Bachelor of Science (Honours)
School of Earth & Environmental Science
Graham, Luke Michael, Analysis of the weathering profile associated with the near surface 2 Lens & B Lode of the Giant Broken Hill PB-ZN-AG Orebody, Perilya Limited's Southern Operation, Broken Hill NSW, Bachelor of Science (Honours), School of Earth & Environmental Science, University of Wollongong, 2014.
The Southern Operations (CML 8) is situated within the Curnamona Province of Western New South Wales, along the southern extent of the Giant Broken Hill Pb-Zn-Ag orebody. Previous estimates of the near surface reserves of both 2 Lens and B Lode between sections 10 – 30 have been calculated to consist of 705 kT of ore at 81 kT combined Pb/Zn. However the metallurgical recovery (floatability) of these reserves may be substantially lower than previously estimated due to the oxidation of hypogene ore following climatic adjustment (prevailing arid regime) during the last glacial maximum. Therefore whilst the identification of a secondary zone within the central mining field has been substantially documented by previous academics, with mineral assemblages correlating to a two-phase oxidation cycle following the decline in the regions palaeo-water table (illuvial zone), the irregularity of the orebody‟s geometry, mineralogy (internal stratification) and structural geology indicates that a simple paragenetic model cannot be applied over the entire mine sequence. As a result field-based observations, whole rock geochemistry and petrographic analysis were used to describe the mineralogical/elemental nature of the secondary zone within the southern mining district, relative to observations made by earlier academics within the central mining leases. These investigations further support the notion of two-phase oxidation cycle with samples within both the gossanous and complex carbonate zone of 2 Lens and B Lode exhibiting a diversification of secondary minerals within several morphological forms, relative to the overprinting of the palaeo-supergene blanket following redissolution. However in comparison with the central mining district the southern extent of 2 Lens and B Lode notably displays a less extensive secondary zone, with only an estimated 1681.53 t (2.076% of the reserve) of pre-existing hypogene ore having undergone oxidation to form secondary minerals (i.e. cerussite and smithsonite). This can notably be attributed to substantial sulphide armouring of enclosing siliceous (low grade blue quartz lode) and metasedimentary units within both the clastic calc-silicate and garnet quartzite horizon, in relation to the orebody‟s plunge 20° to the south (gradual increase in overburden). Whilst localised increases in the extent and intensity of the secondary zones can be further correlated to the transgression of several shear zones which trend coplanar to the orebodies (i.e. E1SZ and BLSZ) in which both adjoining wall rocks and high grade zones have notably undergone partial to complete oxidation, forming a series of limonitic webwork/boxwork structures after cerussite. However based on the analysis of drill core these zones notably decline in abundance from between 33.0 and 53.0 m over a transitional redox barrier (~13.0 m) with the underlying hypogene ore. Therefore due to the low intensity and extent of the secondary zones related to both 2 Lens and B Lode the deposit has been further classified as a low risk-high yield reserve.