Copper isotopes tracing metal transport and concentration at the Whakaari embryonic porphyry copper deposit
Date
2023
Authors
Tilby, J. T.
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Abstract
The genesis of porphyry copper deposits (PCD) is difficult to study due volcanic destruction and intense alteration. The stratovolcano Whakaari, in New Zealand, provides a modern analogue of an embryonic PCD, with early-stage transport and concentration mechanisms ongoing and recorded in the rock record. Copper isotope fractionation is heavily influenced by changeable REDOX conditions and fluid interactions, which are thought to be primary processes in PCD formation; copper isotopes present as a powerful tracer of formation mechanisms. A suite of lava samples and crater lake sediments are analysed for comparison between igneous processes and a primary hydrothermal endmember. This study uses whole rock major and trace element analysis, copper isotope analysis and petrography. δ65Cu values range between -0.11‰ and 0.59‰, with all but one sample being considered isotopically heavy. The range of values are not representative of a mantle source and indicate that there are processes affecting copper transport outside of magma ascent. δ65Cu values show insignificant correlation between rock evolution, and do not conform to Rayleigh fractionation modelling that would be indicative of transport via igneous processes. Values are consistent with those expected of sulphide minerals deposited from magmatic brines and are observed in several of the lava samples and sediments. Cu isotope analysis furthers our understanding of metal transport processes at Whakaari and can be applied to a broader understanding of porphyry copper genesis. Analysis of additional hydrothermal endmembers, combined with Sn, Fe and Zn isotopes to investigate REDOX conditions, will supplement the findings presented in this study.
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School of Physical Sciences
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Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, YEAR
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