Journal of the Southern African Institute of Mining and Metallurgy
versão On-line ISSN 2411-9717
CLAY, A.N.; MYBURGH, J.A.; ORFORD, T.C. e LEMMER, C.. Using simple statistics to define confidence limits for reliable quantitative definition of mineral resources - the Venmyn Variance Tower. J. S. Afr. Inst. Min. Metall. [online]. 2012, vol.112, n.11, suppl., pp. 985-992. ISSN 2411-9717.
In recent times, there has been criticism of the minerals industry over the lack of quantifiable boundaries between Inferred, Indicated, and Measured resources. A recent initiative through the United Nations aims to try to converge the mineral resource classification systems. Since the oil and gas industry uses a probabilistic approach to defining reserve boundaries, it is appropriate to introduce a similar statistical methodology for minerals. The Venmyn Variance Tower has been developed based upon traditional statistics to utilize historical and ongoing information in order to quantify variance of geological and chemical parameters and the boundaries and logic for quantitative mineral resource classification. It is proposed that a less than 50% variance from the mean of all sample parameters is required to achieve the classification threshold to define an Inferred Resource whereas between 20-10% is needed for an Indicated Resource and less than 10% variance from the mean is needed to declare a Measured Resource. These limits are similar to those used by the oil and gas industry, and it is suggested that these thresholds be adopted as an industry standard to ensure consistent quantitative reporting. While this process is intended to use statistics of an orebody to provide quantifiable and defendable boundaries, it cannot be carried out unless the geology of the mineral deposit is understood and the borehole samples can be categorized into appropriate populations for which the statistics are valid. This means that competent geologists are always required to work with and understand the implications of the Variance Tower results. This paper is intended to form the basis of a series of publications that establish a process to take mineral projects along a quantifiable and logical development path. Hence, no specific field example of the practical application of this process is given here.
Palavras-chave : mineral resource definitions; mineral asset recognition; number of boreholes; variance tower; probabilistic approach; confidence limits; @RiskTM..