Geology and geothermometry of vein-type W-Sn deposits at Pennaichaung and Yetkanzintaung Prospects, Tavoy Township, Tennasserim Division, southern Burma

Abstract

The Pennaichaung and Yetkanzintaung W-Sn Prospects are located in Tavoy Township, Tennasserim Division, southern Burma. The W-Sn mineralization at the Pennaichaung is closely related with a small, satellitic granitoid pluton of presumably Late Mesozoic age, which intruded the metaclastic rocks of Mergui Group (mostly Carboniferous). The mineralized quartz veins at the Pennaichaung penetrated the granitoid-metasedimentary rocks contact. In contrary to the Pennaichaung deposit, the W-Sn veins at the Yetkanzintaung are exclusively in the metasedimentary rocks of slates and quartzites of Margui Group. Mineralized quartz veins in the Pennaichaung area trend NNE-SSW, NW-SE and NE-SW with a maximum thickness of 30 cm, but only quartz veins trending NNE-SSW are found to be productive and contained economically workable wolframite and cassiterite. Majority of the mineralized quartz veins in the Yetkanzintaung area trend approximately N-S with easterly dip of 50°–70°. The thickness of the ore veins in the Yetkanzintaung area are thinner than those of the Pennaichaung and range from 1 cm to 20 cm with an average width of 5 cm. Fluid inclusion studies of the quartz from the ore veins cutting the granitoid in the Pennaichaung area have yielded a filling temperature range of 170°–270°C with a maximum mode of 220°C, while quartz crystals from the ore veins in the nearby metasedimentary rocks gave a filling temperature range of 140°–220°C with a maximum mode of 160°C. Hence, the Pennaichaung deposit was thought to have emplaced under a filling temperature range of 140°–270°C. A similar low filling temperature range was recorded for the Yetkanzintaung deposit. Quartz from the Yetkanzintaung ore veins have yielded filling temperatures of 200°–240°C, whereas the fluorites associated with the mineralized quartz veins gave a temperature range of 140°–160°C. Limited freezing runs indicate a salinity of less than 5 NaCl equivalent weight percent for inclusions in quartz from both orebodies. No fluid inclusion evidence of boiling of ore fluids nor presence of liquid CO₂ was observed in this study. Thus, the ore fluids responsible for the W-Sn mineralization at the Pennaichaung and Yetkanzintaung areas were of low temperature, diluted, CO₂-deficient, NaCl brines.