Abstract
Acid mine drainage (AMD) is a major environmental problem in many active and formermining regions worldwide. Prediction of the nature of effluents released from mine sites
and their environmental impacts is a challenging and dynamic problem as AMD is
affected, both by the textural and compositional features of sulphide ores and their
weathered spoils and by water-rock interactions in receiving waters.
This thesis examines AMD processes in the headwater region of the Tintillo River (a high
level tributary of the Odiel River) that receives effluents draining the spoil heaps of the
Corta Atalaya (CA) mine, Iberian Pyrite Belt (IPB), South-West Spain. The district and CA
itself represent some of the largest massive sulphide mines in the world. The aim of the
work presented here is to assess AMD generation and impacts around the CA mine
focusing on, (a) AMD generation processes in the mine and its spoil heaps and (b) the
impacts of site AMD on river water chemistry and river morphology.
Tintillo River waters are extreme examples of AMD-affected Mg-SO4 type waters
characterised by high S, Mg, Fe and Al concentrations and low pH (~2.56). Intense
sulphide oxidation at all scales has resulted in the release of high concentrations of Fe
and SO4 and accessory metals (e.g. Cu, Zn, Cd, As and Co) into the fluvial network with
concomitant dissolution of gangue minerals and hydrolysis reactions leading to the
mobilisation of Mg, Al, Si, K and Na. Future differential rates and products of weathering
between the meta-rhyolites that dominate CA spoil could profoundly affect the partitioning
of major and trace elements (e.g. metals co-precipitated, adsorbed and or otherwise
retained by current secondary mineral accumulations), impacting the subsequent parts of
the system.
Two major geomorphological expressions (terrace formations and evaporite
accumulations) are the result of hydrogeochemical processes following outwash of acidic
effluents at the study site. Secondary minerals at the site significantly influence the
geochemical fractionation of hazardous elements. Dissolution of soluble salts
(characteristically Mg- varieties of magnesiocopiapite, epsomite, and hexahydrite) and
neo-formed jarosites from spoil and riverine hinterlands results in an annual cycle of rapid
metal and acidity transference from CA spoil and Tintillo headwaters to the downstream
environment. The high affinity of jarosites for heavy metals and the capacity of watersoluble
evaporites to coprecipitate, adsorb and/or scavenge a suite of toxic metals
(including Co, Cu, Mn, Zn, Ni and Cd) result in geomorphological and secondary mineral
interfaces that are major and dynamic conduits for metal transport within and through the
system, particularly during flood events.
| Date of Award | 2017 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | Andrew Cundy (Supervisor) |