Distribución y ocurrencia de alteración hidrotermal y mineralización asociada al Plutón Cabeza de Vaca, sector Quebrada Carrizalillo, III Región de Atacama, Chile
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2021
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es
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Universidad Andrés Bello
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Resumen
El Plutón Cabeza de Vaca de edad Paleoceno inferior, aflora 46 km al SE de la comuna
de Tierra Amarilla en el sector de la Quebrada Carrizalillo. Este Plutón de composición
granodiorítica, corresponde a un sistema porfídico que alberga numerosas chimeneas de brechas
de turmalina y vetas de turmalina asociadas. Las brechas están constituidas por clastos
granodioríticos y dioríticos porfídicos, en una matriz de turmalina, cuarzo, óxidos e hidróxidos de
Fe, junto a sulfuros de calcopirita y bornita; óxidos de cobre de crisocola, atacamita, brochantita,
cuprita y cobre nativo. Procesos de oxidación y lixiviación tanto en el Plutón como en brechas han
conducido a una extensa capa de enriquecimiento de cobre, lo que permite la subdivisión del
depósito en zonas de lixiviación-oxidación, mixto e hipógeno primario. La secuencia paragenética
definida para este depósito incluye 5 etapas: una etapa magmática-hidrotermal, compuesta por una
paragénesis mineral de feldespato potásico, biotita secundaria y magnetita. Sobreimpuesta por una
etapa hidrotermal primaria temprana, que implica la alteración clorita- en granodioritas,
acompañada de diseminaciones de pirita. Seguida por la etapa hidrotermal principal asociada a
brechización de turmalina, con desarrollo de alteración cuarzo-sericita en los fragmentos y
mineralización metálica de calcopirita junto a menores cantidades de pirita. Posteriormente se
desarrolla una etapa de enriquecimiento supérgeno que implica el remplazo de sulfuros hipógenos
de cobre por calcosina y covelina, en donde la pirita y magnetita son parcialmente reemplazadas
por hematita y gohetita, en estrecha relación con oro nativo. Finalmente, una etapa hidrotermal
tardía, en la etapa temprana se sobreimpone caolinita a todas las alteraciones anteriormente
descritas, generando alteración argílica en las rocas, en las que progresivamente comienzan a
ocurrir los minerales del grupo de la illita y esmectitas. La alteración supérgena posterior, se
caracteriza por las asociaciones cuarzo-caolinita- dickita-sepiolita y alunita-jarosita-caolinitacuarzo residual, donde ocurre la lixiviación completa de los sulfuros.
Specifically at 46 km SE of the commune of Tierra Amarilla in the sector the Quebrada Carrizalillo, it emerges a Pluton called Cabeza de Vaca from Lower Paleocene, which contains numerous pipes of tourmaline breccias and tourmaline veins associated with this Pluton. Mainly constituted by clasts of granodioritic and porphyritic dioritic composition, in a matrix of tourmaline, granular quartz, Fe oxides and ore minerals, characterized by chalcopyrite and bornite, also copper oxides such as chrysocolla, atacamite and brochantite. They present alterations and mineralization before and after the development of their structures, typical of porphyry systems. Oxidation and leaching processes both in the pluton and on breccias have led to an extensive copper enrichment layer, which allows the subdivision of the deposit into mineralized areas with mineralogical domains of oxidation, mixed and hypogenic enrichment. The paragenetic sequence consists of four stages: the first one is a magmatic-hydrothermal stage, which consists by a mineral paragenesis of feld-k, biotite II and magnetite. Moreover, that phase is overlapped by an early primary hydrothermal stage that implies a replacement of the development of chlorite-epidote alteration, accompanied by pyrite and disseminated magnetite into granodiorites. The second one is the main hydrothermal stage which refers to a replacement of quartz-sericite alteration into tourmaline breccia clasts and metallic mineralization of chalcopyrite and few amounts of pyrite. Later, it develops a supergene enrichment stage which implies a replacement of hypogene copper sulfides into chalcocite and covellite, where pyrite and magnetite are partially replaced into hematite and goethite, related to native gold. Finally, there is a late hydrothermal stage which is divided into two stages, the early one is an overlapping of kaolinite into the whole alterations mentioned, developing an argillic alteration where ore minerals from illite and smectites group are arising into rocks. The post-supergene alteration is characterized by quartz-chalcocite-dickitesepiolite and alunite-jarosite-chalcocite-quartz associations
Specifically at 46 km SE of the commune of Tierra Amarilla in the sector the Quebrada Carrizalillo, it emerges a Pluton called Cabeza de Vaca from Lower Paleocene, which contains numerous pipes of tourmaline breccias and tourmaline veins associated with this Pluton. Mainly constituted by clasts of granodioritic and porphyritic dioritic composition, in a matrix of tourmaline, granular quartz, Fe oxides and ore minerals, characterized by chalcopyrite and bornite, also copper oxides such as chrysocolla, atacamite and brochantite. They present alterations and mineralization before and after the development of their structures, typical of porphyry systems. Oxidation and leaching processes both in the pluton and on breccias have led to an extensive copper enrichment layer, which allows the subdivision of the deposit into mineralized areas with mineralogical domains of oxidation, mixed and hypogenic enrichment. The paragenetic sequence consists of four stages: the first one is a magmatic-hydrothermal stage, which consists by a mineral paragenesis of feld-k, biotite II and magnetite. Moreover, that phase is overlapped by an early primary hydrothermal stage that implies a replacement of the development of chlorite-epidote alteration, accompanied by pyrite and disseminated magnetite into granodiorites. The second one is the main hydrothermal stage which refers to a replacement of quartz-sericite alteration into tourmaline breccia clasts and metallic mineralization of chalcopyrite and few amounts of pyrite. Later, it develops a supergene enrichment stage which implies a replacement of hypogene copper sulfides into chalcocite and covellite, where pyrite and magnetite are partially replaced into hematite and goethite, related to native gold. Finally, there is a late hydrothermal stage which is divided into two stages, the early one is an overlapping of kaolinite into the whole alterations mentioned, developing an argillic alteration where ore minerals from illite and smectites group are arising into rocks. The post-supergene alteration is characterized by quartz-chalcocite-dickitesepiolite and alunite-jarosite-chalcocite-quartz associations
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Proyecto de título (Geólogo)
Palabras clave
Alteraciones Hidrotermales, Mineralización, Chile, Región de Atacama