Types Of Gold Deposits Research Articles

Age and mineralization processes of decratonic lode gold deposits in the southern North China Craton: Constraints from trace elements, in-situ S-Pb isotopes and Rb-Sr geochronology of pyrite from the Chen’er gold deposit

The Chen’er gold deposit, with 27 tons of known Au reserves, is one of the typical gold deposits in the Xiaoqinling district along the southern part of the North China Craton. In order to better understand the gold precipitation time and mineralization process, we report in-situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) trace element analyses, elemental maps, and the Rb-Sr and S-Pb isotopic composition of sulfides from the Chen’er gold deposit with a view to gain insights into the mineralization time and process. Trace element analyses and elemental maps of pyrite show that the content of As is low and has no correlation with Au, indicating As is unlikely to have controlled the Au incorporation into pyrite. Gold mainly occurs as solid solutions in the Py Ⅰ and Py Ⅱ, and as Au-Ag and/or Au-Te sub-micrometer inclusions in Py III. The Rb-Sr isotopic data on sulfides from the Chen’er deposit yielded an isochron age of 129.2 ± 3.4 Ma, which overlaps with the previously reported 40Ar/39Ar age of hydrothermal mica, indicating that the gold mineralization occurred in the Early Cretaceous. The in-situ sulfur isotope values of sulfides from stage Ⅱ to stage III fluctuate significantly (the average value decreases from 4.95 to −0.24‰) and were affected by physicochemical parameters of the mineralization process, especially ƒO2. In addition, the δ34S values are in a narrow range (-1.34 to 5.24‰), indicating a magmatic source for the sulfur. In-situ Pb isotopic compositions of the pyrite and galena of stage Ⅱ and stage III are relatively constant with 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb values in the range of 37.264–37.595, 15.364–15.423, 16.992–17.078, respectively, indicating a mixed mantle-crust origin. Based on the new geochronological, geochemical and isotopic data presented in this study, and combined with those from previous studies, we suggest that the lode gold deposits in the Xiaoqinling district are magmatic hydrothermal ore deposits, with metal and ore-forming fluid originating primarily from the mantle, coupled with the cratonic reactivation during the Early Cretaceous.

Mineralogy, Geochemistry, and Geochronology of the Yehe-Shigna Ophiolitic Massif, Tuva-Mongolian Microcontinent, Southern Siberia: Evidence for a Back-Arc Origin and Geodynamic Implications

The new results have been represented of mineralogical–geochemical and geochronological studies of rocks of the Yehe-Shigna ophiolite massif located in the Tuva-Mongolian microcontinent in the northern part of the Central Asian orogenic belt (Eastern Sayan, Southern Siberia). The Yehe-Shigna ophiolite massif is part of the Belsk-Dugda ophiolite belt. The structural position, age, and geochemical characteristics of the belt indicate its formation in the setting of the back-arc basin of the Shishkhid intraoceanic island arc, developing in the period of 810–750 million years. It is assumed that together with the same-age formations of the Oka accretion wedge and the Sarkhoi active margin, it formed on the convergent margin of the Gondwana supercontinent. Its basement is represented by the Archean-Early Precambrian crystalline rocks and carbonate cover (“Gargan Glyba”). The gold-bearing Neoproterozoic deposits with dominant gold-telluride assemblages are localization in large ophiolites thrust zones along with the frame of the “Gargan Glyba”. They are allochthonous with respect to the Late Neoproterozoic-Cambrian Tuva-Mongolian island arc of the Siberian continent. A similar type of gold deposit is probably worth looking for ophiolites thrust zones in other Precambrian Gondwana-derived microcontinents.

Origin of the Dayingezhuang gold deposit in the Jiaodong district, eastern China: Insights from trace element character of pyrite and C-O-S isotope compositions

The Dayingezhuang gold deposit is a giant gold deposit in the Jiaodong district, with explored gold reserves of 283 t. After decades of research, sources of ore-forming fluids remain controversial, resulting in continuous controversy on the origin of this deposit. In this study, trace elements of pyrite and C-O-S isotopic data are presented to provide constraints on the ore-forming fluids of the Dayingezhuang gold deposit. Two types of gold-related pyrite were identified. Py1, hosted in quartz-pyrite veins, has subhedral to anhedral textures with developed micro-fissures. Py2, hosted in quartz-polymetallic sulfide veins, is generally subhedral to anhedral and intergrown with polymetallic sulfides. Both Py1 and Py2 are characterized by Co/Ni <1, which supports that the ore-forming fluids are metamorphic fluids with the addition of sedimentary materials. The calcite CO isotope suggests a mantle-derived source mixed with sediments. Combined with the anomalously high δ34S values, the ore-forming fluids that generated the Dayingezhuang gold deposits were most likely originated from the mantle lithosphere which is metasomatized and fertilized by the subducted Paleo-Pacific Plate and its overlying marine sediments. This model is similar to the common genesis of worldwide orogenic type gold deposits which suggests that the Dayingezhuang gold deposit may be of orogenic origin.

Genesis of the Maoling gold deposit in the Liaodong Peninsula: Constraints from a combined fluid inclusion, C-H-O-S-Pb-He-Ar isotopic and geochronological studies

The large tonnage Maoling gold deposit (25 t @ 3.2 g/t) is located in the southwest Liaodong Peninsula, North China Craton. The deposit is hosted in the Paleoproterozoic metamorphic rocks. Four stages of mineralization were identified in the deposit: (stage I) quartz-arsenopyrite ± pyrite, (stage II) quartz-gold- arsenopyrite-pyrrhotite, (stage III) quartz-gold- polymetallic sulfide, and (stage IV) quartz-calcite-pyrrhotite. In this paper, we present fluid inclusion, C-H-O-S-Pb-He-Ar isotope data, zircon U-Pb, and gold-bearing sulfide (i.e. arsenopyrite and pyrrhotite) Rb-Sr age of the Maoling gold deposit to constrain its genesis and ore-forming mechanism. Three types of fluid inclusions were distinguished in quartz-bearing veins, including liquid-rich two-phase (WL type), gas-rich two-phase (GL type), and daughter mineral-bearing fluid inclusions (S type). Fluid inclusions data show that the homogenization at temperatures 197 to 372 °C for stage I, 126 to 319 °C for stage II, 119 to 189 °C for stage III, and 115 to 183 °C for stage IV, with corresponding salinities of 3.7 to 22.6 wt.%, 4.7 to 23.2 wt.%, 5.3 to 23.2 wt.%, and 1.7 to 14.9 wt.% NaCl equiv., respectively. Fluid boiling was the critical factor controlling the gold and associated sulfide precipitation at Maoling. Hydrogen and oxygen stable isotopic analyses for quartz yielded δ18O = −5.0‰ to 9.8‰ and δ D = −133.5‰ to −77.0‰. Carbon stable isotopic analyses for calcite and ankerite yielded δ13C = −2.3‰ to −1.2‰ and O = 7.9‰ to 14.1‰. The C-H-O isotope data show that the ore-forming fluids were originated from magmatic water with meteoric water input during mineralization. Hydrothermal inclusions in arsenopyrite have 3He/4He ratios of 0.002 Ra to 0.054 Ra, and 40Ar/36Ar rations of 1225 to 3930, indicating that the ore-forming fluids were dominantly derived from crustal sources almost no mantle input. Sulfur isotopic values of Maoling fine-grained granite range from 6.‰1 to 9.8‰, with a mean of 7.7‰, δ34S values of arsenopyrite from the mineralized phyllite (host rock) range from 8.9‰ to 10.6‰, with a mean of 10.0‰, by contrast, δ34S values of sulfides from ore vary between 4.3‰ and 10.6‰, with a mean of 6.8‰, suggesting that sulfur was mainly originated from both the host rock and magma. Lead radioactiveisotopic analyses for sulfides yielded 206Pb/204Pb = 15.830–17.103, 207Pb/204Pb = 13.397–15.548, 208Pb/204Pb = 35.478–36.683, and for Maoling fine-grained granite yielded 206Pb/204Pb = 18.757–19.053, 207Pb/204Pb = 15.596–15.612, and 208Pb/204Pb = 38.184–39.309, also suggesting that the ore-forming materials were mainly originated from the host rocks and magma. Zircon U-Pb dating demonstrates that the Maoling fine-grained granite was emplaced at 192.7 ± 1.8 Ma, and the host rock (mineralized phyllite) was emplaced at some time after 2065.0 ± 27.0 Ma. Arsenopyrite and pyrrhotite give Rb–Sr isochron age of 188.7 ± 4.5 Ma, indicating that both magmatism and mineralization occurred during the Early Jurassic. Geochronological and geochemical data, together with the regional geological history, indicate that Early Jurassic magmatism and mineralization of the Maoling gold deposit occurred during the subducting Paleo-Pacific Plate beneath Eurasia, and the Maoling gold deposit is of the intrusion-related gold deposit type.

Experimental study on the effective measurement of the total homogenization temperature of high internal pressure CO&lt;sub&gt;2&lt;/sub&gt;-rich fluid inclusions in orogenic gold deposits: A case study of the Yufeng gold deposit, Eastern Tianshan Orogen

形成于中-深成条件下的造山型金矿的成矿流体属于H₂O-NaCl-CO₂体系，金矿化阶段的石英中发育大量的富CO₂流体包裹体。长期以来，用常规冷热台对其进行显微测温热力学研究时，较高的内压力会造成绝大多数CO₂充填度>0.4的包裹体在尚未达到完全均一状态前就发生爆裂或泄露，导致所测的完全均一温度值明显偏离真实值，甚至无法测得完全均一温度，这制约了对造山型金矿床成矿条件的认知。针对该问题，本文以东天山玉峰金矿床富金矿石中的H₂O-NaCl包裹体（A型）和H₂O-NaCl-CO₂包裹体（AC型）为研究对象，介绍了利用最新型热液金刚石压腔（HDAC-VT型号）测试富CO₂高内压的AC型包裹体完全均一温度的实验流程与结果，并将实验数据与Linkam THMSG600冷热台测得的A型、AC型包裹体的完全均一温度进行了对比分析。实验结果表明，热液金刚石压腔能够有效阻止富CO₂流体包裹体在升温过程中发生爆裂、泄露等非弹性体积改变现象的发生，从而获得有效的完全均一温度。同时，本文还提出了一个新的压力-温度拟合线两线相交法，对热液金刚石压腔所测富CO₂流体包裹体的完全均一温度数据进行校正，以最大程度上减少外压力造成的影响，获得更为接近真实成矿流体的完全均一温度。基于此，获得玉峰金矿床的成矿温度和成矿压力分别为312~343℃和181~268 MPa。本文的实验研究工作显示了热液金刚石压腔在中-深成造山型金矿富CO₂成矿流体的研究领域具有重要应用前景。;The ore-forming fluids of orogenic gold deposits normally belong to a H₂O-NaCl-CO₂ system, and there are usually lots of CO₂-rich fluid inclusions hosted in the quartz at the gold mineralization stage. The trapped fluid inclusions in this type of gold deposit usually have high internal pressures since they are formed at a mid-deep depth in the earth's crust. For a long time, almost all researchers carry out the homogeneous thermomechanical properties study on CO₂-rich inclusions (CO₂ phase filling ratio>0.4) under a 1atm pressure condition. However, when the internal pressure is greater than the external confining pressure, the fluid inclusion will be deformed, such as stretching, leakage and decrepitating, which eventually lead to the measured total homogenization temperature (THT) deviate significantly from the actual value, or even cannot be measured. In order to solve these problems, we choose H₂O-NaCl (A-type) and H₂O-NaCl-CO₂ (AC-type) inclusions in quartz minerals from Yufeng orogenic gold deposit in Eastern Tianshan Orogen as the research object to measure their THTs with high internal pressures by using the latest hydrothermal diamond-anvil cell (HDAC; HDAC-VT type). At the same time, this manuscript compares the THTs obtained by a HDAC-VT with those by a Linkam THMSG600 heating-freezing stage. Our experimental results show that the HDAC can effectively prevent the inelastic volume change of CO₂-rich fluid inclusions during heating process, and consequently obtain an effective THT. In order to minimize the influence of external pressure on the measured THTs and obtain more reliable and accurate metallogenic temperatures, we propose a new two pressure-temperature fitting lines intersection method to calibrate the THTs of CO₂-rich fluid inclusions measured by a HDAC. Based on these improvements, the ore-forming temperatures and pressures of the Yufeng gold deposit are estimated to be 312~343℃ and 181~268MPa, respectively. The experimental work in this paper suggests that the HDAC has an important application prospect in the research field of CO₂-rich fluid inclusions from orogenic gold deposits.

A preliminary study of reserve estimate and resource potential assessment of critical elements in the Jiaodong gold deposits, China

通过对大尹格庄和夏甸两个超大型金矿床的精金矿与尾矿砂中关键元素含量的分析，发现相对于华北克拉通地壳元素丰度，本次分析的稀贵元素Co、Rh、Ir和Ru，稀散元素Cd、Te和Se，稀有元素W和In均发生了不同程度的富集；特别是Te、Co和Cd超常富集达到伴生组分综合评价品位。根据伴生有用组分综合评价规范和金矿选矿报告相关参数，分别估算了金矿石和精金矿中可利用的关键金属矿产储量，其中夏甸金矿床内Te储量为69吨（精金矿中52吨）、Co储量为604吨（精金矿中413吨），大尹格庄金矿床内Cd储量为224吨（精金矿中206吨），这些均可直接回收利用。矿物学和矿物化学综合研究表明：Te主体以碲金矿、碲银矿、碲铋矿、碲铅矿和陈国达矿等独立矿物存在，与可见金密切共生；Co常以微量元素形式分布在金成矿早阶段的粗粒黄铁矿和磁黄铁矿中；Cd主要以类质同象的形式赋存于金成矿晚阶段的闪锌矿、黄铁矿和黄铜矿中。进一步通过对典型金矿床中黄铁矿原位和/或单矿物的Te与Co含量对比、并结合矿石中Co与Cd元素组成及其区域地球化学空间分布特征，综合约束了其超常富集特征与资源潜力，揭示新城、玲珑和寺庄金矿床及栖霞异常区分别有约2329吨、1035吨、1553吨和22790吨Co资源量，乳山、新城和焦家金矿床有约1529吨、126吨、216吨Te资源量，仓上、新立、三山岛、寺庄和新城金矿床、以及栖霞和招平北段异常区分别有约47.6吨、78吨、63.7吨、69吨、3564吨、7120吨和696吨Cd资源量；即胶东金矿集区具备近期被综合利用或作为未来潜在接替资源的Co、Te和Cd资源条件，且其展布区域广泛、资源潜力巨大。初步研究已显示胶东具有形成大型-超大型Cd、Te和Co矿床的资源条件，但关键金属资源的空间分布极不均一、其超常富集机理与规律尚不清楚，亟需深入研究。;Through analysis of critical element content in fine gold mine and tailing sands of the two super-large gold deposits of Dayingezhuang and Xiadian, it is found that relative to abundance of elements in crust of the North China Craton, rare and precious elements Co, Rh, Ir and Ru, scattered elements Cd, Te and Se, and rare elements W and In have all been enriched to different degrees; Especially, extreme enrichment of Te, Co and Cd has reached the comprehensive evaluation grade of associated components. According to comprehensive evaluation specifications of associated useful components and relevant parameters of gold beneficiation report, the available critical metal reserves in gold ores and fine gold mines were estimated respectively. The Te reserves in the Xiadian gold deposit are 69 tons (52 tons in fine gold mine), Co reserves are 604 tons (413 tons in the fine gold mine), and the Cd reserves in the Dayingezhuang gold deposit are 224 tons (206 tons in the fine gold mine), all of which can be directly recycled. Mineralogy and geochemistry studies show that Te mainly exists as independent minerals such as gold telluride, silver telluride, bismuth telluride, lead telluride and Chenguoda mineral, and they are closely associated with visible gold; Co is often distributed in the form of trace elements in the coarse-grained pyrite in the early stage of the gold mineralization; Cd mainly occurs in the sphalerite, pyrite and chalcopyrite in the late stage of gold mineralization in the form of isomorphism. Furthermore, by comparing the Te and Co content of pyrite in situ and/or single minerals in typical gold deposits, combined with the elemental composition of Co and Cd in the ore and its regional geochemical spatial distribution characteristics, the extreme enrichment characteristics are comprehensively restricted. The Xincheng, Linglong and Sizhuang gold deposits and the Qixia anomaly area have about 2329 tons, 1035 tons, 1553 tons, and 22790 tons of Co potential resources, respectively, and the Rushan, Xincheng and Jiaojia gold deposits have about 1529, 126, and 216 tons of Te resources, the Cangshang, Xinli, Sanshandao, Sizhuang and Xincheng gold deposits, and the Qixia and northern Zhaoping anomaly areas are about 47.6 tons, 78 tons, 63.7 tons, 69 tons, 3564 tons, 7120 tons and 696 tons of Cd resources, respectively; that is, the Jiaodong gold mining area has the Co, Te, and Cd resource conditions that are comprehensively utilized in the near future or as potential replacement resources in the future, and its spread area is wide and the resource potential is huge. Preliminary studies have shown that Jiaodong has the resource conditions for the formation of super-large Cd deposits, large-scale Te and Co deposits, but the spatial distribution of critical metal resources is extremely uneven, and its extreme enrichment mechanism and law are still unclear, and in-depth research is urgently needed.

Genesis of visible gold in pyrite in the Zhaoxian gold deposit, Jiaodong gold province, China: Constraints from EBSD micro-structural and LA-ICP-MS elemental analyses

Pyrite (FeS2) is one of the most common hosts for gold (Au) in different types of gold deposits, including visible and invisible gold. For visible gold in pyrite, it remains unclear whether it resulted from remobilization of invisible gold in the gold-hosting pyrite or from external input. This paper reports a case study from the Zhaoxian gold deposit, which is the deep extension of the well-known Jiaojia gold deposit, in the Jiaodong gold province. The texture and composition of Au-bearing pyrite from the Zhaoxian deposit were studied with petrographic, Electron Back-Scattered Diffraction (EBSD) mapping, and Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) methods. Four types of pyrite (Py-1 to Py-4), corresponding to four generations of veins, i.e., the pre-ore V1, syn-ore V2 and V3, and post-ore V4, were distinguished. Py-2 is volumetrically the most abundant among the four, and is the main host of visible gold. LA-ICP-MS analyses of pyrite indicate that gold contents in most analysis points are below the detection limit, with measured Au contents ranging from 0.02 to 0.17 ppm (median 0.09 ppm) in Py-1, and 0.03 to 2.45 ppm (median 0.07 ppm) in Py-2. EBSD analyses indicate that pyrite (Py-2) display brittle deformation features including microstructures, lattice dislocation, and grain boundary displacement. Visible gold in Py-2 occurs in micro-fractures, cavities, and grain boundaries. The generally low contents of Au in pyrite, including Py-2, and the brittle deformation features, suggest that the visible gold grains did not result from remobilization of invisible gold from pyrite. Rather, the majority of gold was introduced by fluids after the formation of the gold-hosting pyrite. These fluids were derived from the same sources as those precipitating the gold-hosting pyrite, but were more evolved and enriched in Au. Circulation of these auriferous ore-forming fluids in microfractures of pyrite and interstitial space resulted in precipitation of visible gold.

Application of the AMT Method to Gold Deposits: A Case Study in the Qinling Metallogenic Belt of North China Craton

The Lushi gold polymetallic ore-concentration area, located in the southern margin of North China Craton, is an important polymetallic ore district in the Qinling metallogenic belt. The Jianbeigou gold deposit is an important quartz vein type gold deposit in this district. In order to reveal the geological structure of the Jianbeigou gold deposit to guide deep prospecting, the EH4 conductivity image system was used in the Jianbeigou area. The sections obtained by the audio magnetotellurics method (AMT) indicate that the steeply dipping low resistivity zone in the area has a good corresponding relationship with the location of the known shallow ore bodies, and an extension in the deep. The low resistivity anomaly zone obtained by the inversion results are well correlated with the gold mineralization zone of the ore bodies, indicating good deep prospecting and exploration potential in this area. Based on geological and geophysical evidences, this paper inferred the possible occurrence location and depth range of the buried ore bodies. The AMT survey results reflect good exploration potential of the mining area and provide a geophysical basis for deep prospecting.

Mineral paragenesis of the Anfangba gold deposit, western Qinling Orogen, China: Implication for coupled dissolution-reprecipitation reactions and the liquid bismuth collector model

The newly discovered Anfangba gold deposit is hosted in the Middle Triassic pumpellyite-actinolite facies metamorphosed turbidites in the western Qinling Orogen, Central China. It is characterized by a pyrite-quartz vein type, a medium-high temperature, and the development of visible gold and abundant bismuthides. It is the first reported Au-Bi-associated deposit in this area and remains poorly understood. In this study, the mineral paragenesis has been studied to further understand ore formation, including sulfides (pyrite, chalcopyrite, pyrrhotite, bornite, bismuthinite, tetrahedrite and arsenopyrite), Cu-Bi(Sb) sulfosalts (emplectite, wittichenite, and skinnerite), sulfoselenide (unnamed sulpho-tellurian nevskite), tetradymite group minerals (joséite-A, joséite-B and tetradymite), native bismuth and electrum. The physicochemical conditions of the ore-forming process can be estimated based on the mineral paragenetic sequence. The calculated logαH2S and logfO2 of the main mineralization stage are higher than −2.25 and lower than −37.96, respectively. EPMA mapping indicated that ore-forming fluid with low sulfur and oxygen fugacities may have played an important role in provoking the activity of the semimetals such as Bi, Sb, Se and Te. This may have result in the formation of accessory minerals, including native bismuth, skinnerite and an unnamed sulpho-tellurian nevskite via coupled dissolution-reprecipitation (CDR) reactions. Mineralography, EPMA and LA-ICP-MS analysis have revealed a close relationship between Au mineralization and Bi-blebs. It suggests that the “liquid bismuth collector model” contributed to the Au enrichment of the Anfangba deposit. As the coexistence of native bismuth and bismuthinite is commonly seen in different types of hydrothermal gold deposits, the presence of Bi-melts and the influence of the “liquid bismuth collector model” in these gold deposits may have been underestimated.

Metal source of gold deposits in the Jiaoxibei area, Eastern China: Insights from trace element analysis of gold and pyrite

AbstractThe metal source of gold deposits in the Jiaoxibei area, eastern China, has been investigated by many researchers, but no consensus has been reached so far. In this study, three typical gold deposits, the Xinli, Jiaojia, and Dayingezhuang deposits, were selected for trace element analysis of gold and pyrite to constrain the metal source. Pyrite from these three deposits has similar morphological and compositional characteristics, and can be divided into three types: Py1 with euhedral to subhedral textures, Py2 with subhedral to anhedral textures with micro‐fractures, and Py3 with subhedral to anhedral textures and intergrowing polymetallic sulfides. Among them, Py2 and Py3 were formed in the main ore‐forming stage and they are the dominant host minerals of visible gold. In these deposits, visible gold occurs mainly in micro‐fractures or as inclusions in Py2 and Py3. Most of the pyrite has extremely low concentration of invisible gold, indicating that visible gold in the Jiaoxibei district is not a product of the remobilization of invisible gold from earlier pyrite. Both Py2 and Py3 are characterized by low Co concentration of &lt;100 ppm and Co/Ni ratio of &lt;1, which are similar to those of pyrite in sedimentary rocks. Therefore, ore‐forming metals of these gold deposits in the Jiaoxibei district may originate mainly from a sediment‐related metal source.

CSAMT constraints on the metallogenic mechanism of the Zhaishang gold deposit, West Qinling, China

Whether the ore-forming fluids and materials of Zhaishang Carlin/Carlin-like type gold deposit were derived from concealed Mesozoic intermediate–acidic intrusive rocks through deep faults is controversial. In this study, eight CSAMT profiles were used to investigate the electrical resistivity structure of this deposit using high-resolution 2-D inversion. A ∼1 km wide high-resistivity (>3000 Ωm) body was observed at the base of the resistivity model (∼600 m). Two slightly NE-dipping high-conductivity channels were also observed along two sides of the high-resistivity body that connected to the gold-bearing quartz veins at the surface. The data suggest that the high-resistivity body is a Mesozoic granite and the two high-conductivity channels are fault zone conductors, which may be the wings of an NE-trending anticline that formed under regional compressive stress during the Caledonian orogeny. Their reactivation during the Indosinian and Yanshanian periods likely formed conduits for rising deeply-sourced ore-forming fluids (likely magmatic water). These conduits also promoted ground and meteoric water infiltration and mixing with the rising fluids. Accordingly, at least some of the ore-forming fluids and materials in the Zhaishang deposit were derived from Mesozoic granites through concealed faults, which can provide new geophysical constraints for discussions of the deposit’s metallogenic mechanism.

Magmatic-hydrothermal origin for Carlin-type Au deposits: Evidences from in-situ S-Pb isotopic compositions of sulfides, the Chang’an Au deposit, southern Ailaoshan tectonic zone

The Chang’an Au deposit is a large Au deposit located in the south of the Ailaoshan-Red River tectonic zone, southwestern margin of the South China block. The deposit exhibit characters similar to Carlin-type Au deposits in Nevada and Dian-Qian-Gui “Golden Triangle”, including tectonic evolution (deformed and rifted cratonic margins), orebody controlled by lithology and structure and invisible Au ionically bound in arsenian pyrite and pyrite. Mineralization is controlled by a strike-slip fault and occurs as barren milky quartz veins, disseminated gold-bearing pyrite and arsenopyrite in the Early Paleozoic sandstone, siltstone and limestone. Gold is invisibly and ionically bound in arsenopyrite and pyrite or locally occurs as isolated native gold crystals (micron scale). Wall rock alteration includes sulfide, silicic, sericite and decarbonized alterations. Three hydrothermal mineralizing stages (I, II, III) can be identified: milky quartz-pyrite (I), quartz-sericite-pyrite-arsenopyrite (II) and dolomite-calcite-quartz (III). Different from those deposit in Dian-Qian-Gui, numerous plutons intruded in and around the mine. The syenite dikes are pyritized, thus, formed prior to the mineralization while lamprophyre dikes are unaltered and crosscut by the syenite dikes. The syenite dikes yielded zircon U − Pb ages of ca. 35.8 Ma and the lamprophyre yielded similar Ar-Ar age of ca. 36.6 Ma, largely constraining the age of Au mineralization. In situ S–Pb isotopic compositions for ore pyrite and arsenopyrite were measured by fs-LA-MC-ICP-MS. Sulfides from Chang’an show a uniform range from –6.4‰ to + 4.6‰, a typical characteristic of magmatic-derived S. Such sulfur isotopic compositions are similar to those of sulfides from Carlin-type Au deposits, but different from those of sulfides from orogenic-type deposit, which commonly exhibit a wide range of δ34S values. Pb isotopic ratios of pyrite and arsenopyrite are similar to those of the intrusive rocks in the deposit with more radiogenic Pb, suggesting that the metal is probably sourced from the coeval intrusive rocks and sedimentary wall rocks. Combined with the low Au concentrations of the sedimentary wall rocks, Au in the Chang’an deposit are probably sourced from the intrusive rocks. Differences between the Chang’an deposit and typical orogenic-type Au deposit include: (1) Orebodies in the Chang’an deposit exhibit transitional contact relationship with the host rocks and boundaries between them are defined by cut-off grade while these boundaries in typical orogenic-type deposits are clearly defined. (2) Sulfidized and decarbonized alterations are quite significant in the Chang’an deposit but commonly absent in typical orogenic-type deposits. (3) The Chang’an deposit have lower CO2 contents of ore-forming fluids and more shallow ore-forming depth relative to typical orogenic-type deposits. Based on the ore deposit geology, dating and isotopic data, the Chang’an mineralization is similar to typical Carlin-type gold deposit, formed by ore fluids originated from a deep magmatic S source in an post-collisional intracontinental setting at ca. 36 Ma.

Tectonics, geochronology, and mineralization of the Shuidegou gold deposit in the Mianlue belt, western Qinling Mountains, China

The gold mineralization in the Mianlue belt, western Qinling Mountains, has been a hotspot in geoscience research in recent years. In particular, important breakthroughs have been achieved in terms of prospecting in the medium-sized Shuidegou gold deposit, located in the middle of the Mianlue belt. Here, we present the results of systematic tectonic and chronological analyses conducted on the Shuidegou gold deposit. The reconstructed zircon U–Pb chronologies of the ore-bearing altered rocks and of the ore-bearing vein demonstrated that the Shuidegou gold deposit formed at ~183 Ma and was further enriched at ~ 150 Ma. The macro- and micro-structures identified in deformed geologic bodies and quartz c-axis fabrics in the mining area suggest a division of the deformation sequence into four phases, corresponding to: (1) a Mid–Late Triassic collision and convergence of middle–deep deformation structures during the main orogenic period (D1); (2) a Late Triassic–Early Jurassic collision and convergence during the late-stage thrust-nappe tectonic deformation (D2); (3) a Mid–Late Mesozoic shallow strike-slip shear structure stage during intracontinental orogeny (D3); (4) post-Cretaceous, shallow brittle thrust extrusion strike-slip structure (D4). Based on the deformation and zircon U–Pb chronological features of the Shuidegou gold deposit, we believe that the main metallogenic age (~183 Ma) corresponds to the thrust-shear deformation stage (D2) and that it is genetically connected with magmatism. Notably, the late-stage further enrichment(~150 Ma) occurred in the sinistral strike-slip stage. Ore-bearing fluids may have been restricted by the far-field effect of the Pacific plate subduction along the eastern edge of East Asia. Based on the macro- and micro-deformation features, the chronological data relative to the key geologic bodies, and the regional geologic background, we subdivided the mineralizing process of the Shuidegou gold deposit is composed into three stages: (1) the formation of an ore-guiding channel, (2) the deposition and mineralization of ore-forming elements, and (3) a later further enrichment. The study of ore-controlling structure showed that the development of the Shuidegou gold deposit was mainly controlled by WNW- (E–W) and NNE-trending structures during the two metallogenic periods (~183 Ma and ~ 150 Ma, respectively). Concerning this aspect, the Shuidegou gold deposit contrasts with some typical gold deposits in the same region.

Application of portable X-ray and micro-X-ray fluorescence spectrometry to characterize alteration and mineralization within various gold deposits hosted in southern New Brunswick, Canada

New Brunswick hosts multiple types of gold deposits related to various stages of Appalachian orogenesis. Some of these structurally controlled deposits are considered intrusion-related; however, the majority have characteristics of orogenic deposits. The geochronology and genesis of the gold and antimony deposits in southern New Brunswick have been studied to varying degrees, but the relationship between mineralization and tectonism remains unresolved. This study involves the examination and comparison of auriferous quartz (-carbonate) veins associated with orogenic and intrusion-related gold mineralization of southern New Brunswick. The Belleisle Bay and Annidale groups (Annidale area) are host to mainly orogenic type gold mineralization, whereas in the Cookson and Mascarene groups (Clarence Stream area), gold mineralization is characterized as intrusion-related. For this study, the Devil Pike Brook deposit and Sheba Pit, East Scotch Settlement BP gold occurrences and the Bald Hill antimony deposit represent the Annidale area, whereas the South (Central and East subzones), George Murphy, Richard, and Jubilee zones represent gold mineralized areas in the Clarence Stream region.To facilitate the geochemical investigation of the various deposits and occurrences, an Olympus Vanta™ portable X-ray fluorescence spectrometer (pXRF) was used to rapidly analyse the composition of the different auriferous quartz (-carbonate) veins and characterize the alteration assemblages related to gold mineralization. The precision and accuracy of the pXRF data was monitored through QA/QC procedures, with the resulting corrected pXRF data undergoing principal component analysis (PCA) to fully interrogate the large data set.The PCA results highlight hydrothermal alteration and mineralization geochemical trends in the studied orogenic and intrusion-related gold deposits and occurrences. Some gold pathfinder elements reflect these different trends on the PC analysis on the studied samples. From the different PCs, various information about alteration and mineralization can be deduced. In Annidale area PC1 retrieves positive loadings of S, Cu, As, Pb, Zn, Fe, and Sb consistent with mineralization, PC2 displays positive loadings of Ca, Sr, Y, Mn and Ti, and PC3 extracts information about K, Rb, Ba, Zr, and Al consistent with alteration. In the Clarence Stream area, PC1 retrieved information about Al, K, Zr, Ba, Nb, Th and Rb consistent with alteration, PC2 displays positive loadings of As, Sb, Fe, Co, and S consistent with mineralization and PC3 extracts information about Zn, Pb, Mn, Fe, Cu, S and Si.Data obtained from the micro-X-Ray fluorescence–energy dispersive spectrometer (μ-XRF) analyses of the same sample suite concur with the alteration and mineralization characteristics identified using pXRF; these data indicate that chloritic and sericitic alteration with sulphides are associated with quartz (-carbonate) veins. The μ-XRF analysis is also helpful to further investigate sulphide and gold mineralization, as well as to locate potentially datable minerals, such as titanite, rutile, zircon, apatite, and monazite, in the gold-bearing quartz (-carbonate) veins; these data identified rutile and titanite in the Annidale samples and apatite in Clarence Stream samples that are being followed up geochronologically.

Роль окружающей среды в размещении апокарбонатного золотого оруденения Чакылкалянского мегаблока (Южный Узбекистан)

Analysis of the available information and the results of many years of research on gold deposits in Uzbekistan made it possible to identify the main unconventional types of deposits. Among them, the most interesting are apocarbonate, crustal, sulfide-carbonaceous and apovolcanogenic quartzite (Upper-Kattakashkasai ore occurrence). The apocarbonate type is widespread in Uzbekistan, has been studied in sufficient detail and information is provided on it in this article. The article examines the existence, distribution and genesis of ores of Karlin type gold deposits. The generalizing characteristics of the Karlin type gold mineralization are given. The issues of geochemical specialization of the Paleozoic strata of the Chakylkalyan megablock are considered, the most favorable stratolevel for the localization of mineralized zones is determined, and the features of carbonate rocks in the process of gold deposition during reactions with silicic solutions are characterized. Based on the materials of regional geochemical profiling, the behavior of the main ore-forming elements in the rocks of both carbonate and volcanogenic-terrigenous strata is analyzed. As a result of the analysis, subclarkic contents of the main ore-forming elements (As, Co, Ni, Pb, Cu, Ag, V, Cr, Sc) were revealed, which create increased concentrations in gold-bearing pyrites of both apocarbonate gold mineralization and related formations.

Geology, hydrothermal alteration and mineralization of the Carlin-type gold deposit at South Ratatotok, Southeast Minahasa Regency, North Sulawesi Province, Indonesia

South Ratatotok in North Sulawesi, Indonesia is one of the regions that was once a gold-producing region in North Sulawesi. Mesel gold deposit in this region is approved as Carlin type gold deposit with a total of resources of 12.25 Mt @5.21 g/t Au. Near the Mesel deposit, gold mineralization is currently discovered prospects such as Leon, Bulex Hill, Heind’s Find and Monkey Forest. This study is aimed to elucidate the types and distribution of hydrothermal alteration and ore mineralization encountered in these four prospect areas. Research methods including field work (including geological and hydrothermal alteration mapping, rocks and ore sampling) and various laboratory works consisting of petrographic analysis, ore microscopy, X-Ray Diffraction (XRD) and fire assay were performed. As a result, the study area is composed of several lithological units including limestone, volcanic breccia, porphyritic andesitic intrusion units as well as colluvial deposit. The wall rocks have been suffered by various hydrothermal alteration as follows: silicification in limestone, carbonatization in volcanic breccia, argillic alteration in volcanic breccia and propylitic alteration developed in porphyritic andesitic intrusion, minor decarbonatization associated with limestone and minor oxidation in volcanic breccia. Gold mineralization is present as a replacement type in very fine size of sulphides and gold is closely associated with silicified limestone. Ore chemistry by fire assay analysis indicates that gold and silver contents vary from 0.012 g/t to 2.41 g/t Au, and <0.5 g/t to 2.1 g/t Ag, respectively. The increase of gold content is geochemically followed by high values of Ag, As, Sb, Cu, Pb, Zn and by low value of Hg because of oxidation. Supergene process was also the key factor in the enrichment of gold where the oxidized ore has relatively higher gold grade than in non-oxidized ore.

Lithium isotopic systematics of ore-forming fluid in the orogenic gold deposits, Jiaodong Peninsula (East China): Implications for ore-forming mechanism

There are rare studies on the Li isotope systematics of ore-forming fluids in the mesothermal deposits, especially in the orogenic gold deposits. We carried out systematic Li isotopic analyses on whole-rock granite samples, and quartz and pyrite were separated from both the altered-rock type and quartz-vein type gold deposits from the Canzhuang gold deposit of the Jiaodong Peninsula (East China) with purposes of shedding lights on the ore-forming fluid evolution and ore-forming mechanism. Altered granite and unaltered granite yield δ7Li values of 12.6‰ and 1.9‰, respectively, indicating that fluid-related alteration can change the Li isotopic composition of granite significantly and ore-forming fluid is enriched in heavy Li isotope. The δ7Li values of quartz and pyrites from the altered-rock type gold deposits range from 5.5‰ to 21.1‰ and from 0.5‰ to 16.8‰, respectively. The δ7Li values and Li contents of quartz are positively correlated in the altered-rock type gold deposit, with the two figures in the first mineralization stage (5.5–13.7‰ and 0.3–1.1 ppm) being significantly lower than that in the second stage (17.9–20.8‰ and 1.0–10.4 ppm) and the third stage (17.3–21.0‰ and 1.1–4.2 ppm). This is consistent with the lithium isotopic compositions of pyrites of the altered-rock type gold deposits, with δ7Li values of pyrites in the first stage (0.5–2.8‰) being significantly lower than that in the second stage (2.3–16.8‰) and the third stage (5.8–6.2‰). Collectively, these features demonstrate that the Li isotopic compositions of the altered-rock type gold deposits were controlled mainly by interaction between ore-forming fluid and host granites, and that the ore-forming fluids in three stages belong to different pulses of fluid injection and evolve separately. On the contrary, the quartz and pyrite from the quartz-vein type gold deposits yield δ7Li values of 9.4‰ ~33.6‰ and 0.5‰ ~24‰, respectively, which are different from that of the altered-rock type gold deposits. In addition, the lithium isotopes of quartz show no correlation with the lithium contents of quartz, and the δ7Li values of quartz and pyrites decrease gradually from the first to the third metallogenic stage, with δ7Li ranging from 33.6‰ to 9.4‰ for quartz, and from 24‰ to 0.5‰ for pyrite. Based on the fractionation calculation, we suggest that Li isotope variation of the quartz-vein type gold deposits was ascribed to the Rayleigh fractionation in a close metallogenic system. This work demonstrates that the orogenic gold deposits display a significant Li isotopic fractionation and the lithium isotopes of quartz and pyrite are potential in providing insights into the evolution processes of mesothermal hydrothermal systems.

Geological position of the gold-sulfide-quartz deposits of the Chilean active margin

Research subject. The gold-sulphide-quartz deposits of Central Chile are typical prospecting objects, having small ore intervals (from the first tens of centimetres to 1 m), intermittent and nested ore distribution and extremely uneven gold contents.Materials and methods. The patterns of ore mineralization distribution are considered against the background of the results of modern geophysical studies of the lithosphere: the Moho surface, density and thermal regime of the upper mantle. Detailed studies were conducted on the Yapin ore field.Results. It was shown that the faults controlling gold-sulphidequartz mineralization are derivatives of shear tectonics under the conditions of a transpression regime along the Chilean active margin. At an early stage, these faults developed in a right-shift environment, which was accompanied by the introduction of diabase dikes into the northeastern faults, and gold-sulfide-quartz mineralization superimposed on the dikes was deposited during the left-shift stage. The geological structure of the deposits in the ore field Yapin was characterized. It was shown that a diverse mineralization is developed in the ore field - copper-porphyry, IOCG-type and gold-sulphide-quartz. According to geochemical data, the latter is characterized by a clear enrichment of chalcophilic elements (Au, As, Ag, Cd, Cu, Bi, Pb, Zn, Te, Co). The marked enrichment of Bi, Te and Co ores indicates the participation of magmatic fluid in ore formation and the similarity of the mineralization of the Escondida deposit with the type of gold deposits associated with granitoid intrusions. According to geochemical features, gold-sulphide-quartz mineralization in the general zoning pattern occupies a boundary position between IOCG-type objects and copper-porphyry deposits.Conclusions. The conclusion is drawn about the independence of gold-sulphide-quartz mineralization and its difference from epithermal gold deposits. It is noted that, in the volcanic belts of the North-East of Russia, the prospects for discovering unconventional gold-sulphidequartz deposits similar to those of Central Chile are rather real.

Origin of ore-forming fluids of Tokuzbay gold deposit in the South Altai, northwest China: Constraints from Sr–Nd–Pb isotopes

• A low I Sr (t) fluid system is required for formation of Tokuzbay gold deposit. • Pb isotopes of sulfides are similar with the ore hosting Altai Formation. • The gold mineralization may have originated from the metamorphic dehydration of sediments of Altai Formation. Orogenic gold deposits are the most important gold resource in the world. It is controversial whether their ore-forming fluids were sourced from metamorphic dehydration of the crust or the mantle. The Tokuzbay gold deposit is a typical orogenic-type gold deposit in the Central Asian Orogenic Belt , providing a case for discussing the source of ore-forming fluids. The auriferous quartz veins are fault-controlled and occur mainly in metamorphic sediments of Devonian Altai Formation and minor in diorite dikes, forming three ore types, i.e., quartz vein, altered metamorphic sediments and altered diorite dikes. We studied the Sr–Nd–Pb isotope characteristics of the ore sulfides, and magmatic and metamorphic rocks from the Tokuzbay gold deposit, and thereby discuss the source of the ore-forming fluids. The 87 Sr/ 86 Sr ratios of meta -sediment hosted ores scatter between 0.709474 and 0.715238, and I Sr (292 Ma) values range from 0.706570 to 0.714045. The diorite dikes hosted ores show more restricted 87 Sr/ 86 Sr ratios ranging from 0.706963 to 0.711519, and I Sr (292 Ma) values ranging from 0.706777 to 0.710612. The wall rocks of the Altai Formation have I Sr (292 Ma) values of 0.711778 and 0.714409, which are higher than ore sulfides. This indicates that the I Sr (292 Ma) values of initial ore-forming fluids that interacted with the Altai Formation are no higher than 0.706777, which is the lowest I Sr (292 Ma) value for disseminated ores. The calculated ( 143 Nd/ 144 Nd) i ratios and ε Nd (292 Ma) values for meta -sediment hosted ores range from 0.511882 to 0.512464, and −7.4 to 4.0, respectively. The calculated ( 143 Nd/ 144 Nd) i ratios and ε Nd (292 Ma) values for diorite dike hosted ores vary from 0.512293 to 0.512562, and from 0.6 to 5.9, respectively. The meta -sediments of Altai Formation show ε Nd (292 Ma) values ranging from −6.8 to −4.4 with an average of −5.8, which are lower than those of ore sulfides. This indicates that the ε Nd (292 Ma) values for the fluids that interacted with the wall rocks cannot be lower than 4.5, which is the average value for disseminated ores. The calculated ( 208 Pb/ 204 Pb) i , ( 207 Pb/ 204 Pb) i , and ( 206 Pb/ 204 Pb) i values of ore sulfides are 37.796–38.989, 15.512–15.707, 17.988–18.100, respectively. The wall rocks of the Altai Formation show relatively higher ( 206 Pb/ 204 Pb) i ratios, indicating that the ore-forming fluid that interacted with the Altai Formation are not higher than 17.988, which is the lowest values of sulfides from disseminated ores. Based on the Sr–Nd–Pb isotope data, we suggest the possible ore-forming fluids should have lower I Sr (292 Ma) values, higher ε Nd (292 Ma) values, and lower ( 206 Pb/ 204 Pb) i values compared to the those of ore sulfides and were possibly sourced from a source compositionally similar to the diorite dikes in addition to wall rocks of Altai Formation. Combining with the regional metamorphism and tectonic evolution , we suggest that the ore fluids have originated from the metamorphic dehydration of sediments of Altai Formation in the South Altai during the collision between Altai Orogen and Junggar Plate.

Comparison of U-spatial statistics method with Classical Statistics results in the determination of geochemical anomalies of Epithermal Gold in Khoshnameh area, Hashtjin, Iran

In this study, methods based on the distribution model (with and without personal opinion) were used for the separation of anomalous zones, which include two different methods of U-spatial statistics and mean plus values of standard deviation (). The primary purpose is to compare the results of these methods with each other. To increase the accuracy of comparison, regional geochemical data were used where occurrences and mineralization zones of epithermal gold have been introduced. The study area is part of the Hashtjin geological map, which is structurally part of the folded and thrust belt and part of the Alborz Tertiary magmatic complex. Samples were taken from secondary lithogeochemical environments. Au element data concerning epithermal gold reserves were used to investigate the efficacy of these two methods. In the U- spatial statistics method, and criteria were used to determine the threshold, and in the method, the element enrichment index of the region rock units was obtained with grouping these units. The anomalous areas were identified by, and criteria. Comparison of methods was made considering the position of discovered occurrences and the occurrences obtained from these methods, the flexibility of the methods in separating the anomalous zones, and the two-dimensional spatial correlation of the three elements As, Pb, and Ag with Au element. The ability of two methods to identify potential areas is acceptable. Among these methods, it seems the method with criteria has a high degree of flexibility in separating anomalous regions in the case of epithermal type gold deposits.