STRUCTURAL AND GEOCHEMICAL EVOLUTION OF A MINERALIZED VOLCANIC VENT AT CERRO DE PASCO, PERU

Persistent Link:
http://hdl.handle.net/10150/187533
Title:
STRUCTURAL AND GEOCHEMICAL EVOLUTION OF A MINERALIZED VOLCANIC VENT AT CERRO DE PASCO, PERU
Author:
Rogers, Ralph David
Issue Date:
1983
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Najor Cu-Pb-Zn-Ag mineralization is associated with a dissected volcanic vent, approximately 2 Km in diameter, at Cerro de Pasco, Peru. Vent fill material, including volcaniclastic agglomerate, bedded and welded tuff, and rootless blocks, document more than one kilometer of subsidence of the floor of the vent. A concave-upward conical fold distorts the vent-fill material, thus recording a late structural collapse. Resurgent igneous activity is evidence by quartz monzonite porphyry dikes and a group of interpenetrating dacite domes intruded along the vent margin. Hydrothermal ore deposition occurred during the final stage in the evolution of this volcanic system. The volcanic system is best described as a caldera system that has experienced igneous resurgence. Mineralization is associated with three distinctive fracture sets. Fractures in Set I parallel the strike and dip of the vent margin and formed as a result of slumping along the vent margin. Fractures in Set II occur between the vent margin and the Longitudinal Fault and formed as a result of strike-slip motion along that fault. Fractures in Set III have a consistent east-west strike, converge at depth to a quartz monzonite porphyry dike, and formed in response to emplacement of the dike. Alteration zones have developed parallel to fracturecontrolled flow channels. Quartz-alunite-kaolinite is developed closest to vein mineralization. This assemblage grades into quartz-phyllosilicate-kaolinite away from the veins, and this latter zone in turn grades into calcite-chlorite-epidote further from the veins. Hydrothermal solutions were localized by the permeable zones along the vent margin. The first hydrothermal minerals deposited were pyrite and silica. These formed a large massive sulfide replacement body. Subsequently, ~300°C solutions equilibrated with the early formed pyrite and continued to ascend upward and outward into what would become the main ore zone. As these solutions moved into the oxidized environment of the upper levels of the volcanic vent they deposited pyrite and enargite in veins and generated hydrogen ions that hydrolitically altered the adjacent wallrocks. Changes in solution composition accompanying alteration are discussed.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Geochemistry -- Peru -- Cerro de Pasco.; Geology, Structural.; Volcanism -- Peru -- Cerro de Pasco.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Geosciences; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Guilbert, John
Committee Chair:
Guilbert, John

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleSTRUCTURAL AND GEOCHEMICAL EVOLUTION OF A MINERALIZED VOLCANIC VENT AT CERRO DE PASCO, PERUen_US
dc.creatorRogers, Ralph Daviden_US
dc.contributor.authorRogers, Ralph Daviden_US
dc.date.issued1983en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractNajor Cu-Pb-Zn-Ag mineralization is associated with a dissected volcanic vent, approximately 2 Km in diameter, at Cerro de Pasco, Peru. Vent fill material, including volcaniclastic agglomerate, bedded and welded tuff, and rootless blocks, document more than one kilometer of subsidence of the floor of the vent. A concave-upward conical fold distorts the vent-fill material, thus recording a late structural collapse. Resurgent igneous activity is evidence by quartz monzonite porphyry dikes and a group of interpenetrating dacite domes intruded along the vent margin. Hydrothermal ore deposition occurred during the final stage in the evolution of this volcanic system. The volcanic system is best described as a caldera system that has experienced igneous resurgence. Mineralization is associated with three distinctive fracture sets. Fractures in Set I parallel the strike and dip of the vent margin and formed as a result of slumping along the vent margin. Fractures in Set II occur between the vent margin and the Longitudinal Fault and formed as a result of strike-slip motion along that fault. Fractures in Set III have a consistent east-west strike, converge at depth to a quartz monzonite porphyry dike, and formed in response to emplacement of the dike. Alteration zones have developed parallel to fracturecontrolled flow channels. Quartz-alunite-kaolinite is developed closest to vein mineralization. This assemblage grades into quartz-phyllosilicate-kaolinite away from the veins, and this latter zone in turn grades into calcite-chlorite-epidote further from the veins. Hydrothermal solutions were localized by the permeable zones along the vent margin. The first hydrothermal minerals deposited were pyrite and silica. These formed a large massive sulfide replacement body. Subsequently, ~300°C solutions equilibrated with the early formed pyrite and continued to ascend upward and outward into what would become the main ore zone. As these solutions moved into the oxidized environment of the upper levels of the volcanic vent they deposited pyrite and enargite in veins and generated hydrogen ions that hydrolitically altered the adjacent wallrocks. Changes in solution composition accompanying alteration are discussed.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectGeochemistry -- Peru -- Cerro de Pasco.en_US
dc.subjectGeology, Structural.en_US
dc.subjectVolcanism -- Peru -- Cerro de Pasco.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorGuilbert, Johnen_US
dc.contributor.chairGuilbert, Johnen_US
dc.contributor.committeememberConey, Peteren_US
dc.contributor.committeememberDavis, Georgeen_US
dc.contributor.committeememberEastoe, Chrisen_US
dc.contributor.committeememberNorton, Denisen_US
dc.contributor.committeememberTitley, Spenceren_US
dc.identifier.proquest8323747en_US
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