Geology, geochronology, fluid inclusion and H-O isotope geochemistry of the Luoboling Porphyry Cu-Mo deposit, Zijinshan Orefield, Fujian Province, China

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• 作者：Jun Zhong ; Yan-Jing Chen ; Franco Pirajno ; Jing Chen ; Jing Li ; Jin-Ping Qi ; Nuo Li
• 关键词：Molybdenite Re&ndash ; Os age ; Stable isotope ; Fluid inclusion ; Luoboling porphyry Cu&ndash ; Mo deposit ; Zijinshan orefield ; Fujian Province China
• 刊名：Ore Geology Reviews
• 出版年：March, 2014
• 年：2014
• 卷：57
• 期：Complete
• 页码：61-77
• 全文大小：4552 K

文摘

The Luoboling Cu-Mo deposit in the Zijinshan Orefield, Fujian province, southeastern China, is a large porphyry deposit hosted by the Sifang granodiorite and the Luoboling granodiorite porphyry. The largest Cu-Mo orebody is saddle-shaped with various types of hydrothermal veinlets. Intensive hydrothermal alteration in the deposit is characterized by outward zoning from potassic, overprinted by phyllic alteration, to phyllic and alunite-dickite alteration. Based on the mineral assemblages and crosscutting relationships of veins, the ore-forming process can be divided into three stages, namely: an early-stage K-feldspar + quartz 卤 magnetite 卤 molybdenite veins associated with potassic alteration; a middle-stage quartz + molybdenite + chalcopyrite + pyrite veins in phyllic zone; and a late-stage quartz 卤 gypsum veins in the phyllic and alunite-dickite alteration zones. Six molybdenite separates yield a Re鈭扥s isochron age 104.6 卤 1.0 Ma, which is identical to the age of emplacement of the Sifang and Luoboling granodiorite porphyries. Three types of fluid inclusions (FIs) were observed at the Luoboling deposit: 1) NaCl-H₂O (aqueous), 2) daughter mineral-bearing and 3) CO₂-H₂O fluid inclusions. FIs of the early and middle stages are predominantly vapor-rich aqueous and daughter mineral-bearing inclusions, together with minor CO₂-rich and liquid-rich aqueous inclusions; whereas the late-stage minerals only contain liquid-rich aqueous inclusions. Homogenization temperatures and salinities of FIs trapped in the early-stage minerals range from 420 to 540 掳C and 0.4 to 62.9 wt.% NaCl equiv., respectively. FIs of the middle-stage yield homogenization temperatures of 340 to 480 掳C and salinities of 0.5 to 56.0 wt.% NaCl equiv. CO₂ content and the oxygen fugacity (indicated by daughter minerals) of FIs trapped in middle-stage minerals are lower than those in the early stage. The liquid-rich aqueous inclusions of the late-stage homogenize at temperatures of 140 to 280 掳C, yielding salinities of 0.4 to 8.4 wt.% NaCl equiv. The minimum estimated pressures of the three stages are 30-70 MPa, 10-40 MPa and 1-10 MPa, respectively, corresponding to minimum ore-forming depths of 1-2.8 km. Fluids trapped in early, middle and late stages yield 未D values of 鈭?#xA0;67鈥?to 鈭?#xA0;54鈥? 鈭?#xA0;54鈥?to 鈭?#xA0;70鈥? and 鈭?#xA0;62鈥? and 未¹⁸O values of 5.4鈥?to 6.7鈥? 2.8鈥?to 4.2鈥? and 鈭?#xA0;2.1鈥? respectively. Fluid boiling, which resulted in the formation of stockworks and the precipitation of sulfides, occurred in the early and middle stages. The fluids subsequently evolved into a low temperature, low salinity system in the late stage, along with an input of meteoric water. The Luoboling porphyry Cu-Mo system was developed in a transition from continental arc to back-arc extension region, which was related to the westward subduction of the paleo-Pacific plate beneath the Huanan Orogen.