Exploration potential of Cu isotope fractionation in porphyry copper deposits
We examined the copper isotope ratio of primary high temperature Cu-sulfides, secondary low temperature Cu-sulfides (and Cu-oxides) as well as Fe-oxides in the leach cap, which represent the weathered remains of a spectrum of Cu mineralization, from nine porphyry copper deposits. Copper isotope rati...
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Veröffentlicht in: | Journal of geochemical exploration 2009-07, Vol.102 (1), p.1-6 |
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Sprache: | eng |
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Zusammenfassung: | We examined the copper isotope ratio of primary high temperature Cu-sulfides, secondary low temperature Cu-sulfides (and Cu-oxides) as well as Fe-oxides in the leach cap, which represent the weathered remains of a spectrum of Cu mineralization, from nine porphyry copper deposits. Copper isotope ratios are reported as
δ
65Cu‰
=
((
65Cu/
63Cu
sample/
65Cu/
63Cu
NIST 976 standard)
−
1) ⁎ 10
3. Errors for all the analyses are ±
0.14‰ (determined by multiple analyses of the samples) and mass bias was corrected through standard-sample-standard bracketing. The overall isotopic variability measured in these samples range from −
16.96‰ to 9.98‰.
Distinct Cu isotopic reservoirs exist for high temperature hypogene, enrichment, and leach cap minerals. Chalcopyrite from high temperature primary mineralization forms a relatively tight cluster of
δ
65Cu values of 1‰ to −
1‰ whereas secondary minerals formed by low temperature reveal a range of
δ
65Cu values from −
16.96‰ to 9.98‰. Secondary chalcocite is relatively heavy with
δ
65Cu varying from −
0.3‰ to 6.5‰. Leach cap minerals dominated by Fe-oxides (jarosite, hematite and goethite) are relatively light ranging from −
9.9‰ to 0.14‰. Although the dataset is relatively small (
n
=
50 total minerals analyzed), a combination of these data with values from previously published reports [Zhu, X.K., O'Nions, R.K., Guo, Y., Belshaw, N.S. and Rickard, D., 2000. Determination of natural Cu-isotope variation by plasma-source mass spectrometry; implications for use as geochemical tracers. Chemical Geology, 163(1–4): 139–149.;
Larson et al., 2003; Mathur, R. et al., 2005. Cu isotopic fractionation in the supergene environment with and without bacteria. Geochimica et Cosmochimica Acta, 69(22): 5233–5246.; Markl et al., 2006, and Maher et al., 2007], show a distinct pattern of heavier isotopic signature in supergene samples and a lighter isotopic signature exists in the leach cap and oxidation zone minerals. The pattern could be used as a tool for exploration geology by providing the following information: 1) Identification of highly fractionated copper isotope ratios in copper sulfide and Fe-oxide samples that indicate supergene processes and the extent of leaching and enrichment copper 2) Identification of highly fractionated copper isotope ratios in surface and/or groundwaters that indicate the active weathering copper sulfides that experienced significant enrichment
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ISSN: | 0375-6742 1879-1689 |
DOI: | 10.1016/j.gexplo.2008.09.004 |