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TitleComparison of groundwater composition from the Monturaqui and Punta Negra basins, northern Chile: implications for porphyry copper exploration
AuthorRissmann, C W FORCID logo; Leybourne, M IORCID logo; Benn, C; Kidder, J AORCID logo; Pearson, L K
SourceGeochemistry: Exploration, Environment, Analysis vol. 22, 2022 p. 1-15,
Alt SeriesNatural Resources Canada, Contribution Series 20210244
PublisherGeological Society of London
Mediapaper; digital; on-line
File formatpdf
Lat/Long WENS -69.1000 -68.3000 -24.3000 -24.7000
Subjectsmineralogy; geochemistry; groundwater; porphyry deposits; porphyry copper; molybdenum; selenium; hydrogeochemistry; exploration; mineral exploration; evaporites
Illustrationslocation maps; geological sketch maps; plots; ternary diagrams; tables
Released2022 02 14
AbstractGroundwaters recovered from the Salar de Punta Negra and Monturaqui basins in the Atacama Desert of northern Chile exhibit distinctly different isotopic, major, trace, and porphyry copper elemental compositions related to contrasting morphostructural, geochemical, and hydrodynamic settings. Comparison of these distinct groundwater signatures with groundwaters fromknown porphyry copper deposits (Salar de Hamburgo and Spence Deposit), can be used to determine if either basin might be prospective for porphyry copper mineralization. Groundwaters within the Punta Negra Basin exhibit geochemical characteristics consistent with other closed basin settings throughout the arid Andes. Elemental and isotopic compositions within the Punta Negra Basin reflect closed basin evaporitic processes consistent with the hyperarid, volcanic setting of the central Andes. Pathfinder metals and isotopic compositions are not consistent with porphyry copper type mineralization as described for groundwaters within the Salar de Hamburgo Basin, and the Spence Deposit. Within the Monturaqui Basin the geochemical composition of groundwaters are characteristic of diffuse hydrothermal activity. Sulfur isotopic composition within thewaters of the northern Monturaqui Basin exhibit d34SCDT isotopic signatures that fall within the range for sulfide mineralization as reported for groundwaters in and around the Spence Deposit and the Salar de Hamburgo. However, porphyry copper related elements within the Monturaqui Basin are impoverished relative to groundwaters of the Spence and Escondida Deposit. Such impoverishment in porphyry related elements, taken in conjunction with enriched d13CPDB compositions, elevated groundwater temperatures, groundwater compositions dominated by HCO3, SO4, and Si, and the proximity of the Monturaqui Basin to the current magmatic arc are consistent with a volcanic hydrothermal origin. In summary, the groundwater geochemistry of the Monturaqui and Punta Negra Basins are not indicative of porphyry copper-type mineralization.
Summary(Plain Language Summary, not published)
Mineral exploration is notoriously difficult in areas where bedrock hosted metal deposits are obscured by transported materials. In hyper arid northern Chile the bedrock is partly obscured by 10's of meters of Atacama gravels and groundwater interaction between waters and mineral deposits can result in the dispersion of dissolved metals, which can be an effective tool for mineral exploration. This study provides interpretive tools to differentiate geochemical signatures of base metal deposits form other background solute sources.

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