Study On Geological Characteristics And Metallogensis Of Changshanhao Gold Deposit In Inner Mongolia

The western section of the northern margin of the north China craton, is one of the most important gold metallogenic provinces in North China. The gold deposits and prospects hosted by the low-grade metamorphic detrital rocks are widely distributed in two parallel east-west-trending Proterozoic rift belts:the Bayan Obo belt in the north, and the Chaiertaishan belt in the south. The Changshanhao gold deposit is a super large gold deposit found in the Bayan Obo belt in recent years. Predecessors have done many geological exploration works on the Changshanhao gold deposit. However, the scientific research work remains relative lag, which more or less has influence on the understanding of the deposit and its periphery and deep prospecting work. Based on collecting, restuding the results of previous studies and combined with field geological survey and detailed indoor research work, this research has analyzed the environment and the geological characteristics of the Changshanhao gold deposit, discussed the relationship between the magmatic action and the gold mineralization, summed up the genesis of the deposit, proposed a metallogenic model and prospecting directions. At last, the same types of gold deposits of the domestic and foreign occurs in epimetamorphic clastic rocks were analyzed. The understanding made by the paper is as follows:1. The gold mineralization of the Changshanhao gold deposit occurs in the low-grade metamorphic clastic rocks of the Proterozoic Bayan Obo group as stratoid layer, stratiform and lenticular, the gold mineralization have a close spatial relationship with various types of granitoid intrusions.2. The granitoid intrusions of the Chanshanhao gold mining area and its adjacent region are mainly formed in the Hercynian period, can be divided into two phases:the first stage is the early period of Early Permian (293-286Ma), the granitoid intrusions occurs as stocks, dyke swarms or apophysis, and the magmatic action lasted about7Ma, speculated that the magmatic rocks may be the product of the partial melting of the enriched mantle; the second stage is the Middle Permian (274-268Ma), the granitoid intrusions are A-type granitoids (Al), which probably formed in the extensional tectonics environment with low pressure and high temperature. On the whole, the late magmatic action in large scale, the early stage granite batholith is exposed, late order to smaller rock strains, lasted about6Ma. Two granite intrusive age difference of17Ma body, indicating the environment by extrusion to extensional environment.3. The Ar-Ar isotopic dating results of the pyrite quartz veins in the Changshanhao gold deposit show that the age of the late stage hydrothermal activity related to the gold mineralization is246-256Ma.4. The initial mineralization age of the Changshanhao gold deposit is the Middle Proterozoic, and subjected to the superimposition of Hercynian tectonic and magmatic activities, the mineralization can be divided into two main stages, namely the initial mineralization stage of the Middle Proterozoic and the superimposition stage of Hercynian tectonic and magmatic activities. The Changshanhao gold deposit is a product of Hercynian tectonic-magmatic and fluid-related activities, and which played an important role during the ore-forming processes of the Changshanhao gold deposit.5. The Changshanhao, Zhulazaga and Saiyinwusu gold deposits are the largest ones occurs in two parallel east-west-trending Proterozoic rift belts. The geological features and environment of these gold deposits are very similar, the gold mineralization of which occurs in the Proterozoic carbonous sandstone, siltstone, carbonous phyllite, phyllite, slate and schist as stratoid layer, stratiform, stockwork and vein. Systematic geological investigations indicate that the wall rocks of these deposits and prospects vary from place to place, but most of them show an intimate spatial-temporal relation with the Caledonian ductile-brittle fractures zone and Hercynian intrusive dyke swarm. These gold deposits are similar to the Muruntau gold deposit, Uzbekistan, and belong to mesothermal vein-type gold deposit related to intrusive rocks.6. The Mineralization of the Changshanhao, Zhulazaga and Saiyinwusu gold deposit occurs in the Middle Proterozoic and Hercynian respectively, and the time of which are consistent with the occurrence of ancient continent block cracking, oceanic crust and continental block subduction, orogenesis event. The seawater sedimentation and marine volcano activities of the Middle Proterozoic caused by the intensive rifting occurring within the Early Precambrian continent or along its margin resulted in the ground preparation of gold and other ore-forming materials, and formed a number of gold source beds and protore along a certain strata. The gold deposits can be formed by Hercynian tectonic-magmatic activities through the following two ways:one is the early ore source layer superimposed reformation; the other is the formation of the gold deposits directly by the penetration of host rock of ore-bearing fluid.7. The volcano-sedimentary rock strata are widely distributed in the north margin of the North China craton, and among which some stratigraphic units have many anomaly occurrences of the gold, arsenic and mercury elements. The Geological environment, lithology and structure characteristics of these stratigraphic units are very similar to the Changshanhao, Zhulazaga and Saiyinwusu gold mineralization area. In addition, the variouss types of folds and faults are well developed in the stratigraphic units, and which cut by a series of alkaline-rich intrusive dyke swarms, are favorable for the exploration of concealed gold deposit.