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| dc.contributor.supervisor | Shemang, Elisha M. | |
| dc.contributor.supervisor | Bineli-Betsi, Thiery Olivier | |
| dc.contributor.author | Kelepile, Tebogo | |
| dc.date.accessioned | 2019-01-29T14:33:09Z | |
| dc.date.available | 2019-01-29T14:33:09Z | |
| dc.date.issued | 2017-05 | |
| dc.identifier.citation | Kelepile,Tebogo (2017) Geology, mineralogy, geochemistry and alteration patterns of banana zone copper-silver mineralisation , Ghanzi-Chobe belt, northwest-Botswana, Masters Theses, Botswana International University of Science and Technology, Palapye | en_US |
| dc.identifier.uri | https://repository.biust.ac.bw/handle/123456789/40 | |
| dc.description | Theses (MSc-Geology)----Botswana International University of Science and Technology, 2017 | en_US |
| dc.description.abstract | The Banana Zone Cu-Ag Prospect is within the SW-NE trending Ghanzi-Chobe Belt (GCB), which extends from the Namibia-Botswana border in the south to Shinamba Hills in the north near the Botswana-Zambia border. The Banana Zone is also part of the Ghanzi Project owned by Khoemacau Copper Mining and situated between the Ghanzi and Maun townships, in Botswana. The Banana Zone has inferred resource of over 225.4 million metric tonnes (Mt) grading 0.64% Cu and 8.1 g/t Ag. The GCB consists of deformed and metamorphosed (greenschist) metasedimentary rocks of the Ghanzi Group, that is commonly subdivided into four formations: the Kuke Formation, Ngwako Pan Formation, D’Kar Formation, and Mamuno Formation, in ascending stratigraphic order. In this study only two formations including the Ngwako Pan and the D’Kar Formations were investigated. The Ngwako Pan Formation is made up of continental siliciclastic sediments, mainly immature to submature sandstone with siltstone and shale intercalations, while the D'Kar Formation contains shallow marine to lacustrine grey-green and locally carbonaceous mudrocks (siltstone and mudstone/shale) with fine-grained sandstone and minor limestone to marlstone. The Cu-Ag mineralisation is hosted at the contact between hematite-rich Ngwako Pan and reduced organic matter-bearing D'Kar Formations. The presence of reduced organic matter is likely to have controlled Cu-Ag precipitation by providing a reducing environment required for the precipitation of sulphides. Petrographic and geochemical data were combined in order to decipher the petrogenesis of the Neoproterozoic clastic sedimentary succession of the Ngwako Pan and the D’Kar Formations associated with the Banana Zone Cu-Ag mineralisation. Sandstone of the Ngwako Pan and the D’Kar Formations is arkose and subarkose, composed of quartz (Q),feldspars (F), and lithic fragments (L). Moreover, geochemically the sandstone of the Ngwako Pan and the D’Kar Formations is considered as potassic and classified as arkose. Therefore, sandstone of both the Ngwako Pan and the D’Kar Formations is chemically and compositionally immature. On the other hand, mudrocks of the D’Kar Formation are finely laminated and are dominated by muscovite, sericite, chlorite, and quartz. The carbonate rocks of the D’Kar Formation are composed of pinkish-white crystalline limestone and yellowish grey or greyish black marlstone characterised by laminations that are marked by undulating marly and silty layers that give the rock a “zebra-skin” appearance. The marlstone exhibits variable degree of deformation from shearing to folding and recrystallisation. The modified chemical index of weathering (CIW’) values indicated an intense chemical weathering of the source rock. The dominance of detrital quartz and feldspar grains coupled with Al2O3/TiO2 ratios (average 29.67 and 24.52 for the sandstone of the Ngwako Pan and D’Kar Formations, respectively) and Ni and Cr depletion in this sandstone, suggests a dominant felsic source. However, high concentrations of Ni and Cr and a low Al2O3/TiO2 ratio (<20) in the mudrocks of the D’Kar Formation indicate a mixed source. Provenance of the investigated sandstone and mudrocks samples is further supported by the REE patterns, the size of Eu anomaly, as well as La/Co, Th/Co, Th/Cr, and Cr/Th ratios, which show a felsic source for the sandstone of both the Ngwako Pan and D’Kar formations and an intermediate source for the mudrocks of the D’Kar Formation. Detrital modes (QFL diagrams) and geochemical characteristics of the sandstone of the Ngwako Pan and D’Kar Formations indicate that the detritus were probably supplied from a heavily weathered felsic continental block and deposited in a continental rift setting (passive margin) in a humid environment. The source rocks might have been the Palaeoproterozoic basement rocks (granitoids and granitic gneiss) and the Mesoproterozoic Kgwebe volcanic rocks exposed north of the study area. In addition, these basement rocks underlying the Neoproterozoic sedimentary succession that host the mineralisation, demonstrate the largest potential as metal source. Numerous mineralisation styles were identified within the Banana Zone. These include: (i) disseminated mineralisation; (ii) vein-controlled mineralisation; (iii) breccia-related mineralisation; (iv) cleavage-controlled mineralisation; and (v) micro-pore space filling mineralisation styles. The hypogene ore phases are dominated by chalcopyrite, bornite, and chalcocite. Sphalerite and galena occur in minor quantities and mostly observed in veins. On the other hand, the supergene ore phases are dominated not only by chalcocite, digenite, and covellite, all formed at the expenses of chalcopyrite, bornite, and chalcocite, but also malachite. As no Ag-bearing mineral was observed, Ag is possibly occurring in chalcocite and in tetrahedrite/tennantite and galena as isomorphic admixtures.Sulphides display complex textural relationships that demonstrate multiple mineralising events spanning from diagenesis through metamorphism and deformation to post-tectonic events. The early diagenetic to late diagenetic mineralisation is supported by the presence of framboidal pyrite, nonfracture-controlled distribution of both sulphides and gangue phases and replacement textures of Cu-sulphides after diagenetic cement and pyrite. Furthermore, the occurrence of sulphides in pre-folding bedding-parallel veins and brecciated zones supports early tectonic mineralisation, while the mineralisation in veins that did not experience deformation demonstrates a post-tectonic stage. The host rocks are variably hydrothermally-altered and alteration occurs as pervasive and vein-controlled signifying a complex fluid flow history. The typically observed evolution is from high-temperature sodic-calcic (albitisation) to K-silicates (phyllic) to low temperature Mg-rich (propylitic) and carbonate-quartz assemblages. Most of the Cusulphides mineralisation occurs predominantly within zones of Mg-rich (propylitic) and carbonate-quartz alteration. Supergene processes are also observed in areas of high permeability, and have played a vital role in the remobilisation and upgrading of the primary mineralisation. The temporal relationship between hydrothermal alteration assemblages and hypogene ore minerals indicates that the mineralisation took place at a temperature range of ≤60 - 400◦C and under weakly acidic to near-neutral and alkaline pH conditions. The mineralising fluids possibly were moderately saline (as supported by fluid inclusion data from a similar study at Boseto Mine (15-20 wt.% equiv. NaCl)), dense and moderately oxidised during earlier phases and became highly saline during the tectonic period. On the other hand, the association of chalcocite with iron oxide/hydroxide suggests a second generation of supergene chalcocite, which forms at temperature below 103ºC and pH of about 3.5, whereas malachite developed at near-neutral to alkaline pH (4-9) conditions. | en_US |
| dc.language.iso | en | en_US |
| dc.publisher | Botswana International University of Science and Technology | en_US |
| dc.subject | Banana zone | en_US |
| dc.subject | Sandstone | en_US |
| dc.subject | Ngwako Pan | en_US |
| dc.subject | D'kar | en_US |
| dc.subject | Botswana | en_US |
| dc.title | Geology, mineralogy, geochemistry and alteration patterns of Banana zone copper-silver mineralisation , Ghanzi-Chobe belt, northwest-Botswana | en_US |
| dc.description.level | msc | en_US |
| dc.description.accessibility | unrestricted | en_US |
| dc.description.department | ees | en_US |
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