| TAZ-TFG-2022-2703 |
Caracterización mineralógica del yacimiento Candelaria (Gallinero de Cameros, La Rioja)
Andrés Escorihuela, Alejandro
Fanlo González, María Isabel (dir.)
Universidad de Zaragoza,
CIEN,
2022
Departamento de Ciencias de la Tierra, Área de Cristalografía y Mineralogía
Graduado en Geología
Resumen: At the end of the 19th century several small underground metal mines were exploited in the Cameros Massif. Now, one of them, the Candelaria ore deposit, located in Gallinero de Cameros (La Rioja), has been studied. The main objective of this study is to characterize the geology and mineralogy of this mine. A mapping of the inside of the mine has also been done.
During the Titonian-Albian, there was a rifting period that caused the formation of the Cameros Basin, with the deposition of more than 6500 meters of sediments in continental and transitional environments. The mineralisation is hosted in the Tera Group, which is the first depositional sequence in which the basin is divided. After the Alpine orogeny, the normal faults that had formed during the extensional stage were reactivated as thrusts and the Cameros Massif was formed.
The samples taken in the mine were analysed with optical and electronic microscope to determine the mineralogy, composition and mineral paragenesis. The host rock is mainly an organic-rich shale layer, and the microconglomerates and sandstones around it. The mineralisation consists of disseminations, fracture-filling and replacements of copper sulphides and sulfosalts, mainly tennantite, chalcopyrite and bornite, but also arsenopyrite, with supergene covellite, azurite and malachite. The arsenic-rich mineral tennantite was the first copper mineral to form, while arsenopyrite was the last one to precipitate, originating large euhedral crystals.
The event has been linked to the Albian-Coniacian hydrothermal metamorphism event, although its origin remains unclear. The connate fluids and meteoric water that leaked into the sediments would have been mobilized by temperature and pressure gradients originated by the infilling of the basin. During their circulation, they would have leached the oxidized metals of the continental sediments and would have been transformed into brines and enriched in sulphur due to the interaction with the evaporites of the Keuper facies. These oxidized brines would have been driven preferentially through the faults that were originated during the rifting stage, which would work as high-permeability conduits. The precipitation of the sulphides was induced by the presence of reduced organic-rich layers, pyrite, shale clasts and carbonates, which acted as metal traps. These characteristics enable us to classify the Candelaria mine as a redbed-hosted stratiform deposit.
During the Titonian-Albian, there was a rifting period that caused the formation of the Cameros Basin, with the deposition of more than 6500 meters of sediments in continental and transitional environments. The mineralisation is hosted in the Tera Group, which is the first depositional sequence in which the basin is divided. After the Alpine orogeny, the normal faults that had formed during the extensional stage were reactivated as thrusts and the Cameros Massif was formed.
The samples taken in the mine were analysed with optical and electronic microscope to determine the mineralogy, composition and mineral paragenesis. The host rock is mainly an organic-rich shale layer, and the microconglomerates and sandstones around it. The mineralisation consists of disseminations, fracture-filling and replacements of copper sulphides and sulfosalts, mainly tennantite, chalcopyrite and bornite, but also arsenopyrite, with supergene covellite, azurite and malachite. The arsenic-rich mineral tennantite was the first copper mineral to form, while arsenopyrite was the last one to precipitate, originating large euhedral crystals.
The event has been linked to the Albian-Coniacian hydrothermal metamorphism event, although its origin remains unclear. The connate fluids and meteoric water that leaked into the sediments would have been mobilized by temperature and pressure gradients originated by the infilling of the basin. During their circulation, they would have leached the oxidized metals of the continental sediments and would have been transformed into brines and enriched in sulphur due to the interaction with the evaporites of the Keuper facies. These oxidized brines would have been driven preferentially through the faults that were originated during the rifting stage, which would work as high-permeability conduits. The precipitation of the sulphides was induced by the presence of reduced organic-rich layers, pyrite, shale clasts and carbonates, which acted as metal traps. These characteristics enable us to classify the Candelaria mine as a redbed-hosted stratiform deposit.
Tipo de Trabajo Académico: Trabajo Fin de Grado
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