GEOLOGY AND GENESIS OF THE GRANITIC NIOBIUM-TANTALUM-RUBIDIUM DEPOSIT IN SHIHUIYAO AREA, INNER MONGOLIA

The Shihuiyao Nb-Ta-Rb polymetallic deposit is a large rare metal deposit that was recently found in Xilinhot City, Inner Mongolia, China. By electronic microprobe (EMP) and X-ray fluorescence spectrometry (XRF) analyses on minerals and whole rock compositions of ores, with discussion on the geological characteristics and controlling factors as well as genesis of the deposit, the following results can be demonstrated: 1) The ores of this deposit belong to alkaline granite type series. 2) The Nb-Ta minerals in the ores mainly include manganocolumbite, columbite-tantalite, columbitemanganotantalite, wodginite and microlite. 3) This deposit may be an integrated product of crystallization of granitic magma in early stage and hydrothermal metasomatic interaction later, of which the latter is the main metallogenic stage of Nb, Ta and Rb; 4) The Nb-Ta-Rb mineraling genesis and enrichment patterns show that the mineralization is closely related to the albitization and greisenization of granite. The ore bodies mainly occur in altered granites, strictly controlled by NE-trending structures in distribution. Therefore, the albitized and greisenized granites are direct indicators for the prospecting of these metals. In addition, the areas where the Early Yanshanian granites outcrop are probably prospective targets for the rare metals. 5) The basic idea for Nb-Ta-Rb prospecting in Shihuiyao area is to seek for the uplift and the shallow parts of the small albitized granite rock mass emplaced in later stage around the main granite bodies.