Proceedings of the 7th World Congress on Mechanical, Chemical, and Material Engineering (MCM'21)
Prague, Czech Republic Virtual Conference – August, 2021
Paper No. MMME 121
DOI: 10.11159/mmme21.121

Gold Characterization of the San Luis Alta Mine, Ayacucho, Perú
Pura Alfonso1, Elsa Ccolqque1, Maite Garcia-Valles2, Maria Terersa Yubero1, Roger Gaona1, Arnau
Martínez1
Universitat Politècnica de Catalunya, Dept. d’Enginyeria Minera, Industrial i TIC
Av de les Bases de Manresa 61-73, 08242 Manresa, Spainmaria.pura.alfonso@upc.edu; elidaccf@gmail.com; rogergb8@hotmail.com; arnaumartalc@gmail.com
2Universitat de Barcelona, Dept. de de Mineralogia, Petrologia i Geologia Aplicada
Carrer Martí i Franquès, s/n, 08028 Barcelona, Spainmaitegarciavalles@ub.edu
1Extended Abstract
To obtain optimal results of a gold mining activity is essential to know the distribution of gold and its mineralogy. TheSan Luis Alta gold mine (Ayacucho, Peru) is an example of this. In this artisanal gold mine the ore is processed by cyanidationin the treatment plant. For an efficient process the reagent used will depend on how the gold is found [1]. The present work
has been carried out to determine the gold characteristics to design an optimal processing of the materials from San Luis.
The gold grades and the mineralogy of the veins and from several tailings produced along the exploitation history of thismine veins were determined.
The San Luis mine is located in the Arequipa segment of the Coastal Batholith, which is rich in hydrothermal golddeposits. The mineralization consists in veins hosted in diorites and granodiorites from the Tiabaya Super-Unit. This deposit
belongs to the intrusive-related type [2]. Mineralization is mainly found in NW-SE in veins of some tens of decimetres wideand dipping about 70 °. In other cases, the veins are sub-horizontal mantos. These veins are filled with quartz and abundantiron oxides. Locally, areas rich in minerals with Cu-rich minerals are present, with alterations of malachite and azurite.
Sulfides are mainly pyrite and minor chalcopyrite, sphalerite and galena.
Gold grades and tellurium content were analyzed. Mineralogy was studied with scanning electron microscopy andmineral chemistry was determined using an electron microprobe.
The gold content in the veins usually is between 40 and 60 g/t, but locally reach 121 g/t. the Te content vary between
less than 10 and 180 g/t. Gold appears either in large grains, visible to the naked eye or, more frequently, in grains of lessthan 10 µm. Gold is encapsulated in Fe oxides, quartz and pyrite. There is a massive pyrite zone, which does not containgold. Two different generations of gold minerals are distinguished in veins from the San Luis deposit. In the first generation,
it occurs as native gold associated with pyrite. In the second generation, gold occurs as tellurides. The most abundant goldtellurides are petzite (Ag3AuTe2) and calaverite (AuTe2) Other tellurides present are silvanite ((Ag,Au)2Te4), hessite (Ag2Te)and kawazulite (Bi2(Te,Se,S)3).
The process carried out consists of cyanidation after oxidation in an alkaline environment. Cement is added to maintaina high pH. This processing allows a relatively high recovery. After the treatment the tailings contain less than 1 g/t Au. Theold tailings heaps from the mercury amalgamation treatment that was previously carried out contain more than 40 g/t Au.

References[1] L. Lorenzen, J.S. Deventer and W.M. Landi, “Factors affecting the mechanism of the adsorption of arsenic species onactivated carbon,” Minerals Eng., vol. 8, pp 557-569, 1995.
[2] P. Alfonso, H. Anticoi, T. Yubero, M. Bascompta., L. Henao, M. Garcia-Valles, S. Palacios and J. Yáñez “Theimportance of mineralogical knowledge in the sustainability of artisanal gold mining: A mid-south Perú case,” Minerals,
vol. 9, no 6, p. 345, 2019.

MMME 121-1