The established crown pillar extraction method at Gold Fields Australia Ltd.'s Crusader Mine, leads to the significant dilution and poor recovery of ore due to caving of the overlying loose rockfill. The application of selectively injecting specifically developed 'FB200' ettringite (calcium sulphoaluminate hydrate) type cement grout into loose rockfill to form a stabilised rockfill material, enables an artificial crown pillar to stabilise the surrounding rock mass and prevent caving of the overlying loose rockfill during crown pillar extraction. Investigation of the geomechanical criteria for crown pillar extraction beneath stabilised rockfill has enabled the safe and efficient extraction of two crown pillars at the Crusader Mine.

La methode actuelle d'extraction des piliers horizontaux à la mine Crusader dont la proprietaire est le Goldfields Australia Ltd amène à une dilution sensible du minerai, à cause de l'effondrement du remblai peu compacte qui se trouve au-dessus. Par moyen d'injection selective du coulis de ciment FB200 ettringite (sulfoaluminate de calcium hydrate) qui a ete developpe specifiquement pour cette application, un pilier artificiel est cree et celui-ci empêche l'effondrement du remblai pendant l'extraction du pilier de minerai au-dessous. A la suite des etudes geotechniques de la methode, deux piliers horizontaux à la mine Crusader ont ete extraites, de manière efficace et sûr.

Die feststehende Krone Pfeiler Extraktionsmethode beim Crusader Mine von Gold Fields Australien GmbH, fuehrt wegen caving des overlying lockerer rockfill zur bedeutungsvollen Verduennung und schlechtem Wiederfinden des Erzes. Der Antrag, ausdruecklich entwickelten ‘FB200’ ettringite selektiv zu spritzen, (Kalzium-sulphoaluminate-Hydrat) Art kittet Mörtelschlamm in lockeren rockfill, um ein stabilisiertes rockfill-Material zu bilden, ermöglicht einem kuenstlichen Kronenpfeiler, die umliegende Steinmasse zu stabilisieren und caving des overlying wahrend des Kronenpfeilerherausziehens lockeren rockfill zu verhindern. Untersuchung der geomechanical-Kriterien fuer Kronenpfeilerherausziehen unter stabilisiertem rockfill hat dem sicheren und tuechtigen Herausziehen von zwei Kronenpfeilern beim Crusader Mine ermöglicht.

Introduction

At Gold Fields Australia Ltd.'s (formerly WMC Resources Ltd.) Crusader Mine, significant resources have been sterilised due to the placement of loose rockfill above the crown pillars. Potential exists for the recovery of such crown pillars via the application of selectively injecting low viscosity cement grouts into the overlying loose rockfill to form an artificial stabilised rockfill crown pillar.

Due to the recent global turndown in the resource sector, and increasing social pressures to maximise resource recovery, significant benefits are to be gained by the Australian mining industry via the development of improved guidelines for the extraction of such sterilised mine pillars.

The Crusader Mine

The Crusader Mine is owned and operated by Gold Fields Australia Ltd (formerly WMC Resources Ltd.). The mine is located approximately 700 km north-east of Perth, Australia, and 23 km west of Leinster in the Eastern Goldfields region of Western Australia.

The orebody is associated with a flexure in the contact between an ultramafic and basalt unit which dips to the west at 50–60° and plunges to the north at 20–30°. The contact is highly sheared with a thickness of between 0.2 to 1.5 m. Splay structures come off the hangingwall.

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