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Geology and geochronology of the Banchang distal Cu-Mo skarn deposit, Central China
Mineralium Deposita ( IF 4.8 ) Pub Date : 2024-03-22 , DOI: 10.1007/s00126-024-01256-5
Zhaoyi Li , Guiqing Xie , Shengli Li , Yuan Wei

Banchang is the largest Cu-Mo deposit (348 Mt @ 0.32% Cu and 428 Mt @ 0.07% Mo) in the Qinling orogenic belt, Central China. Orebodies are hosted in the contact between several granitoid dikes and graphite-bearing marble of the Neoproterozoic Yanlinggou Formation. Wallrock alteration comprises garnet skarn, pyroxene skarn, chlorite skarn, and stockwork chlorite-altered marble. Three hydrothermal stages are indicated: (I) prograde skarn stage, (II) retrograde skarn stage, and (III) main sulfides stage. New zircon U-Pb data show two magmatic events, including early Paleozoic granite porphyry (442 − 427 Ma), and late Mesozoic biotite monzogranite porphyry and late Mesozoic granite porphyry (147 − 146 Ma). The zircon trace element compositions show that the late Mesozoic granitoids with ∆FMQ = -0.7 to 2.3 (avg. 0.5; EuN/EuN* > 0.6) resemble the Cu ore-related granitoid in the Qinling orogenic belt and indicate high oxygen fugacity and water contents in the magma. The early Paleozoic granitoids have ∆FMQ= -2.4 to 0.6 (avg. -0.7; EuN/EuN* < 0.2). Electron Probe Microanalysis (EPMA) on the prograde garnet and pyroxene reveal predominantly andradite (And40 − 94Gro0−51) and diopside (Di53 − 98Hd10−55) compositions, respectively. The garnet Fe3+ contents decreases whereas the pyroxene Fe2+ contents increases from the late Mesozoic granitoid dikes to the marble. This suggests a gradual evolution of the skarn from an oxidized to a reduced state. Stage III sulfide minerals have δ34S = -2.1 to 4.8‰, indicating a magmatic origin. The temporal-spatial relationships, magmatic oxygen fugacity and water contents, zoning of prograde skarn minerals, and the source of sulfur indicate a genetic link between the skarn mineralization and late Mesozoic granitoid dikes. This study proposes a distal Cu-Mo skarn ore deposit model associated with granitoid dikes and some implications for mineral exploration in the Qinling orogenic belt and elsewhere.

更新日期:2024-03-22
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