A report on copper skarn deposit at Phu Lon, Amphoe Sang Khom Changwat Nong Khai

Abstract

Based on the geological and petrographical studies and chemical analysis of drill-core and outcrop samples, the geology and mineralization at the Phu Lon area are revealed. The Phu Lon prospect is a Cu-Fe-Au-Ag skarn deposit of porphyry-related type. The copper- and iron-rich zones are hosted predominantly in the garnet-pyroxene skarn that is developed metasomatically at the contact between the diorite-monzodiorite intrusions and a marble with minor calcsilicate unit. The main stage of iron mineralization probably took place during the prograde garnet-pyroxene skarn formation and was genetically related to the diorite-monzodiorite. The ore minerals include magnetite, minor chalcopyrite and pyrite, and occur in the form of massive patches or bands in the skarn. Quartz monzonite porphyry – monzonite dikes/stocks post-date the diorite-monzodiorite and the garnet-pyroxene skarn. Extensive alterations overprinting on both intrusive and volcanic rocks (i.e., potassic, phyllic and propylitic) are probably related to the cooling of quartz monzonite porphyry-monzonite. Close accompanying the alterations, the main stage of copper mineralization and retrograde skarn alteration of epidote-chlorite-calcite commenced. The mineralization occurs in the from of chalcopyrite-pyrite-quartz veins/veinlet networks predominantly in the skarn unit. Other associated minerals include magnetile, hematite and molybdenite. Trace amounts of gold and silver are chemically detected and probably associated with the copper mineralization. Their contents are comparable to those of the similar copper-gold deposit class. It is attractive for persuading further exploration.