Low-latitude meteoric fluid flow along the Cloncurry Fault, Cloncurry district, NW Queensland, Australia: geodynamic and metallogenic implications

Abstract

Hydrothermal alteration within the Mount Isa Block (MIB) is typically largely to have ceased at the end of the Isan Orogeny (ca. 1.50 Ga). However, late, large brittle quartz-rich vein systems, including those of the Cloncurry Fault, cut Mesoproterozoic tectonic fabrics, intrusions and products of regional Na–Ca hydrothermal alteration. Associated features display affinities to iron oxide–Cu–Au ore deposits, including specular hematite-bearing veins and Cu–(Au–U–LREE–Ba) mineralization. Stable isotope data suggest late veins in the vicinity of the Cloncurry Fault, Eastern Fold Belt (EFB), formed from fluids with δ18OH2O and δDH2O (250 °C) of −4‰ to +3‰ and −22‰ to −4‰, respectively. The high δDH2O, moderate δ18OH2O and CaCl2–NaCl-rich character of the saline fluids indicates they were mixtures of low-latitude meteoric fluids and evaporite-derived basinal brines, which, with time, became progressively dominated by meteoric water, deposited barite and cooled.

The low-latitude meteoric signature demonstrates that the fault-fracture systems were active when in equatorial regions. Paleomagnetic data for the MIB, and the Australian protocontinent, together with structural and thermal considerations, and geochronological arguments suggest the veins probably formed sometime after 1.10 Ga, and potentially as late as during the Alice Springs Orogeny (ca. 0.34 Ga). The late quartz veining was unrelated to two phases of regional Na–Ca alteration and economically significant Fe oxide–Cu–Au mineralization at 1.60–1.58 and 1.53–1.50 Ga.