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Copper-gold fertility of arc volcanic rocks; a case study from the Early Permian Lizzie Creek volcanic group, NE Queensland, Australia

Helge Behnsen, Carl Spandler, Isaac Corral, Zhaoshan Chang and Paul H. G. M. Dirks
Copper-gold fertility of arc volcanic rocks; a case study from the Early Permian Lizzie Creek volcanic group, NE Queensland, Australia
Economic Geology and the Bulletin of the Society of Economic Geologists (December 2020) Pre-Issue Publication

Abstract

The Early Permian Lizzie Creek Volcanic Group of the northern Bowen Basin, NE Queensland, Australia, has compositions that range from basalt through andesite to rhyolite with geochemical signatures (e.g., enrichment in Cs, Rb, Ba, U, Th, and Pb, depletion in Nb and Ta) that are typical of arc lavas. In the Mount Carlton district the Lizzie Creek Volcanic Group is host to high-sulfidation epithermal Cu-Au-Ag mineralization, whereas farther to the south near Collinsville ( approximately 50 km from Mount Carlton) these volcanic sequences are barren of magmatic-related mineralization. Here, we assess whether geochemical indicators of magma fertility (e.g., Sr/Y, La/ Yb, V/Sc) can be applied to volcanic rocks through study of coeval volcanic sequences from these two locations. The two volcanic suites share similar petrographic and major element geochemical characteristics, and both have undergone appreciable hydrothermal alteration during, or after, emplacement. Nevertheless, the two suites have distinct differences in alteration-immobile trace element (V, Sc, Zr, Ti, REE, Y) concentrations. The unmineralized suite has relatively low V/Sc and La/Yb, particularly in the high SiO (sub 2) rocks, which is related to magma evolution dominated by fractionation of clinopyroxene, plagioclase, and magnetite. By contrast, the mineralized suite has relatively high V/Sc but includes high SiO (sub 2) rocks with depleted HREE and Y contents, and hence high La/Yb. These trends are interpreted to reflect magma evolution under high magmatic H (sub 2) O conditions leading to enhanced amphibole crystallization and suppressed plagioclase and magnetite crystallization. These rocks have somewhat elevated Sr/Y compared to the unmineralized suite, but as Sr is likely affected by hydrothermal mobility, Sr/Y is not considered to be a reliable indicator of magmatic conditions. Our data show that geochemical proxies such as V/Sc and La/Yb that are used to assess Cu-Au fertility of porphyry intrusions can also be applied to cogenetic volcanic sequences, provided elemental trends with fractionation can be assessed for a volcanic suite. These geochemical tools may aid regional-scale exploration for Cu-Au mineralization in convergent margin terranes, especially in areas that have undergone limited exhumation or where epithermal and porphyry mineralization may be buried beneath cogenetic volcanic successions.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: Pre-Issue Publication
Title: Copper-gold fertility of arc volcanic rocks; a case study from the Early Permian Lizzie Creek volcanic group, NE Queensland, Australia
Affiliation: James Cook University, Economic Geology Research Centre, Townsville, Queensl., Australia
Published: 20201228
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 83
Accession Number: 2021-011652
Categories: Economic geology, geology of ore depositsGeochemistry of rocks, soils, and sediments
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. col., 2 plates, 1 table, geol. sketch maps
S21°00'00" - S19°30'00", E146°30'00" - E148°04'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute.
Update Code: 2021
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