Formation of strata-bound ore deposits in China: studies on fluid inclusions

Abstract

Fluid inclusion studies were made on the basis of the geological data on the strata-bound ore deposits of China including those of Pb, Zn, Au, Ag, Sb, U, Hg, W, quartz-crystal and sparry calcite. An attempt was made to approach the model of formation for each type of ore deposits by considering the material sources, the migration of fluids and the conditions of mineralization. It is found that ore-forming fluids (especially H2O) originate as heated underground water reacts with the wallrocks and dissolves Na+, Ca2+, K+, Cl+, HCl− and Mg2+. The ore-forming elements and other components including sulfur are derived mainly from the wallrocks. The ore fluids are mainly of NaCl−Ca−HCO3−H2O system with salinities ranging from 4 to 14 wt.% NaCl equivalent and densities ranging from 0.9 to 1.0 g/cm3. It may be concluded that the deposits were formed at temperatures ranging from 150 to 250°C under pressures from 300 to 1000 bars. Ore deposition may have been controlled by temperature and pressure or by the mixing among different fluids.