ABSTRACT:
The LaRonde orebody is a world-class Au-Ag-Cu-Zn massive sulphide lenses complex with reserves extending from surface down to 3110 meters and still open at depth. Production is ongoing from 980 meters to 2360 meters below surface through the 2240 meter deep Penna Shaft, which is the deepest single lift shaft in the western hemisphere. Due to the large vertical dimension of the orebody, mining operations intersect a wide variety of environments. As the stress to strength ratio of the rock rises, the behavior of the rock mass changes drastically, from hard and brittle, to soft and squeezing. As a result, rock mechanics and ground control practices have evolved considerably as mining activities progressed deeper and the limits of conventional support systems were reached. This paper focuses on observed field behavior of support systems in the wide range of ground conditions found at LaRonde. In particular, this paper addresses the limitations of current support systems and provides preliminary results of a new ¡°hybrid bolt¡± that can overcome most of the limitations of current systems.
1 INTRODUCTION
1.1 LaRonde
Located near the village of Preissac in Northern Quebec, the LaRonde mine has been in operation since 1988. Over 600 employees are operating the complex, for an average production of 7250 tonnes per day. The 2240 meters deep Penna Shaft is used to hoist the ore. Production is ongoing between level 98 (980 meters below surface) and level 236 (2360 meters below surface), from 4 distinct mining horizons. Figure 1 presents a longitudinal view of the LaRonde orebody. As of 2005, reserves at LaRonde totaled over 17 million tonnes of ore, for over 1.6 million ounces of gold (m). The LaRonde orebody remains open at depth, with reserves as deep as 3110 meters below surface. Until late 2005, 215 was the lowest production level.
