Analytical data for the platinum-group elements (PGE) and gold on 17 samples from sulfidemineralized and -unmineralized rocks of the lower portion of the upper zone and two samples from the main zone of the eastern Bushveld Complex are presented. Almost all samples contain less than 100 ppb total PGE, indicating that the sulfide-enriched layers of the upper zone generally contain only negligable amounts of PGE. However, PGE enrichment previously reported from a sulfide-bearing anorthosite below the lower magnetite layer 2 has been confirmed by microscopic investigations and is interpreted as a zone locally enriched by hydrothermal fluids.
Increasing PGE concentrations and Pd/Ir and Pt/Pd ratios with stratigraphic height indicate differences in the behavior of the PGE. Incompatibility follows the sequence Ir < Rh < Ru < Pd < Pt, with Pt being approximately eight times more incompatible than Ir. Rocks below and above the main magnetite layer are characterized by two different PGE patterns which are seen as the effect of a magma-mixing event which resulted either from a breakdown of density stratified liquid layers or an influx of a small volume of new magma at the level of the main magnetite layer.Rocks below the main magnetite layer display a chondrite-normalized PGE pattern similar to that of the Picket Pin Pt-Pd deposit in the Stillwater Complex.
Mineral resource and ore reserve estimates are founded on two sources of data: tonnage and grade. The tonnage is a product of volume and density; both of which are estimates. Density impacts numerous operational factors, which include, but are not limited to, mine design, mine planning, equipment selection and operational performance. Hence, density is a significant parameter and its determination requires similar care as the measurement of grade. This paper provides an overview of methods used to determine density within the Anglo American Group. It is not the purpose of this paper to identify a preferred method, but to highlight the importance of choosing the best suited practice for a project or mine site. In addition, a case study comparing two different density determination methods applied to the same rock samples from the Los Bronces Copper mine in Chile was undertaken and the results of that study are presented here. Selecting the most appropriate method to determine density and comparing results from two or more techniques against each other, together with other suitable quality control procedures, is considered to be essential for mining operations and exploration projects in order to reduce risk and to improve operational performance, which in turn increases profit margin.
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