Electron microprobe analyses of ore minerals and H–O,S isotope geochemistry of the Yuerya gold deposit,eastern Hebei,China: Implications for ore genesis and mineralization

The Yuerya gold deposit in eastern Hebei Province, China, is located on the eastern margin of the North China Craton and is hosted by Mesozoic Yanshanian granitoid rocks and adjacent Mesoproterozoic Gaoyuzhuang Formation carbonates. The auriferous quartz veins in this deposit are dominated by pyrite, with subordinate sphalerite, chalcopyrite, and galena in a quartz-dominated gangue that also contains calcite, dolomite, barite, apatite, and fluorite. Gold is present as native gold and electrum, which are generally present as micron-size infillings in microfissures within pyrite and less commonly as tiny inclusions within pyrite, quartz, and tellurobismuthite. The pyrite in this deposit has high Co/Ni ratios and contains elevated concentrations of both of these elements, suggesting that the Yuerya gold deposit has a magmato-hydrothermal origin and that the ore-forming fluids that formed the deposit leached trace elements such as Co, Ni, As, and Au during passage through Archean metamorphic rocks, Mesoproterozoic carbonates, and the Yanshanian Yuerya granitoid. Pyrite in the study area has S/Se ratios and S isotopic compositions that suggest that the sulfur (and by inference the gold) within the deposit was sourced from magmato-hydrothermal fluids that were probably originally derived from Archean metamorphic rocks and Yanshanian granitoids. Tellurobismuthite in the study area is closely intergrown with gold and was the single telluride phase identified during this study. The fineness of gold associated with tellurobismuthite is greater than the fineness of gold associated with pyrite, although the fine particle size of the gold surrounded by tellurobismuthite means that the recovery of this gold is difficult, in turn meaning that the tellurobismuthite has little significance to the economics of the Yuerya gold deposit. Only trace amounts of sulfides are associated with the tellurobismuthite within the Yuerya gold deposit, suggesting that this mineral was deposited under conditions of low fS₂ and/or high fTe₂. In addition, the presence of tellurides within the Yuerya gold deposit reflects a genetic relationship between the deposit and magmatism. Quartz from mineralized veins in the study area has δ¹⁸O values of 11.2‰–12.9‰ and the fluids that formed these veins have δD values of − 78.3‰ to − 72.1‰. The δ³⁴S values of pyrite within the deposit are rather restricted (2.3‰–3.5‰). These data, combined with the trace element geochemistry of sulfides within the deposit, suggest that the formation of the Yuerya gold deposit was closely related to both Archean metamorphic rocks and the Yanshanian Yuerya granitoid.     

Multistage mineralization in the Haoyaoerhudong gold deposit,Central Asian Orogenic Belt:Constraints from the sedimentary-diagenetic and hydrothermal sulfides and gold

The Central Asian Orogenic Belt,as one of world-class gold economic belts,preserves a number of giant,large black shale-hosted gold deposits,while it is still debated for origin of sulfides and gold mainly due to lack of identification for multiple stages of sulfides.The Haoyaoerhudong gold deposit is hosted in a sequence of Mesoproterozoic carbonaceous and pyritic slate,phyllite,and schist that form a tight syncline along the north margin of the North China Craton.Detailed petrography of the host rocks and mineralization have defined five stages of pyrites.The earliest form of pyrite(Py₁)occurs as fine-grained dispersed pyrite in black carbonaceous slate and medium-to coarse-grained disseminated pyrite in pyrite-rich layers,contains relative low gold and high arsenic content,indicating a syn-sedimentary or diagenetic in origin.Stage Ⅱ pyrite(Py₂)occurs with garnet and quartz inclusions and Py₃ occurs as pyrite veins,contains higher gold and lower As content,and are interpreted to have formed from the dissolution-reprecipitation of Py₁ during the peak metamorphism or post-peak metamorphism.Stage Ⅳ pyrite(Py₄)from the pyrite-quartz veins crosscut the metamorphic garnet,contains the highest gold concentrations and other trace elements,and is considered to have formed post-peak metamorphism.Abundant native gold,electrum,and maldonite occur as inclusions within Py₄ and monazite and in fractures that crosscut garnet.While,Py₅ with typical remobilized feature is thought to be a product of melting of former pyrites(Py₁ to Py₄)triggered by the large-scale Hercynian magmatism.The sedimentary/diagenetic Py₁ have δ³⁴S values that range from +12.4‰to +16.2‰.Later generations of sulfides,including Py₂ to Py₅,and Ccp₂ to Ccp₃,have δ³⁴S values from +9.5‰to +12.7‰.Monazite with maldonite inclusions from quartz-pyrite veins yielded an intercept age of 341.3±6.6 Ma,while coarse grained monazite associated biotite along fractures in the reefs yielded an intercept age of 254.6±8.2 Ma.The paragenetic,textural,chemical,and isotopic data suggest three distinct gold producing episodes at Haoyaoerhudong gold deposit.Gold and arsenic were clearly initially concentrated in organic muds,and enriched along the structures of diagenetic arsenic-rich pyrite.Subsequently,accompanying metamorphism and deformation,gold was liberated from the dissolution of diagenetic pyrites to form the pyrite veins.Finally,accompanying transformation of pyrite into pyrrhotite,gold was released into the metamorphic fluids to become concentrated as native gold,electrum,and maldonite in pyrite-quart veins.Monazite with age of 341 Ma from quartz-pyrite veins suggests that the third major gold mineralizing event in Haoyaoerhudong occurred before the Hercynian magmatism,suggesting that the Haoyaoerhudong deposit is a typical orogenic gold deposit rather than intrusion-related deposit.     

1 Geological Environment of Mineralization

Abstract The Puziwan gold deposit is a special linear cryptoexplosive breccia type deposit found in northeastern Shanxi, China, in recent years. The deposit is located in a secondary metallogenic belt of the most famous Au‐Ag polymetallic metallogenic belt along the north margin of the North China platform. The secondary metallogenic belt is a synmagmatic tension‐shear fault‐fracture belt of ENE linear trend. The Indosinian cryptoexplosive breccia body, quartz monzonitic porphyry (beschtauite breccia), quartz monzonite (243.7 Ma, K‐Ar), Yanshanian granite‐porphyry (105±6 Ma, Rb‐Sr) and orebodies mostly occur as dykes or veins and short lenses along the structural fracture belt. The orebodies are emplaced in the fractured cryptoexplosive breccia body in the tectonomagmatic belt and their attitude is consistent with that of the breccia body. The orebodies have two types: one is shallow‐seated thick and big ones, which are short‐lenticular in plan and wedge‐shaped in cross section, shallow buried, large in size and high‐grade; the other is lean orebodies, which occur as parallel veins at depths. The ores are mainly of Au‐Ag polymetallic sulphide‐rich breccia type. Pyrite (limonite) is the dominant metallic mineral, with subordinate chal‐copyrite, galena, sphalerite, tenantite, native gold, electrum, native silver and argentite. The gangue minerals consist mainly of quartz and plagioclase, with subordinate carbonate minerals, alunite chalcedony and kaolin. Kaolinization is the characteristic alteration type. Sulphide minerals contain abundant trace minerals such as Cu, Pb, Ag, Sb and Hg, while in the ores Ag, Cu, Pb, Zn, As and Sb are the best indicator element assemblage of Au. The δ³⁴S(%_o) values of the ores rane from ?3.2%_o to 5.3%_o, with average ?0.102%_o. The δO H₂O(%_o) and δ(%_o) values are in the ranges from ?3.1%_o to 7.73%_o and from ?64%_o to ?90%_o respectively. The Pb isotopic compositions of the rocks and ores in this region indicate that Pb comes from three tectonic sources—upper mantle, lower crust and orogenic belt. The inclusion homogenization temperature are in the ranges of 110 to 220°C and 230 to 310°C, which suggests that the deposit formed under meso‐epithermal conditions. The ore‐forming pressures range from 6 to 32 MPa and the depths are 230 to 1200 m. In view of the above, the Puziwan gold deposit is genetically ascribed to a high‐sulphur (alunite‐kaolin) meso‐epithermal gold deposit related to subvolcanic rocks. This gold deposit formed during the Indosinian stage (245.9±0.3 Ma) and then was influenced by a thermal event in the Yanshanian stage (142.9±0.5 Ma).     

Lithologic controls on mineralization at the Lagunas Norte high-sulfidation epithermal gold deposit, northern Peru

The 13.1-Moz high-sulfidation epithermal gold deposit of Lagunas Norte, Alto Chicama District, northern Peru, is hosted in weakly metamorphosed quartzites of the Upper Jurassic to Lower Cretaceous Chimú Formation and in overlying Miocene volcanic rocks of dacitic to rhyolitic composition. The Dafne and Josefa diatremes crosscut the quartzites and are interpreted to be sources of the pyroclastic volcanic rocks. Hydrothermal activity was centered on the diatremes and four hydrothermal stages have been defined, three of which introduced Au ± Ag mineralization. The first hydrothermal stage is restricted to the quartzites of the Chimú Formation and is characterized by silice parda, a tan-colored aggregate of quartz-auriferous pyrite–rutile ± digenite infilling fractures and faults, partially replacing silty beds and forming cement of small hydraulic breccia bodies. The δ³⁴S values for pyrite (1.7–2.2?‰) and digenite (2.1?‰) indicate a magmatic source for the sulfur. The second hydrothermal stage resulted in the emplacement of diatremes and the related volcanic rocks. The Dafne diatreme features a relatively impermeable core dominated by milled slate from the Chicama Formation, whereas the Josefa diatreme only contains Chimú Formation quartzite clasts. The third hydrothermal stage introduced the bulk of the mineralization and affected the volcanic rocks, the diatremes, and the Chimú Formation. In the volcanic rocks, classic high-sulfidation epithermal alteration zonation exhibiting vuggy quartz surrounded by a quartz–alunite and a quartz–alunite–kaolinite zone is observed. Company data suggest that gold is present in solid solution or micro inclusions in pyrite. In the quartzite, the alteration is subtle and is manifested by the presence of pyrophyllite or kaolinite in the silty beds, the former resulting from relatively high silica activities in the fluid. In the quartzite, gold mineralization is hosted in a fracture network filled with coarse alunite, auriferous pyrite, and enargite. Alteration and mineralization in the breccias were controlled by permeability, which depends on the type and composition of the matrix, cement, and clast abundance. Coarse alunite from the main mineralization stage in textural equilibrium with pyrite and enargite has δ³⁴S values of 24.8–29.4?‰ and $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ values of 6.8–13.9?‰, consistent with H₂S as the dominant sulfur species in the mostly magmatic fluid and constraining the fluid composition to low pH (0–2) and logfO₂ of ?28 to ?30. Alunite–pyrite sulfur isotope thermometry records temperatures of 190–260 °C; the highest temperatures corresponding to samples from near the diatremes. Alunite of the third hydrothermal stage has been dated by ⁴⁰Ar/³⁹Ar at 17.0?±?0.22 Ma. The fourth hydrothermal stage introduced only modest amounts of gold and is characterized by the presence of massive alunite–pyrite in fractures, whereas barite, drusy quartz, and native sulfur were deposited in the volcanic rocks. The $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ values of stage IV alunite vary between 11.5 and 11.7?‰ and indicate that the fluid was magmatic, an interpretation also supported by the isotopic composition of barite (δ³⁴S?=?27.1 to 33.8?‰ and $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ ?=?8.1 to 12.7?‰). The Δ³⁴S_py–alu isotope thermometry records temperatures of 210 to 280 °C with the highest values concentrated around the Josefa diatreme. The Lagunas Norte deposit was oxidized to a depth of about 80 m below the current surface making exploitation by heap leach methods viable.     

Effective elastic thickness of Zealandia and its implications for lithospheric deformation

Zealandia was once located at the active Gondwana margin and experienced complicated tectonic evolution from continental breakup to subduction and oblique slipping along the plate boundary. Here, we investigate the lithospheric thermal and rheological properties via spatial variations in effective elastic thickness (T_e). Using the topography, sediment thickness and gravity data, the fan wavelet coherence method is employed to recover T_e values. The effects of dynamic topography and gravity in the subduction zone on the estimated T_e are considered and removed. The final results reveal that the T_e variation pattern generally coincides well with the tectonic regimes. Relatively high T_e values up to 22 km are observed in North Island and the southernmost part of South Island, while central and northern South Island are dominated by smaller T_e values (~15 km) similar to those of the surrounding submerged plateaus. We interpret the relatively high T_e values as indicating the combined lithospheric strength due to the contacting plates in the subduction zone. To the north along the Tonga-Kermadec subduction zone, the lithosphere surprisingly exhibits anomalously high T_e values, ranging from 22 to 36 km, which contradicts the geological evidence of normal faults developed in the incoming Pacific Plate and the magmatism in the overlying Australian Plate that generally contribute to low lithospheric strength. We speculate that the high-T_e zone is related to the large bathymetry and gravity anomalies in the bending plate and controlled by non-isostatic factors. Finally, we find widespread low T_e values covering the entire arcs and oceanic basins in northern Zealandia, which may indicate that regional lithospheric thinning associated with delamination weakened the integrated strength of the lithosphere.     

中甸普朗还原性斑岩型铜矿床：矿物组合与流体组成约束

成矿流体高氧逸度是斑岩铜矿床模式的一个基本原则。虽然亚洲单个矿体储量最大的普朗铜矿床的成矿母岩——普朗复式岩体具氧化性岩浆特点,但其矿物组合及流体成分却与还原性斑岩型铜金矿床一致:矿石中以发育大量磁黄铁矿为特征,构成黄铜矿-磁黄铁矿-黄铁矿为主的矿物组合,不发育表征高氧逸度的原生磁铁矿和硫酸盐(硬石膏等)矿物;成矿流体中含较多CO₂、CO和CH₄等还原性组分,氧逸度低于铁橄榄石-磁铁矿-石英缓冲剂。成矿流体中还原性组分可能来源于普朗复式岩体周围的含碳质千枚岩或深部铁镁质岩浆。还原性流体中铜元素的溶解度比氧化性流体中的低,但金元素的溶解度不受氧化还原条件的影响;而CH₄可使SO₂还原形成S^2-,为辉钼矿的形成提供物质基础;可能是导致普朗铜矿床Cu品位偏低而伴生大量Au、Mo矿化的主要原因之一。普朗铜矿床还原性特征的厘定有益于深入研究其矿床成因、乃至区域斑岩型铜矿床成矿机制。     

Indicator-Based Geostatistical Models For Mapping Fish Survey Data

Marine research survey data on fish stocks often show a small proportion of very high-density values, as for many environmental data. This makes the estimation of second-order statistics, such as the variance and the variogram, non-robust. The high fish density values are generated by fish aggregative behaviour, which may vary greatly at small scale in time and space. The high values are thus imprecisely known, both in their spatial occurrence and order of magnitude. To map such data, three indicator-based geostatistical methods were considered, the top-cut model, min–max autocorrelation factors (MAF) of indicators, and multiple indicator kriging. In the top-cut and MAF approaches, the variable is decomposed into components and the most continuous ones (those corresponding to the low and medium values) are used to guide the mapping. The methods are proposed as alternatives to ordinary kriging when the variogram is difficult to estimate. The methods are detailed and applied on a spatial data set of anchovy densities derived from a typical fish stock acoustic survey performed in the Bay of Biscay, which show a few high-density values distributed in small spatial patches and also as solitary events. The model performances are analyzed by cross-validating the data and comparing the kriged maps. Results are compared to ordinary kriging as a base case. The top-cut model had the best cross-validation performance. The indicator-based models allowed mapping high-value areas with small spatial extent, in contrast to ordinary kriging. Practical guidelines for implementing the indicator-based methods are provided.     

东秦岭杨斜金矿区石英闪长玢岩锆石U-Pb年代学、地球化学特征及地质意义

杨斜中型金矿床是东秦岭杨斜-丰北河地区典型的石英脉型金矿床,成矿与区内石英闪长玢岩密切相关,具中高温蚀变特征及矿物组成。LA-ICP-MS锆石U-Pb测年结果表明,石英闪长玢岩锆石²⁰⁶Pb/²³⁸U加权平均年龄为149.5±2.7 Ma,谐和年龄为149.5±2.1 Ma,属晚侏罗世。岩石地球化学研究显示,石英闪长玢岩具有高SiO₂(65.53%~65.76%)、高Al₂O₃(15.65%~15.87%)、富碱(N₂O+K₂O=8.07%~8.30%)及贫MgO(1.37%~1.40%)特征,属于高钾钙碱性准铝质系列岩石;相对富集Rb、Ba、K、Pb、Sr等大离子亲石元素和LREE,亏损Nb、Ta、Ti等高场强元素和HREE;其高Sr、高Sr/Y、低Y和低Yb值及正Eu异常等特征参数,与典型埃达克质岩一致,岩浆应起源于加厚下地壳的部分熔融。综合研究认为,杨斜金矿属岩浆期后热液型金矿床,成岩成矿时代一致,形成于秦岭造山带晚侏罗世-早白垩世陆内俯冲向伸展转换的构造环境。     

西南三江甭哥金矿床磷灰石地球化学特征及地质意义

甭哥金矿床位于西南三江造山带北段的义敦弧南缘,属于与富碱侵入岩有关的金矿床。目前,对其成矿机理认识仍较为薄弱,制约了资源评价和找矿勘查进展。本文选取甭哥金矿床强矿化的正长斑岩和弱矿化的黑云辉石正长岩中的磷灰石作为研究对象,详细剖析磷灰石的地球化学特征,探讨其记录的成岩成矿信息。结果表明,磷灰石的稀土元素含量特征及配分模式显示富碱岩浆主要来自于壳幔混合的源区,黑云辉石正长岩中磷灰石的(La/Sm)N、(La/Yb)N、(Sm/Yb)N值和Sr含量呈正相关,说明长石结晶对岩浆结晶分异有重要的影响;正长斑岩中磷灰石具有高Sr/Y、Ce/Pb值,而Th/U、(Sm/Yb)N值较低,指示强烈的流体活动参与了岩浆结晶过程;磷灰石挥发分(F、Cl)含量及比值特征指示金矿成矿流体主要来自地幔源区,成矿与富碱、高氯的成矿流体有关。磷灰石Mn氧逸度计估算结果显示,甭哥富碱侵入岩具有高氧逸度特性,但两种不同岩性岩石的氧逸度具有差异性。其中,正长斑岩的logf_(O_2)值为-12～-10. 3,黑云辉石正长岩的logf_(O_2)值为-15. 5～-11. 1,磷灰石中SO_3含量及Ga含量也暗示正长斑岩的氧逸度高于黑云辉石正长岩的特征;结合磷灰石低Mn、Ga含量和高的Cl、SO_3含量,反映甭哥金矿床金的成矿是在高氧逸度条件下金氯络合物迁移、富集而沉淀的结果。因而,磷灰石的地球化学特征对金矿床成矿过程示踪和勘查评价具有重要的指示意义。     

Laboratory parallel-beam transmission X-ray powder diffraction investigation of the thermal behavior of nitratine NaNO<Subscript>3</Subscript>: spontaneous strain and structure evolution

Present work provides in-situ structural data at a fine temperature scale from RT to the melting point of nitratine, NaNO₃. From the analysis of log e ₃₃ versus log t plots, it is possible to prove that an univocal indication on the R \( \overline{3} \) c (low temperature, LT) → R \( \overline{3} \) m (high temperature, HT) transition mechanism cannot be obtained because of the relevant role played by the arbitrary assumptions required for defining the c ₀ dependence from temperature of the HT phase. This is due to the occurrence of excess thermal expansion for the HT phase. A significantly better fit for an Ising-spin structural model over a non-Ising rigid-body one has been obtained for the LT phase. Moreover, the Ising model led to a smooth variation of the oxygen site x fractional coordinate throughout the transition. The structure of the HT polymorph has been successfully refined considering an oxygen site at x, 0, ½, with 50% occupancy. Such model was the only acceptable one from the crystal chemical point of view as the alternative model (oxygen site at x, y, z with 25% occupancy) led to unrealistically aplanar \( {\text{NO}}_{3}^{ - } \) groups.     

Geology and Metallogenesis of the Sawayaerdun Gold Deposit in the Southwestern Tianshan Mountains, Xinjiang, China

The Sawayaerdun gold deposit, located in Wuqia County, Southwest Tianshan, China, occurs in Upper Silurian and Lower Devonian low‐grade metamorphic carbonaceous turbidites. The orebodies are controlled by a series of NE‐NNE‐trending, brittle–ductile shear zones. Twenty‐four gold mineralized zones have been recognized in the Sawayaerdun ore deposit. Among these, the up to 4‐km‐long and 200‐m wide No. IV mineralized zone is economically the most important. The average gold grade is 1–6 g/t. Gold reserves of the Sawayaerdun deposit have been identified at approximately 37 tonnes and an inferred resource of 123 tonnes. Hydrothermal alteration is characterized by silicification, pyritization, arsenopyritization, sericitization, carbonatization and chloritization. On the basis of field evidence and petrographic analysis, five stages of vein emplacement and hydrothermal mineralization can be distinguished: stage 1, early quartz stage, characterized by the occurrence of quartz veins; stage 2, arsenopyrite–pyrite–quartz stage, characterized by the formation of auriferous quartz veinlets and stockworks; stage 3, polymetallic sulfide quartz stage, characterized by the presence of auriferous polymetallic sulfide quartz veinlets and stockworks; stage 4, antimony–quartz stage, characterized by the formation of stibnite–jamesonite quartz veins; and stage 5, quartz–carbonate vein stage. Stages 2 and 3 represent the main gold mineralization, with stage 4 representing a major antimony mineralization episode in the Sawayaerdun deposit. Two types of fluid inclusion, namely H₂O–NaCl and H₂O–CO₂–NaCl types, have been recognized in quartz and calcite. Aqueous inclusions show a wide range of homogenization temperatures from 125 to 340°C, and can be correlated with the mineralization stage during which the inclusions formed. Similarly, salinities and densities of these fluids range for each stage of mineralization from 2.57 to 22 equivalent wt% NaCl and 0.76 to 1.05 g/cm³, respectively. The ore‐forming fluids thus are representative of a medium‐ to low‐temperature, low‐ to medium‐salinity H₂O–NaCl–CO₂–CH₄–N₂ system. The δ³⁴S_CDT values of sulfides associated with mineralization fall into a narrow range of ?3.0 to +2.6‰ with a mean of +0.1‰. The δ¹³C_PDB values of dolomite and siderite from the Sawayaerdun gold deposit range from ?5.4 to ?0.6‰, possibly reflecting derivation of the carbonate carbon from a mixed magmatic/sedimentary source. Changes in physico‐chemical conditions and composition of the hydrothermal fluids, water–rock exchange and immiscibility of hydrothermal fluids are inferred to have played important roles in the ore‐forming process of the Sawayaerdun gold–antimony deposit.     

Geochemical characteristics of gold mineralization of the Huai Kham On deposit,Sukhothai Fold Belt,Northern Thailand

The Huai Kham On gold deposit is located in the central part of the Sukhothai Fold Belt, northern Thailand. The Sukhothai Fold Belt represents an accretionary complex formed by subduction and collision between the Indochina and Sibumasu Terranes. There are many small gold deposits in the Sukhothai Fold Belt; however, the styles and formation environments of those gold deposits are not clear. The geology of the Huai Kham On deposit consists of volcanic and volcanosedimentary rocks, limestone, and low‐grade metamorphic rocks of Carboniferous to Triassic age. Gold‐bearing quartz veins are hosted by volcanic and volcanosedimentary rocks. The quartz veins can be divided into four stages. The mineral assemblage of the gold‐bearing quartz veins of Stages I and II comprises quartz, calcite, illite, pyrite, native gold, galena, chalcopyrite, and sphalerite. Quartz veins of Stage III consist of microcrystalline quartz, dolomite, calcite, pyrite, native gold, and chalcopyrite. Veins of Stage IV consist of calcite, dolomite, chlorite, and quartz. Fluid inclusions in quartz veins are classified into liquid‐rich two‐phase (Types I_A and I_B), carbonic‐aqueous (Type II), and carbonic (Type III) fluid inclusions. The homogenization temperatures of Types I_A and II fluid inclusions that are related to the gold‐bearing quartz veins from Stages I to III ranged from 240° to 280°C. The δ¹⁸O values of quartz veins of Stages I to III range from +12.9 to +13.4‰, suggesting the presence of a homogeneous hydrothermal solution without temperature variation such as a decrease of temperature during the formation of gold‐bearing quartz veins from Stages I to III in the Huai Kham On gold deposit. Based on the calculated formation temperature of 280°C, the δ¹⁸O values of the hydrothermal solution that formed the gold‐bearing quartz veins range from +3.2 to +3.7‰, which falls into the range of metamorphic waters. The gold‐bearing quartz veins of the Huai Kham On deposit are interpreted to be the products of metamorphic water.     

Hydrothermal alteration associated with Mesozoic granite-hosted gold mineralization at the Sanshandao deposit,Jiaodong Gold Province,China

The Sanshandao gold deposit (reserves of more than 200 t Au and average grade of 3.96 g/t), located at northwestern edge of the Jiaodong Peninsula, eastern North China Craton, is one of the largest gold deposits in the Jiaodong gold province. In this deposit, disseminated- and stockwork-style ores are hosted in Mesozoic granitoids; mineralization and alteration are largely controlled by the regional Sanshandao–Cangshang fault. Host granitic rocks for the deposit display a complex paragenetic sequence of alteration and mineralization. Activities of the Sanshandao–Cangshang fault created structurally controlled permeability allowing for infiltration of hydrothermal fluids, leading to diffusive K-feldspar alteration on the two fault planes. Later, large scale diffusive sericitization symmetrically developed across the main fault, and partially overprinted the earlier K-feldspar alteration. Following the sericitization, relatively small scale silicification occurred, but now it is only retained in the hanging wall of the main fault. Subsequently, the fault gouge formed as a “barrier layer”, which is impermeable for later fluids to move upward. After that, strong pyrite–sericite–quartz alteration occurred only in the footwall of the main fault, and was accompanied by gold precipitation. The last stage carbonation and quartz-carbonate veins marked the waning of gold-related hydrothermal activity. Mass-balance calculations indicate complex behaviors of different types of elements during fluid–rock interaction. Most major elements were affected by intensive mineral replacement reactions. As expected, the fluid-mobile elements, LILE and LREE, generally show moderate to high mobility. It is notable that even the commonly assumed fluid-immobile elements, such as HREE and HFSE, tend to be changed to various degrees. In addition, Y–Ho, Zr–Hf and Nb–Ta fractionations are observed in altered domains. Studies on alteration assemblages and fluid inclusions suggest that the ore-forming fluids were characterized by low salinity (≤ 8.4 wt.% NaCl equiv.), moderate temperature (300–400 °C), weakly acidic (pH: 3–5), and relatively reducing (log f_O2: ~–28) characteristics. In this type of fluids, gold was most likely transported as Au(HS)₂⁻ complex. With alteration going on, log (a_K⁺/a_H⁺) of fluids generally decreased due to significant formation of secondary K-bearing minerals. In addition, there might be a decrease of f_O2 from pre-gold alteration stage to the main gold mineralization stage, and decrease of f_O2 was probably one of the factors controlling gold precipitation. The Sr and Nd isotopic compositions of hydrothermal minerals, combined with previous H–O and He–Ar isotopic studies, indicate that the hydrothermal fluids were mainly derived from crustal sources (e.g., degassing of felsic magmas and meteoric water), but with involvement of mantle derived components. The gold mineralization event just coincided with reactivation of the North China Craton, as marked by asthenosphere upwelling, voluminous igneous rocks, and high crustal heat flow, which may have provided sufficient heat energy and fluid input required for the formation of the gold deposits.     

Geological and Geochemical Characteristics of the Zhulazhaga Gold Deposit in Inner Mongolia, China

Located in Alxa Zuoqi (Left Banner) of Inner Mongolia, China, the Zhulazhaga gold deposit is the first largescale gold deposit that was found in the middle-upper Proterozoic strata along the north margin of the North China craton in recent years. It was discovered by the No. l Geophysical and Geochemical Exploration Party of Inner Mongolia as a result of prospecting a geochemical anomaly. By now, over 50 tonnes of gold has been defined, with an average Au grade of 4 g/t. The ore bodies occur in the first lithological unit of the Mesoproterozoic Zhulazhagamaodao Formation (MZF), which is composed mainly of epimetamorphic sandstone and siltstone and partly of volcanic rocks. With high concentration of gold,the first lithological unit of the MZF became the source bed for the late-stage ore formation. Controlled by the interstratal fracture zones, the ore bodies mostly appear along the bedding with occurrence similar to that of the strata. The primitiveore types are predominantly the altered rock type with minor ore belonging to the quartz veins type. There are also some oxidized ore near the surface. The metallic minerals are composed mainly of pyrite, pyrrhotite and arsenopyrite with minor chalcopyrite, galena and limonite. Most gold minerals appear as native gold and electrum. Hydrothermal alterations associated with the ore formation are actinolitization, silicatization, sulfidation and carbonation. A total of 100 two-phase H2O-rich and 7 three-phase daughter crystal-beating inclusions were measured in seven goldbearing quartz samples from the Zhulazhaga gold deposit. The homogenization temperatures of the two-phase H2O-rich inclusions range from 155 to 401℃, with an average temperature of 284℃ and bimodal distributions from 240 to 260℃ and 300 to 320℃ respectively. The salinities of the two-phase H2O-rich inclusions vary from 9.22wt% to 24.30wt% NaCl eqniv, with a mode between 23 wt% and 24wt% NaC1 equiv. Comparatively, the homogenization temperatures of the threephase daughter crystal-beating inclusions vary from 210 to 435℃ and the salinities from 29.13wt% to 32.62wt% NaCl equiv. It indicates that the ore-forming fluid is meso-hypothermal and characterized by high salinity, which is apparently different from the metamorphic origin with low salinity. It suggests a magmatic origin of the gold-bearing fluid. The δ^18O values of quartz from auriferous veins range from 11.9 to 16.3 per mil, and the calculated δ^18OH2O values in equilibrium with quartz vary from 1.06 to 9.60 per mil, which fall between the values of meteoric water and magmatic water. It reflects that the ore-forming fluid may be the product of mixing of meteoric water and magmatic water.Based on geological and geochemical studies of the Zhulazhaga gold deposit, it is supposed that the volcanism in the Mesoproterozoic might make gold pre-concentrate in the strata. The extensive and intensive Hercynian tectono-magmatic activity not only brought along a large number of ore-forming materials, but also made the gold from the strata rework. It can be concluded that the ore bodies were mainly formed in late hydrothermal reworking stage. Compared with typical gold deposits associated with epimetamorphic clastic rocks, the Zhulazhaga deposit has similar features in occurrence of ore bodies, ore-controlling structure, wall-rock alterations and mineral assemblages. Therefore, the Zhulazhaga gold deposit belongs to the epimetamorphic clastic rock type.     

Genesis and geological and geochemical characteristics of Qixia gold deposit, Shandong, China

The Qixia gold deposit is one of the important quartz vein-type deposits hosted in metamorphic rocks in the east of Shandong, China. Compositionally the wolframite which is associated with gold mineralization in the deposit is rich in iron, but poor in manganese, showing that this mineral crystallized from hydrothermal solution at low temperature. The temperatures at the main metallogenic stage of the Qixia gold deposit are within the range of 160–270°C. The gaseous phases in fluid inclusions are dominated by H₂O and CO₂, while Na⁺, Ca²⁺ and Cl⁻ are the major species in the fluid phase with K⁺ and F⁻ present in relatively small amounts. The salinities of fluids are 4.2 wt% –8.0 wt% NaCl equiv. Meanwhile, the fluid is characterized by either Ca²⁺ < Na⁺ < K⁺ (in five samples) or Na⁺ < Ca²⁺ < K⁺ (in two samples), quite similar to the composition of ore-forming fluid derived from meteoric water. Primary data on the hydrogen and oxygen isotopic compositions of the ore-forming fluid fall within a wide range: = − 56‱ − 95‱. and = − 3. 6‱ − 4. 5‱ relative to SMOW. These isotopic values fully reflect the distribution features of meteoric water which has exchanged with the metamorphic rocks of the Jiaodong Group at different temperatures and W/ R ratios, and the metallogenic process is characterized by low W/R ratios. The Rb-Sr isochron age of the Qixia gold deposit is 125.8 ± 1.7 Ma, with (⁸⁷Sr/⁸⁶Sr)_i being 0.7168, and the time interval between the gold deposit and its country rocks (granite or metamoprhic rocks) is very large. The formation of the Qiaxia gold deposit is directly related to the evolution of geological history in eastern Shandong, and a genetic model in which the deep convective circulating meteoric water reacts with the country rocks can be used to explain the metallogenic mechanism of the deposit. This project was financially supported by the National Natural Science Foundation of China (No. 49000020).     

贵州省水银洞金矿地质特征及成因浅析

水银洞金矿是滇黔桂“金三角”卡林型金矿的重要代表,金矿体赋存于二叠系龙潭组与茅口组不整合界面间,受背斜轴部断裂构造控制,走向上具波状起伏向东倾伏、空间上具多个矿体上下重叠的特点。该矿床属产于沉积碳酸盐岩和构造蚀变体中的“卡林型”金矿,为构造-热液成矿,同时具有中—低温超高压成矿特点。     

Zircon Lu-Hf systematics and the evolution of the Archean crust in the southern Superior Province,Canada

A combined Lu-Hf and U-Th-Pb isotopic study was made of 25 zircons and 2 whole rocks from the late Archean crust (2,888-2,668 Ma) in the southern Superior Province, Canada. The relative abundances of U, Th, Lu and Hf in zircons from the low grade Michipicoten and Gamitagama greenstone belts show variable patterns which in part reflect the bulk compositional differences of their parent rocks. Zircons from the high grade lower crustal regions adjacent to these belts (Kapuskasing Structural Zone) are distinguished from the low grade zircons by their strong depletions of Lu and Hf. The low Hf contents imply that the growth of metamorphic zircon involves a significant fractionation of the Zr/Hf ratio.Initial Hf isotope ratios for Hf in zircons from the low grade rocks are correlated with silica enrichment of their host rocks. e _Hf varies from +9.2 to –1.3 and data from similar rock types exhibit correlations of e _Hf with time. Whole rock basalt analyses yield e _Hf values of +8.7 and +11.3 suggesting their derivation from a depleted mantle. The basalt data fall on an evolution trend which implies that differentiation from a chondritic mantle occurred at 3,100-2,900 Ma. Low e _Hf values (–1.3 to +1.4) for rhyolites and granites are consistent with a derivation involving remelting of old crust similar to a 2,888 Ma granite with e _HF of +0.5. Significantly higher values (+1.4 to +3.9) are found in zircons from 2,748-2,682 Ma dacites and tonalites suggesting that their parent rocks had higher Lu/Hf ratios. This may indicate that their parent rocks were mafic. However, there is some evidence that the possible lower crustal source reservoirs of these rocks may have undergone processes early in their histories which increased their Lu/ Hf ratios. This would give rise to the higher e _Hf values observed in their derivatives.     

四川木里梭罗沟金矿床载金黄铁矿原位微量元素特征

甘孜–理塘缝合带是四川重要的金矿带之一。梭罗沟大型金矿床是该带上的典型矿床,但其矿床成因仍存在争议。为了准确厘定其矿床成因,本文对梭罗沟金矿床中的它形和自形（五角十二面体）的载金黄铁矿进行了LA-ICP-MS原位微量元素分析。结果显示梭罗沟它形黄铁矿元素含量变化较小,较为集中,而自形黄铁矿具有明显的核–幔–边结构,元素含量变化范围较大。总体上,两种黄铁矿中Au与As均具有明显的正相关性,但Au与FeS₂和Co/Ni值具有负相关性。它形黄铁矿和自形黄铁矿的Co/Ni值分别为0.2和57.1,两者都具有较高的Au和较低的Ag含量;这表明它形黄铁矿主体来源于沉积作用,受后期成矿热液改造,而自形黄铁矿属于热液成因。梭罗沟金矿床成矿过程为火山–沉积岩中的Au在变质热液作用下再活化富集的结果,属于典型的造山型金矿床。     

黑龙江省漠河市782高地铌多稀有金属矿床的地质特征及找矿标志

黑龙江省漠河市782高地铌多稀有金属矿床位于漠河市北偏西38 km处,是近年来在大兴安岭北部发现的一个铌资源量达到中型规模的矿床,也是至今在黑龙江省内发现的唯一的铌多稀有金属矿床。矿床的大地构造位置处于额尔古纳地块,漠河前陆盆地与富克山-兴华变质基底杂岩的交接部位。区域地球化学分析显示与稀有金属有关的元素组合为U、Th、Nb、Be;区域地球物理特征表明该区处于航空放射性高场中。勘查结果表明,稀有金属矿化产于晚寒武世—早奥陶世碱长花岗岩顶部,呈似层状、板状产出,矿床Nb2O5、Ta2O5、Y2O3、ZrO2平均品位分别为0.12%、0.0087%、0.108%、0.80%,最高品位分别为0.529%、0.0354%、0.309%、1.18%。主要围岩蚀变为钠长石化,铌等稀有金属矿化与其呈正相关关系。初步研究表明,该矿床形成于早奥陶世拉张伸展背景之下,与该时期板块裂解有关,为一处岩浆晚期自交代矿床。文章旨在分析和讨论该矿床的产出地质环境、矿床地质特征和找矿标志,为额尔古纳地块相似类型的矿床的勘查提供理论参考。