Bulletin of the Geological Society of Malaysia, Volume 20, August 1986, pp. 423 – 471
1 Economic Geology Division, Department of Mineral Resources, Bangkok 10400, Thailand
2Department of Geology, Chulalongkorn University, Bangkok 10500, Thailand
Abstract: The granitic complexes in the Mae Chedi area, Wing Pa Pao district, Chiang Rai province, northern Thailand, comprise two granitic suites. The first, the GM-series, is associated with the known primary tin-tungsten mineralization and composed of fine-grained biotite (GM-1), fine-grained muscovite-bearing biotite (GM-2), and fine- to medium-grained leucocratic (GM-3) granites. The second, the GR-series, is generally referred to as tin-tungsten barren granite. It is composed of porphyritic biotite (GR-1), medium- to coarse-grained biotite (GR-2), and fine- to medium-grained leucocratic (GR-3) granites.
Both granitic series are geochemically calc-alkaline, peraluminous, and S-type granites. However, the GM-series appears to be less silicic than that of the GR-series and is characterized by higherTiO2, Al2O3, Fe2O3, FeO, MnO, MgO, CaO, P2O5, H2O+, Li, F, Sr, Ba, Zr, Sn, W, Cu, Zn, Ni, Ce and lower Rb contents. Relative differences in N2O and K2O contents between the GM-1, GM-2 and the GR-1, GR-2 are not remarkably sharp. However, the GM-3 is notably lower in Na2O but higher K2O contents than that of the GR-3. This and petrographic evidences have led to the belief that the GM-3 is the late metasomatic alteration product of the GM-1, whereas the GR-3 is the late magmatic differentiation product of the GR-1.
The primary tin-tungsten mineralizations occur in the area where small granitic plutons of the GM-series intrude metabasite. The tin and tungsten ores are commonly found·in/or adjacent to quartz veins and veinlets cutting through the GM-granitic series, and less commonly, in the metabasite. Wall-rock alterations are characterized by K-feldspathization, tourmalinization, chloritization; sericitization, muscovitization and albitization.