ABSTRACT: This paper presents causes for elevated hazards in orebodies with inclined far-field stresses and shows that numerical and empirical approaches used in the analysis of orebodies under normal far-field stress loading conditions can give misleading conclusions when applied to sheared orebodies. Example procedures for identifying potential hazards in sheared orebodies and planning for such hazards are given using the FZone of Campbell Red Lake Mine. The F-Zone of the Campbell Red Lake Mine is not continuous, has offsets and is under shear loading and thus is unique in the study of orebodies under shear loading. The primary objective of this study was to provide guidelines for the safe and economic extraction of remnant sill and boxhole pillars in the F-Zone. The guidelines were to include identification of safe and economic distances of drifts (drift layout) for remote access to the orebody. A Drifts@Risk approach developed for drifting in stressed ground at the Laurentian University Geomechanics Research Centre was utilized to establish setbacks for future developments and the identification of the optimum drift layout.
1 OREBODIES IN SHEAR
Experience at the Geomechanics Research Centre (GRC) over the past ten years from three orebodies under shear loading (major far-field stress oblique to strike) shows several characteristic problems that differentiate them from those having major far-field stresses normal to strike. In these orebodies pillars and sills that occur at relatively shallow depths are more prone to spalling and rockbursting. The direction of mining also impacts the location and intensity of rockmass degradation in these orebodies (Falmagne, 2001). 1.1 Quirk and Lac Shortt mines Two previous practical cases can be cited where the stress field was inclined to the orebody plane rendering the mines rockburst-prone.