Application of Micro-Analytical Techniques to Au-bearing Samples from El Peñòn, Chile

Mineral system understanding

Dr Andrew Menzies

Universidad Católica Del Norte

Knowledge of the distribution of minerals and elements within a deposit is key to determining the most efficient mineral processing procedure, especially in epithermal deposits where numerous factors can impact on the Au-Ag recovery. El Peñòn is a low-sulfidation epithermal deposit, incorporating numerous veins of different grades, with various geometallurigcal classifications from oxide to sulphide and various mixtures of the two. The mineral processing cycle incorporates cyanide as the primary reagent in the gold recovery, which reacts easily with Mn, oxidizing the cyanide and transforming it into a cyanate, thus increasing the cyanide consumption, affecting recovery, and increasing production costs. In addition, the process solution generates a gel that obstructs plant pipe-lines affecting the process and maintenance. A protocol is proposed incorporating various micro-analytical techniques to obtain the most cost effective and relevant information as timeously as possible. This includes the mineralogical and elemental scanning using μXRF of large samples (up to 20 x 18 cm analytical area) from different veins representing the various geometallurgic units. As sample preparation is minimal, analytical turn around time is quick. Based on the μXRF results, a subset of key (and commonly Au-Ag enriched) samples can be analysed in detail by crushing or mounting specific rock fragment specimens to obtain statistically more relevant Au-Ag mineralogy information using e-beam automated mineralogy combined with SEM-EDS point analysis. This study will present a range of these results from El Peñòn, with specific emphasis on the Mn and Au relationship and the impact on mineral processing.

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