The origin of Ag–Au–S–Se minerals in adularia-sericite epithermal deposits: constraints from the Broken Hills deposit, Hauraki Goldfield, New Zealand

The 7.1 Ma Broken Hills adularia-sericite Au–Ag deposit is currently the only producing rhyolite-hosted epithermal deposit in the Hauraki Goldfield of New Zealand. The opaque minerals include pyrite, electrum, acanthite (Ag₂S), sphalerite, and galena, which are common in other adularia-sericite epithermal deposits in the Hauraki Goldfield and elsewhere worldwide. Broken Hills ores also contain the less common minerals aguilarite (Ag₄SeS), naumannite (Ag₂Se), petrovskaite (AuAgS), uytenbogaardtite (Ag₃AuS₂), fischesserite (Ag₃AuSe₂), an unnamed silver chloride (Ag₂Cl), and unnamed Ag?±?Au minerals. Uytenbogaardtite and petrovskaite occur with high-fineness electrum. Broken Hills is the only deposit in the Hauraki Goldfield where uytenbogaardtite and petrovskaite have been identified, and these phases appear to have formed predominantly from unmixing of a precursor high-temperature phase under hypogene conditions. Supergene minerals include covellite, chalcocite, Au-rich electrum, barite, and a variety of iron oxyhydroxide minerals. Uytenbogaardtite can form under supergene and hypogene conditions, and textural relationships between uytenbogaardtite and associated high-fineness electrum may be similar in both conditions. Distinguishing the likely environment of formation rests principally on identification of other supergene minerals and documenting their relationships with uytenbogaardtite. The presence of aguilarite, naumannite, petrovskaite, and fischesserite at Broken Hills reflects a Se-rich mineral assemblage. In the Hauraki Goldfield and the western Great Basin, USA, Se-rich minerals are more abundant in provinces that are characterized by bimodal rhyolite–andesite volcanism, but in other epithermal provinces worldwide, the controls on the occurrences of Se-bearing minerals remain poorly constrained, in spite of the unusually high grades associated with many Se-rich epithermal deposits.     

Genesis of gold and silver sulfides at the Ulakhan deposit (northeastern Russia)

Geology and mineralogy of the Ulakhan Au-Ag epithermal deposit (northeastern Russia, Magadan Region) are considered. A four-stage scheme of mineral formation sequence is proposed. Concentrations of Au and Ag in minerals of early and late parageneses were determined. It has been established that uytenbogaardtite is associated with native gold and hypergenesis stage minerals — goethite, hydrogoethite, or limonite replacing pyrite. The compositions of uytenbogaardtite (Ag₃AuS₂), acanthite (Ag₂S), and native gold were studied. The composition of the Ulakhan uytenbogaardtite is compared with those of Au and Ag sulfides from other deposits. Thermodynamic calculations in the system H₂O–Fe–Au–Ag–S–C–Na–Cl were carried out, which simulate the interaction of native gold and silver with O₂- and CO₂-saturated surface waters (carbonaceous, sulfide-carbonaceous, and chloride-sodium-carbonaceous) in the presence and absence of acanthite and pyrite at 25 °C and 1 bar. In closed pyrite-including systems, native silver and kustelite are replaced by acanthite; electrum, by uytenbogaardtite, acanthite, and pure gold; and native gold with a fineness of 700–900‰, by pure gold and uytenbogaardtite. Under the interaction with surface waters in the presence of Ag₂S and pyrite, Au-Ag alloys form equilibrium assemblages with petrovskaite or uytenbogaardtite and pure gold. The calculation results confirmed that Au and Ag sulfides can form after native gold in systems involving sulfide-carbon dioxide solutions (H₂Saq > 10^–4 m). The modeling results support the possible formation of uytenbogaardtite and petrovskaite with the participation of native gold in the hypergenesis zone of epithermal Au-Ag deposits during the oxidation of Au(Ag)-containing pyrite, acanthite, or other sulfides.     

(Au,Ag)Te2 Minerals from Epithermal Gold Deposits in Japan

Chemical composition and mode of occurrences of (Au, Ag)Te₂ minerals such as calaverite (AuTe₂), sylvanite (AuAgTe₄) and krennerite ((Au, Ag)Te₂) in epithermal gold telluride ores from Suzaki, Kawazu and Teine are examined. In the ores from Suzaki, (Au, Ag)Te₂ minerals occur in microbands of tellurides and fine quartz. The minerals in telluride bands change from krennerite, via calaverite‐native tellurium, to sylvanite, in the order of crystallization. A sample from Kawazu contains sylvanite and native tellurium with stutzite, hessite and tetradymite in the coarser gray quartz part. The Teine sample also contains sylvanite and native tellurium with barite and quartz. The peak patterns of XRD of calaverite, krennerite and sylvanite from Suzaki are almost identical to that of JCPDS 43–1472, JCPDS 8–20 and JCPDS 9–477, respectively. The Te, Au, Cu, and Ag contents of calaverite from Suzaki range from 56.4 to 57.9 wt.%, from 41.6 to 42.6 wt.%, from 0.28 to 0.45 wt.% and from 0.14 to 0.31 wt.%, respectively, corresponding to the formula Au_0.97Ag_0.01Cu_0.02Te₂. The Te, Au, Ag, and Cu contents of krennerite from Suzaki range from 59.6 to 61.4 wt.%, from 31.3 to 33.6 wt.%, from 4.91 to 6.13 wt.% and from 0.66 to 0.80 wt.%, respectively, corresponding to the formula Au_0.71Ag_0.22Cu_0.05Te₂ with Au and Ag ranging from 0.68 to 0.74 and from 0.20 to 0.25, respectively. The Te, Au, Ag, and Cu contents of sylvanite from Suzaki range from 61.5 to 63.4 wt.%, from 24.1 to 27.4 wt.%, from 10.0 to 12.5 wt.% and from 0.00 to 0.12 wt.%, respectively. The Te, Au, Ag, and Cu contents of sylvanite from Kawazu range from 62.7 to 63.3 wt.%, from 23.5 to 24.1 wt.%, from 12.0 to 12.5 wt.% and from 0.09 to 0.16 wt.%, respectively. The Te, Au, Ag, Cu and Fe contents of sylvanite from Teine range from 61.8 to 63.5 wt.%, from 23.6 to 24.7 wt.%, from 11.9 to 13.3 wt.%, from 0.01 to 1.65 wt.% and from 0.00 to 0.02 wt.%, respectively. The average formulae of sylvanite from Suzaki, Kawazu, and Teine are expressed as Au_1.06Ag_0.94Cu_0.02Te₄, Au_1.00Ag_0.95Cu_0.02Te₄ and Au_1.01Ag_0.95Cu_0.06Te₄, respectively. Judging from the mineral assemblages of these ores and other localities, Au–Te mineralization in the Japanese Islands can be divided into four types: native gold–calaverite at Date and Agawa, krennerite(?native tellurium) at Osore‐zan and Mutsu, sylvanite–native tellurium–hessite at Teine, Kawazu, Kobetsuzawa, and Kato, and polyminerallic assemblages at Suzaki and Kushikino. The pH–Eh diagram of aqueous tellurium species and tellurium minerals at 250°C indicates that (Au, Ag)Te₂ minerals in epithermal gold telluride mineralization would have been formed under middle to low Eh and acidic (to intermediate) pH conditions. It is possible that dilute tellurium‐containing fluid would scavenge dilute gold.     

桂西那弱银金矿床矿物组合特征及银和金的赋存状态研究

广西天峨那弱银金矿床以银矿为主,共/伴生金及铅、锌、锑等金属,矿物组合在右江盆地内为首次发现。矿体受那弱背斜及其轴向断层控制,赋矿层位为中三叠统百逢组含钙质浊积岩系。矿石矿物以硫锑铅矿、铁闪锌矿、黄铁矿、毒砂和方铅矿为主;脉石矿物主要有石英、方解石、绢云母等。主要矿石矿物由早到晚的生成顺序为:毒砂→黄铁矿→铁闪锌矿→硫锑铅矿→方铅矿。单矿物化学分析显示硫锑铅矿含Ag最高,其次为闪锌矿;黄铁矿含Au相对较高。EPMA测试结果表明Ag于方铅矿中含量最高,其次为硫锑铅矿;主要矿石矿物中毒砂含Au相对较高,其余矿物中Au含量均偏低。因矿石中的铅矿物主要为硫锑铅矿,可以认为那弱银金矿床的Ag主要赋存于硫锑铅矿中,Au主要赋存于毒砂与黄铁矿中,二者均以显微-次显微状态赋存于载体矿物中。根据矿物组合及其相互交代、切割关系等特征,将矿床划分为2个成矿期共4个成矿阶段。其中,第一成矿期为金的成矿期,矿物组合为黄铁矿和毒砂,由于后期成矿作用的叠加,仅保留一个成矿阶段;第二成矿期为银铅锌成矿期,矿物组合为方铅矿-闪锌矿-硫锑铅矿;包含第二至第四共3个完整的成矿阶段。该矿床Ag、Au共生是不同期次成矿作用叠加的结果。     

Zun-Ospa Gold Deposit,Eastern Sayan: Geology,Ore Composition,and Genesis

The paper discusses the geology of Zun-Ospa gold deposit, which is situated near the Ospino ophiolitic nappe in the southeastern part of the Eastern Sayan, and the ore composition therein. The deposit is related to the tectonic mélange zone and is characterized by distinct structural control. Three consecutive mineral assemblages formed within a temperature range of 380°–170°C: (i) native gold–quartz–pyrite, (ii) gold–quartz–polysulfide, and (iii) silver–sulfosalt. The ore was deposited from low-concentration (5.2–14.2 wt % NaCl equiv.) solutions without CO₂, with the predominance of Mg and Fe chlorides and an admixture of Na and K chlorides. The major ore minerals are pyrite, chalcopyrite, galena, and sphalerite; identified subordinate minerals are pyrrhotite, pentlandite, heazlewoodite, fahlore (tennantite, freibergite), Ni and Ag sulfosalts (ullmannite, miargyrite, polybasite, stephanite), Ag sulfides (mckinstryite, argentite); Au minerals are represented by electrum, kuestelite, and native gold of medium to low fineness. The geological, mineralogical, geochemical, and isotopic characteristics of ore indicate a metamorphic–hydrothermal genesis of mineralization related to the formation of a mélange zone in the duplex strike-slip structure. The sources of ore components are host rock complexes that have been subjected to tectonic deformations, among which rocks of an ophiolitic association predominate, along with fragments of initial hydrothermal–sedimentary ore, granitic, terrigenous, and carbonate rocks. The Late Paleozoic (352 Ma) age of mineralization corresponds to the stage of postcollision shear deformations within the entire Central Asian Foldbelt.     

Peculiarities of Ore Formation at the Teploe Ag–Au Deposit,Northeast Russia

The mineralogical–geochemical and thermobarogeochemical features of the Teploe Ag–Au epithermal deposit are considered. The dissolution and redeposition of ore minerals are a result of thermal metamorphism. The redistribution of Ag leads to the formation of lenaite and exsolution structures in minerals of the Cu–Ag–S system; abundant stromeyerite, jalpaite, and mckinstryite compose a significant amount of ores. The atypical physicochemical parameters of the formation of ores include high (for epithermal mineralization) temperatures and low salinity and density of the fluid typical of a dry vapor. The results of fluid inclusion study ascribe the Teploe deposit to an intermediate class of epithermal deposits.     

利用电子探针研究甘肃陇南赵家庄金矿载金矿物特征

应用偏光显微镜与电子探针相结合的手段是研究载金矿物的主要方法。本文采用镜下鉴定和电子探针分析技术,对赵家庄金矿中载金矿物含量、形态特征及其与其他矿物的空间关系开展研究,并对载金矿物进行定性和定量分析,探寻具有找矿意义的载金矿物和总结标志矿物特征。结果表明:研究区金矿石中主要载金矿物为黄铁矿,少量为黄铜矿、闪锌矿,这些载金矿物中Au含量依次为:细晶黄铁矿粗晶黄铁矿草莓状黄铁矿黄铜矿。不同时期的黄铁矿(粗晶黄铁矿、细晶黄铁矿、草莓状黄铁矿)中Au的分布均匀,但存在差异性,主要表现为细晶黄铁矿和草莓状黄铁矿中的Au含量较高(平均含量0. 14%～0. 18%),这种现象表明此类矿物为构造热液期形成,金易富集。Au以两种形式存在,一种是"可见金"包裹于脉石矿物中,或以裂隙金的形式嵌布在矿物晶隙及裂隙中;另一种是"不可见金"以纳米级颗粒金的形式存在于载金矿物中,也是Au的主要存在形式。本研究为后期矿床的成因、成矿过程和成矿机理研究提供了佐证,同时易于根据含金矿物的特征选择合适的选冶方法。     

Minerals in the Triassic carbonaceous silicites of Sikhote Alin

Over 60 minerals, including native elements, intermetallic compounds, haloids, sulfides, sulfates, arsenides, oxides and hydroxides, silicates, borosilicates, wolframates, phosphates and REE phosphates, were established in Triassic siliceous rocks of Sikhote Alin. Allothigenic and authigenic minerals in the carbonaceous silicites were formed over a long period through several stages. Judging from morphology, chemical composition, and structural position, K-feldspar (K-Fsp), illite, kaolinite, metahalloysite, monazite, xenotime, zircon, rutile, or its polymorphs are the disintegration products of sialic rocks of continental crust. Authigenic sulfides are dominated by diagenetic pyrite (fine-crystalline, microglobular, framboidal, as well as those developed after biogenic siliceous and carbonate fragments), which has been formed prior to precipitation of siliceous cement and lithification of siliceous rocks. Most of other sulfides (sphalerite, galena, chalcopyrite, pyrrhotite, argentite, pentlandite, antimonite, ulmanite, and bravoite), arsenides and sulfoarsenides (arsenopyrite, nickeline, skutterudite, cobaltite, glaucodot, and gersdorffite), wolframates (scheelite and wolframite), intermetallides (Cu₂Zn, Cu₃Zn₂, Cu₃Zn, Cu₄Zn, CuSn, Cu₄Sn, Cu₈Sn, Cu₄Zn₂Ni, Ni₂Cu₂Zn, Ni₄Cd), and native elements (Au, Pd, Ag, Cu, Fe, W, Ni, Se) were crystallized later (during catagenesis after the lithification and brecciation of siliceous beds) from metals involved in the easily mobile fractions of bitumens. Supergene mineral formation was mainly expressed in the sulfide oxidation and replacement of diagenetic pyrite by jarosite and iron hydroxides.     

Gold Mineralization of the Gatsuurt Deposit in the North Khentei Gold Belt,Central Northern Mongolia

Mineral assemblages, chemical compositions of ore minerals, wall rock alteration and fluid inclusions of the Gatsuurt gold deposit in the North Khentei gold belt of Mongolia were investigated to characterize the gold mineralization, and to clarify the genetic processes of the ore minerals. The gold mineralization of the deposit occurs in separate Central and Main zones, and is characterized by three ore types: (i) low‐grade disseminated and stockwork ores; (ii) moderate‐grade quartz vein ores; and (iii) high‐grade silicified ores, with average Au contents of approximately 1, 3 and 5 g t^?1 Au, respectively. The Au‐rich quartz vein and silicified ore mineralization is surrounded by, or is included within, the disseminated and stockwork Au‐mineralization region. The main ore minerals are pyrite (pyrite‐I and pyrite‐II) and arsenopyrite (arsenopyrite‐I and arsenopyrite‐II). Moderate amounts of galena, tetrahedrite‐tennantite, sphalerite and chalcopyrite, and minor jamesonite, bournonite, boulangerite, geocronite, scheelite, geerite, native gold and zircon are associated. Abundances and grain sizes of the ore minerals are variable in ores with different host rocks. Small grains of native gold occur as fillings or at grain boundaries of pyrite, arsenopyrite, sphalerite, galena and tetrahedrite in the disseminated and stockwork ores and silicified ores, whereas visible native gold of variable size occurs in the quartz vein ores. The ore mineralization is associated with sericitic and siliceous alteration. The disseminated and stockwork mineralization is composed of four distinct stages characterized by crystallization of (i) pyrite‐I + arsenopyrite‐I, (ii) pyrite‐II + arsenopyrite‐II, (iii) galena + tetrahedrite + sphalerite + chalcopyrite + jamesonite + bournonite + scheelite, and iv) boulangerite + native gold, respectively. In the quartz vein ores, four crystallization stages are also recognized: (i) pyrite‐I, (ii) pyrite‐II + arsenopyrite + galena + Ag‐rich tetrahedrite‐tennantite + sphalerite + chalcopyrite + bournonite, (iii) geocronite + geerite + native gold, and (iv) native gold. Two mineralization stages in the silicified ores are characterized by (i) pyrite + arsenopyrite + tetrahedrite + chalcopyrite, and (ii) galena + sphalerite + native gold. Quartz in the disseminated and stockwork ores of the Main zone contains CO₂‐rich, halite‐bearing aqueous fluid inclusions with homogenization temperatures ranging from 194 to 327°C, whereas quartz in the disseminated and stockwork ores of the Central zone contains CO₂‐rich and aqueous fluid inclusions with homogenization temperatures ranging from 254 to 355°C. The textures of the ores, the mineral assemblages present, the mineralization sequences and the fluid inclusion data are consistent with orogenic classification for the Gatsuurt deposit.     

北山地区金矿床金的赋存状态和金矿物特征

甘肃北山地区金矿床主要有岩浆热液型金矿床和与韧性剪切带有关的金矿床,矿化类型为石英脉型和蚀变岩型。金多呈独立金矿物形式出现,少放许呈分散状;金矿物以银金矿为主,次为自然金,平均成色７７２;金矿物以粒间金、裂隙金、连生金、连生金和包体金等形成嵌布于石英、黄铁矿、方铅矿及闪锌矿等主要载物较为发育。金矿物特征反映出本区金矿床的成矿物质主要来源于变质岩,华力西－印支期中酸性岩浆活动是主要的动力源。     

新疆哈密卡拉塔格块状硫化物矿床金银赋存状态研究

新疆哈密红海黄土坡VMS矿床位于东天山卡拉塔格隆起带,是卡拉塔格矿集区内新发现的块状硫化物矿床。矿体产于卡拉塔格隆起带核部火山沉积岩建造中,具有典型的VMS型矿床“上层下脉”二元结构特征。该矿床中含金硫化物矿石主要有块状黄铁矿黄铜矿、块状黄铁矿黄铜矿闪锌矿、块状黄铁矿闪锌矿黄铜矿和块状闪锌矿。文中在对各类含金硫化物矿石进行详细的矿相学研究基础上,结合扫描电子显微镜与能谱仪联用技术(SEM/EDS),对硫化物样品中金、银的赋存状态进行研究。结果表明,4种块状硫化物中的主要矿物形成于多个期次,主要包括VMS成矿期(黄铁矿阶段、闪锌矿黄铜矿黝铜矿方铅矿阶段、石英重晶石阶段)、热液叠加期(石英黄铁矿黄铜矿闪锌矿方铅矿阶段)和表生期(铜蓝纤铁矿阶段)。矿区首次发现4颗金银金属互化物(银金矿、碲银矿),其较大的化学成分差异指示了热液环境由中酸性中性转变为更有利于Au、Ag迁移沉淀的偏碱性。后期的偏碱性热液对VMS成矿期形成矿物产生了交代作用,使得Au、Ag活化再富集。由于后期热液叠加改造,红海VMS型矿床中Au、Ag不仅赋存于VMS成矿期后期中低温闪锌矿黄铜矿阶段,也赋存于VMS成矿期早期中高温黄铁矿阶段,并贯穿整个热液叠加期。各含金矿物组合中除4颗金银金属互化物外Au多呈显微不可见状态,推测Au、Ag主要以原子或离子形式赋存于矿物晶格中或矿物空位处。     

Genetic Environment of the Intrusion-related Yuryang Au-Te Deposit in the Cheonan Metallogenic Province, Korea

Abstract. The Yuryang gold deposit, comprising a Te‐bearing Au‐Ag vein mineralization, is located in the Cheonan area of the Republic of Korea. The deposit is hosted in Precambrian gneiss and closely related to pegmatite. The mineralized veins display massive quartz textures, with weak alteration adjacent to the veins. The ore mineralization is simple, with a low Ag/Au ratio of 1.5:1, due to the paucity of Ag‐phases. Ore mineralization took place in two different mineral assemblages with paragenetic time; early Fe‐sulfide mineralization and late Fe‐sulfide and Au‐Te mineralization. The early Fe‐sulfide mineralization (pyrite + sphalerite) occurred typically along the vein margins, and the subsequent Au‐Te mineralization is characterized by fracture fillings of galena, sphalerite, pyrrhotite, Te‐bearing minerals (petzite, altaite, hessite and Bi‐Te mineral) and electrum. Fluid inclusions characteristically contain CO₂ and can be classified into four types (Ia, Ib, IIa and IIb) according to the phase behavior. The pressure corrected temperatures (≥500d?C) indicate that the deposit was formed at a distinctively high temperature from fluids with moderate to low salinity (<12 wt% equiv. NaCl) and CH₄ (1?22 mole %). The sphalerite geo‐barometry yield an estimated pressure about 3.5 ?2.1 kbar. The dominant ore‐deposition mechanisms were CO₂ effervescence and concomitant H₂S volatilization, which triggered sulfidation and gold mineralization. The measured and calculated isotopic compositions of fluids (δ¹⁸O_H2^O = 10.3 to 12.4 %o; δD_H2^O = ‐52 to ‐77 %o) may indicate that the gold deposition originated from S‐type magmatic waters. The physicochemical conditions observed in the Yuryang gold deposit indicate that the Jurassic gold deposits in the Cheonan area, including the Yuryang gold deposit are compatible with deposition of the intrusion‐related Au‐Te veins from deeply sourced fluids generated by the late Jurassic Daebo magmatism.     

Mineralogy and textural relationships among sulphosalts and related minerals in the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway

Several distinct assemblages of Pb-Sb, Pb-As, Cu-Pb-Sb and Cu-Fe-Zn-Sn sulphosalts are identified in sulphide samples from Bleikvassli mine, Norway. Detailed optical microscopy and electron probe microanalysis have permitted investigation of textural relationships between minerals and compositional variations between different ore types. Tetrahedrite, typically containing 10–16?wt.% Ag (rare freibergite containing 25–30?wt.% Ag has also been identified in two samples), stannite (Cu₂(Fe>Zn)SnS₄), and meneghinite, CuPb₁₃Sb₇S₂₄, are widely distributed as trace constituents throughout massive pyritic and galena-rich ores. Native antimony and pyrargyrite occur in trace amounts in all ore types, as the breakdown products of earlier sulphosalts. Several distinct types of wall-rock mineralisation are present at Bleikvassli. Of considerable mineralogical interest are the coarse-grained sulphide mobilisates within the wall rock which contain a distinct?and characteristic suite of Pb-As sulphosalts:?tennantite?+?jordanite (Pb₁₄As₆S₂₃)?+?seligmannite (CuPbAsS₃) ± dufrenoysite (Pb₂As₂S₅). Bournonite (CuPbSbS₃) is the only Sb-bearing sulphosalt recognised in significant amounts within the mobilisates, meneghinite and tetrahedrite being conspicuously absent. These mobilisates display considerable Au enrichment; electrum can be confirmed, intimately associated with jordanite and tennantite. Appreciable Sb (up to 3?wt.%) is contained within galena in the mobilisates, in contrast to galena from massive ores which contains only negligible Sb. Contents of Ag and Bi in galena vary considerably in all ore types, but confirm earlier suggestions that galena is a major Ag-carrier at Bleikvassli. Boulangerite (Pb₅Sb₄S₁₁), jamesonite (FePb₄Sb₆S₁₄) and gudmundite (FeSbS) occur in trace amounts. Sn-sulphosalts are represented by kësterite, (Cu₂(Zn> Fe)SnS₄), but commonly zoned with respect to Zn/Fe ratio, in the mobilisates, rather than by stannite. A rare type of mobilisate, also in the wall rock, in which chalcocite and bornite are the main minerals, contains native Ag, stromeyerite (AgCuS), mckinstryite ((Ag,Cu)₂?S), Ag-free tetrahedrite, an unnamed Cu-Ag-Fe sulphide (Cu₃Ag₂FeS₄) and native Bi, myrmekitically intergrown with chalcocite. Although a comprehensive genetic model for the wall-rock mineralisation at Bleikvassli is largely impossible given the limitations in the present state of knowledge regarding mechanisms involved in remobilisation processes, a multi-stage model of remobilisation during regional metamorphism is considered to best explain the observations. An interplay of different solid- and liquid-state remobilisation mechanisms, in various combinations, is required to account for the macro- and microscopic observations. Remobilisation probably began during the earlier stages of metamorphism, with crystallisation and further remobilisation taking place during the entire metamorphic cycle, giving rise to the extensive chemical and mineralogical diversity observed today. Preserved mineral assemblages and their textural relationships reflect a complex sequence of replacement and decomposition reactions taking place during the latest phase of late-metamorphic crystallisation and subsequent cooling.     

Mineral chemical investigation on sulfide mineralization of the Istala deposit,Gümüşhane,NE-Turkey

The mineralogy of the Istala deposit, Gümüşhane, northeastern Turkey, was studied in detail, and a geochemical investigation was carried out using electron probe micro-analysis (EPMA). Sphalerite, galena, chalcopyrite and pyrite are the major sulfide minerals found in the Istala deposit, with minor amounts of bornite, idaite, tetrahedrite–tennantite, anilite, yarrowite, mckinstryite, covellite and chalcocite. In addition to these, barite and a small quantity of quartz occur as gangue minerals. Based on the textural relations and mineral assemblages, five different stages of crystallization have been recognized. Mineral paragenesis of the first four stages has been found to be similar, whereas clear enrichment has been observed in the modal abundance of the copper sulfide mineral assemblage at the fifth-stage ore formation. Whole-rock geochemical analyses of the Istala ore show an enrichment of Ag content up to 3328 ppm. Optical observations and EPMA study indicated that abundant silver mineralization was found in the Istala ore, especially during the later-stage ore deposition. Repetition to the presence of native silver in the samples, a significant amount of silver was incorporated in bornite, idaite, tetrahedrite–tennantite, anilite, yarrowite, mckinstryite, covellite and chalcocite, whereas a trace amount of silver has been detected in sphalerite, galena, chalcopyrite and pyrite. The homogenization temperatures (T_h) of the primary fluid inclusions were measured between 98 and 284 °C, with frequency peaks around 140 °C, 190 °C and 240 °C. All data obtained support the theory that later stage copper-rich sulfides, formed under the low temperature conditions, are responsible for the large amounts of silver content in the Istala mine.     

Mineralogy of the Boroo Gold Deposit in the North Khentei Gold Belt,Central Northern Mongolia

Mineral assemblages and chemical compositions of ore minerals from the Boroo gold deposit in the North Khentei gold belt of Mongolia were studied to characterize the gold mineralization, and to clarify crystallization processes of the ore minerals. The gold deposit consists of low‐grade disseminated and stockwork ores in granite, metasedimentary rocks and diorite dikes. Moderate to high‐grade auriferous quartz vein ores are present in the above lithological units. The ore grades of the former range from about 1 to 3 g/t, and those of the latter from 5 to 10 g/t, or more than 10 g/t Au. The main sulfide minerals in the ores are pyrite and arsenopyrite, both of which are divisible into two different stages (pyrite‐I and pyrite‐II; arsenopyrite‐I and arsenopyrite‐II). Sphalerite, galena, chalcopyrite, and tetrahedrite are minor associated minerals, with trace amounts of bournonite, boulangerite, geerite, alloclasite, native gold, and electrum. The ore minerals in the both types of ores are variable in distribution, abundance and grain size. Four modes of gold occurrence are recognized: (i) “invisible” gold in pyrite and arsenopyrite in the disseminated and stockwork ores, and in auriferous quartz vein ores; (ii) microscopic native gold, 3 to 100 µm in diameter, that occurs as fine grains or as an interstitial phase in sulfides in the disseminated and stockwork ores, and in auriferous quartz vein ores; (iii) visible native gold, up to 1 cm in diameter, in the auriferous quartz vein ores; and (iv) electrum in the auriferous quartz vein ores. The gold mineralization of the disseminated and stockwork ores consists of four stages characterized by the mineral assemblages of: (i) pyrite‐I + arsenopyrite‐I; (ii) pyrite‐II + arsenopyrite‐II; (iii) sphalerite + galena + chalcopyrite + tetrahedrite + bournonite + boulangerite + alloclasite + native gold; and (iv) native gold. In the auriferous quartz vein ores, five mineralization stages are defined by the following mineral assemblages: (i) pyrite‐I; (ii) pyrite‐II + arsenopyrite; (iii) sphalerite + galena + chalcopyrite; (iv) Ag‐rich tetrahedrite‐tennantite + bournonite + geerite + native gold; and (v) electrum. The As–Au relations in pyrite‐II and arsenopyrite suggest that gold detected as invisible gold is mostly attributed to Au⁺¹ in those minerals. By applying the arsenopyrite geothermometer to arsenopyrite‐II in the disseminated and stockwork ores, crystallization temperature and logfs₂ are estimated to be 365 to 300 °C and –7.5 to –10.1, respectively.     

安徽金寨迎峰崖含金银富铅锌多金属矿工艺矿物学研究

为查清安徽金寨迎峰崖含金银富铅锌多金属矿矿区内矿石的物质组分及矿物嵌布特征,采用化学多元素分析、光片和薄片镜下鉴定、X射线衍射分析以及单矿物组分分析等方法,对矿石的物质组分、矿物的嵌布特征进行分析测试。结果表明,矿石中主要矿物为方铅矿、闪锌矿、黄铜矿、黄铁矿、石英等。方铅矿、闪锌矿以包裹嵌镶或黏连镶布为主,细小的方铅矿与其他矿物毗邻,交代成因的闪锌矿呈融滴状分布于被交代矿物之上。Au充填于黄铁矿晶隙中;Ag在方铅矿中富集,主要以化合物形式存在;闪锌矿中有害组分Cd（2 697 mg/kg）严重超标,其他有害组分为Fe、S、As等。矿石矿物颗粒粒度以中粗粒为主。研究结果可为矿物分离及后期的开发利用提供参考。     

Formation of gold–silver sulfides and native gold in Fe–Ag–Au–S system

We carried out experiments on crystallization of Fe-containing melts FeS₂Ag_0.1–0.1xAu_0.1x (x = 0.05, 0.2, 0.4, and 0.8) with Ag/Au weight ratios from 10 to 0.1. Mixtures prepared from elements in corresponding proportions were heated in evacuated quartz ampoules to 1050 ºC and kept at this temperature for 12 h; then they were cooled to 150 ºC, annealed for 30 days, and cooled to room temperature. The solid-phase products were studied by optical and electron microscopy and X-ray spectroscopy. The crystallization products were mainly from iron sulfides: monoclinic pyrrhotite (Fe_0.47S_0.53 or Fe₇S₈) and pyrite (Fe_0.99S_2.01). Gold–silver sulfides (low-temperature modifications) are present in all synthesized samples. Depending on Ag/Au, the following sulfides are produced: acanthite (Ag/Au = 10), solid solutions Ag_2–xAu_xS (Ag/Au = 10, 2), uytenbogaardtite (Ag/Au = 2, 0.75), and petrovskaite (Ag/Au = 0.75, 0.12). They contain iron impurities (up to 3.3 wt.%). Xenomorphic micro- (<1–5 μm) and macrograins (5–50 μm) of Au–Ag sulfides are localized in pyrite or between the grains of pyrite and pyrrhotite. High-fineness gold was detected in the samples with initial ratio Ag/Au ≤ 2. It is present as fine and large rounded microinclusions or as intergrowths with Au–Ag sulfides in pyrite or, more seldom, at the boundary of pyrite and pyrrhotite grains. This gold contains up to 5.7 wt.% Fe. Based on the sample textures and phase relations, a sequence of their crystallization was determined. At ~1050 ºC, there are probably iron sulfide melt L₁ (Fe,S ? Ag,Au), gold–silver sulfide melt L₂ (Au,Ag,S ? Fe), and liquid sulfur L_S. On cooling, melt L₁ produces pyrrhotite; further cooling leads to the crystallization of high-fineness gold (macrograins from L₁ and micrograins from L₂) and Au–Ag sulfides (micrograins from L₁ and macrograins from L₂). Pyrite crystallizes after gold–silver sulfides by the peritectic reaction FeS + L_S = FeS₂ at ~743 ºC. Elemental sulfur is the last to crystallize. Gold–silver sulfides are stable and dominate over native gold and silver, especially in pyrite-containing ores with high Ag/Au ratios.     

Au–Ag–Te Mineralization of the Low‐Sulfidation Epithermal Aginskoe Deposit,Central Kamchatka,Russia

Mineralogic studies of major ore minerals and fluid inclusion analysis in gangue quartz were carried out for the for the two largest veins, the Aginskoe and Surprise, in the Late Miocene Aginskoe Au–Ag–Te deposit in central Kamchatka, Russia. The veins consist of quartz–adularia–calcite gangue, which are hosted by Late Miocene andesitic and basaltic rocks of the Alnei Formation. The major ore minerals in these veins are native gold, altaite, petzite, hessite, calaverite, sphalerite, and chalcopyrite. Minor and trace minerals are pyrite, galena, and acanthine. Primary gold occurs as free grains, inclusions in sulfides, and constituent in tellurides. Secondary gold is present in form of native mustard gold that usually occur in Fe‐hydroxides and accumulates on the decomposed primary Au‐bearing tellurides such as calaverite, krennerite, and sylvanite. K–Ar dating on vein adularia yielded age of mineralization 7.1–6.9 Ma. Mineralization of the deposit is divided into barren massive quartz (stage I), Au–Ag–Te mineralization occurring in quartz‐adularia‐clays banded ore (Stage II), intensive brecciation (Stage III), post‐ore coarse amethyst (Stage IV), carbonate (Stage V), and supergene stages (Stage VI). In the supergene stage various secondary minerals, including rare bilibinskite, bogdanovite, bessmertnovite metallic alloys, secondary gold, and various oxides, formed under intensely oxidized conditions. Despite heavy oxidation of the ores in the deposit, Te and S fugacities are estimated as Stage II tellurides precipitated at the log f Te₂ values ?9 and at log fS₂ ?13 based on the chemical compositions of hypogene tellurides and sphalerite. Homogenization temperature of fluid inclusions in quartz broadly ranges from 200 to 300°C. Ore texture, fluid inclusions, gangue, and vein mineral assemblages indicate that the Aginskoe deposit is a low‐sulfidation (quartz–adularia–sericite) vein system.     

Silver and silver-bearing minerals at the Um Samiuki volcanogenic massive sulphide deposit, Eastern Desert, Egypt

The Um Samiuki Zn–Cu–Pb–Ag mineralisation, south Eastern Desert, Egypt is hosted by felsic volcanic rocks which form part of the 712-Ma-old, east-west-trending Shadli Volcanic Belt. Two major occurrences of massive sulphides are present at the top of rhyolitic breccia in the Western and Eastern mine areas. In each occurrence, a bornite-bearing zone is overlain by a pyrite-chalcopyrite-bearing zone and underlain by a disseminated, Cu-depleted zone. In the massive sulphide ore, sphalerite, chalcopyrite, pyrite, galena, bornite and tetrahedrite–tennantite are major minerals, whereas arsenopyrite, pyrrhotite, molybdenite and magnetite are accessory phases. Covellite and digenite are common secondary minerals. Bornite, tetrahedrite–tennantite and covellite contain high amounts of silver (averages of 1.97, 1.39 and 1.82 wt% respectively). Based on mineralogical balance calculations, bornite and covellite accommodate 80% of silver in the Um Samiuki deposit. Ag was incorporated in the crystal structure of the early-crystallised copper sulphides and sulphosalts and silver minerals. The temperature, sequential precipitation of the fluids and the structure of the crystallising phases control the distribution of silver. Post-depositional deformation and metamorphic processes caused liberation, remobilisation and redeposition of silver within the massive sulphides.Editorial handling: D. Lentz     

Characteristics of Gold Mineralization at the Ciurug Vein, Pongkor Gold-Silver Deposit, West Java, Indonesia

Abstract. The Pongkor Gold‐Silver Mine, Bogor district, West Java, is approximately 80 km southwest of Jakarta. The gold and silver mineralization in the area is present in a deposit consisting of an epithermal vein‐system named individually as the Pasir Jawa, Gudang Handak, Ciguha, Pamoyanan, Kubang Cicau, and Ciurug veins. In the area studied, rocks of basaltic‐andesitic composition are dominated by volcanic breccia and lapilli tuff, with andesite lava and siltstone present locally. The hydrothermal alteration minerals in the Ciurug area are typical of those formed from acid to near‐neutral pH thermal waters, where the acid alteration is distributed from the surface to shallow depth, while the near‐neutral pH alteration becomes dominant at depths. The Ciurug vein shows four main mineralization stages where each discrete stage is characterized by a specific facies; these are, from early to late: carbonate‐quartz, manganese carbonate‐quartz, banded‐massive quartz and gray sulfide‐quartz facies. The major metallic minerals are pyrite, sphalerite, chalcopyrite and galena; they occur in almost each mineralization stage. Bornite was observed only in the southern part of the Ciurug vein at a depth of 515 m, and the occurrence of this mineral is reported here for the first time. Electrum and silver sulfides (mostly acanthite) are minor, whereas silver sulfosalts, stromeyerite and mckinstryite, and covellite are in trace amounts. The silver sulfosalts have compositional ranges of pearceite, antimon‐pearceite and polybasite. Most of the electrum occurs coexisting with other sulfide minerals, as inclusions in pyrite grains, with very little as inclusions in chalcopyrite or sphalerite. Gold grades within the Ciurug vein vary from 1.2 to hundreds of ppm, where the highest gold grade occurs in the latest mineralization stage in a thin sulfide band in vein quartz. Fluid inclusion microthermometry of calcite and quartz indicates deposition throughout the mineralized veins in the range from 170 to 230d?C and from low salinity fluids (predominantly lower than 0.2 wt% NaCl equiv.). Fluid inclusions occur with features of boiling.