Controls of sulphide mineralisation at the kamoa copper deposit, with an emphasis on structural controls
Date
2016
Authors
Banza, Franck Twite
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Abstract
The Kamoa copper deposit, situated approximately 25 km west of the Kolwezi Cu-Co district of
the Democratic Republic of Congo, is one of the largest high-grade undeveloped copper
deposits in the world. Kamoa is a new discovery which occurs on the western edge of the
Congolese portion of the Central African Copperbelt. Two main rock units are present at
Kamoa, sandstone and conglomerate of the Mwashya Subgroup of the Roan Group, and
overlying diamictite and interbedded siltstone-sandstone of the Grand Conglomérat unit of the
Nguba Group. The deposit occurs along a stratigraphically controlled redox boundary at the
base of the Grand Conglomérat. The Kamoa deposit occurs broadly within a NNE-trending
structural high bound to the west by the West Scarp fault and to the east by the Kansoko trend.
Within this area the host rocks dip gently away from two localized domes, which expose rocks
of the Mwashya Subgroup.
Drill core data indicate that the Kamoa deposit includes areas of higher and lower grade, some
of which appear at the deposit scale to be related to known or interpreted faults. The aim of
this study was to determine the role of structure(s) in the genesis and distribution of hypogene
copper sulphides, and to identify the nature of those structures and their timing relative to
mineralisation. Detailed structural logging in drill core has focused on analysis of foliations,
folds, mesoscopic faults, strain shadows and strain fringes. True thickness isopach maps were
used to investigate spatial relationships of mineralisation with facies/thickness changes and
faults throughout the deposit.
In the southern part of the Kamoa deposit, a linear NNW zone of abrupt change in stratal
thickness named the “Mupaka Fault” is oblique to the localised domes and correlates well with
higher copper grades. This fault may represent an important transport path for the
hydrothermal fluids in the Kamoa deposit. Thickness variations, facies change, steep bedding
and rotated mesoscopic faults demonstrate that the Mupaka Fault is a syn-sedimentary growth
fault that occurs during the deposition of the Nguba Group rocks. The close relationship
between copper mineralisation and structures demonstrates that structures played a significant
role in the formation of ore at Kamoa. Zones of thickness variations of stratigraphic units may
represent potential prospective areas for future exploration work.
The development of S1 foliation, strain shadows and strain fringes is coeval and related to a NW
shortening direction. The Kolwezian deformation event is believed to be responsible for the
development of these structures. Strain fringes reveal a straight orientation of fibres during
coaxial deformation; this supports the interpretation of a single phase of deformation within
the Kamoa deposit. The non-deformed distal part of the fringe, the straight orientation of
fibres, the lack of undulose extinction and recrystallisation features demonstrate the simple
geometry of strain shadows and strain fringes. These characteristics suggest a new growth of
minerals under low temperature and high pressure fluid. The analysis of minerals within fringes
suggests little potential for remobilisation of minerals in strain shadows and strain fringes
because none of the mechanisms of recrystallisation (bulging, subgrain rotation and grain
boundary migration) have been observed. A syn- or post-orogenic origin of copper sulphides,
probably related to the Lufilian orogeny is proposed.
Description
A Dissertation submitted to the Faculty of Science, University of the
Witwatersrand, Johannesburg, in fulfilment of the requirements for the
degree of Master of Science.
December, 2016
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Citation
Banza, Franck Twite. 2016. Controls of sulphide mineralisation at the Kamoa copper deposit, with an emphasis on structural controls, University of the Witwatersrand, https://hdl.handle.net/10539/23734