Tin-tungsten mineralized granite at Mae Chedi area, Wiang Pa Pao District, Chiang Rai Province, Northern 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 OM-series, is associated with the known primary tin-tungsten mineralization and composed of fine-grained biotite (GM-1), fine-grained muscovite-bearing biotite (OM-2), and fine- to medium-grained leucocratic (GM-3) granites. The second, the OR-series, is generally referred to as tin-tungsten barren granite. It is composed of porphyritic biotite (OR-1), medium- to coarse-grained biotite (OR-2), and fine- to medium-grained leucocratic (OR-3) granites . . Both granitic series are geochemically calc-alkaline, peraluminous, and S-type granites. However, the OM-series appears to be less silicic than that of the OR-series and is characterized by higherTi02 , ~03 , F~03 , FeO, MnO, MgO, CaO, P20 5, ~o+, Li, F, Sr, Ba, Zr, Sn, W, Cu, Zn, Ni, Ce and lower Rb contents. Relative differences in N~O and KzO contents between the OM-1, OM-2 and the OR-1, OR-2 are not remarkably sharp. However, the OM-3 is notably lower in N~O but higher KzO contents than that of the GR-3. This and petrographic evidences have led to the belief that the OM-3 is the late metasomatic alteration product of the OM-1, wheq:as the OR-3 is the late magmatic differentiation product of the OR-1. The primary tin-tungsten mineralizations occur in the area where small granitic plutons of the OM- series intrude metabasite. The tin and tungsten ores are commonly found· in/or adjacent to quartz veins and veinlets cutting through the OM-granitic series, and less commonly, in the metabasite. Wall-rock alterations are characterized by K-feldspathization, toumtalinization, chloritization; sericitization, muscovitization and albitization.