Hydrothermal Alteration and Mineralization of the Middle to Late Jurassic Dabaoshan Porphyry Cu Deposit in South China

Abstract The Dabaoshan porphyry Cu deposit (420 kilotons (kt) of Cu @ 0.36%) is located in South China. The newly discovered Cu orebodies are hosted in the dacite porphyry adjacent to a granodiorite porphyry. The alteration and mineralization timing and stages of the porphyry Cu deposit were not well‐constrained. In this study, we combine field mapping, petrography, whole‐rock geochemistry, hydrothermal rutile U‐Pb dating and Cu isotopes to synthesize an ore model at Dabaoshan. In situ hydrothermal rutile U‐Pb dating yields an age of 159 ± 13 Ma, which brackets the timing of porphyry Cu mineralization. From top to bottom, the alteration zones in Dabaoshan are divided into quartz‐sericite, biotite, chlorite‐epidote, and chlorite‐sericite subzones. Veins are classified into four stages (Stage 1 to 4) with Stage 4 quartz‐sericite‐chalcopyrite veins being the main Cu ore‐bearing veins. The mineralized dacite porphyry has high SiO 2 , but low MgO, CaO, and Na 2 O contents. The chalcopyrite hosted in veins exhibits δ 65 Cu = values ranging from –1.29‰ to 0.51‰. Such copper isotope fractionation is attributed to vapor‐brine phase separation, and mixing of fluids from different geochemical reservoirs. The timing of Cu mineralization and hydrothermal alteration support that the Jurassic granodiorite porphyry is an ore‐forming intrusion at Dabaoshan.