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Drainage geochemistry of the three main basins of the arid agricultural-mining Coquimbo region (Chile): Balance of a decade of studies, 2000-2010

Science et changements planétaires / Sécheresse. Volume 22, Number 4, 244-52, Octobre-Novembre-Décembre 2011, Articles de recherche

DOI : 10.1007/s10661-010-1814-8.

Résumé

Summary

Author(s) : Jorge Oyarzún, Hugo Maturana, Ricardo Oyarzún, Universidad de La Serena Departamento Ingeniería de Minas Casilla 539 Benavente 980 La Serena Chile, Centro de Estudios Avanzados en Zonas Aridas Raúl Bitrán s/n La Serena Chile.

Summary : This paper presents the results of a decade-long environmental geochemistry research program on the three watersheds of the arid Coquimbo Region, north central Chile, where mining and agriculture are the principal economic activities. The studies include water and sediment geochemistry. Among the principal conclusions of these studies are the extremely high Cu, and high As and Zn contents of the fine-grained fraction of the fluvial sediments of the northern, Elqui river watershed, which reaches an average of 0.1-0.2% Cu. These contents are related to acid drainage originating in the El Indio (gold-copper-arsenic) district located on the Andean head of the Elqui river basin and surrounded by advanced argillic hydrothermal alteration. It is, however, also due to the erosion of tailing deposits on the flank of major rivers and creeks, products of small to medium scale copper mining. The major copper-(molybdenum) ore deposit of the Region, the world-class Los Pelambres porphyry copper deposit, is located at the head of the southern Choapa river basin. Surprisingly, the Choapa river water and fine-grained sediments do not present high Cu or Mo contents. This fact is interpreted in terms of the dominant mafic rock types of the deposit, and its rather weak hydrothermal alteration, which have the potential to neutralize the generation of metallic - rich acid drainage.

Keywords : acid drainage, arid environment, international collaboration, water quality

Pictures

Figura 1 Región de Coquimbo, mostrando las tres cuencas consideradas en este trabajo y sus principales ríos, ciudades y zonas de actividad minera. E: embalse.

Figura 2 Río Toro, cuenca del Río Elqui. La costra blanca sobre las riberas está constituida por sulfatos producto del drenaje ácido.

Figura 3 Embalse Puclaro, curso medio del Río Elqui.

Figura 4 Curso superior del Río Grande, cuenca del Río Limarí.

Figura 5 Embalse de relaves “Quillayes”, Compañía Minera Los Pelambres, Río Cuncumén, cuenca del Río Choapa.