Neoformation of exotic copper minerals from gel-like precursors at the Exótica deposit, Chuquicamata, Chile

Abstract At the Exótica deposit, south of giant porphyry copper deposit Chuquicamata (Atacama Desert, Chile), Cu-rich groundwater seeped out at several locations in open pit (Mina Sur) during sampling 2009–2011. their outflows, these solutions formed blueish and greenish copper-bearing gel-like precipitates. These gels contained atacamite sulfate hydroxides such as devilline, spangolite, posnjakite, schulenbergite, brochantite, which were identified by XRD, SEM, ESEM, FTIR. The formation gel materials was studied under humid dry conditions after maturation water evaporation. Atacamite found associated to outflowing saline with pH 5.7, SO 4 /Cl weight ratios 0.42–0.48, /NO 3 0.48–0.50. are seen an expression lower aquifer Calama basin. Most (spangolite, schulenbergite) slightly acidic freshwaters (pH 6.0 6.5, 3.08–4.99, 2.52–3.13). In contrast, devilline near neutral alkaline 7.2 7.8, ratio 8.34, 6.05). Non-copper-bearing precipitates evaporation supernatant from gel. Gypsum precipitated first, then blödite (sodium-magnesium sulfate), finally halite. Slightly negative sulfur isotope values suggest that source neoformed is primarily oxidation sulfides rather than sedimentary origin. copper-gel seeps they might represent a modern precursor latest atacamite-brochantite-gypsum mineralization event Exótica. data support linked inflow Cl-SO -dominated basin into Chuquicamata-Exótica-Radomiro Tomic complex.