The acid mine drainage potential of the Platreef, Northern Limb of the Bushveld Complex, South Africa
Date
2010-03-08T07:59:07Z
Authors
Lishman, Katherine Louise
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The Acid Mine Drainage (AMD) potential of rocks at an exploration project on the
Platreef in the northern limb of the Bushveld Complex has been investigated. The
Platreef Project, at an advanced stage of exploration, is located north of Mokopane in
the Limpopo Province of South Africa. A total of 242 samples were selected from
borehole core and 11 tailings samples were obtained from Mintek Laboratory. Quality
control samples were inserted and all the rock samples were dispatched for whole
rock geochemistry and static Acid Base Accounting (ABA) analysis. Once the static
ABA results were received, a sub-set of 20 samples was selected for kinetic test
analysis. Of the tailings samples, three were sent for whole rock geochemistry
analysis, six for static ABA analysis and five for kinetic test analysis.
Using criteria developed within the context of coal mining in South Africa and based on
international criteria, the static ABA results were used to classify the rocks according to
acid producing potential. These results revealed that high risk acid producing
(Pegmatitic Gabbro-Norite, Melanorite, Norite Cycles, Feldspathic Pyroxenite, Hornfels
and Marginal Zone Norite) and low risk acid producing rock-types (Pyroxenite, Dolerite,
Quartz Feldspar, Aplite) may be mined at the Platreef site. The kinetic test and whole
rock geochemistry results provided further insight into the acid producing potential of
the rock types and revealed that Gabbro-Norite and Dolomite (altered to Calcsilicate
Hornfels) have the potential to generate acid despite being classified as non-acid
generating/potentially acid neutralizing. The tailings results proved contradictory and
this is thought to be due to non-representative sampling. It is recommended that a new
suite of representative tailings samples be generated and sent for static ABA and
kinetic test analysis once the metallurgical treatment process has been finalised.
Future work should be directed to better understand the merits and downfalls of the
different analytical methods used to quantify AMD in order to better interpret
contradictory results.
This laboratory based analysis of AMD potential provides a “worse case scenario” of
the rock types to be mined. Weighted volume calculations of the mean sulphur content
and the mean Net Neutralising Potential (Closed) of material to be mined initially on
Turfspruit indicate that it is unlikely that AMD will be generated from the tailings dams
or waste rock piles generated from mining in this region. This study has shown,
however, that AMD could result if high risk acid producing Platreef material is
stockpiled at the site prior to treatment for extended periods of time. Local zones of
potentially acid-producing material may occur within rock volumes dumped over the
Life of Mine (Marginal Zone Norite, Hornfels, Gabbro-Norite, and Dolomite) or exposed
in the pit floor (Marginal Zone Norite, Hornfels, Dolomite), and these should be
managed carefully to ensure that AMD does not result. The Quartzite samples
produced contradictory results during this study and, as this rock type occurs in the
Footwall to the Platreef, it is recommended that further Quartzite samples be sent for
static ABA and kinetic test analyses. This study has identified the potential AMD risks
facing the future mine at the Platreef Project and will enable the mine management to
minimize these risks during the mine design phase. These results should fit into a
larger framework of objectives and on-site conditions with time in order to effectively
manage AMD risk over the Life of Mine.