Geochronological constraints on the polymetamorphic evolution of the granulite-hosted Challenger gold deposit: implications for assembly of the northwest Gawler Craton

Abstract

A temperature-time history for the granulite-hosted Challenger gold deposit in the Christie Domain of the Gawler Craton, South Australia, has been derived using a range of isotopic decay systems including U-Pb, Sm-Nd, Rb-Sr and 40Ar/39Ar. Nd model ages and detrital zircon ages suggest a protolith age of ca 2900 Ma for the Challenger Gneiss. Gold mineralisation was probably introduced under greenschist/amphibolite-facies conditions towards the end of the Archaean, between 2800 and 2550 Ma. However, evidence for the exact age and P-T conditions of this event was almost completely removed by granulite-facies metamorphism during the Sleafordian Orogeny, which peaked around ca 2447 Ma. Cooling to 350°C occurred before 2060 Ma. It is possible that the Christie Domain was then subject to further sedimentation and volcanism in the period ca 2000-1800 Ma before reburial and a second period of orogeny around ca 1710-1615 Ma. During this second orogeny, the eastern Christie Domain experienced heterogeneous fluid-induced retrograde metamorphism at lower green-schist- to amphibolite-facies conditions, with metamorphic grade varying between structural blocks. At this time, the Challenger deposit was subject to greenschist-facies conditions (not significantly hotter than 350°C), while at Mt Christie (50 km to the south) lower amphibolite-facies conditions prevailed and to the west the Ifould Block experienced extensive plutonism. A third very low-temperature thermal pulse around ca 1531 Ma, which reached ∼ 150-200°C, is recorded at the Challenger deposit. It is likely that the global Grenvillian Orogeny (1300-1000 Ma) was a major period of domain exhumation and juxtaposition. Show more