The Study Of Jiama Polymetallic Copper Deposit-Controlling Structure In Mozhugongka County, Tibet

Based on large-scale mapping in mining district,observation of regional geological section,combining with relevant analysis and a systemic study on controlling structure of JiaMa Polymetallic copper deposit–in Maizhokunggar County of Tibet, I get the following understanding :The Jiama polymetallic copper deposit was located at the south margin of LinZhou Mesozoic Basin which was in the central south of Gangdese-Nianqing Tanggula (terrane)plate. At the same time, this deposit extended in the front of JiaMa-kajun shoving-slipping tectonics system whose strike is roughly NWW. Basically, it is a typical epigenetic deposit.The Shoving-slipping tectonics system of JiaMa-kaJunGuo was composed of Acidic volcanic rocks mingled with carbonatite which belong to the littoral phase in the type of Passive continental marginal rift, sandstone and shale structure in the Late Triassic Epoch-early Cretaceous. That is to say, the Shoving-slipping tectonics system of JiaMa-kaJunGuo was formed under these processes:First,the rift valley type of sediments is effected by prometaphase Paleogene's closed collision and orogeny in Brahmaputra(45Ma±)Which resulted in the boundary of former rift basin and the inner part of contemporaneous growth faulting character inversion and detachment at the bottom of the settled basin layer system occurring along the edge that called"ineinander schieben effect"(Liu ZhaoChang ,1996)and forming southward fold by the effect of pushed-over ;after the collision in early Neogene(15Ma±),because of the effect of strike-slipping and stretching, the Reverse fault and the bottom detached fracture system had been transformed into the nappe fracture system, and thus caused the inner part of this nappe fracture systemloosing and spreading. Subsequently, the magmatic hydrothermal solution in Himalayan period intruded, accompany with mineralization and deposition formed. The Jia Ma–KaJunGuo shoving-slipping tectonics system, generally started in the north of MoZhuQu area, and formed by the southern push-over along the Jiang Ri A–JingBuGong spading fracture zone. The distance from south to north is around 20km,and 4 belts in this direction, namely forward belt ,front belt, central belt, and the back belt. The gliding nappe of copper mountain was located at the tail skirt of the forward belt, and cuased by opposite sliding (south to north) of the block(J3d+ K1l) in high position. The front of sliding nappe was identified as the thrust, and the tail skirt of sliding nappe was identified as the ordinary fault. The inner part of sliding nappe had a complicated construction, such as various fold. In addition, there are slipping-kink fold and inverted fold growth and klippe structure .The JiaMa–KaJunGuo shoving-slipping tectonics system and the associated sliding nappe structure system controlled the JiaMa deposit . XiaGongPu composite syncline and NiuMaTang composite anticline can be conceived as the secondary fold in the north of Hong-Ta anticline, which controlled the numberⅠore body in the JiaMa deposit. In the north of Hong-Ta anticline, especially the frontal zone of the sliding nappe in Copper Mountain controlled the numberⅡore body in JiaMa deposit.Miocene granodiorite-granodiorite magmatic hydrothermal solution, migrated to deposit area along the pushed-over fracture system, storing in the crush location of pushed-over anticlinal fold core(J3d)and LinBuZong Fm, in addition , the shielded effect from the carbonaceous clasolite series brought the hydrothermal solution and resulted in skarnization and carbonatite in DuoDiGou Fm, the hornfelsing of clasolite around LinBuZong Fm . Finally, the deposition of porphyre type was caused by the later ore-bearing fluid overlapping and infusing, the doposition of skarn type, hornstone type were formed at the same time.