Abstract
The fluid inclusion study of the Mamut porphyry copper deposit, Sabah, Malaysia was carried out as part of studies of the ore-forming fluids and mineralization of porphyry copper deposits from the Southwestern Pacific island arcs. Polyphase fluid inclusions which contain halite, sylvite, hematite, anisotropic unidentified minerals, and opaque minerals, are observed abundantly in the vein quartz. Gaseous inclusions are also abundant, but liquid inclusions are few. It is inferred from the disappearance temperature of halite that the salinity of fluid would have been in a range between 35 to 55 wt.% NaC1 equivalent concentration. The homogenization temperature of polyphase inclusion ranges from 300°to 480°C, whereas that of liquid inclusion is between 280°C and 325°C. The "boiling" of the fluid is manifested by an intimate coexistence of gaseous and polyphase inclusions, in some samples. The numeral ratio of polyphase inclusion to the total number of inclusion becomes higher in the ore-shell or biotite zone, and at lower levels of the orebody. A low value of the ratio from the core of the orebody is attributable to the abundance of gaseous inclusions. An intimate relation between the abundance of chalcopyrite in sulfide minerals and polyphase inclusions suggests an important role of highly saline fluids in the copper mineralization. It is concluded that the ore-forming fluids at the Mamut porphyry copper deposit were rich in nonvolatile materials including chlorides and that the pressure of the fluids was low enough to emanate the vapor phase. Such characterisitics of fluids at the Mamut deposit are similar to those of the porphyry copper deposits in the southwestern United States.
