Fluid evolution and ore genesis of Huaduoshan Cu-Mo prospect, Duobaoshan ore field, Northeastern China: Evidence from fluid inclusions, H-O-S-Pb isotopes, geochronology and geochemistry

Abstract

The Huaduoshan Cu-Mo prospect is located in the Duobaoshan orefield, Northeast China. The Cu-Mo mineralization occurs in the granodiorites as veinlet-disseminated. The ore-forming process can be divided into four mineralization stages: (I) quartz-pyrite-magnetite; (II) quartz-pyrite-chalcopyrite±molybdenite; (III) quartz-pyrite-molybdenite-chalcopyrite-sphalerite and (IV) quartz-calcite-minor pyrite. Liquid-rich two-phase aqueous (L-type), vapor-rich aqueous (V-type) and daughter-minerals three-phase (S-type) fluid inclusions (FIs) were identified at Huaduoshan. The last two types of FIs are absent in stage III-IV. The homogenization temperatures of FIs from stages I-IV are 375-438, 335-378, 283-335, and 223-267 摄氏, with corresponding salinities of 2.4-50.4, 2.1-44.9, 2.7-10.1, and 1.7-7.3 wt. % NaCl eqv., respectively. The H-O isotope data of quartz in stages I (δ18OH2O = 6.1‰ to 8.0‰, δDH2O = -102.4‰ to -94.6‰) show a magmatic origin of ore-forming fluid, the decreasing δ18OH2O (-6.8 to 3.2‰) and δDH2O (-117.1 to -98.5‰) values of quartz in stage II-IV show the fluid mixing with meteoric water. The S-Pb isotopic values (δ34S = -2.7 to 0.8‰; 206Pb/204Pb = 18.236-18.599, 207Pb/204Pb = 15.504-15.557, 208Pb/204Pb = 37.816-38.629) of pyrites indicate that the ore-forming materials are magmatic origin. Fluid boiling and mixing may be the major mechanisms of ore precipitation. Zircon U-Pb age (172.1 ± 0.5 Ma) and geochemical data indicate that the ore-related granodiorites are I-type rocks formed in subduction setting of the Paleo-Pacific Ocean Plate in Early-Middle Jurassic. In conclusion, we propose that Huaduoshan Cu-Mo prospect is a porphyry deposit and has potential for further exploration of porphyry Cu-Mo prospecting.