The theory and practice of particulate sampling grew out of the need for accurate assays of the grades of ores, concentrates, and coals that were traded in the mining areas of the USA and UK in the period between 1850 and 1930. The origins of sampling theory and practice are deeply embedded in the financial implications associated with sampling and follow-up trading of ores and concentrates. In fact, so prolific were the authors and writers about the issues involving the sampling of ores and concentrates that Sharwood and von Bernewitz (1922) from the US Bureau of Mines compiled a list of 906 pieces of literature on sampling up to July 1921. Some of the more famous sampling and blending authors of the time were Reed (1882),

This paper presents an overview of the pioneering work of Pierre Gy on the Theory of Sampling (TOS) over a period of 66 years-a monumental legacy of dedicated work to the science of sampling. It starts with the early years, beginning in 1949, when Gy worked tirelessly, often in isolation, and not without resistance from other scientists, to create a systematic, mathematically based framework within which every error arising from sampling of a heterogeneous material can be identified (named), analysed and explained. Gy is widely remembered for "The Formula", which expresses the variance of the fundamental sampling error (FSE) in terms of the mass, fragment top-size and various other compositional attributes of the minerals of interest. But as early as 1947 the seeds of two related questions were planted: "How... to sample" and "How much... material should one take", which eventually evolved to become the Theory of Sampling, essentially completed in 1975. Presentation of this famous equation to the scientific community led to a period of intense practical experimentation on stationary lots that continues to this day. Gy also addressed the challenge of sampling from fluxes and here identified the variability due to autocorrelation between samples taken from flowing streams that led ultimately to the discipline of chronostatistics, a study of variability in one-dimensional streams. The scope and depth of Gy's research endeavours grew during the 1960s and led to his encounter with metallurgical balance and reconciliation. As a result, Gy developed the idea of proportional sampling that allows several material streams to be sampled according to the same selection probability with very efficient reconciliation benefits. The TOS was also further extended to include the problems that producers faced in regard to bed blending. Gy was a prolific writer and published over 250 different articles and books, with his last four papers published in the

Grade control in underground mines aims to deliver quality tonnes to the process plant via the accurate definition of ore and waste. It comprises a decision-making process including data collection and interpretation; local estimation; development and mining supervision; ore and waste destination tracking; and stockpile management. The foundation of any grade control programme is that of high-quality samples collected in a geological context. The requirement for quality samples has long been recognised, where they should be representative and fit-for-purpose. Once a sampling error is introduced, it propagates through all subsequent processes contributing to data uncertainty, which leads to poor decisions and financial loss. Proper application of the Theory of Sampling reduces errors during sample collection, preparation, and assaying. To achieve quality, sampling techniques must minimise delimitation, extraction, and preparation errors. Underground sampling methods include linear (chip and channel), grab (broken rock), and drill-based samples. Grade control staff should be well-trained and motivated, and operating staff should understand the critical need for grade control. Sampling must always be undertaken with a strong focus on safety and alternatives sought if the risk to humans is high. A quality control/quality assurance programme must be implemented, particularly when samples contribute to a reserve estimate. This paper assesses grade control sampling with emphasis on underground gold operations and presents recommendations for optimal practice through the application of the Theory of Sampling.

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