Fluid Inclusion and Stable Isotope Studies at Don Sixto,a Precious Metal Low Sulfidation Deposit in Mendoza Province,Argentina

The Don Sixto mining area in Mendoza province, central‐western Argentina, contains an epithermal low sulfidation Au–Ag deposit. It is a small deposit (～4 km²), with a gold resource of 36 t. In Don Sixto, ore minerals are disseminated in the hydrothermal quartz veins and hydrothermally altered volcanic‐pyroclastic rock units of Permian–Triassic age. On the basis of the texture, ore mineral paragenesis and cross cutting relationship of gangue minerals, seven stages of mineralization were recognized and described. The first six stages are characterized by quartz veins with minor amounts of base metal minerals and the last stage is represented by fluorite veins with minimal quantities of base metal minerals; the precious metal mineralization is mainly related to the fourth stage. The hydrothermal veins exhibit mainly massive, crustiform and comb infilling textures; the presence of bladed quartz replacement textures and quartz veins with adularia crystals are indicative of boiling processes in the system. Fluid inclusion and complementary stable isotope studies were performed in quartz, fluorite, and pyrite samples from the vein systems. The microthermometric data were obtained from primary, biphasic (liquid‐vapor) fluid inclusion assemblages in quartz and fluorite. The maximum values for salinity and homogenization temperature (T_h) came from the stage IV where quartz with petrographic evidence of boiling has average values of 4.96 wt% NaCl_equiv. and 286.9°C respectively. The lower values are related to the last stage of mineralization, where the fluid inclusions in fluorite have average salinities of 1.05 wt% NaCl_equiv. and average homogenization temperatures of 173.1°C. The oxygen and sulfur isotopic fractionation was analyzed in quartz and pyrite. The calculated isotopic fractionation for oxygen in the hydrothermal fluid is in the range of δ¹⁸O_H2O = ?6.92 up to ?3.08‰, which indicates dominance of a meteoric source for the water, while sulfur reaches δ³⁴S_H2S = 1.09‰, which could be reflecting a possible magmatic, or even a mixed source.     

吉林延边五凤、五星山金矿床地球化学特征及其成因

五凤和五星山金矿为延边地区中生代火山岩金、铜成矿带中典型的金矿床.通过岩石化学、成矿元素、流体包裹体和同位素组成等方面的分析,提出五凤和五星山金矿床属于典型的冰长石-绢云母型浅成低温热液型金矿床,其形成是深部火山-热液流体系统与浅成大气流体的混合.成矿构造环境与陆内造山带后期垮塌机制有关,造山带的垮塌与古太平洋板块斜向俯冲导致的大型走滑剪切有密切的成因联系.     

Geology and ages of porphyry and medium- to high-sulphidation epithermal gold deposits of the continental margin of Northeast China

The continental margin of Northeast China, an important part of the continental margin-related West Pacific metallogenic belt, hosts numerous types of gold-dominated mineral deposits. Based on ore deposit geology and isotopic dating, we have classified hydrothermal gold–copper ore deposits in this region into four distinct types: (1) gold-rich porphyry copper deposits, (2) gold-rich porphyry-like copper deposits, (3) medium-sulphidation epithermal copper–gold deposits, and (4) high-sulphidation epithermal gold deposits. These ore deposits formed during four distinct metallogenic stages or periods, at 123.6 ± 2.5 Ma, 110–104 Ma, 104–102 Ma, and 95.0 ± 2 Ma, corresponding to periods of Cretaceous intermediate–acid volcanism and late-stage emplacement of hypabyssal magmas along the northern margin of the North China platform. The earliest stage of mineralization (123.6 ± 2.5 Ma) corresponds to the formation of medium-sulphidation epithermal copper – gold deposits and was associated with a continental margin magmatic arc system linked to subduction of the Pacific Plate beneath the Eurasia. This metallogenesis is closely related to high-K calc-alkaline intermediate–acid granite and pyroxene – diorite porphyry magmatism. The second and third stages of mineralization in the study area (110–104 Ma and 104–102 Ma, respectively) correspond to the formation of gold-rich porphyry copper, porphyry-like copper, and high-sulphidation gold deposits, with metallogenesis closely related to sodic or adakitic magmatism. These magmas formed in a continental margin magmatic arc system related to oblique subduction of the Pacific Plate beneath the Eurasia, as well as mixing of crust-derived remelted granitic and mantle-derived adakitic magmas. During the final stage of mineralization (95.0 ± 2 Ma), metallogenesis was closely related to sodic or adakitic magmatism, with diagenesis and metallogenesis related to the disintegration or destruction of the Pacific Plate, which was subducted beneath the Eurasian Plate during the Mesozoic.     

贵州低温热液型汞、锑、金矿床成矿谱系——以晴隆大厂、兴仁紫木凼和铜仁乱岩塘为例

贵州是我国低温热液型汞、锑、金矿的重要产区,但对其成矿时代一直存在不同看法.本次研究采用Sm-Nd同位素等时线法对晴隆大厂锑矿、兴仁紫木凼金矿和铜仁乱岩塘汞矿区的萤石、方解石分别进行了同位素年代学的研究,结果表明晴隆大厂锑矿中的方解石(Sm-Nd等时线年龄为148±13 Ma,钕初始值为0.512256)和萤石(Sm-...     

内蒙古苏尼特右旗毕力赫金矿床成矿地质特征

毕力赫金矿床产在华北板块北部边缘成矿带之白乃庙构造岩浆活化带内,是近年新发现的金矿床.金矿化发生在火山杂岩侵入体与围岩接触的破碎蚀变带中,与硅化、钾长石化围岩蚀变作用密切相关.矿体严格受蚀变带控制,呈透镜状、囊状、板状等,向南东方向侧伏.成矿流体为低盐度流体,成矿温度属于中低温.矿床成因类型为与次火山岩有关的浅成低温热液型.     

新疆伊宁县塔北铅锌矿床地质特征和S、Pb、C、O同位素组成

塔北铅锌矿床是西天山吐拉苏盆地中新近勘查成功的一个重要热液型铅锌矿床。矿体赋存于晚泥盆世-早石炭世大哈拉军山组第五岩性段酸性凝灰岩中,受断裂构造控制。矿石硫化物的δ³⁴S值介于0.5‰~7.3‰,估算获得成矿流体的总硫同位素值δ³⁴S_∑S约2.7‰,具岩浆硫的特征。晚期石膏的δ³⁴S值为4.7‰~5.3‰,表明石膏可能是火山热液中的SO₂发生歧化反应或火山喷发带出的H₂S挥发分在近地表的氧化环境中反应生成的。矿石铅同位素组成十分稳定,并与大哈拉军山组火山岩的铅同位素组成相似,指示成矿物质来源于赋矿火山岩。碳、氧同位素组成指示成矿流体中碳主要来源于深部岩浆。塔北铅锌矿床可能属于矿化较深的浅成低温热液型矿床。     

A Low‐Sulfidation Epithermal Mineralization in the River Reef Zone,the Poboya Prospect,Central Sulawesi,Indonesia: Vein Textures,Ore Mineralogy,and Fluid Inclusions

The Poboya Prospect lies along the North Northwest ‐ South Southeast Palu‐Koro Fault Zone in the central part of the West Sulawesi Arc. The geology of the area consists of the Palu Metamorphic Complex overlain by the Paleogene‐Neogene Tinombo Formation of volcanosedimentary rocks, the Celebes Molasse sediment, and Late Cenozoic granitic rocks. Petrography, scanning electron microscope with energy‐dispersive spectrometry (SEM‐EDS), electron probe microanalyzer (EPMA), and fluid inclusion microthermometry were carried out to examine vein textures, ore mineralogy, and characteristics of the ore‐forming fluid responsible for mineralization in the River Reef Zone, the Poboya Prospect. Textures of quartz‐carbonate veins in the River Reef Zone include massive micro‐comb, moss, colloform, crustiform, mosaic, feathery, flamboyant, lattice bladed, ghost bladed, parallel bladed, and saccharoidal textures representing primary growth, recrystallization, and replacement. The homogenization temperature and fluid salinity are 240–250°C and 0.3–0.7 wt% NaCl eq., respectively. Ore minerals precipitated in the early stage consist of electrum, naumannite‐aguilarite, chalcopyrite, pyrite, marcasite, sphalerite, and pyrrhotite. Apart from pyrrhotite, these ore minerals were also precipitated in the late stage along with selenopolybasite, freibergite, argyrodite, pyrargyrite, and galena. Selenium more preferably occurs as the crystallographic replacement of sulfur in naumannite‐aguilarite, argyrodite, pyrargyrite, selenopolybasite, and freibergite instead of as independent selenide minerals. The low‐sulfidation epithermal deposit in the River Reef Zone, the Poboya Prospect, illustrates the potential of the West Sulawesi Arc, particularly along the Palu‐Koro Fault Zone, to host epithermal gold mineralization.     

Sediment‐Hosted Gold Deposits in Southeast Asia

Sediment‐hosted gold (SHG) deposits are becoming more widely recognized in the Southeast Asian region. They are characterized by very fine‐grained gold, typically occurring in stratabound jasperoid replacement and structurally controlled orebodies in calcareous or carbonaceous sedimentary rocks, which are commonly distal to porphyry copper–gold deposits. Gold mineralization is associated with anomalous As‐Sb‐Hg‐Tl and is normally concentrated in the arsenic‐rich rims of pyrite and arsenopyrite grains (commonly refractory). The examples discussed in this paper are located in Southeast Asian countries, and all occur in island or continental arc terrains. SHG deposits have many features comparable to the Carlin deposits in Nevada; however, they differ in tectonic setting, their shallow level of emplacement, fluid composition, and probable metal source. As such, the Southeast Asian examples described in this compilation may be classified as “Carlin‐like” but not “Carlin‐type.” Furthermore, they appear to represent a subclass of low‐temperature epithermal deposits, with most occurrences showing late‐stage colloform quartz vein events. Indeed, they are better described as sediment‐hosted epithermal gold deposits. Several examples are multimillion ounce deposits, such as Sepon, Laos, with its endowment of more than 4 million ounces of gold. Mesel, Sulawesi, and Bau (Jugan and Tai Parit), Sarawak, also possessed multimillion ounce resources prior to mining. Two centuries of Chinese alluvial and eluvial mining at Buduk in northwest Kalimantan has produced a significant unrecorded amount of gold. Structurally controlled feeder zones frequently contain higher‐grade gold mineralization (e.g. Mesel), and constitute valid exploration targets. More recently discovered deposits, such as those in Myanmar (Gegalaw, Taungzaw, and Katsena) and the Philippines (Hijo and Las Cogon), remain to be thoroughly explored. Most of the deposits (Sepon, Mesel, Abong, Sihayo, Jugan, Tai Parit, Hijo, and Lascogon) can be directly linked spatially and genetically to gold–copper porphyry intrusive centers. It is postulated that localities with no obvious connection to known porphyry deposits (Buduk, Ban Bak, Kyaukpahto, Gegalaw, Taungzaw, and Katsena) may represent district‐scale exploration targets for porphyry copper–gold deposits. In terms of discovery techniques, of the 13 SHG deposits discussed here, several were sites of historical mining (Mesel, Bau, and Kyaukpahto). The majority, however, are virgin deposits discovered in the past 25 years by intuitive area selection followed by systematic regional geochemical exploration programs and routine geological inspections. At the project scale, electrical resistivity techniques, such as controlled‐source audio frequency magnetotellurics (CSAMT) and induced polarization (IP), have proven to be useful for mapping blind jasperoid bodies and associated feeder zones and silicified structures. Traditional field mapping and stream float sampling in tropical regions are also effective exploration tools. Deposits that have significant jasperoid development may have conspicuous positive topographic relief, depending on erosion level.     

印度尼西亚索林帕萨铜多金属矿成矿流体地球化学和矿床成因

文章对印度尼西亚索林帕萨铜多金属矿含矿石英脉流体包裹体进行了显微测温与氢氧同位素测定,发现石英脉中含有3种类型的流体包裹体:A.纯液相水溶液包裹体;B.富液相气液两相水溶液包裹体和C.富气相气液两相水溶液包裹体,其中以B类为主.三种流体包裹体同时出现,表明石英脉形成时流体可能发生过沸腾作用.成矿流体均一温度为198.9℃～356.4℃,冰点温度为-0.6℃～-2.3℃,相应流体盐度变化范围为0.94%～3.76%NaCleq..质谱测定显示成矿流体的氢氧同位素组成分别为占δDH2O=-61.0‰～-81.0‰,δ18OH2O=-3.08‰～0.17‰,表明成矿流体主要为大气降水,不排除有少量岩浆水加入.根据成矿流体地球化学与围岩蚀变类型,初步推断该矿属于酸性-硫酸盐(高硫)型的浅成低温多金属矿床,沸腾作用是成矿物质沉淀的主要因素.