初论内蒙古长山壕金矿床的成矿时限

长山壕金矿床是近年来在白云鄂博裂谷带上发现的一处具有代表性的超大型金矿床,是中国最大的金矿之一。对长山壕金矿区内含矿石英脉中的黑云母和白云母进行了40Ar/39Ar同位素年代测定,结果表明矿石中黑云母的形成年龄为256.3±1.8Ma,白云母的形成年龄为250.9±1.5Ma~246.0±1.6Ma。结合前人对该区域岩体的测年结果推测出大规模岩浆活动不仅为成矿提供重要的热源,而且提供了重要的物质来源。岩浆演化后期的热液中成矿物质的出溶沉淀是主要的成矿过程,随着温度降低,压力减小,含矿热液中的黑云母和白云母相继结晶,含矿热液中的金及其他成矿元素也在此期间沉淀聚集。

Metallogenic age of the Changshanhao gold deposit in Inner Mongolia, China

The Changshanhao gold deposit is a super large gold deposit found in the Bayan Obo belt in recent years, and one of the largest gold mines in China. This paper is focused on the relationship of the magmatic activity and mineralization in the Changshanhao gold deposit. The ⁴⁰Ar/³⁹Ar isotopic dating of biotite and muscovite from the auriferous quartz veins in Changshanhao gold deposit indicated that the formation age of biotite was 256.3±1.8Ma and the formation age of muscovite was from 250.9±1.5Ma to 246.0±1.6Ma. Combined with the dating results of the region rock of predecessors, it is inferred that large-scale magmatic activity is not only the important heat source for the mineralization, but also the main material source for the mineralization. The precipitation of ore-forming materials from the hydrothermal system is the main ore-forming process in the late magmatic evolution, with the temperature and the pressure decreasing, biotite and muscovite in the ore-bearing hydrothermal successively crystallized, and at the same time, gold and other ore-forming elements in the ore-bearing hydrothermal precipitated and gathered. 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. 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, restudying 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. 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. 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 about 7Myr, 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 (A1), 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 about 6Myr. Two granite intrusive age difference of 17Myr body, indicating the environment by extrusion to extensional environment. 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 is 256~246Ma.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.