Abstract:

Abstract: The intimate coexistence of MVT PbZn deposits with oilgas reservoir suggests a genetic linkage between mineralization and hydrocarbon accumulation. The PbZn deposit from Heba in southeastern Sichuan Basin occurred in the paleogas reservoir in Dengying Formation, and its distribution area of PbZn deposit is much smaller than that of paleogas reservoir although both of them coexisted intimately. The mineralization fluid of PbZn deposit is characterized by high salinity(21.33%23.83% NaCl) and enrichment of organic matter, and its homogeneous temperature concentrated in 122134 ℃. The ages of RbSr and SmNd of fluorite coexisting with sphalerite suggest that the mineralization took place in 128130 Ma. Multiphase accumulation and destruction of hydrocarbon can be recognized in this paleooil/gas reservoir. The first hydrocarbon accumulation and destruction took place in the OrdovicianMiddle Silurian and the end of the Silurian, respectively. The second accumulation of hydrocarbon took place during the Permian and the middle Triassic, the oil began thermal cracking and formed gas reservoir as the burial depth of oil reservoir increased during the late Triassic and Jurassic; the paleogas reservoir was destroyed during the Yanshanian. The thermal cracking of oil and destruction of paleogas reservoir are responsible for mineralization of PbZn deposit. The thermal cracking of oil produced some H2S and the super pressure resulting from thermal cracking had the H2S dissolved in the water to supply sulphur for mineralization of PbZn deposit;tectonic uplift resulted in the destruction of the paleogas reservoir, and the brine with H2S lying under the paleogas reservoir migrated up and mixed with mineralization fluid leading to the formation of PbZn deposit.

Key words: MVT Pb-Zn deposit, oilgas reservoir, coupling of mineralization and accumulation, DengyingFormation