Abstract
M.Sc.
The Mamatwan mine is situated at the most southern end of the world’s largest landbased
resource of manganese, the Kalahari manganese field. The mine is operated by
South African Manganese Corporation Limited (SAMANCOR) and is the largest open pit
manganese mine in the world. The sedimentary manganese ore bed is interbedded with
iron-formation of the Hotazel Formation of the Early Paleoproterozoic Voëlwater
Subgroup of the Transvaal Supergroup. The open pit Mamatwan mine has a proven
economic ore reserve of between 300 and 400Mt and produces 1.2Mt of manganese ore
annually, of which 0.5Mt of ore is beneficiated and shipped through the harbour at Port
Elizabeth. The remaining ore is railed to ferro-alloy plants at Meyerton and Newcastle.
Carbonate-rich manganese lutite mined at the Mamatwan Mine is widely known as
Mamatwan-type ore. It has a manganese content ranging from 30 – 38%. Only a small
portion (15m of a total thickness of 49m) of the ore bed, containing an average of 38%
Mn, is being mined and processed at present. The larger portion of the ore bed is not
utilized. This study focuses on the physical and chemical characteristics of the ore bed in
more detail in order to make suggestions on how to a) reduce waste by upgrading the
upper parts of the lower manganese ore bed, or b) to improve the current recovery from
the present economic zone. A second part of this study pays special attention to the
lithostratigraphy of the lower manganese ore bed. The focus is on the paragenetic
sequence and the diagenetic evolution of the braunite lutite that constitutes the
manganese ore.
The Mamatwan-type ore can be described as diagenetic to very low-grade metamorphic
carbonate-bearing braunite manganolutite. Based on geochemical and mineralogical
data, the lower manganese ore body was previously subdivided into eleven lithogically
distinct zones. Based on detailed diamond drill core logging and with the aid of
geochemical and physical data of two selected drill cores, an additional thirteen
subzones were identified in this study. These new subzones were found to be consistent
across the entire study area, located to the west and north of the present Mamatwan open
pit.
The paragenetic sequence recognised in the ore of the lower manganese ore bed can be
subdivided into four stages, namely: (a) sedimentation, which is represented by fine
lamination and the presence of fine-grained “dusty hematite”. (b) early diagenesis as
represented by micritic carbonate matrix and possibly braunite, (c) late diagenesis or
low-grade metamorphism are represented by coarse grained hausmannite, specularitic
hematite, partridgeite and Mn-calcite, and supergene alteration that occurs immdediately
below the contact of the ore bed to the unconformably overlying Tertiary Kalahari
Formation. This supergene altered zone is marked by the presence of Mn4+ oxides such
as cryptomelane, manjiroite, romanechite and pyrolusite, in addition to barite.
The results obtained in this study permit definition of two sedimentary cycles within the
manganese ore bed at the Mamatwan mine. Both cycles are defined by a carbonate-rich
finely laminated zone at the base, overlain by a central manganese-rich economic zone,
capped by manganese lutite that is enriched in carbonate ovoids. The two manganeserich
zones are known as the M (lower) and X (upper) zone, and are characterized by the
replacement of carbonate ovoids by hausmannite. The two Mn-rich zones are chemically
and physically almost identical, with the M zone 7.5m thick and the X zone 5.5m thick.
However, in the present mining configuration only the M zone is being mined. The most
important result arising from the present study is the recommendation to restructure the
future mining operation in order to mine not only the M zone, but also the X zone.