Fluid Inclusion Characteristics Research Articles

Geology, mineralization, and fluid inclusion characteristics of the Lermontovskoe reduced-type tungsten (±Cu, Au, Bi) skarn deposit, Sikhote-Alin, Russia

The Lermontovskoe deposit (∼48Kt WO3; average 2.6% WO3, 0.24% Cu, 0.23g/t Au) is situated in a W-Sn-Au metallogenic belt that formed in a collisional tectonic environment. This tungsten skarn deposit has a W-Au-As-Bi-Te-Sb signature that suggests an affinity with reduced intrusion-related Au deposits. The deposit is associated with an intrusion that is part of the ilmenite-series, high-K peraluminous granitoid (granodiorite to granite) suite. These rocks formed via mantle magma-induced melting of crustal sources.The deposit comprises reduced-type, pyroxene-dominated prograde and retrograde skarns followed by hydrosilicate (amphibole-chlorite-pyrrhotite-scheelite-quartz) and phyllic (muscovite/sericite-carbonate-albite-quartz-scheelite-sulfide, with abundant apatite) alteration assemblages. Fluid inclusions from the skarn assemblages indicate high-temperature (>500°C), high-pressure (1400–1500bars) and high-salinity (53–60wt% NaCl-equiv.) magmatic-hydrothermal fluids. They were post-dated by high-carbonic, methane-dominate, low-salinity fluid at the hydrosilicate alteration stage. These fluids boiled at 360–380°C and 1300–1400bars. The subsequent phyllic alteration started again with a high-temperature (>450°C), high-pressure (1000–1100bars) and high-salinity (42–47wt% NaCl-equiv.) fluid, with further incursion of high-carbonic, methane-dominated, low-salinity fluid that boiled at 390–420°C and 1150–1200bars. The latest phyllic alteration included the lower-temperature (340–360°C), lower pressure (370–400bars) high-carbonic, methane-dominated (but with higher CO2 fraction), low-salinity fluid, and then the low-temperature (250–300°C) H2O-CO2-CH4-NaCl fluid, with both fluids boiled at the deposit level. The high-salinity aqueous fluids are interpreted to have come from crystallizing granitoid magma, whereas the reduced high-carbonic fluids probably came from a deeper mafic magma source. Both of these fluids potentially contributed to the W-Au-As-Bi-Te-Sb metal budget. Decreasing temperatures coupled with high aCa2+ and fluid boiling promoted scheelite deposition at all post-skarn hydrothermal stages.The deposit is characterized by limited downdip extent of mineralized zones and abundant coarse-grained muscovite-quartz (+apatite, scheelite) aggregates that formed at the phyllic alteration stage. Together with presence of high-temperature, high-pressure and high-salinity fluids directly exsolving from crystallizing magma, this suggests a root level of the mineralized magmatic-hydrothermal system of reduced W skarn deposits.

Ore-forming mechanism of Xiajinbao gold deposit in Pingquan, Hebei based on fluid inclusions and stable isotopes

The Xiajinbao gold deposit is located in Yong'an—Xiayingfang—Maojiagou polymetallic metallogenic belt, which is an important metallogenic belt in North China block. In this paper, we present a detailed study on fluid inclusions and stable isotopes of the Xiajinbao gold deposit, Hebei Province, China, aiming at discussing the ore source, evolution of ore-forming fluid and ore-forming mechanism of the deposit. The macroscopic geological characteristics, S and Pb isotopic analysis results show that the source of ore-forming materials is mainly from granitic magma, and subordinately from country rocks. H and O isotopic composition features indicate that the ore-forming fluid is mainly derived from magmatic water. Fluid inclusion characteristics show that the ore-forming fluid experienced boiling during the early mineralization stage, which led to the precipitation of gold. Fluid mixing dominated the precipitation of the ore-forming materials during the middle and late stages. The gold precipitation was caused by water/rock reaction throughout the whole ore-forming process.

Geology, mineralization, stable isotope, and fluid inclusion characteristics of the Vostok-2 reduced W-Cu skarn and Au-W-Bi-As stockwork deposit, Sikhote-Alin, Russia

The large (>180KtWO3 and at least 10–15 t Au) Vostok-2 deposit is situated in a metallogenic belt of W, Sn-W, Au, and Au-W deposits formed in late to post-collisional tectonic environment after cessation of active subduction. The deposit is related to an ilmenite-series high-K calc-alkaline plutonic suite that, by its petrologic signatures, is transitional between those at W-dominant and Au-dominant reduced intrusion-related deposits. Consistently, besides large W-Cu skarns of the reduced type, the deposit incorporates quartz stockworks with significant Au-W-Bi mineralization also formed in a reduced environment. The hydrothermal stages include prograde and retrograde, essentially pyroxene skarns, hydrosilicate (amphibole, chlorite, quartz) alteration, and phyllic (quartz, sericite, albite, apatite, and carbonate) alteration assemblages. These assemblages contain abundant scheelite associated with pyrrhotite, chalcopyrite and, at the phyllic stage, also with Bi minerals, As-Bi-Sb-Te-Pb-Zn sulfides and sulfosalts, as well as Au mineralization. The fluid evolution included hot, high-pressure (420–460°C, 1.1–1.2kbar), low-salinity (5.4–6.0wt% NaCl-equiv.) aqueous fluids at the retrograde skarn stage, followed by lower temperature cyclic releases of high-carbonic, low salinity to non-carbonic moderate-salinity aqueous fluids. At the hydrosilicate stage, a high-carbonic, CH4-dominated, hot (350–380°C) low salinity fluid was followed by cooler (300–350°C) non-carbonic moderate-salinity (5.7–14.9wt% NaCl-equiv.) fluid. At the phyllic stage, a high-carbonic, CO2-dominated, moderately-hot (330–355°C, 0.9kbar) low salinity fluid was followed by cooler (230–265°C) non-carbonic moderate-salinity (6.6–12.0wt% NaCl-equiv.) fluid. A homogenized magmatic source of water (δ18OH2O=+8.3 to +8.7‰), and a sedimentary source of sulfur (δ34S=−6.9 to −6.2‰) and carbon (δ13Cfluid=−20.1 to −14.9‰) at the hydrosilicate stage are suggested. A magmatic source of water (δ18O=+8.6 to +9.2‰) and a sedimentary source of sulfur (δ34S=−9.3 to −4.1‰) but a magmatic (mantle- to crustal-derived) source of carbon (δ13Cfluid=−6.9 to −5.2‰) are envisaged for fluids that formed the early mineral assemblage of the phyllic stage. Then, the role of sedimentary carbon again increased toward the intermediate (δ13Cfluid=−16.4 to −14.5‰) and late (δ13Cfluid=−16.3 to −14.7‰) phyllic mineral assemblages. The magmatic differentiation was responsible for the fluid enrichment in W, whereas Au and Bi could also have been sourced from mafic magma. The decreasing temperatures, together with elevated Ca content in non-boiling fluids, promoted scheelite deposition at the early hydrothermal stages. The most intense scheelite deposition at the phyllic stage was caused by CO2 removal due to boiling of CO2-rich fluids; further cooling of non-boiling fluids favoured joint deposition of scheelite, Bi and Au.

Nature and evolution of fluids associated with specularite-bearing Fe and Au-PGE (Jacutinga) mineralization during the Brasiliano orogeny in the eastern São Francisco Craton, Minas Gerais, Brazil

Hydrothermal fluids related to the development of the Araçuaí Orogen during the Brasiliano Cycle have affected Paleoproterozoic banded iron formation-bearing sequences along the eastern border of the São Francisco Craton. Controversy surround the origin of specularite in high-grade schistose iron ore-bodies in the Serpentina Range (“Serpentina-type” ore) versus specularite-rich, S-free Au-PGE quartz veins (“Jacutinga-type”) that occur at the eastern border of the Quadrilátero Ferrífero mining district. Chemical and thermobarometric characteristics of fluid inclusions from Serpentina-type quartz-specularite veins show that metamorphic aqueous-saline fluids of low to moderate temperature (i.e. salinity between 6.3 and 13.7wt% NaCleqv and homogenization temperatures from 91° to 228°C) were responsible for silica leaching and Fe enrichment along shear zones in the Statherian Serra da Serpentina Group. These Serpentina-type fluids present a distinct pattern with Na>Ca≫K. The fluids are depleted in Li, Na, Ba, Ca, K, Cu and Mg; and enriched in As and Sr in comparison to the Jacutinga-type fluids. In contrast, other two distinct fluids and chemical processes were involved to precipitate Fe oxides with Au-PGE in Jacutinga-type veins. The first type is an aqueous-carbonic fluid from the Catas Altas and Itabira deposits. These Jacutinga-type fluids present a pattern with Na>K>Ca≫Mg and K>Li>Ba>Sr. The fluids are interpreted to be of Brasiliano age and are typically associated with anatectic pegmatites from Santa Maria de Itabira. The high salinity of these brines (23.2–25.3wt% NaCleqv) from the Itabira ore likely originated from their percolation through evaporitic layers, from salt concentration during deformation, or from fluid/rock interactions. Mixing between high-temperature aqueous-carbonic pegmatite-forming fluids and low-temperature aqueous metamorphic brines could have induced an abrupt change in the physical-chemical conditions of the system, which led to Au and PGE precipitation in the Itabira Jacutinga-type deposit. A second Jacutinga-type fluid is observed at the Gongo Soco and Barão de Cocais deposits. This fluid is interpreted as an aqueous-saline metamorphic fluid with the pattern Na>Ca>K≫Mg, low-to-moderate-salinity (4.3–16.4wt% NaCleqv) and temperatures of 77° to 305°C. It is relatively enriched in B; depleted in Li, Ba, Na, Cu, Zn and K; and follows the trend K>Li>Ba. In both types of fluids responsible for Jacutinga-type mineralization, gold was transported as chlorine complexes under acidic and oxidizing conditions. The metal precipitation may have occurred due to a rapid depressurization during failure of shear zones operating in the upper levels of the crust, or variations in the pH and redox conditions during the interaction with the host dolomitic itabirite.

Geology, mineralization, and fluid inclusion characteristics of the Skrytoe reduced-type W skarn and stockwork deposit, Sikhote-Alin, Russia

The Skrytoe deposit (>145 Kt WO3, average grade 0.449% WO3) in the Sikhote-Alin orogenic system (Eastern Russia) is situated in a metallogenic belt of W, Sn-W, Au, and Au-W deposits formed in a late to post-collisional tectonic environment after cessation of active subduction. It is localized within a mineralized district of reduced-type skarn W and veined Au (±W) deposits and occurrences related to the Early Cretaceous ilmenite-series plutonic suite. The deposit incorporates large stockworks of scheelite-bearing veinlets related to propylitic (amphibole, chlorite, quartz) and phyllic (quartz, sericite, albite, apatite, and carbonate) hydrothermal alteration. The stockwork cuts flat-lying mafic volcanic rocks and limestone partially replaced by pyroxene skarn that host the major W orebodies. Scheelite is associated with pyrrhotite and/or arsenopyrite, with minor chalcopyrite and other sulfide minerals; the late phyllic stage assemblages hosts Bi and Au mineralization. The fluid evolution included low-salinity moderate-temperature, moderate-pressure (∼370–390 °C, ∼800 bars) methane-dominated carbonic-aqueous fluids that formed post-skarn propylitic alteration assemblages. Then, at the phyllic stage, there has been an evolution from methane-dominated, moderate-temperature (330–360 °C), low-salinity (<12.3 wt% NaCl equiv.) fluids forming the early quartz-sericite-albite-arsenopyrite assemblage, through lower temperature (290–330 °C) methane-dominated, low-salinity (∼9–10 wt% NaCl equiv.) fluids forming the intermediate quartz-sericite-albite-scheelite-pyrrhotite assemblage, to yet lower temperature (245–320 °C) CO2-dominated carbonic-aqueous low-salinity (∼1–7 wt% NaCl equiv.) fluids forming the late quartz-sericite-sulfide-Bi-Au assemblage. Recurrent fluid immiscibility (phase separation) and cooling probably affected W solubility and promoted scheelite deposition. The stable isotope data support a sedimentary source of carbon (δ13Cfluid = ∼−21 to −10 ‰), a magmatic source for water (δ18OH2O = +7.4 to +7.7 ‰), and dominantly crustal-derived source of sulfur (δ34S = −4.6 to −2.9 ‰) in the hydrothermal fluids. This is consistent with the development of larger, longer crystallizing crustal intermediate to felsic magma chambers in the late to post-collisional tectonic environment, with their protracted magmatic evolution advancing magmatic differentiation and partitioning of W into magmatic-hydrothermal fluid. The dominating role of the crustal-derived magmatic water, sulfur, and carbon appears to be an important feature of reduced W skarn deposits related to ilmenite-series granitoids.

Coupling relationship between reservoir diagenesis and gas accumulation in Xujiahe Formation of Yuanba–Tongnanba area, Sichuan Basin, China

The relationship between reservoir tightening time and gas charge period are the key subjects that have not been well solved considering the studies on the tight sand gas accumulation mechanism and enrichment regularity. The diagenetic evolution history, interaction sequence of organic–inorganic in aquiferous rock, gas charge history, the tightening mechanism of tight sandstone reservoir and the relationship between reservoir tightening time and gas accumulation period of the Xujiahe Formation have been analyzed in the Yuanba–Tongnanba area of the Sichuan Basin. It has been confirmed that the main reason for the tight sandstone reservoir formation is the intensive mechanical compaction which has dramatically reduced the sandstone reservoir quality, and it resulted to a semi-closed to a closed diagenetic fluid system formation at the early diagenetic stage. In the semi-closed to a closed diagenetic fluid system, at the later part of the diagenetic stage, the fluid circulation is not smooth, and the migration of the dissolution products are blocked, hence, the dissolution products mainly undergo the in situ precipitation and cementation. Such dissolution products block the dissolution pores and the residual primary pores; and the stronger the dissolution is, the higher the cement content is, which makes the reservoir further tightened. The hydrocarbon generation and expulsion history of source rocks and reservoir fluid inclusion characteristics in the Xujiahe Formation show that the charge of natural gas occurs in the Middle Jurassic–Early Cretaceous (mainly Early Cretaceous). A comprehensive analysis of the reservoir tightening history, gas charge history, and interaction sequence of organic–inorganic aquiferous in rock indicate that the sandstone reservoir experienced a tightening process when gas charging took place in the Xujiahe Formation in the Yuanba–Tongnanba area of the Sichuan Basin.

Genesis of the Haigou gold deposit, Jilin Province, NE China: evidence from fluid inclusions,40Ar/39Ar geochronology and isotopes

The Haigou gold deposit is one of the largest known lode gold deposits in the Jiapigou‐Haigou gold belt of the Yanbian area of NE China. Although this area contains a significant amount of gold mineralization, identifying new resources has been problematic. Here, we present the results of a systematic study of the ore geology and fluid inclusion characteristics of deep‐seated mineralization in this area, as compiled from previous research. We use these data to determine the genetic processes that formed these deposits and outline the key criteria that should be used for future exploration. The Haigou deposit is hosted by a monzonitic granite (monzonite) with mineralization present within quartz veins. The gold mineralization is associated with silicification, and four stages of mineralization have been identified: milky quartz, pyrite‐quartz, quartz‐polymetallic sulphides and quartz‐carbonate. The second and third stages host the majority of the mineralization. Three main types of fluid inclusion are present within the deposit: CO2–H2O, aqueous and pure CO2. The early milky quartz vein stage of mineralization hosts CO2–H2O and aqueous inclusions, whereas the main stages of mineralization are associated with all three types of fluid inclusions, which are randomly distributed but are especially well developed within pyrite‐quartz veins. These stages of mineralization are also associated with clusters of CO2–H2O inclusions that coexist with large but variable amounts of aqueous phase fluid inclusions. The only fluid inclusions associated with the later stages of mineralization are aqueous inclusions within calcite‐quartz veins. Microthermometric data indicate that the inclusions associated with metallogenesis homogenize at 145–410 °C and contain medium‐ to low‐salinity fluids (&lt;11.93 wt.% NaCl equivalent). The mineralization in this area formed during the Middle Jurassic (163–161 Ma), as evidenced by40Ar/39Ar dating of hydrothermal sericite from the main stage of mineralization. Integrated C‐H‐O‐S‐Pb isotope analysis indicates that the initial ore‐forming fluid was derived from CO2‐rich magmas produced by the anatexis of lower crustal material. This fluid is then mixed and underwent fluid immiscibility during ore formation. The Haigou gold deposit is a typical medium‐ to low‐temperature quartz lode gold deposit that formed after the collision of continental terranes during the transition from compressive to extensional tectonics. The data presented here indicate that this area has significant potential for deep‐seated mineralization; an area that should be the focus of future exploration. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Effect of magmatic hydrothermal on gas reservoir formation in Permian-Lower Triassic source rocks in Huangqiao Area, South China

The main source rocks for gas reservoirs in Huangqiao area of Lower Yangtze region in south China are Permian-Lower Triassic marine strata with high maturity, including carbonate and clastic rocks. A series of geochemical experiments have been carried out in order to reveal the forming mechanism of large gas reservoirs. Geochemical characteristics of crude oils show the source kitchen, which contributes to the large gas reservoir formation, has changed from kerogen cracking to oil cracking. Based on the results of geological evidences, abnormal distribution of vitrinite reflectance, and fluid inclusion characteristics, magmatic hydrothermal is believed to be existed in Huangqiao area. The magmatic hydrothermal changes the source kitchen in two ways. First, the source rock evolution is accelerated by thermal provided by magmatic hydrothermal. Second, it provides hydrogen in the water contained in magmatic hydrothermal to improve liquid hydrocarbons transforming into gases. Thus, the magmatic hydrothermal might considered to be an important factor forming large-scale gas reservoirs in South China.

Geology, mineralization, and fluid inclusion characteristics of the Chorukh-Dairon W–Mo–Cu skarn deposit in the Middle Tien Shan, Northern Tajikistan

The Chorukh-Dairon deposit is part of the metallogenic belt of WMo, CuMo, AuW, and Au deposits along the Late Paleozoic active continental margin of the Tien Shan. It is related to the Late Carboniferous multiphase pluton, with successive intrusive phases of early monzogabbro through monzonite-quartz monzonite to monzogranite and leucogranite, and the latest lamprophyre dikes. The deposit is an example of complex W–Mo–Cu magmatic-hydrothermal system related to magnetite-series shoshonitic igneous suite. It contains zones of W–Cu–Mo oxidized prograde and retrograde skarns, with abundant scapolite, plagioclase, K-feldspar, andradite garnet, magnetite, as well as molybdoscheelite and minor chalcopyrite, and molybdenite. Skarns are overprinted by hydrosilicate alteration assemblages, with amphibole, chlorite, epidote, quartz, calcite, scapolite, albite, scheelite, and chalcopyrite, and are cut by quartz-carbonate-barite-fluorite-sulfide veins.The fluid evolution included a release of high temperature (~400–500°C), high pressure (900–1100 to 700–800bars), high salinity magmatic-hydrothermal aqueous chloride fluid, with its direct separation from crystallizing magma and formation of prograde and retrograde skarns. Fluid enrichment in Ca (up to 15–22wt.% CaCl2) at the retrograde skarn stage was possibly related to magmatic differentiation and provided intense molybdoscheelite deposition from a homogenous fluid. In contrast, hydrosilicate alteration assemblages were formed at lower temperatures (~350–400°C) initially from a homogenous and then from a boiling Ca-rich (20–22wt.% CaCl2) magmatic-hydrothermal fluid, with the latter contributing to the most intense scheelite deposition. The stable isotope data (δ13CCO2=−3.0±0.5‰ and δ18ОH2O=+6.5±0.5‰, δ34S=+7.5to+7.7‰) obtained for the hydrosilicate stage minerals suggest significant fluid sourcing from magmatic and meteoric waters as well as from sedimentary rocks enriched in seawater sulfate, possibly evaporites, although a strongly homogenous character of the isotopic composition reveals intense isotope homogenization in a magmatic chamber. Some light sulfur isotope enrichment of sulfides from the quartz-carbonate-barite-fluorite-sulfide veins (δ34S=+6.0 to +6.1‰) may be linked to the evolution of the magmatic source toward more mantle-related sulfur species, as these veins were formed after emplacement of the late mafic (lamprophyre) dikes.

Geological setting and fluid inclusion characteristics of a lead-copper-barium occurrence hosted in a Neoproterozoic mafic sill at Kiatak, Northumberland Island, Northwestern Greenland

We describe a Pb-Cu-Ba occurrence in Northumberland Island, Northwestern Greenland. Mineralization occupies the brecciated upper contact domain of a Neoproterozoic diabase sill belonging to the Franklin-Thule dike swarm (720–716Ma), with pyrite-bearing black shales of the Dundas Group, upper Thule Supergroup. The host tholeiitic diabase sill is of different composition (low TiO2 and P2O5) than the locally crosscutting dikes (high TiO2 and P2O5). Chloritization, carbonatization and silicification are intense in proximity to sulfides. Coarse grained, open space-filling galena and minor chalcopyrite are accompanied by 2 generations of calcite and 2 of barite. Galena contains significant amounts of Ag (av. 400ppm), Sb (av. 700ppm), Se (av. 20ppm), traces of Bi, Cd, and Sn. Fluid inclusions in the gangue of the Kiatak occurrence indicate two fluid types. Prior to galena precipitation, a CaCl2-NaCl-rich aqueous brine (~20wt.%eq NaCl) cooled from temperatures >300°C and was trapped first in early calcite, and with further cooling, in barite together with solid bitumen inclusions. Following galena crystallization, secondary inclusions containing a similar brine, but of lower salinity, higher Ca:Na ratio, and lower temperature, were trapped in calcite. Corrosion of galena was followed by precipitation of lower temperature (~100°C) barite from a second fluid, comprising immiscible water and CH4. Despite its location in the contact between shale and large mafic sill, the low-temperature mineralization postdates the cooling of the sill, and may be related to basinal fluid circulation controlled by regional extensional faults parallel to diabase dikes. Although uneconomic, the Kiatak occurrence may be witness to a larger metallogenic process that could have formed significant SEDEX type metal concentrations in strata within the Thule Supergroup.

Fluid Inclusion Studies on Quartz Veinlets at the Ali Javad Porphyry Copper (Gold) Deposit, Arasbaran, Northwestern Iran

Ali Javad porphyry copper-gold deposit is located in Arasbaran porphyry copper belt at northwestern Iran, some 20 km east of Sungun Mine. Porphyry mineralization at the Ali Javad deposit occurred in post-Oligocene quartz monzonite bodies which intruded in the Eocene volcanic rocks. Mineralization occurred as veins, veinlets and dissemination both as hypogene and supergene type. Several types of veinlets were distinguished during the study of the deposit. Fluid inclusion studies on fluids trapped in quartz which were taken from drill core samples indicated a wide range of homogenization temperature in the veinlets from 138&#176C to 565&#176C which their salinity demonstrated 33 - 61 wt% NaCl equivalent. Mineralizing fluids density at the deposit was 0.8 - 1.2 g/cm3. Fluid inclusion studies suggested that Ali Javad deposit is an Au-rich porphyry copper deposit; its fluid inclusion features were comparable with other porphyry deposits.

Characteristics of Hydrocarbon Fluid Inclusions and Their Significance for Evolution of Petroleum Systems in the Dabashan Foreland, Central China

Field investigation combined with detailed petrographic observation indicate that abundant oil, gas, and solid bitumen inclusions were entrapped in veins and cements of sedimentary rocks in the Dabashan foreland, which were used to reconstruct the oil and gas migration history in the context of tectonic evolution. Three stages of veins were recognized and related to the collision between the North China block and the Yangtze block during the Indosinian orogeny from Late Triassic to Early Jurassic (D1), the southwest thrusting of the Qinling erogenic belt towards the Sichuan basin during the Yanshanian orogeny from Late Jurassic to Early Cretaceous (D2), and extensional tectonics during Late Cretaceous to Paleogene (D3), respectively. The occurrences of hydrocarbon inclusions in these veins and their homogenization temperatures suggest that oil was generated in the early stage of tectonic evolution, and gas was generated later, whereas solid bitumen was the result of pyrolysis of previously accumulated hydrocarbons. Three stages of hydrocarbon fluid inclusions were also identified in cements of carbonates and sandstones of gas beds in the Dabashan foreland belt and the Dabashan foreland depression (northeastern Sichuan basin), which recorded oil/gas formation, migration, accumulation and destruction of paleo‐reservoirs during the D2. Isotopic analysis of hydrocarbon fluid inclusions contained in vein minerals shows that δ13C1 of gas in fluid inclusions ranges from –17.0‰ to –30.4‰ (PDB) and δD from –107.7‰ to –156.7‰ (SMOW), which indicates that the gas captured in the veins was migrated natural gas which may be correlated with gas from the gas‐fields in northern Sichuan basin. Organic geochemical comparison between bitumen and potential source rocks indicates that the Lower Cambrian black shale and the Lower Permian black limestone were the most possible source rocks of the bitumen. Combined with tectonic evolution history of the Dabashan foreland, the results of this study suggest that oil was generated from the Paleozoic source rocks in the Dabashan area under normal burial thermal conditions before Indosinian tectonics and accumulated to form paleo‐reservoirs during Indosinian collision between the North China block and the Yangtz block. The paleo‐reservoirs were destroyed during the Yanshanian tectonic movement when the Dabashan foreland was formed. At the same time, oil in the paleo‐reservoirs in the Dabashan foreland depression was pyrolyzed to transform to dry gas and the residues became solid bitumen.

Shear Zone Controlled Sulfide-gold Occurrences and their Fluid Inclusion Characteristics in the Northern part of Eastern Dharwar Craton, Southern India

Abstract Brittle to semi-brittle shear zones near Gogalgatti, Mincheri and Yerjanti villages in the northern part of Eastern Dharwar craton show sporadic sulfide and gold occurrences. These shear zones are confined to a late Archaean (2.5 Ga) granitoid complex, consisting of TTG gneisses and granite plutons. Intense mylonitization, brecciation and fracturing are conspicuous in all the three shear zones. The mineralization is of disseminated type and the ore minerals are confined to fracture filling quartz veins. The veins are mainly parallel to the shear zones with minor veins showing cross- cutting relationship. The observed sulfide minerals in decreasing order of abundance are pyrite, chalcopyrite, arsenopyrite, tennantite and sphalerite with minor oxide minerals represented by specular hematite. Random chip sampling in Gogalgatti shear zone gave gold values from 0.52 to 0.65 ppm. However, similar sampling from Mincheri has not indicated any gold, though one of the polished sections of the samples from this area showed an exsolved gold globule within arsenopyrite. In the mineralized veins of these shear zones, primary inclusions of both type I (H2O) and type II (H2O-CO2) are more conspicuous. Secondary inclusions, though present, are mostly affected by deformation. Sulfide minerals are associated with moderate to high saline, type I fluids formed in the early stage of mineralization in all the three shear zones, whereas gold precipitated from high saline (28 -30 wt% NaCl eqvi. in Gogalgatti and ~29% wt% NaCl eqvi. in Mincheri) type II fluids in the later stages, in Gogalgatti and Mincheri shear zones. The temperature of fluid ascent has been determined to be 100 - 200° C in epithermal conditions of mineralization at a depth of 150 to 200 m. Granitoids, in which these shear zones are located, form the main source of hydrothermal fluids, which ascented and precipitated in the structural domains.

Charnockite magmatism during a transitional phase: Implications for late Paleoproterozoic ridge subduction in the North China Craton

The Trans-North China Orogen (TNCO) is a major Paleoproterozoic collisional belt along which the Western and Eastern Blocks of the North China Craton were amalgamated. The Lüliang Complex occurs along the western margin of this belt and incorporates several arc magmatic suites, supracrustal sequences, granitoids and charnockites. Here we investigate the Luyashan charnockite suite, as well as the surrounding granitoids, from this complex. We present results from petrology, fluid inclusions, mineral chemistry, whole rock geochemistry and zircon U–Pb and Lu–Hf isotopic studies. The charnockites are dominantly anhydrous with the typical presence of orthopyroxene. Microthermometric and laser Raman spectroscopic data on fluid inclusions in the charnockite characterize the trapped fluids as dominantly CO2 with traces of N2 and CH4. Geochemically, the charnockite suite shows compositional variation from monzogabbro through gabbroic diorite and diorite to monzodiorite. They are dominantly calc-alkaline and ferroan type and display distinct enrichment in large ion lithophile elements with depletion in HREE. They also show prominent negative anomalies of Nb, Ta, Sr and Ti, and positive anomalies of Rb, Pb, Zr and Hf indicating crustal components in the magma source. The majority of the granitoid suite shows 207Pb/206Pb mean ages in the range of 2172–2032Ma, correlating with similar ages reported from various groups in the Lüliang Complex, the formation of which is correlated with subduction along an active convergent margin. However, the charnockites which intrude the granitoids and their dioritic enclaves are clearly younger and show tightly constrained emplacement ages in the range of 1853–1872Ma. The recrystallized zircons in the older granitoids also show similar ages, suggesting a prominent thermal event at this time. These ages are close to the timing of final collision between the Western and Eastern Blocks of the North China Craton and associated high-grade metamorphism at ca. 1.85Ga. The zircon Lu–Hf isotope data reveal dominantly negative ɛHf(t) values (−8.7 to −0.1) and their TDMC (2477–3042Ma) suggest that the magma sources mainly involved Meso- to Neoarchean reworked crustal components with limited input of Paleoproterozoic juvenile components. Our study reveals that charnockite magmatism and regional metamorphism in the western margin of the TNCO broadly overlap in space and time. The geochemical features, mineral assemblages and fluid inclusion characteristics of the charnockites suggest that the rocks were derived from high temperature (900–1000°C), CO2-enriched and anhydrous (less than 3%H2O) magmas. The magma evolved into more hydrous conditions during cooling marked by the crystallization of amphiboles at 800–850°C. The geochemical features of the charnockite suite also suggest that these rocks were formed during a transitional phase from syn-subduction to collision. Such a scenario is compatible with a tectonic setting involving the subduction of an oceanic ridge when flushing of heat and CO2-rich fluids from asthenosphere into the overriding plate might have occurred through the slab window, generating hot and anhydrous magmas through melting of the basement rocks. The slab window mechanism would also account for broadly coeval high-temperature and high pressure granulites reported from the TNCO. We therefore speculate that the formation of the Luyashan charnockite suite might have been associated with ridge subduction at the terminal stage of the convergence.

Characteristics of Fluid Inclusions and Metallogenesis of Annage Gold Deposit in Qinghai Province, China

The Annage gold deposit is located at the east part of the eastern Kunlun orogenic belt. The characteristics of ore-forming fluids and metallogenesis were discussed by using fluid petrography, micro-thermometry and hydrogen-oxygen isotope analysis. Three stages, namely quartz-pyrite stage (A), quartz-polymetallic-sulfide stage (B) and quartz-ankerite stage (C) were included in the hydrothermal process as indicated by the results of this study. Inclusions developed in ore-bearing quartz veins from stages A and B are of three types: aqueous inclusions (type I), CO2-bearing inclusions (type II) and pure CO2 inclusions (type III). All three types of inclusions, mainly type I, are presented in stage A, having homogenization temperatures at 180°C - 360°C, and salinities ranging from 0.53% to 21.44%. In addition to development of type I inclusions, type II and III inclusions increase significantly in stage B, with homogenization temperatures ranging from 160°C to 330°C, and salinities are from 1.32% to 22.01%. Based on micro-thermometry, fluids in Annage deposit are of H2O-NaCl-CO2 type with medium-high temperature (140°C - 395°C) and medium-low salinity (0.53% - 22.01%). Results of hydrogen-oxygen isotope analysis show that ore-forming fluid is mainly CO2-rich magmatic fluid, mixed with shallow groundwater or metamorphic hydrothermal in the late mineralization stages. Calculated metallogenic pressures are in the range of 79 - 130MPa corresponding to a maximum depth of 4.8 km. The Annage deposit is a mesothermal quartz vein type gold deposit.

The Characteristics of Fluid Inclusions in Sphalerite of Dengfuxian Granite‐related Tungsten Deposit, SE China

The Characteristics of Fluid Inclusions in Sphalerite of Dengfuxian Granite‐related Tungsten Deposit, SE China

Some Features of Fluid Inclusions in Garnets from the Seleteguole Skarn Cu‐Mo Deposit, Jinghe County, Xinjiang, China

the deposit. Light brownish red garnet occurred as 3-10 mm sized disseminated spots in white hornfelsed felsic tuff which is directly in contact with the Cu-mineralized granite porphyry stock. Brown garnet occurred as massive aggregates of 2-6 mm sized tetragonal trisoctahedron crystals in the garnet skarn, which is close to the Cumineralized granite porphyry stock, with irregular quartz stockwork veins and local flaky molybdenite. Yellowish green garnet occurred as aggregates of 3-5 mm sized rhombic dodecahedron crystals in greyish white hornfelsed siltstone which is relatively far away from the

Fluid Inclusion and Isotopic Characteristics of the Dongleiwan Skarn Deposit in Jiangxi Province

Fluid Inclusion and Isotopic Characteristics of the Dongleiwan Skarn Deposit in Jiangxi Province

Fluid Inclusion Characteristics of the Kalatage Meiling Cu‐Au Deposit in Eastern Tianshan Mountains, NW China

Fluid Inclusion Characteristics of the Kalatage Meiling Cu‐Au Deposit in Eastern Tianshan Mountains, NW China

Fluid Inclusions Characteristics of the Hutouya Lead‐Zinc Polymetallic Deposit in Qimantage Area, Qinghai Province, China

Fluid Inclusions Characteristics of the Hutouya Lead‐Zinc Polymetallic Deposit in Qimantage Area, Qinghai Province, China