Lanthanide contamination and strong positive europium anomalies in the surface sediments of the Santa Rosalia copper mining region, Baja California Peninsula, Mexico.

摘要

A study was conducted to investigate the range of concentrations of rare earth elements (REEs) and characterize their shale-normalized signatures in different types of sedimentary materials from the mining region of Mexico and in the surface sediments of the adjacent Gulf of California. The average REE concentrations in the different sedimentary materials of the study area decreased in the order: solid wastes > copper mineral > beach sands > arroyo sediments > marine sediments. Lanthanum (La), a representative of light REE, was highest in arroyo sediments collected near abandoned mines (38-79 mg/kg) from deposits of solid wastes produced by copper ore smelting and in beach sands (208-289 mg/kg). The spatial distribution of ytterbium (Yb), a representative of heavy REE, showed almost the same pattern with that of La. The spatial distributions of La and Yb contents in marine sediment samples revealed the existence of two 'hot spots': Santa Rosalia harbour and deeper part of the Gulf of California, where the concentrations of these REEs were much higher than the values recorded for the sediments at the margin of the Santa Rosalia mining region. Results demonstrated the tendency of samples with high positive europium (Eu) anomaly to be related to the solid wastes of ore smelting and beach sands. Copper-bearing minerals and most of the samples from local arroyos, mining wastes and their derivatives - heavily contaminated black beach sands and polluted sediments from the impact zone (mainly Santa Rosalia harbour and vicinity) showed light REE enrichment and a positive Eu anomaly..