sulfur Corn9& tlsrls (1978) 4t oon A Kloft (1976) 5N chrrl!! & t6!ry (1974) 161 N Plttrlck (1978) 16N atoms. The S content does seemto decreaseslightly Chon& Petruk (19&l) 14 tl Pstrrtcl (1984) 2t il Cher et al. (1980) 4N 9r$rtct & Hall 0984) 25S as the Cu content decreases,but the maximum den- C!tulozl & Eeran (1973) 1tl Petnk et.al. (1971) 9tl Cor (197?) 9t{ Rlabo & Srck (1984) 25 tl sity in population occursnear 10 Cu and 13 S atoms. Cz@nske & H.ll (1975) TN Rans@ (l$9) t!l tloelbr (t925) t38 N Rlley (1974) 24 tl The papcity of data sets (6) with detectableSe does ltrlnln-Barkovskly€t al. (1970) 3N Srnd6tl & teoft (1981) 2tI Eld@ or !1. 0984) 73 l{ shl@d. & lllMqrl (1972) tdN not permit any generalizationregarding the mechan- Godovolkov& Ilrydsheva (1973) 88 tl Shl@kl (1974) ut{ Hlt & Tuppsr (1979) 12N Sprlngor (1969) e9r ism of Se substitution. Hatl (1972) 10s SUnlry & Iror (1982) 4ll flall & Cz@rrl€ (1972) 3N Sugakl ot al. (1975) 38S Hlneo (1904) 26 il Suglkl ot rl. (1984) 3N finng & il€yer (1982) 8N Tlt80h & [ort@tq (1973) 16S Sb, As, Bi and Te contents lul A L€e (1980) t0 il Torlutr ! liort@io (19n ) tndolev ot al.