Gold Characterization by MLA and Technological Tests: Discussion of Sample Preparation and Results

Abstract

Gold has been present throughout the history of mankind and used to make jewelry and coins, and recently, it is put into use in industry. The price of gold in international market had a significant increase, surpassing 100 % in the last 5 years. Thereby, deposits with low levels of gold content as well as gold with complex associations or in a very fine particle size became exploitable again, allowing new projects and expansion of existing ones. However, as maximum process efficiency is indispensable and deep knowledge of the characteristics of these minerals and their behavior in face of beneficiation processes. Consequently, an accurate routine for mineralogical and technological characterization is essential. This chapter presents a methodology for characterizing low-grade ores with fine-grained gold. The procedure was conducted in three different samples from different regions, mineralogical assemblages, and grades.

Gold grains and their associations were characterized by SEM-based automated image analysis using the MLA SPL_Lt method, which consists in the initial search of gold, as well as other quite heavy minerals (e.g., platinum, silver, etc.), by atomic number contrast (backscattered electrons) and further identification of these phases and their mineral associations by EDS spectra. The automated routine is set up for allowing the identification of gold grains measuring down to 0.5 μm. Gold extraction assays were accomplished by amalgamation and cyanidation leaching of products from heavy liquid separation. The grades and partition of gold among mineral separation products are discussed in order to evaluate the significance of the gold density preconcentration prior to the characterization by an automated image analysis system. The results attained at mineralogical studies are correlated to the extraction of gold.