Genetic link between Mississippi Valley-Type (MVT) Zn-Pb mineralization and hydrocarbon accumulation in the Nanmushu, northern margin of Sichuan Basin, SW China

Abstract

The coexistence of Zn-Pb deposits and oil/gas reservoirs demonstrates that a close genetic link between them. The Nanmushu is a large Mississippi Valley-Type (MVT) Zn-Pb deposit discovered on the northern margin of the Yangtze block in recent years. The deposit is hosted in the Ediacaran Dengying Formation dolostone, accompanied by large amount of bitumen in the orebodies. The MVT Zn-Pb deposit overlaps with the paleo-oil/gas reservoir horizontally, and sandwiched in the paleo-oil/gas reservoirs at depth. The Cambrian Guojiaba Formation may have provided not only the oil for paleo-oil/gas reservoirs, but also ore metals for the Zn-Pb mineralization. With increasing burial depth, the Guojiaba Formation may have become more mature to form metal-rich fluids, and the metals migrated and accumulated with hydrocarbons to form a paleo-oil reservoir. Large-scale Zn-Pb mineralization may have occurred in the destruction process of paleo-gas reservoir. With the deep burial of paleo-oil reservoir, the paleo-oil reservoir may have transformed into a paleo-gas reservoir. Decoupling of metals and hydrocarbons during the paleo-gas reservoir formation may have provided the ore metals. Thermal sulfate reduction (TSR) during the paleo-oil/gas reservoirs formation may have provided the hydrogen sulfide for mineralization. Decompression and cooling during the paleo-gas reservoir destruction may have formed extensive metal sulfide precipitation and mineralization.