The Formation And Evolution Of Hydrothermal Fluids In The MVT Lead-zinc Deposits In Northern Margin Of Sichuan Basin

The survey of MVTPb-Zndeposits which on the northern margin of the Sichuan Basin Dengying Formation shows the Pb-Zndeposits and bitumen left by paleo-oil reservoir in space is a symbiotic relationship. Both of them are concentrated in the top of the fourth section of Dengying Formation. The ore-bearing layer is relatively thin. Not only in the vertical, but also in the plane, the distribution of bitumen are much larger. It can be seen in hand specimen and microscopic that the Pb-Zn mine and bitumen are symbiotic. With the microscopic, it can be observedthat there is bitumen in some samples of sphalerite, which shows a certain degree of genetic relationship between the two.The analysis of the cross-cut relations between various types of authigenic minerals, such as zinc, galena, quartz, dolomite, barite, fluorite and so on, it reveals there are seven phases paleo-fluid. The first phase of brine water fluid formed microtekdolomite. The second phase of the paleo-oil reservoir fluid formed the first generation of bitumen. The third phase of ore-bearing hydrothermal fluid formed quartz, dolomite, the first generation of barite and the first generation of Pb-Zn mine. The fourth phase of the paleo-oil reservoir fluid formed the seconed generation of bitumen. The fifth phase of brine water fluid formed grain dolomite and quartz. The sixth phase of ore-bearing hydrothermal fluid formed the the seconed generation ofPb-Zn mine. The seventh phase of brine water fluid formed quartz, fluorite and the seconed generation of barite.Based on the research of the fluid inclusions traped by all kinds of authigenic mineral in Dengying Formation, the type of the fluid inclusions are ravealed. The barite formed by the third hases of ore-bearing hydrothermal fluid andthe seventh phase of brine water fluid traped liquid H2O-inclusions, gas and liquid H2O-inclusions, and also strontianite(SrCO3), witherite(BaCO3) and S. The quartz and fluorite formed by the fifth and seventh phases of brine water fluid traped gas and liquid H2O-inclusions and methane inclusions.The temperature measuring experiment showed that the time of two paleo-oil reservoirs are late Cambrian and Permian-Middle Triassic. After the seconed paleo-oil reservoir turned into gas reservoir, its preservation conditions was good once, the pressure coefficient reached 1.29-1.83. But during the Himalayan movement, the gas reservoir was damaged by lage-scale uplift of Dengying Formation, and the gas-water interface moved up. Sothe automorphic quartz wraps bitumen. The time of two lead-zinc mineralization and ancient reserviord obviously match.The gas-liquid H2 O inclusions and methane inclusions trapped bythe authigenic minerals formed during the two phases of paleo-oil reservoirs are all contain CH4, CO2 and H2 S. Especially the daughter mineral of S in the two generations of barite, it indicates that there was TSR reaction in the two paleo-oil reservoirs. The TSR reaction provided a source of S for the lead and zinc mineralization.