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This petrographic, stable isotopic and fluid inclusion microthermometric study of the Upper Jurassic limestones of an onshore field, Abu Dhabi, United Arab Emirates (UAE) compares diagenesis in flanks and crest of the anticline. The results revealed that the diagenetic and related reservoir quality evolution occurred during three phases, including: (i) eogenesis to mesogenesis 1, during which reservoir quality across the field was either deteriorated or preserved by calcite cementation presumably derived from marine or evolved marine pore waters. Improvement of reservoir quality was due to the formation of micropores by micritization of allochems and creation of moldic/intragranular pores by dissolution of peloids and skeletal fragments. (ii) Obduction of Oman ophiolites and formation of the anticline of the studied field was accompanied by cementation by saddle dolomite and blocky calcite. High homogenization temperatures (125–175 °C) and high salinity (19–26 wt% NaCl eq) of the fluid inclusions, negative δ 18 O VPDB values (−7.7 to −2.9‰), saddle shape of dolomite, and the presence of exotic cements (i.e. fluorite and sphalerite) suggest that these carbonates were formed by flux of hot basinal brines, probably related to this tectonic compression event. (iii) Mesogenesis 2 during subsidence subsequent to the obduction event, which resulted in extensive stylolitization and cementation by calcite. This calcite cement occluded most of the remaining moldic and inter−/intragranular pores of the flank limestones (water zone) whereas porosity was preserved in the crest. This study contributes to: (1) our understanding of differences in the impact of diagenesis on reservoir quality evolution in flanks and crests of anticlines, i.e. impact of hydrocarbon emplacement on diagenesis, and (2) relating various diagenetic processes to burial history and tectonic events of foreland basins in the Arabian Gulf area and elsewhere. [ABSTRACT FROM AUTHOR]

Apatite is a concentrator of F and Cl, which play a significant role in the formation of minerals of platinum-group elements of pneumatolitic origin. There are three apatite generations in Norilsk magmatic sulfide ores. Apatite I occurs in sulfide bodies and rims of fluid alteration above sulfide droplets in disseminated ores. Its composition evolved from hydroxyl-chlorapatite to chlorapatite. Apatite I associates with Tiрbiotite, titanomagnetite, ilmenite with baddeleyite lamellae, anhydrite, Ti-poor kaersutite, Cl-bearing hastingsite and edenite, djerfisherite, bartonite, and minerals of the Pt and Au groups. Apatite I contains up to 2.3 wt % lanthanides, primarily Ce, La, and Nd. Apatite I is overgrown and replaced by apatite II, the composition of which evolved from hydroxyl-chlor-fluorapatite to fluorapatite. Apatite II often occurs also as individual crystals in massive sulfides and contains up to 0.9 wt % lanthanides. The pneumatolitic chlorapatite and fluorapatite contain ~0.5 wt % SiO2. The composition of apatite indicates discrete evolution of fluids released during the crystallization of Norilsk sulfide melts: from water-chloride to chloride at the first state, and from water-chlorite-fluoride to essentially fluoride at the second stage. The lanthanides released during the replacement of chlorapatite I by fluorapatite II were probably incorporated in pneumatolitic zoned orthite-(Ce). In the areas affected by prehnite-pumpellyite metamorphism, apatite I and apatite II within metamorphosed sulfide ores are partly or completely replaced by apatite III, which varies in composition from hydroxyl-chlorapatite to hydroxylapatite poor in fluorine and lanthanides. The lanthanides released during the replacement of apatite I and II by metamorphic hydroxylapatite III were probably incorporated in metamorphic unzoned orthite-(Ce). [ABSTRACT FROM AUTHOR]

Granites and pegmatites in the Strange Lake pluton underwent extreme enrichment in high field strength elements (HFSE), including the rare earth elements (REE). Much of this enrichment took place in the most altered rocks, and is expressed as secondary minerals, showing that hydrothermal fluids played an important role in HFSE concentration. Vasyukova et al. (2016) reconstructed a P-T-X path for the evolution of these fluids and provided evidence that hydrothermal activity was initiated by exsolution of fluid during crystallisation of border zone pegmatites (at ~450–500 °C and 1.1 kbar). This early fluid comprised a high salinity (25 wt% NaCl) aqueous phase and a CH 4  + H 2 gas. During cooling, the gas was gradually oxidised, first to higher hydrocarbons (e.g., C 2 H 6 , C 3 H 8 ), and then to CO 2 , and the salinity decreased to 4 wt% (~250–300 °C), before increasing to 19 wt%, due to fluid-rock interaction (~150 °C). Here, we present crush-leach fluid inclusion data on the concentrations of the REE and major ligands at different stages of the evolution of the fluid. The chondrite-normalised REE profile of the fluid evolved from light REE (La-Nd)-enriched at high temperature (~400 °C, Stages 1–2a) to middle REE (Sm-Er)-enriched at 360 to 250 °C (Stages 2b–3) and strongly heavy REE (Tm-Lu)-enriched at low temperature (150 °C, Stage 5). These changes in the REE distribution were accompanied by changes in the concentrations of major ligands, i.e., Cl − was the dominant ligand in Stages 1, 2, 4 and 5, whereas HCO 3 − was dominant in Stage 3. Alteration of arfvedsonite to aegirine and/or hematite contributed strongly to the mobilisation of the REE. This alteration released middle REE (MREE) and heavy REE (HREE), which either partitioned into the fluid or precipitated directly as bastnäsite-(Ce), ferri-allanite-(Ce) or gadolinite-(Y). Replacement of primary fluorbritholite-(Ce), which crystallised from an immiscible fluoride melt and altered to bastnäsite-(Ce), was also important in mobilising the REE (MREE). This paper presents the first report of the distribution of the REE in an evolving hydrothermal fluid. Using this distribution, in conjunction with information on the changing physicochemical conditions, the study identifies the sources of REE enrichment, reconstructs the path of REE concentration, and evaluates the REE mineralising capacity of the fluid. Finally, this information is integrated into a predictive model for REE mobilisation applicable not only to Strange Lake but any REE ore-forming system, in which hydrothermal processes were important. [ABSTRACT FROM AUTHOR]

The Qiman Tagh W-Sn ore belt is located in the westernmost sector of the East Kunlun Orogen, NW China. It has been recognized as a unique W-Sn belt that formed in the early Paleozoic and related to closure of the Proto-Tethys. To understand the evolution of ore-forming fluids and its relationship with the tectonic setting of East Kunlun Orogen, we report the results obtained from fluid inclusion and H-O isotopic studies of ores and quartz veins for the Qiman Tagh W-Sn ore belt. Mineralization in Qiman Tagh includes four stages characterized by quartz-cassiterite-wolframite assemblage stage 1, quartz ± scheelite assemblage stage 2, quartz-polymetallic sulfides stage 3, and ore-barren veins stage 4. The former two stages are conducive to mineralization, while the latter two stages are less important. The fluid inclusions are distinguished between CO 2 -H 2 O (C-type) and NaCl-H 2 O (W-type) in composition, containing a trace of CH 4 , N 2 , C 2 H 6 , SO 2 , and CO 3 2– . Cassiterite and quartz in stage 1, instead of wolframite, contain a great deal of C-type inclusions. All inclusions in minerals of stage 1 yield homogenization temperatures of 230.1–384.1 °C (peaking at 310–320 °C), with salinities lower than 14.76 wt% NaCl equiv. and bulk densities of 0.63–0.89 g/cm 3 . The stage 2 minerals contain both two types of inclusions, yielding homogenization temperatures of 183.4–335.9 °C (peaking at 280–290 °C), with salinities lower than 14.53 wt% NaCl equiv. and bulk densities of 0.66–0.97 g/cm 3 . Fluid inclusions in minerals of stages 3 and 4 are mainly W-type and homogenized at temperatures of 140.6–277.6 °C (peaking 210–220 °C), and 116.9–255.1 °C (peaking 160–170 °C), respectively. The H-O isotopic systematics shows that the fluids were dominated by magmatic water in stages 1 and 2, but by meteoric water in stages 3 and 4. Integrating all the geological and geochemical data, we conclude that the fluids forming the Qiman Tagh W-Sn ore belt evolved from granite-derived, CO 2 -rich and reducing, to meteoric water-dominated, CO 2 -poor and oxidizing. Fluid immiscibility, cooling and interaction with rocks are main mechanisms for metallic deposition. [ABSTRACT FROM AUTHOR]

[Display omitted] • Li was derived from crust and ore fluids were initially magmatic water and later mixed with meteoric water. • CH 4 and CO 2 in the fluid were sourced from water-rock reaction with the graphitic-bearing wallrocks. • Fluid cooling, boiling and immiscibility control ore deposition. The Weilasituo Li-Sn-Cu-Zn polymetallic deposit is located in the southwestern Great Xing'an Range (GXR), and crypto-explosive breccia-type and hydrothermal vein-type mineralization are developed in the mining area. With the Early Cretaceous amazonite granite as the mineralization center, the greisen-type Li(-Rb) mineralization is developed in the crypto-explosive breccia pipe above the granite, and the quartz vein-type Sn(-W-Mo) and Cu-Zn(-Ag) mineralization is successively developed in the surrounding Paleoproterozoic Xilinguole complex, forming mineralization zoning. The polymetallic metallogeny comprises early Li (Rb) through Sn(-W-Mo) to late Cu-Zn(-Ag) mineralization, and can be divided into six stages: (I) zinnwaldite–topaz–fluorite, (II) quartz–arsenopyrite–cassiterite–sphalerite–wolframite, (III) quartz–molybdenite–polymetallic sulfides, (IV) quartz–arsenopyrite–pyrite–chalcopyrite, (V) quartz–chalcopyrite–pyrrhotite–sphalerite–galena ± pyrite, and (VI) quartz–calcite–fluorite. Fluid inclusions (FIs) in the zinnwaldite, topaz and fluorite of Li(-Rb) ore phase contain high-temperature medium-salinity (348–404℃; 5.09–9.60 wt%) vapor–liquid two–phase aqueous type (vapor–liquid ratio: 35–70 %), similar to intermediate-density (ID) type FIs, and represent a single-phase fluid directly exsolved from the magma; FIs in the Sn(-W-Mo) ore phase quartz contain daughter mineral-bearing three-phase (SVL), vapor (V), vapor-rich two-phase aqueous (LV) and liquid-rich two-phase aqueous (VL) type, reflecting fluid boiling; FIs in the Cu-Zn(-Ag) ore phase quartz contain CH 4 ± CO 2 two-phase FIs and VL-type FIs, indicating fluid immiscibility. Lithium isotope data show that the Li ore-forming material was crustal derived, while H-O isotope data indicate that the ore fluid was derived from magmatic water and mixed with meteoric water in the late Cu-Zn(-Ag) ore phase; Carbon isotope data suggest that the CH 4 and CO 2 in the FIs were sourced from the fluid-rock reaction between the hydrothermal fluid and with the Xilinguole Complex graphite-bearing wallrocks. Raman spectroscopy shows that stage Ⅱ-Ⅴ FIs contain CH 4 and CO 2 , whose content increased markedly from the Sn(-W-Mo) to Cu-Zn(-Ag) stage, indicating that CH 4 and CO 2 are enriched continuously with fluid migration and fluid-rock reaction. We conclude tha the initial single-phase ID Li-Rb-W-Sn-rich fluid was exsolved from the magma, and formed the Li(-Rb) mineralization in the crypto-explosive breccia pipe as the temperature dropped. Subsequently, the fluid entered the faults and the pressure dropped, causing fluid boiling, and triggered the proximal Sn(-W-Mo) vein-type mineralization. With the fluid migration and more water–rock reaction, CH 4 and CO 2 are continuously enriched and fluid immiscibility occurred, forming the distal Cu-Zn(-Ag) vein-type mineralization. [ABSTRACT FROM AUTHOR]

Seafloor hydrothermal sulfides at slow-spreading mid-ocean ridges (MORs) are of economic and scientific significance. The formation of newly discovered submarine hydrothermal sulfides on the South Mid-Atlantic Ridge (SMAR), particularly with respect to the fluid evolution, remains poorly understood. The Xunmei hydrothermal field is a typical volcanic dome-type hydrothermal field at 26°S on the SMAR. Based on the mineralogical zonation and assemblages, six distinct ore-forming stages were identified from low- to high-temperature stages with a seafloor weathering stage. The crystallinity of pyrite/marcasite and grain size of chalcopyrite increase gradually from the outer rim to the inner conduit of a sulfide chimney. The positive δ34S V-CDT values of pyrite/marcasite (2.1‰–8.2‰), chalcopyrite (2.5‰–5.6‰), and sphalerite (2.9‰–7.0‰) suggest 62%–91% of S was derived from the leaching of basement basalts, 9%–38% from reduction of seawater sulfate. In situ trace element data for sulfides show enrichments in Mn, Ag, Tl, and Pb in outer zones A and B, while enrichments in Se, In, and Sn in inner zones C and D, indicating an increase in precipitation temperature during chimney growth. Low pyrite Co contents, low Tl/Pb, low Sb/Pb, low Bi/Pb, high As, Ag, Cu, and Pb concentrations, suggesting that the pyrites precipitated from fluids that may have undergone supercritical phase separation during their ascent. High-temperature, Cl-depleted, vapor-rich hydrothermal fluids discharged into ambient cold seawater over multiple stages and probably evolved from low (<240 °C) to medium (∼ 263 °C) and high (∼ 317 °C) temperatures, reached a highest temperature of ∼335 °C, and then evolved to medium to low temperatures (∼ 270 °C to <240 °C) during the wanning of hydrothermal venting. The sulfur fugacity (f S 2) likely evolved from a relatively low to high condition within the scope of intermediate sulfidation, and then decreased to low condition. The redox states (f O 2) probably were strongly affected by seawater influx and evolved from relatively oxidized to original reduced conditions. The salinity decreased during chimney growth. Sulfide precipitation in the Xunmei hydrothermal field probably was the result of a combination of fluid-seawater mixing and phase separation. We propose a chimney growth and hydrothermal evolution models for the Xunmei hydrothermal field. • Low pyrite Co contents suggest that the fluids that may have undergone supercritical phase separation during their ascent. • Sulfide precipitation in the Xunmei hydrothermal field was the result of a combination of fluid mixing and phase separation. • Fluid physicochemical conditions during the fluid evolution of chimney growth can be revealed by trace element of sulfide. [ABSTRACT FROM AUTHOR]

(a) LA–SF–ICP–MS U–Pb dating T-W diagram for garnet in the Jinchanghe deposit. (b) The compositions of trace elements in the garnet from the Jinchanghe deposit (GrtI, GrtII, and GrtIII). [Display omitted] • In the Jinchanghe deposit, all three garnet generations belong to the grossular-andradite solid solution series. • The fluid pH changed from weakly acidic to neutral to weakly acidic during garnet crystallization. • Garnet U-Pb ages indicate the deposit may be closely related to arc magmatic rocks formed by Proto-Tethys Ocean subduction. The Jinchanghe polymetallic Fe-Cu-Pb-Zn deposit is located in the northern region of the Baoshan Block in western Yunnan. Using electron probe micro-analysis and laser ablation inductively coupled plasma mass spectrometry, we analyzed the major, trace, and rare earth elemental contents of garnets from the Jinchanghe deposit. Moreover, U-Pb dating was performed using the laser ablation sector field inductively coupled plasma mass spectrometry (LA-SF-ICP-MS) method to determine the direct mineralization age of the Jinchanghe deposit. Petrographic analyses revealed three garnet generations: early (GrtI), middle (GrtII), and late (GrtIII). GrtI (And 55.69-64.47 Gro 30.28-41.21 Ura + Pyr + Spe + Alm 2.35-5.49) was characterized by irregular shapes and weak optical properties, and primarily comprised Fe-rich grossular. GrtII (And 53.69-96.17 Gro 2.78-45.07 Ura + Pyr + Spe + Alm 0.59-2.12) was characterized by andradite, in which GrtIIa was a homogeneous body, whereas GrtIIb shows exhibited oscillatory zoning with abnormal interference colors. Fine-veined andradite aggregates were predominant in GrtIII (And 70.51-90.33 Gro 6.34-27.80 Ura + Pyr + Spe + Alm 1.03-3.32). The GrtI, GrtIIa, and the rims of GrtIIb were depleted in heavy rare earth elements and enriched in light rare earth elements, with positive Eu anomalies, indicating that these garnets crystallized from mildly acidic magmatic hydrothermal fluids. However, the cores of GrtIIb had negative Eu anomalies and may have crystallized from a relatively neutral Cl-rich fluid. GrtIII was severely depleted in light rare earth elements with positive Eu anomalies, indicating the presence of a weakly acidic environment. Accordingly, owing to a decrease in temperature and an increase in oxygen fugacity, the pH of the Jinchanghe deposit may have transitioned from an early weakly acidic to neutral, then to a late weakly acidic environment. Furthermore, the ages of GrtII and GrtIII ranged from 520 to 496 Ma, which places the formation of the Jinchanghe deposit during the Late Cambrian. The deposit is closely related to the arc magmatic rocks produced by the subduction of the Proto-Tethys Ocean. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pyrite-bearing veins at Qulong can be divided into seven subclasses. • The contents of Co and Ni and the ratios of Co/Ni and Ni/Se in pyrite can be used to investigate the evolution of fluid composition, temperature and oxygen fugacity. • Changes in trace elements and S isotopes in pyrite can be used to investigate the evolution of magmatic-hydrothermal fluids. The post-collisional Qulong porphyry Cu-Mo deposit is the largest in the Gangdese Cu belt, southern Tibet. Despite many previous studies, the evolution of ore-forming fluids in the Qulong deposit remains controversial. Pyrite-bearing veins at Qulong can be divided into seven subclasses, including Mt-type, Bt-type, A-type, B-type, C-type, D-type, and E-type veins. To decipher the evolution of magmatic-hydrothermal fluids at Qulong, in situ LA-ICP-MS trace element and sulfur isotope compositions of pyrites from different veins were analyzed. The δ34S values (+1.01‰ to + 4.28‰) for pyrites indicate a magmatic sulfur source and the high Se/S ratios of pyrite at Qulong are consistent with hydrothermal fluids being mainly magma-derived. The low Co/Ni ratio (0.01–0.1) of pyrite in Mt-type vein suggests that the earliest magmatic-hydrothermal fluids may have contributed from mafic magma injection. From Mt- to Bt- to A-type veins, the δ34S values in the hydrothermal fluids decrease as the temperature decreases, whereas the Cu and Co contents increase and the As and Ni contents decrease. In B- and C-type veins, the relatively high and stable Co and Ni contents and the range of δ34S isotope values in pyrite indicate the existence of multiple-stages of magmatic-hydrothermal fluids during the main mineralization period. During the late stages of mineralization, the decrease of Co, Ni and As contents and increase of Cu in pyrite in D- and E-type veins, as well as the narrow range of δ34S values, may be due to decreasing temperature as a result of fluid dilution caused by mixing with meteoric waters. The slightly negative δ34S fluid values for chalcopyrite (-1.56‰ to −0.75‰) in sample Q711-1968 also suggests the addition of external water at Qulong. [ABSTRACT FROM AUTHOR]

Orebodies in the Xiadian gold deposit in the Jiaodong Peninsula, China are mainly hosted in the Mesozoic granitoids, controlled structurally by the Zhaoyuan–Pingdu Fault Zone, and occur as disseminated and cataclastic altered type. Four mineralization stages were identified as follows: quartz–pyrite stage (I), gold‐bearing fine‐grained pyrite–quartz stage (II), polymetallic sulfide–quartz stage (III), and quartz–carbonate stage (IV). Quartz was classified as including quartz granules with dentation boundaries (I), cataclastic quartz grain assemblages (II and III), and rod‐like quartz grains (IV). Petrography, laser Raman analysis, and microthermometry of fluid inclusions in these stages (in both tunnel and borehole samples) reveal (a) CO2–H2O fluid inclusions (C–H type), (b) CO2–H2O ± CH4 fluid inclusions (C–H–CH4 type), and (c) aqueous fluid inclusions (H type). Fluid immiscibility caused by fluid mixing caused rapid precipitation of gold. The ore‐forming fluid of the Xiadian gold deposit evolves from an H2O–CO2–NaCl ± CH4 system with medium temperature and salinity to an H2O–NaCl system with low temperature and salinity, from CO2‐rich to CO2‐poor in composition and from a mixture of magmatic water with increasing meteoric water as δ18OH2O values. Sulphur isotope compositions suggest a mixed source of ore metal, and the Jiaodong Group may be a major source for sulphur. Fluid parameters of borehole samples indicate that there is the same fluid system for Au precipitation at different depths and fault gouge with poor permeability may play a crucial role in forming a relatively closed semi‐open space for Au precipitation. Integrating the data obtained from the studies including regional geology, ore geology, and fluid inclusions and stable isotope geochemistry, the Xiadian gold deposit is concluded as an orogenic‐type gold deposit formed in the tectonic transition from compression to extension. [ABSTRACT FROM AUTHOR]

The mineral assemblages, mode of occurrence, and chemical compositions of coexisting fahlore and sphalerite from the Darasun gold deposit have been described. Three generations of fahlore and three generations of sphalerite have been recognized. The FeS content in sphalerite coexisting with fahlore ranges from 0.8 to 9.4 mol %. The complete solid solution series Fe-tetrahedrite-Zn-tetrahedrite-Fe-tennantite-Zn-tennantite reflected in Sb/(Sb + As) and Fe/(Fe + Zn) ratios ranging from 0 to 0.97 and from 0.07 to 1.00, respectively, with a predominant negative relationship between these ratios has been identified for the first time at the deposit. Stepped, oscillatory, and combined stepped-oscillatory growth zonings within fahlore grains and heterogeneous aggregates of fahlore have been found. Fahlore is enriched in As with respect to Sb, and Zn-tetrahedrite is followed by Fe- and Zn-tennantite from early to late generation; Zn-tetrahedrite is followed by Fe-tennantite in zoned grains and overgrown rims; sphalerite crystallized at decreased temperature and sulfur fugacity. The evolution of the chemical composition of fahlores was caused by the evolving temperature, fluid salinity, and conditions of metal migration. [ABSTRACT FROM AUTHOR]

The majority of hydrothermal vein systems of economic interest occur at relatively shallow crustal levels, although many of them formed at significantly greater depths. Their present position is a consequence of uplift and erosion. Although, many aspects of their formation are well constrained, the temporal chemical evolution of such systems during uplift and erosion is still poorly understood. These vein minerals comprise calcite, dolomite-ankerite, siderite-magnesite, anhydrite and gypsum forming the last gangue assemblages in Jurassic and Tertiary sulphide-fluorite-quartz-barite veins of the Schwarzwald mining district, SW Germany. Mineral textures of samples from nine localities reveal that in these sequences, mineral precipitation follows a recurring pattern: early calcite is followed by anhydrite or gypsum, siderite and/or dolomite. This succession may repeat up to three times. In-situ (LA-ICP-MS) U-Pb age dating of 15 carbonates from three subsequent generations of the late-stage vein assemblage yield robust ages between 20 and 0.6 Ma. Each mineral sequence forms in a distinctive period of about 2–5 Ma. These ages clearly relate these late-stage mineral phases to the youngest geological episode of the Schwarzwald, which is associated with the Cenozoic Rhine Graben rifting and basement uplift. Based on thermodynamic modelling, the formation of the observed mineral assemblages required an deeply sourced Mg-, Fe- and SO 4 -rich fluid (b), which was episodically mixed with a shallow crustal HCO 3 -rich fluid (a). As a consequence of fluid mixing, concentrations of Mg, Fe and SO 4 temporarily increased and initiated the formation of the observed sulphate-carbonate mineral sequences. This discontinuous large-scale vertical fluid mixing was presumably directly related to episodes of active tectonics associated with the Cenozoic strike-slip regime of the Upper Rhine Graben. Analogously, episodic fluid mixing is a major key in the formation of older (Jurassic to early Tertiary) Pb-Zn-fluorite-quartz-barite assemblages in the same specific vein systems, albeit involving different fluid compositions. Late-stage hydrothermal (∼20–70 °C) vein assemblages reported in this study record the transition from deep (>2 km) to very shallow (0–1 km) crustal conditions. As a consequence of successive uplift, increasing proportions of shallower and cooler (∼50–70 °C) fluids could take part in such mixing processes. Associated changes in the fluid composition caused the vein mineralogy to change from sulphide-quartz-fluorite-barite to calcite-anhydrite/gypsum-siderite-dolomite, as the system passively ascended closer to the surface. [ABSTRACT FROM AUTHOR]

Abstract: The Jiama deposit is a large copper deposit in Tibet. Mineralization occurs in three different host rocks: skarn, hornfels and porphyry. A detailed fluid inclusion study was conducted for veins in the different host rocks to investigate the relationship between fluid evolution and ore‐forming processes. Based on examination of cores from 36 drill holes, three types of veins (A, B and D) were identified in the porphyries, four types (I, II, III and IV) in the skarn, and three (a, b and c) in the hornfels. The crosscutting relationships of the veins and that of the host rocks suggest two hydrothermal stages, one early and one late stage. Fluid inclusions indicate that the Jiama hydrothermal fluid system underwent at least two episodes of fluid boiling. The first boiling event occurred during the early hydrothermal stage, as recorded by fluid inclusions hosted in type A veins in the porphyries, type a veins in the hornfels, and wollastonite in the skarns. This fluid boiling event was associated with relatively weak mineralization. The second boiling event occurred in the late hydrothermal stage, as determined from fluid inclusions hosted in type B and D veins in the porphyries, type I to IV veins in the skarns, and type b and c veins in the hornfels. This late boiling event, together with mixing with meteoric water, was responsible for more than 90% of the metal accumulation in the deposit. The first boiling only occurred in the central part of the deposit and the second boiling event took place across an entire interlayered structural zone between hornfels and marble. A spatial zoning of ore‐elements is evident, and appears to be related to different migration pathways and precipitation temperatures of Cu, Mo, Pb, Zn, Au and Ag. [ABSTRACT FROM AUTHOR]

The Oligocene Huagang Formation is the main sandstone reservoir in the Xihu Sag, situated in the east of the East China Sea Shelf Basin. With an integrated approach of thin-section petrography, ultra-violet fluorescence microscopy, scanning electron microscopy, and isotope geochemistry, the different diagenetic features were identified, the typical diagenetic parasequences were established, and the diagenetic fluids evolution history were reconstructed for the Oligocene Huagang Formation sandstone reservoir in the south of Xihu Sag. The Huagang Formation sandstone reservoir is now in Period B of the mesodiagenesis, which has undergone significant diagenetic alterations such as mechanical compaction, Pore-lining chlorite cement, feldspar dissolution, quartz cementation and dissolution, and carbonate cementation. Three types of carbonate cements (early siderite, medium ferrocalcite and late ankerite) were identified in the Huagang Formation sandstone reservoir. The carbon and oxygen isotopic compositions of carbonate cements show that the early calcite precipitate from alkaline lacustrine environment whereas the late carbonate cements were closely related to the organic acids. To the Huagang Formation sandstone reservoir, it has experienced two main episodes of dissolution during diagenesis. The early dissolution is that unstable components such as feldspar, lithic fragments, and carbonate cement were dissolved by acidic water. The second dissolution is that quartz and other silicate minerals were dissolved under the alkaline condition. Two main phases of hydrocarbon charging occurred in this study area. The first hydrocarbon emplacement was prior to the medium carbonate cementation but posterior to feldspar dissolution and the onset of quartz cementation at the end of the Miocene. The second hydrocarbon charging occurred in the Quaternary period after the late carbonate precipitation. [ABSTRACT FROM AUTHOR]

The Qinglong deposit is a newly-characterized, large Sb-(Au) deposit in the Youjiang basin (Guizhou, SW China). Four mineralization stages are identified (i.e., pre-ore, early-ore, late-ore and post-ore) in this study based on crosscutting relationships. Our study shows that the Qinglong Sb mineralization (early-ore stage) was dominated by quartz-stibnite ± fluorite, whilst the Sb-Au mineralization (late-ore stage) comprises quartz-stibnite ± pyrite. Electron Probe Microanalysis (EPMA) indicates that the Au is present as Au 1+ in the arsenian pyrite. Besides, our new fluid inclusion data from fluorite, stibnite and quartz show that the Sb-Au-rich hydrothermal fluids were derived from the mixing fluids consisting of H 2 O, NaCl, hydrocarbon and minor CO 2 . In the early-ore stage, the ore-forming fluids are characterized by medium to low temperatures (161–294 °C, mean: 220 °C), medium to low salinities (0.35–13.18 wt% NaCl equiv.), low pH, and the presence of hydrocarbons and CO 2 . In comparison, the late-ore stage ore-forming fluids are featured by low temperatures (113–255 °C, mean: 175 °C), low salinities (0.18–6.30 wt% NaCl equiv.) and nearly neutral pH. The δ 34 S ∑S values (−2.8 to 2.3‰) of the ore-forming fluids suggest that the sulfur at Qinglong was dominantly magmatic-derived. From the early-ore to late-ore stage, the ore-forming fluid temperature and oxygen fugacity ( f O 2 ) decrease but the pH increases (from acidic to neutral). Such physicochemical transition may have significantly decreased the Sb solubility from 10 s to 100 s of ppm to 0.001 ppm. Therefore, we propose that fluid mixing was the main process that substantially reduced the fluid temperature and oxygen fugacity, which effectively lowered the Sb solubility and led to abundant stibnite precipitation. The stibnite precipitation had likely decreased the H 2 S concentrations of the ore-forming fluids, thereby destabilizing the AuHS 0 complexes in the fluids and caused local Au precipitation. [ABSTRACT FROM AUTHOR]

The recently discovered polymetallic Shazigou Mo–W–Pb–Zn ore field is located at the northern margin of the North China Craton. This integrated metallogenic system is comprised of quartz vein mineralization in three deposits: Shazigou Mo–W, Jindouzishan Pb–Zn and Mantougou Pb–Zn. The total reserves are estimated to be 50 kt Mo, 626 t WO 3 , 244 kt Pb and 150 kt Zn. Molybdenite Re–Os dating of five quartz vein-type ores yielded a mean model age of 243.8 ± 1.6 Ma (MSWD = 0.81) and hydrothermal zircons yielded a concordant U–Pb age of 245 ± 2.6 Ma (MSWD = 0.65). These results suggest that the mineralization was formed in the early Triassic and could be related to Paleo-Asian Ocean subduction. Microthermometry and quartz fluid inclusion compositions indicate that fluids related to the Mo–W mineralization were mainly derived from magmatic sources and precipitated under relatively high temperature (280–340 °C) and salinity conditions (6–9 wt% NaCl equiv.), whereas subsequent Pb–Zn mineralization-related fluids may have been modified by metamorphic and meteoric waters. The discovery of the Shazigou ore field suggests conditions may be favourable for more extensive mineralization in the western Xilamulun Mo metallogenic belt at the northern margin of the North China Craton. [ABSTRACT FROM AUTHOR]

Understanding geochemical processes is an important part of geothermal exploration to get information about the source and evolution of geothermal fluids. However, in most cases knowledge of fluid properties is based on few parameters determined in samples from the shallow subsurface. This study presents a new approach that allows to conclude from the combination of a variety of these data on processes occurring at depth in a geothermal reservoir. The neural network clustering technique called “self-organizing maps” (SOMs) successfully distinguished two different geothermal settings based on a hydrochemical database and disclosed the source, evolution and flow pathways of geothermal fluids. Scatter plots, as shown in this study, are appropriate presentations of element concentrations and the chemical interaction of water and rock at depth. One geological setting presented here is marked by fault dominated fluid pathways and minor influence of volcanic affected fluids with high concentrations of HCO 3 , Ca and Sr. The second is a magmatically dominated setting showing strong alteration features in volcanic rocks and accommodates acidic fluids with high SO 4 and Si concentrations. Former studies, i.e., Giggenbach (1988), suggested Cl, HCO 3 and SO 4 to be generally the most important elements for understanding hydrochemical processes in geothermal reservoirs. Their relation has been widely used to classify different water types in geothermal fields. However, this study showed that non-standard elements are at least of same importance to reveal different fluid types in geothermal systems. Therefore, this study is an extended water classification approach using SOM for element correlations. SOM have been proven to be a successful method for analyzing even relatively small hydrochemical datasets in geothermal applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Samples from the contact zone between ore body and dolostone are used to characterize ore-forming process. • Textural and chemical composition of dolomite indicate intensive fluid-rock interaction. • Systematic S and Pb isotope variations of sulfides reflect various replacement of dolostone and precipitation of sulfides. • The pH change has played an important role in ore deposition. • A new model for the ore-forming process was proposed for the Huize deposit. Study on the ore-forming process is crucial for comprehending the mechanisms of metal enrichment and facilitating mineral exploration. The Huize deposit in southwestern China is characterized by significant Pb and Zn resources, as well as economic coproducts of Ge and Ag. In spite of extensive studies, the key factors for ore deposition remain controversial. Mineral textures, in situ trace elements of dolomite, and S and Pb isotopes of sphalerite and galena from the contact zone between ore body and wall rocks were used to decipher this issue. The contact zone samples are further divided into three parts at the thin section scale: ore, transitional zone, and wall rock dolostone. In the ore part, dolomite is characterized by irregular replacement. In the transitional zone, dolomite displays a core-rim texture with dolomite in the core and Fe- and Mn-rich dolomite in the rim. In the wall rock part, the Fe- and Mn-rich dolomite occur as veins. From the ore, through the transitional zone, to the wall rock, the contents of Ca, Mg, and rare earth elements in dolomite increased, whereas the contents of Mn, Fe, In, and V decreased, indicating interaction between ore-forming fluids and dolostone. The LREE depletion of hydrothermal dolomite in three zones is caused by fluid-rock interaction and retention of Cl- complexes. Negative Eu and Ce anomalies indicate that fluids evolve from alkaline to weakly acidic at relatively low temperatures. The δ34S values of sphalerite generally decrease from the ore to the transitional zone, consistent with the kinetic fractionation of sulfur isotopes due to the precipitation of sulfides. The Pb isotopic composition of galena generally increases from the ore, transitional zone, to the wall rock, reflecting increased involvement of dolostone. The detailed ore-forming process can be summarized as follows. When hydrothermal fluids, with higher ore elements, higher δ34S value, and low Pb isotope composition, enter the wall rock that has relatively high Pb isotopic composition, intense fluid-rock interaction occurs, and elements and isotopes are exchanged, forming dolomite-dominated alteration and Pb-Zn sulfides. During this process, the fluids evolve from alkaline to neutral and weakly acidic. Therefore, we suggest that the change in the pH due to the replacement of dolostone has played an important role in ore deposition. [ABSTRACT FROM AUTHOR]

Extensional fractures filled with calcite are widespread in the ultra-deep reservoir sandstones of the Cretaceous Bashijiqike Formation (>6000 m) in the Kuqa Depression, western China. Microstructures of calcite veins provide an excellent opportunity for investigating fracture opening processes in a tectonically active, ultra-deep foreland basin setting. The syntaxial calcite vein is the dominant type and is formed through a single crack-seal event. Calcite crystals in fractures show blocky and elongated blocky shapes. The textural and geochemical characteristics of syntaxial calcite veins were investigated in detail using optical cathodoluminescence, trace element distributions and stable carbon and oxygen isotopes. Calcite veins were inferred to have precipitated from a mixture of seawater and meteoric water. ∑REE + Y and elemental concentrations of Mg2+, Mn2+, Fe2+ and Sr2+ both increase from fracture walls to the center. This process was controlled by temperature, crystal growth rate and variations in elemental concentration in a relatively closed environment. Medium REE-bulge patterns after Post Archean Average Shale (PAAS) normalization, negative δCe and positive δEu anomalies all indicate that calcite wall-rock cements and veins may inherit constituents from seawater and from meteoric water containing feldspar-weathering components, respectively. Both 13δC PDB and 18δO SMOW of the parent fluids imply that calcite veins were primarily precipitated from seawater under a relatively closed diagenetic environment. Considering the scope and timing of the transgression of the Tethyan Ocean in the study area, meteoric water may have been retained prior to the seawater invasion (65 Ma). The mixing of meteoric water and seawater within the reservoir could be the primary origin of the fluids forming the calcite veins. • Syntaxial calcite veins are firstly documented in ultra-deep clastic reservoirs via CL petrography and in situ geochemical analysis. • Blocky and elongate blocky crystals in syntaxial calcite veins in the Cretaceous Bashijiqike Formation were formed through a single crack-seal process. • Stable isotope, REE and paleoenvironmental analysis indicate that calcite veins were precipitated from fluids of mixed meteoric water and seawater. [ABSTRACT FROM AUTHOR]

The sulfur isotopic composition and trace element content recorded in sedimentary pyrite have been widely used as a proxy to establish the geochemistry of pyrite-forming fluids. However, a continuous and complete evolution process of these fluids from the sedimentary period to diagenetic period remains not well constrained. The middle Jurassic strata (the Yan'an Formation containing coal seams and its overlying Zhiluo Formation hosting U deposits in the sandstone) in the northeastern Ordos Basin contain four kinds of microenvironments favorable for pyrite formation, namely coal, carbonaceous debris in barren gray sandstone, barren gray sandstone without carbonaceous debris and U mineralized gray sandstone from bottom to top, providing a good opportunity to decode pyrite formation in response to synsedimentary/diagenetic fluid evolution. In these microenvironments, pyrite named as PC, PD, PB and PM respectively, displays a variety of micro morphologies (framboidal, euhedral, infilling, irregular and cement) formed during sedimentary and diagenetic stages. PC has δ34S values ranging from −36.1 to +26.5 ‰ and low contents of total trace elements (from 6.7 to 58 ppm of Co + Ni + As + Se + Mo). PD and PB present δ34S signatures from −33.6 to +14.4 ‰ and from +9.7 to +22.2 ‰, respectively, with moderate trace element contents (from 21 to 111 ppm and from 23 to 80 ppm, respectively). PM resulting from the oxidation of PD and PB shows negative δ34S values (from −16.9 to −11.1 ‰ for framboidal pyrite and from −56.7 to −34.8 ‰ for euhedral pyrite + pyrite cement) and high trace element contents varying from 350 to 931 ppm. Detailed sulfur isotope and trace element microanalyses indicate that S involved in the formation of pyrite is derived from the fractionation process of organic sulfur in the coal, while Fe and trace elements originate from the surface-derived meteoric water. A paragenetic sequence from early PC, to PD and PB, and finally PM implies an evolution trend of δ34S values increasing first and then decreasing (bacterial sulfate reduction for framboids and Ostwald ripening for euhedral pyrite and pyrite cement of PM) and gradual enrichment of trace elements from synsedimentary to diagenetic fluids. The quantitative results can contribute to a better understanding of synsedimentary/diagenetic fluid evolution both locally and regionally for sedimentary strata in the low-temperature system. • Synsedimentary/diagenetic fluid evolution in middle Jurassic strata was quantitatively characterized. • Sedimentary pyrite displays a variety of morphologies, with a broad range of δ34S values and trace element contents. • Pyrite is the result of encounter of hydrocarbon fluids moving upward and meteoric water migrating downward. [ABSTRACT FROM AUTHOR]

• Water and gas samples from the manifestations reveals to be of meteoric origin and magmatic influx. • Nearly neutral pH manifestations and immature waters is due to dilution with shallow groundwater. • Recharge elevation investigated at elevation ranges from ∼750 to 1378 masl. • Tangkuban Perahu contains six distinct reservoirs hosted in sedimentary and volcanic rocks. Tangkuban Perahu and nearby volcano-hosted geothermal prospects are believed to be important for future power generation in West Java, Indonesia. Recharge areas of these prospects and geothermal fluid evolution are not yet fully understood. This study aims to describe the fluid origin, processes, and evolution of geothermal fluids concerning the recharge and the conceptual model of the Tangkuban Perahu Geothermal Systems (TPGS). Sampling and analyses of geothermal waters, rainwater, and gases collected in fumaroles and other manifestations were implemented in this study. Isotopic results of δ18O and δ2H collected from thermal and rainwater indicate deep-circulating meteoric origin, at an infiltration altitude range between 753 and 850 m in low terrain. Meanwhile, the high-standing terrain indicates the recharge zone to be within the wall of the Sunda Caldera and mountain slopes. Chondrite normalized patterns reveal an overall flat trendline that suggests the enrichment of Lower Rare Earth Elements (LREEs) in the central part of Tangkuban Perahu which is derived from the magmatic influx. The non-atmospheric gases origin was diagnosed by the lower N 2 /Ar (≤ 38) and is characterized by meteoric origin. The positive δ18O shifts from Ciater (CT), Batu Gede (BG), and Domas Crater (KwD) geothermal waters samples comparatively to the local meteoric lines are influenced by the interaction with wall rocks or magmatic influx. In these geothermal systems, the meteoric water infiltrated to the depth is heated, mixed with near-surface water, and followed by partial discharge as thermal springs along the faults. The resultant Tangkuban Perahu conceptual model has six distinct reservoirs with five geothermal systems hosted in the sedimentary (northern parts) and volcanic rock composition in the central and southern parts. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Textural-chemical evolution of Fe-As-S sulfide minerals can be a pertinent approach to evaluate the sources of the different ore-forming fluids. • Gold precipitation occurs due to destabilization of Au-bisulfide complexes during the phase separation. • O-H isotope data suggest involvement of meteoric water during late- to post ore-stages. The Zarshuran gold deposit (155 t Au, average grade: 2.63 g/t), NW Iran, provides a new paradigm for understanding the multicomponent ore-forming processes and metallogeny of gold during the evolution of hydrothermal fluids. It is characterized by auriferous quartz veins and gold coexisting with disseminated Fe-As-S sulfide minerals that are hosted in a sequence of Early Cambrian metasedimentary rocks. A complex paragenesis is defined by five sulfide stages: pre-ore stage pyrite (Py0), early ore-stage pyrite (Py1 and Py2), middle ore-stage pyrite (Py3a, Py3b, and Py3c), late ore-stage pyrite (Py4), and post ore-stage pyrite (Py5). Py0 with framboidal texture is characterized by relatively low concentrations of As, Au, Cu, and Sb, and has a broad range of negative δ34S values from −28.2 to −3.7 ‰, indicating microbial reduction of marine sulfate. Py1 and Py2 show porous texture with As-rich bright bands also having high Au (mean: 18.4 ppm). Similarly, narrow ranges in δ34S from −3.6 to +3.2 ‰ likely suggest a deep-seated magmatic sulfur source. In the middle ore-stage, Py3a cryptocrystalline cores have a range of positive δ34S (+5.4 to +26.7 ‰) values and high concentration of As(-Au), whereas later well-crystallized outer rim Py3c is Co(-Ni) rich, has a much more restricted δ34S range (−2.9 to +1.4 ‰), indicating an evolution of fluid composition from As-rich to Co-rich. Most of the gold (mean: 20.2 ppm) and trace elements (Hg, Ag, Sb, and Tl) were deposited in Py4, whose δ34S values (+5.4 to +26.7 ‰) show that ore fluid sulfur in this stage was mainly sourced from a mixture of magmatic sulfur with minor input of reduced sedimentary rocks. Low gold and trace element content with slightly negative δ34S values (–8.5 to –4.2 ‰) of Py5 show that they were likely formed from a metal-poor oxidizing fluid. The mineralizing fluid system can be described as carbonic-aqueous with low to moderate salinity (3.2–15.1 wt% NaCl equiv.) and medium temperature of 285 to 317 °C (early ore-stage) and 255 to 290 °C (late ore-stage), which suggests that phase separation was responsible for gold precipitation during late ore-stage As-Hg-Sb sulfide veins. The δ18O fluid ranges from −7.8 to +4.2 ‰, and the δD values for fluid inclusions in mineral range from −105 to −65 ‰, suggesting involvement of meteoric water during late- to post ore-stages. Our results indicate that the Zarshuran is a distal disseminated gold deposit formed during southward subduction of the Proto-Tethys oceanic lithosphere beneath the northern margin of Gondwanan terranes through the early Cambrian. [ABSTRACT FROM AUTHOR]

The Kozbudaklar scheelite skarn deposit in the Tavşanlı Zone, located approximately 22 km southeast of Bursa, is hosted by the Triassic calcic İnönü Marble and Eocene Topuk Pluton. At least four stages have been recognized through skarn evolution. Scheelite skarn distributed close to the Topuk Pluton occurred during the early (stage 1) and late (stage 2) prograde substages. The early prograde endo and exoskarn are composed of hedenbergite (Hd 96 Joh 4 )–plagioclase (An 55–64 ) and hedenbergite (Hd 61–94 Joh 4–7 ), accompanied by calcic garnet (Grs 38–94 Sps 1–5 Alm 0 ) and scheelite (Pow 1–6 ). The second stage represents a relatively oxidized mineralogy dominated by diopside (Hd 16–48 Joh 0–9 ), subcalcic garnet (Grs 24–92 Sps 0–11 Alm 0–31 ) and scheelite (Pow 7–32 ). The stage 3 and 4 mineral assemblages are characterized by few hydrous minerals in the retrograde stage and intense fracturing. Fluid inclusions from skarn rocks are indicative of multiple fluid events: (1) low-moderate salinity (5–16 wt.%NaCl equiv.) inclusions homogenized dominantly by a high-temperature (308 °C to > 600 °C) liquid phase in stage 1. Fluid inclusions in an early garnet homogenized over a similar temperature range (440 °C and 459 °C) into both liquid and vapor phases. Eutectic temperatures ranging from − 61.7 °C to − 35.0 °C that indicate the presence of H 2 O–NaCl–(± MgCl 2 ± CaCl 2 )–CO 2 solutions; (2) coexisting daughter mineral-bearing high salinity (29.5 ≥ 70 wt.%NaCl equiv.) and vapor-rich moderate salinity (11.5–16.7 wt.%NaCl equiv.) inclusions that homogenized in the liquid phase by the disappearance of the vapor phase at a similar temperature range (308 °C to > 600 °C) in stage 2. Eutectic temperatures range from − 67.9°C to − 51.8°C that shows the presence of H 2 O–NaCl–CO 2 –(± CH 4 /N 2 ) solutions; (3) low-moderate salinity (12.5–7.6 wt.%NaCl equiv.) and temperature (320 °C to 215 °C) inclusions homogenized by the liquid phase in stage 3. Eutectic temperatures range from − 59.5 °C to − 44.2 °C indicating the presence of H 2 O–NaCl–(± MgCl 2 ± CaCl 2 )–CO 2 solutions; (4) inclusions of low salinity (9.9–0.9 wt.%NaCl equiv.) and homogenization temperature (183 °C to 101 °C) in stage 4. These data show that the Kozbudaklar skarn deposit was formed in a magmatic–hydrothermal system. In this model, carbonaceous fluids may have been exsolved from the plutonic rock during its emplacement and crystallization. Fluid inclusion data indicate that fluid boiling and immiscibility occurred at temperatures between 440 °C and 459 °C and pressures ranging from 50 MPa to 60 MPa based on hydrostatic considerations. Early scheelite was precipitated with relatively reduced mineral compositions. As a result of depressurization, Mo-rich scheelite with oxidized minerals formed via high salinity and vapor-rich inclusions. The second scheelite mineralization occurred in a normal hydrothermal system by an infiltration mechanism at pressures between approximately 40 and 1.5 MPa. At shallow depths (< 1.5 MPa) with increasing permeability, sulfide and oxide minerals were deposited in the retrograde stage, greatly assisted by meteoric water. Finally, as a result of the diminishing of ore-forming fluids, post-depositional barren quartz and calcite veins were formed. [ABSTRACT FROM AUTHOR]

A series of fault-related folds developed in the Dabei Gas Field of the Kuqa Depression, western China form major traps for hydrocarbon accumulation. The Bashijiqike (K 1 bs) sandstone reservoirs in the different fault-related folds of the Dabei Gas Field display similar excess fluid pressure, formation water type and salinity, and as well as light oil and gas properties. The light oil and gas in the K 1 bs sandstone reservoir of the traps share the same source and were generated at a thermal maturity level of 1.4–1.6% R o and 1.7–2.3% R o , respectively. To investigate the fluid evolution in the fault-related fold traps, an integrated fluid inclusion analysis was performed including petrography, fluorescence spectroscopy, microthermometry, Laser Raman spectroscopy and thermodynamic modeling. The fluid evolution recorded by the fluid inclusions in the different fault-related folds indicates that the formation fluid was characterized by low salinity at normal hydrostatic pressure from approximately >9–5 Ma. From 5 to 3 Ma the formation water salinity and fluid pressure increased rapidly. The formation water attained the highest salinity at approximately 3 Ma to present while the pore fluid overpressure decreased with time in the reservoir. Two episodes of oil and one episode of gas charge were identified in the K 1 bs sandstone reservoir with the second episode of oil charge occurring around 5–4 Ma, while the gas charge occurred around 3–2 Ma. The injection of new fluids associated with oil and gas charge caused changes of the formation water salinity in the different fault-related fold traps within the gas field. The fluid evolution in the Dabei Gas Field can be used to indicate fault-related fluid flow as the thrust faults are suggested to be the primly pathways for fluid migration and the fluid flow was controlled by the reactivation of these thrust faults. The similarity of the oil and gas charge histories, formation water salinity and fluid pressure evolution in the K 1 bs sandstone reservoirs among the different fault-related traps in the Dabei Gas Field implies that the fault-related fluid flow process and activation of the thrust faults were concomitant since approximately 9 Ma. [ABSTRACT FROM AUTHOR]

The worldclass Dahongshan iron-oxide copper gold (IOCG) deposit is hosted within the late Paleoproterozoic Dahongshan Group in the Kangdian region, SW China. The orebodies are spatially associated with sub-volcanic intrusions and are structurally controlled. Extensive metamorphic overprinting during the Neoproterozoic makes it difficult to determine the initial compositions of the ore fluids. Tourmaline, however, is a useful phase for this purpose because of its refractory nature and chemical diversity. It occurs widely in the four stages of mineralization and alteration of the Dahongshan deposit, including pre-mineralization sodic alteration (stage I), iron-oxide mineralization (stage II), sulfide mineralization (stage III), and late quartz-calcite veining (stage IV). The temporal association between tourmaline and hydrothermal alteration provides an excellent opportunity to investigate the fluid evolution. Tourmaline from all four stages belongs to the alkali group and ranges from dravite to schorl in composition. In-situ B-isotope analyses of tourmaline conducted by LA-MC-ICPMS yielded a total range of δ 11 B values from − 14.7‰ to + 5.9‰ and the values show significant variations among the different stages. Tourmaline of stage I albitization has δ 11 B values from − 14.7‰ to − 5.7‰. Stage II tourmaline from Fe-oxide ores shows δ 11 B values of − 11.6‰ to − 6.1‰, similar to those of stage I, whereas stage III tourmaline from Cu-sulfide ores displays significantly heavier isotopes with δ 11 B values from − 4.4‰ to − 0.6‰. Tourmaline of stage IV, represented by barren quartz-calcite-tourmaline veins in intensely-altered wall rocks, has positive δ 11 B values from + 2.9‰ to + 5.9‰. The observed variations of B isotopes cannot be produced by fractionation of the ore fluids alone. Mixing of B from at least two distinct sources, a magmatic source and external sources with highly positive δ 11 B values, are hence proposed on the basis of geological constraints and modal calculations. The calculated oxygen isotope compositions of fluids in equilibrium with hydrothermal minerals that associated with tourmaline from stage II, stage III, and stage IV are 7.4‰ to 10.2‰, 8.4‰ to 8.6‰, and 3.8‰ to 8.0‰. The decreasing trend of δ 18 O of fluids from stage II to stage IV is consistent with the incursion of external basinal brines by fluid mixing. Our dataset thus demonstrates that ore fluids of Dahongshan IOCG system were initially of magmatic origin (stages I and II) and were later progressively modified by mixing with external brines (stages III and IV). [ABSTRACT FROM AUTHOR]

The Jinchang Cu-Au deposit in Northeast China contains more than 76 tons of Au and 4683 tons of Cu with average ore grades of 11.34 g/t Au and 1.44% Cu. The deposit is typical of porphyry types and consists of gold orebodies mainly hosted in a ∼113 Ma granitic porphyry and breccia pipes within the porphyry intrusion. Mineralization is closely associated with early potassic alteration and late phyllic alteration. Pyrite is the main Au-bearing mineral and contains 1.48–18.9 ppb Re and 11.4–38 ppt common Os. Extremely low common Os concentrations and high Re/Os ratios are indicative of derivation of ore-forming materials from the crust. Low Re in pyrite from the Jinchang deposit may indicate a mixing source of mantle and crust or a crustal source. Five Re-Os isotopic analyses yield a model 1 isochron age of 114 ± 22 Ma (2σ, MSWD = 0.15), similar to the age of the host porphyry. Pyrite contains detectable Co, Ni, Cu, Zn, As, Ag, Au, Sb, Pb and Bi. Pyrite has Co/Ni ratios similar to that of volcanogenic and hydrothermal sulfide deposits, indicating a magmatic-hydrothermal origin, and has Au and As contents similar to that of porphyry-epithermal systems. Pyrite grains from potassic and phyllic alteration stages have different trace element contents, reflecting the evolution of ore-forming fluids from magmatic dominated to magmatic mixed with meteoric water. In combination with regional geology, our new results are suggestive of origin of the Jinchang Cu-Au deposit from contemporary intrusions of granitic porphyries related to the Early Cretaceous subduction of the Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

The Silurian Niur carbonates at Dahaneh-Kalut and Ozbak-Kuh sections (Tabas block, eastern Central Iran) have been pervasively dolomitized. Four types of dolomite, consisting of replacive dolomite (Rd1–Rd3) and saddle dolomite cements (Cd), were discriminated by texture, cathodolouminscence petrography and geochemical analyses. Rd1 dolomite occurred as a very fine (10–25 μm), planar-e to planar-s dolomite that replaced marine limestones. Rd2 dolomite is a planar-s to planar-e, medium crystalline dolomite (100–400 μm). Rd3 dolomite is a very coarse (400 μm–2 mm), non-planar crystalline dolomite with sweeping extinction, and Cd dolomite occurred as voids- and fractures-filling saddle dolomite (5–10 mm) with strong sweeping extinction. Field and petrographic observations demonstrated that Rd3 and Cd occur only at the Dahaneh-Kalut section and are related to mafic volcanic rocks and fractures at the base of the Niur Formation. The δ 18 O (−8.45 to −6.06‰ VPDB) and δ 13 C (−0.01 to 0.99‰ VPDB) values suggest that Rd1 dolomite was precipitated at the early stage of dolomitization from Silurian seawater, whereas Rd2 dolomite formed from similar fluids at higher temperatures upon burial. The δ 18 O (−13.80 to −9.47‰) and δ 13 C (−1.66 to 0.76‰) values and fluid inclusion data (T h : 122 to 175 °C, salinity: 18.68 to 24 wt% NaCl eq.) revealed that Rd3 and Cd were precipitated from hot, saline fluids with a magmatic origin. The Mn, Fe, Na and Sr concentrations of Rd3 and Cd, suggest that the responsible dolomitizing fluids were more enriched with respect to these elements and had a different origin relative to the Rd1 and Rd2 dolomitizing fluids. These results revealed that the late Ordovician to early Silurian passive rifting phase generated a local thermal gradient that increased heat flow and thermal convection of diagenetic fluids that led to the precipitation of Rd3 and Cd as pervasive hydrothermal dolomite. The network of fractures and faults that formed during the rifting phase provided open conduits for hydrothermal fluids. These results emphasize the importance of both tectonic setting and thermal conditions in the generation and circulation of dolomitizing fluids as well as in massive dolomitization. [ABSTRACT FROM AUTHOR]

The Glojeh district contains silver- and base metal-rich epithermal veins and is one of the most highly mineralized locations in the Tarom-Hashtjin metallogenic province, northwestern Iran. It consists of four major epithermal veins, which are located in the South Glojeh and North Glojeh areas. Alteration in the Glojeh district consists of propylitic, sericitic, and argillic assemblages, as well as extensive silicification. The ore-bearing veins comprise three paragenetic stages: (1) early Cu-Au-As-Sb-Fe-bearing minerals, (2) middle stage Pb-Zn-Cu-Cd-Ag-bearing minerals, and (3) late hematite-Ag-Bi-Au-Pb mineralogy. The veins are best classified as the product of an early high-sulfidation hydrothermal system, which was overprinted by an intermediate sulfidation system that was rich in Ag and base metals. Hematite is locally altered to goethite in zones of as much as 40 m in width during supergene alteration and the goethite is an important exploration tool. Fluid inclusions from the early, middle, and late stages, respectively, have salinities and homogenizations temperatures ranging from 5 to 11 wt.% NaCl eq. and 220 °C to 340 °C, to 1 to 8 wt.% NaCl eq. and 200 °C to 290 °C and finally to. 0.1 to 2 wt.% NaCl eq. and 150 °C to 200 °C. The oxygen isotope values in quartz range from 8.8 to 13.3‰ and most calculated fluid δ 18 O values are between 4 and 8‰, suggesting a magmatic fluid with some meteoric water contamination. Sulfur isotope values for chalcopyrite, pyrite, sphalerite, and galena are mainly − 7.3 to + 1.3‰ and − 0.3 to + 8.4‰ for North Glojeh and South Glojeh, respectively. Sulfur isotope data suggest a magmatic origin. Boiling, isothermal mixing, and dilution are the main mechanisms for ore deposition in the Glojeh veins. Recent 40 Ar/ 39 Ar age measurements of 42.20 ± 0.34 Ma and 42.56 ± 1.47 Ma for the North Glojeh and South Glojeh veins, respectively, overlap with the 41.87 ± 1.58 Ma age of the Goljin intrusion in the northern part of the district, which we interpret as the main heat source controlling the hydrothermal systems. [ABSTRACT FROM AUTHOR]

Alto de la Blenda is a ∼6.6-Ma intermediate-sulphidation epithermal vein system in the Farallón Negro Volcanic Complex, which also hosts the 7.1-Ma porphyry-Cu-Au deposit of Bajo de la Alumbrera. The epithermal vein system is characterised by a large extent and continuity (2 km × 400 m open to depth × 6 m maximum width) and an average gold grade of ∼8 g/t. The vein is best developed within an intrusion of a fine-grained equigranular monzonite, interpreted as the central conduit of a stratovolcano whose extrusive activity ended prior to porphyry-Cu-Au emplacement at Bajo de la Alumbrera, which is in turn cut by minor epithermal veins. The Alto de la Blenda vein consists predominantly of variably Mn-rich carbonates and quartz, with a few percent of pyrite, sphalerite, galena and other sulphide and sulphosalt minerals. Four phases of vein opening, hydrothermal mineralisation and repeated brecciation can be correlated between different vein segments. Stages 2 and 3 contain the greatest fraction of sulphide and gold. They are separated by the emplacement of a polymictic breccia containing clasts of quartz feldspar porphyry as well as basement rocks. Fluid inclusions in quartz related to stages 2 to 4 are liquid rich with 2-4 wt% NaCl(eq). They homogenise between 160 and 300 °C, with very consistent values within each assemblage. Vapour inclusions are practically absent in the epithermal vein. Quartz fragments in the polymictic breccia contain inclusions of intermediate to vapour-like density and similar low salinity (∼3 wt% NaCl(eq)), besides rare brine inclusions containing halite. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of epithermal inclusions indicate high concentrations of K, Fe, As, Sb, Cs, and Pb that significantly vary within and through subsequent vein stages. Careful consideration of detection limits for individual inclusions shows high gold concentrations of ∼0.5 to 3 ppm dissolved in the ore fluid, which contains variably high sulphur concentrations in excess over Fe and other chalcophile metals. Compositional variations are interpreted to reflect cooling and contraction of lower-density magmatic fluids at depth, like those preserved in porphyry clasts that were mechanically transported up by the polymictic breccia. Ore mineral precipitation from the magmatic fluid occurred by further cooling and possibly minor mixing with surface-derived water, leading to sulphide saturation, de-sulphidation of the magmatic fluid and consequent gold precipitation. The absence of flash boiling and/or reduction by carbonaceous host rocks has led to relatively modest but constant gold grades in the carbonate-base metal-gold veins of Alto de la Blenda. [ABSTRACT FROM AUTHOR]

The six main Triassic gold deposits of the Yangshan gold belt are hosted by Devonian metasedimentary rocks and Triassic granitic dikes. It has been suggested by previous workers that they are best classified as either Carlin-like or orogenic gold deposit types. Sulfide minerals spatially associated with disseminated and quartz vein-hosted gold mineralization at Yangshan were deposited in five stages that include syn-metamorphic, early ore, main ore, late ore, and post-ore stages. Based on the relationships defined by ore-mineral assemblages and paragenesis, H, O, C, S, Pb, and Sr isotopic data were obtained from sulfides, quartz, and ore host rocks. The δ 18 O values of quartz from gold-bearing veins range from 15.9‰ to 21.5‰, and the calculated δ 18 O H2O values of ore-forming fluids vary from 6.4‰ to 11.8‰, which are consistent with those from typical orogenic gold deposits. The δD H2O values of fluid-inclusions extracted from the quartz vary from − 82‰ to − 56‰, which are in accord with the δD H2O values of most orogenic gold deposits. Interpretation of the δ 13 C CO2 values (− 4‰ to − 2.5‰) in fluid inclusion, shows that marine carbonate is the dominant source for the carbon in the ore-forming fluids, with a minor contribution from magmatic sources. The δ 34 S values of hydrothermal pyrite, arsenopyrite, and stibnite range from − 6.6‰ to 3‰, which suggests sulfur is derived from a deep source. The Pb isotope values for hydrothermal sulfides from both the granitic dike-hosted ores and phyllite-hosted ores overlap the fields for their respective wall rocks, which suggests the source of lead is either the local host rocks, or ore-related fluids that may have pervasively penetrated the host rocks. The age-corrected ( 87 Sr/ 86 Sr) i values of pyrite are 0.70627 to 0.71304, and values for arsenopyrite are 0.71258 to 0.71294, showing that the strontium in the ore fluid could have been derived from the granitic dikes and the regionally extensive Mesoproterozoic to Neoproterozoic Bikou Group. The concordance of δ 34 S, Pb and ( 87 Sr/ 86 Sr) i values between those for hydrothermal sulfides and country rocks suggests that these crustal rocks contributed the gold that was subsequently concentrated in the ore deposits. The syn-metamorphic stage and early ore stage fluids were likely derived from the country rocks during prograde metamorphism at depth. The oxygen isotope compositions indicate relatively widespread interaction of such fluids with δ 18 O-rich country rocks during the main ore stage. Compared with most orogenic gold deposits and Carlin-type gold deposits, the gold deposits in the Yangshan gold belt exhibit isotopic characteristics that are most like those of orogenic gold deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tourmalines has boron sources from I-type granitoid and metasedimentary rocks. • A fluid mixing between a magmatic-hydrothermal fluid and meteoric waters leaching metasedimentary rocks is responsible for mineralization. • The enrichment of Sn in tourmaline highlights the tin prospecting potential. A detailed textual and geochemical study of tourmaline is presented to trace fluid evolution and ore genesis of the Laodou gold deposit in West Qinling Orogen, Northwest China. Based on petrographic observations and relationships to gold mineralization, three generations and five types of tourmaline were identified. The pre-ore tourmaline generation (Tur A) occurs as phenocryst replacement within quartz diorite porphyry (Tur A1) and metasomatic filling in hydrothermal breccia (Tur A2). It shows intense oscillatory zoning and variable Mg/(Mg + Fe) ratios (0.30–0.67), implying rapid compositional changes controlled by host-rock composition and fluid-rock interaction. The syn -ore tourmaline generation (Tur B) forms as open-space filling (Tur B1) and peripheral overgrowth (Tur B2) of Tur B1. It occurs in quartz-tourmaline and quartz-stibnite-sphalerite-tourmaline veins. Narrow Mg/(Mg + Fe) range (0.48–0.76), poor chemical zoning and more homogeneous compositions of Tur B reflect a higher fluid flux. The post-ore tourmaline generation (Tur C) occurs as monopolar overgrowths developed at the − c pole of previous tourmaline within granitoids and hydrothermal veins. This has a composition between dravite and foitite with Mg/(Mg + Fe) from 0.65 to 0.95 and no zoning, which reflect formation under low-temperature conditions. Relatively high Sn, Nb and Ta concentrations, LREE enrichment accompanied by strong positive Eu anomalies of Tur A mostly support a magmatic-hydrothermal origin. Slight LREE enrichment and low abundances of ΣREE of Tur B are caused by progressive input of meteoric waters. Tur C shows relative enrichment in Ba, depletions in V and Ni, and a flat REE pattern with negative Eu anomalies, suggesting a metamorphic source. Boron isotope compositions suggest that boron of Tur A (δ11B average − 6.49 ‰) is sourced from an I-type melt involved with the Laodou quartz diorite porphyry, while the lighter δ11B values in paragenetically younger tourmaline (Tur C with δ11B average − 9.10 ‰) support cooling and a metamorphic input sourced from argillaceous slate of the Lower Permian Daguanshan Group. The variations in textural characteristics, chemical and boron isotope compositions from Tur A to Tur C support a fluid mixing between a magmatic-hydrothermal fluid and meteoric waters leaching metasedimentary rocks. Typical morphology, core-to-rim decrease in Mg/(Mg + Fe), Fe3+Al −1 , (□XAl)(Na R 2+) −1 and (AlO)(R 2+OH) −1 vectors, decreasing Na, Ca concentrations and Eu anomalies of tourmaline may record cooling, oxidation and dilution during fluid evolution. This process is possibly caused by fluid mixing and results in gold precipitation. Boron sources, as well as fluid provenance and evolution interpreted by tourmaline provide insight into the Laodou deposit as an intrusion-related gold deposit. [ABSTRACT FROM AUTHOR]

[Display omitted] • Gold precipitation occurs due to destabilization of Au-bisulfide complexes during wall rock sulfidation (deceasing of ƩS total) and fluid phase separation. • The Atash-Anbar deposit can be classified as an IS epithermal gold deposit. • The ore-forming fluids, sulfur, and metals were derived primarily by devolatilization of the volcanic and subvolcanic magmatic rocks. The newly discovered Atash-Anbar gold deposit, with ∼2 Mt of ore grading 2.13 g/t Au (locally up to 14 g/t), is located in the Buin-Zahra Range, central-northern Iran. Hosted by Middle Eocene (ca. 39.0 Ma) volcanic-subvolcanic rocks, the Au-polymetallic orebodies occur as NW− and NE − trending quartz-sulfide veins that are structurally controlled by NW-trending faults. The Middle Eocene host rocks are characterized by high-K calc-alkaline, peraluminous signatures, and moderately Eu negative anomalies (Eu/Eu* = 0.2–0.6). Four primary paragenetic stages of veining have been recognized: (I) smoky-grey quartz-chalcopyrite stage, (II) grey-white quartz-polysulfide stage, (III) white-pinkish barite-sulfide stage, and (IV) late quartz-carbonate stage. Fluid inclusion investigations coupled with laser Raman analyses indicate that the ore-forming fluids were formed in a NaCl − H 2 O ± CO 2 system with two types of FIs: two phase, liquid-rich inclusions (type I) and two phase, vapor-rich inclusions (type II). The primary coexisting types I and II inclusions are observed in gold-bearing ore-stage II, sharing similar homogenization temperatures in the range of 233–286 °C and 243–281 °C, but contrasting salinity values of 10.7–14.8 and 14.6–15.5 wt% NaCl equivalent, respectively. Fluid inclusion examinations show that fluid phase separation occurred concurrently with gold precipitation during the ore-stage II. The δ18O fluid values calculated from the δ18O SMOW and δD SMOW values of the inclusions in quartz veins are 4.9–11.1 ‰ and −84.6 ‰ to −68.3 ‰, respectively. δ13C PDB and δ18O SMOW values of Fe-dolomite are −6.5 ‰ to −5.0 ‰ and 3.1 ‰–4.9 ‰, respectively. H–O–C isotope data indicate magmatic origin of initial ore-forming fluids with minor addition of meteoric water through time. The δ34S values (−3.1 ‰ to −1.2 ‰, avg. = −2.0 ‰) of the ore-stage II sulfides suggest that sulfur comes from a homogeneous magmatic source. The Pb isotopic compositions of sulfides (207Pb/204Pb = 15.420–15.525, 206Pb/204Pb = 18.423–18.536, 208Pb/204Pb = 37.135–38.208) indicate that the Pb in the Atash-Anbar gold deposit is a mixture of crust and mantle components. We conclude that (1) the Atash-Anbar is an IS epithermal system that (2) resulted from Eocene subduction of the NeoTethys Ocean plate beneath the central Iran plate and thus (3) ore-forming fluid and its metal components (i.e., Ag, Pb, and Zn) were emanated through crystallization of the final phase of a granite porphyry intrusion. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Lijia tin deposit is formed at 428–430.5 Ma. • This deposit is genetically related to the Lijia granite. • Ore fluids are generated by mixing of 84% magmatic fluids and 16% meteoric water. • Muscovite records the processes of fluid evolution and fluid-rock interaction. • The interaction between the ore-forming fluids and the host granite plays a key role for the cassiterite precipitation. Early Paleozoic Sn mineralization is rarely reported in South China. Here we carried out the detailed studies of deposit geology, cassiterite U-Pb dating, muscovite geochemistry and H-O isotopes on the Early Paleozoic Lijia Sn deposit in South China to constrain its genesis. The Lijia Sn deposit is hosted in the Yuechengling granitic batholith and characterized by greisen-type and quartz vein-type mineralization. Four stages of alteration and veining are recognized according to mineral assemblages and crosscutting relationships: pre-ore tourmalinization and silicification alteration of the Lijia granite (stage I), cassiterite-tourmaline-quartz vein and associated cassiterite greisen (stage II), and post-ore calcite-quartz-fluorite vein and calcite veinlet (stage III and IV, respectively). Two generations of the cassiterite in the cassiterite greisen, identified by cathodoluminescence imaging, yield the U-Pb concordant ages of 430.5 ± 3.7 Ma and 428 ± 2.2 Ma, respectively. The zircon U-Pb ages and geochemical features of the Lijia granite as well as the characteristics of alteration and mineralization indicate that the Lijia granite is Sn-bearing one and brings about the Sn mineralization. H-O isotopic compositions of the quartz from the Lijia granite reveal that the magmatic fluids have the δ18O values of 10.6–10.7‰ and the δD values of −57‰ to −62‰. The ore-forming fluids (δ18O 6.5–7.4‰, δD −64‰ to −69‰) responsible for cassiterite precipitation are derived from the mixing of magmatic fluids with minor meteoric water whereas more meteoric water is involved in the post-ore calcite-quartz-fluorite vein stage. Based on mineral assemblages, internal textures and chemical compositions, muscovite is divided into four generations from early to late: the Mus 1 and Mus 2 in the cassiterite greisen, the Mus 3 in the cassiterite-tourmaline-quartz vein and the Mus 4 in the phyllic alteration in the stage III. From the Mus 1 to the Mus 3, muscovite Rb, Cs, Zn, Li, V, Sc and Ga contents gradually decrease whereas boron shows an increasing trend, which might have been caused by the successive precipitation of hydrothermal minerals such as muscovite. Significantly higher Sr and Ba contents of the Mus 2 than the Mus 1 are likely related to the decomposition of the K-feldspar and plagioclase in the host granite. The combination of the precipitation of the early mineral phases, the decomposition of K-feldspar and the involvement of a large amount of meteoric water gives rise to the decrease of W, Sn, B, Rb, Cs and Sr contents and the increase of Ba, Ti, Mg, Li, Sc, V, Cr, Ga, Nb and Ta contents of the Mus 4 in the stage III. A key mechanism responsible for the formation of the Lijia Sn deposit is the interaction between the ore-forming fluids and the host granite. This study confirms the Early Paleozoic tin mineralization event in South China. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two generations of garnet and two episodes of magmatic-hydrothermal fluids during the prograde skarn formation. • The first generation of garnet formed in the magmatic-hydrothermal transition stage. • The mixing of meteoric water was identified in the late prograde skarn. Origin of garnet in skarn (magmatic vs. hydrothermal) and the prograde skarn fluid evolution are still controversial. Two generations of garnet (Grt1, Grt2) were identified at the Tongshankou deposit: Grt1 is anisotropic with oscillatory zoning and resorbed boundary, whilst Grt2 grew around Grt1 and formed oscillatory rims. In-situ LA-ICP-MS U-Pb dating of Grt1 and Grt2 yielded a lower intercept 206Pb/238U age of 142.4 ± 2.8 Ma (n = 57; MSWD = 1.16) and 142.3 ± 9.6 Ma (n = 60; MSWD = 1.06), respectively, coeval with the ore formation and ore-related granodiorite emplacement. Positive Eu anomaly, non-CHARAC Y/Ho value and low TiO 2 content, together with the mineral assemblages indicate that both Grt1 and Grt2 have a hydrothermal origin. The existence of melt and melt-fluid inclusions in Grt1, together with similar LREE-enriched patterns to the granodiorite, further indicate that Grt1 may have formed in the magmatic-hydrothermal transition. Higher U contents and LREE-enriched patterns of Grt1 indicate that fluid I is mildly acidic pH and low f O 2. The inner gray Grt2 rims (Grt2A) is HREE-enriched with low U contents, indicating that fluid II has nearly neutral pH and high f O 2. The wider Y/Ho range and LREE-enriched patterns of the outer light-gray Grt2 rims (Grt2B) show that the evolved magmatic fluid II had mixed with an external fluid, characterized by being mildly acidic pH and with high f O 2. Our results suggest that the prograde skarn-forming fluids can be multistage at Tongshankou, and the mixing of meteoric water may have been prominent in the prograde skarn stage. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Mufushan Complex (MFSC) is a major producer of Nb-Ta-Li-Be rare metals in China. • Two stages (early magmatic and later hydrothermal) of pegmatite crystallization. • Coltan U-Pb constrains on long-lived Nb-Ta mineralization as 138 Ma and 125 Ma in MFSC. • Zircon Hf isotopes trace melt and metal sources of Nb-Ta to metasedimentary units. The Mufushan Complex (MFSC), located in northeastern Hunan, is a significant producer of Nb-Ta-Li-Be rare metals in South China. The present study examines the genetic relationship, material provenance, fluid evolution, and metallogeny of the co-developed ore-free pegmatite (OFP) and ore-bearing pegmatite (OBP) in granite-related pegmatite-type Nb-Ta rare-metal deposits in MFSC. Three minerals (columbite-tantalite (coltan), zircon, and monazite) were chosen for analysis. The coltan grains display both primary crystallization structures (crystal homogeneity, oscillatory zonings, and primary growth rims) resulting from equilibrium and disequilibrium reactions due to localized changes in the physicochemical conditions and environment, as well as later replacement structures (alteration rims, patches, irregular zonations, and complex zonations) from metasomatic replacement processes related to hydrothermal fluid activity. The coltan yielded two weighted mean 206Pb/238U ages of 138.1 ± 2.1 Ma and 125.3 ± 2.0 Ma corresponding to magmatic and hydrothermal Nb-Ta mineralization ages. For the OFP, zircons also yielded two weighted mean 206Pb/238U ages of 138.4 ± 0.8 Ma and 131.5 ± 0.7 Ma, whereas monazite gave a weighted mean U-Pb age 142.9 ± 1.2 Ma. The ages of 142–138 Ma and 131 Ma represent the early and late stages of OFP crystallization and barren pegmatites in the MFSC, respectively. Zircon Lu-Hf isotopic compositions link rare-metal metallogenesis to the Lengjiaxi Group, which was the source material to the Mufushan composite batholith. Calculated ε Hf (t) values and T DM2 ages from the OFP (−7.6 to −3.6 and 1676–1418 Ma, respectively) and the OBP (−14.1 to +4.9 and 2976–1548 Ma, respectively) are akin to those of schists and metasandstones of the metasedimentary Lengjiaxi Group. We propose a long-lived (ca. 13-Myr) event involving two metallogenic episodes of Nb-Ta mineralization in the Mufushan region. This study demonstrates the potential of zircon, coltan, and monazite for fingerprinting minerals and classifying the mineralization potential of pegmatite veins. [ABSTRACT FROM AUTHOR]

The Mianning–Dechang (MD) REE belt of Sichuan, China is one of the most important REE belt in China, which includes Maoniuping, the third largest REE deposit in the world and a series of large to small REE deposits. Mineralization styles varied across the belt, as well as within different parts of the same deposit. Styles include vein-stockworks, pegmatites, breccias and disseminated REE mineralization. Based on geological, geochemical and inclusion studies, this paper proposes a new model for carbonatite hosted REE mineralization. The results show that ore-forming fluid is derived from carbonatite magma, which has high temperature, pressure and density, and is characterized by high K, Na, Ca, Sr, Ba, REE and SO 4 contents. The supercritical ore fluid underwent a distinctive evolution path including phase separation, exolution of sulfate melt and unmixing between aqueous fluid and liquid CO 2 . Rapid geochemical evolution of a dense carbonatite fluid causes REE mineralization and associated alteration to occur within or proximal to the source carbonatite. Veins, pegmatites and carbonatite comprise a continuum of mineralization styles. Veins occur in the outer zone of the upper levels of the deposit. Pegmatites occur in the inner zone of upper levels, whereas disseminated REE ore occurs at the base of the carbonatite. High water solubility in the carbonatite magma and low water, high REE in the exsolved ore-forming fluids, imply that a giant carbonatite body and deep magma chamber are not necessary for the formation of giant REE deposits. [ABSTRACT FROM AUTHOR]