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Bracketing the Age of Magmatic-Hydrothermal Activity at the Cerro de Pasco Epithermal Polymetallic Deposit, Central Peru: A U-Pb and Ar-40/Ar-39 Study

Bracketing the Age of Magmatic-Hydrothermal Activity at the Cerro de Pasco Epithermal Polymetallic Deposit, Central Peru: A U-Pb and Ar-40/Ar-39 Study
Bracketing the Age of Magmatic-Hydrothermal Activity at the Cerro de Pasco Epithermal Polymetallic Deposit, Central Peru: A U-Pb and Ar-40/Ar-39 Study
The Cerro de Pasco epithermal Cordilleran base metal deposit in central Peru consists of two mineralization stages which are spatially and genetically related to a mid-Miocene diatreme-dome complex. In order to constrain the duration of the magmatic-hydrothermal system at Cerro de Pasco, U-Ph age determinations and Hf isotope determinations have been conducted on single zircon grains. Biotite from intrusive rocks, and sericite and alunite related to the first and second mineralization stages, respectively, have been used for stepwise IR-CO2 laser Ar-40/Ar-39 age determinations. This study has been complemented by Rb-Sr analyses of sericite and associated pyrite. Single crystal zircon U-Pb analyses yield ages of 15.36 +/- 0.03 Ma for an accretionary lapilli tuff from a collapsed block within the diatreme, 15.40 +/- 0.07 Ma for it dacite porphyry dome in the diatreme, 15.35 +/- 0.05 and 15.16 +/- 0.04 Ma for two quartz monzonite porphyry dikes emplaced into the diatreme-dome complex that are within a time span of 350,000 yr. There is no field evidence for any magmatic activity predating the formation of the diatreme-dome complex. Stepwise IR-CO2 laser Ar-40/Ar-39 ages have been determined on sericite and alunite. The latter formed during the second mineralization stage in advanced argillically altered domes and from halos of oxidized enargite-pyrite veins in the Venecocha and Santa Rosa area, located on the northwestern margin of the diatreme-dome complex and on the southern part of the Cerro de Pasco open pit, respectively, Ar-40/Ar-39 alunite ages cluster between 14.54 +/- 0.08 and 14.41 +/- 0.07 Ma. This age consistency suggests that advanced argillic alteration related to the second mineralization stage at Cerro de Pasco formed during a period of 100,000 yr. Three significantly younger alunite ages of 1.2.39 +/- 0.06, 12.13 +/- 0.07 Ma, and 10.94 +/- 0.10 M, probably reflect partial resetting by late circulating fluids. Therefore, it appears that magmatic-hydrothermal activity at Cerro de Pasco Pasco lasted about 1 m.y., from 15.4 to.14.4 Ma, similar to the duration in the nearby mid-Miocene Colquijirca district. An attempt to more precisely date the first mineralization stage, bracketed by the quartz monzonite. dikes (15.1 Ma) and the second mineralization stage (14.5 Ma) failed: the Ar-40/Ar-39 ages of sericite in the alteration halo of the pyrite-quartz body are not reliable, Probably due to inherited argon derived from Precursor micas in Paleozoic clasts of the diatreme breccia. This is indicated by Rb-Sr data on sericite which indicate binary mixing between Miocene magmatic mid Paleozoic basement sources and do not carry any age, information.
0361-0128
479-504
Baumgartner, Regina
feced635-52a0-46a0-8e52-0177a91fcfd2
Fontbote, Lluis
5fdb6900-3f7b-48b8-bb3e-eaa46bb8c6f7
Spikings, Richard
f9f41452-60b2-4a7c-aa26-037d677d8863
Ovtcharova, Maria
2ee9c374-db38-4d29-ac4b-f8d8d42e6523
Schaltegger, Urs
9b9d1a9b-f13c-48bf-9b5b-be4372a73a3b
Schneider, Jens
cc84d554-55fd-4c14-aa54-0f64e8127792
Page, Lawrence
882ffb87-67c1-4ec5-9921-5002653b4294
Gutjahr, Marcus
5babbbc4-2a1a-48df-a2e3-d87b2483ea9c
Baumgartner, Regina
feced635-52a0-46a0-8e52-0177a91fcfd2
Fontbote, Lluis
5fdb6900-3f7b-48b8-bb3e-eaa46bb8c6f7
Spikings, Richard
f9f41452-60b2-4a7c-aa26-037d677d8863
Ovtcharova, Maria
2ee9c374-db38-4d29-ac4b-f8d8d42e6523
Schaltegger, Urs
9b9d1a9b-f13c-48bf-9b5b-be4372a73a3b
Schneider, Jens
cc84d554-55fd-4c14-aa54-0f64e8127792
Page, Lawrence
882ffb87-67c1-4ec5-9921-5002653b4294
Gutjahr, Marcus
5babbbc4-2a1a-48df-a2e3-d87b2483ea9c

Baumgartner, Regina, Fontbote, Lluis, Spikings, Richard, Ovtcharova, Maria, Schaltegger, Urs, Schneider, Jens, Page, Lawrence and Gutjahr, Marcus (2009) Bracketing the Age of Magmatic-Hydrothermal Activity at the Cerro de Pasco Epithermal Polymetallic Deposit, Central Peru: A U-Pb and Ar-40/Ar-39 Study. Economic Geology, 104 (4), 479-504. (doi:10.2113/gsecongeo.104.4.479).

Record type: Article

Abstract

The Cerro de Pasco epithermal Cordilleran base metal deposit in central Peru consists of two mineralization stages which are spatially and genetically related to a mid-Miocene diatreme-dome complex. In order to constrain the duration of the magmatic-hydrothermal system at Cerro de Pasco, U-Ph age determinations and Hf isotope determinations have been conducted on single zircon grains. Biotite from intrusive rocks, and sericite and alunite related to the first and second mineralization stages, respectively, have been used for stepwise IR-CO2 laser Ar-40/Ar-39 age determinations. This study has been complemented by Rb-Sr analyses of sericite and associated pyrite. Single crystal zircon U-Pb analyses yield ages of 15.36 +/- 0.03 Ma for an accretionary lapilli tuff from a collapsed block within the diatreme, 15.40 +/- 0.07 Ma for it dacite porphyry dome in the diatreme, 15.35 +/- 0.05 and 15.16 +/- 0.04 Ma for two quartz monzonite porphyry dikes emplaced into the diatreme-dome complex that are within a time span of 350,000 yr. There is no field evidence for any magmatic activity predating the formation of the diatreme-dome complex. Stepwise IR-CO2 laser Ar-40/Ar-39 ages have been determined on sericite and alunite. The latter formed during the second mineralization stage in advanced argillically altered domes and from halos of oxidized enargite-pyrite veins in the Venecocha and Santa Rosa area, located on the northwestern margin of the diatreme-dome complex and on the southern part of the Cerro de Pasco open pit, respectively, Ar-40/Ar-39 alunite ages cluster between 14.54 +/- 0.08 and 14.41 +/- 0.07 Ma. This age consistency suggests that advanced argillic alteration related to the second mineralization stage at Cerro de Pasco formed during a period of 100,000 yr. Three significantly younger alunite ages of 1.2.39 +/- 0.06, 12.13 +/- 0.07 Ma, and 10.94 +/- 0.10 M, probably reflect partial resetting by late circulating fluids. Therefore, it appears that magmatic-hydrothermal activity at Cerro de Pasco Pasco lasted about 1 m.y., from 15.4 to.14.4 Ma, similar to the duration in the nearby mid-Miocene Colquijirca district. An attempt to more precisely date the first mineralization stage, bracketed by the quartz monzonite. dikes (15.1 Ma) and the second mineralization stage (14.5 Ma) failed: the Ar-40/Ar-39 ages of sericite in the alteration halo of the pyrite-quartz body are not reliable, Probably due to inherited argon derived from Precursor micas in Paleozoic clasts of the diatreme breccia. This is indicated by Rb-Sr data on sericite which indicate binary mixing between Miocene magmatic mid Paleozoic basement sources and do not carry any age, information.

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Published date: June 2009
Additional Information: Times Cited: 0

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Local EPrints ID: 191621
URI: https://eprints.soton.ac.uk/id/eprint/191621
ISSN: 0361-0128
PURE UUID: d98ef831-6552-463b-b5ac-fc1c4f797443

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Date deposited: 23 Jun 2011 10:06
Last modified: 18 Jul 2017 11:35

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