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Verónica Oliveros Dania Tristá-Aguilera Gilbert Féraud Diego Morata Luis Aguirre Shoji Kojima Fernando Ferraris 《Mineralium Deposita》2008,43(1):61-78
The Michilla mining district comprises one of the most important stratabound and breccia-style copper deposits of the Coastal
Cordillera of northern Chile, hosted by the Middle Jurassic volcanic rocks of the La Negra Formation. 40Ar/39Ar analyses carried out on igneous and alteration minerals from volcanic and plutonic rocks in the district allow a chronological
sequence of several magmatic and alteration events of the district to be established. The first event was the extrusion of
a thick lava series of the La Negra Formation, dated at 159.9 ± 1.0 Ma (2σ) from the upper part of the series. A contemporaneous intrusion is dated at 159.6 ± 1.1 Ma, and later intrusive events are
dated at 145.5 ± 2.8 and 137.4 ± 1.1 Ma, respectively. Analyzed alteration minerals such as adularia, sericite, and actinolite
apparently give valid 40Ar/39Ar plateau and miniplateau ages. They indicate the occurrence of several alteration events at ca. 160–163, 154–157, 143–148,
and 135–137 Ma. The first alteration event, being partly contemporaneous with volcanic and plutonic rocks, was probably produced
in a high thermal gradient environment. The later events may be related either to a regional low-grade hydrothermal alteration/metamorphism
process or to plutonic intrusions. The Cu mineralization of the Michilla district is robustly bracketed between 163.6 ± 1.9
and 137.4 ± 1.1 Ma, corresponding to dating of actinolite coexisting with early-stage chalcocite and a postmineralization
barren dyke, respectively. More precisely, the association of small intrusives (a dated stock from the Michilla district)
with Cu mineralization in the region strongly suggests that the main Michilla ore deposit is related to a magmatic/hydrothermal
event that occurred between 157.4 ± 3.6 and 163.5 ± 1.9 Ma, contemporaneous or shortly after the extrusion of the volcanic
sequence. This age is in agreement with the Re–Os age of 159 ± 16 Ma obtained from the mineralization itself (Tristá-Aguilera
et al., Miner Depos, 41:99–105,2006). 相似文献
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Abstract. Formation conditions of some vein-type copper deposits of the Tocopilla district (Deseada, San Jose, Santa Rosa) and the Gatico district (Yohanita, Toldo-Velarde, Argentina) in the Coastal Cordillera of northern Chile were inferred from mineral paragenesis and fluid inclusion data, and were compared with those of neighboring stratiform copper deposits. The vein-type copper deposits are hosted in Late Jurassic dioritic to quartz-dioritic plutons intruding extensively an andesite-dominant volcanic pile of the Jurassic La Negra Formation. Primary mineralization is characterized by chalcopyrite + magnetite + pyrite + bornite, and supergene alteration of these minerals produced anilite, covellite, atacamite and chrysocolla. The hypogene mineral assemblage indicates relatively high sulfur fugacity and weakly oxidized conditions, distinct from the stratiform copper deposits formed under low sulfur fugacity and moderately oxidized conditions. Furthermore, the fluid inclusion data of the vein-type deposits indicate high temperature (401–560C) and high salinity (39–68 wt% NaCl equiv.) ranges in contrast to the stratiform deposits, suggesting that this type of deposits formed by magma-associated hypersaline ore fluids. 相似文献
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Castro-Correa Carmen-Paz Aldunce Ide Paulina Wyndham Vásquez Katherine Mena Maldonado Dania Pérez Tello Sonia 《Natural Hazards》2020,103(2):2427-2440
Natural Hazards - This article analyzes the impact of socio-natural disasters on social capital at a local level, studying the cases of the communities of Chañaral and Diego de Almagro after... 相似文献
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Recent studies on mineralogy, geochronology, fluid inclusion and stable isotope (Pb, Os, S, C, O, Sr) characteristics were reviewed to determine constraints for genetic models of the Chilean manto‐type copper deposits. The Chilean manto‐type deposits are divided into the two geologic categories of the northern areas (Arica–Iquique, Tocopilla–Taltal) and the central areas (Copiapó, La Serena, Santiago). The former is distributed in the coastal range composed of Jurassic andesite‐dominated volcano‐sedimentary piles and younger plutonic intrusions, and yields chalcocite (‐digenite) and bornite as the principal hypogene copper sulfides. The latter is hosted mostly in Lower Cretaceous volcano‐sedimentary sequences, and has chalcopyrite‐rich mineral associations. The fluid inclusion data indicate that the primary copper mineralization was commonly generated in the temperature range 150–360°C under low‐pressure conditions near the boiling curve, mediated with relatively saline brines. Generally, homogeneous Pb and S isotope compositions for primary copper minerals imply direct magma source or leaching of igneous rocks. Pb and Os isotope data published for some deposits, however, suggest that ore‐forming metals were derived mainly from the volcano‐sedimentary host rocks. The noticeably negative isotope ratios of primary sulfide sulfur and hydrothermal calcite carbon of some central area deposits indicate influx of sedimentary rock components, and the high 87Sr/86Sr initial ratios of hydrothermal calcite from the Tocopilla–Taltal area deposits imply contribution of the contemporaneous seawater or marine carbonates. These isotopic constraints imply a formation mechanism in which the Chilean manto‐type copper deposits formed epigenetically in the process of hydrothermal interaction of non‐magmatic surface‐derived brine with the volcano‐sedimentary host rocks, which is inferred to have been induced by a deep‐seated plutonic complex as the possible heat source. 相似文献
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Dania Tristá-Aguilera Fernando Barra Joaquin Ruiz Diego Morata Oscar Talavera-Mendoza Shoji Kojima Fernando Ferraris 《Mineralium Deposita》2006,41(1):99-105
The Lince–Estefanía stratabound copper deposit in the Michilla district is one of the most important deposits in the Coastal Cordillera of northern Chile and is one of the most representative of this type of deposit. Chalcocite and bornite characterize the main stage of hypogene copper sulfide mineralization. Rhenium and osmium isotopes are used here to constrain the age of hypogene mineralization and the source of osmium contained in these ore minerals. A Re–Os isochron yielded an age of 160±16 Ma (2σ), with an associated initial 187Os/188Os ratio of 1.06±0.09 (mean square of weighted deviates=1.8). This age is consistent with available geochronological data from volcanic rocks that host the mineralization and associated alteration phases. The high initial 187Os/188Os ratio indicates a lower crustal component for the source of Os and, by inference, the Cu sulfides that contain this Os. Late hematite occurs as an isolated phase or, more commonly, is associated with the chalcocite–bornite and supergene chalcocite–covellite associations. Analyses performed on pure hematite indicate a disturbance of the Re–Os system, and hence, this mineral phase is not useful as a Re–Os geochronometer. 相似文献
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