Broken ore density (BOD) is an important parameter in planning a block cave mine. However, its assessment is complicated by the heterogeneous nature of its distribution within a draw column, varying from a denser central plug-flow zone and decreasing outwards towards outer perimeter shear bands. The BOD further decreases immediately above the drawpoint due to the development of a loosening zone that develops in response to mucking. This makes determining BOD a challenging task, hindered by the inability to measure it in situ. To address this, several key factors influencing BOD are investigated including the influence of primary and secondary fragmentation, air gap thickness, draw rate and column height. Data is used to link primary and secondary fragmentation to broken ore size distributions. From these, a conceptual framework and empirical procedures are presented for evaluating BOD within draw columns during block caving for feasibility and early stage mine planning and design.
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