Orebody modelling for exploration: the western mineralisation, Broken Hill.

Abstract

The Broken Hill Zn-Pb-Ag deposit (Australia) is the largest base metal deposit in the world (Large et al. 2005)1. Despite almost 130 years of mining, core logging is still undertaken qualitatively. Most old core has disappeared. The Western Mineralisation is the subject of this study and it is soon to be exploited in the Rasp Mine. The 77 Western Mineralisation drill cores provided an opportunity to statistically evaluate 3,215 surface and underground samples. In this process, 61,696 data were acquired from magnetic susceptibility measurements and quantitative mineralogical, lithological and textural core logging. These data sets were integrated with assay, specific gravity, collar and survey data. The large data sets2 (93,192) were treated by statistical methods such as univariate and bivariate analyses, compositional data analysis, statistical test, linear multivariate regression, cluster analysis, principal component analysis, variogram analysis and univariate ordinary kriging estimation. Moreover, the previous data set of mineral chemistry was evaluated by correspondence analysis, compositional data analysis and principal component analysis. The statistical results were demonstrated in variety of diagrams such as bar diagrams, core log diagrams, contour plots, correspondence map, map of PC loading and PC score, biplot, 3D biplot and 424 cross-sections of the orebody. It was shown that Bi and Sb are pathfinder elements for the Western Mineralisation and that these elements form a broader halo around sulphide masses whereas Ag, As and Cd form a small halo. Galena-sphalerite rich ores have a higher proportion of magnetic pyrrhotite and magnetic susceptibility can be used to evaluate proximity to sulphide masses. Statistical studies suggest that Broken Hill might not be an isolated deposit and that the "next" Broken Hill may not be identical. Predictor elements for Pb are Fe, Ag and Bi and for Zn are Cd, Sb and Ag. Optimal sampling is on 22m and 10m along and across strike respectively and a 20 × 20 × 10 m polygon is the optimum size for block model analysis. The Western Mineralisation at Broken Hill is zoned from a Pb-Zn-S-Cd rich upper portion to a Cu-Ag-As-Bi rich lower portion. Variations within the Western Mineralisation may be primary features but are more likely to derive from intense tectonism. 1 Harvard (UTS) Style - 6th edition (version 2004) has been used for the purpose of citation and referencing. <http://www.lib.uts.edu.au/students/discover-your library/referencing-and-writing/endnote/styles> 2 The data base (Excel Format), additional diagrams and satellite maps of this thesis are provided in supplementary files included on a CD to this thesis.