Massive sulfide deposits in continental volcanic basins at the lower Yangtze Valley, Southeast China

Two Mesozoic continental basins in the Lower Yangtze Valley of Southeast China host a number of iron oxide and sulfide ore deposits that have been previously interpreted as magmatic-hydrothermal mineralization associated with prophyry intrusions. Our work indicates, however, that a significant part of the metallogenic history in this area prodated the sub-volcanic emplacement of the porphyry intrusive rocks. The ore-forming process is thought to have included an early event of massive sulfide formation in continental fault-bounded basins, which products were subsequently reworked and metal-enriched by the porphyry-related hydrothermal system. Detailed reconstruction of the geological relationships between the ores and their host-rocks, coupled with interpretation of the textural, mineralogical and paragenetic characteristics of the various types of ores in several different deposits in the area, collectively suggest asyngenetic, volcanic-exhalative origin for the lens-shaped, massive pyrite-anhydrite ores related to Mesozoic volcanic activity. Evidence for this includes synsedimentary structures and soft-sediment deformation features, widespread, siliceous, and anhydriterich chemical sediments (exhalites) associated with the massive sulfides, and iron sulfide-oxide replacement relationships.