THE CHARACTERISTICS OF THE EVOLUTION OF THE PRECAMBRIAN CRUST IN NORTHERN JIANGXi AND THEIR RELATIONSHIP WITH MINERALIZATION

With the Jiangnan thin-shelled collision belt as the boundary,the Precambrian crust in northern Jiangxi may be divided into the northern and southern areas. In the northern area,the lower part of the cover belongs to the flysch and spilite-quartz keratophyre formations of marginal-sea turbidite facies.There is a copper source bed.The Tongmen Group belongs to the continental and littoral molasse formation,in which there occur more than two metal sulfide source beds.The Zhanggongshan Group in the southern area belongs the volcanic flysch and spilite-keratophyre formations of oceanic turbidite facies,in which are contained four Cu-W-Au source beds. In the early.Proterozoic,northern Jiangxi was in the stage of development of an oceanic eugeosynclines.The Dabie movement caused the basement of the northern area to begin consolidation,and in the middle Proterozoic the area evolved into a marginal sea.On the other hand,the southern area still belonged to the oceanic eugeosyncline.In the late proterozoic,the Jinning movement caused the northern area to be further consolidated and to be elevated to become land;while the basement of the southern area was metamorphosed and folded,and the outer sea had migrated to southern Jiangxi. In the Mesozoic,large-scale basement slip-shear collision took place from southeast to northwest in northern Jiangxi,and there were formed three gigantic NEE-trending thin-shelled collision ductile nappe shear zones.In these zone there occurred a series of granite masses of continental crust remoulding type, which reacted with the source beds to form some W,Sn and Au deposits.Possibly owing to the difference in the slip rate of various segments of the shear zones, a set of transverse fault zone resulted,and the magma of syntectic mixed type was emplaced along the NW-trending faults,thus forming a series of porphyry deposits.In the intersection,many diapir dome structures of granites with a high content of volatile constituentes,which constitute the perspective areas of tin and fluorite ores.