Giant metasomatic system formed during exhumation of mid‐crustal Proterozoic rocks in the vicinity of the Cloncurry Fault, northwest Queensland

Abstract

A giant alteration system including approximately 200 km2 of rocks dominated by the secondary mineral assemblages lies near the prominent lineament formed by the Cloncurry Fault in the southeast of the Proterozoic Mt Isa Inlier. Alteration affected rocks that had previously undergone sillimanite zone metamorphism under pressures of at least 300 MPa. The main lineament was produced by postorogenic brittle transcurrent motion with limited displacement. It exploits older D1 faults and occupies different structural positions within F2 fold limbs that were reactivated as late/post‐D2 shear zones. Metasomatism and vein emplacement occurred under a range of retrograde conditions during the transition from a compressional regime in a ductile regional metamorphic environment, through late‐ to post‐orogenic granitoid emplacement, and ultimately high‐level brittle faulting. The dominant sodic‐calcic alteration occurred in multiple overprinting fluid buffered systems at 400–500°C with pressures initially above 200 MP...