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Porphyry fertility in the Northparkes district: indicators from whole-rock geochemistry

Citation

Wells, TJ and Meffre, S and Cooke, DR and Steadman, JA and Hoye, JL, Porphyry fertility in the Northparkes district: indicators from whole-rock geochemistry, Australian Journal of Earth Sciences ISSN 0812-0099 (2020) [Refereed Article]

Copyright Statement

Copyright 2020 Geological Society of Australia

DOI: doi:10.1080/08120099.2020.1715477

Abstract

Four economic porphyry Cu–Au deposits and several prospects have been investigated in the Northparkes district, part of the Ordovician to early Silurian Junee–Narromine Belt of the Macquarie Arc, New whole-rock geochemical data from the Northparkes porphyry Cu–Au district, NSW, indicate that the mineralising intrusive complexes exhibit distinct arc signatures that are transitional from high-K calc-alkaline to silica-saturated alkalic. Based on ratios of Sr/Y vs Y (e.g. Sr/ Y > -20 and Y < -17ppm) the mineralising intrusions are interpreted to have crystallised from fractionated hydrous melts indicating the suppression of plagioclase crystallisation in favour of hydrous mineral phases. This interpretation is supported by listric-shaped rare earth element curves and the presence of primary hornblende phenocrysts indicating elevated magmatic water contents. There is an association of mineralising intrusions with a low Zr trend both in the mineralised Northparkes district intrusive rocks and in mineralised porphyry-related intrusive rocks globally. A newly developed fertility indicator ratio Zr/Y -10% is more accurate at identifying the mineralised rocks at Northparkes than the conventional Sr/Y vs Y fertility indicator diagram, successfully identifying 92% of the mineralising intrusions, mainly owing to the fact that it is less affected by hydrothermal alteration. The insensitivity of Zr–Y to alteration makes this indicator a useful new tool that may lead to enhanced probabilities for future discoveries in the Northparkes district, broader Macquarie Arc and altered rocks globally.

KEY POINTS

1. Mineralising intrusions in the Northparkes district have distinct Zr vs Y concentrations.

2. The Zr vs Y indicator of magmatic fertility is less sensitive to alteration than Srbased indicators.

3. The Zr vs Y magmatic fertility indicator identified at Northparkes is not unique and identifies mineralising intrusions in other porphyry fields.

Item Details

Item Type:Refereed Article
Keywords:macquarie arc, Northparkes, porphyry fertility, Ordovician intrusive rocks, prospectivity indicators
Research Division:Earth Sciences
Research Group:Geochemistry
Research Field:Exploration Geochemistry
Objective Division:Mineral Resources (excl. Energy Resources)
Objective Group:Mineral Exploration
Objective Field:Copper Ore Exploration
UTAS Author:Wells, TJ (Mr Tristan Wells)
UTAS Author:Meffre, S (Dr Sebastien Meffre)
UTAS Author:Cooke, DR (Professor David Cooke)
UTAS Author:Steadman, JA (Dr Jeffrey Steadman)
ID Code:137296
Year Published:2020
Deposited By:CODES ARC
Deposited On:2020-02-07
Last Modified:2020-04-08
Downloads:0

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