Performance of Sample Preparation for Determination of Gold in Samples of Geological Origin

Abstract

We investigate the performance of sample preparation of gold ores using vibratory (bowl, ring and puck type) mills in common use in mineral analytical laboratories. The main criteria for effective grinding are using reduced grinding charge masses ≤ ca. 50% of nominal bowl capacity and using a grinding aid to prevent caking. We show that gold particles of millimetre scale can be comminuted to ≤ 100 µm by grinding in silica flour, bauxite, synthetic carborundum, or mixtures of silica and these materials using times of up to 5 min and that 95% < 50 µm is achievable with extended grinding. This suggests that modified grinding techniques can be used to make sample masses ≤ 5 g viable for routine determination of gold in geological samples. We also demonstrate homogenisation of a gold‐bearing copper sulfide mineral flotation concentrate alone and in mixtures with silica by extended grinding at reduced charge masses. To support this work, we develop a convenient new benchmark of gold ore sample preparation performance ‘G’, an apparent maximum gold particle size interpolated from replicate analytical variance in order to overcome the limitations of laborious sieve fraction analysis of gold particle size. We show useful agreement between G and sieve fraction analysis of gold particle size in samples and test the viability of G experimentally and by analysis of literature data.

Statistical evaluation of the uncertainties in the characterization of South African mine tailings

“…where H E is the relative homogeneity, which was calculated based on the mean sample mass and the number of observations. The objective is to obtain a low homogeneity factor (≤ 10%), that will eventually lead to the requirement of a small sample mass that will give an uncertainty of ≤5% at a 95% confidence interval, according to Equation 3, 20 where UNC is the required uncertainty at a specific confidence interval.…”

Atomic spectrometry update – a review of advances in environmental analysis

“…Reverse aqua regia was an efficient reagent for Au extraction under the high temperature conditions (240–270 °C) employed and was preferable to HF- aqua regia because it only released limited amounts of Hf and Ta, whose oxides would otherwise cause significant interferences. Daniel et al 252 evaluated procedures for preparing gold ores using various types of mills in common use. Optimal performance required the use of a grinding aid such as silica flour or bauxite to avoid caking; a 1 + 1 mixture of silica and bauxite proved to be as effective as grinding in 100% silica.…”

Guest Editorial: Special Issue Based on the 2018 IAG Geoanalysis Conference

“…The remaining three contributions are concerned with technical advances in sample processing an analysis. Daniel et al (2019) investigate and refine sample preparation methods for extraction and determination of gold. They showed that a modified grinding technique allowed reliable results to be obtained for small test portion masses.…”

“…Daniel et al . () investigate and refine sample preparation methods for extraction and determination of gold. They showed that a modified grinding technique allowed reliable results to be obtained for small test portion masses.…”