Masters Dissertation
Mineralogy and provenance of the TiO₂ - ilmenite heavy mineral sand deposit of Nataka


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Publication Details
Author list: Elias, Sílvio José
Publication year: 2017
Start page: 1
End page: 123
Total number of pages: 123

Abstract
The Nataka heavy mineral sand deposit occurs along the northeast
Mozambique coastline. It comprises a regional Pleistocene elliptical
structure extending from Somalia, passing through Kenya, Tanzania,
Madagascar and Mozambique, to Richards Bay in South Africa. The deposit
consists of fine- to medium- grained, unconsolidated red sediments,
hosting heavy minerals. The deposit mineral assemblage is made up of
non-valuable phases comprising mostly magnetite, hematite, chromite,
monazite, and the valuable phases dominated by ilmenite (50.91 wt. %),
with additional zircon and rutile (9.96 and 3.52 wt. % respectively).
The total heavy minerals comprise about 5% volume, of which 2 % are
valuable heavy minerals making up about 445 Mt (million tonnes) probable
resources. This study focuses on the mineralogical characterization of
ilmenite from the Nataka deposit, alongside with sediment provenance.
Mineralogical and chemical characterisation of ilmenite undertaken on 32
samples from 16 selected drill holes using a combination of QEMSCAN and
EPMA revealed that the ilmenite has undergone different stages of
alteration, at distinct environment conditions, yielding products
spanning from hydrated ilmenite to leucoxene. The alteration dominantly
involved groundwater, which was oxidizing and acidic, hence the
predominance of ilmenite-pseudorutile alteration. Long exposure to
direct sunshine has been hypothesized as a different process that might
have favoured the direct alteration of ilmenite to leucoxene and of
pseudorutile to leucoxene, on a smaller scale. The major impurities in
the ilmenite are Al and Si, which are enriched in the advanced ilmenite
alteration products (leucoxene), where they fill pores and cracks.
Chromium impurities occur as discrete grains of chrome spinel. The
compositional variety of magnetite, Cr-spinel, tourmaline, zircon and
rutile indicate major contribution from granitoid terranes, subjected to
granulite metamorphic facies (750 to 1000 :C), and minor contribution
from mafic plutonic intrusions. The granitoid field as a sediment source
area if analysed in conjunction with zircon ages (1100 – 900 Ma, 900 –
700 Ma, and 650 – 500 Ma), and zircon δ¹⁸O (7.07 ‰) is consistent with
preferential sourcing from the proximal Mesoproterozoic Nampula Complex,
with some contribution from igneous plutonic rocks from Xixano, Lalamo
and Montepuez Complexes.



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Last updated on 2017-05-06 at 11:26