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REE -Mineralogy and Geochemistry of Virtasalmi kaolins, SE Finland
Thair Al-Ani Geological Survey of Finland, FI-02151 Espoo
Olli Sarapää Geological Survey of Finland, FI-96101 Rovaniemi
INTRODUCTION
Mineralogical and geochemical
study on Virtasalmi kaolin occurrences includes three objectives.
1) To determine the abundance and
distribution of REE in the studied
kaolin profiles.
2) To address the factors controlling
the distribution pattern and behaviour of REE during kaolinization
process.
3) To find out the potential of Virtasalmi kaolins for ionic adsorption
type REE-deposits. The samples for
mineralogical and chemical studies
were selected from the drill cores of
the Litmanen, Eteläkylä, Vuorijoki
and Montola deposits. The detailed
description of these deposits has
been presented by Sarapää (1996).
Geological setting of Virtasalmi kaolins
Geological setting of Virtasalmi kaolins
MINERALOGY
The main minerals are kaolinite,
quartz, with minor amounts of illite. Micro-analysis of studied kaolin
samples revealed the occurrences of
euhedral to subhedral (typically; 20
µm in length and 5 µm in diameter)
micro-size crystals of resistant heavy
miner minated in the kaolins, chiefly Ce-monazite, Th-bearing monazite, and xenotime. The microanalysis of the monazite grains reporting
the following composition: 38% - 70
% LREE, 5- 7% CaO and 25- 55%,
P205.
2. Chondrite-normalized REE patterns of the kaolins show an overall
enrichment of LREE (Lan/Smn=3-5
and Lan/Ybn = 6-19), HREE depletion (Gdn/Ybn = 1.3-2.6) and slightly negative Eu anomaly (Eu/Eu*>1),
probably inherited from the parent
rocks. The HREE and Y complexes
remained in solution, separated from
the LREE and subsequently precipitated at deeper levels of weathering
profiles.
High
HREE
contents
in
REE constituents in Virtasalmi kaolins
some studied profiles were also favoured by adsorption of REE and Y
onto kaolinite surfaces.
It is noted that the percentage content of Ce and La to be
more than 50% comparing to other REE as seen in circular form
Total REE content in parent rocks and kaolinite
The average ΣREE in samples of
the kaolin samples from Virtasalmi
is much higher than parent rocks
especially in Eteläkylä kaolin deposits. The behaviour of REE with
depth strongly suggests that a very
large proportion of REE enriched
in kaolinite and depleted in parent
rocks.
SUMMARY
1.Two factors cause the REE concentration in Virtasalmi kaolins: (1) REE
enrichment, 50-85% related to ionic
adsorption from solution onto kaolinite and halloysite minerals during
weathering process. (2) The residual
REE-bearing minerals, such as monazite and zircon, derived from parent rocks were the second source of
REEs enrichment in kaolins.
3. The present study also show, that
the total REE content of kaolin in basal part of weathering profile reaches
maximum 0.1-0.2% in aqua regia soluble form at Litmanen and Eteläkylä
deposits.
References
Sarapää, Olli, 1996. Proterozoic primary kaolin deposits at Virtasalmi, southeastern Finland. Espoo: Geological Survey of Finland.
152 p. + 6 app.
www.gtk.fi