Genesis of the fluorite in the Ordovician and its significance to the petroleum geology of Tarim basin
塔里木盆地奥陶系萤石成因及其油气地质意义

A special type of oil pool,with fluorite bed as reservoir,has been found from the upper Odovician of TZ45 well in central Tarim Basin.To determine the genesis of the fluorite and the formation age of the hydrothermal-dissolved carbonate reservoir in the Ordovieian of central Tarim Basin and other places,the relationship among hydrothermal mineralization,hydrothermal dissolution and hydrocarbon accumulation has been probed synthetically through different analyses,ineluding electron spin resouance(ESR)dating, REE,trace element,fluid inclusion laser raman,fluid inclusion hydrogen and oxygen isotope,and sulfur isotope analysis.At present, most scholars consider that the fluorite was formed in late Permian by the magmatic fluids associated with the volcanic activities in Tarim Basin,and concurrently there was an episode of hydrothermal dissolution.This study proved that the fluorite,developed in the Odovieian carbonate in Tz45 well and Baehu-Kerpin area,was probably formed by the low-temperature meteoric circular hydrothermal fluids.Filled in the dissolution-enlarged space along the fault belt,the fluorite in Tz45 well deposited in the late Yanshanian- Himalayan and has no necessary tie with the Hereynian magmatic fluids.However,filled in the caves ahmg the weathering crust of the Ordovieian carbonate outcrops,the fluorite in Bachu-Kerpin area was formed in Hercynian,and there is a good correlation in age between the mineralization and the volcanic thermal activity.So the dissolution of the Odovician carbonate by the fluorite hydrothermal fluids in Tz45 well occurred in late Yanshanian-Himalayan