The Structure of Ore‐controlling Strain and Stress Fields in the Shangzhuang Gold Deposit in Shandong Province, China

AbstractThe Shangzhuang altered‐rock type gold ore deposit is located in the middle segment of and controlled by the Wang'ershan fault zone in the northwestern part of the Jiaodong gold province, China. The deformation evolution, 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 and the final NW‐striking compression. The mineralization happened during the third stage in which the maximum principal stress gradually transited from NE to NW. The 3‐D 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 maximum principal stress is NW‐striking, the fault zone is relatively extensional and it is suitable for the influx and emplacement of ore‐forming fluids. The compression‐shear strain field during the mineralization is characterized by the Λ‐type structure, the positive flower structure, etc. Orebodies are mostly equidistantly located in the dilatational spaces, which are 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 bears self‐similarity at multiple scales, including the orebody, ore deposit and orefield. The self‐similarity of the structure comprises the subequidistant distribution of fractures at the same scale and the similar shape of the fractures at various scales. Yet, due to the special geological structure, the orebodies are mostly located in the hanging wall in the Shangzhuang deposit, which is different from most deposits in the Jiaodong gold province. Analyses of the ore‐controlling stress and strain fields in the deposit provide an important basis for deposit seeking.