Gold Mineralization in Hainan Province of South China: Geological Characteristics, Geodynamic Settings, and Ore‐deposit Types

metallogenic epoch predominantly at the Mesozoic are sited in Hainan Province, South China (Fig. 1), and occupy proven metal gold reserves of more than 143 t. They are hosted mostly by the lowto middle-grade volcano-clastic sedimentary rocks of the Mesoproterozoic, Silurian and Permian ages, with minor presence within the Cretaceous continental clastics or volcanics. The ore modes mainly include auriferous quartz veins, altered mylonites, and altered cataclasites that were developed along a group of NE-, NNWand NWW-trending shear fracture zones, and NWto NNW-trending intraor interformational detachment fault belts which were associated with folding, shearing and/or transpressional to transtensional deformation. In combination with the tectonic development and magmatic activities, the ore geologies, fluid inclusion geochemistries, C-H-O-S-(Pb) isotopes and the geochronologies consistently indicate that at least there are two ore deposit-types for gold deposition in Hainan Island, i.e. the orogenic-type and the intrusionrelated (Groves et al., 1998, 2003). The predominant, orogenic gold mineralization which produced more than 95% of Au metal reserves in Hainan Island occurred at the Early Mesozoic of ca. 225 Ma age dated by Ar-Ar, K-Ar and Re-Os methods. This ore deposit-type represented by the large-scale Baolun, the Gezhen-type (inclduign Bumo, Erjia, Datian, Baoban, Hongquan, and Tuwaishan), and the Wangxia deposits generally is hosted by the metamorphosed rocks of various ages and related intimately to brittle-ductile shearing. These deposits with native gold as main gold minerals also contain a midddle-temperature, CO2-rich (mainly 4.8-16.8 mol %), low-salinity (generally 3-10.5 wt.% NaCleq.) and near neutral (pH=~7) ore fluid component of H2O + CO2 + CH4. The sulfide volume is low (<5%) whereas the Au/Ag ratios (generally >8%) and gold fineness are high. Linked to the petrographical and geochemical features of the Late Paleozoic to Early Mesozoic (ca. 300-200 Ma) granitoids, the orogenic gold mineralization will be considered to have occurred in a transitional post-orogenic to postorogenic extensional setting in response to South China Indosinian orogeny leading to closure of the Paleotethys Ocean. The ore modes, ore fluid compositions, and mineralizing temperature and pressure conditions, however, suggest that the orogenic gold likely contains two subtypes, i.e. the mesozonal represented by the lode gold ores and the epizonal by disseminated, altered myloniteand cataclasite ores. They represent endmembers of a crustal continuum of orogenic gold emplacement. Moreover, an involvement of magmatic waters into the ore fluids as implied by abundant Bi-AsTe-Mo-S phases overgrown synchronously with the gold minerals especially in the high-grade Baolun deposit cannot be ruled out. The Fuwen Au-dominated Au-Ag ore deposit which is hosted by the Early Cretaceous continental clastics is interpreted as a high-sulfide, intrusion-related deposit and likely occurred at the late Cretaceous. This deposit has some characteristic features as lode gold-dominated ore, high gold grade (average 28-95 g/t Au), extremely high sulfide volume (>50%), Au-dominated Au-Ag-Cu-Pb-Zn metal association, and small amounts of altered minerals XU Deru, ZHOU Yueqiang, SHAN Qiang, NIE Fengjun, HOU Maozhou, WU Chuanjun, FU Yangrong, WANG Zhilin and ZHANG Xiaowen, 2014. Gold Mineralization in Hainan Province of South China: Geological Characteristics, Geodynamic Settings, and Oredeposit Types. Acta Geologica Sinica (English Edition), 88(supp. 2): 815-816.