自然界中的辉锑矿-硒锑矿矿物系列

自然界中的辉锑矿-硒锑矿系列发现于西秦岭寒武系拉尔玛、邛莫金矿床中。与其密切共生的矿物有硒汞矿、硒铅矿、硒质块硫锑铜矿、硒镍矿、自然金以及石英、重晶石等。辉锑矿–硒锑矿系列的显微压力硬度为101.26~103 kg/mm²。主要元素的质量分数为: Sb 43.78%~73.81%,S 0.00%~28.76%,Se 0.00%~49.72%(但缺乏30.59%~43.04%之间的数据)。根据电子探针分析数据中Se/(S+Se)比值(原子比),可将所测矿物系列划分为(含硒质)辉锑矿、硒质辉锑矿、硫质硒锑矿和(含硫质)硒锑矿。矿物系列代表性的反射率(%)：(470 nm)Rg’=42.62~47.62,Rp’=30.83~40.55;(550 nm)Rg’=41.84~46.75,Rp’=31.48~38.85;(590 nm)Rg’=42.25~46.63,Rp’=30.73~39.46;(650 nm)Rg’=43.30~46.48,Rp’=30.01~41.56。两个含Se量为3%~5%含硒质辉锑矿的晶胞参数值为:a=1.120 9~1.121 2 nm,b=1.1299~1.130 3 nm,c=0.384 7~0.384 9 nm;而硫质硒锑矿、硒锑矿的晶胞参数值分别为：a=1.159 1~1.159 3 nm;b=1.172 4~1.174 7 nm;c=0.394 1~0.398 4 nm。晶胞参数的变化与矿物中硫、硒含量变化密切相关。     

邛莫金矿床中的硒辉锑矿

硒辉锑矿产于西秦岭邛莫金矿床中。与其共生的矿物有灰硒汞矿、灰硒铝矿、硒锑矿、硒块硫锑铜矿、硒镍矿、自然金以及石英、重晶石等。该矿物显微硬度VHN50＝68．25～128．0kg／mm2,平均101．26kg／mm2,相当于摩氏硬度3．15、30个测点的电子探针分析结果（％）：Sb57．75～66．79（平均63．25）,S11．86～21．62（平均17．30）,Se12．82～29．12（平均19．27）,据其平均值计算的化学分子式为：Sb1．99（S2．07,Se0．93）3．00,简写式为Sb2（S,Se）3。代表性的反射率（％）：（470nm）Rα’＝45．33,Rγ’＝31．03;（550nm）Rα’＝46．75,Rγ’＝33．63;（590nm）Rα’＝46．06,Rγ’＝：33．50;（650nm）Rα’＝45．18,Rγ’＝31．49。对两个Se含量仅达3％～5％的辉锑矿粉晶分析所得晶胞参数值为：a＝1．1209～1,1212nm,b=1．1299～1,1303nm,c＝0．3847～0,3849nm。与辉锑矿相比十分相似。     

邛莫金矿床中块硫锑铜矿含硒性及其特征

硒的块硫锑铜矿产于西秦岭邛莫金矿床中,与其伴生的矿物有硒汞矿、硒铅矿、硒锑矿、斜方硒镍矿、硒铜镍矿、硒质辉锑矿、自然金以及石英、重晶石等。 含硒的块硫锑铜矿平均显微硬度VHN50=247.5kg/mm2,相当于摩氏硬度4.2。电子探 针分析结果(w,％)为：Sb 25.79,Cu 38.20,S 21.12,Se 1 2.76,Hg 0.0 0～1.49(平均0.58),Ag 0.00～0.33(平均0.09),As 0.00～2.01(平均0.76)。根据成分中S e/(S+Se)比值(原子比)＜0.2抑≥0.2,可将所测矿物划分为含硒质块硫锑铜矿与硒质块硫锑 铜矿。它们的化学分子式分别为: (Cu2.84Hg0.01)2.85(Sb1.00A s0.07)1.07(S3.54Se0.46) 4.00和(Cu3.05Hg0.03)3.08(Sb1.07As0.03) 1.10(S2.77Se1.23)4.00。代表性的反射率(％): (470nm) Rγ'=22.84～22.50, Rα'= 27.92～27.99; (550 nm) Rγ'= 22.63～22.76, Rα'=2 7. 79～28.11; (590nm) Rγ'=22.92～22.08, R α'=28.27～28. 72; (650nm) Rγ'=23.08～23.76, Rα'=28.79～29.13。     

我国甘肃硒汞矿的发现及研究

硒汞矿产于甘肃省拉尔玛金矿床中,主要共生矿物有石英、重晶石、辉锑矿、黑辰砂、自然金等。硒汞矿呈铅灰色到黑色,金属光泽,性脆。粒度0.01～0.36mm。比重D=8.27,摩氏硬度2.5。电子探针定量分析结果的平均值(%):Hg 71.50,Se 25.21,S 1.88,Au 0.19,Ag 0.07,Te 0.09,As 0.06,Sb 0.04,Fe 0.04,总和99.08。空间群。a=0.6081(1)nm,Z=4。     

卡林型金矿床中自然砷的特征与成矿物理化学条件示踪

在"滇黔桂"、"川甘陕"两个金三角密集区内的某些卡林型金矿床中,自然砷矿物的存在并非个别现象。自然砷呈致密块状、致密凝胶体状(肾状)、脉状或微细脉状产出。自然砷呈他形粒状,颗粒大小变化较大,一般为0.05～0.50mm,最大可达2mm。反光显微镜下为白色,显微硬度为114.21～150.60kg/mm2,相当于摩氏硬度3.27～3.59。矿物主要化学成分As的质量分数为92.74%～99.74%,并含有S0.18%～5.25%,Sb0.04%～3.65%。矿物为三方晶系,晶胞参数值a=0.3759nm,c=1.0527nm。利用矿床中含砷矿物的共生组合特点及热力学资料,探讨了卡林型金矿床形成的温度、成矿流体的f(O2)、f(S2)变化范围及金以金砷络合物形式迁移的可能性。     

Paragenesis and geochemistry of ore minerals in the epizonal gold deposits of the Yangshan gold belt,West Qinling,China

Six epizonal gold deposits in the 30-km-long Yangshan gold belt, Gansu Province are estimated to contain more than 300 t of gold at an average grade of 4.76 g/t and thus define one of China's largest gold resources. Detailed paragenetic studies have recognized five stages of sulfide mineral precipitation in the deposits of the belt. Syngenetic/diagenetic pyrite (Py₀) has a framboidal or colloform texture and is disseminated in the metasedimentary host rocks. Early hydrothermal pyrite (Py₁) in quartz veins is disseminated in metasedimentary rocks and dikes and also occurs as semi-massive pyrite aggregates or bedding-parallel pyrite bands in phyllite. The main ore stage pyrite (Py₂) commonly overgrows Py₁ and is typically associated with main ore stage arsenopyrite (Apy₂). Late ore stage pyrite (Py₃), arsenopyrite (Apy₃), and stibnite occur in quartz ± calcite veins or are disseminated in country rocks. Post-ore stage pyrite (Py₄) occurs in quartz ± calcite veins that cut all earlier formed mineralization. Electron probe microanalyses and laser ablation-inductively coupled plasma mass spectrometry analyses reveal that different generations of sulfides have characteristic of major and trace element patterns, which can be used as a proxy for the distinct hydrothermal events. Syngenetic/diagenetic pyrite has high concentrations of As, Au, Bi, Co, Cu, Mn, Ni, Pb, Sb, and Zn. The Py₀ also retains a sedimentary Co/Ni ratio, which is distinct from hydrothermal ore-related pyrite. Early hydrothermal Py₁ has high contents of Ag, As, Au, Bi, Cu, Fe, Sb, and V, and it reflects elevated levels of these elements in the earliest mineralizing metamorphic fluids. The main ore stage Py₂ has a very high content of As (median value of 2.96 wt%) and Au (median value of 47.5 ppm) and slightly elevated Cu, but relatively low values for other trace elements. Arsenic in the main ore stage Py₂ occurs in solid solution. Late ore stage Py₃, formed coevally with stibnite, contains relatively high As (median value of 1.44 wt%), Au, Fe, Mn, Mo, Sb, and Zn and low Bi, Co, Ni, and Pb. The main ore stage Apy₂, compared to late ore stage arsenopyrite, is relatively enriched in As, whereas the later Apy₃ has high concentrations of S, Fe, and Sb, which is consistent with element patterns in associated main and late ore stage pyrite generations. Compared with pyrite from other stages, the post-ore stage Py₄ has relatively low concentrations of Fe and S, whereas As remains elevated (2.05～3.20 wt%), which could be interpreted by the substitution of As^? for S in the pyrite structure. These results suggest that syngenetic/diagenetic pyrite is the main metal source for the Yangshan gold deposits where such pyrite was metamorphosed at depth below presently exposed levels. The ore-forming elements were concentrated into the hydrothermal fluids during metamorphic devolatilization, and subsequently, during extensive fluid–rock interaction at shallower levels, these elements were precipitated via widespread sulfidation during the main ore stage.     

硒硫锑矿的首次发现及其初步研究

硒硫锑矿首次发现于西秦岭南亚带拉尔玛金-铜-铀建造矿床中。与其共生的矿物有:自然金,灰硒汞矿,灰硒铅矿,硒锑矿,辉砷铜矿,辉砷镍矿,硒硫锑铜矿,另外还有两种含硒的矿物可能是硒镍矿,硒金矿。该矿物颗粒细小,粒度为0.01—0.5mm。显微硬度VHN_(50)=68.25—128.0kg/mm~2。电子探针分析结果(W_B/%):Sb 59.75—68.52,S 12.08—23.71,Se6.88—27.50。据其平均值所计算的分子式为Sb_(2.0455) Hg_(0.0051) (S_(2.1818)Se_(0.8182)_3,简写式为Sb_2(S,Se)_3。含硒量低的硒硫锑矿的粉晶数据与辉锑矿大致相似。     

皖南锑矿带富硒,碲辉锑矿的矿物学特征及其地质意义

本文讨论了皖南锑矿辉锑矿的产形、形态、物性、化学成分、硫同位素组成等特征，得出如下结论：辉锑矿形成于中低温热液环境，辉锑矿的ａ０值与形成温度呈负相关；辉锑矿为富Ｓｅ，Ｔｅ辉锑矿，Ｓｅ，Ｔｅ有综合利用价值；皖南锑矿带很可能是Ｓｅ，Ｔｅ成矿远景区。     

A Study on the Mineralization of the Woxi Au–Sb–W Deposit,Western Hunan,China

The Woxi Au–Sb–W deposit in the western Hunan Province, China, is of hydrothermal vein type characterized by a rare mineral assemblage of stibnite, scheelite and native gold, of which gold fineness ranges from 998.6 to 1000. The mineralization sequence observed in the deposit is, from early to late, coarse‐grained pyrite – scheelite – stibnite – Pb–Sb–S minerals – sphalerite (+ cubanite) – fine‐grained pyrite. Native gold may have precipitated with scheelte. Microthermometric and LA–ICP–MS analyses of fluid inclusions in scheelite, quartz associated with scheelite and stibnite and barren quartz clarified that there may be at least three types of hydrothermal fluids during the vein formation in the Woxi deposit. Scheelite and native gold precipitated from the fluid of high temperature and salinity with high concentrations of metal elements, followed by stibnite precipitation. The later fluid of the highest temperature and salinity with low concentrations of the elements yielded the sphalerite mineralization. The latest fluid of low temperature and salinity with low concentrations of the elements is observed mainly in barren quartz. The remarkably high Au/Ag concentration ratios determined in the fluid inclusions in scheelite might be the reason for the extremely high gold fineness of native gold.     

Minerals of the beudantite–segnitite series from the oxidation zone of the Berezovskoe gold deposit,middle Urals: Chemical variations,behavior of admixtures,and antimonian varieties

In the oxidation zone of the Berezovskoe gold deposit in the middle Urals, Russia, minerals of the beudantite–segnitite series (idealized formulas PbFe₃ ³⁺ AsO₄)(SO₄)(OH)₆ and PbFe₃ ³⁺ AsO₄)(AsO₃OH)(OH)₆, respectively) form a multicomponent solid solution system with wide variations in the As, S, Fe, Cu, and Sb contents and less variable P, Cr, Zn, Pb, and contents K. The found minerals of this system correspond to series from beudantite with 1.25 S apfu to S-free segnitite, with segnitite lacking between 1.57 and 1.79 As apfu. Segnitite at the Berezovskoe deposit contains presumably pentavalent Sb (up to 15.2 wt % Sb₂O₅ = 0.76 Sb apfu, the highest Sb content in the alunite supergroup minerals), which replaces Fe³⁺. The Sb content increases with increasing As/S value. On the contrary, beudantite is free of or very poor in Sb (0.00–0.03 Sb apfu). Many samples of segnitite are enriched in Cu (up to 8.2 wt% CuO = 0.83 Cu apfu, uncommonly high Cu content for this mineral) and/or in Zn (up to 2.0 wt% ZnO = 0.19 Zn apfu). Both Cu and Zn replace Fe. The generalized formula of a hypothetic end member of the segnitite series with 1 Sb apfu is Pb(Fe³⁺ M ²⁺Sb⁵⁺)(AsO₄)₂(OH)₆, where M = Cu, Zn, Fe²⁺. The chemical evolution of beudantite–segnitite series minerals at the Berezovskoe deposit is characterized by an increase in the S/As value with a decrease in the Sb content from early to late generations.     

甘肃枣子沟金矿床成矿过程分析——来自矿床地质特征、金的赋存状态及稳定同位素证据

枣子沟金矿位于同仁-夏河-岷县金成矿带,矿区赋矿地层为三叠纪中统古浪堤组下段细碎屑岩及灰岩,并发育大量闪长质脉岩。矿体既产于地层中,也出现在脉岩或其接触带中,但其产状均严格受NE、NW及近SN向3组断裂构造控制,控矿构造为高角度的张剪性及旋扭性断裂。热液成矿期可划分为黄铁矿-石英阶段,黄铁矿-毒砂-(闪锌矿-方铅矿-黄铜矿-辉银矿-绢云母-绿泥石-)石英阶段,辉锑矿-石英-方解石阶段及石英-方解石阶段。围岩蚀变类型主要为硅化、方解石化及绢云母化。环境扫面电镜及电子探针测试数据表明,金呈显微可见金存在于矿物裂隙和粒间隙中或以纳米不可见金捕获在载金矿物中。成矿期不同硫化物金的质量分数均高出检测限,其范围为0.003%～0.658%,平均值为0.257%。枣子沟金矿床具有卡林型金矿床的典型特征。氢氧同位素数据显示成矿流体主要来自大气水,硫同位素数据则表明硫主要来自沉积地层。其成矿过程可能为深切割断裂导通地下水,在深部被加热循环萃取围岩中成矿物质,并在浅表张性断裂中充填交代围岩,致使成矿物质沉淀富集成矿。金的迁移形式可能存在AuH3SiO04、Au(HS)2-、H2Au(Sb,As)S02和HAu(Sb,As)S3-等多种迁移方式。成矿早阶段可能以金硅络合物的解体为主,成矿晚阶段则可能是硫氢(锑)络合物发生解体,致使金与硫化物同时沉淀,以显微纳米金的形式包含在硫化物中。     

Invisible gold in ore and mineral concentrates from the Hillgrove gold-antimony deposits, NSW, Australia

Vein-hosted mesothermal stibnite-gold mineralisation at the Hillgrove Au-Sb mine in northeastern New South Wales has a halo of veinlet and disseminated auriferous arsenopyrite and arsenian pyrite in metasedimentary and granitic host rocks. About 50–55% of the gold produced at Hillgrove occurs invisibly in arsenopyrite and pyrite. Gold losses of ∼20% into tailings are due to this mineral chemical factor. From PIXE probe analyses, it has been found that arsenopyrite contains 255–1500 ppm Au and pyrite 24–223 ppm Au, with Au contents of each mineral correlating moderately with As content. Arsenopyrite and pyrite also contain anomalous values of Cu, Ag and Sb, whereas paragenetically later stibnite contains little invisible gold, but minor Fe, As, Ag, Cu and Pb. The precipitation of invisible gold in arsenopyrite and pyrite by a possible (Fe, Au)³⁺= (As-S)³⁻ substitution mechanism may have been facilitated by rapid, non-equilibrium conditions involving pressure decreases and wall rock reaction (sulphidation, carbonatisation), as a prelude to the main stage of stibnite and gold deposition. Received: 15 January 1999 / Accepted: 12 October 1999     

Low-temperature crystal structures of stibnite implying orbital overlap of Sb 5s2 inert pair electrons

The crystal structure of stibnite [Sb₂S₃, Pnma, a=11.314(2), b=3.837(2), c=11.234(3) Å, V= 487.7(3) ų at 293 K] was refined in situ at 230, 173, and 128 K. It is a major characteristic of the structure that the Sb–S secondary bonds enclosing Sb 5s² inert lone-pair electrons at 293 K are significantly shorter than the corresponding sum of the Sb and S van der Waals radii. Concerning the temperature dependence, although both the polyhedral volume and the cation eccentricity of the two SbS₇ polyhedra exhibit continuous contractions with decreasing temperature, the sphericity values remain constant, indicating isotropic shrinkage. Consequently, the geometries of Sb 5s² inert lone-pair electrons and ligand atoms remain unchanged at low temperatures. This is because the crystal structure of stibnite at low temperature induces contraction with attractive interactions, which is called the orbital overlap between Sb 5s² inert lone-pair electrons and ligand orbitals to maintain the coordination environment. In this case, Sb 5s² lone-pair electrons are not inert, but active. Such orbital overlaps of inert lone-electron pairs can provide a reasonable explanation for shorter secondary bonds and lower band gap energy of the binary compounds containing heavy elements such as Sb, Te, Pb, and Bi, which are key factors in tracing the origins of color, luster, and semiconductivity of their minerals or compounds.     

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.     

浙江火山岩区金矿床黄铁矿的找矿矿物学研究

论文给出了中国浙江火山岩区金矿床中黄铁矿的微量元素、形态和物理性质找矿标型特征.例如.(在许多)浙江火山岩区重要金-银矿床中黄铁矿相对富含铅、锌、钼、锡、砷、锑、铋而贫钴,镍、硒、碲:并且S/Se、Ag/Au、Pb/Ni、Se/Te、(As+sb+Bi)/(Se+Te)比值较高,Co/Nj、Ag/Pb、Ag/Zn、Cu/Zn和(Co+Ni)/(Pb+Zn)比值较低,再如含金黄铁矿比不含金黄铁矿的反射率低.总之,黄铁矿的标型性研究对于寻找金矿具有重大的理论意义和实际意义.     

Sulfur Isotope Study on Hg and Sb Deposits in Japan

Abstract. Sulfur isotope ratios of cinnabar from Hg deposits and stibnite, jamesonite and berthierite from Sb deposits in Japan are examined in order to understand metallogeneses of Hg and Sb deposits in Japanese island arcs. The studied Hg and Sb deposits include the Hg deposit at Yamato‐suigin (Honshu) and the Sb deposit at Ichinokawa (Shikoku) in the Southwest Japan arc. In addition, Hg deposits including Itomuka and Ryushoden in central Hokkaido and Hg and Sb mineralizations in Northeast Japan arc are examined. The δ³⁴S values of cinnabar from the Hidaka‐Kitami district, central Hokkaido, including the Itomuka and Ryushoden deposits range widely, from ‐10 to +16 %o, the highest values encountered at the Samani deposit. The δ³⁴S values of cinnabar from other areas in Japan range from ‐12 to +5 %o, having δ³⁴S values higher than +2 %o from southwestern Hokkaido (Meiji deposit), Shikoku (Suii deposit) and Kyushu (Hasami and Yamagano deposits). On the other hand, the δ³⁴S values of stibnite from all areas in Japan range from ‐14 to +5 %o, having positive δ³⁴S values higher than +2 %o up to +5 %o from southwestern Hokkaido (Yakumo, Toyotomi and Teine deposits) and eastern‐central Honshu (Hachiman and Daikoku deposits). The variation in δ³⁴S values of Hg and Sb deposits may reflect the variation in δ³⁴S values of country rocks or variation in mixing ratio of sulfur extracted from the country rocks, sulfur derived from seawater sulfate, and sulfur derived from magmatic emanations. The relatively high δ³⁴S values of cinnabar and stibnite higher than +2 %o from southwestern Hokkaido, eastern‐central Honshu and Kyushu are probably caused by contribution of volcanic emanation from arc magmas having positive σδ³⁴S values, whereas the positive δ³⁴S values of cinnabar higher than +2 %o from Suii deposit in Shikoku may be attributed to structurally substituted sulfate in limestone country rocks and/or sulfur derived from seawater sulfate. However, the wide range of the δ³⁴S values of cinnabar from the Hidaka‐Kitami district, central Hokkaido, is difficult to explain at this moment. Other relatively low, negative δ³⁴S values of cinnabar and stibnite, berthierite from other areas in Japan may be attributed to 1) incorporation of isotopically light sedimentary sulfur or sulfur derived from ilmenite‐series silicic magma, or 2) less contribution of volcanic emanation from arc magmas having positive σδ³⁴S values.     

Migration paths and precipitation mechanisms of ore-forming fluids at the Shuiyindong Carlin-type gold deposit,Guizhou, China

Shuiyindong is one of the largest and highest grade stratabound Carlin-type gold deposits in China. This paper reports on the results of petrographic studies, electron microprobe analyses (EMPA) of arsenian pyrite, and the mass transfer during mineralization and alteration, and it presents the deposit-scale distributions of Au, As, Sb, Hg, Tl, and trace elements in a representative cross section across the Shuiyindong Carlin-type gold deposit, Guizhou Province. The main objectives were to identify the precipitation mechanisms of minerals, or elements from fluids, and the migration paths of ore-forming fluids.Petrographic and EMPA studies indicate that gold in the primary ores is mainly hosted by arsenian pyrite. Mass transfer associated with alteration and mineralization shows that Au, As, Sb, Hg, Tl, and S were significantly added to all mineralized rocks, Fe₂O₃ and SiO₂ were immobile in the main orebodies that are hosted in bioclastic limestone, and CaO, Na₂O, Sr, and Li were removed from country rocks. The relations between Fe and S indicate that the sedimentary rocks at the Shuiyindong deposit contain more iron than is needed to combine with all of their contained sulfur to form pyrite. This suggests that sulfidation and decarbonation were the principal mechanism of gold precipitation at the Shuiyindong deposit. Hg, Sb, and As commonly formed sulfide minerals, such as stibnite, realgar, and orpiment, in late-stage quartz–calcite veins, or absorbed by organic matter in argillite. Fluid cooling presumably led to depositions of stibnite, realgar, and orpiment in late-stage quartz–calcite veins. Organic matter likely served as a reductant in argillite for the ore fluids, causing the precipitation of As, Sb, Hg, and S, as well as Au.Deposit-scale distributions of gold and other relevant elements reflect the passage of fluids through the rocks. Rock strata and structures allowed the ore-forming fluids to migrate horizontally along the unconformity surface of the Middle–Upper Permian, converge on the high position of an anticline, and then ascend into the overlying strata along the anticlinal axis. The distributions of the major and trace elements show that elements that accompanied the ore-forming fluids include Au, As, Sb, Hg, Tl, and S, and that Na₂O and Li were exhausted in the Longtan Formation at the anticlinal core during gold mineralization. The enrichment of Co, Cr, and Ni in the Longtan Formation at the anticlinal core might be associated with deformation that formed the anticline, or with gold mineralization. Different host rocks were preferentially mineralized by different elements. The bioclastic limestone is commonly enriched in Au, whereas the argillite is preferentially enriched in As, Hg, Sb, and Tl. The zonation of ore-forming elements in the deposit appears to be Sb–Tl–As–Hg–Au–Hg–As (from bottom to top). Enrichment of Au, As, Sb, Hg, and Tl provides useful guidance for the exploration for Carlin-type gold deposits in Guizhou. Anomalies of As and Hg in soil or stream sediment might be an important clue and these elements can be used as indicator elements. Ore-forming fluids migrated along the unconformity surface of the Middle–Upper Permian and the anticlinal axis, so these are favorable sites for exploration for Carlin-type gold deposits in Guizhou.     

Geological and geochemical characteristics of the Baogudi Carlin-type gold district (Southwest Guizhou,China) and their geological implications

The newly discovered Baogudi gold district is located in the southwestern Guizhou Province, China, where there are numerous Carlin-type gold deposits. To better understand the geological and geochemical characteristics of the Baogudi gold district, we carried out petrographic observations, elemental analyses, and fluid inclusion and isotopic composition studies. We also compared the results with those of typical Carlin-type gold deposits in southwestern Guizhou. Three mineralization stages, namely, the sedimentation diagenesis, hydrothermal (main-ore and late-ore substages), and supergene stages, were identified based on field and petrographic observations. The main-ore and late-ore stages correspond to Au and Sb mineralization, respectively, which are similar to typical Carlin-type mineralization. The mass transfer associated with alteration and mineralization shows that a significant amount of Au, As, Sb, Hg, Tl, Mo, and S were added to mineralized rocks during the main-ore stage. Remarkably, arsenic, Sb, and S were added to the mineralized rocks during the late-ore stage. Element migration indicates that the sulfidation process was responsible for ore formation. Four types of fluid inclusions were identified in ore-related quartz and fluorite. The main-ore stage fluids are characterized by an H₂O–NaCl–CO₂–CH₄ ± N₂ system, with medium to low temperatures (180–260 °C) and low salinity (0–9.08% NaCl equivalent). The late-ore stage fluids featured H₂O–NaCl ± CO₂ ± CH₄, with low temperature (120–200 °C) and low salinity (0–7.48% NaCl equivalent). The temperature, salinity, and CO₂ and CH₄ concentrations of ore-forming fluids decreased from the main-ore stage to the late-ore stage. The calculated δ¹³C, δD, and δ¹⁸O values of the ore-forming fluids range from − 14.3 to − 7.0‰, −76 to −55.7‰, and 4.5–15.0‰, respectively. Late-ore-stage stibnite had δ³⁴S values ranging from − 0.6 to 1.9‰. These stable isotopic compositions indicate that the ore-forming fluids originated mainly from deep magmatic hydrothermal fluids, with minor contributions from strata. Collectively, the Baogudi metallogenic district has geological and geochemical characteristics that are typical of Carlin-type gold deposits in southwest Guizhou. It is likely that the Baogudi gold district, together with other Carlin-type gold deposits in southwestern Guizhou, was formed in response to a single widespread metallogenic event.

     

P-T-X conditions of hydrothermal fluids and precipitation mechanism of stibnite-gold mineralization at the Wiluna lode-gold deposits,Western Australia: conventional and infrared microthermometric constraints

The Wiluna lode-gold deposits are located in the Archean Wiluna greenstone belt, in the northern sector of the Norseman-Wiluna belt in the Yilgarn Craton of Western Australia. They are hosted in subgreenschist facies meta-basalts, and controlled by the Wiluna strike-slip fault system and associated shear veins and breccias. The 13 individual lode-gold deposits have produced around 115 t Au from 1901 to 1946 and 1986 to today. Historically, they also produced 38.3 t As and 3.5 t Sb. Gold formed in two stages: stage 1 gold-pyrite-arsenopyrite is finely disseminated in the wallrock and breccia fragments, whereas stage 2 gold-stibnite is located in massive shear veins and breccia matrix, as fracture-fill and in banded-colloform textured veins. Stibnite-gold orebodies only occur in some of the deposits (e.g., Moonlight and northern part of the West Lode) and also display a restricted vertical extent, being preserved only in the uppermost 200 m of stibnite-bearing lodes.Petrographic, conventional, and infrared microthermometric and laser-Raman analysis on stibnite-bearing quartz veins and breccias reveal that the antimony- and gold-rich hydrothermal fluid was of mixed H₂O-NaCl-CO₂±CH₄ type. Microthermometric measurements reveal maximum homogenization temperatures of 340 °C (average 290±25 °C), and a wide range of salinities between 0.2 and 23 eq. wt% NaCl. Aqueous-carbonic fluid inclusions contain variable X_CO2+CH4 (0.03 to 0.82), with the carbonic phase containing a maximum X_CH4 of 0.21.Combined petrographic and microthermometric evidence suggests that the fluid inclusion properties reflect fluid immiscibility of a low-salinity, medium X_CO2+CH4, homogeneous parent fluid at about 290 °C and pressures between 700 and 1,700 bar. Fluid immiscibility was triggered by cyclic pressure release during fault-zone movement. The decompression (adiabatic cooling) of the hydrothermal fluids shifted the ore fluid to lower temperatures, significantly reduced the degree of stibnite undersaturation, and caused stibnite to precipitate. The deposition of stibnite reduced the ore-fluid H₂S concentration, thereby destabilized gold bisulfide complexes in solution, and caused gold precipitation locally. This mechanism explains the intimate spatial association of stibnite and gold in quartz veins and breccias in the stibnite-gold orebodies at Wiluna.Editorial handling: B. Lehmann     

我国首次发现的杂铅矿

杂铅矿（Izoklakeite）^[1]是一个Ag-Cu—Pb—Sb—Bi硫盐矿物。1984年发现于我国广西芒场锡—多金属矿床块状锡石—石英—硫化物矿石中。与毒砂、黄铜矿、黝铝矿、方铅矿（少）、浓红银矿和自然铋,有时也与自然锑等密切共生。文中给出了杂铅矿的若干特征参数。