Fluid Inclusion Studies in Relation to Hydrothermal Altera- tion and Mineralization at the Koloula Porphyry

The Koloula Igneous Conlplex on the island of Guadalcanal, l)art of the P, ritish Solomon Islands Protectorate, consists of a calc-alkaline sequence of 26 intrusive phases ranging from leucogabbro through diorites and granodiorites to andesire dikes. The internlediate and felsic rocks of the younger central part of the complex are host to porphyry copper mineralization. characterized by two well-defined separate alteration svstems. The earlier or "A " system has five distinguishal)le concentric zones. The innermost is sulfide free and contains K feldspar-quartz-nlag-netite-actinolite-pyroxene (salite). It is succeeded by zones containing potassic and propylitic assenlblages, with chalcopyrite and bornite associated with the potassic zones. The later, or "B " systenl, is characterized by four zones in which sericite and lesser amounts of clay minerals predonlinate. Fluid inclusion assemblages are closely shnilar to those from porphyry copper deposits of the Bingham type. Three types of inclusions are common: gas-rich, nloderatelv saline, highly saline inclusions which contain NaC1 ñ KC1 ñ henlatite ñ birefringen