Constituent minerals and REE contents of the granite and Sn skarn ores from the Pin Yok mine, southern Thailand

Abstract

    Tin skarn ores from the Pin Yok mine, southern Thailand, were studied for Sn and REEbearing minerals, because these elements are generally rich in "tin granites" and are supposed to be enriched in the surrounding rocks, especially of skarn-type ore deposits. The related granite of possibly Triassic age contains no magnetite (i.e., ilmenite-series granites) but biotite and some secondary muscovite, and is high in silica (75.0 % SiO₂) and potassium (5.2% K₂O) , with moderate contents of Sn (12 ppm) and REE+Y (232 ppm). Accessory REE+Y-bearing minerals observed under the microscope, are allanite, monazite, zircon and apatite in this granite.
    The Sn skarn ores are composed of clinopyroxene (40~90 vol.%), grossular garnet (2~20 vol.%), stilpnomelane (2~20 vol.%), ilvaite (~5 vol.%), calcite (~10 vol.%), and quartz (~10 vol.%). Arsenic is locally abundant up to 4,490 ppm As, as possibly arsenopyrite. Tin contents of the skarn ores go up to 7,070 ppm Sn. Cassiterite but no malayaite, in very fi ne grain size, has been identifi ed by microscopic observation and qualitative analyses by EPMA. REE+Y contents are high in two samples of 327 ppm (77110903-6) and 260 ppm (77110309-5). Yet, no REE and Y-bearing minerals have been identified, except for some grains of allanite. Other skarn ores were found to be very low in REE+Y contents.