Tóm tắt

Granitoids of the Ben Giang – Que Son complex are exposed in the southwestern part of the Truong Son mountain range in Vietnam. Tectonically, the range consists of Truong Son Fold Belt and Kontum Massif. This magmatic complex is composed of mafic to felsic intrusions with petrographical composition ranging from gabbro to biotite-hornblende-bearing granite and granosyenite. The main rock-forming minerals are: Plagioclase, quartz, K-feldspar, hornblende and biotite. The granitoids associated with gold mineralization are recognized in Dak Blo commune, Dak Glei district, Kontum province. They underwent K-feldspar alteration; following is sericitisation, which partially overprint the earlier alkali alteration. These granitoid rocks have a relatively low and wide range of SiO₂ contents (50 to 70 wt%), low TiO₂ (<1.0 wt%), but high total alkaline content (6.9-9.6 wt%) with most K₂O/Na₂O ratios>1.0. They are calc-alkaline, metaluminous to weakly peraluminous, and show characteristics of I-type granites. Generally, the granitoids are enriched in large ion lithophile elements, and depleted in high field strength elements when compared to primitive mantle values. Rocks associated with gold mineralization are mainly biotite-bearing granites, which are beresitized. Two main styles of gold mineralization are recognized: (1) quartz-vein hosted, this style occur mainly in felsic granitoids and gold concentrated within the veins together with sulphides; and (2) disseminated, gold occurs as free native metal with sulphides, hematite in the alteration zone of beresitized granites. The ore-forming fluids have relative high salinity (13-24 wt% NaCl equiv.) and low temperature (150–250°C).