Native copper in DSDP sediment cores from the Angola Basin

Abstract

LEG 40 of the Deep Sea Drilling Project (DSDP) drilled two holes in the Angola Basin: site 364 and site 365 (Fig. 1). Native copper was found in two samples (364-5-2, 19–21 cm and 364-5-2, 22-24 cm) from one of the cores taken at site 364. The botryoidal form of most of the copper grains initially suggested formation in situ and the subsequent discovery of copper casts of planktonic foraminifera removed any lingering thoughts of contamination. This is not the first report of native copper in DSDP cores. Most other occurrences have, however, been found in basement rocks (for example, site 282) or in the sediments immediately overlying basement rocks (site 105), whence the copper was presumably derived. The copper reported here occurs at least 3 km above volcanic basement rocks, and no copper has yet been found in samples above or below it. Only at site 149 (Venezuelan Basin) has copper previously been found in non-basement-associated sediments. There it occurs as “a number of very small metallic incrustations” in one core of pelagic clay1.