Forming conditions and ore content of fluid-explosive breccias of the Sherlovogorsky tin-polymetallic deposit (Eastern Transbaikalia)
The Sherlovogorsky tin-polymetallic deposit is located in East Transbaikalia in the zone of East- Aginsky deep fracture. The deposit is confined to fluid-explosive breccias (FEB), developed in the intrusion of quartz porphyries. The absolute age of quartz porphyries is 136-153 million years, which corresponds to the late Jurassic - early Cretaceous periods. The analysis of the diagram (Pb - (Y+Nb)) testifies to formation of quartz porphyries in continental conditions. In the discrimination diagram FeO* / (FeO+MgO) - SiO2 their values also take place in the granitoid field of continental epeirogenic elevations. To find out the degree of granite differentiation Pb/Sr ratio is most often used. It is established that Pb/Sr > 0,3 are peculiar for all rare-metal and differential granites of I and S types. Values of quartz porphyries of the Sherlovogorsky deposit change from 10,65 up to 16,85, that specifies a very significant degree of their differentiation. Stockwork type of mineralization prevails at the Sherlovogorsky deposit. In the higher, practically depleted part of the deposit, stannous mineralization is located in quartz porphyries and explosive breccias. Fragments and cement of breccias are mostly quartz porphyries. Cement of breccias has quartz-tourmalinic structure. In the upper level of the deposit tin mineralization is developed, created with explosive breccias formation, in the lower level - polymetallic mineralization, connected with rocks of basic substratum. In the lower part of the deposit, with the rocks basic substratum of gabbro, diorites, diabases, basalts with the dependent parting of serpentenites, plumbic-zinc stockwork mineralization prevails. The correlation analysis has revealed a rather close bond of tin with arsenopyrites (r = 0,48), boron (r = 0,41). Close bond of tin with boron testifies that tin mineralization is connected with the formation of FEB where quartz-tourmalinic mineralization is one of the basic components of cement. Lead, zinc and tin do not form close correlation bonds. The explanation is that tin and polymetallic mineralizations are formed in various conditions and have different sources. The last proves by the fact that tin mineralization is confined to the fissure-vein zone of meridional strike and polymetallic mineralization - to fissure-vein zone of northeastern strike. Thus, tin mineralization of the Sherlovogorsky deposit is connected with the formation of FEB, being extreme differentiates of the quartz-porphyries formed in continental conditions. Polymetallic mineralization is formed in regenerative conditions. Its sources, most likely, are rocks of basite substratum.