Abstract:
A combination of petrography and geochemistry (XRF, ICP-OES and ICP-MS) was utilized in
order to investigate the magma source(s), magma evolution and petrogenesis implications of
the Kgwebe Volcanic Formation (KVF) rock units in the Ghanzi-Chobe Belt portion of the
Kalahari Copper Belt (NW Botswana). Based on their texture, the KVF rock units were
discriminated into amygdaloidal rocks, porphyritic mafic flows, pyroclastic rocks, porphyritic
subvolcanic bodies, quartz-feldspar porphyries and clastic sedimentary rocks (intercalated with
amygdaloidal rocks). The amygdaloidal rocks commonly crosscut by calcite veins, are
characterized by amygdales-filled vesicles set in hyalopilitic groundmass. The porphyritic
mafic flows are essentially made up of plagioclase laths set in a sericitised groundmass. The
pyroclastic rocks are made up of both phenocrysts and lithic fragments set in a fine-grained
microlithic groundmass. Porphyritic subvolcanic bodies are characterized by high content in
subrounded epidote (after plagioclase) set in a microcrystalline groundmass. The quartz feldspar porphyries are characterized by quartz and feldspar phenocrysts in variable
proportions set in a fine-grained groundmass of variable colour. Magmatic rocks of the KVF
represent two geochemically contrasting series that are not co genetic and derived from
different geotectonic settings. The amygdaloidal rocks, porphyritic mafic flows, pyroclastic
rocks and porphyritic subvolcanic bodies are subalkaline basalt in composition, whereas the
quartz-feldspar porphyries span from the rhyolite/dacite (mostly) to the andesite/andesite basalt
(accessorily) field compositions. Likewise, while quartz-feldspar porphyries are consistently
high-K calc-alkaline bodies, their spatially associated amygdaloidal rocks, porphyritic mafic
flows, pyroclastic rocks and porphyritic subvolcanic bodies counterparts are calc-alkaline.
Similarly, quartz-feldspar porphyries are within plate bodies, whereas the more mafic KVF
units are arc-related. Furthermore, the ferroan quartz-feldspar porphyries generated from the
crust and the magnesian amygdaloidal rocks, porphyritic mafic flows, pyroclastic rocks and
5
porphyritic subvolcanic bodies are mantle-derived, with however, significant crustal
contamination fingerprints. Textural evidences (resorbed, embayed and rounded phenocrysts)
as well as the inferred high-water content (as supported by the abundance of plagioclase
phenocrysts) also suggest a rapid magma ascent and magma mixing occurred during the KVF
eruption, which was both effusive and explosive. Concomitant volcanism and sedimentary
processes likely occurred as supported by the intercalation of clastic sedimentary rocks within
volcanics of the KVF. Furthermore, The KVF rock units' Cu and Ag quantities were calculated
to be 1183 million tonnes and 42 million tonnes, respectively. Because the total metal budget
of the KCM deposits exceeds 500 million tonnes, the KVF is likely to have accounted for some
extent to the total metal budget at the KCM property. But apart from the KVF, additional
sources of Cu and Ag such as Ngwako Pan and D’Kar formations are to be considered.
Esther, E (2024). Mineralogical and geochemical characterisation of the Kgwebe volcanic formation in the Ghanzi-Chobe belt portion of the Kalahari copper belt: insights into copper and silver source (s). Afribary. Retrieved from https://track.afribary.com/works/mineralogical-and-geochemical-characterisation-of-the-kgwebe-volcanic-formation-in-the-ghanzi-chobe-belt-portion-of-the-kalahari-copper-belt-insights-into-copper-and-silver-source-s
Esther, Elias "Mineralogical and geochemical characterisation of the Kgwebe volcanic formation in the Ghanzi-Chobe belt portion of the Kalahari copper belt: insights into copper and silver source (s)" Afribary. Afribary, 12 Apr. 2024, https://track.afribary.com/works/mineralogical-and-geochemical-characterisation-of-the-kgwebe-volcanic-formation-in-the-ghanzi-chobe-belt-portion-of-the-kalahari-copper-belt-insights-into-copper-and-silver-source-s. Accessed 19 Nov. 2024.
Esther, Elias . "Mineralogical and geochemical characterisation of the Kgwebe volcanic formation in the Ghanzi-Chobe belt portion of the Kalahari copper belt: insights into copper and silver source (s)". Afribary, Afribary, 12 Apr. 2024. Web. 19 Nov. 2024. < https://track.afribary.com/works/mineralogical-and-geochemical-characterisation-of-the-kgwebe-volcanic-formation-in-the-ghanzi-chobe-belt-portion-of-the-kalahari-copper-belt-insights-into-copper-and-silver-source-s >.
Esther, Elias . "Mineralogical and geochemical characterisation of the Kgwebe volcanic formation in the Ghanzi-Chobe belt portion of the Kalahari copper belt: insights into copper and silver source (s)" Afribary (2024). Accessed November 19, 2024. https://track.afribary.com/works/mineralogical-and-geochemical-characterisation-of-the-kgwebe-volcanic-formation-in-the-ghanzi-chobe-belt-portion-of-the-kalahari-copper-belt-insights-into-copper-and-silver-source-s