An overview of the relationship between granitoid intrusions and gold mineralisation in the Archaean Murchison Province, Western Australia

Abstract

Abstract. In the Archaean Murchison Province of Western Australia, granitoid batholiths and plutons that intruded into the ca. 2.7-2.8 Ga and ca. 3.0 Ga greenstone belts can be divided into three major suites. Suite I is a ca. 2.69 Ga monzogranite-granodiorite suite, which was derived from anatexis of old continental crust and occurs as syn-tectonic composite batholiths over the entire province. Suite II is a trondhjemite-tonalite suite (termed Itype) derived from partial melting of subducted basaltic crust, which intruded as syn-to late-tectonic plutons into the greenstone belts in the northeastern part of the province where most of the major gold deposits are situated. One of the Suite II trondhjemite plutons has a Pb-Pb isochron age of 2641 ___ 36 Ma, and one of the structurally youngest tonalite plutons has a minimum Pb-Pb isochron age of 2630.1 _ 4.3 Ma. Suite III is a ca. 2.65-2.62 Ga A-type monzogranite-syenogranite suite which is most abundant in the largely unmineralised southwestern part of the province. Gold deposits in the province are mostly hosted in brittle-ductile shear zones, and were formed at a late stage in the history of metamorphism, deformation and granitoid emplacement. At one locality, mineralisation has been dated at 2636.8 _ 4.2 Ma through a pyritetitanite Pb-Pb isochron. Lead and Sr isotope studies of granitoids and gold deposits indicate that, although most gold deposits have initial Pb isotope compositions most closely similar to those of Suite II intrusions, both Suite I and Suite II intrusions or their source regions could have contributed solutes to the ore fluids. These preliminary data suggest that gold mineralisation in the Murchison Province was temporally and spatially associated with Suite II 1-type granitoids in the northeastern part of the province. This association is consistent with the concept that Archaean gold mineralisation was related to convergent-style tectonic settings, as generation of both Suite II I-type granitoids and hydrothermal ore fluids could have been linked to the dehydration and partial fusion of subducted oceanic crust, and old sialic crust or its anatectic products may also contribute solutes to the ore fluids. Integration of data from this study with other geological and radiogenic isotope constraints in the Yilgarn Block argue against direct derivation of gold ore fluids from specific I-type granitoid plutons, but favour a broad association with convergent tectonics and granitoid magmatism in the late Archaean.

Review of the application of isotopic studies to the genesis of Cu‐Au mineralisation at Olympic Dam and Au mineralisation at Porgera, the Tennant Creek district and Yilgarn Craton

“…These are the Victory mine at Kambalda (Clark et al 1988), the Griffins Find deposit, located in the Southwestern Gneiss Terrane (Barnicoat et al 1991) and the Reedys deposit in the Murchison Province (Wang et al 1993). In total, there are seven deposits where the age of mineralisation is considered to be known (Table 1).…”

Constraints on the age of granitoid emplacement, metamorphism, gold mineralization, and subsequent cooling of the Archean greenstone terrane at Big Bell, Western Australia

“…The granitoid plutons of the province have been subdivided petrographically into an early suite of foliated and recrystallized granodiorites to monzogranites, constituting most of the the batholiths, and into two post-tectonic suites of unmetamorphosed diorite-granodiorite-tonalite and monzogranitesyenogranite stocks (Watkins and Hickman, 1990;Wang et al, 1993). Recent U-Pb zircon ages indicate that the established relative time frame needs to be revised (Wiedenbeck and Watkins, 1993;Schi0tte and Campbell, 1996).…”

“…The combined field and geochronologic data establish that the Big Bell orebodies formed by replacement after the peak of metamorphic recrystallization in the greenstone terrane, and indicate that two separate events of gold-sulfide-scheelite mineralization are present. The age of main gold mineralization (2662 _+ 5 Ma) at Big Bell is older than all previous ages obtained froln gold deposits in the Yilgarn eraton, which range froln 2639 _+ 4 to 2602 + 8 Ma (Clark et al, 1989;Barnicoat et al, 1991;Wang et al, 1993;Kent and Mc Dougall, 1995). The latter ages are based on the U-Pb, Pb-Pb, and K-Ar systems in hydrothermal titanire, rutile, and muscovite.…”

SHRIMP U-Pb geochronological constraints on Archean volcanic-hosted massive sulfide and lode gold mineralization at Mount Gibson, Yilgarn Craton, Western Australia

“…The geochemistry of the northeast granite porphyry ( Table 1) is typical of the Murchison Suite II post-tectonic granitoids defined by Watkins and Hickman (1990), which lie 'along a calc-alkaline trend toward fractionated K-rich compositions Average analyses (*) for M urchison recrystallized monzogranite and post-tectonic granitoid (Suite II) are given for comparison; regional data taken from Wang et al (1993) on an Na•20-K20-CaO ternary diagram (Fig. 3).…”