In light of the apparent productivity benefits provided by mechanised stoping, Impala Platinum Limited commissioned a study to investigate its possible implementation for mining reserves located 1200–1700 m below surface. This paper records the methodology employed for designing a support system for such mechanised mining, as well as initial conclusions of the work done. Preliminary results show the concept to be technically feasible; work was however stopped due to financial non-viability.

En consideration des benefices de production apparents que donne l'exploitation par gradins mecanisee, Impala Platinum Limited a commissionne une etude visant à examiner sa mise en oeuvre possible pour des reserves minières situees à 1200–1700 m sous la surface. L'etude presente rapporte la methodologie employee pour creer un système de support pour ce genre d'exploitation mecanisee, ainsi que les conclusions initiales de ce projet. Les resultats preliminaires montrent que le concept est techniquement faisable; cependant le travail fut arrête à cause de difficultes de rentabilite.

Im Licht des offensichtlichen Produktivitatsnutzens auf Grund mechanisierten Stossbaus, kommissionierte Impala Platinum Limited eine Studie, die dessen mögliche Implementierung fuer den Abbau von Reserven 1200–1700 m unterhalb der Oberflache untersuchen soll. Dieses Elaborat dokumentiert sowohl die Methode die fuer das Design eines Unterstuetzungssystems fuer eine derartige mechanisierte Abbauweise angewendet wird als auch die anfanglichen Konklusionen der geleisteten Arbeit. Anfangliche Resultate zeigen daß das Konzept technisch durchfuehrbar ist; die Arbeit wurde jedoch wegen der finanziellen Nichtrealisierarkeit gestoppt.

Introduction

Impala Platinum Limited is situated some 30 km North of Rustenburg in the North West Province and exploits the Western lobe of the Bushveld Igneous Complex for platinum group metals from a 12000 hectare lease area. The shallow-dipping Merensky reef and UG2 chromitite seam are currently accessed by thirteen shaft systems and mined from 30 to 1100 metres along a 25 km strike length.

The 16 shaft project, the first fourth-generation "deep" shaft complex, will exploit reserves between 1200 and 1700 m below surface. The geotechnical environment will change from "shallow" to "intermediate" with the increased mining depth, requiring new design and support strategies.

Trackless mechanised stoping, commonly used on shallow Bushveld chrome mines, promised a faster production build-up and greater tonnages than conventional narrowreef stoping, thus reducing costs and improving financial viability. As part of the pre-feasibility study, Spencer Rock Mechanics Consultancy was contracted to assist with designing a room and pillar layout for the project.

Design considerations and approach

With the range of depths being considered for the 16 shaft project, the magnitude of stope closure critically affects the operating viability of the trackless equipment. The design approach therefore centred on the principle of creating a stable pillar system to maintain pillar stresses at acceptable levels and to minimise the amount of stope closure.

The starting point for the design process was to determine the pillar strength characteristics of both the Merensky and UG2 seam types for the primary and secondary extraction phases. This required specialised 3-dimensional non-elastic modelling which was undertaken by Itasca Africa (Pty) Ltd.

This content is only available via PDF.
You can access this article if you purchase or spend a download.