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New Ar-40/Ar-39 alunite ages from the Colquijirca district, Peru: evidence of a long period of magmatic SO2 degassing during formation of epithermal Au-Ag and Cordilleran polymetallic ores

Bendezu, Ronner; Page, Laurence LU ; Spikings, Richard; Pecskay, Zoltan and Fontbote, Llus (2008) In Mineralium Deposita 43(7). p.777-789
Abstract
We present Ar-40/Ar-39 data acquired by infra-red (CO2) laser step-heating of alunite crystals from the large Miocene Colquijirca district in central Peru. Combined with previously published data, our results show that a long (at least 1.3 My) and complex period of magmatic-hydrothermal activity associated with epithermal Au-(Ag) mineralization and base metal, Cordilleran ores took place at Colquijirca. The new data indicate that incursion of magmatic SO2-bearing vapor into the Colquijirca epithermal system began at least as early as similar to 11.9 Ma and lasted until similar to 10.6 Ma. Four alunite samples associated with high-sulfidation epithermal Au-(Ag) ore gave Ar-40/Ar-39 plateau ages between similar to 11.9 and similar to 11.1 Ma... (More)
We present Ar-40/Ar-39 data acquired by infra-red (CO2) laser step-heating of alunite crystals from the large Miocene Colquijirca district in central Peru. Combined with previously published data, our results show that a long (at least 1.3 My) and complex period of magmatic-hydrothermal activity associated with epithermal Au-(Ag) mineralization and base metal, Cordilleran ores took place at Colquijirca. The new data indicate that incursion of magmatic SO2-bearing vapor into the Colquijirca epithermal system began at least as early as similar to 11.9 Ma and lasted until similar to 10.6 Ma. Four alunite samples associated with high-sulfidation epithermal Au-(Ag) ore gave Ar-40/Ar-39 plateau ages between similar to 11.9 and similar to 11.1 Ma (compared to the previously documented similar to 11.6 to similar to 11.3 Ma). By combining individually these new ages with crosscutting relationships, the duration of the Au-(Ag) deposition period can be estimated to at least 0.4 My. Three new Ar-40/Ar-39 plateau ages on alunite associated with the base-metal Cordilleran ores are consistent with previously obtained ages, all of them between 10.83 +/- 0.06 and 10.56 +/- 0.06 Ma, suggesting that most of the sulfide-rich polymetallic deposits of Smelter and Colquijirca formed during this short period. The recognition of consecutive alunite-bearing and alunite-free mineral assemblages within both the Au-(Ag) and the base-metal Cordilleran ores may suggest that SO2-bearing magmatic vapor entered the epithermal environment as multiple discontinuous pulses, a number of which was not necessarily associated in time with ore fluids. It is likely that a period of SO2-bearing vapor degassing longer than 11.9 to 10.6 Ma may be recognized with further more detailed work. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Cordilleran, Ar-40/Ar-39 geochronology, high sulfidation, epithermal, alunite, Colquijirca, Peru
in
Mineralium Deposita
volume
43
issue
7
pages
777 - 789
publisher
Springer
external identifiers
  • wos:000258718500004
  • scopus:51049123609
ISSN
0026-4598
DOI
10.1007/s00126-008-0195-1
language
English
LU publication?
yes
id
0bf02d1c-f2bf-4a27-8c19-5ef714fbae58 (old id 1249314)
date added to LUP
2008-11-10 13:30:19
date last changed
2017-01-01 05:07:11
@article{0bf02d1c-f2bf-4a27-8c19-5ef714fbae58,
  abstract     = {We present Ar-40/Ar-39 data acquired by infra-red (CO2) laser step-heating of alunite crystals from the large Miocene Colquijirca district in central Peru. Combined with previously published data, our results show that a long (at least 1.3 My) and complex period of magmatic-hydrothermal activity associated with epithermal Au-(Ag) mineralization and base metal, Cordilleran ores took place at Colquijirca. The new data indicate that incursion of magmatic SO2-bearing vapor into the Colquijirca epithermal system began at least as early as similar to 11.9 Ma and lasted until similar to 10.6 Ma. Four alunite samples associated with high-sulfidation epithermal Au-(Ag) ore gave Ar-40/Ar-39 plateau ages between similar to 11.9 and similar to 11.1 Ma (compared to the previously documented similar to 11.6 to similar to 11.3 Ma). By combining individually these new ages with crosscutting relationships, the duration of the Au-(Ag) deposition period can be estimated to at least 0.4 My. Three new Ar-40/Ar-39 plateau ages on alunite associated with the base-metal Cordilleran ores are consistent with previously obtained ages, all of them between 10.83 +/- 0.06 and 10.56 +/- 0.06 Ma, suggesting that most of the sulfide-rich polymetallic deposits of Smelter and Colquijirca formed during this short period. The recognition of consecutive alunite-bearing and alunite-free mineral assemblages within both the Au-(Ag) and the base-metal Cordilleran ores may suggest that SO2-bearing magmatic vapor entered the epithermal environment as multiple discontinuous pulses, a number of which was not necessarily associated in time with ore fluids. It is likely that a period of SO2-bearing vapor degassing longer than 11.9 to 10.6 Ma may be recognized with further more detailed work.},
  author       = {Bendezu, Ronner and Page, Laurence and Spikings, Richard and Pecskay, Zoltan and Fontbote, Llus},
  issn         = {0026-4598},
  keyword      = {Cordilleran,Ar-40/Ar-39 geochronology,high sulfidation,epithermal,alunite,Colquijirca,Peru},
  language     = {eng},
  number       = {7},
  pages        = {777--789},
  publisher    = {Springer},
  series       = {Mineralium Deposita},
  title        = {New Ar-40/Ar-39 alunite ages from the Colquijirca district, Peru: evidence of a long period of magmatic SO2 degassing during formation of epithermal Au-Ag and Cordilleran polymetallic ores},
  url          = {http://dx.doi.org/10.1007/s00126-008-0195-1},
  volume       = {43},
  year         = {2008},
}