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

The Huaduoshan Cu-Mo prospect is 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), vapour-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 stages III and IV. The homogenization temperatures of FIs from stages I to IV are 375-438, 335-378, 283-335, and 223-267 degrees C, 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 (delta 18OH2O = 6.1-8.0%0, delta DH2O = -102.4--94.6%0) show a magmatic origin of ore-forming fluid; the decreasing delta 18OH2O (-6.8-3.2%0) and delta DH2O (-117.1--98.5%0) values of quartz in stage II-IV show the fluid mixing with meteoric water. The S-Pb isotopic values (delta 34S = -2.7-0.8; 206Pb/204Pb = 18.236-18.599; 207Pb/204 Pb = 15.504-15.557; 208Pb/204Pb = 37.816-38.629) of pyrites indicate that the ore-forming materials are of 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 the subduction setting of the Paleo-Pacific Ocean Plate in the Early-Middle Jurassic. In conclusion, we propose that the Huaduoshan Cu-Mo prospect is a porphyry deposit and has potential for further exploration of porphyry Cu-Mo prospecting.