Geochemical characteristics of gold related Ben Giang-Que Son granitoids in the southern part of Truong Son Fold Belt of Vietnam
Nguyen Thi Bich Thuy1*, Le Quoc Hung3, Nguyen Thi Xuan1, Bùi The Anh1, Ho Thi Thu3, Minh Pham2, Phan Duc Le3, Nguyen Duc Chinh1 and Tran Ba Duy1
1Vietnam Institute of Geosciences and Mineral Resources, Thanh Xuan, Hanoi
2Faculty of Geology, University of Science, 227 Nguyen Van Cu Street, Ho Chi Minh City
3General Department of Geology and Minerals, Hanoi
* Corresponding author: thuynguyendcks@yahoo.com
Abstract: 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).
Keywords: Gold related Ben Giang–Que Son granitoid, petrography, geochemistry, southwest Truong Son Belt, Vietnnam.
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