Harmony's Unisel Gold Mine, situated in Welkom, Free State Province is an intermediate-depth low-grade operation that is currently mining three different reef bands, namely the Leader Reef, Middle Reef, and Basal Reef. Historically, stope support has consisted mainly of timber packs. However, installing packs at a high stope width where the dip varies between 25° and 35° has proved challenging.

Alternative support units were investigated, but none were available to fulfil the ideal design. The development of a new support product, together with Elbroc Mining, has resulted in a positive solution to this problem.

The new support unit sufficiently supports the stopes and ensures stability from a rock engineering perspective. It also has mining engineering benefits like improved efficiencies, reduced logistical tramming, ease of installation, and improved production rates, and thus offers economic benefits for the operation.

INTRODUCTION

Unisel Shaft is situated centrally within the Free State goldfield. The goldfield forms the southwestern corner of the greater Witwatersrand Basin and mining is focused on two auriferous conglomeritic horizons, the Basal and Leader reefs. Both reef horizons lie within the Central Rand Group of the Witwatersrand Supergroup.

Structurally, the Free State goldfield represents a north-pitching asymmetrical syncline, which closes towards the south. The syncline is split along its axis by the De Bron Fault and associated north-south trending faults.

The Basal Reef is extensively developed around the southwestern corner of the Witwatersrand Basin. It strikes north-south in the section east of the Stuurmanspan Fault and northwest to southeast in the section west of the Stuurmanspan Fault. The Basal Reef sub-outcrops against the Leader Reef to the south of the mining area within the lease area. To the west, the Basal Reef sub-outcrops against the Leader Reef beyond the lease area.

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