Native copper in ODP Site 642 tholeiites

Abstract

Native Cu occurs in amygdules, fractures and groundmass of tholeiites from Site 642 on the Voring Plateau. Similar occurrences have been reported in other tholeiites of the early Tertiary North Atlantic Volcanic Province drilled at Deep Sea Drilling Project Sites 342 on the Voring Plateau and 553 on the Rockall Plateau. The flows containing the native Cu have distinctive alteration patterns characterized by the combination of reddened flow tops, distinctive pastel coloration of the upper parts of the flows, relative abundance of celadonite, and the presence of native Cu. These associations suggest that subaerial weathering and subsequent seawater-basalt interaction are related to the occurrence of native Cu. An additional factor may be the increase in compatibility of Cu in silicates and Fe- Ti oxides that may accompany sub-solidus oxidation of basaltic flows. Native Cu occurrences in Site 642 tholeiites have some striking similarities to the large native Cu deposits in the Pre-cambrian basalts of the Keweenaw Peninsula, Michigan, that are suggestive of similar mineralization processes. -Author