Abstract
This article evaluates the efficiency, benefits and limitations of pre-concentration by density separation for process mineralogy studies of low-grade gold ore. The pre-concentration by density aims to generate a product with a high content of gold and to maximize the number of gold-bearing particles characterized, thereby increasing the representativity and reducing the number of polished sections to be analyzed. Pre-concentration by density was carried out for a low-grade sulfide gold ore (0.96 ppm) from the north of Brazil. The sample was ground to below 1.7 mm, sieved down to 0.037 mm and subjected to density separation, amalgamation of the heavy product and cyanide leaching of all products. Gold was assessed in each product to evaluate the separation recovery and distribution. The finer the particle size, the higher the gold distribution in the heavy product, due to a higher degree of liberation of gold and sulfides; these values varied from 65% to 84% in fractions below 0.60 mm and decreased from 40% to 13% in the coarser fractions. Regarding gold distribution, fractions finer than 0.84 mm indicates a notable increase on gold recovery by amalgamation, indication higher surface exposure.
Highlights
In sulfidic refractory gold ores, gold particles may be highly disseminated and locked up in sulfides in the form of pyrite and arsenopyrite
There are a limited number of approaches to the separation of dense minerals focused on pre-concentration by density separation; when used along with automated mineralogical techniques, laboratorial separations can provide a very powerful method for quantifying populations of gold fundamental to ore characterization and plant optimization studies in the gold industry
Several polished sections prepared from the heavy product were analysed by scanning electron microscope (SEM)/EDS
Summary
In sulfidic refractory gold ores, gold particles may be highly disseminated and locked up in sulfides in the form of pyrite and arsenopyrite. Two typical problems can affect the results of gold ore concentration: variations in the gold grade and in the representativity of the samples (Zhou et al, 2004; Coetzee et al, 2011; Ueda et al, 2016). Samples that contain high-grade variations may hinder the determination of a suitable number of polished sections to examine. The grade of gold in milled products and tailings is usually low, and this leads to a low proportion or a limited number of gold grains in polished sections. For low-grade refractory sulfide ore, it is slow and expensive to study sufficient numbers of polished sections to adequately address the possible statistical error
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