Holistic management of sulphides at Rio Tinto Iron Ore's Pilbara mine sites

Abstract

Rio Tinto Iron Ore (RTIO) manages eleven mines in the Pilbara region, Western Australia. Three of these mines have previously or are currently mining black shale that contains varying amounts of pyrite. Several new deposits currently being evaluated and existing mines that may progress below water table in the future, will also encounter this waste material. The black shale presents not just an acid rock drainage risk but also a spontaneous combustion risk. This paper presents the black shale management strategy and provides an overview of the relevant activities undertaken by RTIO. The strategy can be divided into two components which firstly involve defining the risk and secondly involve managing the risk. The mineral waste management plan is used to identify specific mineral waste hazards by:

•geochemical characterisation of waste material,

•undertaking mine site specific risk assessments,

•characterising the receiving environment,

•identifying sulfidic boundaries in geological and mining models,

•quantifying the amount of sulfidic material in medium and long-term mine plans, and

•designing and sequencing black shale waste dumps.

Once a mine exposes black shale the Spontaneous Combustion and Acid Rock Drainage management plan is used and the major activities are:

•regular site meetings with a representative from every group that works with black shale;

•compliance with safe working procedures for site specific and detailed activities;

•regular training;

•the use of specific explosives to prevent premature detonation;

•ongoing geochemical characterisation;

•acid water management, monitoring and analysis;

•regular internal and external auditing of procedures and practices; and

•closure planning assessments and preparations (ie cover trials, geochemical void modelling, geochemical waste dump modelling).

The success of this holistic strategy is evident by the awareness of personnel within the business, thorough understanding of the geochemistry and by undertaking proactive management of black shale during mining. The strategy and management plans adopted by Rio Tinto Iron Ore have activities that other mine sites with potentially acid forming material may like to consider implementing.