Abstract
Mineralogy and gold processing techniques from several mining areas of the Nazca-Ocoña gold belt, Mid-South Peru, were investigated to assess the efficiency of gold extraction methods in relation to their mineralogy. The deposits from this belt are intrusion gold related to mineralization in quartz veins. Native gold occurs as micrometric grains encapsulated in pyrite and in minor amounts in other sulfides and quartz. Electrum is found mainly in fractures of pyrite and attains up to 35 wt. % Ag. In addition to these occurrences, gold tellurides also occur and they are abundant in San Luis. Gold processing is carried out by amalgamation with mercury and/or cyanidation. The comparison of the gold grade in the mineralizations and in the residual tailings indicates that a significant amount of gold is not recovered using the mercury amalgamation process and also, in the case of the gold recovery by cyanidation, except when cement was added to the cyanide solution. This was due to an increase in the pH that favours the dissolution of the gold matrix. In the cyanidation process carried out in tailings previously treated with mercury, part of the mercury retained in them is released to the atmosphere or to the cyanidation fluids.
Highlights
Artisanal gold mining (ASM) is a widespread activity that involves more than million workers [1].It was estimated that in 2013 there were about million gold artisanal miners worldwide [2]
Determination of the nature of the minerals that constitute the host rocks of the gold-bearing veins is important because they have an effect on the grinding characteristics, are necessary to define the effectiveness of cyanidation [26], and have to be quantified to predict the possible generation of acid mine drainage produced during the mining activities
In the Nazca-Ocoña belt, gold-bearing veins are filled with quartz and minor amounts of calcite appear only in some of them
Summary
Artisanal gold mining (ASM) is a widespread activity that involves more than 15 million workers [1]. It was estimated that in 2013 there were about 16 million gold artisanal miners worldwide [2] This number increased up to 20 million in 2017, which represents 50% of the total number of artisanal and small-scale miners [3], with an estimated gold production between 380 and 450 t/year [2]. Artisanal gold represents between 20% and 30% of all the extracted gold in the world [4]. This ratio could be even higher because the commercial activities of artisanal mining are poorly ruled and information can be obtained from field surveys of miners and Artisanal Mining Associations, and from traders who buy gold directly from miners [2]. Gold mining is one of the most important economic activities in Peru, to the point that thanks to this activity Peru is no longer considered a developing country but an upper-middle income country [5,6,7]
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