An overview of the relationship between granitoid intrusions and gold mineralisation in the Archaean Murchison Province,Western Australia |
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| Authors: | LG Wang N J McNaughton D I Groves |
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| Institution: | (1) Key Centre for Strategic Mineral Deposits, Department of Geology and Geophysics, University of Western Australia, 6009 Nedlands, WA, Australia |
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| 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 I-type) 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 I-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. |
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