Hydrocarbon- and ore-bearing basinal fluids: a possible link between gold mineralization and hydrocarbon accumulation in the Youjiang basin, South China

The timing of gold mineralization in the Youjiang basin is still in dispute and a wide range of ages has been reported for individual deposits. Among the limited isotopic data, the Rb-Sr date of 206 A +/- 12 Ma for Au-bearing hydrothermal sericite at Jinya as well as the Re-Os date of 193 A +/- 13 Ma on auriferous arsenian pyrite and 40Ar/39Ar date of 194.6 A +/- 2 Ma on vein-filling sericite at Lannigou may provide the most reliable age constraints on gold mineralization. This age range is comparable with the estimated petroleum charging age range of 238-185 Ma and the Sm-Nd date of 182 A +/- 21 Ma for the pore- and fissure-filling calcite associated with bitumen at the Shitouzhai paleo-oil reservoir, corresponding to the late Indosinian to early Yanshanian orogenies in South China. The close association of Carlin-type gold deposits and paleo-oil reservoirs, the paragenetic coexistence of bitumens with ore-stage minerals, the presence of abundant hydrocarbons in the ore fluids, and the temporal coincidence of gold mineralization and hydrocarbon accumulation all support a coeval model in which the gold originated, migrated, and precipitated along with the hydrocarbons in an immiscible, gold- and hydrocarbon-bearing, basinal fluid system. The timing of gold mineralization in the Youjiang basin is still in dispute and a wide range of ages has been reported for individual deposits. Among the limited isotopic data, the Rb-Sr date of 206 A +/- 12 Ma for Au-bearing hydrothermal sericite at Jinya as well as the Re-Os date of 193 A +/- 13 Ma on auriferous arsenian pyrite and 40Ar/39Ar date of 194.6 A +/- 2 Ma on vein-filling sericite at Lannigou may provide the most reliable age constraints on gold mineralization. This age range is comparable with the estimated petroleum charging age range of 238-185 Ma and the Sm-Nd date of 182 A +/- 21 Ma for the pore- and fissure-filling calcite associated with bitumen at the Shitouzhai paleo-oil reservoir, corresponding to the late Indosinian to early Yanshanian orogenies in South China. The close association of Carlin-type gold deposits and paleo-oil reservoirs, the paragenetic coexistence of bitumens with ore-stage minerals, the presence of abundant hydrocarbons in the ore fluids, and the temporal coincidence of gold mineralization and hydrocarbon accumulation all support a coeval model in which the gold originated, migrated, and precipitated along with the hydrocarbons in an immiscible, gold- and hydrocarbon-bearing, basinal fluid system.