Genesis of strata-bound ore deposits in central Guangxi, South China: Fluid inclusion and isotope constraints.

摘要

Numerous strata-bound ore deposits in central Guangxi, South China are hosted by Devonian sediments. They include sandstone-hosted copper sulfide deposits, carbonate-hosted base metal sulfide and barite vein deposits, and chert-hosted bedded barite deposits.; The geological setting of the bedded barite deposits, the geochemical signatures of cherts and barites, and {dollar}deltasp{lcub}34{rcub}{dollar}S and {dollar}deltasp{lcub}18{rcub}{dollar}O values of barites, indicate that the deposits were formed by mixing of a hydrothermal fluid rich in SiO{dollar}sb2{dollar} and Ba with seawater whose dissolved sulfates were enriched in heavy S and O isotopes.; For the barite vein deposits, studies were conducted on the geological setting, paragenesis, fluid inclusions, {dollar}deltasp{lcub}34{rcub}{dollar}S and {dollar}deltasp{lcub}18{rcub}{dollar}O values of barites, and {dollar}deltasp{lcub}13{rcub}{dollar}C and {dollar}deltasp{lcub}18{rcub}{dollar}O values of carbonates. The results suggest the existence of shallow Late Devonian seawater and deep meteoric water circulations around and in the fractures hosting barite veins. Sulfates in the seawater were enriched in heavy isotopes of S and O. The meteoric water was rich in Ba. Mixing of the two fluids caused precipitation of barites in veins.; For the central Guangxi mineral district as a whole, constraints on mineralization were obtained from the geological setting, temperature and salinity of mineralizing fluids, {dollar}deltasp{lcub}34{rcub}{dollar}S and {dollar}deltasp{lcub}18{rcub}{dollar}O values of barites, {dollar}deltasp{lcub}34{rcub}{dollar}S values of sulfides, and Pb isotope ratios of sulfides. The constraints suggest the presence of shallow Late Devonian seawater and deep meteoric water circulations around a fracture zone in central Guangxi. Various ore deposits in the district were formed at different locations in the fracture zone by mixing the Cu, Pb, Zn, Ba, and SiO{dollar}sb2{dollar}-bearing meteoric water with the sulfate or sulfide-bearing seawater.; The central Guangxi mineral district is only one of the seven Devonian carbonate-hosted base metal sulfide mineral districts in South China. Genetic evidence was drawn from the geological setting, salinity, Pb isotopic compositions of the basement rocks and of sulfides in the Devonian and Pre-Devonian sediment-hosted ore deposits, and {dollar}deltasp{lcub}34{rcub}{dollar}S values of sulfides in the Devonian sediment-hosted ore deposits. The evidence implies the existence of multiple central Guangxi-type convection cells during the Late Devonian in South China.