Anthropogenic and authigenic uranium in marine sediments of the central Gulf of California adjacent to the Santa Rosalía mining region

Abstract

To investigate the causes of uranium (U) enrichment in marine sediments in the eastern sector of the Gulf of California, surface sediments and sediment cores were collected adjacent to the Santa Rosalı´a copper mining region in the Baja California peninsula. Three coastal sediment cores were found to display high concentrations of U (from 54.2 ± 7.3 mg kg-1 to 110 ± 13 mg kg-1) exceeding those found in the deeper cores (1.36 ± 0.26 mg kg-1 in the Guaymas Basin to 9.31 ± 3.03 mg kg-1 in the SR63 core from the suboxic zone). The contribution of non-lithogenic U (estimated using scandium to normalize) to the total U content in sediments of three coastal cores varied from 97.2 ± 0.4 % to 98.82 % versus 49.8 ± 3 % (Guaymas Basin) to 84.2 ± 8.2 % (SR62 core) in the deeper cores. The U content record in a lead-210 (210Pb)-dated core had two peaks (in 1923 and 1967) corresponding to the history of ancient mining and smelting activities in Santa Rosalía.