RARE MINERALS of In, Сd, Mo, and W in GOLD-BASE METAL VEINS of the BUGDAYA Au-Mо(W)-PORPHYRY DEPOSIT, EASTERN TRANSBAIKALIA, RUSSIA Galina D

New Data on Minerals. М., 2008. Volume 43 13

RARE MINERALS OF In, Сd, Mo, AND W IN GOLD-BASE METAL VEINS OF THE BUGDAYA Au-Mо(W)-PORPHYRY DEPOSIT, EASTERN TRANSBAIKALIA, RUSSIA Galina D. Kiseleva, Vladimir A. Kovalenker, Nikolay V. Trubkin, Sergey E. Borisovsky, and Andrey V. Mokhov Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, RAS, [email protected] New data on a number of rare minerals of In, Cd, Mo, and W, which have been obtained using modern analytical techniques, are described in this article. These minerals have been identified in gold-rich polymetallic ore super- imposed on Mo(W) stockwork porphyry mineralization. Indium mineralization presents extremely rare dzhalindite In(OH)3 that was previously described in Russia only from deposits Dzhalinda, Amur region and Verkhnee, Primorsky krai as supergene mineral. Tungsten and molybdenum are concentrated in rare intermediate phase of the wulfenite-stolzite series Pb(W0.74Mo0.26)O4, and Cd, in greenockite CdS. Occurrence of well-shaped cubic crystals of dzhalindite exclusively in quartz and association of the mineral with sphalerite, native silver, and electrum allow suggesting its hypogene origin (in contrast to previous findings as supergene pseudomorphs after indium sulfide). However, additional investigation is required to establish formation conditions of dzhalindite. 4 figures, 22 references. Keywords: dzhalindite, Mo-bearing stolzite sphalerite, greenockite, Bugdaya porphyry deposit, Eastern Trans- baikalia, polymetallic veins, gold mineralization.

Geological structure, ore mineralogy, and Our investigations indicated that ore of stages of mineralization the Bugdaya deposit where about 70 mineral were identified is characterized by more The Bugdaya Au-Mо(W) porphyry de- variable and complex mineralogy that pre- posit, eastern Transbaikalia located 18 km viously reported. Pyrite, galena, sphalerite, SW of the Shakhtama mine in the interfluve molybdenite, chalcopyrite, and scheelite of the Gazimur and Unda rivers is hosted in are the most abundant. Arsenopyrite, the central volcanic dome of concentrically- fahlores, As-rich pyrite, magnetite, and radial structure. This dome is located in the hematite are less abundant. Small amounts southeastern large Variscan granitoid pluton of various bismuth (aikinite series, that was intruded by the Late Jurassic sub- matildite-galena series, and Cu-Ag-Pb-Bi-S volcanic granite-porphyry and rhyolite-por- system) and antimony (polybasite, phyry. pearceite, and their Te-bearing analogues; Mo-W ore is hosted in a stockwork that is boulangerite; and bournonite) minerals are column-shaped in vertical section and oval, frequently observed. Rare minerals are na- in plan of 1100 x 800 m in size. This stock- tive silver, kustelite, tellurides and sulfotel- work comprises variably oriented quartz- lurides, wurtzite, dzhalindite, and molybdenite veins and veinlets (few to tens greenockite. Two latter minerals are de- cm thick) with local scheelite, which arrange around stock of silicified rhyolite (granite) scribed below. Gold-silver alloy with fine- porphyry. Gold (1–2 to 100–150 g/t, less ness ranging from 962 to 223 were found to frequent higher) is hosted in steep quartz- be associated with minerals from base metal sulfide veins (250–300 m long and from few veins and veinlets. to 3–4 cm thick), which also contain the Quartz is dominant gangue mineral; main resources of Pb and Zn (Kharitonov et chalcedony, carbonates, muscovite al., 2003). (sericite), phlogopite, tourmaline, potassi- 14 New Data on Minerals. М., 2008. Volume 43 um feldspar, kaolinite, smectites, and fluo- hedral crystals of dzhalindite were men- rite are minor. Covellite, chalcocite, bornite, tioned, when hydroxides of rare and trace ferrimolybdite; rare ilsemannite and elements at the Tsumeb deposit, Namibia stolzite; cerussite, barite, and anglesite were and deposits of Nevada, USA were de- described from supergene zone. scribed (Yakhontova and Zvereva, 2000). Four major stages of hydrothermal min- Complete description of dzhalindite eralization are recognized: (1) pre-ore; (2) from deposits in other countries is available quartz-molybdenite; (3) gold-base metal; only from the Mount Pleasant deposit and (4) post-ore (Kovalenker et al., 2007). (Sutherland, 1971), where this mineral asso- Pre-ore K-feldspatization and strong silicifi- ciated with quartz, calcite, and galena was cation occurred after emplacement of sub- found in veinlet cutting sphalerite. volcanic rhyolite-(granite)-porphyry stock. Mode of occurrence and mineral assem- Then, Mo-W stockwork of the quartz- blage. For the present, we identified cubic molybdenite stage was formed. Gold-base crystals of dzhalindite In(OH)3 only in one metal veins accompanied with sericitization section of quartz-sulfide vein at 50 m depth and pyritization of wall rocks are located in below surface. Ore minerals replacing min- the structures cutting Mo-W mineraliza- erals of quartz-molybdenite stage occurred tion. Precipitation of late stage chalcedony, close to dzhalindite are quartz-galena-chal- quartz, and carbonates as veins and veinlets copyrite-sphalerite segregations with small accompanied with argillization and insignif- amount of pyrite and fahlore (predominant icant redeposition of earlier minerals com- tennantite) and enriched in gold (predomi- plete the hydrothermal mineral-forming nant electrum with fineness 698 to 748). Ag- process. gregates of base metal sulfides are strongly Rare dzhalindite and greenockite were fractured, healed by tennantite, then brec- probably precipitated at the end of gold- ciated again, and cemented by fine-grained base metal stage. quartz with crystal size ranging from 40 to 70 μm. Dzhalindite Dzhalindite presents square and rectan- gular well-crystallized grains, and less fre- Indium mineralization was found as quent other sections of cube (triangular, dzhalindite In(OH) that had been previous- 3 rhombic, trapezoid, and hexagonal) (Fig. 1, ly described in Russia only from tin ore of 2). Size of crystals varies from 30 to 94 μm, deposits Dzhalinda, Amur region, Khingan most frequent, from 50 to 70 μm. Locally, in- Minor (Genkin and Murav’eva, 1963) and tergrowths of several crystals are observed. Verkhnee, Kavalerovo district Primorsky Frequency of dzhalindite is 70 crystals in krai (Gorelikova et al., 2008) as pseudo- section 4 x 2 cm in size. morphs after indite. Dzhalindite was identi- Dzhalindite occurs only in the areas, fied at some tin deposits in the other coun- where late quartz cements fragments of tries including Zinnwald-Cinovec (border grains of high-Fe sphalerite-I (4.1–6.54 wt. between Czechia and Germany) (Jansa et % Fe). According to spectral analysis, this al., 1998); Mangabeira, Brazil (Moura and sphalerite contains, %: 0.03–3 Cu, 0.1–0.2 Francisquinibotelho, 2000); and Mount Cd, 0.03–0.5 Mn, 0.008–0.08 Аg, and Pleasant, Canada (Sutherland, 1971). The 0.002–0.05 In. Fine disseminated chal- mineral was found at the Flambeau Cu-Au- copyrite is frequently observed in spha- Ag deposit, Wisconsin, USA; Kamazu Au- lerite-I. Few 1 mm grains of galena-I inter- Ag-Te-Mn deposit, Japan; and Lavrion, grown with rare tennantite occur among Greece nickel (annabergite) deposit. Octa- fragments of sphalerite-I. Rare Minerals of In, Сd, Mo, AND W in Gold-base metal Veins of the Bugdaya Au-Mо(W)-porphyry deposit, eastern Transbaikalia, Russia 15

Fig. 1. Dzhalindite and associated minerals. (a) Photomicrograph of well-shaped crystal of dzhalindite (In) overgrown by minerals of the

CuS-Cu2S (CuxS) system in quartz (dark gray), the same minerals to- gether with greenockite (CdS) overgrow sphalerite (ZnS), thin polished section. (b) Photomicrograph of the same dzhalindite crystal that is transparent with weak coloration, yellow reflections of greenockite are well seen in sphalerite, cross polars, strong light. (c) BSE image of dzhalindite (rotated 30o) with pro- nounced zoning. (d) BSE image of greenockite rim (light gray) with admixture of chalcocite in quartz.

Fig. 2. Fe-rich variety of dzhalindite and distribution of Fe and In in it. (a) Photomicrograph of brown crystals of dzhalindite in quartz; one of the crystals (right low) is overgrown

by minerals of the CuS-Cu2S system; yellow mineral is greenockite; thin polished section, cross polars, strong light. (b) BSE image of dzhalindite crystal (red point in Fig. 2a). (c) X-ray map of In in the crystal; (d) X-ray map of Fe (zoning is remarkable, Fe is lower in the core) in the crystal. 16 New Data on Minerals. М., 2008. Volume 43

Most fragments of sphalerite-I are Electrum is present in quartz in slightly rimmed by thin (from portions to first tens less amount than native silver and occurs as μm; less frequent more) aggregates of the small clotted segregations and isometric

СuS Cu2S system minerals (Fig. 1). Micro- grains (2–70 μm) with imperfect faces. scopically and chemically, covellite and Much larger (up to 176 μm) segregations of phases Сu1.79S Сu1.82S, which are optically electrum in sphalerite-I are isometric or and compositionally close to chalcocite slightly elongated and have smooth and were identified among these minerals. Non- more frequently rounded outlines. Fineness stoichiometric composition is probably of electrum (about 700) from this assem- caused by fine admixture of covellite in blage (mean of 40 point analyses) is usual chalcocite but other minerals of the СuS- for rich ore and slightly lower than average

Cu2S system such as djurleite and anilite are value (about 730) at the deposit. also possible. Elevated Ag (1.1–1.7 wt. %) All these minerals spatially associated is a feature of these minerals. Silver substi- with dzhalindite are not intergrown with it tutes univalent copper or is related to fine and occur not more than tens microns of the inclusions of Ag-bearing minerals. In addi- mineral. In single instance, 4 μm inclusion tion to these minerals, greenockite (Fig. 1a, of electrum with approximately equal b, d) and galena-II are frequently observ- weight portions of Au and Ag was observed able in the rims. Development of galena-II in dzhalindite. after covellite and its few tens μm thick Optical parameters and physical proper- veinlets filled interstices between grains of ties. Dzhalindite was identified on the basis greenockite and chalcocite are remarkable. of composition, optical parameters, and Sphalerite-II, greenockite, pyrite, native symmetry similar to synthetic phase silver, and electrum were identified in In(OH)3 produced by reaction of alkalis and dzhalindite-bearing quartz. Few sphalerite- salts of indium during boiling (Fricke, Seitz, II is observed adjacent to fragments of spha- 1947) and natural dzhalindite, that was de- lerite-I as euhedral isometric or slightly scribed as new mineral in (Genkin and Mu- elongated and rounded crystals of several rav’eva, 1963). Due to small sizes of the tens μm in size. In contrast to sphalerite-I, it dzhalindite segregations, X-ray diffraction is characterized by strong brownish yellow study of the mineral was failed. reflections and does not contain inclusions Dzhalindite is dark gray under reflected of chalcopyrite; rims of the other minerals light and significantly brighter than quartz are extremely rare. but darker than scheelite. Reflectance of Pyrite was observed in small amount as dzhalindite is about 8–9% that is consistent trails of tiny (4–5 μm) well-shaped cubic with measurements at l = 589 nm (yellow crystals. Such trails can overgrow crystals of light) 8.2% (Genkin and Murav’eva, 1963). dzhalindite. Internal reflections are weak, whitish or yel- Relatively small amount of native silver lowish, with slight translucence on crystal is hosted only in dzhalindite-bearing margins. quartz as intergrowths of curved 80 μm Cross polars microscopic observation at long wire-shaped crystals and less fre- maximum lighting shows that sections of quent, as clotted segregations with un- the dzhalindite cubes are transparent and even lobe-shaped outlines of few to first semitransparent, locally pinkish-yellowish tens μm in size. Native silver (8 point or practically colorless, with yellowish analyses) is distinguished by insignificant amber (to light brown) tint (Fig. 2a). Be- (tenths wt. %) Zn, Cu, and S; tween these varieties, there are all interme- 0.04–0.3 wt. % Te and 0.2–0.43 wt. % Au. diate varieties dominated by practically col- Rare Minerals of In, Сd, Mo, AND W in Gold-base metal Veins of the Bugdaya Au-Mо(W)-porphyry deposit, eastern Transbaikalia, Russia 17 orless transparent crystals (Fig. 1b). Relief is parent variety of dzhalindite was analyzed substantially lower than that of quartz and for comparison (Fig. 2). Like the transparent slightly lower than sphalerite. Dzhalindite is variety, Fe content in the core is low but well polished; surface of crystals is smooth slightly higher (0.9 wt. %). Concentration of and flaw-free. iron in one of the darkest zones is four times All crystals of dzhalindite are zoned with higher (3.6 wt. %). Thus, the observable zon- alternated darker and lighter zones. It is ing in dzhalindite results from oscillated Fe clearly seen in back scattered electron content in the crystals. It should be noted, (BSE) images (Figs. 1c, 2b) made with JSM- the iron concentration in dzhalindite from 5610 and JSM-5300 analytical scanning type locality is much higher (In/Fe = 4) electron microscopes (ASEM). ASEM study that is caused different mode of its forma- of the crystal surface shows that zoning is tion, pseudomorphous replacement of in- also displayed in relief probably indicating dite, which contains Fe. different density and hardness of zones. The Species of iron in dzhalindite are not yet revealed zoning is caused by different com- established. Light brown tint of the mineral position of the zones (Fig. 2 d). can indicate three-valence iron and in this Thickness of the zones decreases out- case, Fe is probably present as fine com- ward from 4 μm to portions of microns. In- pounds rather than substitutes In in the termediate zones have smoothed tops mineral structure because of sufficiently (edges) with smoothing increasing to the great difference in ionic radii (nm, coordi- margin that can testify to certain dissolution nation number is 6): 0.076 Fe3+ and 0.094 of the growing crystals. Same faces of the in- In3+. Presence of iron as fine compounds of termediate zones are curved. Outer zone of Fe3+ is confirmed by variable mineral color the crystal is compared with core and near- that is probably caused by local enrichment ly elsewhere is cubic. In many cases, these of mineralizing fluids in Fe3+ . outer zones (as crystal faces) are oriented at According to (Roy and Shafer, 1954), just o approximately 45 to the earlier intermedi- In(OH)3 is stable phase at 245°С and below ate zones. The normal rhythmic zoning (pressure 703 kg/cm2). At temperature high- without crystallographic reorientation of er than 245° (the same pressure), In(OH)3 the outer zone and final faces occurs in the transformed into InОOH. Over 435°C, only smaller crystals. In such crystals, no features phase In2O3 is stable. The temperature of for- of dissolution (smoothed apices, inclusions mation of studied dzhalindite can be esti- of other minerals, roughness of faces of in- mated only indirectly, because there are no termediate zones etc.) during growth are fluid inclusion data for host quartz and observed. dzhalindite itself. However, homogenization The chemical composition of the mineral temperature of fluid inclusions in gold-bear- was determined with a JSM-5300 analytical ing quartz from similar quartz-base metal scanning electron microscope equipped veins at the Bugdaya deposit ranges from with energy dispersion system. The near 225 to 205°C (Kovalenker et al., 2007); inclu- colorless transparent variety of dzhalindite sions in cleiophane homogenize at contains, wt. %: 63.27 In, 34.68 O, and in- 217–140°C. Fluids are sulfate-hydrocar- significant Fe. In this case, Fe is minimal bonate with high degree of oxidation

(0.61 wt. %) in homogeneous core and reori- (CO2/CH4 > 100). The results obtained com- ented outer zone of the crystals. Slightly bined with spatial association of dzhalindite more Fe (1.08 wt. %) is detected in one of the with low-temperature minerals (gold-silver darker (in back-scattered electrons) inter- mineralization, sphalerite-II, greenockite, mediate zones. The light brown semitrans- and galena-II) most probably testify to the 18 New Data on Minerals. М., 2008. Volume 43 formation temperature of the minerals no The chemical composition of greenock- higher than 225°C. All these data can indi- ite (2 point analyses) determined using a rectly indicate that in contrast to supergene JSM-5300 analytical scanning electron mi- dzhalindite from the Dzhalinda and croscope equipped with energy dispersion Verkhnee deposits, this mineral found at system is close to stoichiometric, wt. %: Bugdaya is probably formed under hypo- 74.08–76.5 Cd, 21.93–23.5 S. Theoretical gene conditions. However, additional study composition is as follows, wt. %: 77.81 Cd is required to infer certain conditions of its and 22.19 S. Deficiency of Cd is caused by formation. Yakhontova and Zvereva (2000) admixture of Zn (up to 2.19 wt. %) and Cu emphasized ambiguous formation condi- (up to 1.71 wt. %). tions of dzhalindite; Sutherland (1971) just Conditions of formation. According to states a fact that dzhalindite cuts sphalerite. most publications, natural greenockite is formed exclusively under low-temperature Greenockite conditions. In this case, it can be both su- Mode of occurrence and mineral assem- pergene and hypogene. Often, the exact de- blage. Greenockite is constantly associated termination of the origin is difficult. It is with dzhalindite and is observed only in sec- caused by similar morphology of supergene tions with dzhalindite. It is more abundant and hypogene grains (for example, in our case, a presence of the mineral as rims) and than sphalerite-II. The mineral occurs as ir- associated minerals whose precipitation is regular and more frequent, elongated possible in both settings. Recently, papers, rounded clusters up to 50 μm in size hosted where greenockite is attributed with high in late quartz usually adjacent to dzhalin- validity to hypogene minerals, were pub- dite. Traces of the mineral are observed lished. For example, Pletnev (1998) as- some distance of dzhalindite. Greenockite signed greenockite to hypogene minerals. as few to 10 μm thick rims around spha- Greenockite is present in sublimates of the lerite-I (Fig. 1d) is extremely characteristic. lowest temperature (300–600°C) fumarole Locally, chalcocite invading to both miner- field of the Kudryavy volcano (Chaplygin, als occurs along contact between spha- 2008). According to fluid inclusion study lerite-I and greenockite. Locally, late galena (Tombros et al., 2005), deposition tempera- emplaced as fine inlets into intergrain space ture of the Ag-Au-Te epithermal mineraliza- of sphalerite-I and greenockite fills inter- tion associated with greenockite is 215°C stices between these minerals. No inter- that is within range of precipitation of late growths of greenockite with other minerals quartz and cleiophane 225–140°C given were established. when dzhalindite was described. Optical parameters and physical proper- Impurities of Cd in sphalerite (up to ties. Under reflected light, greenockite is tenths wt. %) and tetrahedrite containing up gray with weak greenish tint. Its reflection is to 2.97–3.64 wt. % Сd in rich ore were prob- slightly higher than that of sphalerite. Cross able source of cadmium to form greenock- polars microscopic observation at maximum ite. Cadmium appears to release during dis- lighting shows that greenockite is bright solution and recrystallization of these min- lemon or yellow, transparent or semitrans- erals at late stage of hydrothermal process. parent (Figs. 1b, 2a). Strong internal reflections hide anisotropy. Relief is lower than Mo-bearing stolzite (“chillagite”*) that of sphalerite. Greenockite is well pol- Name of rare mineral “chillagite” exist- ished; surface of crystals is smooth and flaw- ed for almost whole last century starting free. 1 – The mineral that we identified should be apparently called Mo-rich stolzite due to strong predominance of W over Mo. * – mineral was discredited by the Commission on New Minerals and Mineral Names, International Mineralogical Association (CNMMN) IMA. Rare Minerals of In, Сd, Mo, AND W in Gold-base metal Veins of the Bugdaya Au-Mо(W)-porphyry deposit, eastern Transbaikalia, Russia 19

Fig. 3. BSE inages of the stolzite-wulfenite series mineral. (a) Rosette-shaped Mo-rich stolzite (St) in galena (PbS); the mineral fills fracture in galena and is rimmed by covellite (Cv) (upper part); muscovite (Mu) in the core of Mo-rich stolzite; white spot in the upper part is sputtering defect. (b) Veinlet-shaped Mo-rich stolzite intergrown with anglesite (An) at the contact between galena and quartz (Q); laths of muscovite (Mu) are observed in Mo-bearing stolzite. from the first original description of this of supergene transformation (sampling mineral in 1912 from Christmas Gift Mine, depth is 50 m below surface) mineralogy of Chillagoe, Queensland, Australia (Ullman, ore became more complex and along with 1912). The mineral turned out intermediate appearance of ferrimolybdite and less fre- member of the PbWO4 (stolzite) PbMoO4 quent ilsemannite formed after molybden- (wulfenite) solid solution series, where ite, this rare intermediate phase of the lead stolzite and wulfenite have the same space molybdate-tungstate series fills fractures group I41/а. Later investigation of the min- and cavities in galena and some other mineral from the same deposit showed that it erals of the gold-base metal veins. should be considered as W-rich wulfenite, The sample containing Mo-rich stolzite which, in contrast to its pure variety, crys- is highly sulfidized gold-rich fragment of – tallizes in space group I4 due to W-Mo or- vein with content of sulfides about 75%. Sul- dering (Jury et al., 2001). fides are dominated by practically fresh The phases similar in composition and pyrite of two generations, chalcopyrite, and called as “chillagite” were described from galena with covellite and insignificant chal- ores of several deposits in the eastern cocite, which occur as thin films on these Transbaikalia (Syritso et al., 1964), includ- minerals or fill microfractures in them. ing the Shakhtama mine group in Gaz- Other minerals, sphalerite, various sulfos- imur-Zavodsky district (Chureva, 1948) alts including tetrahedrite and Cd-bearing and Dzhida tungsten deposit (Korzhinsky tetrahedrite, Te-bearing polybasite (aver- et al., 1959). It was found at deposits in age ~4% Te), matildite, and wittichenite are other regions (Smol’yaninova et al., 1963; subordinated. Quartz is predominant Yushkin et al., 1972). gangue mineral. In addition, there are mus- Mode of occurrence and mineral assem- covite (no more than 2%) and anglesite (no blage. The mineral was identified in the vein more than 1%) filling fractures in quartz and gold-base metal mineralization superim- galena. In the sample, we observed ex- posed on the earlier tungsten-molybdenum tremely great amount (for this deposit) of stockwork. Such superimposition resulted native gold and electrum grains of three in the complex Au-Ag-Mo-W-Pb-Zn-Bi generations with fineness ranging from 962 mineralization. In addition, in consequence to 504. Gold-silver phases cutting covellite 20 New Data on Minerals. М., 2008. Volume 43

Fig. 4. Composition of the РbMoO4-PbWO4 series minerals from various deposits all over the World (W and Mo concentrations – in atomic percent). (1, 3) Christmas Gift [(1) Mingaye, 1916; (3) Ullman, 1912]; (2) Akchatau, Central Kazakstan (Smol’yaninova and Senderova, 1963); (4) Eastern Trans- baikalia (Zuev, 1959); (5) Northeastern Russia (Gladyshev, 1949); (6) Bug- daya deposit; (7) Shakhtama mines, Eastern Transbaikalia (Chureva, 1948).

as thin (1–3 μm) veinlets have the lowest beam, the mineral has bluish-greenish lumi- fineness. nescence with intensity close to fluorite and Mo-rich stolzite occurs predominantly scheelite. in cavities and along cleavage in galena; The chemical composition of the mineral and less frequent, at the contact of galena determined with a CAMECA MS-46 elec- with quartz, muscovite and other minerals tron microprobe corresponds to formula of the gold-base metal veins (Fig. 3). There- Pb(W0.74Mo0.26)O4. Insignificant Fe, Ca, and fore, galena and occasionally other sulfides in one analysis Sr were detected. The of the Bugdaya deposit are enriched in W/Mo ratio of previously described molybdenum and especially in tungsten (up “chillagites” widely ranges from 0.59 to 4.03 to 4125 g/t W), with inclusions of primary (Fig. 4). The chemical composition of the minerals of these elements being absent in examined mineral significantly dominated them. Mo-rich stolzite overgrows laths of by W (W/Мо = 2.9) is the closest to potassium mica if they occur in galena or at “chillagite” from the Shakhtama mines. contact with it. Segregations of Mo-rich Small sizes of the grains prevented more de- stolzite are locally rimmed by covellite (Fig. tailed study of this mineral, particularly, in- 3a). Mo-rich stolzite is also observed in vein- vestigation of its crystal structure. Intimate lets as intergrowths with anglesite (Fig. 3b). association of examined Mo-rich stolzite Optical parameters and physical proper- with covellite and anglesite, which are char- ties. Segregations of Mo-rich stolzite do not acteristic minerals of the oxidized zone, in- exceed hundredths mm in size. It occurs as dicate supergene origin of the mineral. spear- or lath-shaped crystals elongated along cleavage and locally slightly curved Conclusions with the length/width ratio ranging from 6 to 10. In cavities, the mineral occurs as 1. The following factors favored the for- rosette radiant intergrowths (Fig. 3a). Under mation of rare and exotic minerals at the reflected light, it is light gray, with reflec- Bugdaya deposit: (1) ore-forming fluids tion being higher than that of anglesite and evolved from high-temperature through close to sphalerite. Mo-rich stolzite is medium- and low-temperature to super- anisotropic with remarkable birefraction gene; (2) juxtaposition (telescoping) of dif- that is slightly smoothed by very strong yel- ferent stage mineral assemblages in some lowish internal reflections. Under electron structures; and (3) multiple brecciation of Rare Minerals of In, Сd, Mo, AND W in Gold-base metal Veins of the Bugdaya Au-Mо(W)-porphyry deposit, eastern Transbaikalia, Russia 21 ores, corrosion and dissolution of minerals posits in the region is comparable to that in with release of trace elements and their in- sphalerite from the Bugdaya deposit. corporation into new compounds at local Coexisting greenockite and dzhalindite geochemical barriers. in ore of the Bugdaya deposit can indicate a 2. According to spatial association of Cd generality of the processes, which formed and In minerals with early sphalerite, one of these minerals. the major ore component, they were formed 4. Spatial combination of late gold-base as a result of dissolution and recrystalliza- metal and earlier high-temperature Mo-W tion of sphalerite. mineralizations and ore fracturing favored In-bearing early sphalerite is character- the formation of rare supergene mineral of istic of many deposits in the eastern Trans- the PbWO4–PbMoO4 series with formula baikalia, though indium content in this min- Pb(W0.74Mo0.26)O4 and similar in composi- eral rarely reaches tenths percent and inti- tion to that at the Shakhtama mines at the mate correlates with a presence of tin min- near-surface levels of the Bugdaya deposit. erals at the deposits implying identification 5. Localization of examined minerals in of Sn minerals at the Bugdaya deposit. It is gold-rich areas, which are characterized by more probable because at the neighboring elevated jointing and combination of differ- Shakhtama Mo-porphyry deposit, where in- ent stage assemblages is important to indi- dium (up to 50 g/t) was detected in minerals cate multiple reworking of these areas of of the base metal ore (bulk analysis), stan- orebodies and unique formation conditions nite was found (Sotnikov et al., 1995). of such rare minerals. Crystallization of dzhalindite and shape and composition of the mineral similar to Acknowledgments phase synthesized by the reaction of ammo- nia with indium salts during boiling and We are grateful to candidates of sciences mineral assemblages allow suggesting the O.Yu. Plotinskaya and S.V. Yudentsev, re- formation of dzhalindite at the Bugdaya de- searchers of our institute, for advises and as- posit as a result of neutralization of thermal sistance during preparation of manuscript. solutions corroding sphalerite and contain- This study was supported by the Russian ing indium released from the latter. The for- Foundation for Basic Research (project no. mation temperature of dzhalindite probably 07–05–00517). was close to that of late cleiophane (about 140oC). Planned study of fluid inclusions References from dzhalindite will provide more valid Chaplygin I.V. Mineral-forming system of conclusions on the origin of the mineral. the Kudryavy volcano, Iturup Island // 3. Despite greenockite was found at the Problems of geology ore deposits, mineral- uranium deposits in the eastern Trans- ogy, petrology, and geochemistry. Proc. baikalia, it is rare mineral in base metal ores Sci. Conf. IGEM RAS, Moscow. 2008. of this region. Lack of local analytical equip- P. 269–273. (In Russian.) ment to study minerals probably prevented Chureva M.N. Chillagite from the eastern the findings of greenockite in ores of the Transbaikalia // Zap. VMO. 1948. Ser. 2, base metal deposits in the eastern Trans- Part 77 (1). P. 103–104. (In Russian.) baikalia, which were investigated in detail Fricke R. and Seits A. Kristalline Hydroxide mainly in the middle of the last century. It des Indiums und Scandiums // Zeitschr. should be added that Cd content in some anorg. Chem. 1947. Bd. 255. H. 1–3. generations of sphalerite from most de- P. 13–15. 22 New Data on Minerals. М., 2008. Volume 43

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