Evaluation of land reclamation with MPTS at AngloGold Ashanti: a chronosequence approach.
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Date
September, 2015
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Abstract
Mining generally destabilizes environments and the entire ecosystem. To ensure that mining
activities co-exist harmoniously with the human and physical environment, guidelines have
been developed which all mining companies are obliged to comply. Reclamation is a
desirable and necessary remedy to return the mined areas to an acceptable environmental
condition whether for resumption of the former land use or for a new use. The research was
carried out at Anglogold Ashanti, Obuasi Mines Ltd to evaluate land reclamation with MPTs.
The study was in two parts: a sociological survey and a field evaluation. The survey was
conducted in 3 communities namely: Binsere, Sansu and Kunka using semi-structured
questionnaires, focus group discussions and personal observations. Eighty – one respondents
were interviewed comprising of environmental experts of the mining company, the
Community Relation Officer, Chiefs/Opinion leaders and selected households. The field
experiment was carried out on four reclaimed sites of the ages of 3, 6, 9 and 12 years and a
cocoa farm which has never been mined as the control. Soil samples were taken at three
depths of 0 – 20, 20 - 40 and 40 – 60 cm from the four reclaimed sites and the control with a
hand held auger and analysed for soil fertility parameters and selected heavy metal
contaminants. The study revealed high community participation in the land reclamation
exercise ranging from weed and fire control, supply of local seeds, seedling establishment
and maintenance of reclaimed sites. Multipurpose trees: Gmelina spp, Cedrella odorata,
Cassia siamea, Cassia mangium, Anegreila robusta, Daniella ogea, Mansonia and
Terminalia superba, Terminalia ivorensis, Khaya ivorensis, Triplochitin scleroxylon and
Entandrophragma utile were used in reclaiming mined out sites. The company uses the
following reclamation processes and procedures to rehabilitate the disturbed sites:
earthworks/slope battering, spreading of oxide material, spreading of top soil, construction of
crest drains and broadcasting of cover crops to control run-off and erosion, tree planting and
II
field maintenance. It was observed that land reclamation had significant effect on the pH of
the soil. The 12 year old reclaimed site recorded the highest percentage base saturation of
87.9% with the lowest of 61.8% recorded on the 9 year reclaimed site. Soil total nitrogen and
SOC content were higher in the top 0 – 20 cm depth than the 20 – 40 and 40 – 60 cm depth.
Exchangeable acidity ranged from 0.71 to 1.08. Soil Arsenic content was highest in the 3 year
old site (9.44 mgkg
-1
) and least in the control site (0.48 mgkg
-1
). Highest lead concentration
of 1.45 mgkg
-1
was recorded on the 3 year old site and the lowest of 0.67 mgkg
-1
on the
control site. Copper was highest in the 3 year reclaimed site and the depth of 0 – 20 cm also
recorded the highest value. The highest micronutrients were recorded on the 3 year old
reclaimed site thus there was drop in the soil micronutrients with increase in years of
reclamation.
Description
A thesis submitted to the Department of Materials Engineering of the College of Engineering, in partial fulfilment of the requirements for the award of the degree of Master of Science, in Environmental Resources Management, 2015