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

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 greenschist- 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. [ABSTRACT FROM AUTHOR]