Tectonic Evolution And Mineralization Of The Zaozigou Gold Deposit,Gansu Province

The Zaozigou gold deposit, located at the Xiahe-Hezuo gold belt of western Qinling range, is one of a recently discovered large-scale-reservoir middle-low temperature hydrothermal deposits. Its ore potential probably is huge at the depth. As one of typical and representative gold deposits in the western Qingling area, the distribution of ore bodies in the Zaozigou deposit are tightly related with fault activities, showing that the activation of fault plays important roles in the gold mineralization. The geochemistry of intrusions, sources of ore-forming materials, the metallogensis of the deposit have been well studied by many experts and scholars. However, few researches have been done on the ore-controlling structures, which is very useful for ore-prospecting. Funded by the older-mine prospecting project, and on the basis of summarization prior data and our own field detailed observations, this paper is mainly to reveal the evolution of ore-controlling tectonic stress field and discuss the relationship between structure and mineralization in order to provide guidance to ore prospecting. The main achievements are included as following.The Xiahe-Hezuo region is located at northern parts of the Xiahe-Lixian high-angle thrust structure belt, where NW-trending and SW-dipping regional thrust faults are widely developed. Chevron folds and "Z" shaped folds are widely spread in the region, suggesting the regional thrusting movement direction is from SW to NE.Joints and scratch lineations in the deposit were detailed measured in the field in order to identify the principal stress direction by traditional and modern methods of tectonic stress field, and to divide the stage and time of the tectonic stress field by the tectonic superposition, conjugating relation and diagenesis ages of magmatic rock and mineralization. The tectonic stress field in the Zaozigou area can be divided into three stages and five periods. The first stage was the basement deformation during the Hercynian following by the regional deformation and magma emplacement in early time of the Indo-sinian before the mineralization. The second stage was the main mineralization stage, and could be divided into two periods. During the early period, gold mineralization took placed in the SN- and NE-trending fracture zones in middle Indosinian as response to the regional NE-NEE-direction compressional deformation. Massive antimony mineralization in NW-trending low-angle fracture zones occurred in the late Indosinian, as a result of NWW-direction compressional stress. Ore bodies were usually locally dislocated by fault activities after the metallogensis.The relationship between tectonic activities and mineralization characteristics were further discussed, suggesting that the evolution of the tectonic stress field was consistent with the mineralization. The fracture zone experienced multi-stages activities was relatively favorable for the formation of high-grade ore-bodies. It was finally proposed that the conjugating areas of the NE-trending faults with its low grade branch faults and intersection regions of NE-trending faults with low angle NW-trending faults are much favorable for the respecting high-grade ore-bodies at the depth.