The structure of ore-controlling strain and stress field in Shangzhuang gold deposit in Wangershan fault zone in Shandong Province, China
|Location||International Geological Congress,oslo 2008|
|Holding Date||11 October 2008|
The Shangzhuang altered-rock type gold ore deposit is located in the middle segment of the Wangershan fault zone in the northwestern part in the Jiaodong gold province, China. The deformation evolution and the structure of strain and stress fields and its ore-controlling effect in the Shangzhuang deposit are discussed in this paper. It is revealed that the deformation evolution has mainly undergone four phases: the early ductile deformation, the second NE-striking horizontal simple shear, the third NE-striking compression-shear shear and the final NW-striking compression; and the mineralization happened during the third stage in which the maximum principal stress gradually transited from NE to NW. The 3D numerical simulations of the stress field show that, on the condition that the maximum principal stress is NE-striking, the fracture development in the fault zone is favored, while when the direction of the maximum principal stress is NW-striking, the fault zone shows relatively extensional and it is suitable for the influx and emplacement of metallogenic fluid. The compression-shear strain field during the mineralization is characterized by the ¦ث-type structure, the positive flower structure, etc. Orebodies are mostly equidistantly located in the dilatational space, which is distributed in the integral compressional circumstances. And the dilatational spaces are developed where the fault attitude changes or shear joint systems develop. In the overall compression-shear stress field, the strain field processes self-similarity at multiple scales, including orebody, ore deposit and orefield etc. The self-similar structure comprises the semi-equidistant distribution of the orebodies at the same scale and the similar appearance of the fracture shape and so on at various scales. Yet due to the special geological structure, the orebodies is mostly located in the hanging-wall in Shangzhuang deposit, which is different from the most deposits in the region. Analysis of ore-controlling stress and strain field in the deposit provide important basis for deposit-seeking.