The Constraints of Carbonaceous Mudstone Re-Os and Detrital Zircons U-Pb Isotopic Dating on the Diagenetic and Metallogenic Ages from the Dabaoshan Copper Deposit in Guangdong Province

Abstract

BACKGROUND: With the development of high-precision negative thermal ionization mass spectrometry (N-TIMS) technology, Re-Os isotopic dating of carbonaceous mudstone is more and more widely used in the determination of sedimentary age. The controversy over the diagenetic and metallogenic ages of the Dabaoshan copper deposit in Guangdong Province has always been a key restricting the study of the genetic mechanism.OBJECTIVES: To constrain the diagenetic and metallogenic ages of the Dabaoshan copper deposit.METHODS: Re-Os isotope ratios were determined by high precision N-TIMS after dissolving carbonaceous mudstone powder by reverse aqua regia in the Carius tube. Zircon U-Pb age was determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS).RESULTS: (1) The contents of Re and Os ranged from 0.976×10-9 to 2.997×10-9 and 0.067×10-9 to 0.115×10-9, respectively. The 187Re/188Os ratio varied from 78.236 to 154.799, and the 187Os/188Os ratio varied from 1.642 to 1.885. The Re-Os isotopic isochron age of black carbonaceous mudstone was 195±28Ma (n=6, MSWD=17). (2) The 206Pb/238U age ranged from 2631 to 236Ma, including two Mesozoic zircons, accounting for 2.50% of the total zircons, 19 Paleozoic zircons, accounting for 23.8% of the total zircons, 58 proterozoic zircons, accounting for 73% of the total zircons, 1 Archean zircon, accounting for 1% of the total zircons. The results of detrital zircon U-Pb age were broad and developed multiple peak periods, among which the youngest source magmatic zircon was formed in the Indosinian period.CONCLUSIONS: The diagenetic and metallogenic age of the Dabaoshan copper deposit in Guangdong Province was constrained to the early Yanshanian. The distribution characteristics of detrital zircon U-Pb age further indicate that the Lower Jurassic Jinji Formation was formed at the stable continental margin, and its detrital material comes mainly from the ancient continental basement