Mineralogical and geochemical modification of manganese ore in response to fluid flow through the Hotazel Formation of the Kalahari Manganese Field, Northern Cape Province, South Africa
- Authors: Vafeas, Nicholas Andrew
- Date: 2018
- Subjects: Geology - South Africa - Northern Cape , Mineralogical chemistry - South Africa - Northern Cape , Manganese ores - South Africa - Northern Cape
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/292777 , uj:31822
- Description: Abstract: The Kalahari Manganese Field hosts the largest land based manganese resource in the world, comprising several variants of manganese ore-types including diagenetic/Mamatwan-type, supergene, hydrothermal/Wessels-type and thrust-related manganese ore. The lower manganese ore bed of the Hotazel Formation from five mines was investigated and analysed petrographically. Four of the five mines were further analysed geochemically and include Mamatwan mine in the south of the lower Kalahari Manganese Field, Sebilo Manganese Resources and United Kalahari Manganese mine in the central lower Kalahari Manganese Field and Gloria mine in the north of the lower Kalahari Manganese Field. The lower manganese ore bed from these mines is structurally located below the N-S trending Blackridge Thrust Fault and comprises diagenetic, low-grade, high carbonate-bearing ore. The ore from Mamatwan mine bears the closest similarities to a proposed original protolith comprising abundant kutnohoritic and calcitic ovoidal concretions, ribbons and lenses that are variably distributed within a braunite I and kutnohorite matrix. The highest manganese content is found within the lower half of the lower manganese ore bed and exhibits a Mn2O3 content of 30-45 wt %. In the central part of the lower Kalahari Manganese Field, diagenetic ore is located at shallow depths just below the Kalahari unconformity and as a result is subjected to the effects of classic supergene alteration. These effects have resulted in the replacement of much of the diagenetic carbonate and oxides by supergene oxyhydroxides, including cryptomelane, psilomelane and pyrolusite. The development of these phases, coupled with the removal of carbonates has increased the manganese content to 40-55 wt %. In addition, the precipitation of classic supergene phases resulted in an increase in bulk chemical potassium and barium abundances within the ore, as well as the residual enrichment of vanadium. The manganese ore in the area of Mukulu is positioned above the Blackridge Thrust Fault and as such, has been displaced several tens of kilometres eastwards. The resultant ore exhibits signs of Wessels event alteration, reaching Mn2O3 abundances of 60-80 wt % and is significantly coarse-grained relative to the diagenetic ore. Three stages of alteration were identified in the Thrust Manganese ore i.e. Stages 1, 2 and 3, and closely resemble the... , Ph.D. (Geology)
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- Authors: Vafeas, Nicholas Andrew
- Date: 2018
- Subjects: Geology - South Africa - Northern Cape , Mineralogical chemistry - South Africa - Northern Cape , Manganese ores - South Africa - Northern Cape
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/292777 , uj:31822
- Description: Abstract: The Kalahari Manganese Field hosts the largest land based manganese resource in the world, comprising several variants of manganese ore-types including diagenetic/Mamatwan-type, supergene, hydrothermal/Wessels-type and thrust-related manganese ore. The lower manganese ore bed of the Hotazel Formation from five mines was investigated and analysed petrographically. Four of the five mines were further analysed geochemically and include Mamatwan mine in the south of the lower Kalahari Manganese Field, Sebilo Manganese Resources and United Kalahari Manganese mine in the central lower Kalahari Manganese Field and Gloria mine in the north of the lower Kalahari Manganese Field. The lower manganese ore bed from these mines is structurally located below the N-S trending Blackridge Thrust Fault and comprises diagenetic, low-grade, high carbonate-bearing ore. The ore from Mamatwan mine bears the closest similarities to a proposed original protolith comprising abundant kutnohoritic and calcitic ovoidal concretions, ribbons and lenses that are variably distributed within a braunite I and kutnohorite matrix. The highest manganese content is found within the lower half of the lower manganese ore bed and exhibits a Mn2O3 content of 30-45 wt %. In the central part of the lower Kalahari Manganese Field, diagenetic ore is located at shallow depths just below the Kalahari unconformity and as a result is subjected to the effects of classic supergene alteration. These effects have resulted in the replacement of much of the diagenetic carbonate and oxides by supergene oxyhydroxides, including cryptomelane, psilomelane and pyrolusite. The development of these phases, coupled with the removal of carbonates has increased the manganese content to 40-55 wt %. In addition, the precipitation of classic supergene phases resulted in an increase in bulk chemical potassium and barium abundances within the ore, as well as the residual enrichment of vanadium. The manganese ore in the area of Mukulu is positioned above the Blackridge Thrust Fault and as such, has been displaced several tens of kilometres eastwards. The resultant ore exhibits signs of Wessels event alteration, reaching Mn2O3 abundances of 60-80 wt % and is significantly coarse-grained relative to the diagenetic ore. Three stages of alteration were identified in the Thrust Manganese ore i.e. Stages 1, 2 and 3, and closely resemble the... , Ph.D. (Geology)
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Petrography and geochemistry of the Hotazel Formation on Mukulu 265, Kalahari Manganese Field, Northern Cape Province
- Authors: Vafeas, Nicholas Andrew
- Date: 2016
- Subjects: Geology - South Africa - Northern Cape , Manganese ores - Kalahari Desert , Iron ores
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/124793 , uj:20960
- Description: Abstract: With the need for steel ever increasing, the Kalahari Manganese Deposit is a resource of great economic importance and as such, the need for accurate data and comprehensive studies on the manganese and iron ores are vital. The Mukulu 265 project area is positioned along the border of the high (Wessels-type) to low (Mamatwan-type) grade manganese ore and like the neighbouring N’chwaning and Wessels mines, is subject to: intrusions by diabase dykes; thrusting and subsequent overlapping of strata; normal faulting and associated Wessels event enrichment; and erosion along two separate unconformities, namely the Mapedi/Gamagara and the Kalahari unconformities. As a result of these structural evolutionary events, both the iron and the manganese ores vary in grade, mineralogy and texture from north to south and east to west. This variation is the result of contact metamorphism and associated igneousrelated hydrothermal fluids; supergene alteration along the Mapedi/Gamagara unconformity; and metasomatic alteration along the reactivated north-south striking normal faults. The latter is responsible for the systematic residual enrichment in manganese content and the increase in high-grade minerals in the manganese ore, as well as the subsequent leaching of carbonates and silicates that is witnessed in the northern section of Mukulu 265. Based on varying degrees of alteration from south to north on Mukulu 265, the banded iron formation, hematite lutite and manganese ores have been broadly categorised into three classes, namely least altered (LA), partially altered (PA) and highly altered (HA). The LA rock-types are considered to be closest to the primary rock-types found on Mukulu 265 and show relatively little alteration compared to the PA and HA samples. From the LA to the HA manganese ore samples, there is a clear increase in manganese oxides such as hausmannite, predominantly at the expense of carbonates such and kutnohorite and dolomite, particularly within the ovoids. Sampling and analysing the manganese ore by visually distinguishing common subzones, reveals a distinct pattern within the lower manganese ore beds of the selected boreholes that shows a lateral geochemical trend. This geochemical trend exhibits higher concentrations in manganese with lower concentrations in undesired elements such as iron within the lowercentral portion of the lower manganese ore bed. The geochemical pattern exhibited by the ore zones forms the basis by which the ore grade changes with depth and thus underpins its importance for selective mining processes. An interpretation of the ore genesis based on geochemical and mineralogical results for the lower manganese ore bed, suggests that the... , M.Sc. (Geology)
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- Authors: Vafeas, Nicholas Andrew
- Date: 2016
- Subjects: Geology - South Africa - Northern Cape , Manganese ores - Kalahari Desert , Iron ores
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/124793 , uj:20960
- Description: Abstract: With the need for steel ever increasing, the Kalahari Manganese Deposit is a resource of great economic importance and as such, the need for accurate data and comprehensive studies on the manganese and iron ores are vital. The Mukulu 265 project area is positioned along the border of the high (Wessels-type) to low (Mamatwan-type) grade manganese ore and like the neighbouring N’chwaning and Wessels mines, is subject to: intrusions by diabase dykes; thrusting and subsequent overlapping of strata; normal faulting and associated Wessels event enrichment; and erosion along two separate unconformities, namely the Mapedi/Gamagara and the Kalahari unconformities. As a result of these structural evolutionary events, both the iron and the manganese ores vary in grade, mineralogy and texture from north to south and east to west. This variation is the result of contact metamorphism and associated igneousrelated hydrothermal fluids; supergene alteration along the Mapedi/Gamagara unconformity; and metasomatic alteration along the reactivated north-south striking normal faults. The latter is responsible for the systematic residual enrichment in manganese content and the increase in high-grade minerals in the manganese ore, as well as the subsequent leaching of carbonates and silicates that is witnessed in the northern section of Mukulu 265. Based on varying degrees of alteration from south to north on Mukulu 265, the banded iron formation, hematite lutite and manganese ores have been broadly categorised into three classes, namely least altered (LA), partially altered (PA) and highly altered (HA). The LA rock-types are considered to be closest to the primary rock-types found on Mukulu 265 and show relatively little alteration compared to the PA and HA samples. From the LA to the HA manganese ore samples, there is a clear increase in manganese oxides such as hausmannite, predominantly at the expense of carbonates such and kutnohorite and dolomite, particularly within the ovoids. Sampling and analysing the manganese ore by visually distinguishing common subzones, reveals a distinct pattern within the lower manganese ore beds of the selected boreholes that shows a lateral geochemical trend. This geochemical trend exhibits higher concentrations in manganese with lower concentrations in undesired elements such as iron within the lowercentral portion of the lower manganese ore bed. The geochemical pattern exhibited by the ore zones forms the basis by which the ore grade changes with depth and thus underpins its importance for selective mining processes. An interpretation of the ore genesis based on geochemical and mineralogical results for the lower manganese ore bed, suggests that the... , M.Sc. (Geology)
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