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)