Doctoral thesis
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Fluid Processes and Sources in an Epithermal Polymetallic Zoned Deposit: Colquijirca, Central Peru

ContributorsCasanova, Vincent
Number of pages216
Imprimatur date2021-09-20
Defense date2018-06-18

The district of Colquijirca, in central Peru, hosts high-sulfidation Au-Ag and polymetallic (Cu-Zn-Pb-Ag-Au-Bi-Sb) Cordilleran mineralization centered on the Marcapunta diatreme-dome complex. This study focuses on the sources of fluids, metals, and sulfur, and on fluid processes such as cooling, fluid-rock interaction, and fluid mixing, leading to the formation of the 6.5 km-long Cordilleran mineralization. A combination of in-situ techniques including fluid inclusion microthermometry, SIMS δ18O, bulk trace element, and multi-isotopic (S, Sr, Pb) analyses of leachates and residues of ore and gangue minerals has been used. The study indicates that the deposit was formed at temperatures between 300 and 180°C by fluid pulses of dominantly magmatic origin with low to moderate salinities (<7 wt% NaCl eq.) mostly at shallow depths (< 500 m below the paleosurface). The highest temperatures are recorded close to the Marcapunta diatreme-dome complex. Radiogenic isotope (Sr and Pb) analyses suggest that the magmatic fluid pulses had varying degrees of interaction with crustal rocks and/or basinal fluids prior to reaching the site of mineralization. Between the distinct magmatic fluid pulses, the system was dominated by meteoric water.

In addition to the work on fluid processes in the Colquijirca district, a chapter of this study is dedicated to the physics of near-infrared (NIR) microthermometry. Using FTIR spectrometry and NIR-microthermometry of synthetic fluid inclusions in different opaque minerals, it has been shown that local overheating of the sample is caused by radiative heating from the light source and may lead to an underestimation of phase change temperatures. A protocol to bypass the pitfalls of near-infrared (NIR) microthermometry is proposed.

Citation (ISO format)
CASANOVA, Vincent. Fluid Processes and Sources in an Epithermal Polymetallic Zoned Deposit: Colquijirca, Central Peru. 2021. doi: 10.13097/archive-ouverte/unige:176573
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