Characteristics of Cu isotopes from chalcopyrite-rich black smoker chimneys at Brothers volcano, Kermadec arc, and Niuatahi volcano, Lau basin

• Published in: Mineralium deposita 2015-10, Vol.50 (7), p.811-824
• Main Authors: Berkenbosch, H. A., de Ronde, C. E. J., Paul, B. T., Gemmell, J. B.
• Format: Article
• Language: English
• Subjects: Chemical analysis; Copper; Earth and Environmental Science; Earth Sciences; Fractionation; Geology; High temperature; Isotope fractionation; Isotopes; Metamorphism; Mineral Resources; Mineralogy; Ocean floor; Seawater; Volcanoes; Water analysis
• ISSN: 0026-4598; 1432-1866
• DOI: 10.1007/s00126-014-0571-y

We 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 δ 65 Cu = −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 δ 65 Cu values as representing a mantle source for the chimney Cu, in agreement with δ 65 Cu values for mantle rocks. The few higher δ 65 Cu 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 (