Abstract:

The Xiong’ershan ore concentration area is located in the middle eastern part of the Qinling orogenic belt. Multi-stage tectonic activity leads to regional multi-level faults，among which the first-grade fault is a deep fault with multi-stage activity and structural inheritance characteristics，which controls the distribution of original source of ore-forming materials and regional mineralization.The second-grade fault controls the distribution of metallogenic belts.The third and fourth grade faults are the main ore hosting faults.The regional extension and tectonic extension in Yanshanian period led to extensive magmatic activities，which provided important material and energy sources for mineralization.The interaction between the Yanshanian mantle and the crust led to large-scale magmatic activities and tectonic movement，thus forming a large number of precious and nonferrous metal deposits of different stages and scales in the area.The Dongcaogou deposit is a new gold-silver deposit discovered in the Xiong’ershan ore concentration area in recent years，which is still in the stage of exploration and development.Field structural analysis shows that the orebody of the Dongcaogou deposit is strictly controlled by faults.From the end of Indosinia to the early Yanshanian，the structure in the near EW direction is dominant in this region，with minor NNE-near SN direction faults.Five stages of tectonic activities in the deposit were identified in this study，and their sequence and tectonic stress field are as follows：The first stage tectonic stress field is near SN compression，the second stage tectonic stress field is near EW compression，the third stage tectonic stress field is NW compression，these three stages fault are pre-mineralization structures，the fourth stage tectonic stress field is NNE compression，which is a fault structure in the syn-mineralization，and the late stage tectonic stress field is converted into extension due to stress relaxation.The fifth stage tectonic stress field is NE compression，which is a post-mineralization fault.According to the occurrence，kinematics and deformation characteristics，the ore-control faults can be divided into structural fracture zone （strong structural deformation zone） and steep fault.The study of the time-space relationship between structure and mineralization shows that the ore-controlling faults in the early and late ore-forming stages have obviously difference in structural characteristics.In the early ore-forming stage （late Indosinian early Yanshanian） ，the ore-controlling faults are compressive faults and show obvious ductile brittle deformation where S-C structures and tectonic schistosity zones are developed，reflecting a tectonic stress field of nearly S-N compression. In the late ore forming stage （middle and late Yanshanian） ，the ore-controlling faults are characterized by tensile faults and brittle deformation，and the ore veins are characterized by typical expansive filling veins，which suggested that tectonic stress field is nearly E-W oriented extension.The ore-controlling faults in different directions in the area are multi-directional conjugate fault systems formed under the near S-N direction compression，and the secondary faults derived from them.The assembly patterns of the compound conjugate fault system control the spatial distribution and pattern of ore bodies in the Dongcaogou Au-Ag deposit.

Key words: ore-controlling fault, tectonic stress filed, ore-control regularity, tectonic evolution, Dongcaogou Au-Ag deposit, Xiong’ershan ore concentration area