The Revenue Granite intruded as a sill into carbonate-rich, evaporitic Sediments of the Mt Isa Inlier in the mid- Proterozoic. The granite was altered by high-temperature saline fluids shortly after eiriplacement. The alteration assemblages include albite, Cl-rich scapolite and diopside. Scapolitization and albitization both involve substantial losses of Fe, Mg and K from the host rock, and gains in Na and Ca. The mineral assemblages and mass-transfer calculations indicate that the metasomatizing fluids were Na-, Ca-, Cl-bearing brines. Formation of pyroxene in veins relatively late in the metasomatic history was probably a consequence of Saturation of the fluid in Fe and Mg due to relatively local circulation (on the Order of 100 m) of the fluids through overlying dolerites. Stahle isotope data suggest that the fluids were of dominantly magmatic origin. A > l% difference in δl8O values between the top and bottom of the Revenue Granite probably relates to the pattem of fluid circulation. Deformation was continuous throughout metasomatism, and fluid flow was strongly structurally controlled.
- Mt Isa
- Salt-rich fluids