URL: https://geoscience.data.qld.gov.au/dataset/cr137388
Oxidation of copper sulfide minerals during weathering generates uniquely heavier copper isotope signatures in solutions (higher relative proportion of 65Cu to 63Cu). This reaction has the potential to be used as a mineral exploration tool. In this contribution, we apply this technique to saline groundwater samples with low copper concentrations (less than 1 ppb, with the mean values at 250 part per trillion) in the Mount Isa Block. Given the high salt content and low copper concentration of the groundwater samples, several chemical separation techniques were tested, and a new method was developed that eliminates unwanted ions in the measured solution. A spatial analysis of 42 samples reveals that copper isotope compositions in groundwater near mineralisation record a range of values (delta65Cu= 1.2 to 4.4 per mil) that mimics known waters derived from chalcopyrite and/or chalcocite weathering from 6 deposits that range from -1 to +3 per mil. Water located off known deposits has either higher or lower copper isotopic values. The wide range of values potentially reflects all known processes that cause copper isotopic fractionation, however the geographic congruence of known mineralisation overlapping with predicted copper isotopic fractionation induced by sulfide weathering implies that sulfide oxidation generated these copper isotope values. The data demonstrate the utility of copper isotope measurements in groundwater as a technique to identify sulfide weathering associated with mineralisation under cover.
Bibliographic reference: Mathur, R., Mahan, B., Godfrey, L., Degeling, H., Tang, J., Dirks, P., Rea, P., Paitl, K., Lasinsky, C. A technique for measuring copper isotopes in low concentration (parts per trillion) salts derived from dried Mount Isa inlier groundwaters. Queensland Geological Report 2023/01.
ISSN 2206-0340
ISBN 978-1-9256-0941-7