The genetic relationship between Pb-Zn deposits and paleo-oil reservoirs in Mayuan, northern Sichuan Basin

Mayuan is one of the important lead-zinc deposits in northern Sichuan Basin, and its mineral formation is Cambrian Dengying Formation. Field and microscope studies revealed early bitumen and sphalerite, with associated galena. The biomarker of bitumen is very similar to that of the source rocks of Gjiaba Formation. The main sources of Pb-Zn deposits and paleo-oil reservoirs are the lower Cambrian Guojiaba Formation. The Rb-Sr isotopic isochron age of lead-zinc mineralization is(486.7±3.1) Ma, probably related to the formation and destruction of the first paleo-oil reservoirs. Sphalerite and barite inclusions contain CH₄ and a small amount of H₂S, bitumen, whereas lead-zinc mineralization fluids are rich in pyrolysis products of paleo-oil reservoirs. Hydrocarbon generation, hydrocarbon expulsion, the initial transport extraction of "double source layer" in the lead and zinc elements, the first paleo-oil reservoirs and the short-term TSR produced by the reduction of sulfur and lead-zinc complex precipitation all provided the material basis, and the first paleo-oil reservoirs eventually destroyed the residual early bitumen.