A Study on Introducing Sublevel Open Stoping (SLOS) in the Hishikari Mine

The Hishikari Mine is the only major gold mine operating in Japan, whose production rate in 2008 was around 184,000 tonnes with the average gold grade of 42.8 g/t. The gold veins are extracted mainly by drifting and bench stoping with backfill. Blasted waste rocks are generally used as backfill materials and crushed waste rocks with cement (cemented rock fill) are used for larger stopes. In order to extract the KE-2 vein with wider mineralization and lower grade, being closely located to the narrower KE-3 vein with higher gold grade, we have studied the applicability of the sublevel open stoping (SLOS) with cemented rock fill through in-situ measurements of rock mass displacements and numerical stress analyses for evaluating the stability of the KE-2 large SLOS stopes and interaction with the KE-3 bench stopes. We have used a bi-linear stress-strain characteristics of backfill for modeling the nonlinear compaction of cemented rock fill, whose stiffness increases with wall displacements of the backfilled stopes. The non-linear compaction may affect support characteristics of backfill, the present paper, therefore, incorporates the two-stage/bi-linear compaction modeling of backfill in FLAC3D in order to analyze the supporting effects of the cemented rock fill and to investigate the required backfill quality and mining sequence for more stable and steady operations of the KE-2 and KE-3 stopes.