Influence of Preexisting Low Metamorphic Grade Sedimentary Successions on the Distribution of Iron Oxide Copper-Gold Mineralization in the Olympic Cu-Au Province, Gawler Craton

Abstract

The primary driver for mineralization in the Olympic Cu-Au province of the eastern Gawler craton, South Australia, was a major early Mesoproterozoic thermal event, partly manifest as extensive A-type, I-type, and mafic magmatism. Magmatism of this age is present across the Gawler craton and the Curnamona province to the east, yet hematite-rich, iron oxide copper-gold (IOCG) deposits are apparently restricted to a north-south belt along the eastern margin of the Gawler craton. Whereas geochemical differences between the early Mesoproterozoic granites in the eastern versus western Gawler craton appear to influence the type of mineralization in these regions, there are also stark differences in the nature of the rocks into which these magmas intruded. Metamorphic data from the Gawler craton and Curnamona province show that most of the western, southern, and northern Gawler craton underwent amphibolite- to granulite-facies metamorphism, either during a ca. 2465 to 2410 Ma event (Sleafordian orogeny), a ca. 1730 to 1690 Ma event (Kimban orogeny), or both. In contrast, across the eastern Gawler craton and Curnamona province, potentially evaporate-bearing sedimentary successions including the ca. 1750 Ma Wallaroo Group and ca. 1710 to 1640 Ma Willyama Supergroup, were largely unmetamorphosed prior to the early Mesoproterozoic magmatic and metallogenic event. Thus, a clear spatial partitioning of Paleoproterozoic orogenesis exists in the western, southern, and northern Gawler craton, including a broad spatial correlation between rocks of low metamorphic grade and the region of IOCG mineralization. Multiple fluid sources (e.g., sedimentary, metamorphic, and magmatic) were important in generating the chemistry suitable to precipitate Cu-Au-U-REE–bearing minerals in the Olympic Cu-Au province. Therefore, we suggest that the preservation of rocks at low metamorphic grade containing formation waters and porosity provided a fertile geochemical environment into which high-temperature, felsic and mafic magmas, and their associated hydrothermal cells were emplaced and developed. This example from the eastern Gawler craton and Curnamona province suggests that prior orogenic events can operate as a first-order control on the location of large mineral provinces.