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Characteristics of Cu isotopes from chalcopyrite-rich black smoker chimneys at Brothers volcano, Kermadec arc, and Niuatahi volcano, Lau basin
journal contribution
posted on 2023-05-18, 07:26 authored by Berkenbosch, HA, de Ronde, CEJ, Paul, BT, John GemmellJohn GemmellWe analysed primary chalcopyrite from modern seafloor ‘black smoker’ chimneys to investigate high-temperature hydrothermal Cu isotope fractionation unaffected by metamorphism. Samples came from nine chimneys collected from Brothers volcano, Kermadec arc, and Niuatahi volcano, Lau backarc basin. This is the first known study of Cu isotopes from submarine intraoceanic arc/backarc volcanoes, with both volcanoes discharging significant amounts of magmatic volatiles. Our results (n = 22) range from δ65Cu = −0.03 to 1.44 ± 0.18 ‰ (2 sd), with the majority of samples between ∼0.00 and 0.50 ‰. We interpret this cluster (n = 17) of lower δ65Cu values as representing a mantle source for the chimney Cu, in agreement with δ65Cu values for mantle rocks. The few higher δ65Cu values (>0.90 ‰) occur (1) within the same chimneys as lower values, (2) randomly distributed within the chimneys (i.e. near the top and bottom, interior and exterior), and (3) within chalcopyrite of approximately the same age (<1 year). This suggests the higher δ65Cu values are not related to oxidation by mixing with ambient seawater, but to isotopic variation within the vent fluids over a relatively short time. Theoretical studies demonstrate significant isotopic fractionation can occur between aqueous and vapourous complexing species. When combined with evidence for periodic release of magmatic volatiles at Brothers, we believe vapour transport of Cu is responsible for the observed isotopic fractionation. When compared to global δ65Cu data for primary chalcopyrite, volcanic arc chimneys are most similar to porphyry copper deposits that also form from magmatic-hydrothermal processes in convergent tectonic settings.
Funding
Australian Research Council
AMIRA International Ltd
ARC C of E Industry Partner $ to be allocated
Anglo American Exploration Philippines Inc
AngloGold Ashanti Australia Limited
Australian National University
BHP Billiton Ltd
Barrick (Australia Pacific) PTY Limited
CSIRO Earth Science & Resource Engineering
Mineral Resources Tasmania
Minerals Council of Australia
Newcrest Mining Limited
Newmont Australia Ltd
Oz Minerals Australia Limited
Rio Tinto Exploration
St Barbara Limited
Teck Cominco Limited
University of Melbourne
University of Queensland
Zinifex Australia Ltd
History
Publication title
Mineralium DepositaVolume
50Issue
7Pagination
811-824ISSN
0026-4598Department/School
School of Natural SciencesPublisher
Springer-VerlagPlace of publication
175 Fifth Ave, New York, USA, Ny, 10010Rights statement
Copyright 2015 Springer-Verlag Berlin HeidelbergRepository Status
- Restricted