The Shaquanzi Zn–Pb deposit, located in the Central Tianshan Terrane, is mainly hosted by siliceous slates and carbonaceous marbles of the Mesoproterozoic Kawabulake Group, and its mineralization / alteration can be divided into skarn period (I: early skarn stage, II: late skarn stage), quartz-sulfide period (III: early sulfide stage, IV: late sulfide stage and V: quartz-calcite stage) and supergene period (VI: supergene alteration stage). The W-type fluid inclusions (FIs) were identified in the garnet, chlorite, quartz, and calcite in skarn and quartz-sulfide periods. Detailed fluid inclusion study shows temperature of fluids decreased from Stage I (510 – 520 °C) through, Stage III (481 – 507 °C), Stage IV (248 – 417 °C, peak at 280 – 400 °C) to Stage V (148 – 260 °C, peak at 200 – 220 °C), with salinities of 20.8 – 22.2 wt.% NaCl eqv., 19.8 – 29.1 wt.% NaCl eqv., 10.6 – 27.8 wt.% NaCl eqv. (peaks at 20 – 23 wt%), and 21.6 – 29.9 wt.% NaCl eqv. (peak at 23 – 27 wt%), respectively, indicating that the ore-forming fluids consisted of a high-medium salinity and Na-Mg-Fe-Ca-rich fluid system, and may have evolved from high-medium temperature to medium temperature. The H–O isotopic compositions varied from Stage III (δ18OH2O = 7.7‰ – 9.0‰ and δDH2O = −105‰ to −91‰) through Stage IV (δ18OH2O = 2.6‰ to 4.3‰ and δDH2O = −114‰ to −111‰) to Stage V (δ18OH2O = −4.2‰ to −3.7‰ and δDH2O = −119‰ to −96‰), suggesting that the ore-forming fluid sources may have evolved from magmatic fluids to meteoric water. The average δ34SH2O values of the early sulfide, late sulfide, and quartz-calcite stages are 5.7‰, 8.5‰ and 14.0‰, respectively, indicating that the sulfur in the early stage was mainly derived from magmatic hydrothermal sulfur, while the increase of the δ34SH2O values in the late stages is likely to be sourced from the Kawabulake Group through water-rock reaction. Above all, we propose that the Shaquanzi may have been a skarn-type Zn–Pb deposit.
The Taoguanping molybdenum deposit is located in the west of the Mangling pluton in the Northern Qinling Belt, but its fluid characteristics and ore-forming process are unclear, hindering the understanding of its ore genesis and genetic model. The paragenetic sequence of the Taoguanping molybdenum deposit can be divided into: quartz–K-feldspar–sulfide stage (Stage I), quartz–polymetallic sulfide stage (Stage II), and quartz–calcite stage (Stage III). Stage I is characterized by disseminated molybdenite mineralization associated with siliceous and K-feldspar alteration in the medium- to fine-grained monzogranite, representing the early mineralization. Stage II is the main mineralization featured by coarse-grained quartz–sulfide veins, e.g., quartz–molybdenite and quartz–biotite–molybdenite ± pyrite ± chalcopyrite veins, crosscutting monzogranite and host rocks. Stage III is late hydrothermal veins to crosscut former minerals. Detailed fluid inclusion study shows that temperature and salinity of fluids decreased from Stage I (peaks at ca. 320–380 ℃ and 3.7–13.6 wt% NaCl eqv.), through Stage II (peaks at ca. 260–300 ℃ and 1.2–11.8 wt% NaCl eqv.) to Stage III (peaks at ca. 180–220 ℃ and 0.4–8.9 wt% NaCl eqv.), accompanied by fluid mixing and boiling. The H–O isotopes of quartz (δDfluid = –72‰ to –53‰ and δ18Ofluid = 9.1–10.9‰) suggest Stage II fluids are magmatic–hydrothermal origin mixed with minor meteoric water. The in-situ sulfur isotope of pyrite (–33.4‰ to –13.4‰ and 0‰ to 7.8‰) indicates Stage II fluids being mainly magmatic–hydrothermal origin, with participation of strata materials inferred by presence of Stage II euhedral to anhedral pyrite with inclusion-rich domains and CH4 in Stage II fluid inclusions during fluid–rock interaction. In combination of this study and regional tectonic setting, we propose that the Taoguanping molybdenum deposit underwent porphyry and hydrothermal vein-type mineralization, contributed by medium- and fine-grained monzogranite and possible granite porphyry, respectively, which should be ascribed to a porphyry mineralization system and formed in a post-collisional setting during the Late Mesozoic.
The Jinchuan Ni-Cu-PGE deposit is the single largest magmatic Ni-sulfide deposit in the world, with three different hypotheses on its ore-forming processes (e.g., in-situ sulfide segregation of sulfide-bearing magma, deep segregation with multiple injections of magma, and hydrothermal superimposition) mainly based on study of whole-rock geochemistry and isotopes (e.g., S-Sr-Nd-Hf). In this study, we mainly concentrated on magnetite textural and geochemical characteristics from different sulfide ores to clarify the genetic types and geochemical difference of the Jinchuan magnetite, and to explore a new credible ore-forming process by magnetite formation process when combined with detailed deposit geology. Three types of magnetite from massive and disseminated sulfide ores were observed by different textural analysis, and they were shown to have different genetic types (mainly in geochemistry) and trace elemental features. Type I magnetite is subhedral to anhedral from massive Ni- (or Fe-) and Cu-rich sulfide ores, with apparent magmatic origin, whereas Type II (dendritic or laminar crystals) and III magnetite (granular crystals as disseminated structures) from disseminated Cu-rich sulfide ores may have precipitated from late stage of melts evolved from a primitive Fe-rich and sulfide-bearing system with magmatic origin, but their geochemistry being typical of hydrothermal magnetite, videlicet, depletions of Ti (< 20 ppm), Al (< 51 ppm), Zr (0.01–0.57 ppm), Hf (0.03–0.06 ppm), Nb (0.01–0.14 ppm), and Ta (0.01–0.21 ppm). Such different types of magnetite can be clearly distinguished from concentrations and ratios of their trace elements, such as Ti, V, Co, Ni, Zn, Zr, Sn, Ga, and Ni/Cr. Those different types of Jinchuan magnetite crystallized from (evolved) sulfide-bearing systems and their geochemistries in trace elements are controlled mainly by evolution of ore-related systems and geochemical parameters (e.g., T and fO2), with the former playing a predominant role. Combining the previous literature with this study, we propose that the Jinchuan deposit formed by multiple pluses of sulfide-bearing magma during fractional crystallization, with the emplacing of more fractionated and sulfide-bearing magma during sulfide segregation playing a predominant role. During this multiple emplacement and evolving of sulfide-bearing systems, Type I magmatic magnetite crystallized from primitive and evolved Fe-rich MSS (monosulfide solid solution), while Type II and III magnetite crystallized from evolved Fe-rich MSS to Cu-rich ISS (intermediate solid solution) during sulfide fractionation, with those Type II and III magnetite having much higher Cu contents compared with that of Type I magnetite.
<p>Supplemental Text: Analytical Methods. Figure S1: Cathodoluminescence images of representative zircons for U-Pb dating and Lu-Hf isotope analyses for the Mangling intrusive complex. Figure S2: Chondrite-normalized REE patterns of analyzed zircons for the Mangling intrusive complex. Figure S3: Field photographs showing relationships of the granitic rocks of the Mangling intrusive complex. Figure S4: Harker diagrams of selected major and trace elements against SiO2 for the Mangling intrusive complex. Table S1: Zircon U-Pb dating results for the dioritic and granitic rocks of the Mangling intrusive complex. Table S2: Whole-rock major- (wt%), trace- (ppm), and rare earth (ppm) element compositions for the dioritic and granitic rocks of the Mangling intrusive complex. Table S3: Zircon trace element compositions (ppm) for the dioritic and granitic rocks of the Mangling intrusive complex. Table S4: Zircon Lu-Hf isotopic data for the dioritic and granitic rocks of the Mangling intrusive complex. Table S5: Summary of geochronological data for the Mangling intrusive complex. Table S6: Zircon trace element compositions (ppm) for the mineralized granitic rocks of porphyry molybdenum deposits in Central and NE China.</p>
To constrain the ore-fluid source(s) of the Laoshankou Fe-Cu-Au deposit (Junggar orogen, NW China), we analyzed the fluid inclusion (FI) noble gas (Ar, Kr and Xe) and halogen (Cl, Br and I) compositions in the hydrothermal epidote and quartz. Four hypogene alteration/mineralization stages, including (I) pre-ore Ca-silicate, (II) early-ore amphibole-epidote-magnetite, (III) late-ore pyrite-chalcopyrite, and (IV) post-ore hydrothermal veining, have been identified at Laoshankou. Stage II FIs have salinity of 15.7 wt.% (NaCl eq.), I/Cl molar ratios of 75 × 10−6–135 × 10−6, and Br/Cl molar ratios of 1.4 × 10−3–2.1 × 10−3. The moderately-high seawater-corrected Br*/I ratios (0.5–1.5) and low 40ArE/Cl slope (~10−5) indicate the presence of sedimentary marine pore fluid, which was modified by seawater reacting with the Beitashan Fm. volcanic rocks. Stage III fluid is more saline than their stage II and IV counterparts, reaching up to 23.3 wt.% (NaCl+CaCl2 eq.) close to halite saturation (~26 wt.%). The fluid has I/Cl ratios of 75 × 10−6–90 × 10−6 and Br/Cl ratios of 1.5 × 10−3–1.8 × 10−3. Considering the increasing 40ArE/Cl trend toward bittern brine and the higher 36Ar content than air-saturated water (ASW), a bittern fluid source is inferred from seawater evaporation, which was modified by interaction with organic-rich marine sedimentary rocks. Stage IV FIs have lower temperature (110–228 °C) and Br/Cl (0.90 × 10−3–1.2 × 10−3), but higher 36Ar content than ASW, indicative of dissolved evaporite or halite input. Considering also the low δDfluid (−114‰ to −144‰) and δ18Ofluid (2.1‰–3.5‰) values, meteoric water (with minor dissolved evaporites) likely dominated the stage IV fluid. The evaporites may have formed through continuous evaporation of the stage III surface-derived bittern. Involvement of non-magmatic fluids and different ore-fluid origins in stages II and III suggest that the ore-forming process was different from a typical magmatic-hydrothermal fluid-dominated skarn mineralization, which was previously proposed for Laoshankou. Our noble gas and halogen study at Laoshankou provide new insights on the fluid sources for the Paleozoic Fe−Cu (−Au) deposits in the Central Asian Orogenic Belt (CAOB), and our non-magmatic fluid source interpretation is consistent with the basin inversion setting for the mineralization.
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