Geología y génesis del antiguo distrito La Campana, comuna de Olmué, provincia de Marga-Marga, región de Valparaíso, Chile
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2020
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Universidad Andrés Bello
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Resumen
El Distrito La Campana, es catalogado como un depósito tipo Skarn de Cu y
muestra una variación en su mineralización a lo largo de una zona de falla con
orientación ~N30°W. Está localizado en el segmento más meridional y occidental de la
Franja Ferrífera chilena (Sillitoe, 2003) donde ocurren variedades de depósitos del tipo
veta, estratoligados y skarn. Esta franja contiene depósitos con tipo IOCG y
antecedentes del tipo Skarn, lo cual no ha sido considerado en estudios anteriores dentro
del distrito, como tampoco la distribución de los tipos de alteraciones o las relaciones
texturales en la mineralización. Este trabajo tiene como objetivo verificar los controles de
la mineralización y la distribución de las alteraciones, y generar un modelo de evolución
que se ajuste al Distrito La Campana con el propósito de revelar detalles de su génesis
y la evolución de los fluidos hidrotermales, a través de variaciones texturales en las
menas, perfiles, columnas estratigráficas, mapeo de estructuras y recopilación de
trabajos anteriores. Los resultados revelan que, con respecto a la litología, se presentan
de oeste a este la unidad volcanosedimentaria “Las Gualas” (Fm. Horqueta) en contacto
semi concordante hacia el techo con la unidad volcánica y sedimentaria marina “Granizo”
(Fm. Lo Prado) intruidas por las unidades “Diorítica”, y “La Campana” y “Portezuelo”
(gabrodioritas y monzogranitos) hacia el este. Las estructuras indican tendencias
principales al NW y NNW a NS con ramificaciones y secundarias posteriores al NE que
cortan y las desplazan hacia el este de forma transversal. La mineralización primaria
muestra asociaciones de magnetita-pirita±calcopirita en zonas de alteración sódicocálcica
(actinolita-albita) con vetillas AA y calcopirita-esfalerita-pirita, pirrotina y
molibdenita en alteración retrógrada (cuarzo-albita-epidota-calcita-sericita-esmectita)
indicando tanto mineralización/alteración tipo IOCG como de tipo skarn. Además, ocurre
alteración prógrada (granate-piroxeno) con vetillas “P-R”, alteración potásica (biotitafeldk)
con vetillas A, EB y B, y una alteración propilítica periférica. La mineralización
secundaria es de covelina, brocantita y calcosina lo que sugiere un enriquecimiento
supérgeno. Se concluye que el Distrito La Campana se desarrolla bajo un fuerte control
estructural y se relacionaría a depósitos tipo IOCG-Skarn de Cu o Cu-Zn (Pb-Ag) y
posiblemente a un sistema de porfídico, como lo muestra la evolución textural de la
mineralización (estado de sulfuración bajo a intermedio-alto) y la distribución de las
alteraciones potásica-prógrada junto a una sódico-cálcica y propilítica periférica.
La Campana District is classified as a Cu Skarn type deposit and shows a variation in its mineralization along a fault zone with trending ~N30°W. It’s located in the southernmost and westernmost segment of the IOCG Belt (Lower Cretaceous) (Sillitoe, 2003) where different vein, stratabound and skarn deposits take place. This belt contains deposits with alteration and mineralization of the IOCG type (sodic-calcic) (Vivallo, 2009; Barra et al., 2017) and records of the skarn type (prograde-retrograde) (Sillitoe, 2003) which, have not been considered in previous studies within the district area, neither the distribution of the types of alterations or textural relationships in the mineralization. This work aims to verify mineralization controls, distribution of alterations and to generate an evolution model that fits to La Campana District with the purpose of revealing the genesis details and evolution of hydrothermal fluids, through of textural variations in ores, geological sections, stratigraphic columns, structural mapping and previous reports. Results reveal that, from west to east regarding lithology, “Las Gualas” (Horqueta Fm.) is a volcano-sedimentary unit presented in semi-concordant contact towards the ceiling with “Granizo” (Lo Prado Fm.) volcanic and marine sedimentary unit, both intruded from west by “Dioritica” unit (diorites) “La Campana” and “Portezuelo” units (gabrodiorites and monzogranites, respectly) to the east. Structures indicate major NW and NNW to NS trends with splays, and a late secondary NE trend cutting and moving it eastward transversely. Primary mineralization is presented as magnetite-pyrite±chalcopyrite associations in sodic-calcic (actinolite-albite) alteration zones with “AA” veins and chalcopyrite-sphalerite-pyrite, pyrrhotite and molybdenite in retrograde (quartz-albiteepidote- calcite-sericite-smectite) alteration zones indicating both IOCG mineralization/alteration and Skarn type. In addition, a prograde alteration (garnetpyroxene) occurs with “P-R” veins, potassic alteration (biotite-feldk) with “A”, “EB”, and “B” veins, and a peripheral propylitic alteration. Secondary mineralization occurs covelline, brochantite and chalcosite, which suggests a supergenic enrichment. In conclusion, La Campana District developed under strong structural controls and would be related to IOCG-Skarn Cu or Cu-Zn (Pb-Ag) deposits and possibly to a porphyry system, as shown by the textural evolution of mineralization (low to intermediate-high sulphidation state) and the distribution of potassic-prograde alterations together with a sodic-calcic and peripheral propylitic alterations.
La Campana District is classified as a Cu Skarn type deposit and shows a variation in its mineralization along a fault zone with trending ~N30°W. It’s located in the southernmost and westernmost segment of the IOCG Belt (Lower Cretaceous) (Sillitoe, 2003) where different vein, stratabound and skarn deposits take place. This belt contains deposits with alteration and mineralization of the IOCG type (sodic-calcic) (Vivallo, 2009; Barra et al., 2017) and records of the skarn type (prograde-retrograde) (Sillitoe, 2003) which, have not been considered in previous studies within the district area, neither the distribution of the types of alterations or textural relationships in the mineralization. This work aims to verify mineralization controls, distribution of alterations and to generate an evolution model that fits to La Campana District with the purpose of revealing the genesis details and evolution of hydrothermal fluids, through of textural variations in ores, geological sections, stratigraphic columns, structural mapping and previous reports. Results reveal that, from west to east regarding lithology, “Las Gualas” (Horqueta Fm.) is a volcano-sedimentary unit presented in semi-concordant contact towards the ceiling with “Granizo” (Lo Prado Fm.) volcanic and marine sedimentary unit, both intruded from west by “Dioritica” unit (diorites) “La Campana” and “Portezuelo” units (gabrodiorites and monzogranites, respectly) to the east. Structures indicate major NW and NNW to NS trends with splays, and a late secondary NE trend cutting and moving it eastward transversely. Primary mineralization is presented as magnetite-pyrite±chalcopyrite associations in sodic-calcic (actinolite-albite) alteration zones with “AA” veins and chalcopyrite-sphalerite-pyrite, pyrrhotite and molybdenite in retrograde (quartz-albiteepidote- calcite-sericite-smectite) alteration zones indicating both IOCG mineralization/alteration and Skarn type. In addition, a prograde alteration (garnetpyroxene) occurs with “P-R” veins, potassic alteration (biotite-feldk) with “A”, “EB”, and “B” veins, and a peripheral propylitic alteration. Secondary mineralization occurs covelline, brochantite and chalcosite, which suggests a supergenic enrichment. In conclusion, La Campana District developed under strong structural controls and would be related to IOCG-Skarn Cu or Cu-Zn (Pb-Ag) deposits and possibly to a porphyry system, as shown by the textural evolution of mineralization (low to intermediate-high sulphidation state) and the distribution of potassic-prograde alterations together with a sodic-calcic and peripheral propylitic alterations.
Notas
Tesis (Geología)
Palabras clave
Análisis de los Suelos, Mineralización, Evolución Genética, Control Biológico, Skarn, IOCG, Cretácico Inferior, Estado de Sulfuración