Fluid Inclusion Characteristics Research Articles

Fluid inclusion characteristics and mechanisms of tin mineralisation in the Jialong tin polymetallic deposits, Jiuwandashan–Yuanbaoshan, northern Guangxi, China

The Jiuwandashan–Yuanbaoshan area, which is located in the western Jiangnan orogenic belt, has experienced frequent tectonic and magmatic events, and contains extensive Neoproterozoic Sn–polymetallic deposits. The Jialong Sn–polymetallic deposit is located in the northeastern part of the Neoproterozoic Yuanbaoshan granite and superimposed Sirong ductile shear zone and represents the first Caledonian Sn–polymetallic deposit discovered in this area. In this study, we investigated the mechanisms of Caledonian Sn mineralisation using the numerous types of fluid inclusions that formed during the main mineralisation stage. Liquid-rich inclusions (Wa-type) have a wide range of homogenisation temperatures (180–302 °C) and a bimodal distribution of salinities (8–10 and 21–22 wt% NaClequiv). Gas-rich inclusions (Wb-type) have homogenisation temperatures of 379–383 °C and salinities of 4.34–4.49 wt% NaClequiv. The homogenisation temperatures of CO2-rich liquid inclusions (Ca-type) are 222–248 °C, and the salinities are 11.32–13.45 wt% NaClequiv, indicating the fluid underwent significant boiling. δ18Owater values vary from 1.1 to 5.3‰ VSMOW, with δD = −65 to −35‰ VSMOW. The ore-forming fluid has the characteristics of a typical metamorphic hydrothermal fluid. There is a significant difference in δ34S values between the mafic–ultramafic and granitic rocks in the study area, indicate the ore-forming materials were derived mainly from metamorphosed sedimentary rocks of the Sibao Group. The Jialong Sn–polymetallic deposit is a typical example of Caledonian Sn mineralisation, but there was no coeval magmatism, although the Sirong ductile shear zone was active during the period of Sn mineralisation. During the Caledonian activity of the Sirong ductile shear zone, ductile shear deformation resulted in the generation of metamorphic fluids from distal Neoproterozoic strata. This fluid migrated to the northwest under the influence of a pressure gradient, underwent decompression-driven boiling and precipitated Sn and other elements.

Understanding the Hydrocarbon Accumulation Process in Deep–ultradeep Oil and Gas Reservoirs in Complex Structural Areas—The Qixia Formation in the Shuangyushi Structure in Northwestern Sichuan Basin, China

Deep-ultradeep oil and gas reservoirs in complex structural areas have typically undergone multistage tectonic processes that have a considerable influence on the hydrocarbon composition, isotopic composition, and other geochemical characteristics of petroleum. By assessing the charging period of hydrocarbon accumulation during a particular age we can determin these changes. We studied the characteristics of fluid inclusions developed in the dolomite reservoir in the Middle Permian Qixia Formation in the Shuangyushi structure of the northwestern Sichuan Basin using methods such as inclusion petrography, microbeam fluorescence fluorescence spectroscopy, and inclusion homogenization temperature. Furthermore, the main peak wavelength of the fluorescence spectrum, red–green ratio/chromatic parameter, Q650/500, as well as the chromatic parameter corresponding to emission flux at 535 nm (QF535) and their correlations with the homogenization temperature distribution, were used to identify the charging period of hydrocarbons in the Qixia Formation. The results show that different types of fluid inclusions were developed in the Qixia Formation. The fluorescence of hydrocarbon inclusions is mainly blue, with a small amount of yellow–green and orange–yellow. The max of orange–yellow, yellow–green, and blue fluorescence of the hydrocarbon inclusions range between 562 ∼ 579 nm, 497 ∼ 548 nm, and 447 ∼ 497 nm, respectively. The distribution of the homogenization temperatures during the same period ranges from 100 °C to 110 °C, from 120 °C to 140 °C, and from 160 °C to 170 °C, respectively. By combining the burial and thermal evolution histories of the Qixia Formation, we concluded that the Qixia Formation has experienced three stages of oil and gas charging, with the time of 204, 185 and 158 Ma. This method is of great significance to determine the date and duration of oil and gas accumulation, and provides technical support for the recovery of ultra-deep hydrocarbon accumulations in complex structural areas.

Combined effect of magmatic fluid–seawater mixing and host rock alteration on the formation of gold-enriched massive sulfides in the Forecast vent field, southern Mariana Trough

Massive sulfides and sulfide-bearing breccia were collected from the Forecast vent field in the southern Mariana Trough. These samples exhibit varying degrees of hydrothermal alteration and/or mineralization, with the former type having significant enrichments in Au (up to 101 ppm). In this study, detailed analyses of mineralogy, geochemistry, S isotope, and fluid inclusion were conducted to understand the unusual Au-rich mineralization. Mineralogical investigations and geochemical analyses (LA–ICP–MS and EPMA) of dominant sulfide minerals indicate that electrums, the main phase of Au mineralization, are characterized by two different generations based on mineralogical relationships and fineness. Early-stage high fineness electrums (930–981 ‰) are associated with sphalerite under relatively high-temperature fluid conditions, whereas galena is main host mineral related to late-stage low fineness electrums (773–868 ‰). Sphalerite geothermometry (231–264 °C), the occurrence of colloform textured sulfides, and microthermometric characteristics of fluid inclusions (Th = 220–304 °C; Salinity = 1.4–6.6 wt% NaCl equivalent; a general trend of decreasing salinity with decreasing Th) indicate that significant decreases in H2S activity, attributed to seawater dilution and rapid precipitation of sulfide minerals, facilitated the efficient destabilization and deposition of Au transported as sulfide complexes from hydrothermal fluids. In particular, the lower 34S values (+0.2 ‰ to + 1.3 ‰) of sulfides compared to those of arc/back-arc lavas (δ34S = +5‰ to + 11 ‰), along with the prevalence of CO2 in the vapor phase of fluid inclusions, reflect that the significant contribution of magmatic volatile influx supplied most of the sulfur and metals (including Au) to the Forecast hydrothermal fluids. Additionally, the abundance of montmorillonite and varying proportions of sulfide and gangue minerals observed in hydrothermal samples suggest that the chemical buffering of fluids by associated substrates and/or sediments could be another significant factor in promoting Au-rich mineralization. Therefore we conclude that the combination of magmatic fluid–seawater mixing and host rock alteration plays an important role in the formation of Au-enriched massive sulfides in the Forecast vent field.

Microbial and hydrothermal dolomite formation in Early Cretaceous lacustrine sediments in Yin'e Basin: Insights from petrology and geochemistry

Dolomite is widely present in geological history, but its origin has always been a prominent problem that troubles sedimentologists. For lacustrine dolomite, current research has not yet provided a reliable explanation for its complex genesis mechanism. The Early Cretaceous lakes in Northwest China host various morphological dolomites, providing valuable materials for exploring the origin of dolomites. According to their petrological and mineralogical characteristics, it can be divided into thick laminated dolomite, thin laminated dolomite, dolomitic mudstone, and vein dolomite. The ratios of trace elements and rare earth elements show that these dolomites precipitated in a brackish–suboxic environment. The high δ13C values (>8 ‰VPDB) of thick laminated dolomite and some thin laminated dolomite suggest the involvement of methane-producing microorganisms in the precipitation of dolomite, and the appearance of microscale/nanoscale spherical dolomite aggregates and the dispersed organic matter around dolomite particles jointly confirm that microbial-mediated biological activity promotes dolomite precipitation. The dolomite stoichiometry (mole % MgCO3) confirms that thick laminated dolomite was deposited in a restricted shallow water environment, while dolomitic mudstone is mainly deposited in relatively open water areas. The thin laminated dolomite in the shale laminae represents short-term or seasonal climatic and environmental fluctuations. In addition, some carbonate minerals of dolomitic mudstone in shallow water environment recrystallized by post-depositional hydrothermal effect, resulting in δ18O value decreased (<−10 ‰VPDB). The vein dolomite is characterized by high rare earth content and low δ13C and δ18O values, and its Sr isotope (0.712894 ± 0.000374) values reflect that the hydrothermal fluid may have been formed by the mixing of infiltrating lake water and crustal magmatic water. According to the characteristics of fluid inclusions, it is inferred that the hydrothermal fluid has the characteristics of low temperature (108.3 °C–159.8 °C), medium salinity (3.5 wt%–14.3 wt% NaCl) and high density (0.95–1.00 g/cm3). The microbial mediation and tectonic hydrothermal fluids play an important role in the formation of the Early Cretaceous lacustrine dolomite.

Petrology, phase equilibria modelling, and fluid inclusion study of mafic granulites from Bhavani Suture Zone, Southern India

We report new petrology, mineral chemistry, P–T conditions, and fluid inclusion data on mafic granulites from the Mettupalayam region along the Bhavani Suture Zone, Southern Granulite Terrane, India. Phase equilibria modelling of mafic granulites yielded peak P–T conditions of 780–860 °C and 7.6–10.1 kbar followed by a near isothermal decompression along a clockwise P–T path. The trapped fluid inclusions in the peak metamorphic minerals display a melting temperature range from −57.4 °C to −56.6 °C, close to the triple-point temperature of pure CO2. The primary inclusions homogenized at −18.9 °C to +0.2 °C, corresponding to density values of 0.93–1.03 g/cm3. Homogenization of the secondary inclusions occurred within the range from −6.3 to +18.1 °C, corresponding to low CO2 densities of 0.79–0.96 g/cm3. From the textural characteristics of the high-density primary carbonic fluid inclusions, we interpret these inclusions as the CO2-rich syn-metamorphic fluid present during the high-grade metamorphism. The secondary fluids characterised by lower densities have undergone re-equilibration during the exhumation stage (decompression) from the peak granulite-facies metamorphism along a clockwise P–T trajectory. This interpretation is consistent with the occurrence of hornblende + plagioclase symplectite around the porphyroblastic garnet, suggesting decompression. We infer that the high-density CO2 was the dominant syn-metamorphic fluid components present during the granulite-facies metamorphism in the Mettupalayam region. Such carbonic fluids, possibly derived by degassing from carbonates or mantle sources, probably played a significant role in stabilizing high-grade mineral assemblages along this collisional suture zone.

Hydrothermal Alteration, Ore Mineralization, and Fluid Inclusions Study of the Mount Muro Low Sulphidation Epithermal Deposit, Murung Raya Regency, Central Kalimantan Province, Indonesia

Abstract Mount Muro is a part of the ‘Central Kalimantan Gold Belt’, which is found in Murung Raya Regency, Central Kalimantan Province, Indonesia. The study area is part of the Mount Muro mineralized district which includes Serujan Project, Bantian Project, and Kerikil Project. In order to optimize the production yield of the Mount Muro mine, it is important to understand the update data and analyses about the ores characteristics along with their mineral associations and the paleo-fluids involved in it. This research aims to elucidate the mineralization model based on their alteration mineral assemblages, ore minerals formation, and their hydrothermal fluids characteristics. This research is dealing with characteristics of wallrock hydrothermal alteration using X-Ray Diffraction (XRD) and thin section to identify the associations of hydrothermal alteration minerals, ore microscopy to identify the type, associations, and paragenesis of the ore minerals, and fluid inclusions studies which include fluid inclusions petrography and microthermometry measurements to identify paleo-fluid characteristics in the research location. Four alteration types based on their mineral assemblages are identified, namely argillic, silicification, propylitic, and sericitization alterations. Silicification is marked by abundant quartz ± illite ± smectite. Propylitic alteration is typified by chlorite + smectite + calcite + quartz ± epidote ± illite ± adularia. Argillic alteration is presence by clay minerals such as illite + smectite + kaolinite + palygorskite. Sericite + chlorite + illite + smectite assemblage is key minerals of sericitization alteration. Metalliferous and ore minerals are found as native gold, acanthite-argentite, native silver, electrum, pyrite, sphalerite, galena, chalcopyrite, tetrahedrite, tennantite, chalcosite, covellite, goethite, and hematite. Based on fluid inclusion studies on the quartz veins, four fluid inclusion types are identified, namely type I (monophase, liquid rich) where L = 100%, type II (liquid rich, L+V) where L&gt;50%, type III (vapor rich, V+L) where V&gt;50%, type IV (vapor rich, V) where V = 100%. Homogenization temperature (Th) mean of banded vein ranged from 279°C - 284°C, with salinity mean 4.2 - 2.6 wt% eq. NaCl and formed around 806 - 711 meters depth under paleosurface. Homogenization temperature (Th) mean of cockade vein 278°C, with salinity mean 2.3 - 2.4 wt% eq. NaCl and formed around 728 - 726 meters depth under paleosurface. Homogenization temperature (Th) mean of massive barren vein is 267°C, with salinity 2.2 wt% eq. NaCl and formed around 607 meters depth under paleosurface. Binary plot between Th and salinity result and coexisting liquid-rich and vapor-rich fluid inclusions confirm that boiling processes took major place during the ore mineralization. Based on ore mineralogy, hydrothermal alteration mineral assemblage, and fluid inclusions characteristics, deposit is categorized into a deep low sulphidation epithermal deposits type, specifically in transition of precious metal to basemetal zone.

Fluid inclusions in quartz of the gold-ore occurrences and gold-quartz intergrowths from placers in the Sololi uplift of the Olenyok arch (Yakutia)

Fluid inclusions have been studied in vein quartz with gold sulfide mineralization from metamorphosed sandstones of the Eekite series and metarhyolites of the Early Proterozoic, in quartz breccia from the zone of overlapping gold mineralization on the Early and Middle Permian sandstones, as well as in the gold quartz intergrowths from the Sololi River placer. It has been revealed that formation of quartz breccias occurred within a wide temperature interval from 230 to 425 ºC, with predominance of carbon dioxide and nitrogen in the vapor phase. It is suggested that the increased nitrogen content may be associated with a chemical reaction between the fluid and ammonium-containing silicates of host rocks, in which nitrogen in the form of NH4+ isomorphically replaces potassium at the regressive stage of metamorphism. At the same time, it is possible that mantle nitrogen, which was transported along the Anabar-Eekite deep fault, participated in formation of the studied breccias. The close homogenization temperatures and similar nature of the water-salt composition for the fluid inclusions of quartz veins that inject the Eekite series meta-rocks and meta-rhyolites indicate the synchronism of their formation and attribute them to the common stage of ore formation. Quartz veins with gold sulfide mineralization were the primary sources of pebbles with gold-quartz intergrowths from the Sololi River, this is evidenced by similarity of principal characteristics of fluid inclusions. Oxidizing conditions of the mineralization serve as favorable factor for the Au deposition, it is indicated by the predominant CO2 content in fluid inclusions, keeping role of a geochemical barrier and leading to an elevated gold content in quartz veins.

Geochemistry, Mineralization, and Fluid Inclusion Study of the Bayan-Uul Porphyry Au-Cu-(Mo) Deposit, Central Mongolia

The Bayan-Uul porphyry Au-Cu-(Mo) deposit occurs within the Mongol–Okhotsk Orogenic Belt, which is a part of the Central Asian Orogenic Belt. To understand geotectonic, petrogenesis, mineralization, and ore-forming fluid evolution of the Bayan-Uul deposit, we report petrographic and geochemical analyses of host rocks, mineralogy of ores, and fluid inclusion characteristics. Based on petrographic and mineralogical analyses, Cu, Mo, and Au mineralization occurs as disseminated and sulfide-bearing quartz–tourmaline veins hosted within granodiorites, monzodiorites, and diorite porphyry and tourmaline breccia. Four main alteration assemblages are identified: potassic, phyllic, argillic, and quartz–tourmaline alteration. The ore mineralogy of quartz–tourmaline veinlets are classified into A-type veinlets (quartz + tourmaline + chalcopyrite + magnetite + pyrite ± electrum), B-type veinlets (quartz + tourmaline + molybdenum + chalcopyrite + pyrite), and C-type veinlets (quartz + tourmaline + pyrite ± chalcopyrite). Fluid inclusions are found in quartz–tourmaline veinlets consisting mainly of liquid-rich two-phase (L-type), vapor-rich two-phase (V-type), and solid-bearing multi-phase (S-type) inclusions. The homogenization temperatures for the fluid inclusions in A-type, B-type, and C-type veinlets range from 215 to 490°C, 215 to 500 °C, and 160 to 350 °C and their salinity varies from 5.4 to 43.5 wt.%, 16 to 51.1 wt.%, and 3.4 to 24.1 wt.% NaCl equivalent, respectively. Coexistance of (L-type), (V-type), and (S-type) inclusions support fluid boiling. The δ18O values of ore fluids from different mineralizing A-, B-, and C-type veins are 8.7‰, 10.9‰, and 8.4‰, respectively, and the δ34S values of sulfide minerals range from −1.4‰ to 5.3‰, which indicates magmatic origin.

Geology, geochemistry, mineralization and fluid inclusion characteristics of the SW of Hormuz Island banded iron formations, southern Iran

The Hormuz Island banded iron formations (HIBIFs) are situated at the Zagros Folded Zone in southern Iran. The BIFs occur intercalated with the Neoproterozoic Hormuz series, an evaporite and siliciclastic succession with pyroclastic rocks, and were deposited on the continental rift margin of the Arabian plate. The HIBIFs are banded rocks consisting of the alternation of dark Fe-rich and reddish-brown Si-rich layers, and belong to oxide facies iron formations. The post-Archean Australian shale normalized rare earth elements and yttrium patterns of HIBIFs have the characteristics of both hydrothermal solutions and seawater. The sharp positive Eu anomaly (2.10–6.90) may be inherited from high-temperature hydrothermal solutions, while slightly negative Ce anomalies (0.57–0.82) are inherited from seawater. The homogenization temperature and salinity of primary fluid inclusions range from 180.7 to 474.3°C and from 2.24 to 12.85 wt% NaCl, respectively, which suggests that intermediate- to high-temperature hydrothermal fluids and seawater contributed to the formation of the HIBIFs. The Eu/Sm and Sm/Yb ratios in BIFs are between the values of hydrothermal fluids and seawater. In summary, all geological and geochemical data suggest that the HIBIFs are a post-great oxidation event iron formation pulse at the end of the Ediacaran period. However, this is actually not similar to Neoproterozoic syn-glacial iron formations. Instead, this is a new occurrence of iron formation in an overlooked/understudied time period when either global or local conditions were conducive to iron deposition. The iron deposition on Hormuz Island does not appear to be triggered by fluctuating atmospheric oxygen or sea-level variations, but instead may be related to syn-basinal volcanism in the active continental rift margin environment in anoxic submarine condition. Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits

Characteristics of Fluid Inclusions and Hydrocarbon Accumulation Stages of Yingcheng Formation in Dehui Fault Depression

Characteristics of Fluid Inclusions and Hydrocarbon Accumulation Stages of Yingcheng Formation in Dehui Fault Depression

Fluid inclusion characteristics and significance of the QZ7 Well in eastern Qiangtang Basin

Fluid inclusion characteristics and significance of the QZ7 Well in eastern Qiangtang Basin

Sulfur and Carbon–Oxygen Isotopic Geochemistry and Fluid Inclusion Characteristics of the Yolindi Cu-Fe Skarn Mineralization, Biga Peninsula, NW Turkey: Implications for the Source and Evolution of Hydrothermal Fluids

The current study sought to investigate the physiochemical conditions and fluid evolution within the Yolindi Cu-Fe skarn mineralization located in the Biga Peninsula, NW Turkey. This was accomplished through a comprehensive investigation of geological and mineralogical data, along with isotopic analyses of sulfur (δ34S), carbon (δ13C), and oxygen (δ18O) of sulfide and calcite minerals, respectively, as well as fluid inclusion data pertaining to various minerals (e.g., andradite, quartz, and calcite). The Yolindi area features a complex geological framework, including the Paleozoic Kalabak Group (which includes the Torasan, Yolindi, and Sazak formations) and the Triassic Karakaya Complex. These formations were subsequently intruded via Early Miocene Şaroluk granitoids and Hallaçlar volcanics. Skarn formation is zoned into endoskarn and exoskarn types (being categorized into proximal, intermediate, and distal zones), with distinct mineral assemblages indicating concentric and contact metamorphic alteration patterns around the western part of Şaroluk granitoid intrusion in contact with the Torasan formation. The ore mineralogy and paragenesis suggest three distinct stages of evolution: an initial phase of prograde metasomatism characterized by the formation of magnetite and pyrite alongside anhydrous calc-silicate minerals; a subsequent phase of retrograde alteration marked by the formation of epidote, actinolite, and scapolite, accompanied by the occurrence of chalcopyrite and specular hematite; and finally, a post-metasomatic stage involving oxidation processes that led to the development of secondary mineral assemblages containing cerussite, covellite, and malachite. Sulfur isotopes (δ34S) of sulfides from endoskarn (from +0.27 to +0.57‰VCDT) to intermediate exoskarn (from −9.44 to −5.46‰VCDT) zones indicate a diverse sulfur source, including magmatic, sedimentary, and possibly organic matter. δ34S values in hydrothermal fluids suggest a magmatic–hydrothermal origin, with endoskarn and proximal zone fluids showing a slight negative signature and intermediate zone fluids indicating a strong influence from organic-rich or metamorphic sulfur reservoirs. Carbon and oxygen isotopic compositions (δ13C and δ18O) of calcite revealed a progression from marine carbonate signatures in marble samples (from +1.89 to +2.23‰VPDB; from +21.61 to +21.73‰VSMOW) to depleted values in prograde (from −6.0 to +0.09‰VPDB; from +6.22 to +18.14‰VSMOW) and retrograde skarns (from −3.8 to −2.25‰VPDB; from +0.94 to +3.62‰VSMOW), reflecting interactions with high-temperature magmatic fluids and meteoric water mixing. The fluid inclusions in prograde minerals generated under the conditions of fluid boiling exhibited high temperatures, reaching up to 412 °C, and salinities up to 26 wt.% NaCl equivalent. Conversely, the fluid inclusions in retrograde minerals, which were generated due to fluid mixing, exhibited lower temperatures (with an average of 318 °C) and salinities with an average of 4.9 wt.% NaCl equivalent. This indicated that the cooler and more diluted fluids mix with meteoric waters and interact with organic materials in the host rocks. This suggests a multifaceted origin involving various sources and processes. Therefore, this study concluded that the skarn mineralization in the Yolindi area resulted from complex interactions between magmatic, metamorphic, and meteoric fluids, reflecting a dynamic ore-forming environment with implications for the regional metallogeny of Cu-Fe skarn deposits.

Linking carbonate-hosted Zn[sbnd]Pb deposit to deep mantle activity: Evidence from in situ U[sbnd]Pb geochronology of calcite from the world-class Huayuan Zn[sbnd]Pb ore field in South China

Carbonate-hosted ZnPb deposits are a major source of zinc, lead, and some critical raw metal resources worldwide (e.g., germanium and gallium). However, the timing and geodynamics setting of their mineralization remain enigmatic, leading to ongoing debates about their origins. To shed light on these issues, we utilized LA-ICP-MS in situ UPb dating of ore-related calcites to determine the timing and geodynamic setting of mineralization events in the world-class Huayuan carbonate-hosted ZnPb ore field in South China. The petrographic and cathodoluminescence features, fluid inclusion characteristics, and the Pb isotope data indicate that the tested calcites were formed from the same ore-forming fluids as the intergrown sphalerite and were not overprinted by possible later hydrothermal fluids. Our results show that the calcite UPb ages of 510–495 Ma refute the previously proposed Mississippi Valley-type (MVT) model, which suggested that the younger Caledonian orogeny (460–420 Ma) played a significant role in the genesis of the Huayuan ZnPb ore field. Instead, our findings link the formation of this ore field to crustal extension and high heat flux resulting from mantle upwelling events in northeast Gondwana during the Cambrian. The findings indicate that deep mantle processes can trigger shallow crustal fluid circulation to create a giant carbonate-hosted ZnPb ore field in a long-dormant rift.We present a genetic model proposing that the extensive carbonate platform of the Qingxudong Formation was likely a “brine factory” that supplied the brines to the Proterozoic basement through reactivated syn-rift faults. The high heat flux from upwelling mantle not only heated these brines to high temperatures but also caused early maturation of organic matter in the lower Cambrian Niutitang black shales to generate hydrocarbons. The hydrocarbons migrated into the limestone of the Qingxudong Formation. Meanwhile, the hot brines leached Zn and Pb from the Proterozoic basement rock. These ZnPb bearing brines ascended to the Qingxudong Formation where they mixed with the hydrocarbons. These hydrocarbons acted as reducing agents for ZnPb sulfide precipitation, forming the Huayuan giant ZnPb ore field. Furthermore, UPb dating results of syn-mineralization calcite, together with the relationships between the ores and host rocks, indicate that ZnPb mineralization occurred over timespans during or shortly after host-rock deposition and continuing during lithification for several million years in this ore field. The similar prolonged duration of mineralization may be relatively prevalent in other carbonate-hosted ZnPb deposits/ore fields. We therefore recommend that reliable age dating for all mineralization stages is necessary to establish genetic models for carbonate-hosted ZnPb deposits.

Origin and mineralization processes of REE during magmatic-hydrothermal evolution: Insights from in-situ geochemistry of calcite from the Weishan REE deposit, eastern North China Craton

The Weishan REE deposit, hosting more than one million tons of light REE oxides (LREE2O3), is one of the largest LREE deposits in China. It has been considered to be a carbonatite-related REE deposit, but whether carbonatites occurred or not is still controversial, leading to the confusions of how the LREE originated and mineralized. Here, we conducted in-situ elemental and Sr-Nd isotopic analyses on different stages of calcite from the Weishan REE deposit, combined with petrographic and bulk C-O isotopic studies, with the aim to unravel the origin and mineralization processes of REE. Four stages of calcite (Cal-1, Cal-2, Cal-3 and Cal-4) were identified, of which the Cal-1 typically coexists with K-feldspar and quartz while the Cal-2 and Cal-3 coexist with sulfates and REE minerals (e.g., bastnäsite and parisite), respectively. The Cal-4 occurs in the post-ore veinlets and coexists with sulfides. The Cal-1 is characterized by exsolution of carbocernaite along its cleavage planes with highest Na, K, Sr, Ba and LREE contents. The other stages of calcite show continuous decrease of the above elements. Combined with petrographic features and elemental discrimination diagrams, it is concluded that the Cal-1 is magmatic while the others are hydrothermal. These calcites thus indicate a continuous magmatic-hydrothermal evolution. The four stages of calcite show similar isotopic compositions, which are consistent with those of the alkaline silicate rocks in the ore district, suggesting an uniform source or magma chamber for their derivation. Considering the magmatic features of Cal-1, it is inferred that carbonate melts coupled with abundant alkaline fluids were exsolved from the alkaline magmas. Alkalis (e. g., K and Na) were enriched in the magmatic-hydrothermal system with potassic metasomatism being more prevalent, which might play an important role in REE exsolution and transportation. Focused REE deposition occurred shortly after massive deposition of sulfates, indicating that REE-sulfate complexes might be the dominant transporting ligands of REE. The deposition of REE was mainly induced by fluid boiling, as indicated by the boiling/unmixing features of fluid inclusions. The Sr-Nd isotopic compositions of ores and associated alkaline rocks show affinities to the enriched lithospheric mantle (EM) beneath the study region, but are more depleted. Because subduction of the Paleo-Pacific oceanic plate beneath the eastern Asian occurred since the Jurassic, it is inferred that CO2- and REE-rich melts/fluids released from the subducted oceanic slab metasomatized the EM, leading to a REE-rich carbonated mantle. Rollback of the subducted slab occurred during the early Cretaceous, resulting in partial melting of the EM and thus generating the CO2- and REE-rich alkaline magmas. This deposit shows significant hydrothermal features with poorly-developed carbonatites, distinct from the typical carbonatite-related REE deposits in the other places. The REE mineralization is thus considered to be basically controlled by the alkaline magmas rather than the carbonatites.

Fluid inclusions, H-O-S-Pb isotopes, and Rb-Sr geochronology of the Augaro gold deposit, West Eritrea, NE Africa: Implications for ore genesis

Northeast Africa is an emerging world-class gold province due to the numerous lode gold deposits with Au resources of over 43 Moz discovered in the Nubian Shield. The Augaro gold deposit, located in the Adobha-Augaro Cu-Au belt of west Eritrea, is composed of several auriferous quartz veins. The orientations of the auriferous quartz veins in this deposit are strictly controlled by NE-trending shear zones and nearly E-trending fractures. The most common metallic mineral is pyrite, and gold has been identified as native gold, electrum, and calaverite. Fluid inclusion study, H-O-S-Pb isotope analysis, and Rb-Sr dating were carried out in the Augaro gold deposit. A petrographic investigation revealed that fluid inclusions of type W (Liquid-rich aqueous), type C (CO2-rich), and type S (halite-bearing) are prevalent in auriferous quartz veins. The H2O, NaCl, and CO2 are the main components of the metallogenic fluids, which are medium-low temperatures (150–360 °C) and medium to low salinities (<34 wt% NaCl eqv.). The physicochemical features of fluid inclusions indicate that magmatic fluids experienced phase separation earlier in their evolution and mixed with meteoric water subsequently. Rb-Sr dating of fluid inclusions in auriferous quartz suggests that the Augaro gold deposit formed during the post-orogenic stage (543 ± 14 Ma) of East African orogeny in the Late Neoproterozoic, which is a new metallogenic epoch for the lode gold deposits in Nubian Shield. Geological and Geochemical features refer to the Augaro gold deposit being an intrusion-related gold deposit (IRGD).

Mineralization of the Liwu large-scale stratiform copper deposits in Sichuan Province, China: Constraints from fluid inclusions

The Liwu stratiform copper deposit is located in the NW Jianglang dome, western China. Current studies mainly focus on the genetic type and mineralization of this deposit. Detailed fluid inclusion characteristics of metallogenic period quartz veins were studied to reveal the ore-forming fluid features. Laser Raman analysis indicates that the ore-forming fluids is a H₂O-NaCl-CH₄ (-CO₂) system. Fluid inclusions microthermometry shows a homogenization temperature of 181–375°C and a salinity of 5.26%–16.99% for the disseminated-banded Cu-Zn mineralization; but a homogenization temperature of 142–343°C and a salinity of 5.41%–21.19% for the massive-veined Cu-Zn mineralization. These features suggest a medium–high temperature and a medium salinity for the ore-forming fluids. H-O isotopic data indicates that the ore-forming fluids were mainly from the metamorphic and magmatic water, plus minor formation water. And sulfur isotopic data indicates that sulfur was mainly derived from the formation and magmatic rocks. Metallogenesis of the disseminated-banded mineralization was mainly correlated with fluid mixing and water-rock reaction; whereas that of the massive-veined mineralization was mainly correlated with fluid boiling. The genetic type of the deposit is a medium-high temperature hydrothermal deposit related to magmatism and controlled by shear zones. This study is beneficial to understand the stratiform copper deposit.

Geological, geochemical and fluid inclusion features of Kömürlükdere and Göçükdibi Cu-Zn ore (Central Pontides, Turkey): Implications for their genesis

The Kömürlükdere and Göçükdibi Cu-Zn ores are located in the Central Pontide orogenic belt, where Besshi-type deposits (such as Hanönü, Zeybek, Sayyayla [Kastamonu]) have been discovered in last two decades. The Göçükdibi and Kömürlükdere ores are hosted in metabasites and quartz schist that belong to the Middle Jurassic Kunduz metamorphic rocks in the accretionary complex in the Central Pontides. The ore bodies show stratiform features, parallel to schistosity, within an alternation of metabasite and quartz schist succession. The average thicknesses of the ore zone and ore levels within the ore zone are 12 m and 3 cm, respectively. The ore bodies contain chalcopyrite, sphalerite, and magnetite, with dominant pyrite formed during the ore formation phase. Meanwhile, hematite, covellite, malachite, and goethite minerals formed during the supergene processes.Microprobe studies showed that the Fe and Cd content of sphalerite varies from 0.08 to 1.12 wt%, indicating Fe-poor sphalerite, and 0.08–0.27 wt%, respectively. The Zn/Cd ratios (average 274.4 for Kömürlükdere, 288.6 for Göçükdibi) of the sphalerite are comparable to those of the worldwide volcanogenic-massive sulfide (VMS) ore system related to andesitic-basaltic source rocks. The Co/Ni ratio (mean 3.2) of pyrite shows volcanogenic pyrite.The average δ34S of the stratiform pyrites is 3.9 ‰ (ranging from 2.06 ‰ to 5.34 ‰), indicating that the sulfur comes from a large homogeneous source, possibly magmatic. The average homogenization temperature (Th) and salinity of fluid inclusions obtained from quartz and sphalerite are 313 °C and 7.7 % equiv. NaCl, respectively, and similar to those of the global VMS deposits.The metabasites contain an average of 164 ppm Cu, 127 ppm Zn, and 2.2 ppm Sb, which shows enrichment several times greater than the background value of the basalts. Meanwhile the ore levels contain an average 0.23 % and 0.83 % Cu and Zn values, respectively. The trace metal enrichment of associated metabasites and the ore zones is evident for elements such as Cu, Zn, Cd, As, and Sb, indicating that they both precipitated in the same basin as syngenetic, and that there was repeated pulses of metal-rich fluids exhaled into the basin.Field observations and analytical data (mineral chemistry, sulfur isotope, fluid inclusion, etc.) show that the Kömürlükdere and Göçükdibi Cu-Zn ore bodies occurred as Besshi-type deposits within the Middle Jurassic Central Pontide Supercontinent, which developed in the marine environment appropriate to the accretionary complex located along the southern margin of Eurasia.

The Geochemical Characteristics of Fluid Inclusions as Indicators of the Degree of Organic Matter Transformation in Jurassic Sediments of the Em-Egovskaya Summit (Krasnoleninsky Arch, Western Siberia)

The Geochemical Characteristics of Fluid Inclusions as Indicators of the Degree of Organic Matter Transformation in Jurassic Sediments of the Em-Egovskaya Summit (Krasnoleninsky Arch, Western Siberia)

Geology, alteration system and uranium mineralization of Tamusu large uranium deposit, China

Tamusu uranium deposit is located in Yingejing sag in the Bayingobi basin. A rift type structural slope zone developed northwest of the sag. Based on the study of the lithology, lithofacies, whole rock geochemistry, and fluid inclusion characteristics of the deposit, a paragenetic association sequence of altered minerals in the deposit was established, and the characteristics of the source, temperature, salinity, and evolution of the ore-forming fluid in the deposit were discussed. The stratigraphic assemblage structure of the lower member of the Bayingobi Formation (falling-stage system tract, lowstand system tract, and transgressive system tract) laid the foundation for uranium mineralization. The uranium mineralization period of ore deposit can be divided into three stages. The altered mineral assemblages of Stage 1 are mainly composed of hematite, dolomite, iron-bearing dolomite, ankerite, fluorite, euhedral pyrite, and metal sulfide. Stage 2 altered mineral assemblages are dominated by limonite, euhedral-subhedral pyrite, and gypsum. The altered mineral assemblages of Stage 3 are mainly composed of layered gypsum, celestite, and barite. The early uranium ore-forming fluid mainly originated from the deep basin and percolated along the fault and sand body of the lowstand system tract to form uranium orebodies. The fluid inclusion temperature of ore-forming fluid was 211–140 ℃, and the salinity was 4.49%–16.24%. The temperature gradually decreased as the ore-forming fluid evolved, and CO2 was released, causing dolomite, calcite, fluorite, and other minerals to precipitate in the sandstone pores. The late ore-forming fluid mainly originated from supergene oxygen water, which migrated into the basin along the erosion window at the edge of the sag. The fluid inclusion temperature of ore-forming fluid was 100–130 ℃, the salinity was 2.24%–7.02%, and the average was 4.49%. In the late stage of the supergene fluid, the fluid inclusion temperature was 55–79 ℃, and the salinity was 4.96%–5.11%. The ore-forming fluid of the deposit gradually decreased in temperature from the early stage to the late stage of mineralization. In addition, the salinity gradually evolved from high in the early stage to low and evolved to high in the late stage. Sulfophile, lithophile, and rare earth elements precipitated first in the process of fluid action, followed by U, and Sc increased with the U content. A uranium metallogenic model of the deposit was established based on the relationship between the structural, lithology, mineralization alteration, fluid evolution, and uranium mineralization of the basin.

Characteristics of fluid inclusions and metallogenic mechanism of the Longshang skarn type tin polymetallic deposit in eastern Hunan Province, China

矽卡岩型锡矿是全球重要的锡金属来源,但是锡石沉淀成矿机制仍存在较大的争议。垄上矽卡岩型锡矿床位于湘东锡田锡多金属矿田中部,是南岭钨锡成矿带内矽卡岩型锡矿的典型代表。本文在野外考察、矿石矿相学、流体包裹体岩相学研究的基础上,采用流体包裹体组合法对垄上矽卡岩矿床不同矿化阶段代表矿物中的流体包裹体进行了详细研究。结果显示,垄上矽卡岩型多金属矿床成矿阶段可划分为矽卡岩阶段、退化蚀变阶段、云英岩-氧化物阶段、石英硫化物阶段以及萤石碳酸盐化等5个阶段,其中,锡石主要形成于云英岩-氧化物阶段。与锡石密切共生的石英中发育流体包裹体类型主要为富液相、富气相两相水溶液包裹体,含液相CO₂三相水溶液包裹体和纯CO₂型包裹体。流体温度和盐度具有较大的变化范围(200~400℃和2%~9%NaCleqv),指示流体在降温过程中经历了显著的不混溶。与硫化物共生的石英中主要为富液相两相水溶液包裹体,温度和盐度主要集中在190~261℃和3%~7% NaCleqv,指示流体冷却过程同时经历了流体混合。本次研究提出锡田矽卡岩型矿床中流体不混溶是导致云英岩-氧化物阶段锡石沉淀成矿的主要机制,而流体冷却和混合是导致硫化物沉淀的主要原因。