Abstract
Abstract Fundamental Sampling Error (FSE) is generated whenever a sample is taken from a lot of particulate material and is caused by an intrinsic characteristic of every mineral deposit: the constitutional or intrinsic heterogeneity of the ore. FSE is the only error that can never be eliminated in sampling processes, but it can be reduced to acceptable values. The optimisation of sampling protocols is based on the minimisation of FSE and is essential to reduce the deviations of grade estimates for mine planning, process control and mine-to-mill reconciliation. In order to calculate minimum sample masses and to optimise sampling protocols, heterogeneity studies have been developed. The original heterogeneity test (HT), proposed by Gy (1967) and Pitard (1993; 2009), is an experimental method of obtaining the intrinsic heterogeneity (IHL). Most of the heterogeneity studies available in Brazilian literature have been performed on gold deposits, which have higher intrinsic heterogeneity due to the nugget and cluster effects and low grades, unlike base metal deposits. Nickel ores have never been the focus of heterogeneity studies in Brazil or worldwide. Therefore, the factors that compose IHL have never been validated for nickel ores, which was the objective of this article. Based on the results of the heterogeneity test performed on a nickel ore from Niquelandia, Brazil, the standard deviations of FSE were calculated at each stage of the sampling protocol. An optimised protocol is proposed herein, in which the total deviation of FSE is below the maximum value recommended by Pierre Gy’s Theory of Sampling (TOS).
Highlights
This article presents an optimisation study at the plant feed of a nickel mine in Brazil, in order to characterise the intrinsic heterogeneity of the ore fed to the plant and to optimise the current sampling protocol by reducing the Fundamental Sampling Error to the limits recommended by Pitard (1993; 2013)
The objective of this study was to quantify the intrinsic heterogeneity of the ore by the heterogeneity test and optimise the sampling and sample preparation protocols, ensuring that a maximum relative standard deviation of Fundamental Sampling Error (FSE) is generated in each step of the protocol
When increasing the mass of the primary sample to 100 kg for the silicate and blended ores, and to 140 kg for the oxidized ore, the relative standard deviations of FSE are significantly reduced, reaching acceptable values and guaranteeing that the samples are sufficiently representative of the initial lot
Summary
This article presents an optimisation study at the plant feed of a nickel mine in Brazil, in order to characterise the intrinsic heterogeneity of the ore fed to the plant and to optimise the current sampling protocol by reducing the Fundamental Sampling Error to the limits recommended by Pitard (1993; 2013). The test proposed in this study is the standard heterogeneity test (HT) developed by Gy (1967) and Pitard (1993; 2009), which is the only experiment that isolates the Fundamental Sampling Error. The current sampling protocol of the nickel plant feed includes the following stages: primary sampling, crushing, division, pulverisation and selection of an analytical sample (Figure 1). The primary sample is crushed to 0.2 cm and an aliquot of 250 g is taken for pulverisation, which reduces the size of the fragments to 0.0149 cm
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