The Tarcoola Goldfield of the Central Gawler Gold Province, and the Hiltaba Association Granites, Gawler Craton, South Australia

Abstract

The Tarcoola Goldfield, central South Australia, is one of a number within the Central Gawler Gold Province (CGGP) spatially related to Hiltaba Suite granites. This study investigates the origin of mineralisation at Tarcoola, and the petrogenesis of granites at and around Tarcoola. ‘Hiltaba Suite’ granites in the Tarcoola region are assigned to two supersuites, which is expanded to four once granites from the rest of the Gawler Craton are considered. The term Hiltaba Association Granites (HAG) is introduced as the parental unit of the Jenners, Malbooma, Venus and Roxby Supersuites. These criteria are applied to the felsic parts of the comagmatic Gawler Range Volcanics (GRV). The HAG and GRV are grouped as the bimodal Gawler Ranges–Hiltaba Volcano–Plutonic (GRHVP) Association. The felsic components generally have high K, HFSE, LIL, are fractionated and evolved, have moderate to high Fe/Mg, are slightly alkaline, metaluminous to slightly peraluminous, slightly oxidised and high-temperature. The supersuites of the Tarcoola region are the Malbooma Supersuite, which is more strongly evolved and fractionated than the Jenners Supersuite. Both Supersuites are I-type and evolved from a granodiorite composition by fractional crystallisation. The Pegler and Ambrosia Granites (Jenners Supersuite), and are dated at 1591.7 ± 5.8 and 1575.4 ± 7.8 Ma. The Big Tank, Kychering and Partridge Granites (Malbooma Supersuite), and are dated at 1589.9 ± 7.4, 1574.7 ± 4.3 and 1577 ± 8.5 Ma. The Roxby and Venus Supersuites are A-type granites and volcanics, with higher HFSE, F, and zircon saturation temperatures than the I-types. Nd-isotope data indicate that the felsic GRHVP formed by mixing between evolved mantle and crust. Narrow dykes of the high-K Lady Jane Diorite intrude the Tarcoola Goldfield. This unit, and other basalts of the GRHVP, are interpreted to represent mixing between evolved lithospheric and primitive asthenospheric mantle melts. The Paxton Granite at the Tarcoola Goldfield was dated as older than the HAG at ~1720 Ma. The Tarcoola Formation was deposited in an ensialic basin directly onto the Paxton, with the basal Peela Conglomerate Member contains zircons of 1732.8 ± 5.1 Ma and 1714.6 ± 7.9 Ma, and the middle parts of the Tarcoola Formation being deposited at 1656 ± 7 Ma. Mineralisation at the Tarcoola Goldfield is quartz-vein hosted within the Tarcoola Formation, and comprises Au±Pb-Zn. The veins are structurally-controlled. 40Ar/39Ar geochronology and field relationships show that brittle veining, mineralisation, alteration and intrusion of the Lady Jane Diorite, occurred synchronously at ~1580 Ma. A Pb-Pb isotope study at the Tarcoola Goldfield is consistent with sourcing of Pb from the Paxton Granite, but does not exclude a mixed source. A shift in Nd during alteration may show an input from the relatively primitive Lady Jane Diorite. An atlas shows correlations between the four supersuites and the two defined mineral provinces of the Gawler Craton. Notably the Roxby Supersuite is associated nearly exclusive with iron-oxide copper-gold mineralisation in the Olympic Cu-Au Province in the eastern part of the Craton. The I-type Jenners and Malbooma Supersuites are mostly restricted to the CGGP. A position inboard of a subduction zone (hot continental back-arc) rather than anorogenic setting is proposed. Show more