The pitfalls of gold sampling

Multotec’s webinar (delivered by Willem Slabbert, Multotec Specialist: Sampling and Magnetic Separation) explores the challenges of gold sampling in processing plants. He also highlights how to take the guesswork out of sampling and turn it into measurement.

What is gold sampling in process plants?

This is the process of collecting and testing representative composite samples of dry or slurry material to determine whether gold particles are present, in what concentration (or grade) an with what confidence (ore precision level) can the gold deportment be reported to stakeholders and shareholders.

What are the common methods used for gold sampling?

Common gold sampling methods include:

• In ROM and crusher products, cross-belt or falling-stream cutters are used for process control and/or metal accounting sampling.
• In gravity circuits, pan or table checks are used to regularly sample the feed, concentrate, middlings, and tails for process control purposes.
• In grinding/classification circuits, automated slurry samplers are used at metal accounting points like mill discharge and cyclone overflow.
• In leach/CIP/CIL, pulp samples are taken for process control throughout the leach train, as well as solution samples.
• In the thickener/filtration/tailing streams, the final tails (or residue) is sampled for metallurgical accounting.

What equipment is essential for effective gold sampling?

Metallurgical accounting standard sampling of gold should not be compromised and cross stream sampling methods for all metal accounting sampling points is a must.

Multotec is a global leader in wet and dry mineral sampling solutions, offering an extensive range of mining, mineral and industrial samplers that complies to ISO-, AMIRA- and CNAM 007 standards. Learn more about our solutions for sampling, here.

What is the best sampling method?

Gold sampling gurus will tell you that if something can go wrong in sampling, it’ll happen in gold sampling (and it’ll happen in a big way).

This is because gold has high heterogeneity (i.e. significant variability in composition, texture and particle size distribution) and this is emphasised when grades are decrease. In addition, gold is prone to segregation in the slurry pipes and on conveyor systems. In addition, if there is a bias, it’s never equal, so we cannot apply a sampling correction factor.

All of this makes it especially difficult to get an accurate sample in gold processing.

Bias generating sampling (e.g. via various falsely marketed, cheap, non-probalistic sampling devices) is not accurate. Cross-stream sampling (by means of a cross-belt, or cross stream sampler) is the only option that enables a sample that measures the variability that may exist along the width and/or height height of that stream – taking otherwise unnecessary guess work about short range variability and converting it to scientific measurement of gold grade.

Where can you learn about best practices for gold sampling?

Multotec has over 50 years of global experience in mineral processing, offering leading equipment and technology, as well as the latest insights on mineral processing technologies, equipment and processes.

Multotec has a designated sampling advisory service that assists customers in selecting the optimum mineral sampling solution for their application. We also assist in providing a fit-for-purpose, custom-engineered system that meets the mineral sampling requirements on individual process plants. For more information about our sampling advisory service, contact us today.

In addition to this service, we offer regular mineral processing masterclasses (webinars) for the professionals in our industry, as well as customised on-site training and workshops.

Get more information about our training, here and our webinars, here.

Closing thought

Gold sampling can be complex and challenging. It’s essential to understand how to avoid sampling errors (e.g. crushing too finely in dry sampling circuits) and how to employ the right equipment, to get best results. Bias generating devices may be deemed to be more cost-effective, but these don’t lead to quality. Cross-stream sampling solutions – such as those offered by Multotec – are renowned for their years long refinement to allow unbiased and unambiguous sampling results when it matters most.

For information on the subject, contact Multotec. You can watch the complete webinar, here.