The igneous petrogenesis and rare metal potential of the peralkaline volcanic complex of the southern Peak Range, Central Queensland, Australia

Chandler, Ross, and Spandler, Carl (2020) The igneous petrogenesis and rare metal potential of the peralkaline volcanic complex of the southern Peak Range, Central Queensland, Australia. Lithos, 358-359. 105386.

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Abstract

The Oligocene Peak Range Volcanics (PRV) of central Queensland have intruded through, and erupted onto, Permian sedimentary rocks of the Bowen Basin above what is likely to be a lithospheric-scale suture zone. The southern PRV consists of domes and flows of augite (bearing) trachyte, hornblende trachyte, hornblende rhyolite, arfvedsonite rhyolite and aegirine rhyolite. The aegirine rhyolite bodies represent the most evolved rock types, with peralkaline index (molar Na + K/A) values of N1.3 and extreme enrichment in trace elements, including the rare metals Zr, Hf, Nb, Ta, and REE. Clarrys Dome, one of three aegirine rhyolite domes, features a late stage magmatic agpaitic assemblage of dalyite (K2ZrSi6O15), a eudialyte-likemineral and aegirine, which is variably replaced and overprinted by secondary REE carbonates and Zr silicates.

Major and trace element geochemistry are used to show that the suite of PRV rock types represent a fractionation sequence from the least evolved augite trachytes to themost evolved aegirine rhyolites. This rock type range can be modelled by extended alkali-feldspar-dominated fractional crystallisation of an alkali basalt parental melt at a shallowcrustal levels. Initial epsilon(Nd) values across the range of rock types are between +3 to +4, which is consistent with a common mantle source. Thus, the extreme trace element enrichment and high peralkalinity of the aegirine rhyolites is the product of the extended fractionation of a melt formed by low-degree partial melting of a mildly depleted mantle source. The secondary ore mineral assemblage and REE redistribution observed in the core of Clarrys Dome is interpreted to be due to a combination of hydrothermal alteration by fluids derived from subjacent devolatilising magma bodies, and late-stage weathering.

The extreme enrichment of rare metals in the aegirine rhyolite bodies in the southern PRV support their potential to represent low grade, but large tonnage (100 s of Mt) resources of rare metals. Clear evidence of hydrothermal alteration across the region also raised the potential that higher grade rare metal mineralisation produced by hydrothermal activity may exist in the region.

Item ID: 63087
Item Type: Article (Research - C1)
ISSN: 0024-4937
Keywords: Peak Ranges, Peralkaline rhyolite, Rare metals, Agpaitic, Crystal fractionation, Rare earth elements
Copyright Information: © 2020 Elsevier B.V. All rights reserved.
Funders: Australian Research Council (ARC)
Projects and Grants: ARC FT 120100198
Date Deposited: 13 May 2020 07:36
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040304 Igneous and Metamorphic Petrology @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840107 Titanium Minerals, Zircon, and Rare Earth Metal Ore (e.g. Monazite) Exploration @ 50%
97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 50%
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