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Paragenesis and mineral chemistry of alabandite (MnS) from the Ag-rich Santo Toribio epithermal deposit, Northern Peru

Published online by Cambridge University Press:  05 July 2018

G. R. Olivo  and
K. Gibbs
G. R. Olivo*
Affiliation:
Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario, Canada K7P 2L7
K. Gibbs
Affiliation:
Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario, Canada K7P 2L7
*
* E-mail: olivo@geol.queensu.ca
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Abstract

The Miocene, epithermal, Ag-rich polymetallic Santo Toribio deposit is hosted by the volcanics of the Quiruvilva-Pierina subbelt, Northern Peru, which also comprises the world-class, high sulphidation Pierina deposit. The Ag-rich, alabandite-bearing veins of the Santo Toribio deposit formed during two major stages. The early stage is characterized by deposition of arsenopyrite, pyrite, quartz, Mn- sphalerite, stannite, alabandite and minor miargyrite. Sphalerite associated with this stage is exceptionally enriched in Mn (up to 14.5 wt.%) and alabandite is optically and mineralogically zoned. Its brown zones have greater Fe+Sb and smaller Mn contents than the green zones and Fe+Sb replaces Mn in its structure. During this early stage, fs2 must have been high to allow the stabilization of alabandite relative to rhodochrosite. In the second stage, the physicochemical conditions changed and the CO2/S ratio increased, causing dissolution of alabandite and the deposition of abundant rhodochrosite and a second generation of arsenopyrite, pyrite and quartz, sphalerite with chalcopyrite inclusions, mirargyrite, ramdohrite, and finally stibnite. This polymetallic ore probably formed due to an abrupt decrease in H+ and/or Cl- concentration caused by boiling or dilution of the high-salinity hydrothermal fluids and constitutes an example of “intermediate sulfidation-state” epithermal deposits.

Keywords

alabanditeSanto Toribio epithermal depositPeru
Type
Research Article
Information
Mineralogical Magazine , Volume 67 , Issue 1 , February 2003 , pp. 95 - 102
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2003

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Footnotes

†

Present address: SGS Lakefield Research Limited, P.O. Box 4300, 185 Concession Street, Lakefield, Ontario, Canada K0L 2H0

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