Structural Analyse And Its Ore Control Patterns Of Jiama Area,Tibet

The Jiama area is located in the east segment of the Miocene Gangdese metallogenic belt and tectonically belongs to a Cretaceous back-arc basin of the southern Gandese magmatic arc.The Jiama polymetallic copper mine in the study area is a typical super large porphyry-skarn deposit.Although a great deal of research has been carried out and remarkable achievements has been made,research focused on regional tectonic deformation and its sequences is still relatively weak.Therefore,it is very important to launch a detailed structural deformation research and discuss its ore controlling model.Guided by the theory of plate tectonics and continental dynamics,a rich ore pit has been mapped in detail,related data was collected to analyze the structural style in order to build a structural sequences of the area combining with regional literature.the tectonic evolution model and ore-controlling regularity are also discussed.4 stages of tectonic deformation process are recognized in the research region,ranging from deep ductile deformation to shallow brittle deformation.The first stage is near EW ductile shear.The second one is NWW brittle-ductile imbricate fold and thrust.The third one is NW sinistral strike-slip normal fault mainly developed in the contact zone between the Duodigou formation and the Linbuzong formation on the basis of the second stage thrust.The last stage deformation is the brittle near NS normal fault and associated NNW-NNE conjugate fault.Based on large scale mapping as well as drill core logging,the dextural strike-slipe normal fault is the ore control structure,the fault shows a “Z”type on flat plane and a minus flower structure on profile.Based on the study of apatite fission track thermal chronology,the tectonic uplift history of 37 to13 Ma in the Jiama area was obtained,among which the rapid uplift event during 37-30 Ma was related to the fold-thrust of the second stage.The 18~13Ma tectonic thermal event was consistent with the large-scale N-Sextensional structure since middle-late Miocene.Though both Duodigou formation and the Linbuzong formation encounted the first two stage deformation,the latter is at the relatively shallower depth,at which brittleductile deformation is more pervasive.Through a combination of the deformation sequences in the study area with a regional background,the structural control model of the skarn type ore body is established: the migration of ore forming fluid along the third stage strike-slip normal fault led to the skarn ore body in the silicon-calcium interface as well as the hydrothermal filling saddle ore body in the collapse area of the fold hinge inside Linbuzong formation.