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From mines to mesas: a rehabilitation journey at a gold mine in the Pilbara, Western Australia

Paper from the Proceedings of Mine Closure 2015 conference held in Vancouver, Canada, June 1-3, 2015. (downloadable PDF)

Authors: C.D. Tiemann, Newcrest Mining Limited, Australia; M. Wealleans, Environmental Consultant (formerly Newcrest Mining Limited), Australia

Published by InfoMine Inc.
ISBN: 978-0-9917905-9-3
Copyright: 2015, InfoMine Inc.


Abstract

The Telfer gold mine (Telfer) is located approximately 1,800 km north-northeast of Perth, Western Australia (WA), in an arid environment that experiences a hot wet season followed by a warm dry season. In 2004, Telfer embarked on a 10-year research program involving the design and management of large waste rock dumps. Under existing legislative conditions, Telfer is required to design and construct waste rock dumps that are compatible with the regional physiography, stable in the long term and do not present future acid mine drainage risks. In order to meet these conditions, the company initiated a mesa landform project, which involved an extensive ecohydrology program and progressive rehabilitation trials focused on replicating the natural mesas (concave slopes and flat-topped landforms) of the Pilbara region.

The project represents a significant divergence from the traditional approach of surface ripped, berm- and bench-style slopes typical of older mines in WA. This approach has been generally affected by tunnel erosion and rill and gully erosion, both evident in places at Telfer. The project aimed to determine whether these erosion features could be overcome on artificially constructed mesa-styled landforms and, if so, whether they could be integrated into Telfer’s rehabilitation strategy for eventual mine closure.

Project researchers began by collaborating with the University of Western Australia to gain an understanding of ecohydrological processes in the Telfer region. The ecohydrology study aimed to assess the interaction of soils, vegetation and hydrology in the arid zone by analysing water fluxes in a range of natural ecosystems. This information was then used to develop designs and assessment techniques for rehabilitation trials using the mesa concept.

The rehabilitation trials were completed in three stages. Stage 1 was completed in 2007 on a 30-metre-high waste rock dump. The dump was battered down to create a concave slope at angles of 16, 25 and 37 degrees. Four slope treatments were then applied using a combination of soil and competent rock. A series of hummock dumped treatments, for controlling surface water flow, were constructed on the dump’s top surface. Stage 2 trials completed in 2009; this stage involved the rehabilitation of a satellite waste rock dump (20 hectares in area and 25 metres high). It used concave slopes at angles of 7, 16 and 37 degrees with application of hummocks as the surface treatments. The Stage 3 trial was completed in July 2013 on a 60-metre-high waste rock dump with three slope treatments applied. The slope was battered to concave angles of 12, 20, 25 and 37 degrees.

The ecohydrology study and progressive rehabilitation trials showed that a mesa-styled waste rock dump landform incorporating a concave slope and hummock dumped capping system was stable, supported vegetation and met government approval criteria.

Overall, the mesa concept has many additional advantages over the standard berm-batter-berm approach, including a smaller footprint, reduced surface area to rehabilitate, potentially easier landforming and enhanced environmental and aesthetic qualities.

After successfully constructing the three mesa rehabilitation trials and obtaining regulatory approval in 2015, a progressive rehabilitation plan was developed. This included a three-year program encompassing up to 50 hectares, which have now been integrated into the surface mining operations.


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