Rhenium–osmium systematics of the Mount Isa copper orebody and the Eastern Creek Volcanics, Queensland, Australia: implications for ore genesis

Magmatic history of the Eastern Creek Volcanics, Mt Isa, Australia: insights from trace-element and platinum-group-element geochemistry

“…titanium-rich phase which was retained in the mantle during melting in a hydrous environment such as that produced by the metasomatism of the mantle by slabderived fluids during subduction (Brenan et al 1994). The subduction-modified mantle source implied by trace-element trends is consistent with the subcontinental lithospheric mantle source for the Eastern Creek Volcanics suggested by Scott et al (2000) and Gregory et al (2008). Scott et al (2000) interpreted the mafic volcanics of northern Australian Proterozoic terranes including the Eastern Creek Volcanics as the product of melting in the subcontinental lithospheric mantle.…”

“…The observed geochemical trends in the basalts of the Eastern Creek Volcanics can be explained by melting a source in the subcontinental lithospheric mantle that had been previously depleted by partial melt extraction; the previous melt depletion may have occurred during the subduction-related assembly of the Mt Isa Inlier prior to ca 1.95 Ga (McDonald et al 1997;Gregory et al 2008). Melt extraction would have left this mantle material strongly depleted in S, but mildly enriched in the PGE and Cu (Hamlyn et al 1985).…”

“…Furthermore, a Re-depletion age of ca 1.95 Ga suggested the mantle source below the Mt Isa Inlier had undergone a significant melting event at ca 1.95 Ga that modified the mantle composition prior to the melting event related to the extrusion of the Eastern Creek Volcanics (Gregory et al 2008). The age of this melt-depletion event coincides with other isotopic constraints (McDonald et al 1997), which suggest that the Mt Isa Inlier was undergoing accretion involving a major subduction zone at ca 1.95 Ga. McDonald et al (1997) interpreted trace-element signatures, Nd model ages and SHRIMP U-Pb zircon crystallisation ages in felsic rocks of the KalkadoonLeichhardt Belt to suggest that their protoliths were formed as the result of arc magmatism and episodic subduction along the eastern margin of the North Australian Craton between 2.5 and 1.97 Ga, prior to the Barramundi Orogeny at ca 1.89 Ga (Page & Williams 1988).…”

Geology and Mineralogy of Uranium Deposits from Mount Isa, Australia: Implications for Albitite Uranium Deposit Models

“…Nearly all the uranium deposits of the Mount Isa uranium district are hosted by the Eastern Creek Volcanics (ECV) a 7 km thick sequence of extrusive metabasalt layers up to 100 m thick with interbedded metasediments (Figure 1) [6]. Re-Os dating of weakly metamorphosed ECV metabasalt returned an isochron of 1.83 ± 0.05 Ga, probably the best estimate of extrusion age [10]. Rocks of the ECV are intruded by the Sybella batholith dated by U-Pb zircon at 1657 ± 7 Ma [11].…”

Paleomagnetism of the Mt Isa Zn–Pb–Cu–Ag and George Fisher Zn–Pb–Ag deposits, Australia

“…Gregory et al (2008) interpreted the 1372 + 41 Ma age to record a major hydrothermal event at Mt Isa that deposited the chalcopyrite mineralisation, although they also mentioned the possibility that Re-Os isotopes from the Urquhart Shale mixed with those from the ore-forming fluid. Our paleomagnetic results support the alternative mixing model for the 1372 + 41 Ma Re-Os age because the paleopole position at 208N, 598E (A95 ¼ 178) from ca 1360 Ma Morawa Lavas in Australia (Idnurm & Giddings 1988) is significantly different at 95% confidence from the combined Mt Isa and George Fisher pole position at 73.18S, 112.08E (A95 ¼ 7.68).…”