Fluid inclusion and Re-Os isotopic constraints on the timing and origin of the Shimengou Mo deposit, Xixia County, Henan Province.
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摘要: 河南西峡县石门沟钼矿床位于东秦岭北坡的二郎坪地体内,包含斑岩型和石英脉型两类独立的钼矿化,前者呈透镜状产于岩体内,后者呈脉状沿花岗岩裂隙充填。斑岩型钼矿化由花岗岩全岩矿化所致,矿物组合以钾长石-石英-辉钼矿-黄铁矿-磁铁矿-钛铁矿-金红石为标志;石英脉型钼矿化可分为3个阶段,分别以石英-黄铁矿、石英-辉钼矿-黄铁矿-黄铜矿-闪锌矿-方铅矿-辉铋矿和石英-碳酸盐为标志。斑岩型钼矿化石英中发育CO2-H2O型、NaCl-H2O型包裹体以及含子晶包裹体,石英脉型钼矿化早阶段以CO2-H2O型和NaCl-H2O型包裹体为主,中晚阶段仅见NaCl-H2O型包裹体,无矿石英脉包含CO2-H2O型和NaCl-H2O型包裹体。斑岩型钼矿化捕获了H2O-CO2-NaCl体系的初始流体,其温度集中于270~400℃,盐度为4%~13% NaCleqv,流体压力为32~155MPa,对应深度为1.1~5.4km。石英脉型钼矿化早阶段流体为H2O-CO2-NaCl体系,温度集中于240~330℃,盐度集中于2%~10% NaCleqv,压力为14~46MPa和101~153MPa,对应成矿深度3.5~4.6km;中阶段温度降为170~290℃,盐度降为2%~8% NaCleqv;晚阶段均一温度继续降至150~200℃,盐度为1%~6% NaCleqv。石英脉型钼矿化从早阶段到晚阶段,成矿流体盐度随均一温度降低而逐渐降低,指示高温、高盐度、富CO2的岩浆热液与晚阶段低温、低盐度的大气降水的混合作用,导致了钼金属的沉淀。矿区花岗岩成岩年龄为109.8±4.1Ma, 本次研究获得的6件斑岩型钼矿化辉钼矿Re-Os加权平均年龄为109.0±1.7Ma,石英脉型钼矿化辉钼矿Re-Os同位素加权平均年龄为107.1±0.6Ma,略晚于斑岩型钼矿化,与区内燕山晚期的岩浆作用近同时形成,指示成矿作用与燕山晚期的岩浆作用有关,为与侵入岩有关的钼矿床。Abstract: The Shimengou deposit, contains porphyry and quartz vein-type molybdenum mineralization, is mainly hosted in granitoids occurs in the Erlangping Terrane, northern East Qinling Orogen. The quartz vein-type mineralization can be divided into early, middle and late stages, characterized by assemblages of quartz-pyrite, quartz-molybdenite-polymetallic sulfide and quartz-carbonate, respectively. The samples from porphyry mineralization contain three different types of fluid inclusions, including CO2-H2O, NaCl-H2O and daughter mineral-bearing inclusions. The primary fluid inclusions in quartz formed in early stage of quartz vein-type mineralization are major of three-phase CO2-H2O and two-phase NaCl-H2O, while those in middle and late stages minerals only of NaCl-H2O inclusions. The quartz of porphyry mineralization trapped the initial high salinity H2O-CO2-NaCl ore fluids at temperature of 270~400℃ with the pressure up to 155MPa, corresponding to depth of <5.4km. From early to late stages of quartz vein-type mineralization, homogeneous temperatures of fluid inclusions decrease from 240~330℃ (E), through 170~290℃ (M), to 150~200℃ (L); salinities change from 2%~10% NaCleqv (E), through 2%~8%NaCleqv (M), to 1%~6%NaCleqv (L). The range of temperatures and salinities could indicate mixing between hotter, more saline fluids (e.g. deep-seated magmatic) and cooler, more dilute solutions (e.g. meteoric) as the cause of molybdenite deposition. Six molybdenite samples from porphyry mineralization yield a weighted average age of 109.0±1.7Ma, and six samples from quartz vein-type mineralization yield a weighted average age of 107.1±0.6Ma, which shows spatial and temporal association with Late Yanshanian granitoids. The geological and geochemical data are compatible with derivation of fluids and metals from individual plutons suggest that the Shimengou quartz vein-type molybdenum deposit belongs to intrusion-related deposit.
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Key words:
- Fluid inclusion /
- Intrusion-related Mo deposit /
- East Qinling Mo Province /
- Shimengou
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