Hydrothermal Vein-type Deposits Research Articles

Fluid Inclusion, H-O, S, Pb and noble gas isotope studies of the Aerhada Pb-Zn-Ag deposit, Inner Mongolia, NE China

The Aerhada Pb-Zn-Ag deposit is located in the western segment of the Great Hinggan Range Ag-Pb-Zn-Cu-Mo-Au-Fe metallogenic belt in NE China. Orebodies occur mainly as vein type and are hosted by sandstone and siliceous slate. Three stages of primary mineralization, including an early arsenopyrite-pyrite-quartz, a middle polymetallic and silver sulfides-quartz and a late sphalerite-pyrite-calcite-fluorite are recognized. Four types of fluid inclusions have been identified in the ore-bearing quartz and fluorite veins, i.e., liquid-rich, gas-rich, three-phase CO2 aqueous inclusions, and pure gas or liquid aqueous inclusions. Microthermometric studies on fluid inclusions reveal that homogenization temperatures from early to late stages range from 253° to 430°C, 195° to 394°C and 133° to 207°C, respectively. Fluid salinities range from 2.9 to 14.0wt.% NaCl equiv. The vapor composition of the ore fluid is dominated by H2O, CO2 and CH4, with minor proportions of N2. The fluid δ18OH2O and δDH2O values vary from +1.6 to +9.3‰ and −122 to −56‰, respectively, and reflect a magmatic fluid and a meteoric fluid dominant hydrothermal system for the early and late stages of mineralization, respectively. The calculated δ34SH2S values of hydrothermal fluids in equilibrium with sulfides range from +5.2 to +7.1‰, suggesting a mixed source for sulfur, i.e., the local magmatic and sedimentary rocks. The Pb isotope compositions of sulfides are similar to those of the local magmatic and sedimentary rocks, implying that lead and possibly silver relate to these sources. The noble gas isotope compositions of fluid inclusions hosted in ore minerals suggest that the ore-forming fluids were dominantly derived from a deep mantle source. Fluid mixing and dilution are inferred as the dominant mechanisms for ore deposition. The Aerhada Pb-Zn-Ag deposit can be classified as a medium to low temperature hydrothermal vein type deposit.

A synthesis of mineralization styles and geodynamic settings of the Paleozoic and Mesozoic metallic ore deposits in the Altay Mountains, NW China

The Altay Mountains within the Xinjiang region of northwestern China hosts major metallic ore deposits. Here we review the geological characteristics, metallogenic features and tectonic settings of these deposits. The metallic ore deposits in the Altay Mountains occur mainly within four regions: North Altay, Central Altay, South Altay and Erqis. We recognize seven types of metallic ore deposits in the Altay Mountains: VMS, submarine volcanogenic iron, magmatic, skarn, pegmatite, hydrothermal vein (Cu–Zn, Fe) and orogenic gold. Among these types, the VMS, pegmatite, orogenic gold and skarn deposits are the most common. Most of the rare metal pegmatite deposits are distributed in Central Altay, with only a few in South Altay. The VMS, submarine volcanogenic type iron and skarn-type deposits are distributed in South Altay, whereas the orogenic-type gold deposits are distributed in the Erqis Fault belt. The hydrothermal vein-type deposits occur in the Erqis Fault belt and Chonghu’er Basin in South Altay. Magmatic-type deposits are mostly in the Erqis Fault belt and Central Altay. Based on isotopic age data, the VMS, submarine volcanogenic-type Fe and skarn-type Cu, Pb, Zn, Fe mineralization occurred during Early–Middle Devonian (∼410–377Ma), orogenic-type Au, magmatic-type Cu–Ni, and a small number of skarn-type Fe, hydrothermal vein-type Cu–Zn, pegmatite-type rare-metal deposits in Early–Middle Permian (293–261Ma), pegmatite-type rare-metal deposits, few skarn-type Fe deposit in Early–Middle Triassic (248–232Ma), and dominantly represented by pegmatite-type rare-metal deposits in Late Triassic–Early Jurassic (223–180Ma). The metallic ore deposits in the Altay Mountains formed in various tectonic settings, such as the Early–Middle Devonian continental arc and oceanic island arc, Early–Middle Permian post-collisional extensional setting, and Triassic–Early Jurassic intracontinental setting.

Silicification of Hydrothermal Gangue Minerals In Pb-Zn-Cu-Fluorite-Quartz-Baryte Veins

Abstract Late-stage pseudomorphous and perimorphous replacement of euhedral baryte and, to a lesser extent, fluorite and calcite by quartz is a common phenomenon in hydrothermal vein-type deposits. As a consequence of silicification, the primary mineral assemblage might be substantially altered, and therefore this process has a severe negative impact on the economic potential of mineral resources. Although these replacement textures are often reported and have a significant economic importance in mines producing baryte or fluorite of chemical grade, the process that causes this silicification is surprisingly poorly understood. In the present contribution, more than 40 Jurassic–Cretaceous and post-Cretaceous hydrothermal veins from the Schwarzwald mining district, including replacement textures of primary euhedral baryte, fluorite, and calcite, were investigated with respect to their macro- and microscopic textures. It appears that baryte is favorably replaced by pseudomorphs (bladed quartz), while fluorite and calcite are typically replaced by perimorphs. The textures indicate that the mode of replacement of the primary minerals happens continuously and after the initial vein formation. By combining these textural observations with calculated mineral solubilities, a detailed geochemical model has been developed. Existing fluid inclusion data indicate that substantial cooling of the hydrothermal solutions occurs after primary mineral formation. The calculated cooling path reveals opposing solubilities of quartz and the other gangue minerals (baryte, fluorite, and calcite) with decreasing temperature and explains the observed dissolution and precipitation textures. Furthermore, differences in temperature-solubility systematics between baryte on the one hand and fluorite and calcite on the other are responsible for the differences observed in the textures. This agrees with the occurrence of late-stage, low-temperature baryte crystals overgrowing primary baryte assemblages. Conversely, analogous late-stage calcite and fluorite assemblages are only rarely observed. In summary, silicification is a typical cooling effect in various hydrothermal vein-type deposits, but affects different gangue minerals in different ways depending on their temperature-dependent solubility.

Fluid Inclusions, C–H–O–S Isotope and Geochronology of the Bujinhei Pb–Zn Deposit in the Southern Great Xing'an Range of Northeast China: Implication for Ore Genesis

AbstractThe Bujinhei Pb–Zn deposit is located in the southern Great Xing'an Range metallogenic belt. It is a representative medium‐ to high‐temperature hydrothermal vein type deposit controlled by fractures, and orebodies hosted in the Permian Shoushangou Formation. The hydrothermal mineralization is classified into three stages: pyrite ± arsenopyrite–quartz (Stage 1), polymetallic sulfide–quartz (Stage 2), and polymetallic sulfide–calcite (Stage 3). Fluid inclusion petrography, laser Raman analyses and microthermometry indicate that the liquid‐rich aqueous inclusions (L) and vapor‐rich CO2 ± CH4–H2O inclusions (C) occur in the Stage 1 and as medium‐ to high‐ temperature and low‐ to medium‐salinity NaCl–H2O–CO2–CH4 hydrothermal fluids. The liquid‐rich (L) and rare vapor‐rich CO2 ± CH4–H2O inclusions (C) occur in the Stage 2 with medium‐temperature and low‐salinity NaCl–H2O ± CO2 ± CH4 hydrothermal fluids. The exclusively liquid‐rich (L) fluid inclusions are observed in the Stage 3, and the hydrothermal fluid belongs to medium‐temperature and low‐salinity NaCl–H2O hydrothermal fluids. The results of hydrogen and oxygen isotope analyses indicate that ore‐forming fluids were initially derived from the magmatic water and mixed with local meteoric water in the late stage (δ18OH2O‐SMOW = 6.0 to 2.2‰, δDSMOW = −103 to −134‰). The carbon isotope compositions (−18.4‰ to −26.5‰) indicate that the carbon in the fluid was derived from the surrounding strata. The sulfur isotope compositions (5.7 to 15.2‰) indicate that the ore sulfur was also primarily derived from the strata. The ore vein No. 1 occurs in fractures and approximately parallel to the rhyolite porphyry; orebodies have a close spatial and temporal relationship with the rhyolite porphyry. The rhyolite porphyry yielded a crystallization age of 122.9 ± 2.4 Ma, indicating that the Bujinhei deposit may be related to the Early Cretaceous magmatic event. Geochemical analyses reveal that the Bujinhei rhyolite porphyry is high in K2O and peraluminous, and derived from an acidic liquid as a result of strong interaction with hydrothermal fluid during the late magmatic stage; it is similar to A2‐type granites, and formed in a backarc extensional environment. These results indicate that the Bujinhei Pb–Zn deposit was a vein type system that formed in Early Cretaceous and influenced by the Paleo‐Pacific tectonic system.Bujinhei deposit is a representative hydrothermal vein type deposit on the genetic types, and occurs on the western slope of the southern Great Xing'an Range. The ore‐forming fluids were medium‐ to high‐temperature and low‐to medium‐salinity NaCl–H2O–CO2–CH4 hydrothermal fluids, which became medium‐temperature and low‐salinity NaCl–H2O hydrothermal fluids in later stages, and came from magmatic water and mixed with meteoric water, whereas the ore‐forming materials were mainly derived from the surrounding strata. The LA–ICP–MS zircon U–Pb dating indicates that the Bujinhei deposit formed at the period of late Early Cretaceous, potentially in a backarc extensional environment influenced by the Paleo‐Pacific tectonic system.

Major element compositions of fluid inclusions from hydrothermal vein-type deposits record eroded sedimentary units in the Schwarzwald district, SW Germany

Mixing of sedimentary formation fluids with basement-derived brines is an important mechanism for the formation of hydrothermal veins. We focus on the sources of the sediment-derived fluid component in ore-forming processes and present a comprehensive fluid inclusion study on 84 Jurassic hydrothermal veins from the Schwarzwald mining district (SW Germany). Our data derive from about 2300 fluid inclusions and reveal differences in the average fluid composition between the northern, central, and southern Schwarzwald. Fluids from the northern and southern Schwarzwald are characterised by high salinities (18–26 wt% NaCl+CaCl2), low Ca/(Ca+Na) mole ratios (0.1–0.4), and variable Cl/Br mass ratios (30–1140). In contrast, fluids from the central Schwarzwald show even higher salinities (23–27 wt% NaCl+CaCl2), higher Ca/(Ca+Na) mole ratios (0.2–0.9), and less variable Cl/Br mass ratios (40–130). These fluid compositions correlate with the nature and thickness of the now eroded sedimentary cover rocks. Compared to the northern and the southern Schwarzwald, where halite precipitation occurred during the Middle Triassic, the sedimentary basin in the central Schwarzwald was relatively shallow at this time and no halite was precipitated. Accordingly, Cl/Br ratios of fluids from the central Schwarzwald provide no evidence for the reaction of a sedimentary brine with halite, whereas those from the northern and southern Schwarzwald do. Instead, elevated Ca/(Ca+Na), high SO4 contents, and relatively low Cl/Br imply the presence of a gypsum dissolution brine during vein formation in the central Schwarzwald which agrees with the reconstructed regional Triassic geology. Hence, the information archived in fluid inclusions from hydrothermal veins in the crystalline basement has the potential for reconstructing sedimentary rocks in the former overburden.

Application of fractal content-gradient method for delineating geochemical anomalies associated with copper occurrences in the Yangla ore field, China

Fractal and multi-fractal content area method finds application in a wide variety of geological, geochemical and geophysical fields. In this study, the fractal content-gradient method was used on 1:10,000 scale to delineate geochemical anomalies associated with copper mineralization. Analysis of geochemical data from the Yangla super large Cu-Pb-Zn polymetallic ore district using the fractal content-gradient method, combined with other geological data from this area, indicates that ore-prospecting in the ore district should focus on Cu as the main metal and Pb-Zn and Au as the auxiliary metals. The types of deposits include (in chronological order) re-formed sedimentary exhalative (SEDEX), skarns, porphyries, and hydrothermal vein-type deposits. Three ore-prospecting targets are divided on a S–N basis: (1) the Qulong exploration area, in which the targets are porphyry-type Cu deposits; (2) the Zongya exploration area, where the targets are porphyry-type Cu and hydrothermal vein-type Cu-Pb polymetallic deposits; and (3) the Zarelongma exploration area, characterized mainly skarn-type “Yangla-style” massive sulfide Cu-Pb deposits. Our study demonstrates that the fractal content-gradient method is convenient, simple, rapid, and direct for delineating geochemical anomalies and for outlining potential exploration targets.

西藏查藏错铜铅锌矿床成因:C-H-O-S-Pb同位素制约

Chazangcuo Cu-Pb-Zn deposit,hosted by the Linzizong Group volcanic rocks in the west of Gangdese metallogenic belt,is a copper polymetallic deposit discovered in recent years.So far,the genesis of the deposit is still lack of clear under-standing.The results of C,H,O,S,Pb isotopic analysis show that theδ13 CV-PDB values range from -5.60‰ to -2.40‰,δDV-SMOW values range from -111.00‰ to -68.00‰,andδ18 OV-SMOW values range from -8.65‰ to 0.27‰,indicating that the ore-forming fluid mainly derived from the magma hydrothermal in the early time,however,with the mineralization continu-ing,the proportion of atmospheric precipitation gradually turned larger.δ34 SCDT values range from 0.50‰ to 2.50‰ and pos-sess the distribution characteristics of tower,indicating that the sulfur isotope derived from the single magma source.Lead iso-tope ratios are relatively stable and have largeμvalues (more than 9.58),possessing the characteristics of the upper crust lead. The lead isotope characteristics are similar to the ore sulfides from the deposits in the north subzone of Gangdese metallogenic belt,but obviously different from the lead isotope characteristics of volcanic rocks of Dianzhong Formation.Therefore,the au-thors infer that the source of ore-forming materials mainly came from the magmatic source of the upper crust.Combining with the geological characteristics of Chazangcuo deposit,and contrasting the typical magmatic hydrothermal vein-type deposit at home and abroad,the authors think that it belongs to the typical magmatic hydrothermal vein-type deposit.

Mineralogy, mineral chemistry, fluid inclusion, and stable isotope investigations of the Kabadüz ore veins, Ordu, NE-Turkey

Hydrothermal vein-type deposits of the Kabadüz region (Ordu, NE-Turkey) are located in Upper Cretaceous andesitic–basaltic rocks and were formed in fault zones along NW–SE direction lines, with thicknesses varying between a few centimetres up to 2m. The primary mineral paragenesis of the many different ore veins consists of pyrite, chalcopyrite, sphalerite, galena and tetrahedrite–tennantite, with quartz and lesser amounts of calcite and barite as gangue minerals. Electron microprobe analyses indicate that the sphalerite and tetrahedrite–tennantite have low Fe contents, with values less than 3.37wt.% and 1.56wt.%, respectively. The very low Ni and Co contents of the pyrites (<0.04wt.%) and the Zn/Cd ratio of the sphalerite (~ avg. 100) indicate that the hydrothermal solutions were related to felsic magmatic activity. The homogenisation temperatures and calculated salinity data vary between 180–436°C and 0.4–14.7 NaCl % eq., respectively. A well-defined negative correlation between the Th and the salinity data suggests that meteoric water was involved in the hydrothermal solutions. Based on the measured first melting temperatures, CaCl2, MgCl2, NaCl and KCl were dominant in the fluid inclusions. The δ34S compositions of the pyrite, chalcopyrite, sphalerite, and galena mineral separates of the investigated ore veins were measured at between 2.14 and −1.47‰, and the oxygen and hydrogen isotope compositions varied between 7.8–8.5‰ and −40 −57‰, respectively. Based on the sulphur, oxygen and hydrogen isotope compositions, magmatic sources were confirmed for the hydrothermal solutions. Taking into account all of the above data and the granitic intrusions around the area, we concluded that younger granitic intrusions were responsible for the ore mineralisation around the Kabadüz region.

On the origin of sellaite (MgF2)-rich deposits in Mg-poor environments

Sellaite (MgF2) forms from melts, fluids, and gases under variable temperature, pressure, fO₂, and fluid salinity conditions. It is typically associated with, but much rarer, than fluorite (CaF2). The Clara mine near Oberwolfach (Schwarzwald, Germany) is an extensive hydrothermal vein-type deposit, where sellaite occurs in huge quantities (thousands of tons) in veins of mostly Jurassic/Cretaceous age. The sellaite mineralization, occurring in gneisses altered prior to and during sellaite mineralization, represents a stockwork-like network of veins and fissures, which is overlain and sealed by sediments, preventing the inflow of and fluid-mixing with sedimentary formation waters. The occurrence of sellaite is unique among the more than 1000 hydrothermal vein-type occurrences of the Schwarzwald ore district. The favored formation of sellaite compared to fluorite requires the initial Ca/Mg-ratio of the mineralizing fluid to be unusually low. These conditions are possible if fluids equilibrate with pre-altered rocks that lost some or much of their Ca during an earlier hydrothermal alteration event. Indeed, calculations demonstrate that rock-buffered fluids of pre-altered rocks (i.e., gneiss around the Clara mine altered during prior hydrothermal events) show significantly lower Ca/Mg-ratios than fluids equilibrated with unaltered gneisses, because Ca-phases (e.g., the anorthite component of plagioclase) are more prone to hydrothermal destruction. Due to the network-like structure of the sellaite-bearing portion of the Clara fluorite vein, the fluid is shielded from sedimentary formation water, resulting in fractionation processes of the repeatedly ascending mineralizing fluid. In addition, fluid cooling and formation of water-bearing phases like illite that consume fluids, favor sellaite, and later fluorite precipitation. The rarity of this combination of prerequisites explains the limited occurrence of sellaite in hydrothermal vein-type deposits.

江西金溪熊家山钼矿床微量元素地球化学特征及成矿机理&lt;br&gt;The Trace Elements Geochemical Characteristics and Formation Mechanism of Xiongjiashan Molybdenum Deposit, Jinxi, Jiangxi Province

江西金溪熊家山钼矿主要以辉钼矿的形式富集于地层和岩体的破碎及裂隙等空间处，形成了沿着构造方向上展布的脉状、网脉状辉钼矿矿体，初步认为其为岩浆期后热液石英脉型矿床。研究显示该地区同时代的岩浆岩具有相同的来源，加里东期的构造环境与燕山晚期的构造环境具有一定相似性，其可能是该区构造演化的反复性的原因。稀土微量元素特征显示出源岩浆是由下地壳物质部分熔融与上地幔熔融体相互混合而形成的，显示其结晶分异演化过程的相似性，以及形成时的相同的陆–陆同碰撞构造环境，而且铕异常程度的不相同，反应其壳幔混溶的程度不同。其复杂构造环境，利于成矿，成矿是多期次，不同岩脉和与之相对应的多期次的岩浆活动，携带成矿元素：Cu、Mo等和矿化剂S，经岩浆演化形成的流体而成岩成矿。The Xiongjiashan Molybdenum deposit are mainly in the form of molybdenite, which enriched in the rock strata and space of the broken and fractured, and formed molybdenite ore body along the direction of trending vein and stockwork. Preliminary studies suggest that it was the magmatic hydrothermal quartz vein-type deposits. And the con- temporary magmatic rocks have the same source in the region, what’s more, the tectonic environments of caledonian tectonic and Yanshan tectonic was certainly similar, anything else the tectonic evolution of this area may also be a manifestation of repetitive. Trace element characteristics of wich show that the magmatic rocks are from the partial melt mixture of lower crust and upper mantle, such as the crust-mantle mixing. And also it was under the continent-continent collision tectonic environment. And the contents of Eu anomaly that is not the same degree, which corresponding to different levels of the miscibility of the crust-mantle. Extremely favorable environment and complex structures, which was in favor of forming the Molybdenum deposit by the fluid from the formation of rock. The mineralization fluid is closely related with the multi-stage veins that corresponding to the magmatic activity, which carrying ore-forming ele- ments as Cu, Mo and the mineralizer elements of S and so on, lately magmatic evolution ended and the Xiongjiashan Molybdenum deposit formed.

Trace and minor element variations and sulfur isotopes in crystalline and colloform ZnS: Incorporation mechanisms and implications for their genesis

Various models have been proposed to explain the formation mechanism of colloform sphalerite, but the origin is still under debate. In order to decipher influences on trace element incorporation and sulfur isotope composition, crystalline and colloform sphalerite from the carbonate-hosted Mississippi-Valley Type (MVT) deposit near Wiesloch, SW Germany, were investigated and compared to sphalerite samples from 52 hydrothermal vein-type deposits in the Schwarzwald ore district, SW Germany to study the influence of different host rocks, formation mechanisms and fluid origin on trace element incorporation. Trace and minor element incorporation in sphalerite shows some correlation to their host rock and/or origin of fluid, gangue, paragenetic minerals and precipitation mechanisms (e.g., diagenetic processes, fluid cooling or fluid mixing). Furthermore, crystalline sphalerite is generally enriched in elements like Cd, Cu, Sb and Ag compared to colloform sphalerite that mainly incorporates elements like As, Pb and Tl. In addition, sulfur isotopes are characterized by positive values for crystalline and strongly negative values for colloform sphalerite. The combination of trace element contents, typical minerals associated with colloform sphalerite from Wiesloch, sulfur isotopes and thermodynamic considerations helped to evaluate the involvement of sulfate-reducing bacteria in water-filled karst cavities. Sulfate-reducing bacteria cause a sulfide-rich environment that leads in case of a metal-rich fluid supply to a sudden oversaturation of the fluid with respect to galena, sphalerite and pyrite. This, however, exactly coincides with the observed crystallization sequence of samples involving colloform sphalerite from the Wiesloch MVT deposit.

Petrogenetic–metallogenetic setting and temporal–spatial framework of the Yueshan district, Anhui Province, east-central China

The Yueshan district is located in the Anqing–Guichi ore deposit area of the Middle–Lower Yangtze Metallogenic Belt. Two groups of intrusive rocks and three main types of ore mineralization occur in this district: diorite plutons (e.g. Yueshan, Zongpu, Wuheng, and Yangshan) and granite plutons (Hongzhen and Dalongshan), Cu–Au–(Fe) skarn deposits (e.g. Anqing, Tiepuling), Cu–Mo–Au–(Pb–Zn) hydrothermal vein-type deposits (Tongniujing), and hydrothermal uranium mineralization (Dalongshan). Detailed geological and geochemical work suggests that the Cu–Au–(Fe) skarn deposits and the Cu–Mo–Au–(Pb–Zn) hydrothermal vein-type deposits have a close spatial and genetic relationship with the dioritic plutons, whereas the hydrothermal uranium mineralization is associated with A-type granite plutons. Based on the highly precise dating of metal deposits and related plutons in the Yueshan district, such as the molybdenite Re–Os, Os–Os dating, 39Ar–40Ar dating of potassium-bearing minerals and quartz, several Rb–Sr isochrons, SHRIMP zircon U–Pb dating + single-grain zircon U–Pb dating, and the SHRIMP zircon U–Pb dating of Hongzhen granite pluton, we suggest that the extensive magmatism and mineralization in the Yueshan district took place in two episodes: (1) the first episode involved the mineralization of both skarn and vein-type hydrothermal deposits, c.a. 136–139 Ma, related to diorite plutons emplaced at 138.7 ± 0.5 Ma; (2) the second episode attended the hydrothermal uranium mineralization at 106.4 ± 2.9 Ma, related to granite intrusive activity at 126.8 ± 1.0 Ma. These two times of Yueshan petrogenetic–metallogenetic development appear to be consistent with a tectonic environment transition from compression to extension.

Formation of the Wiesloch Mississippi Valley-type Zn-Pb-Ag deposit in the extensional setting of the Upper Rhinegraben, SW Germany

The Mississippi Valley-type (MVT) Zn–Pb–Ag deposit in the Wiesloch area, Southwest Germany, is controlled by graben-related faults of the Upper Rhinegraben. Mineralization occurs as vein fillings and irregular replacement ore bodies consisting of sphalerite, banded sphalerite, galena, pyrite, sulfosalts (jordanite and geocronite), barite, and calcite in the Middle Triassic carbonate host rock. Combining paragenetic information, fluid inclusion investigations, stable isotope and mineral chemistry with thermodynamic modeling, we have derived a model for the formation of the Wiesloch deposit. This model involves fluid mixing between ascending hot brines (originating in the crystalline basement) with sedimentary formation waters. The ascending brines originally had a near-neutral pH (around 6) and intermediate oxidation state, reflecting equilibrium with granites and gneisses in the basement. During fluid ascent and cooling, the pH of the brine shifted towards more acidic (around 4) and the oxidation state increased to conditions above the hematite-magnetite buffer. These chemical characteristics contrast strongly with those of the pore and fracture fluid residing in the limestone aquifer, which had a pH between 8 and 9 in equilibrium with calcite and was rather reduced due to the presence of organic matter in the limestone. Mixing between these two fluids resulted in a strong decrease in the solubility of silver-bearing sphalerite and galena, and calcite. Besides Wiesloch, several Pb–Zn deposits are known along the Upper Rhinegraben, including hydrothermal vein-type deposits like Badenweiler and the Michael mine near Lahr. They all share the same fluid origin and formation process and only differ in details of their host rock and fluid cooling paths. The mechanism of fluid mixing also seems to be responsible for the formation of other MVT deposits in Europe (e.g., Reocin, Northern Spain; Treves, Southern France; and Cracow-Silesia, Poland), which show notable similarities in terms of their age, mineralogy. and mineral chemistry to the MVT deposit near Wiesloch.

Mineralogy, mineral chemistry, and fluid inclusion investigation of Kostere hydrothermal vein-type deposit (Gumushane, NE-Turkey)

Mineralogy, mineral chemistry, and fluid inclusion investigation of Kostere hydrothermal vein-type deposit (Gumushane, NE-Turkey)

Seleniferous minerals of palladium and platinum from ouro preto-bearing mineralisation in Brazil

Selenium is a trace, but characteristic element in the bonanza-style mineralisation of palladiferous gold that triggered two major gold rushes in Brazil (Minas Gerais and Serra Pelada). The auriferous mineralisations of Gongo Soco and Itabira, Minas Gerais, and Serra Pelada, Pará, have Pd–O-bearing, dark-coloured ferruginous coatings on gold ( ouro preto). Depending upon the amount of palladium alloyed with gold, a number of seleniferous minerals of palladium and platinum can be found: chrisstanleyite, Ag 2Pd 3Se 4, a phase analogous to tischendorfite, Pd 8Hg 3Se 9, an argentiferous palladseite-like phase, empirical Pd 5(Hg,Sb,Ag) 2Se 6 and (Pd,Sb,Ag,Hg) 5Se 4, at Gongo Soco; palladseite, ideally Pd 17Se 15, and sudovikovite, PtSe 2, at Itabira; and, exclusively to Serra Pelada, empirical Pd 9PtSe 2, Pd 9Se 2, Pd 3(Se,Bi) and (Pd,Hg,Pb) 3Se. This mineralogical signature of selenium is typical of hydrothermal vein-type deposits formed at relatively low temperatures. Although the synthetic Pd 9Se 2 equivalent is stable at temperatures over 390 °C, fluid inclusion data suggest lower temperatures of formation (< 150 °C). The exclusiveness of Se-bearing, alloy-like phases of palladium to Serra Pelada testifies to its very Pd-rich hydrothermal system.

Geochemistry and evolution of ore-forming fluids of the Yueshan Cu–Au skarn- and vein-type deposits, Anhui Province, South China

The Yueshan mineral belt is geotectonically located at the centre of the Changjiang deep fracture zone or depression of the lower Yangtze platform. Two main types of ore deposits occur in the Yueshan orefield: Cu–Au–(Fe) skarn deposits and Cu–Mo–Au–(Pb–Zn) hydrothermal vein-type deposits. Almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the Yueshan dioritic intrusion. In the vicinity of the Zongpu and Wuhen intrusions, there are many Cu–Pb–Zn–Au–(S) vein-type and a few Cu–Fe–(Au) skarn-type occurrences. Fluid inclusion studies show that the ore-forming fluids are characterised by a Cl −(S)–Na +–K + chemical association. Hydrothermal activity associated with the above two deposit types was related to the Yueshan intrusion. The fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water. In comparison, the hydrothermal activity related to the Zongpu and Wuhen intrusions was characterised by low salinity fluids. Chlorine and sulphur species played an important role in the transport of ore-forming components. Hydrogen- and oxygen-isotope data also suggest that the ore-forming fluids in the Yueshan mineral belt consisted of magmatic water, mixed in various proportions with meteoric water. The enrichment of ore-forming components in the magmatic waters resulted from fluid–melt partitioning. The ore fluids of magmatic origin formed large Cu–Au deposits, whereas ore fluids of mixed magmatic-meteoric origin formed small- to medium-sized deposits. The sulphur isotopic composition of the skarn- and vein-type deposits varies from − 11.3‰ to + 19.2‰ and from + 4.2‰ to + 10.0‰, respectively. These variations do not appear to have been resulted from changes of physicochemical conditions, rather due to compositional variation of sulphur at the source(s) and by water–rock interaction. Complex water–rock interaction between the ore-bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing. Lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore-forming fluids. Hydrodynamic calculations show that magmatic ore-forming fluids were channelled upwards into faults, fractures and porous media with velocities of 1.4 m/s, 9.8 × 10 − 1 to 9.8 × 10 − 7 m/s and 3.6 × 10 − 7 to 4.6 × 10 − 7 m/s, respectively. A decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the Triassic sedimentary rocks led to the deposition of the ore-forming components. The major species responsible for Cu transport are deduced to have been CuCl, CuCl 2 −, CuCl 3 2− and CuClOH, whereas Au was transported as Au 2(HS) 2S 2−, Au(HS) 2 −, AuHS and AuH 3SiO 4 complexes. Cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of Cu deposition. Gold deposition was related to decrease of pH, total sulphur concentration and fO 2, which resulted from fluid boiling and mixing. Geological and geochemical characteristics of the two deposit types in the Yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism. Geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 Ma and represent a continuous process during the Yanshanian time. The cooling of the intrusions and the mineralisation event might have lasted about 6 Ma. The cooling rate of the magmatic intrusions was 80 to 120 °C my − 1 , which permitted sufficient heat supply by magma to the ore-forming system.

Tin mineralization in the Dajing tin–polymetallic deposit, Inner Mongolia, China

Dajing is a large-scale tin–polymetallic deposit that hosts the largest tin mine in North China. It is a hydrothermal vein-type deposit containing Sn, Cu, Pb, Zn, Ag, and minor components Co and In. The deposit consists of more than 690 veins hosted within Upper Permian sedimentary rocks. Three mineralization stages and six ore types are recognized with cassiterite constituting the dominant tin mineral. The SnO 2 content of cassiterite increases in the sequence of mineralization stages shear-deformation→cassiterite–quartz→cassiterite–sulfide (or chalcopyrite–pyrite) stage, while the content of FeO, TiO 2, Nb 2O 5, Ta 2O 5, and In 2O 5 tends to decrease with increases in NiO and Ga 2O 5. It is considered that the negative correlation between SnO 2 and FeO, Nb 2O 5, Ta 2O 5, and In 2O 5 results from elemental substitutions. The early stage cassiterite is much richer in Ta and the later stage cassiterite is much poorer in Ti and Fe than is usual in hydrothermal vein type tin deposits. This is interpreted to indicate that the component of early stage cassiterite reflects a granitic magma source while the composition of later stage cassiterite has a more obvious strata source. The compositional variation of cassiterite corresponds to decreasing crystallization temperatures within each stage and between sequential stages with time. The characteristics of REE in cassiterite from two stages are in accord with that of subvolcanic rocks and the Linxi formation. It suggests that tin transported during the cassiterite–quartz stage may have originated from subvolcanic dikes (e.g., dacite porphyry), while in the cassiterite–sulfide stage, tin may have been derived from wallrock (e.g. siltstone) of the Upper Permian-age Linxi Formation.

Kübler Index and K-Ar Ages of Illite in the Yinshan Polymetallic Deposit, Jiangxi Province, South China: Analyses and Implications

Abstract. The Yinshan polymetallic deposit is a hydrothermal vein-type deposit closely related to Late Jurassic felsic-inter-mediate volcanic-subvolcanic activity in Jiangxi Province, South China. Illite is a major alteration mineral observed in the deposit. Our study shows that the Kübler index of the illite has a close relation to ore-forming fluids of different stages of hydrothermal alteration and mineralization. The early Pb-Zn-Ag mineralization dated at 130–136 Ma is characterized by relatively low water/rock ratios and diffusive fluid movement within phyllite, whereas the later Cu-Au-S mineralization at 122 -125 Ma was accompanied by higher water/rock ratios and localized fluid flow through fractures and channels. Illite formed in the early Pb-Zn-Ag mineralization stage contains swelling layers while the illite formed in the later Cu-Au-S mineralization stage has no swelling layers but was associated with intensive chloritization. The last stage of mineralization (at 104 Ma) was minor and did not produce significant amounts of illite.

PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au-Pd-Pt DEPOSIT, CARAJAS MINERAL PROVINCE, NORTHERN BRAZIL

The Serra Pelada garimpo (1980–1984) was the site of the most spectacular gold rush in recent history, but the mineralogy of the bonanza-style mineralization has not so far been documented in detail. Rediscovery of an early drill-core, recovered in 1982 from the near-surface lateritic portion of the garimpo area, has provided coarse-grained gold aggregates for this study. The centimeter-long aggregates of gold occur in powdery, earthy material. They exhibit a delicate arborescent fabric and are coated by goethite. Four compositional types of gold are recognized: palladian gold with an atomic ratio Au:Pd of 7:1 (“Au7Pd”), Hgbearing palladian gold (Au–Pd–Hg), Pd-bearing gold with up to 3 wt.% Pd (Pd-poor gold) and pure gold. A number of platinumgroup minerals (PGM) are included in, or attached to the surface of, palladian gold: “guanglinite”, Sb-bearing “guanglinite”, atheneite and isomertieite, including the noteworthy presence of Se-bearing PGM (Pd–Pt–Se, Pd–Se, Pd–Hg–Se and Pd–Bi–Se phases, and sudovikovite and palladseite). They define an As–Sb–Hg–Se mineral assemblage typical of hydrothermal vein-type deposits formed at relatively low temperatures. Native palladium, characteristically situated in the goethite coating, is intimately associated with a Pd–O phase. The remarkable occurrence of native platinum associated with Pd-bearing gold, PGM (compositionally close to mertieite-II and isomertieite) and berzelianite from a nearby prospect (Elefante prospect) is also recorded.

Short-chain carboxylates in fluid inclusions in minerals

The carboxylate (formate, acetate, propionate and oxalate) and common inorganic anions (F −, Cl − and SO 2− 4) compositions for aqueous fluid inclusion leachates from 17 mineral samples collected from various deposits have been determined using ion chromatography in conjunction with microthermometric measurements on the fluid inclusions of their host minerals. The minerals, quartz, fluorite, barite, beryl and a few `ore' minerals (wolframite, pyrite and galena), came from hydrothermal vein-type deposits in felsic igneous rocks or Archean metamorphic rocks. The results indicate that short-chain carboxylates are common components in hydrothermal fluids and can be present in considerable amounts. Formic acid (as formate) is the dominant species over other carboxylic acids. The present study raises new questions about the origin and geochemical significance of carboxylates in hydrothermal ore-forming processes.