wAbstract
@The Kalahari Manganese Deposit (KMD) is the largest land-based
manganese deposit, hosting approximately 80% of the world's known,
mineable manganese resources. The deposit, located near Kuruman
in the Northern Cape Province of South Africa, is one of five
erosional relics of the Paleoproterozoic (ca. 2.2 Ga) Hotazel
Formation, with sedimentary manganese ores occurring as up to
50 m thick beds interbedded with banded iron-formation (BIF) and
hematite lutite.
@The study focuses on the manganese ores of the Nchwaning-Gloria
mining area of the northern KMD. In this areas, pronounced mineralogical
and major element alteration was imparted on the sedimentary manganese
ores by a structurally-controlled hydrothermal fluid flow event.
Most notable effects of hydrothermal alteration are the decomposition
and leaching of Ca- and Mg-carbonate, and marked residual enrichment
of manganese. On the basis of mineral assemblages, grade, texture
and geochemical characteristics, three ore types were distinguished
in the studied sample set, classified into least altered (LA),
partially altered (PA) and advanced altered (AA) types. Advanced
altered ores may be further classified into five different types,
based on mineral assemblages that contain hausmannite and/or braunite
as significant minerals. The rare earth element (REE) geochemistry
of these fundamental ore types was studied in detail, to document
REE mobility during hydrothermal alteration.
@Total REE concentrations in LA ores were found to be very low
(14-22 ppm) and remarkably uniform, within the range typically
observed for BIF. Hydrothermal alteration results in residual
enrichment and a much larger scatter in REE contents. A small
Ce anomaly observed in the protolith remains similar in magnitude
when observed in PAAS-normalised REE plots. The data define, however,
a power trend in the (Ce/Ce*) vs (Pr/Pr*)
diagram. Such behaviour is interpreted in terms of a conservative
system that was predominantly protolith-buffered. Local remobilisation
of REE during hydrothermal alteration is attributed to the dissolution
of diagenetic apatite and redistribution of hydrothermal trace
minerals, including neoformed apatite, monazite and cerianite.
Keywords: REE; Kalahari; Manganese; Hydrothermal alteration; Cerium
anomalyx
1. Introduction
2. Methodology
3. Results
@3.1. REE geochemistry
@3.2. REE host minerals
4. Discussion
5. Conclusions
Acknowledgements
References