The hydrochemistry characteristics of the Andalgalá river basin (province of Catamarca, Argentina) are
analyzed in the present study. In this zone there are metal sulphide deposits which could generate acid
mine drainage (AMD). The analyzed information has come fundamentally from the Program of Quality of
Water of the companies that have explored the zone since 1995. Many of the records of water quality
analyzed included systematic errors and have been discarded. Two types of hydrochemistry facies are
observed: 1) in the Minas subbasin, where the sulphide deposits outcrop, the water is sulphate calcium,
with low values of pH and elevated concentrations of metals due to a natural process of sulphide oxidation
(acid rock drainage or ARD) and 2) in the rest of the basin the water is bicarbonate calcium type, with a
low alkalinity due to the carbonated mineral absence in the zone. Due to the lower flow, the acid
contribution of the Minas river is neutralized when mixing with other tributaries, so that when coming out
of the river basin the water quality is acceptable. However, an increase in the acidity transported by the
Minas river by the exploitation of sulphide deposits could jeopardize the current water uses, including
supplying a population of 14,000 inhabitants
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