Natural factors and mining activity bearings on the water quality of the Choapa basin, North Central Chile: insights on the role of mafic volcanic rocks in the buffering of the acid drainage process

Abstract

This contribution analyzes water chemical data for the Choapa basin, North Central Chile, for the period 1980-2004. The parameters considered are As, Cu Fe, pH, EC, SO₄⁻², Cl⁻¹, and HCO[Formula: see text], from samples taken in nine monitoring stations throughout the basin. Results show rather moderate contents of As, Cu, and Fe, with the exception of the Cuncumén River and the Aucó creek, explained by the influence of the huge porphyry copper deposit of Los Pelambres and by the presence of mining operations, respectively. When compared against results obtained in previous researches at the neighboring Elqui river basin, which host the El Indio Au-Cu-As district, a much reduced grade of pollution is recognized for the Choapa basin. Considering the effect of acid rock drainage (ARD)-related Cu contents on the fine fraction of the sediments of both river basins, the differences recorded are even more striking. Although the Los Pelambres porphyry copper deposit, on the headwaters of the Choapa river basin, is between one and two orders of magnitude bigger than El Indio, stream water and sediments of the former exhibit significantly lower copper contents than those of the latter. A main factor which may explain these results is the smaller degree of H( + )-metasomatism on the host rocks of the Los Pelambres deposit, where mafic andesitic volcanic rocks presenting propylitic hydrothermal alteration are dominant. This fact contrast with the highly altered host rocks of El Indio district, where most of them have lost their potential to neutralize ARD.

Surface water quality in a sulfide mineral‐rich arid zone in North‐Central Chile: Learning from a complex past, addressing an uncertain future

“…For water quality sampling, the record exhibits a rather variable time frequency, but in general, they were carried out monthly or bimonthly, previous to and following 2004, respectively. Details associated with chemical analyses conducted by the DGA are described in Oyarzun et al () and Parra et al (). For trend analysis (described below), records of parameters having concentrations less than the detection limit (i.e., censored values) were replaced by that limit.…”

Response of suspended sediment particle size distributions to changes in water chemistry at an Andean mountain stream confluence receiving arsenic rich acid drainage

“…For example, the fate and speciation of iron, zinc, copper, lead, silver, arsenic, antimony, gold, and tin at the Rio Tinto and Rio Odiel in the Iberian Pyrite Belt (Spain) showed a strong dependency on seasonal changes (e.g., winter floods) and pH (ranging from 2.3 to 3.6), which controls the flux and partitioning of toxic metals into the Gulf of Cadiz (Braungardt, Achterberg, Elbaz‐Poulichet, & Morley, ). The connection between geological factors, mining operations, hydrology, and arsenic enrichment in sediments from the Elqui River watershed in northern Chile was described by several works (Galleguillos, Oyarzun, Maturana, & Oyarzun, ; Oyarzun et al, ; Oyarzun, Lillo, Higueras, Oyarzun, & Maturana, ; Oyarzun et al, ; Oyarzun, Oyarzun, Lillo, Maturana, & Higueras, ; Parra et al, ; Ribeiro et al, ). Galleguillos et al () reported that sedimentation at hydraulic facilities was used to attenuate the flux of arsenic in the upper Elqui watershed.…”

Developing tools to evaluate the environmental status of Andean basins with mining activities

“…Cu and Mn peaks obtained at Ll5 had maximum values of 59.5 and 22.5 mg/L, respectively. These values are higher at the Jequetepeque basin than those obtained from rivers located near mine sites worldwide, such as the Andean region, Asia, or Europe (Miller et al, 2004;Lin et al, 2007;Parra et al, 2011;Tarras Wahlberg and Nguyen, 2008;Sarmiento et al, 2011) and similar to values obtained at rivers affected by Rio Tinto Mine in Spain.…”