Discovery of fault-grinding siliceous breccia rock in the Jiurui ore district, Jiangxi Province, and its formation mechanism and mineralization significance
江西九瑞矿集区硅质断裂磨砾岩带的厘定及其成岩成矿意义

Following our previous study on reiterative fault systems and superimposed mineralization in the Jiurui ore district (Jiang et al. , 2010), in this study we conducted a thoroughly investigation on a tectonic-hydrothermal siliceous breccia rock which occurs along the NE trending Yangjishan gold mine-Dingjiashan gold mine-Wangfushan belt. Our study indicates that these siliceous breccia rocks are not sedimentary siliceous rocks in Carboniferous strata as previously thought, but belong to a fault-grinding breccia rock. The rock-forming mechanism of the breccia rocks and their relation to mineralization are also discussed in detail in this paper. Generally speaking, the fault-grinding gravel (grain) include all kinds of boudinage, grinding gravel and cataclastic flow grinding gravel, and it is an indication for maturity of fault zoning texture. Under shearing, the faulted rock may have passed stages of rupturing-fracturing-comminution-grinding and to form a great variety of grinding gravels or grains in different size with appropriate roundness and sphericity. These breccia rocks could have been repeatedly aggregated and fractured, and continuously developed to form a grinding gravel and breccia zone. In the Jiurui ore district, we found that these fault-grinding breccia rocks developed along the main NE-trending structure line of the district and extended tens kilometers long. The breccias are highly silicified with SiO2 contents >90%. The quartz includes both cryptocrystalline and crystalline grains. Some of the breccias contain high Fe2O3 contents, which may indicate presence of primary sulfide ore breccias which have been oxidized to goethite later on. It is likely that these fault rocks were products of Yanshanian tectonic-magmatic-hydrothermal events. In the Chengmenshan and Wushan deposits, we also found various types of pyrite breccias occurring within the Devonian/Carboniferous strata and layer slip fault zone, which may have formed during the Hercynian syn-sedimentary faulting stage. All these different types of breccias composed the ore complex in the district, which show a multiple stage developing feature and superimposed mineralization characteristics. It is also suggested in this paper that the layer slip fault gravel-breccia zones in other sedimentary strata such as the Devonian/Silurian and Silurian/Ordovician at depths are potential mineralization targets that need to pay more attention in future exploration.