The Geochemical Response Mechanism Of Ore Controlling Process In Shizishan Cu-Mo-Au Ore Field In Tongling Region

Shizishan orefield located in Tongling ore concentration area in the metallogenic belt of the middle and lower reaches of Yangtze River. More than fifteen copper and gold deposits occurred in the ore-field, such as Hucun South deposit and Cishan deposit. The distribution of the deposits were controlled by faults, interlaminer slip structure and intrusive contact structure, and closely related with the mid-acid intrusive of Yanshan period. Base on the previous study work, in order to identify the elements concentration and migration patterns in geological bodies, to construct geological-geochemical anomalies pattern, to discuss the controlling geochemical response and its mechanism. in Shizishan orefield, the characteristics of the element anomalies, sulfur and lead isotopic composition and fluid inclusions composition were studied on typical porphyry-skarn type copper-molybdenum-gold polymetallic deposits. The results as follows:Firstly, the ore-forming elements Cu, Mo and Au, the associated elements Ag, As, Sb, Bi, Cd, Sb, W etc., and the mineralizer element sulfur were enriched in Devonian-Triassic stratums, mid-acid intrusive rocks in Yanshan period and the alter rocks(such as marble and skars), on the other side, Ba, Sr, CaO, Na2 O were depleted. Strongly elements migration occurred in metallogenic geochemistry system in Shizishan orefield, which formed a large-scale positive and negativeSecondly, the surface anomalies are consistent with the deeper, Cu, Mo, Au positive anomalies output around the main ore bodies, which has a direct implications for polymetallic mineralization. Sr negative anomalies are near the skarn ore bodies which is a quickly identify indicators for ore body position. Sulfur positive anomalies and Ba, Na2 O negative anomalies not only cover the entire area of mineralization, but also not vanis in the deep of drillings, which implied that a concealed polymetallic mineralized bodies maybe occurred in the deep of orefield.Thirdly, there has a multiple attribute anomalous system in Shizihan orefield which were composed by the negative anomalies system of Ba and Na2 O, the mineralizer element anomaly system of sulfur, the equilibrium system between sulfur and Fe and ore-forming elements, and the ore-forming and association elements anomalies system, as well as the mass balance system of inactive elements such as Zr and Hf. All those anomalous system were controlled by stratums, magmatic rocks and structure.Fourthly, Ore-forming elements of Cu, Mo, and Au and the mineralizer element of sulfur were supplied by deep-seated magm and sulfur enriched formation, such as Honglong-Chuan- shan, Qixia, Gufeng, Dalong, Longtan, Helong mountain as well as Yinkeng formation. The deep-seated magm not only supply ore-forming materials but also provide the important fluid and heat source for the activation and migration in ore-forming process.Fifthly, polymetallic mineralization and elements anomalies were formed in ore-bearing hydrothermal which experienced a evoluation process from high temperature, high salinity to middle-lower temperature and salinity under the tectonic stress, volatile pressure, lithostatic pressure, geothermal gradient and reverse tectonic stress.Finally, a geological and geochemical amonly pattern was constructed in the scale of deposit and orefield, which will provide a basis for geochemical exploration and anomaly evaluation in Tongling ore concentration area.