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1.
黔东南金成矿区位于江南造山带金成矿省的西南端,成矿条件优越。坑头金矿床是黔东南金成矿区的一个中型矿床,在其深部找矿中,发现除石英脉型矿体外,还存在蚀变岩型矿体。然而,这种蚀变岩型矿体的构造形态、蚀变类型、与石英脉型矿体之间关系和金的赋存状态尚不清楚。本研究与当前的勘查工作紧密结合,围绕石英脉型矿体和新发现的蚀变岩型矿体为研究切入点,借助微区分析技术(扫描电镜和电子探针)进行系统的“流体- 蚀变- 成矿”研究。蚀变矿物金红石矿物化学显示为热液成因,具有典型造山型金矿床的金红石标型特征。围岩的沉积- 成岩过程(包括低级变质作用过程),主要形成了草莓状黄铁矿和含铁碳酸盐岩,为后期含金硫化物(黄铁矿和毒砂)的形成提供物质基础(如Fe)。金的成矿富集过程主要经历了绢云母+毒砂+黄铁矿+石英(Ser+Apy+Py+Qtz)阶段、黄铁矿+毒砂+石英(Py+Apy+Qtz)阶段和自然金+石英(Au0+Qtz)阶段。在Ser+Apy+Py+Qtz阶段,主要表现为含矿流体与围岩的初级交代,形成大量浸染状黄铁矿+毒砂的硫化带;Py+Apy+Qtz阶段主要为流体沿着剪切带再交代,形成蚀变岩型矿体;Au0+Qtz阶段主要表现为含金石英大脉的形成。金的赋存状态研究显示,蚀变岩矿体中Au以他形显微- 次显微自然金赋存在蚀变岩硫化物裂隙中,或以化学结合态方式赋存在黄铁矿和毒砂中(后者占主导)。在晚期Au0+Qtz阶段,自然金呈自形、粗粒(~0. 5 mm)赋存在石英脉中。综合研究认为,多期构造(流体)交代导致的溶解- 再沉淀可能是坑头金富集成矿主要原因之一。 相似文献
2.
位于华北克拉通南缘的小秦岭地区是我国仅次于胶东的大型金矿床集中区,但金矿床的成矿物质来源及成因问题一直存在较大争议.以华北南缘小秦岭矿集区东桐峪金矿床中的黄铁矿作为研究对象,在黄铁矿显微结构研究的基础上利用LA-ICP-MS对黄铁矿的微量元素进行原位分析,为进一步认识东桐峪金矿床及区内其他同类型矿床的成因提供新的资料和制约.东桐峪金矿床的黄铁矿从早到晚依次划分为3个世代(PyⅠ、PyⅡ和PyⅢ).PyⅠ主要形成于粗粒黄铁矿-石英阶段,颗粒粗大且自形程度高,呈星点状或斑点状赋存于乳白色石英脉中.PyⅡ主要形成于石英-中细粒黄铁矿阶段,呈半自形-他形结构且裂隙发育,常被晚期石英、多金属硫化物、自然金等矿物充填.PyⅢ主要形成于多金属硫化物阶段,常呈他形粒状结构与黄铜矿、方铅矿及闪锌矿等硫化物密切共生.LA-ICP-MS分析结果显示,PyⅠ中As平均含量为16.63×10-6,Au、Ag和Te含量较低且常位于检测限以下;相较而言,PyⅡ中As含量稍低,而Au、Ag和Te含量略高(其中Au含量为0.10×10-6~0.59×10-6);PyⅢ中Au、Ag和Te含量差异较大且显著升高,其中Au、Te含量最高可达35.58×10-6和79.79×10-6,而As含量较低且大部分数值低于检测限;不同世代黄铁矿的Co/Ni比值基本上都大于1,且PyⅢ的Co、Ni含量和Co/Ni比值明显低于PyⅡ和PyⅠ.以上结果表明,东桐峪金矿床的载金矿物黄铁矿中As的含量很低,金的富集与As无关;不同世代的黄铁矿中Au、Ag和Te之间存在显著且稳定的线性正相关关系,暗示金矿化与Te关系密切.另外,第3世代黄铁矿(PyⅢ)中Au、Ag及Te存在显著富集,指示Te(而不是As)在金和银的迁移、搬运、富集、沉淀等过程中具有重要作用.华北克拉通南缘小秦岭地区晚中生代大规模的金成矿作用及金矿床中普遍存在Te-Au-Ag矿物,且黄铁矿中As含量低、Te含量高等特征,暗示该区金矿床的成矿物质/成矿流体可能来自深部岩浆的脱挥发分或地幔脱气作用,而与区域变质作用的关系不大. 相似文献
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4.
The Mirge-Naqshineh gold district is situated at northwest of Iran with a NW-trending brittleductile shear zone. It is hosted by Precambrian meta-sedimentary and meta-volcanic units traversed by mineralized quartz veins. In terms of cross-cutting relationships and sulfide content three types of quartz veins are identified in the region. Among those, parallel to bedding quartz vein(type Ⅰ) is the main host for gold mineralization. Gold is found in three different forms: 1) submicrometer-size inclusions of gold in arsenian pyrite, 2) as electrum and 3) in the crystal lattice of sulfides(pyrite, galena and chalcopyrite). Six types of pyrite(Py1-Py6) were identified in this ore reserve. Py3 coexists with arsenopyrite and contains the greatest As-Au concentrations. There is a negative correlation between the As and S contents in Py2 and Py3, implying the substitution of sulfur by arsenic. Pyrites and mineralized quartz veins were formed via metamorphic-hydrothermal fluid and reflect the gold-transportation as Au(HS)_2~- under reducing and acidic conditions. The gold precipitation mainly controlled by crystallization of arsenian pyrite during fluid/rock interactions and variation of fO_2. The volcanic host rock has played an important role in gold concentration, as Py3 in this rock contains inclusion of gold particles, but gold is within the lattice of pyrite in phyllite or other units. 相似文献
5.
The Sukari Gold Mine,Eastern Desert—Egypt: structural setting,mineralogy and fluid inclusion study 总被引：1，自引：0，他引：1
The Sukari gold mine (18.8 Mt @ 2.14 g/t Au) is located 15 km west of the Red Sea coast in the southern central Eastern Desert of Egypt. The vein-type deposit is hosted in Late Neoproterozoic granite that intruded island-arc and ophiolite rock assemblages. The vein-forming process is related to overall late Pan-African shear and extension tectonics. At Sukari, bulk NE–SW strike-slip deformation was accommodated by a local flower structure and extensional faults with veins that formed initially at conditions of about 300 °C and 1.5–2 kbar. Gold is associated with sulfides in quartz veins and in alteration zones. Pyrite and arsenopyrite dominate the sulfide ore beside minor sphalerite, chalcopyrite and galena. Gold occurs in three distinct positions: (1) anhedral grains (GI) at the contact between As-rich zones within the arsenian pyrite; (2) randomly distributed anhedral grains (GII) and along cracks in arsenian pyrite and arsenopyrite, and (3) large gold grains (GIII) interstitial to fine-grained pyrite and arsenopyrite. Fluid inclusion studies yield minimum vein-formation temperatures and pressures between 96 and 188 °C, 210 and 1,890 bar, respectively, which is in the range of epi- to mesothermal hydrothermal ore deposits. The structural evolution of the area suggests a long-term, cyclic process of repeated veining and leaching followed by sealing, initiated by the intrusion of granodiorite. This cyclic process explains the mineralogical features and is responsible for the predicted gold reserves of the Sukari deposits. A characteristic feature of the Sukari gold mineralization is the co-precipitation of gold and arsenic in pyrite and arsenopyrite.Editorial handling: H. Frimmel 相似文献
6.
The Hatu, Qi-III, and Qi-V gold deposits in the Hatu–Baobei volcanic–sedimentary basin (west Junggar, Xinjiang) represent the proximal, middle, and distal parts of the Hatu gold district, respectively. Orebodies of these deposits mainly consist of Au-bearing quartz veins and altered host rocks with disseminated sulfide minerals. Six types of pyrite in these mines are studied here to illustrate ore-formation processes. Sedimentary pyrite, including framboidal and fine-grained pyrite, occurs in mudstone-bearing sedimentary rocks or altered volcanic–sedimentary rocks. Framboidal pyrite formed during redox changes in sedimentary layers. Hydrothermal pyrite contains five subgroups, from Py1 to Py5. Porous Py1 formed prior to gold mineralization, and is overgrown by Py2 that contains inclusions of sulfide minerals and native gold. Coarser Py3 coexists with arsenopyrite and native gold, and contains the greatest As concentrations. Gold and antimony are also preferentially concentrated in arsenian Py2 and Py3. The Au–As-deficient Py4 and Py5 formed during the post-ore process. There is a negative correlation between the As and S contents in Py1, Py2, and Py3, implying the substitution of sulfur by arsenic. Gold precipitated under relatively reducing condition in framboid- and graphite-bearing tuffaceous rocks. Cesium, Rb, Sr, La, Ce, Au, As, Sb, Cu, and Pb are concentrated in altered host rocks. The Au-bearing quartz veins and disseminated sulfide mineral orebodies were formed via a co-genetic hydrothermal fluid and formed during different stages. The variation of fO2 during fluid/rock interactions, and crystallization of arsenian pyrite were major factors that controlled gold precipitation. 相似文献
7.
The Fairview and Sheba mines are two of the major gold mines in the Paleoarchean Barberton Greenstone Belt of Southern Africa. At these mines, gold is associated with quartz–carbonate ± rutile veins and occurs both as “invisible” gold finely dispersed in sulfides (primarily pyrite and arsenopyrite), and as visible electrum grains hosted in pyrite. Up to approximately 1000 ppm Au are contained in pyrite, and up to approximately 1700 ppm in arsenopyrite. Mapping of trace element distribution in sulfide minerals using electron microprobe and proton probe techniques revealed multiple events of ore formation and Au mineralisation. At Fairview mine, three stages of pyrite formation were identified, the last of which is associated with arsenopyrite, electrum and other sulfide minerals (sphalerite, chalcopyrite, galena, gersdorffite, and Sb-sulfides). At Sheba mine, pyrite was deposited in two stages, and electrum is associated with the second stage. At both mines, the last stage of sulfide formation is the main stage of Au deposition, and is associated with mobilisation of Au, As, Sb, Cu, Zn, and Ni. The host rock composition seems to have affected the composition of pyrite, since higher Ni and Co concentrations (up to 1.4 and 1.6 wt.%, respectively) have been measured in meta-(ultra)mafic host rocks in comparison with chert and metagreywacke. Arsenopyrite is chemically zoned, and has Sb- and S-rich cores and As- and Ni-rich rims. This zoning indicates variations in fluid compositions (decreasing Sb and increasing Ni), and crystallisation conditions (increasing As content for increasing temperature). Geothermometric estimates based on the As content of arsenopyrite (As ≤ 32 at.%) indicate temperatures up to ~ 420 °C for the crystal rims. Petrographic and cathodoluminescence observations of quartz associated with gold mineralisation show only local brittle deformation, and no plastic deformation. This supports the notion that the ore-transporting veins were emplaced late in the deformation history. Variations of cathodoluminescence of quartz are correlated with changing Al contents (Al ≤ 0.16 wt.%), and can be related to fluctuations in the pH of the mineralising fluids. 相似文献
8.
Gold deposits at El Sid are confined to hydrothermal quartz veins which contain pyrite, arsenopyrite, sphalerite and galena. These veins occur at the contact between granite and serpentinite and extend into the serpentinite through a thick zone of graphite schist. Gold occurs in the mineralized zone either as free gold in quartz gangue or dissolved in the sulfide minerals. Ore-microscopic study revealed that Au-bearing sulfides were deposited in two successive stages with early pyrite and arsenopyrite followed by sphalerite and galena. Gold was deposited during both stages, largely intergrown with sphalerite and filling microfractures in pyrite and arsenopyrite.Spectrochemical analyses of separated pyrite, arsenopyrite, sphalerite and galena showed that these sulfides have similar average Au contents. Pyrite is relatively depleted in Ag and Te. This suggests that native gold was deposited in the early stage of mineralization. Arsenopyrite and galena show relatively high concentrations of Te. They are also respectively rich in Au and Ag. Tellurides are, thus, expected to be deposited together with arsenopyrite and galena. 相似文献
9.
The mesothermal Au deposit at Middagsberget in northern Sweden is associated with irregular stock-works of quartz veins occurring in shear zones across a dioritic intrusion. Alteration in the shear zones is characterized by sericitization, chloritization, the presence of sulphides and several generations of veins and small-scale fractures. Small fractures which are filled with variable amounts of quartz, carbonate, sericite, chlorite, albite and sulphides, are particularly abundant in zones having a high Au content. In general, these fractures are younger than the major quartz veins and were apparently important for strong Au-enrichment. Au is associated with arsenopyrite and it occurs as droplets or interfillings in the arsenopyrite or at the crystal surface; together with pyrrhotite as inclusions in arsenopyrite; as free grains in silicates but close to arsenopyrite; or in very small fractures in carbonates. The Au-mineralization is associated with elevated contents of As, S, Sb and W and depletion of Cu, Zn, Ge and Bi. The entire altered areas are enriched in Au compared with the < 1 to 15 ppb found in the host intrusion. During alteration an initial increase in Na or K was accompanied by a weak enrichment of Au and associated elements together with a depletion of elements such as Ca and Mg. In Au-rich samples this alkali enrichment was overprinted by the carbonate-and sulphide-bearing fractures, which often led to an increased Ca-content. An clear zonation of alteration types has not been found. The host rock has been altered by several generations of fluids: the shear zones were repeatedly ruptured and new small-scale fractures were opened. The different fluids did not, therefore, flow through identical paths although they penetrated the same major zones. This resulted in a complex pattern of variously superimposed alterations. 相似文献
10.
The Bepkong gold deposit is located in the Wa–Lawra belt of the Paleoproterozoic Baoulé-Mossi domain of the West African Craton, in NW Ghana. It occurs in pelitic and volcano-sedimentary rocks, metamorphosed to greenschist facies, in genetic association with zones of shear interpreted to form during the regional D3 deformational event, denominated DB1 at the deposit scale. The ore zone forms a corridor-like body composed of multiple quartz ± carbonate veins surrounded by an alteration envelope, characterized by the presence of chlorite, calcite, sericite, quartz and disseminated pyrite, arsenopyrite plus subordinate pyrrhotite and chalcopyrite. The veins contain only small proportions of pyrite, whereas most of the sulphides, particularly arsenopyrite, occur in the altered host rock, next to the veins. Pyrite is also common outside of the ore zone. Gold is found in arsenopyrite, where it occurs as invisible gold and as visible – albeit micron-size – grains in its rims, and as free gold within fractures cross-cutting this sulphide. More rarely, free gold also occurs in the veins, in fractured quartz. In the ore zone, pyrite forms euhedral crystals surrounding arsenopyrite, but does not contain gold, suggesting that it formed at a late stage, from a gold-free hydrothermal fluid. 相似文献
11.
藏南查拉普金矿床载金矿物特征与金的赋存状态 总被引：1，自引：0，他引：1
黄铁矿和毒砂是卡林型和造山型金矿床重要的载金矿物。文章通过电子探针(EPMA)分析研究了藏南查拉普金矿床不同类型黄铁矿和毒砂中Au、As、S、Fe等元素的含量变化和分布规律,发现不同阶段的黄铁矿具有不同的结构特征和元素组成特点。沉积成岩期黄铁矿(Py1)主要呈草莓状、胶状,常构成环带状黄铁矿的核心,其中金的含量最高,显示了金在沉积成岩期的大量富集。热液期早阶段黄铁矿(Py2)主要呈自形-半自形的立方体,与Py1元素(S、Fe、As)组成相近,显示了一定的继承演化关系。热液期主阶段黄铁矿(Py3)与毒砂共生,多呈自形-半自形的五角十二面体、立方体,常包裹早期的黄铁矿形成环带结构。Py3中As的含量明显升高,其增加量近似等于S的减少量,说明As主要进入黄铁矿晶格替代了S的位置。各个阶段的黄铁矿和毒砂中Au的分布在EPMA微束的分辨率下均显示是不均匀的,Au在Py1和大部分Py2中主要以纳米级自然金(Au0)的形式存在;而在Py3中主要以(Au+)的形式存在,少部分以纳米级自然金(Au0)形式存在。Py1的结构及元素组成与典型卡林型金矿和造山型金矿沉积成岩期黄铁矿的特点相似,而Py3的大量发育则符合卡林型金矿的特征。 相似文献
12.
丘岭金矿床是西秦岭地区重要的卡林型金矿之一, 金矿化赋存于上泥盆统南阳山组和下石炭统袁家沟组地层中, 容矿岩石的岩性为钙质粉砂岩、粉砂质页岩和泥质灰岩.金矿石中主要金属矿物为黄铁矿和毒砂, 非金属矿物则以石英、方解石和绢云母为主.通过对矿石矿物黄铁矿和毒砂的扫描电镜-能谱分析、电子探针分析和激光剥蚀电感耦合等离子体质谱分析, 对丘岭金矿床金的赋存形式和富集机理进行了较为详细的研究.结果表明, 丘岭金矿床中金主要以次显微不可见金的形式存在, 其次为显微可见金.次显微金包括: (1)固溶体金(Au+), 主要存在于环带状细粒黄铁矿的含砷增生边区域和毒砂中, 少量存在于环带状黄铁矿的核部不含砷区域; (2)纳米级自然金颗粒(Au0), 存在于粗晶黄铁矿中.环带状细粒黄铁矿核部的次显微金可能主要以胶体吸附的形式存在, 暗示容矿岩石在沉积成岩过程中有金的初步富集, 而环带状黄铁矿幔部和毒砂中的Au则主要来源于成矿流体, 以S和As的络合物形式搬运.显微可见金主要分布在细粒黄铁矿的晶体边缘和热液蚀变绢云母、石英及方解石中, 粒径通常小于3~5 μm, 其形成可能与成矿流体中金的局部过饱和及成矿流体对细粒黄铁矿和毒砂中次显微金的活化和再次富集有关. 相似文献
13.
Basem A. Zoheir Mohamed G. Abdel-Fattah Sameh M. ElAlfy 《Arabian Journal of Geosciences》2013,6(12):4635-4646
Orogenic, lode gold mineralisation in the South Eastern Desert of Egypt is related to quartz veins spatially and temporally associated with conjugate NW- and NE-trending brittle–ductile shear zones. These structures are assumed to be linked to a regional transpression deformation which occurred late in the tectonic evolution of the area. In the Betam deposit, gold is confined to quartz(±carbonate) veins cutting through tectonised metagabbro and metasedimentary rocks in the vicinity of small granite intrusions. The ore bodies contain ubiquitous pyrite and arsenopyrite, in addition to minor disseminated chalcopyrite, pyrrhotite, galena, tetrahedrite and rare gold/electrum. New ore microscopy and electron microprobe studies indicate that most free-milling Au is intimately associated with the late-paragenetic galena–tetrahedrite–chalcopyrite assemblage. An early Fe–As sulphide assemblage, however, shows minor traces of refractory gold. New mineralogical and geochemical data are used to better constrain on possible element dispersions for exploration uses. This study indicates that parameters that most consistently define primary dispersion of gold in the mine area include pervasive silicification, sericite and carbonate alteration. The trace element data of gold lodes reflect a systematic dispersion of gold and certain base metals. Low-cost, extensive exploration programs may use elevated concentrations of Ag, Sb, Cu and Pb as tracers for Au ore zones in the Betam mine area and surroundings. 相似文献
14.
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. 相似文献
15.
Ashraf Emam 《Arabian Journal of Geosciences》2013,6(12):4619-4634
Gold-bearing quartz lodes from the Egat gold mine, South Eastern Desert of Egypt, are associated with pervasively silicified, highly sheared ophiolitic metagabbro and island-arc metavolcanic rocks. The mineralized quartz veins and related alteration haloes are controlled by NNW-trending shear/fault zones. Microscopic and electron probe microanalyses (EPMA) data of the ore and gangue minerals reveal that fine-grained auriferous sulfarsenides represent early high-temperature (355–382 °C) phases, with formation conditions as (fS2?=??10, and fO2 around ?31). A late, low-temperature (302–333 °C) assemblage includes coarse pyrite, arsenopyrite, and free-milling gold grains (88–91 wt.% Au), with formation conditions as (fS2?=??8 and fO2 around ?30). Gold was impounded within early sulfarsenides, while free-milling gold blebs occur along microfractures in quartz veins and as inclusions in late sulfides. Infiltration of hydrothermal fluids under brittle–ductile shear conditions led to mobilization of refractory Au from early sulfarsenide phases and reprecipitated free gold, simultaneous with silicification of the host rocks. The positive correlation between Au and As favors and verifies the use of As as the best pathfinder for gold targets, along the NNW-trending shear zones. 相似文献
16.
Zhekai Zhou Kotaro Yonezu Akira Imai Thomas Tindell Huan Li Jillian Aira Gabo-Ratio 《Resource Geology》2022,72(1):e12279
The Woxi Au-Sb-W deposit is one of the largest polymetallic ore deposits in the Xuefengshan Range, southern China, hosted in low-grade metamorphosed Neoproterozoic volcaniclastic rocks. The orebodies of the deposit are predominantly composed of banded quartz veins, which are strictly controlled by bedding and faults. Petrographic observations and geochemical results are reported on the occurrence of Au and properties of the ore-forming processes for different stages in the deposit. The veins extend vertically up to 2 km without obvious vertical metal zoning. The ore-forming process can be subdivided into four mineralization stages: Pre-ore stage; Early stage (scheelite-quartz stage); Middle stage (pyrite-stibnite-quartz stage); and Late stage (stibnite-quartz sage). Four types of pyrite (Py0, Py1, Py2, and Py3) were identified in the ores and host-rock: Py0 occurs as euhedral grains with voids in the core, ranging in size from 50 to 100 μm and formed mainly in the Pre-ore stage and Early stage; Py1 occurs as subhedral grains. Small grains (around 10 μm) of Py1 form irregularly shaped clusters of variable size ranging from tens to hundreds of μm and mainly formed in the Middle stage; Euhedral-subhedral fine-grained Py2 formed in the Late stage; Minor subhedral fine-grained Py3 was deposited in the Late-stage. Stibnite is widely distributed in the Middle and Late stage ore veins. No systemic difference was recognized in mineralogical features among stibnite formed in different stages. In addition to native gold, the lattice bound Au+1 widely exists in Py1 and Py2 in the deposit, and widespread Py1 is considered as the main Au-bearing mineral with the highest Au contents. Most elements (such as Co, Ni, Cu, As, Sb, Ba, and Pb) are considered to occur as solid solution within the crystal lattice and/or invisible nanoparticles in sulfides minerals. The Co/Ni ratio of most pyrite is lower than 1, suggesting that the metals in the ore-forming fluid are sourced from sedimentary rocks. The coupled behavior between Au and As; Au and Sb suggests that the substitution of As and Sb in pyrite can enhance the incorporation of Au. Variation of trace elements in pyrites of different stages suggests some information on the mineralization processes: Large ion lithophile elements (such as Ba and Pb) are enriched in Py0 indicating that water-rock reaction occurred in the Early stage; Fine-grained Py1 with a heterogeneous distribution of elements suggests fast crystallization of pyrite in the Middle stage. 相似文献
17.
Mineralogy of the Boroo Gold Deposit in the North Khentei Gold Belt,Central Northern Mongolia 
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下载免费PDF全文 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. 相似文献
18.
Several occurrences of gold-bearing quartz veins are situated along the east–northeast-trending Barramiya–Um Salatit ophiolitic belt in the central Eastern Desert of Egypt. In the Barramiya mine, gold mineralization within carbonaceous, listvenized serpentinite and adjacent to post-tectonic granite stocks points toward a significant role of listvenitization in the ore genesis. The mineralization is related to quartz and quartz–carbonate lodes in silicified/carbonatized wallrocks. Ore minerals, disseminated in the quartz veins and adjacent wallrocks are mainly arsenopyrite, pyrite and trace amounts of chalcopyrite, sphalerite, tetrahedrite, pyrrhotite, galena, gersdorffite and gold. Partial to complete replacement of arsenopyrite by pyrite and/or marcasite is common. Other secondary phases include covellite and goethite. Native gold and gold–silver alloy occur as tiny grains along micro-fractures in the quartz veins. However, the bulk mineralization can be attributed to auriferous arsenopyrite and arsenic-bearing pyrite (with hundreds of ppms of refractory Au), as evident by electron microprobe and LA-ICP-MS analyses.The mineralized quartz veins are characterized by abundant carbonic (CO2 ± CH4 ± H2O) and aqueous-carbonic (H2O–NaCl–CO2 ± CH4) inclusions along intragranular trails, whereas aqueous inclusions (H2O–NaCl ± CO2) are common in secondary sites. Based on the fluid inclusions data combined with thermometry of the auriferous arsenopyrite, the pressure–temperature conditions of the Barramiya gold mineralization range from 1.3 to 2.4 kbar at 325–370 °C, consistent with mesothermal conditions. Based on the measured δ34S values of pyrite and arsenopyrite intimately associated with gold, the calculated δ34SΣs values suggest that circulating magmatic, dilute aqueous-carbonic fluids leached gold and isotopically light sulfur from the ophiolitic sequence. As the ore fluids infiltrated into the sheared listvenite rocks, a sharp decrease in the fluid fO2 via interaction with the carbonaceous wallrocks triggered gold deposition in structurally favorable sites. 相似文献
19.
Qingyan Tang Pengfei Di Man Yu Jian Bao Ying Zhao Dongxiao Liu Yuxi Wang 《Resource Geology》2019,69(3):314-332
The Zaozigou gold deposit lies in the West Qinling orogenic belt, Gansu Province, China. It is one of the largest gold deposits, and the orebodies are hosted in fine‐grained slates intercalated with limestone of the Middle‐Triassic Gulangdi Formation and varied dykes. The gold orebodies are strictly controlled by the NE‐, NW‐, and SN‐trending tensional and shearing faults with high dipping angle. The mineralogy and geochemistry of pyrite and arsenopyrite are measured by electron microprobe. Pyrite has up to 0.12 wt.% Au, and arsenopyrite contains up to 0.17 wt.% Au. The antithetic correlation between S and As indicates the substitution of As for S in pyrite, and arsenic occurs in anionic As1? state in the pyrite structure under the reduced conditions. Pyrite has relatively high Co (~364–2248 ppm) but relatively low Ni (~109–497 ppm) contents, with Co/Ni ratios ranging from ~1.63 to 10.50, indicating that the deposit originated from a volcanogenic fluid and remobilized by hydrothermal fluid. Au in arsenopyrite occurs as cationic Au in solid solution, whereas Au in pyrite is in solid solution and metal nanoparticles (Au0). The texture characteristics and trace element geochemistry among cores, transition zones, and rims of pyrites demonstrate that there are at least four pulses of fluid participating in the generation of pyrite in the deposit. The calculated formation temperatures of the Zaozigou deposit vary from 148°C to 304°C, with an average temperature of 213°C based on Au contents in pyrite. The Pb isotopic compositions of pyrite samples suggest that the metallogenic materials of the Zaozigou deposit were derived from the mantle and upper crust. All the characteristics above lead us to draw the conclusion that the Zaozigou gold deposit is classified as an epithermal deposit. 相似文献
20.
甘肃阳山金矿是迄今为止中国发现的最大金矿。已发现的6个矿段均赋存于泥盆系中,矿石中金属矿物主要为黄铁矿和毒砂。黄铁矿有3种类型:微细粒浸染状、半自形颗粒集合体、自形单晶大颗粒;主要分布在千枚岩、花岗闪长岩、石英脉里,具有多期次多类型的特点。根据黄铁矿的特征,金矿化与石英脉体中细粒浸染状的一期黄铁矿有关。黄铁矿为重要的载金矿物之一,自然金(Au)主要以微细粒的形式赋存于黄铁矿晶体的裂隙内以及晶体与晶体的空隙间。黄铁矿赋存状态和分布特征的研究,对矿区进一步找矿具有指导意义。 相似文献