Growth Zoning in Tetrahedrite-Tennantite from the Hock Hocking Mine, Alma, Colorado

Home , Jalpaite, Tennantite, Tetrahedrite

Canadian Mineralogist Yol.22, pp. 577-582(1984)

GROWTH ZONING IN TETRAHEDRITE-TENNANTITEFROM THE HOCK HOCKINGMINE, ALMA, COLORADO

KENNETH C. RAABE AND RICHARD O. SACK,'. Departmentof Geosciences,Pardue University,West Lafayette, Indiana 47907,U.S.A.

ABSTRACT II.lrRoDUc"rloN The Hock Hocking is a small Pb-Zn-Ag-Au mine witlin the Alma district, Park County, Colorado. Ore occursin The Hock Hocking mine (e.9., Raabe 1983)is a fissure-faults that cut a seriesof pre-Pennsylvaniandolo- small Pb-Zn-Ag-Au mine within the Alma district, mites, quartzites and shales.Ore minerals consistpredomi- on the easternslope of the Mosquito Rangeof cen- nantly of pyrite, chalcopyrite, galenaand sphalerite, along tral Colorado (Fig. l). 91e is lesalizedin northeast- with lesser amounts of tetrahedrite-tennantite, jalpaite, trending fissure-faults within the upper plate of a polybasite, stromeyerite, electrum and native silver in a small reversefault. Wall rocks include a seriesof gangueof manganoandolomite and quartz. Microprobe shallowly dipping pre-Pennsylvaniandolomites, analysis growth-zoned of tetrahedrite-tennantite coexist- quartzitesand shalesintruded by granodioritic por- ing with sphalerite of constant composition shows that phyry sills of Laramide gener- Fe,/Zn is positively conelated with As/(As + Sb) in the semi- age. The fissuresare metal site. Basedon fluid-inclusion temperatures,paftlgene- ally barren exceptin the OrdovicianManitou Dolo- tic constraints and previous experimental studies (Sack & mite and within dolomitic units of the Cambrian Loucks 1983, 1985),it appearsthat the Gibbs energyfor Sawatch Quartzite. the reciprocalreaction CulgZn2SbaSl3 + Cu16FgAsaSl3= Ore mineralsconsist predominantly of pyrite, chal- Cu19Zn2As4S13+ Cu1qFe2SbaS13is temperature-inde- copyrite, galena and sphaleritein a dolomite and pendentover the range 200-500oC. quartz gangue. Shoots within the veins contain tetrahedrite-tennantite, jalpaite, polybasite, Keywords grofih : tetrahedrite-tennantite, zonirg, osmotic stromeyeriteand electrum Aus.72Ags.2s.Secondary equilibrium, Zn-Fe exchange,As/(As + Sb), recipro- processeshave enriched the ores,producing cal reaction, geothermometry,Hock Hocking mine, whe sil- Colorado. ver, covellite, chalcocite,malachite and cerussite, along with various iron and manganeseoxides and hydroxides. SoMMAIRE Microprobe data on pyrite, chalcopyrite,galena, La mine Hock Hocking exploite un petit gisementde Pb- sphalerite, jalpaite and stromeyerite indicate that Zn-Ag-Au dansle district d'Alma, comtd de Park au Colo- theseminerals are homogeneouswithin the precision rado. Le minerai tapisseles fissuresd'un systemede fail- of the analytical method (seeTable 1). Sphalerite les qui recoupedolomites, quartziteset shalesd'6ge pr6- averages0.26 and 0.40 wt.9o Fe and Cd, respectively; Pennsylvanien.On y trouve surtout pyrite, chalcopyrite, Mn and Cu are at the minimum deteclion-limits of galbne, sphal6rite, et, en quantit6s moins importantes, the microprobe. tdtra€drite-tennantite,jalpaite, polybasite,stromeyerite, dlectrum et argent natif dans une ganguede dolomite man- ganifdreet de quartz. L'analyse i la microsondede cris- taux de t6tra€drite-tennantite zon€sen coexistenceavec une DENVER sphal6rite de composition constantemontre que le rapport N Fe/Zn du sulfoselvarie avecle rapport As/(As + Sb) dans le site semi-mdtallique. Vu les tempdratures ddriv€es de COLORADO l'6tude des inclusionsfluides, les contraintesparag6n6ti- €RECKENRIOGE queset les etudeso

Mots-clds: tetraedrite-tennantite, zonation de croissance, .BUENA VISTA 6quilibre osmotique, €changeZn-Fe, As,/(As + Sb), - 50 km r6action r€ciproque, gdothermom6trie, mine Hock Hocking, Colorado. Frc. l. Map of centralColorado, showinglocation of the -t" *h". ."respondence should be addressed. Hock Hocking mine. 577 578 TIIE CANADIAN MINERALOGIST

Frc. 2. Reflectedlight photomicrographsof ore minerals.Letter designationsare as follows: sp sphalerite,gn galena, cp chalcopyrite,jp jalpaite, pb polybasite,td tetrahedrite, el electrum,Ag silver. (A) Electrum' galenaand tetrahedrite- polybasite intergrowth in dolomite from HH45. (B) Native silver rimming tehahedrite in galena from HH50. (C) Tetrahedrite replacedby jalpaite, polybasite and chalcopyrite from HH49. (D) Galena replacedby tetrahedrite-polybasite intergrowth from HH45 (crossednicols).

Dolomite is the main gangue-mineraldeposited identified, but it is probably related to the igneous during ore formation. Compositionally, the dolomite activity that produced the porphyry sills found extends from nearly pure CaMg(CO3)2with a throughout the district. The ore fluid rose from depth few percent Fe to a composition near along a reverse fault, and was tapped off by Ca(Mg6.36Mne.arFe6.2r)(CO3)2.Fe and Mn show a northeast-trending fractures within the upper fault- positive correlation and a near-constantratio of plate. This fluid had a high sulfidation-oxidation approximately l:2. stateand a low pH @igs. 3, 4). Reactionof such a solution with carbonatewall-rocks, such as those of GENESISoF THE ORES the dolomite-cementedSawatch Quartzite, would result in a sharpincrease in pH and the rapid depo- The paragenesisof ore mineralizatiqn at the Hock sition of Fe-poor sphalerite, pyrite, tetrahedrite, Hocking mine is relatively simple. Quartz and minor galena and chalcopyrite. Further upward migration barite were the first vein-mineralsto precipitate, fol- of such fluids produced smaller lead-zinc-silver lowed closely by pyrite. A period of fracturing depositsof replacementtype, such as those found ensued, opening the veins to a new pulse of in the Manitou Dolomite. hydrothermal solution that deposited sphalerile, Stability relationsof coexistingore-minerals only chalcopyrite, tetrahedrile-tennantite, pyrite and provide absoluteconstraints on temperatureof depo- galenain a manganoandolomite gangue(Frg. 2). sition between ll7 and 360"C (Fig. 4). However, Electrum was also depositedat this time. Near the fluid-inclusion studiesof sphaleriteindicate a tem- end of hypogenemineralization, low-temperaturesil- peratureof ?A9t 7'C basedon five fluid inclusions ver minerals were deposited, including jalpaite, in sphaleritefrom HH54. This estimatedoes not stromeyerite and polybasite. include a small positive pressure-correctionthat The sourceof the mineralizingfluid has not been would be within the standarderror of the measure- GROWTH ZONING IN TETRAHEDRITE-TENNANTITE 579 ments. In combination with this temperature,an estimate offls) of 10-10barscan be deducedfrom the iron content of sphalerite(e.g., Czananske 1974; Fie. 5). TETRAHEDRITE-TENNANTTTE E +t Tetrahedrite-tennantite is the most abundant sul- q" fosalt at the mine. It is closely associatedwith ol sphalerite and galena. Tetrahedrite-tennantite is o often replacedby jalpaite; it commonly is rimmed by native silver @ig. 2). Symplectiticintergrowths o, with polybasite are common, especially as.replace- o ments of galena(e.9., Ramdohr 1969). J Microprobe analysesdemonstrate that the Hock I Hocking tetrahedrite is close to the simple stoichio- metry re(Cu,Ag)uror[Cun,(Fe,Zn)2]sM(As,Sb)aS,r, correspondingto an ideal structure with 208 valence electrons per unit cell and full occupancy of the 6 246810 trigonal-planar (TR), 6 tetrahedrd (TET), and 4 semimetal (SM) sites in the formula unit based on NH 13sulfur atoms(Wuensch 1964, Johnson & Jeanloz 1983).Results of twenty-five microprobe analysesof Frc. 3. AIO)-pH mineral-stabilitydiagram calculated at 250'C. Boundaries represent activities of S = 0,1, Hock Hocking tetrahedrite-tennantitefrom sample C:0.1, C*+ --0.1, and Ba2+= 0.@l (modified HH54 give average volues of 10.04t 0.17, from Crerar & Barnes1970. Shadedarea represents sta- L.97t0.07 and 4.@ x.0.22 for the quantities bility field for Hock Hocking ore solution. Boundary (Cu + Ag), (Fe + Zn) and (Sb + As), on the basisof positions only approximate due to lack of data on a l3-sulfur-atom formula unit. Variations in the chemistry of the fluid.

TABLE1. CHEI.IICALCollPostTloll 0F TllEoRE MINEMLS

Pyrl te* 53.55 0.11 na na 46.6t 0.10 0.30 - 0.l0rl 100.77 Chalcop)nl te* 34.93 0.12 n: 29.92 0.10 34,52 0.m 0.10r) 99.89 Galena* 13.40 0.10 :u 0.r0 0.16 0.10 - 86.602) t00.46 sphal eri ter 0.26 65.98 0.403) 99.76 Electm (HH49) 0.14 na na 6.s+ - 23.37 75.64\ 99.69 Electru (HH55) 0.29 na na 0.44 0.12 0.14 o.l4 25.r0 72.s6\) 99.19 Sllver (HH49) - 0.22 na 0.10 0. 10 na 't4.020.26 99,24 99.'t2 Jalpaite (HH49) '14.5714.41 0.28 0.t4 0.30 7l .53 - 100.68 Jalpalte (HH49) 0.ll :' o]o 0.13 0.18 13.45 75.15 - 99.70 (HH49) - ,Q 11 6r ?l n rnq\ 07 oo StMeyerlte 16.27 0.10 '13.89 Polybaslte (HH45) 16.87 l.'14 i.sz 60.94 0.12c' 101,78 Polybaslte (Hltl8) 15.99 0,8 - o.rr 9 .47 64.43 - 99.81 m-ril (HHs4) 25.71 4.12 ols 0,29 7.38 38.56 1.69 - 98.14 25.63 2.64 23.95 0.16 7.47 37.26 2.34 - 99.46 t:: 25.83 3.99 23.04 0.17 7.61 37.08 2.10 - 99.82 - 25.30 1.55 't8.3227.03 0,12 7.52 37.13 2.A1 101.46 26.78 5.68 0.27 8.04 40.16 0.67 - 99.91 - .72 6.43 '17.64 olo 0.31 8.24 40.19 0.59 98.87 26,89 5.31 0.24 7.76 40.39 0.74 - 99,97 25,39 0.88 27.86 0.34 7.44 36.65 2.93 - l0l .50 25.8.1.57 26.51 o.ro 0.17 7.21 36.41 2.9A - 100.23 26.50 4.20 20.91 0.10 0.35 7.43 39,80 1.43 - 100.72 - 26.44 3.77 20.u 0.35 7.70 39.36 ',l.64I .21 99,32 24.85 4.6 tr& 0.u 7.25 37.18 - 99,20 24,U 8.14 17.54 0,51 7.60 9.08 l.t3 - 98.83 24.91 8.77 17.10 0.f5 7,71 *.77 l.t3 - 99.14 26,86"t2.97ll.7l 0.21 7.80 39.87 |.09 - 100.51 25.98 t0.t 3 15.62 0.35 7,97 39.43 0.94 - 100.42 26.55 12.59 11.42 : 0.28 8.17 40.31 0.71 - 100.03 27.86 19.68 0.37 0.73 7.93 42.49 0.39 - 99.45 28.06 20.04 0.40 o.rr 0.60 8.05 43.30 0.26 - 100.82 27.76 19.96 0.78 8.05 42.59 0.46 - 100.20 ito o.ro o.a2 7.88 42.40 0.47 - 99.79 27.98 20.65 0.25 0.74 7.76 42.94 0.3r - 100.62 27.89 20.35 0.41 o.ra 0.71 7.60 42.66 0.22 - 99.99 28.0e m.32 0.31 0.63 8.09 42.6 0.15 - 100.46 27.05 14.63 0.70 8.00 41.00 0.57 - Iot .00 26.45 12.13 10.00 0.59 7.82 4l .13 0.76 - 99.01

Analyses (rt. tr elerents) obtalEd uslng the Purdue UnireFlty automted IAC 500 electrcn mlcrcprobe operatlng at 15 KV, a bean current of 0.25 !A and ii{olc lV correctlons. Standards used lncludei 4e' e1, * and Zn retdls; CuFeS2iAgBlS2; AgBiSe2i CoS2i CuroZn2SbaSr3i CuloFe2Sb{Sl3i Curoznt.3Feo.7 As{Sr3; PbS; Sb2S3. Analytlcal uncertalnty ln nlcrcprobe data ls estlmted to be +21 for mjor s, elerents (> 3.5 rt.g) and !0.10 wt.% for ninor elerents (. 3.5 wt.U). llotatlon: average of all 'analysesi l). Co: 2), Pb: O, Cd;4), Au; m, not analyzed, 580 TTTE CANADIA\I MINERALOGIST

Sb/As and Zn/Fera|ios were detectedwithin single Thompson 1959),sphalerite of constant composition erains of tetrahedrite-tennantite, although zoning requires that the Fe-Zn ratio of a growth zone be patterns occur on too fine a scaleto be resolvedwith governed by the condition of osmotic Fe-Zn ex- the microprobe. The As/Sb and Zn/Fe ratios of te- change-equilibrium: trahedrite-tennantite exhibit a negative sorrelation (Fig. 5). This compositional zoning contrasts with the apparent absencepf 2sning in sphalerite. (a) (a) The mole lraction Xp"r in sphalerite from sample pCul6FqSbaS:r,- r'Cu1sZn2SbaSl3= HH54 was determined to be 0.0030 by atomic (b) (b) absorption and 0.@23 by electron-microprobeanal- lCu16FqSbaS1,- rCulsZn2SboSt3 (1) ysis. Homogeneity with respectto Fe is suggestedby the absenceof color zoning within grains, a sensi tive indicator of Fe homogeneity(Barton e/ al. 1963), where (a) and O) denote any two points in the tetra- Consequently, it is likely that X""r was nearly con- hedrite and the pi expressionsare the chemical stant during the growth of tetrahedrite. potentialsof the I components.Assuming sulfosalts Assuming isothermal precipitation of tetra- to be ideal reciprocal solutions (e.9., Sack 1982,Sack hedrite-tennantite and local equilibrium with respect & Loucks 1985),the condition of osmotic Fe-Zn to Fe-Zt exchangebetween aqueous solutions and exchange-equilibriumfor Cule(Fe,Zn)t(Sb,As)aSt, eachsuccessive gtofih-zone of the sulfosalts(e.9., sulfosalts may be written as

gd g

1000/T K

Frc. 4. A fiS)-temperature diagram of sulfidation reactions applicable to Hock Hocking ore minerals. Sphalerite isoplethsfrom Czamanske(1974). Remainder of data from Barton & Skinner (1979).Shaded area represents deposi- tional conditions of Hock Hocking ore solution lying along the Xp"5 = 0.003 isopleth between 2@-300"C. Abso- lute paragenetic constraints are provided by the presenceof jalpaite (formed near the end of mineralization) and the pyrite-chalcopyrite assemblage.These constraints require ll7 < T < 360'C. The remaining curves on Figure 4 are for comparative purposesonly as the requisite assemblageis not present in the Hock Hocking mine or the sulfidation curve correspondsto reactions in the simple system (e.9., tetrahedrite-famatinite and tennantite-enargite). GROWTH ZONING IN TETRAHEDRITE-TENNANTITE 581

(A) (b) TET mr CoNcrusroNs : Xr" Xzo h K$sr'r zoning in tetrahedrite-tennantite from (a)TET @)rer Chemical mine confirms that the occupancy Xzo xr" the Hock Hocking

-*AG: to,,ff- ol,I,'sv, (2) where AGf is a quantity that describesthe departure of the Gibbs energyof the reciprocalend-members CulsFqSbaS13,Cu16Zn2SbaS,r, CuroFgAsaSl3, ?od CutoZnrAsaSl:,from coplanarity; it is defined by the expression

- t AUx = [(Jcul6zn2As4sl3 sCu16Fe2as4s13J - - ldlurozozsuqsl3Gh,sn"2suas13J (3) q *i E The negative correlation between ln(ZnlFe) and X6" observedin tetrahedrite-tennantite from Hock ? Hocking and other epithermal-mesothermal ore Xc deposits(e.9., Bushn^ell1983) is consistentwith a N positivevalue of AG_i. Sack & Loucks (1985)have X determinedthat AGi is 2.&x.0.12 kcal/gfw x 500'C from Fe-Zn exchangeexperiments between z sphaleriteand tetrahedrite-tennantite with X^ of 0, 0.65 and l; their preliminary dpta suggestthat, to a first approximation, AG ! is temperature- independentover the temperaturerange 365-500'C. If it is assumed that AG i is temperature-in- dependentand that the addition of a small frac- tion of Ag to the trigonal planar sites does not aher the relative energies of Fe and Zn on tetrahedral sites, then the slope rr defined from a plot of lnQffr/.4F) versusX^/(fl +xEy) for the tetrahedrite-tennantite compositionsof a given sample should be relatedto the temperatureof forma- lion viq the expression

T(K) : -(664 x.30)/m) (4) As/(As+So) for Becausethe slope z defined by the tetrahedrite- Frc. 5. Plot of Ln(Xyo/Xi) verszs As/(As+Sb) gowth-zoned tetrahedrite-tennantite from sample tennantite compositions from sample HH54 is HH54. Sulfosatts coexist with homogeneoussphalerite 1.30t 0.10 (seecaption to Fig. 5), applicationof (4) (Xn"s:0.003). Each data-point representsa single to this sample indicates a temperature of formation microprobe determination' Line is a least-squaresfit of 238 t46oc. This estimate was obtained after through data with a slopeof -1.30 and r of -0.76. Tak- eliminating tetrahedrite-tennantite samplesin which ing in=toaccount l*rai n1ffirt*ffr) becomesless there is a large uncertainty in the microprobe deter- uncertain with increasing.W, a conservativeestimate mination of Fe (Fes 0.10 wt.9o). of the uncertaintyin the slopeof I 0.10 was obtained Sb-rich tetrahedrite-tennantite samplesfrom the by determiningthe standarddeviation of slopesobtained defined by the seven mine commonly containedthe most marked concen- by linear regressionof the data sets iompositions (x* > 0.99) and 12 of 17 of Ag. Although the effect of Ag in the tinnantite trations remaining tetrahedrite-tennantitq-c-ompgsitions selected trigonal site upon Fe-Zn exchangein the neighbor- at random. Enor bars h ln(i[f,r/Xffr) were calcu- ing tetrahedral site is unknown, it appearsto be lated from the estimates of analytical uncertainty in minimal within the precisionof t}re data in this study. microprobedata grvenin the captionto Table l. Ana- Data points for Ag-rich samplesare randomly dis- lytical uncertainty in As,/(As + Sb) is not shown, but tributed around the least-squares-fitline in Figure 5. is generallyneejigible by comparison. 582 THE CANADIAN MINERALOGIST of the semimetalsite strongly influencestheFe/Zn Deposits([I'L. Barnes,ed.). Holt, Rinehart and ratio of tetrahedrite-tennantiteat fixed Fe/Znratio Winston, New Yor*, of coexistingsphalerite, temperature and pressure. Positivecorrelation of ln(ZnlFe) wirh Sb/(As + Sb) BusnNsu.,S.E. (1983):Paragenesis and Zoningofthe at constant Fe-Zn exchange potential pFe^ (i.e., Cananeo-Duluth Brecciq Pipe, Sonora, Mexico. Harvard Univ., Cambridge,Mas- constantcomposition of sphalerite)corresponds to Ph.D. thesis, sachusetts. destabilizationof Fe relativetoZn dueto electronic compressioncaused by substituting Sb for As in Cnrnan,D.A. & Bamms,H.L. (1976):Ore solution nearest-neighborsemimetal sites (e.g., Sack & chemistry.V. Solubilitiesof chalcopyriteand chal- Loucks 1985). Within the precision of the data cocite assemblagesin hydrothermal solution at presentedhere, it appearsthat the difference in rela- 200oCto 350"C.Econ. Geol. 71,772-794. tive energiesof Zn Fe.inpure, and idealtetrahedrite (1974): and tennantite, Czarraarsrn,G.K. The FeScontent of sphalerite along the chalcopyrite-pyrite-bornite sulfur fuga- city buffer. Econ. Geol. 69, 1328-1334, [Gfav Lurozozerasr3- G 6u1sr"2A.4s13J M.L. JBaNr.oz,R. (1983):A brillouin-zone - - JonusoN, & [G Luroznzsuasl3G tulsre2stasl3J (5) model for compositionalvariation in tetrahedrite. Amer. Mineral. 68, 220-226. is temperature-independent over the temperature range200-500oC, using the valueof +2.& t 0.12 Raesp,K.C. (1983):Mineralogy and Geochemistryof keal/gfw as determinedby Sack & Loucks (1983). Gold-SilverVeins at theHock HockingMine, Alma, Thus, the analysis of compositional zoning in Colorado. M,S. thesis, Purdue Univ., West Lafayette, Indiana. growth-zoned tetrahedrite-tennantite may have many applications to geothermometry of epither- Rerraoosn,P. (1969):The Ore Minerals and their Inter- mal-mesothermalbonanza silver deposits;at least, growths.Pergamon Press, Oxford, England. it emphasizes the importance of tetrahedrite- tennantite solid solutions as sliding-scaleindicators Secx,R.O. (1982):Spinels as petrogeneticindicators: of the environmentof ore deposition(e.g., Barton activity-composition relations at low pressures. & Skinner 1979,Wu & Petersen1977). Contr. Mineral. Petrology 79, 169-186. & Loucrs, R.R. (1983):Exchange experiments AcKNowLEDGEMENTS betweensphalerite and tetrahedrite-tennantitesolid solutions.Geol. Soc.Amer. Abstr, Programs15, We thank Silver State Mining Company of Vic- 676-677. tor, Colorado for allowing accessto the mine. We & - (1985):Thermodynamic properties of are especiallygrateful to R. Loucks for atomic tetraheddte-tennas+it€s-{.Constraints on the inter- absorption and fluid-inclusion analysesperformed dependenceof the Ag=Qg , Fe=Zn and As = Sb at Florida StateUniversity, L.J. Cabri, R.F. Martin, exchangereactions at 500"C.u4 mer. Mineral, 70 (rn and two anonymous reviewers for their cornments press). and suggestions,and V. Ewing and P. Granchi for (1959): their in was TsoMpsor, J.B;- In. Local equilibrium in assistance typing and drafting. Support processes. provided grants (R.H. metasomatic .Iz Researchesin Geochemis- through NSF EAR 80-0143 try (P.H. Abelson,ed.). John Wiley & Sons,New McCallister) and EAR 82-18286(R.O. Sack). York. Wu, I. & PrrsRsEN,U. (1977):Geochemistry of letra- REFERENcES hedrite and mineral zoning at Casapalca,Peru. Econ. Geol. 72, 993-1016. BanroN,P.8., Jn, Bsruxs, P.M. & Toururr, P., (1963):Equilibrium in ore deposits.Mineral. Soc. WusNscH,B.J. (1964):The crystalstructure of tetra- Arner.Spec. Pap. l, 171-185. hedrite,Cu12SbaS13. Z, Krist. 119,437453. & SrrNNrn,B.J. (1979):Sulfide mineral stabil- ReceivedAugust 11, 1983,revised manuscript accepted ities. .Iz Geochemistry of Hydrothermal Ore January 25, 1984.