Abstract:

The Pha Khieng-Nam Bo area is located in the Muang Long District, Luong Nam Tha Province, Laos PDR. It comprises the Sukhothai fold belt, which is located in Northwest central Indochina. The area is underlain by predominant volcanic rocks and subordinate siliciclastic and carbonate sedimentary sequences. All rocks in the area have variable affected by several phases of deformation, including regional penetrative ductile shearing and folding as well as local brittle faulting and fracturing. Within the Pakieng-Nam Bo area, numerous sulphide occurrences have been discovered, which comprises mostly Cu and Mo (±Au) mineralizations. New geochemical data have demonstrated that the volcanic rocks in the Pha Khieng-Nam Bo area are part of high calc-alkaline series, which has been formed in a subduction environment as a part of the Sukhothai-Bokeo Island Arc system during the Late-Permian to Early-Jurassic. On the basis of ore microscopic and EPMA analyses, these mineralizations can be divided in to two groups including MoPb-Au (±Cu) and Cu-Pb (±Mo) mineralizations. The Mo-Pb-Au (±Cu) mineralization is characterized by very fine-grained of sulfur mineral, which are filled pore spaces of the fracture/breccia systems. Cu-Pb (±Mo) mineralizations are occurred along high strain zones and are more abundant in the Nam Bo area. The presence of epithermal breccia with fine-grained sulfide minerals including pyrite is good indicators for low sulfidation epithermal environment for the Cu-Au mineralization in the Pha Khieng-Nam Bo area.