SUSTAINABILITY TSF management
|Management of Tailings Storage Facilities June 2019
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Process plant tailings deposited in tailings storage facilities (TSFs) represent a significant waste stream produced by mines. By responsibly managing these wastes, we minimise their environmental and potential social impacts and demonstrate our commitment to maintaining our social licence to operate.
All operations have tailings management plans in place, including closure and post-closure management plans. After decommissioning, our TSFs are closed and rehabilitated in line with industry good practice. As at end-2019, our 11 operations – including our three JV sites, being the Asanko gold mine (AGM) in Ghana, Gruyere in Australia and Far Southeast (FSE) in the Philippines – contained 34 TSFs, of which 12 were active. During 2019, we commissioned the TSF at the new Gruyere mine and decommissioned TSF 3 at the Tarkwa mine in Ghana.
Of active TSFs, we have two in-pit TSFs (Agnew and St Ives), six downstream/centre-line TSFs, and four upstream TSFs.
Our mines in Australia and South Africa are located in relatively dry regions and limited amounts of supernatant water are stored in the facilities, significantly improving the overall stability of the facilities. In Ghana, Tarkwa's and Damang's TSFs are designed in accordance with industry best practice. We take extensive measures to confirm that the embankments remain stable throughout both the wet and dry seasons, and over the life of the facility.
Gold Fields is working with Lepanto Mining, our majority partner in the FSE project, to enhance risk mitigating measures for the TSF used by Lepanto Mining for disposal from its nearby gold mine. Since this TSF is located in a region prone to high seismic activity and frequent typhoons, Gold Fields and Lepanto Mining commissioned external consultants to undertake detailed hydrological, seismic and geotechnical reviews in support of improving the overall risk profile of the TSF.
Our technical teams continue to work with Asanko Gold, who manages AGM, to further strengthen risk assessment and governance of the lined and downstream-raised TSF.
Tailings depositions were 20% higher in 2019 than in 2018, amid generally higher production volumes, particularly at South Deep, and the commencement of mining at Gruyere.
All Gold Fields' active TSFs are subject to an independent, external audit every three years – or more frequently where required by local circumstances or regulations – as well as regular inspections and formal reviews by independent Engineers of Record (EoRs). The last external expert review was completed in 2017 and concluded that Gold Fields complied with the ICMM's Position Statement and that its TSFs, which were well managed and designed, did not show any signs of instability.
Gold Fields has progressively been implementing several improvements identified by this review, including:
The next round of independent external audits commenced at the end of 2019 and is due for completion by mid-2020. We have also embarked on a programme to further improve operational safety of our TSFs, including moving away from the construction of upstream facilities to centre-line or downstream designs, where practical, consideration of filtered and dry stacked tailings, as well as in-pit tailings disposal. These initiatives will also be the subject of work at the ICMM to improve critical TSF controls and reduce tailings water content.
In February 2019, the Gold Fields Board strengthened its oversight of the Group's TSFs through the introduction of quarterly TSF management reports, progressive implementation of continuous environmental and geotechnical monitoring, and increased external and independent verification. The Chairperson of the Board Safety, Health and Sustainable Development Committee visited all managed TSFs during 2019 and reported his satisfaction with their management to the Committee.
A new corporate position of Group Head of Tailings was also created and filled with a qualified and experienced geotechnical engineer.
The following activities are planned for 2020, many of which commenced in 2019:
The mining industry's TSFs are in the spotlight following the catastrophic tailings failure at Vale's Feijão iron ore mine in Brumadinho, Brazil, in January 2019, which resulted in the deaths of 270 people. This follows the 19 fatalities during the Samarco TSF failure in 2015, also in Brazil, and significant environmental damage as a result of the Mt Polley tailings dam collapse in Canada in 2014.
After the Samarco incident, ICMM members developed a Tailings Position Statement in 2016 and approved a tailings aspirational goals roadmap in 2018. Gold Fields' Group Tailings Management Guidelines were aligned to the Position Statement in 2017 and strengthened with the inclusion of additional performance guidance and minimum assessment criteria in 2018.
Subsequent to the Brumadinho tragedy, ICMM members, UN Environment and the UN Principles for Responsible Investment established an independent panel of experts to develop a new international standard for TSFs. A public consultation review period for the first draft of a new Global Tailings Standard (GTS) ended in December 2019. It is expected that the new GTS will be finalised during 2020. Upon release, Gold Fields will carry out gap analyses of current TSF governance and operating practices against the new standard, and then commence work on closing identified gaps, where feasible.
The Brumadinho tragedy also prompted the Church of England Pensions Board, along with other investors and UN Environment Programme, to submit a request to hundreds of global mining companies. Gold Fields response is detailed in the report attached above.
Source: Jon Engels www.tailings.info/disposal/conventional.htm
With a downstream TSF, a new embankment raise is constructed, mostly with fill materials, in the downstream slope of the previous raise. The crest of the embankment thereby moves "downstream" or away from the centre of the dam. In upstream TSFs, each new embankment raise is constructed partially on the embankment immediately below and partially on the consolidated tailings beach adjacent to the embankment. The crest of the embankment thereby moves "upstream". The centre-line method is a combination of the upstream and downstream designs. When raised, material is placed on both the tailings and the existing embankment so the embankment crest is raised vertically. In-pit tailings disposal makes use of worked out open pits.
Backfilled tailings are stored underground in previously worked out voids. They are generally mixed with a binder, usually cement, and then pumped underground. Backfilling, where economically and technically viable has several advantages, including avoiding surface deposition, extraction of in situ pillars containing ore, improved underground support and reduced ventilation requirements because voids are filled.