Characterization of the Dongjiahe Zn-Pb deposit, South China: Implication for exploration of Mississippi Valley-type ore in Marinoan cap dolostone

Abstract

The Marinoan cap dolostone overlying the Marinoan glacial deposits (∼650–635 Ma) occurs on almost every continent and shows similar sedimentary structures in all cases. Insights from this study of the cap dolostone-hosted Dongjiahe Mississippi Valley-type (MVT) Zn-Pb deposit, South China, might improve exploration strategies for MVT ore in this unit. The Dongjiahe cap dolostone includes three lithological units in an anticline. The basal and upper units, respectively 1–2 m thick, host Zn-Pb ore. The basal unit develops sheet cracks and breccias, associated with pre-ore dolomite and chalcedony cementation. The dolomite cement is inconsistent in C-O isotopes relative to the neighboring dolostone, indicating the post-depositional cementation. The dolomite and chalcedony alteration created open spaces that were filled by sphalerite and galena. The upper unit of dolostone is laminated and fine crystalline. Folding-related bedding-parallel and −oblique fractures in the unit were filled by pre-ore chalcedony and then by Zn and Pb sulfides. The distribution of ore within the Dongjiahe anticline indicates that the axial zones of anticlines and associated second-order anticlines are favorable locations for fracture generation and mineralization. Therefore, exploration of MVT ore in Marinoan cap dolostones needs to understand the development and distribution of open spaces created by pre-ore mineral alteration and regional folding deformation. In addition, the presence of bitumen indicates that the cap dolostone unit at the Dongjiahe deposit was a hydrocarbon trap that might have played a role in the generation of reduced sulfur that contributed to the Zn-Pb mineralization.