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.

A protocol based on peroxide fusion has been developed for the determination of Au in metallurgical samples and ores covering a wide range of concentrations and diverse mineralogies. The quantity of Na 2 O 2 required was minimised, while maintaining lixiviant efficacy, by the use of mixed NaOH + Na 2 O 2 fluxes. The method was shown to be applicable to the determination of coarsely-particulate gold. Fusion cakes were dissolved in hydrochloric acid and then extracted using methylisobutylketone to provide concentrations appropriate for quantification by graphite furnace atomic absorption spectroscopy and to minimise interferences from dissolved salts. The protocol was tested on a variety of certified reference materials and produced results in excellent agreement (at Au concentrations ranging from 0.05 to 47 µg g -1 ) with the traditional lead fire assay method, while avoiding the health and safety issues associated with that technique. KeywordsGold, peroxide fusion, metallurgical samples, ores Highlights 3 to 5 bullet points (maximum 85 characters, including spaces, per bullet point) Peroxide fusion GFAAS method suitable for routine commercial lab analysis developed Results comparable to Pb fire assay over wide range of mineralogy and concentration Potential for gold losses critically evaluated and found to be minimal Addition of NaOH significantly reduces amount of Na 2 O 2 required