The Mineralogy of the Copper – Gold Ore Deposits at the Phu Kham, Mine, Laos

Abstract

The Phu Kham Cu-Au deposit Porphyry-related skarn-type mineralization, Lao PDR is hosted by complexly deformed, schistose, quartz-sericite-pyrite altered Permo-Carboniferous volcanic, volcaniclastic and intrusive rocks. These rocks occupy the immediate hanging wall of a large NE-dipping thrust fault. Unmineralized, variably deformed red beds of the Mesozoic Khorat basin occur in the foot wall to the thrust. At Phu Kham the well defined foot wall and hanging wall sequences are separated by poorly-stratified quartz-rich conglomerate, breccia and lesser sandstone of uncertain affinities. In previous studies, the conglomerate package has both been included in the Khorat basin succession and interpreted tostratigraphically underlie the Permo-Carboniferous volcanics. Structural studies and additional U-P zircon geochronology were undertaken in 2009 to help clarify geological relations at Phu Kham. Improved constraints on thrust geometry and kinematics were also sought, enabling the deformation history at Phu Kham to be more confidently placed into a regional context. Results indicate the thrust was emplaced from the NE, and thus has greater affinity with deformation patterns in the NW-trending Truong Son fold belt.The conglomerate package is reinterpreted as a syn-orogenic molasse deposited ahead of the Advancing allochthon, but eventually overridden during the final stages of thrustemplacement. Unfortunately, definitive geochronological data supporting this conlusion were not obtained.