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Microthermometry and Raman spectroscopy of fluid inclusions from El Vapor gold mineralizations, Colombia
Microtermometría y espectroscopía Raman de inclusiones fluidas de las mineralizaciones auríferas de El Vapor, Colombia
DOI:
https://doi.org/10.15446/esrj.v22n3.63442Keywords:
Fluid inclusions, Microthermometry, Raman spectroscopy, Gold mineralizations, El Vapor district, reduced fluids, Orogenic. (en)Inclusiones fluidas, Microtermometría, Espectroscopía Raman, Mineralizaciones Auríferas, Distrito de El Vapor, Fluidos Reducidos, Orogénico. (es)
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Epigenetic El Vapor gold mineralization is hosted by the Segovia batholith and sedimentary rocks at both sides of El Nús fault, in the eastern flank of the Colombian Andes central cordillera. Gold mineralization is composed by continuous and discontinuous sigmoidal and stockwork veins and veinlets from a few centimeters to two meters of thickness and by hydrothermal breccias. Ore mineralogy includes Pyrite + Galena + Sphalerite + Chalcopyrite + Pyrrhotite + Proustite - Pyrargyrite. Gold is recognized as inclusions within pyrite, between quartz crystals and as fractures filled within pyrite at a late stage of mineralization. The fluid inclusions in quartz veins occur as clusters of primary inclusions and alignments of secondary and pseudo-secondary inclusions. Based on petrography and Raman spectroscopy, four types of fluid inclusions could be recognized: (1) Type I inclusions, biphasic, liquid-rich, with CO2 (v) + N2 (v) + CH4 (v) + KCl + NaCl + H2O(L), primary inclusions, (2) Type II inclusions, multi-volatile, CO2(V) + CO2(L) + N2(V) + CH4(V) + KCl + NaCl + H2O(L), primary to pseudo-secondary inclusions, (3) biphasic, liquid-rich inclusions, composed of H2O(v) +H2O(L)+KCl+NaCl with secondary origin and two different times of formation (IIIA and IIIB) (4) Type IV inclusions, very rare, three-phasic, secondary inclusions and composed by S+H2O(V)+H2O(L)+KCl+ NaCl. The microthermometric and spectroscopic analysis of fluid inclusions indicates that fluids associated with the first event of mineralization identified in El Vapor have low to moderate salinities (3.5-9.2 wt%NaCl equiv.), with trapping temperatures between 214°C and 350°C and pressures between 0.5kbar and 2.9kbar. There is evidence of the isothermal fluid mixture, and fO2 changes per reaction of fluids in the carbonaceous shales of the Segovia sedimentary rocks could influence the process of gold deposition. Hydrothermal fluids from El Vapor were near neutrality and reduced; similar features have been found in orogenic deposits hosted by turbidite sequences around the world.
Las mineralizaciones epigenéticas de El Vapor se encuentran hospedadas en el Batolito de Segovia y rocas sedimentarias a ambos lados de la falla de El Nús, en el flanco oriental de la Cordillera Central de los Andes Colombianos. Las mineralizaciones auríferas están compuestas por venas y vetillas continuas y discontinuas, sigmoidales y en stockwork desde pocos centímetros hasta dos metros de espesor, así como por brechas hidrotermales.
Los minerales de mena incluyen Pirita + Galena + Esfalerita + Calcopirita + Pirrotina + Proustita – Pirargirita. Oro se presenta como inclusiones dentro de pirita, entre cristales de cuarzo y rellenando fracturas dentro de pirita, en un estadio tardío de mineralización.
Las inclusiones fluidas en las venas de cuarzo se presentan como agrupaciones de inclusiones primarias como alineaciones de inclusiones secundarias y pseudo-secundarias. Con base en petrografía y espectroscopía Raman, se identificaron cuatro tipos de inclusiones: (1) Tipo I, primarias, bifásicas, ricas en líquido, con CO2(v) + N2(v) + CH4(v) + KCl(AQ) + NaCl(AQ) + H2O(L),(2) Tipo II, primarias o pseudo-secundarias, multivolátiles, con presencia de CO2(V) + CO2(L) + N2(V) + CH4(V) + KCl(AQ) + NaCl(AQ) + H2O(L), (3) Tipo III, secundarias, bifásicas, ricas en líquido, compuestas por H2O(v) + H2O(L) + KCl(AQ) + NaCl(AQ), con dos temporalidades diferentes (IIIA y IIIB), (4) Tipo IV, muy escasas, de tres fases, secundarias y compuestas por S + H2O(V) + H2O(L) + KCl(AQ) + NaCl(AQ).
Los análisis microtermométricos y espectroscópicos de las inclusiones fluidas indican que el fluido hidrotermal relacionado con el primer evento de mineralización identificado en el El Vapor, presenta una salinidad baja a moderada (3.5-9.2 wt% NaCl equiv.), temperaturas de entrampamiento entre 214°C y 350°C y presiones mínimas de entrampamiento entre 0.5kbar y 2.9kbar. Debido a la inexistencia de inclusiones fluidas con grados variables de relleno y modos diferentes de homogenización, y teniendo en cuenta las variaciones de salinidad observadas en un rango restringido de temperaturas de homogenización, se propone que un proceso de mezcla isotermal de fluidos, junto con cambios en la fugacidad de oxígeno, generadas por la reacción de los fluidos con los shales carbonosos de las rocas sedimentarias de Segovia, pudieron influenciar el proceso de depósito del oro.
Los fluidos hidrotermales en El Vapor fueron reducidos y cercanos a la neutralidad, características similares han sido encontradas en depósitos orogénicos hospedados en secuencias turbidíticas alrededor del mundo.
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