U-Pb and Re-Os geochronology and geodynamic setting of the Dabaoshan polymetallic deposit, northern Guangdong Province, South China

摘要

The Dabaoshan polymetallic deposit in northern Guangdong Province contains iron, copper, lead, zinc, molybdenum, tungsten and sulfur mineral resources. Porphyry-type Mo(W) and skarn-type Mo-W mineralization occurs along the internal and external contact zones of the granodioritic porphyry, respectively. LA-ICP-MS U-Pb dating of zircons from two granodioritic porphyry samples yielded a weighted mean ~(205)Pb/~(238)U age of 175.8 ±1.5 Ma (MSWD = 0.037) and 175.0 ±1.7 Ma (MSWD = 0.41). They can be pooled together to yield a combined weighted age of 175.4 ± 1.6 Ma (MSWD = 0.26), which is interpreted as the emplacement age of the granodioritic porphyry. Re-Os dating of three molybdenite samples from porphyry and skarn ores yielded consistent model ages of 163.2 ± 2.3 Ma to 165.2 ± 2.4 Ma, with a weighted mean of 163.9±1.3Ma (MSWD = 0.81), which is the age of Mo-W mineralization. These ages are consistent with the molybdenite Re-Os model age (164.7 ±3 Ma) measured by Mao et al. (2004a) for the stratiform Cu-Pb-Zn orebody, and they can yield a weighted mean of 164.0 ±2.5 Ma (MSWD = 0.16). This implies that Mo-W and Cu-Pb-Zn mineralization in the Dabaoshan polymetallic deposit are the products of one mineralization event. The mineralization in the deposit coincides closely with that of Mo-polymetallic mineralization (164-149 Ma) elsewhere in the Nanling region, comprising an important polymetallic metallogenic belt of south China, and corresponds to the second episode of Mesozoic metallogenesis in South China. Combined with previous studies, we suggest that the Dabaoshan polymetallic deposit is related to post-collisional lithosphere extension in the Nanling region of South China. Geological data and Pb isotopic evolution diagrams, together with stable isotopic data of fluid inclusions (δ~(18)O = - 3.75-7.0‰, δD = - 50.7 to - 56.1%o) and ore sulfides (δ~(34)S = - 2-3‰), suggest a genetic relationship between the Dabaoshan polymetallic deposit, the granodioritic porphyry and the dacitic porphyry. These data, combined with the Re content (64.7 to 102.4 ppm) of molybdenite, indicate that the ore-forming components were derived from mixed crustal and mantle sources.