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.     

U-Pb dating of scheelite,wolframite and apatite from the Woxi Au-Sb-W deposit,western Hunan Province and their geological significanceSCIEI北大核心CSCD

沃溪矿床位于湘西雪峰隆起区的转折部位,是该区金锑钨矿床的典型代表。该矿床成矿元素及成矿期次较为复杂,各成矿阶段的形成时代长期存在争议。本次研究在对沃溪矿床详细野外调查及岩相学观察的基础上,对深部中段矿体中的白钨矿、磷灰石及浅部中段矿体中的黑钨矿开展了U-Pb同位素分析。依据本次所获年龄数据,结合观察到的矿脉交切关系、矿物共生组合等特征,本文认为沃溪矿床除了加里东期成矿作用之外,还存在燕山期成矿作用。其中,白钨矿形成相对较早,成矿年龄为149.0±12Ma、144.8±1.7Ma、139.8±6.1Ma;黑钨矿与白钨矿同时生成(或稍晚),成矿年龄为137.8±3.9Ma、134.8±5.1Ma;自然金、辉锑矿主要在白钨矿、黑钨矿形成以后通过沉淀而成,且自然金在晚阶段(125.8±5.6Ma、123.8±4.6Ma)石英-碳酸盐脉中仍有少量产出。综合已有年代学资料推测,沃溪矿床可能在经历了加里东期陆内造山成矿作用之后,还经受了燕山期伸展构造背景下深部流体不同程度的叠加改造作用。而该矿床发现的矿脉原地破裂后被后期矿物胶结等现象,则指示其矿脉的形成与液压致裂作用有关,这种作用导致矿脉反复裂开-愈合,有利于成矿元素(尤其是金)的活化迁移和再富集沉淀。     

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.     

Petrology,Geochemistry, and Fluid Inclusion Microthermometry of Sphalerite from the Laloki and Federal Flag Strata‐Bound Massive Sulfide Deposits,Papua New Guinea: Implications for Gold Mineralization

The Laloki and Federal Flag deposits are two of the many (over 45) polymetallic massive sulfide deposits that occur in the Astrolabe Mineral Field, Papua New Guinea. New data of the mineralogical compositions, mineral textures, and fluid inclusion studies on sphalerite from Laloki and Federal Flag deposits were investigated to clarify physiochemical conditions of the mineralization at both deposits. The two deposits are located about 2 km apart and they are stratigraphically hosted by siliceous to carbonaceous claystone and rare gray chert of Paleocene–Eocene age. Massive sulfide ore and host rock samples were collected from each deposit for mineralogical, geochemical, and fluid inclusion studies. Mineralization at the Laloki deposit consists of early‐stage massive sulfide mineralization (sphalerite‐barite, chalcopyrite, and pyrite–marcasite) and late‐stage brecciation and remobilization of early‐stage massive sulfides that was accompanied by late‐stage sphalerite mineralization. Occurrence of native gold blebs in early‐stage massive pyrite–marcasite‐chalcopyrite ore with the association of pyrrhotite‐hematite and abundant planktonic foraminifera remnants was due to reduction of hydrothermal fluids by the reaction with organic‐rich sediments and seawater mixing. Precipitation of fine‐grained gold blebs in late‐stage Fe‐rich sphalerite resulted from low temperature and higher salinity ore fluids in sulfur reducing conditions. In contrast, the massive sulfide ores from the Federal Flag deposit contain Fe‐rich sphalerite and subordinate sulfarsenides. Native gold blebs occur as inclusions in Fe‐rich sphalerite, along sphalerite grain boundaries, and in the siliceous‐hematitic matrix. Such occurrences of native gold suggest that gold was initially precipitated from high‐temperature, moderate to highly reduced, low‐sulfur ore fluids. Concentrations of Au and Ag from both Laloki and Federal Flag deposits were within the range (<10 ppm Au and <100 ppm Ag) of massive sulfides at a mid‐ocean ridge setting rather than typical arc‐type massive sulfides. The complex relationship between FeS contents in sphalerite and gold grades of both deposits is probably due to the initial deposition of gold on the seafloor that may have been controlled by factors such as Au complexes, pH, and fO₂ in combination with temperature and sulfur fugacity.     

辽宁五龙金矿含金石英脉中石英标型特征及其找矿意义

辽宁五龙金矿含金石英脉中石英晶体的塑性变形显微裂隙和熔融现象普遍发育,在无矿石英脉中上述现象则不发育或缺失.气液包体在含金石英脉中数量多.成矿温度阶段性明显,沸腾现象也较发育.而在无矿石英脉中则反之.据包体化学成分推测成矿溶液化学成分属CO₂-H₂O-Cl-Na-Ca型,而无矿石英脉热液成分为CO₂-H₂O-F(Cl)-K-Ca(Mg)型,石英中微量元素浓集克拉克值(C_k)及相关系数表明Au、Sb、Bi、W、Ag为本区主要成矿元素.且含金石英脉的C_k值均大于无矿石英脉.热发光曲线在含金石英脉中主要为双峰和多峰型,而无矿石英脉则为单峰型,上述石英标型特征作为五龙金矿床石英脉中找金的重要标志.     

祁连山西段党河南山北坡3个不同特征的金矿床研究

黑刺沟金矿床以富As和Sb的微细浸染蚀变岩型金矿化和部分石英脉型锑－金矿化为特征,典型矿物组合为黄铁矿-毒砂(辉锑矿)-石英;贾公台金矿床以少硫化物石英脉型金矿化和蚀变岩型金矿化为特征,As和Sb的质量分数不高,典型矿物组合为黄铁矿-自然金(方铅矿)-石英-钾长石;鸡叫沟金矿床以蚀变岩型金矿化为主,次之为石英脉型金矿化,典型矿物组合为黄铁矿-黄铜矿-石英.3个金矿床的成因均与岩浆岩有密切联系,但各矿区的岩浆岩在岩石学、岩石化学、微量元素及稀土元素特征具有差异,表明其成因不尽相同.这可能是造成3个金矿床地质特征差异的主要原因.     

The Arinem Te‐Bearing Gold‐Silver‐Base Metal Deposit,West Java,Indonesia

The vein system in the Arinem area is a gold‐silver‐base metal deposit of Late Miocene (8.8–9.4 Ma) age located in the southwestern part of Java Island, Indonesia. The mineralization in the area is represented by the Arinem vein with a total length of about 5900 m, with a vertical extent up to 575 m, with other associated veins such as Bantarhuni and Halimun. The Arinem vein is hosted by andesitic tuff, breccia, and lava of the Oligocene–Middle Miocene Jampang Formation (23–11.6 Ma) and overlain unconformably by Pliocene–Pleistocene volcanic rocks composed of andesitic‐basaltic tuff, tuff breccia and lavas. The inferred reserve is approximately 2 million tons at 5.7 g t^?1 gold and 41.5 g t^?1 silver at a cut‐off of 4 g t^?1 Au, which equates to approximately 12.5t of Au and 91.4t of Ag. The ore mineral assemblage of the Arinem vein consists of sphalerite, galena, chalcopyrite, pyrite, marcasite, and arsenopyrite with small amounts of pyrrhotite, argentite, electrum, bornite, hessite, tetradymite, altaite, petzite, stutzite, hematite, enargite, tennantite, chalcocite, and covellite. These ore minerals occur in quartz with colloform, crustiform, comb, vuggy, massive, brecciated, bladed and calcedonic textures and sulfide veins. A pervasive quartz–illite–pyrite alteration zone encloses the quartz and sulfide veins and is associated with veinlets of quartz–calcite–pyrite. This alteration zone is enveloped by smectite–illite–kaolinite–quartz–pyrite alteration, which grades into a chlorite–smectite–kaolinite–calcite–pyrite zone. Early stage mineralization (stage I) of vuggy–massive–banded crystalline quartz‐sulfide was followed by middle stage (stage II) of banded–brecciated–massive sulfide‐quartz and then by last stage (stage III) of massive‐crystalline barren quartz. The temperature of the mineralization, estimated from fluid inclusion microthermometry in quartz ranges from 157 to 325°C, whereas the temperatures indicated by fluid inclusions from sphalerite and calcite range from 153 to 218 and 140 to 217°C, respectively. The mineralizing fluid is dilute, with a salinity <4.3 wt% NaCl equiv. The ore‐mineral assemblage and paragenesis of the Arinem vein is characteristically of a low sulfidation epithermal system with indication of high sulfidation overprinted at stage II. Boiling is probably the main control for the gold solubility and precipitation of gold occurred during cooling in stage I mineralization.     

Metal contents of recent thermal waters, mineral precipitates and hydrothermal alteration in active geothermal fields, Kamchatka

All the Kamchatkan recent hydrothermal systems are restricted to two volcanic zones, Central Kamchatka of Late Miocene-Pliocene age and East Kamchatka, where several active volcanoes are located. Solutions from active hydrothermal systems commonly contain elements, including As, Sb, Hg, Li, Rb, Cs, B, Cu, Pb, Zn, Ag, Au,Sr and Ba, with the first seven predominating. Higher abundances of ore elements occur in active hydrothermal systems with solutions of sodium chloride composition. Those are the Kireunskaya, Dvukhyurtochnaya and Apapelskaya systems in the Central Kamchatka volcanic zone and the Uzon hydrothermal system in the East Kamchatka volcanic zone. The hydrothermal systems are restricted to structures having very long histories of evolution and which are characterized by contrasting types of magmatism. At present chemical precipitates and altered rocks with higher abundances of As, Sb and trace amounts of Au, Ag, Cu, Ph and Zn are forming in the discharge zones of these hydrothermal systems. Large zones of alterations (alunitic quartzites^* and argillites) with high abundances of As, Sb, Hg, Cu, Pb, Ga and Zr occur in the Central Kamchatka volcanic zone. Here zones of mineralization (cinnabar, realgar, stibnite, orpiment, pyrite, chalcopyrite, sphalerite, galena) occur also; native gold, native silver and gudmundite occur rarely.In the recent Uzon caldera hydrothermal system, As-Sb-Hg mineralization with bitumen and oils is now forming. The ore deposit is zoned, with the most abundant ore minerals being realgar, uzonite, alacranite, stibnite and pyrite. Cinnabar, orpiment, marcasite and native mercury occur occasionally, and single grains of native gold, native silver and native copper are present. At present a total of 7000 t As, 350 t Sb and 200 t Hg have been deposited in the mineralization zone at geochemical boundaries. The general geological and geochemical data suggest that at depth the As-Sb-Hg mineralization may change to gold-silver mineralization.     

Geology and inclusion studies on the genesis of the Baolun gold deposit in Hainan Province,South China

The late Triassic Baolun gold deposit hosted by Silurian phyllites is a large‐scale high‐grade gold deposit in Hainan Island, South China. The ores can be classified into quartz‐vein dominated type and less altered rock type. Three mineralization stages were recognized by mineral assemblages. The early stage, as the most important mineralization stage, is characterized by a quartz–native gold assemblage. The muscovite?quartz?pyrite?native gold assemblage is related to the intermedium mineralization stage. In late mineralization stage, native gold and Bi‐bearing minerals are paragenetic minerals. Microthermometry analyses show that the early mineralization stage is characterized by two types of fluid inclusions, including CO₂‐rich inclusions (C‐type) and aqueous inclusions (W‐type). C‐type inclusions homogenize at 276–335°C with an averaged value of 306°C and have salinities of 1.0–10.0 wt% NaCl equivalent (mean value of 4.9 wt% NaCl equivalent). W‐type inclusions homogenize at 252–301°C (mean value of 278°C) with salinity of 4.0–9.7 wt% NaCl equivalent (mean value of 7.4 wt% NaCl equivalent). In intermedium mineralization stage, C‐type and W‐type inclusions homogenize at 228–320°C (mean value of 283°C) and 178–296°C (mean value of 241°C), with salinities of 2.4–9.9 wt% NaCl equivalent (mean value of 6.5 wt% NaCl equivalent) and 3.7–11.7 wt% NaCl equivalent (mean value of 7.7 wt% NaCl equivalent), respectively. No suitable mineral, such as quartz or calcite, was found for fluid inclusion study from late mineralization stage. In contrast, only aqueous inclusions were found from post‐ore barren veins, which yielded lower homogenization temperatures ranging from 168–241°C (mean value of 195°C) and similar salinities (2.6–12.6 wt% NaCl equivalent with averaged value of 7.2 wt% NaCl equivalent). The different homogenization temperatures and similar salinities of C‐type and W‐type from each mineralization stage indicate that fluid immiscibility and boiling occurred. The Baolun gold deposit was precipitated from a CO₂‐bearing mesothermal fluid, and formed at a syn‐collision environment following the closure of the Paleo‐Tethys.     

湘西沃溪钨锑金矿床超纯自然金

湘西沃溪钨锑金矿床产有自然界中十分罕见的超纯自然金。超纯自然金的Au含量在99 %以上 ,Fisher成色接近1000。自然金中含有Ag、Pb、Zn、Cu、As、Sb、Hg、Bi等显微化学组分。与一般自然金相比 ,超纯自然金的Ag 含量显著偏低 ,而Pb、Zn、As、Sb、Hg、Bi等显微化学组分含量趋于偏高 ,且较稳定。理论分析表明 ,超纯自然金的形成与强氧化性的酸性成矿流体有关。流体中金、银主要以MeCl2-(Me=Au或Ag)的络合物形式迁移。推断矿床成矿可能与区域中酸性岩浆活动有成因联系。     

Fluid Inclusion Microthermometry and Implications for the Mechanisms of Ore-Grade Gold Mineralization in Epithermal System, Lalab Orebody, Sibutad, Zamboanga del Norte, Philippines

The Sibutad gold deposit has gold associated in quartz veins. The most important of these is the Lalab orebody, which contains ore‐grade gold, predominantly, in milky quartz veins and veinlets. Here, alteration quartz and fine‐grained crystalline clear and milky quartz were formed from hydrothermal fluids in three stages, namely stages I, II and III. Fluid inclusion microthermometry was carried out on stage I milky quartz, stage II fine‐grained alteration quartz and stage III milky quartz ± barite veins and veinlets. Homogenization temperatures (T_H) are >248°C in stage I, 214–232°C in stage II and 186–239°C in stage III. These fluid inclusions have salinity between 1 and 2 wt% NaCl equivalent. In terms of gold assay, stage I drill‐core samples have gold grades 0.53–0.76 g/ton Au, stage II samples have 1.12–3.70 g/ton Au and stage III samples have 9.06–23.88 g/ton Au. This correlation suggests that gold was precipitated from the stage II and III fluids.     

Typomorpic Characteristics of the Major Minerals in the Puziwan Gold Deposit, Datong, Shanxi, China

Utilizing theories of minerageny and prospecting mineralogy, the authors studied the attitude, morphotype and chemical composition of metallic minerals of pyrite, gold, chalcopyrite, galena and sphalerite, non-metallic minerals of quartz, carbonate, dolomite and rutile in the Puziwan gold deposit. The study shows the following results. （1） The mineral assemblage is complex and the species of sulfide are abundant with occurrences of sulfosalt minerals. （2） The composition in the minerals is complex and there rich micro elements, including As, Sb, Bi, Se, Te, Au, Ag, Cu, Pb, Zn, and Cr, Ni, V. The typomorphic characteristics of the association of the elements and their specific value suggest that gold mineralization is associated with shallow magmatic hydrothermal activity, the oreforming fluid is the mixture of abundant rising alkali magmatic water originating from the mantle or the lower crust and the descending acid atmospheric water. （3） Ankerite, Fe-rich sphalerite, granular Ti-rich rutile are widely distributed, which indicate great denudation depths, high mineralization temperature. The deposit is found in the middle and shallow positions of the porphyry series. The deep layers are not favorable for gold mineralization. （4） Copper minerals are rich in the ores and sulfides have high content of copper, suggesting possible porphyry-type Cu （Au） mineralization in deep positions and the surrounding areas.     

Rb–Sr Dating of Gold‐Bearing Pyrite in the Jinchang Porphyry Cu–Au Deposit,Heilongjiang Province,NE China

The Jinchang Cu–Au deposit in Heilongjiang Province, NE China, is located in the easternmost part of the Central Asian Orogenic Belt. Rb–Sr analyses of auriferous pyrite from the deposit yielded an isochron age of 113.7 ±2.5 Ma, consistent with previously reported Re–Os ages. Both sets of ages represent the timing of Cu–Au mineralization because (i) the pyrite was separated from quartz–sulfide veins of the mineralization stage in granite porphyry; (ii) fluid inclusions have relatively high Rb, Sr, and Os content, allowing precise measurement; (iii) there are no other mineral inclusions or secondary fluids in pyrite to disturb the Rb–Sr or Re–Os decay systems; and (iv) the closure temperatures of the two decay systems are ≥500°C (compared with the homogenization temperatures of fluid inclusions of 230–510°C). It is proposed that ore‐forming components were derived from mantle–crust mixing, with ore‐forming fluids being mainly exsolved from magmas with minor amounts of meteoric water. The age of mineralization at Jinchang and in the adjacent regions, combined with the tectonic evolution of the northeast China epicontinental region, indicates that the formation of the Jinchang porphyry Cu–Au deposit was associated with Early Cretaceous subduction of the paleo‐Pacific Plate.     

Fluid Inclusion Studies of Comb Quartz and Stibnite at the Hishikari Au–Ag Epithermal Deposit,Japan

Fluid inclusion microthermometry was conducted on late‐stage barren comb quartz and the latest stibnite at the Hishikari deposit to characterize the hydrothermal activity responsible for vein formation. Eight fluid inclusion assemblages (i.e. fluid inclusions trapped at the same time, ‘FIAs’) were studied to determine the formation fluid temperatures and salinities for the comb quartz in the Shosen No. 2 vein, Sanjin ore zone, and the stibnite in the Seisen No. 1–1 vein, Yamada ore zone. The average homogenization temperatures (the formation temperatures) of the seven FIAs from the comb quartz were between 207 and 230°C, while the average homogenization temperature (the formation temperature) of an FIA from the stibnite was 113°C. The measured fluid salinities of the seven FIAs from the comb quartz were low, ranging between 0.0 and 1.1 wt% NaCl equiv., indicating that dilute fluids were responsible for the comb quartz formation. By comparison with previous microthermometric data, the formation temperatures of the studied comb quartz were higher than those of columnar adularia and comb quartz at most other veins (generally around 200°C) but were similar to those of columnar adularia at Keisen veins (230°C) in the same ore zone. The higher formation temperatures both in the Shosen and the Keisen veins in the Sanjin ore zone indicate that the fractures corresponding to the vein system at the Sanjin ore zone were main conduits for hot ascending fluids. The low formation temperature of stibnite in the latest stage (113°C) indicates that stibnite precipitation occurred during a waning stage of hydrothermal activity. Combined with previous thermodynamic data on antimony solubilities, the large discrepancy between the formation temperature of the comb quartz (200–230°C) and that of the stibnite suggests that the stibnite may have precipitated as a result of a drastic cooling of the hydrothermal system.     

Evolution of Hydrothermal System at the Dizon Porphyry Cu-Au Deposit, Zambales, Philippines

Abstract. Evolution of hydrothermal system from initial porphyry Cu mineralization to overlapping epithermal system at the Dizon porphyry Cu‐Au deposit in western central Luzon, Zambales, Philippines, is documented in terms of mineral paragen‐esis, fluid inclusion petrography and microthermometry, and sulfur isotope systematics. The paragenetic stages throughout the deposit are summarized as follows; 1) stockwork amethystic quartz veinlets associated with chalcopyrite, bornite, magnetite and Au enveloped by chlorite alteration overprinting biotite alteration, 2) stockwork quartz veinlets with chalcopyrite and pyrite associated with Au and chalcopyrite and pyrite stringers in sericite alteration, 3) stringer quartz veinlets associated with molybdenite in sericite alteration, and 4) WNW‐trending quartz veins associated with sphalerite and galena at deeper part, while enargite and stibnite at shallower levels associated with advanced argillic alteration. Chalcopyrite and bornite associated with magnetite in quartz veinlet stockwork (stage 1) have precipitated initially as intermediate solid solution (iss) and bornite solid solution (bnss), respectively. Fluid inclusions in the stockwork veinlet quartz consist of gas‐rich inclusions and polyphase inclusions. Halite in polyphase inclusions dissolves at temperatures ranging from 360d?C to >500d?C but liquid (brine) and gas (vapor) do not homogenize at <500d?C. The maximum pressure and minimum temperature during the deposition of iss and bnss with stockwork quartz veinlets are estimated to be 460 bars and 500d?C. Fluid inclusions in veinlet stockwork quartz enveloped in sericite alteration (stage 2) consist mainly of gas‐rich inclusions and polyphase inclusions. In addition to the possible presence of saturated NaCl crystals at the time of entrapment of fluid inclusions that exhibit the liquid‐vapor homogenization temperatures lower than the halite dissolution temperatures in some samples, wide range of temperatures of halite dissolution and liquid‐vapor homogenization of polyphase inclusions from 230d?C to >500d?C and from 270d?C to >500d?C, respectively, suggests heterogeneous entrapment of gaseous vapor and hypersaline brine. The minimum pressure and temperature are estimated to be about 25 bars and 245d?C. Fluid inclusions in veinlet quartz associated with molybdenite (stage 3) are dominated by gas‐rich inclusions accompanied with minor liquid‐rich inclusions that homogenize at temperatures between 350d?C and 490d?C. Fluid inclusions in vuggy veinlet quartz associated with stibnite (stage 4) consist mainly of gas‐rich inclusions with subordinate polyphase inclusions that do not homogenize below 500d?C. Fluid inclusions in veinlet quartz associated with galena and sphalerite (stage 4) are composed of liquid‐rich two‐phase inclusions, and they homogenize into liquid phase at temperatures ranging widely from 190d?C to 300d?C (suggesting boiling) and the salinity ranges from 1.0 wt% to 3.4 wt% NaCl equivalent. A pressure of about 15 bars is estimated for the dilute aqueous solution of 190d?C from which veinlet quartz associated with galena and sphalerite precipitated. In addition to a change in temperature‐pressure regime from lithostatic pressure during the deposition of iss and bnss with stockwork quartz veinlets to hydrostatic pressure during fracture‐controlled quartz veinlet associated with galena and sphalerite, a decrease in pressure is supposed to have occurred due to unroofing or removal of the overlying piles during the temperature decrease in the evolution of hydrothermal system. The majority of the sulfur isotopic composition of sulfides ranges from ±0 % to +5 %. Sulfur originated from an iso‐topically uniform and homogeneous source, and the mineralization occurred in a single hydrothermal system.     

湘西沃溪金矿床矿石矿物学特征及深部找矿意义

借助电子探针分析技术,对沃溪矿床V3矿脉深部(29中段)矿体进行了矿石矿物学观察和分析,发现深部矿体自然金中Ag、Sb、Pb、Bi等杂质元素的含量明显比浅部(24中段以上)自然金相应组分的含量偏高,深部自然金的成色(≤995)比浅部自然金的成色(≥999)明显偏低;深部矿体矿石中发育辉锑矿、黄铁矿、闪锌矿、黄铜矿、黝铜矿、硫锑矿、车轮矿等矿物,形成明显比浅部矿体组成复杂的矿物组合,显示矿床深部发育Au-Pb-zn-Bi±Cu的矿化作用.上述表明:沃溪矿床深部可能发育具Au-Pb-zn-Bi±Cu等元素组合的新矿体.它不同于浅部的W-Sb-Au元素组合的特征.因而深部找矿工作应多注重Au-Pb-zn-Bi+Cu多元素矿床.     

The Ore-forming Fluid of the Gold Deposits of Muru Gold Belt in Eastern Shandong, China - a Case Study of Denggezhuang Gold Deposit

Abstract. Denggezhuang gold deposit is an epithermal gold‐quartz vein deposit in northern Muru gold belt, eastern Shandong, China. The deposit occurs in the NNE‐striking faults within the Mesozoic granite. The deposit consists of four major veins with a general NNE‐strike. Based on crosscutting relationships and mineral parageneses, the veins appear to have been formed during the same mineralization epochs, and are further divided into three stages: (1) massive barren quartz veins; (2) quartz‐sulfides veins; (3) late, pure quartz or calcite veinlets. Most gold mineralization is associated with the second stage. The early stage is characterized by quartz, and small amounts of ore minerals (pyrite), the second stage is characterized by large amounts of ore minerals. Fluid inclusions in vein quartz contain C‐H‐O fluids of variable compositions. Three main types of fluid inclusions are recognized at room temperature: type I, two‐phase, aqueous vapor and an aqueous liquid phase (L+V); type II, aqueous‐carbonic inclusions, a CC₂‐liquid with/without vapor and aqueous liquid (LCO₂+VCC₂+Laq.); type III, mono‐phase aqueous liquid (Laq.). Data from fluid inclusion distribution, microthermometry, and gas analysis indicate that fluids associated with Au mineralized quartz veins (stage 2) have moderate salinity ranging from 1.91 to 16.43 wt% NaCl equivalent (modeled salinity around 8–10 wt% NaCl equiv.). These veins formatted at temperatures from 80d? to 280d?C. Fluids associated with barren quartz veins (stage 3) have a low salinity of about 1.91 to 2.57 wt% NaCl equivalent and lower temperature. There is evidence of fluid immiscibility and boiling in ore‐forming stages. Stable isotope analyses of quartz indicate that the veins were deposited by waters with δ^O and δD values ranging from those of magmatic water to typical meteoric water. The gold metallogenesis of Muru gold belt has no relationship with the granite, and formed during the late stage of the crust thinning of North China.     

山西省阳高县堡子湾金矿床矿物标型特征

根据成因矿物学及找矿矿物学观点，系统研究堡子湾金矿床黄铁矿、金矿物、方铅矿、黄铜矿和闪锌矿等金属矿物，石英、碳酸盐、绢(白)云母和金红石等非金属矿物的产状、形态及化学成分标型，结果表明：①矿床中矿物组合复杂，硫化物种类多，有少量硫盐矿物出现；②矿物中微量元素成分复杂，富含As，Sb，Bi，Se，Te等Au活化、迁移有利的矿化搬运剂，Cu，Ph，Zn，Au，Ag等成矿元素和Cr，Ni，V等深源元素；元素矿物组合及其特征比值指示金矿化与深源(下地壳或上地慢)浅成岩浆热液活动(斑岩系统)有关，燕山期石英二长斑岩(角砾岩)是成矿的主导因素；③矿石中大量出现铁白云石、富铁闪锌矿，粒状、富Ti金红石的大量分布，反映矿床剥蚀深度较大，目前可能已揭露至中深部中温带，位于斑岩系统的中下部，深部金矿化不利；④矿石含丰富的铜矿物，其他硫化物矿物中含铜量大，指示深部可能存在斑岩型Cu(Au)矿化。     

Alteration and mineralization styles of the orogenic disseminated Zhenyuan gold deposit,southeastern Tibet: Contrast with carlin gold deposit

Orogenic disseminated and Carlin gold deposits share much similarity in alteration and mineralization.The disseminated orogenic Zhenyuan Au deposit along the Ailaoshan shear zone,southeastern Tibet,was selected to clarify their difference.The alteration and mineralization from the different lithologies,including meta-quartz sandstone,carbonaceous slate,meta-(ultra)mafic rock,quartz porphyry and lamprophyre were researched.According to the mineral assemblage and replacement relationship in all types of host rocks,two reactions show general control on gold deposition:(1)replacement of earlier magnetite by pyrite and carbonaceous material;(2)alteration of biotite and phlogopite phenocrysts in quartz porphyry and lamprophyre into dolomite/ankerite and sericite.Despite the lamprophyre is volumetrically minor and much less fractured than other host rocks,it contains a large portion of Au reserve,indicating that the chemically active lithology has played a more important role in gold precipitation compared to structure.LA-ICP-MS analysis shows that Au mainly occurs as invisible gold in fine-grained pyrite disseminated in the host rocks,with Au content reaching to 258.95 ppm.The diagenetic core of pyrite in meta-quartz sandstone enriched in Co,Ni,Mo,Ag and Hg is wrapped by hydrothermal pyrite enriched in Cu,As,Sb,Au,Tl,Pb and Bi.Different host rock lithology has much impact on the alteration and mineralization features.Carbonate and sericite in altered lamprophyre show they have higher Mg than those developed in other of host rocks denoting that the carbonate and sericite incorporated Mg from phlogopite phenocrysts in the primary lamprophyre during alteration.The ore fluid activated the diagenetic pyrite in meta-quartz sandstone leading the hydrothermal pyrite enriched in Cu,Mo,Ag,Sb,Te,Hg,Tl,Pb and Bi,but the hydrothermal pyrite in meta-(ultra)mafic rock is enriched in Co and Ni as the meta-(ultra)mafic rock host rock contain high content of Co and Ni.However,Au and As shear similar range in both types of host rocks indicating that these two elements most likely come from the deep source fluid rather than the host rocks.It was shown in the disseminated orogenic gold deposit that similar hydrothermal alteration with mineral assemblage of carbonate(mainly dolomite and ankerite),sericite,pyrite and arsenopyrite develops in all types of host rocks.This is different from the Nevada Carlin type,in which alteration is mainly dissolution and silicification of carbonate host rock.On the other hand,Au mainly occur as invisible gold in both disseminated orogenic and Carlin gold deposits.     

Rare earth element geochemistry of the Woxi W–Sb–Au deposit, Hunan Province, South China

The Woxi W–Sb–Au deposit in Hunan, South China, is hosted by Proterozoic metasedimentary rocks, a turbiditic sequence of slightly metamorphosed (greenschist facies), gray-green and purplish red graywacke, siltstone, sandy slate, and slate. The mineralization occurs predominantly (> 70%) as stratabound/stratiform ore layers and subordinately as stringer stockworks. The former consists of rhythmically interbedded, banded to finely laminated stibnite, scheelite, quartz, pyrite and silty clays, whereas the latter occurs immediately beneath the stratabound ore layers and is characterized by numerous quartz + pyrite + gold + scheelite stringer veins or veinlets that are typically either subparallel or subvertical to the overlying stratabound ore layers. The deposit has been the subject of continued debate in regard to its genesis. Rare earth element geochemistry is used here to support a sedimentary exhalative (sedex) origin for the Woxi deposit. The REE signatures of the metasedimentary rocks and associated ores from the Woxi W–Sb–Au deposit remained unchanged during post-depositional processes and were mainly controlled by their provenance. The original ore-forming hydrothermal fluids, as demonstrated by fluid inclusions in quartz from the banded ores, are characterized by variable total REE concentrations (3.5 to 136 ppm), marked LREE enrichment (La_N/Yb_N = 28–248, ∑LREE/∑HREE = 16 to 34) and no significant Eu-anomalies (Eu/Eu = 0.83 to 1.18). They were most probably derived from evolved seawater that circulated in the clastic sediment pile and subsequently erupted on the seafloor. The bulk banded ores are enriched in HREE (La_N/Yb_N = 4.6–11.4, ∑LREE/∑HREE = 3 to 14) and slightly depleted in Eu (Eu/Eu = 0.63 to 1.14) relative to their parent fluids. This is interpreted as indicating the influence of seawater rather than a crystallographic control on REE content of the ores. Within a single ore layer, the degree of HREE enrichment tends to increase upward while the total REE concentrations decrease, reflecting greater influence and dilution of seawater. There is a broad similarity in chondrite-normalized REE patterns and the amount of REE fractionation of the banded ores in this study and exhalites from other sedex-type polymetallic ore deposits, suggesting a similar genesis for these deposits. This conclusion is in agreement with geologic evidence supporting a syngenetic (sedex) model for the Woxi deposit.