The Ban Houayxai epithermal Au-Ag deposit in the Northern Lao PDR: Mineralization related to the Early Permian arc magmatism of the Truong Son Fold Belt

The Ban Houayxai Au-Ag deposit is located in the Truong Son Fold Belt in the northern Lao PDR, mainland SE Asia. The deposit is hosted within an Early Permian volcano-sedimentary unit which is a part of a Late Carboniferous-Early Permian (310-270 Ma) volcanic-plutonic sequence of the Truong Son Fold Belt. The main Au-Ag mineralization stages (i.e., Stages 2 and 3) at Ban Houayxai consist of hydrothermal veins/breccias associated with a carbonate-quartz-sulfides (pyrite-sphalerite-galena-chalcopyrite)-sericite-chlorite-electrum-native silver-stephanite mineral assemblage. Geochronological studies from LA-ICP-MS zircon U-Pb and adularia Ar-Ar and K-Ar dating identified Early Permian, Cretaceous and Eocene ages. The Early Permian age is related to the emplacement of the mineralized volcanic arc sequence, whereas the Cretaceous and Eocene ages represent resetting probably related to Yanshanian and/or Himalayan Orogenies. A regional tectonic reconstruction indicates that the Au-Ag epithermal deposit at Ban Houayxai was formed as a result of southward subduction of an oceanic crust attached to the South China Terrane beneath the Indochina Terrane during the Early Permian. From the metallogenic point of view, the recognition of the old epithermal system at Ban Houayxai implies that the Truong Son Fold Belt possesses high potential for the presence of deeper magmatic-related deposits such as porphyry and porphyry-related skarn deposits.