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Item type:Publication, Neoformation of exotic copper minerals from gel-like precursors at the Exótica deposit, Chuquicamata, Chile(Springer Science+Business Media, 2022-11-16)At the Exótica deposit, south of the giant porphyry copper deposit of Chuquicamata (Atacama Desert, Chile), Cu-rich groundwater seeped out at several locations in the Exótica open pit (Mina Sur) during sampling in 2009–2011. At their outflows, these solutions formed blueish and greenish copper-bearing gel-like precipitates. These gels contained atacamite and copper sulfate hydroxides such as devilline, spangolite, posnjakite, schulenbergite, and brochantite, which were identified by XRD, SEM, ESEM, and FTIR. The formation of the gel materials was studied under humid and dry conditions during and after maturation and water evaporation. Atacamite was found associated to outflowing saline solutions with pH 5.7, SO4/Cl weight ratios of 0.42–0.48, SO4/NO3 ratios of 0.48–0.50. These solutions are seen as an expression of the the lower aquifer of the Calama basin. Most copper sulfate hydroxides (spangolite, posnjakite, schulenbergite) were associated with slightly acidic freshwaters (pH 6.0 to 6.5, SO4/Cl ratios of 3.08–4.99, SO4/NO3 ratios of 2.52–3.13). In contrast, devilline formed in gels with near neutral to slightly alkaline water (pH 7.2 to 7.8, SO4/Cl ratio of 8.34, and SO4/NO3 ratio of 6.05). Non-copper-bearing precipitates formed by evaporation of the supernatant solutions from the gel. Gypsum precipitated first, then blödite (sodium-magnesium sulfate), and finally halite. Slightly negative sulfur isotope values suggest that the sulfur source in the neoformed gels is primarily the oxidation of sulfides rather than sulfate of sedimentary origin. The studied copper-gel seeps suggest that they might represent a modern precursor of the latest atacamite-brochantite-gypsum mineralization event at Exótica. These data support that the atacamite-brochantite-gypsum mineralization at Exótica is linked to the inflow of Cl-SO4-dominated groundwater from the lower saline aquifer of the Calama basin into the Chuquicamata-Exótica-Radomiro Tomic complex. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Sedimentary Evolution of a Late Triassic Salt Giant and a Synchronous Carbonate Unit Between the Peruvian Andean Cordillera and the Brazilian Amazonian Foreland(American Association of Petroleum Geologists, 2023-01-01)Salt giants with mixed evaporites/carbonates are sedimentary systems poorly understood in terms of sequence stratigraphy, tectonic control, and related natural resources. To improve the knowledge of these systems, a sedimentology study of a Late Triassic salt giant between the Subandean fold-thrust belt (SFTB) of Peru and the Brazilian Amazonian foreland (AF) was performed on the pre- to postsalt deposits using field observations, thin-section descriptions, and well-log analysis. In addition, this study was compared with sedimentary observations of Upper Triassic carbonate successions from the Subandean-Cordillera transition zone (SCTZ) documented in previous works. This resulted in the following sedimentary events associated to a relative sealevel fluctuation: first transgression, regression, and second transgression. In the SFTB and AF, during the first transgression, continental/transitional siliciclastic environments with sporadic marine incursions allowing the development of salt ponds were formed first. Subsequently, a salt basin surrounded by a mudflat was established. At the end of the first transgression, carbonate deposits dominated. During the subsequent regression, a sulfate platform was established followed by a salt basin enveloped by mudflats and exposed areas. This regression terminated with the development of a central mudflat and an increase of the exposed areas. In the second transgression, carbonates and an eastward mudflat with gypsum ponds dominated the sedimentation. In the SCTZ, external-platform to deep-basin carbonates dominated the sedimentation during the three events. Based on this evolution, eustatic oscillations of the global oceanic level, and structural features published in previous works, it is interpreted that the deposition of the studied salt giant and external carbonates were controlled by thermal sagging and eustatic sea-level oscillations. The available data suggest the existence of a westward migration of the subsidence from the Norian (mid Late Triassic) to the Triassic-Jurassic boundary that may be caused by slab steepening. Hydrocarbon reservoirs and stratabound, sediment-hosted Cu-Ag and Zn-Pb ore deposit occurrences are also partly controlled by the evolution of the mixed evaporite/carbonate sedimentary system in the region between the SCTZ and the AF.