Metallogenic Conditions And Genesis Of The Galonggema Cu-polymetal Deposit, Qinghai Province

Abstract:Galonggema Cu-polymetal deposit is located in the eastern of the Tethys-Himalayan tectonic domain, which is the strong collision and extrusion zone between Gondwana and Eurasian ancient land. The main producing formation is dacitic and rhyolitic sedimentary rocks of T3bt2. The orebodies occur among the dacitic tuff, tuffaceous siltstone, sericite schist and phyllite, with main ore minerals of pyrite and chalcopyrite ore, pyrite and sphalerite ore, galena ore, sphalerite, as well as chalcopyrite ore etc. In accordance with the the geologic characteristics of ore deposit,the metallization can be divided into two periods including volcanic sedimentary hydrothermal stage (here reviewed as stage A) and the mesothermal sulfide phase (here reviewed as B), which are further subdivided into5metallization stages.Petrological characteristics indicate that volcanic rocks of this area can be classified as volcanic neck relative, volcanic eruption, subvolcanic phase, and volcanic sedimentary facies. Volcanic geochemical characteristics demonstrate that dacite belongs to metaluminous rock series as the extent of its magmatic differentiation is high, regarding as calc-alkaline. In addition, the component of tuff belongs to dacite, showing as high aluminum. Volcanic geochemical characteristics also show that REE Distribution pattern of volcanic rocks is part of LREE. Furthermore, volcanic rocks of Galonggema are formed in active continental margin where is active zone of Continental island arc. The main diagenetic source rock there is Mantle material.Vapor-aqueous fluid inclusion is one of the major fluid inclusions in the ore area. In particular, aqueous-CC>2triphase fluid inclusion, as a secondary fluid inclusion, can be seen occasionally. Results of temperature measurement indicate that there are significant differences on fluid characteristics of Galonggema between two mineralization periods. Besides, an obvious gap could be found in the middle. Thus, Galonggema is a result of two mineralizations. Stage A is characterized by low temperature, representing the volcanic hydrothermal sedimentary and hydrothermal mineralization. The mineralization fluid of stage B begins with high temperature and moderate salinity, derived from a new magmatic activity. According to geological conditions of mineralization, it can be inferred that both the depth and the pressure of mineralization are not much. Furthermore, mineralization has more pressures and mesophilic conditions after going through regional metamorphism, accompanying with the deformation of fold, as well as the foliated role.In conclusion, the formation of Galonggema Cu-polymetal deposit has experienced two mineralization periods, which are volcanic jet (deposition) minerlization of Marine felsic volcanic rocks and mesothermal minerlization invaded by neutral-acidic magma in the later stage. Based on studies stated above, the mineral deposit of metallogenic model has been established.