Mongolia - General Mining

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4 - Independent Geological Report - Mongolia
Figure 3: Schematic diagrams illustrating the
environments for potash deposition in
a) saline lakes
and
b) isolated bodies of seawater.
Due to the relatively low mechanical strength of
evaporites, the whole salt sequences are subject to
intensive deformation of originally horizontal strata.
Furthermore, salt migration and upward movement,
driven by the inverse density contrast between
the salt bodies and their carbonatic and/or clastic
overburden, forms salt domes (diapirs). As a result of
these vertical movements, salt deposits often come
into contact with groundwater and are partially or
completely redissolved.
Brines from natural lakes and pore fluids from
sub-recent/recent evaporite basins are known
as resources for sodium chloride and sodium
carbonate. Such brines are seldom used as a source
for potassium and magnesium salts. In sub-recent
and recent shallow evaporite basins, the source of
potash is the remaining saturated brines enriched in
potassium and magnesium, which occur (i) in the
lakes at the surface or (ii) in the pore cavity of the
young evaporites.
Examples of producing operations are given below:
• Dead Sea Works, Israel: with a concentrated brine
containing about 30% solved salt and a potassium
chloride content of 1.25% equalling 15g/l and a total
annual production of 1.96 million tonnes K O per 2
year (2003) based on solar evaporated Carnallite
• Great Salt Lake, Utah, USA: with a concentrated
brine containing about 27% solved salt and a
potassium content of 0.7% as well as a significant
sulphate concentration, reserves are estimated at 168
million tonnes KCl
• Salar de Atacama, Chile: extracting brine with
15g to 44g potassium per litre and having a capacity
of about 0.5 million tonnes K O per year. The brine
2
of Salar de Atacama has extremely high lithium
contents (0.15%) which makes Salar de Atacama
one of the biggest and richest lithium deposits in
the world.
Two types of potassium salts are recognised as
being economically important; potassium chloride
and potassium sulphate. Potassium chloride (KCl)
occurs as Sylvite, an opalescent or milky white
mineral often occurring with halite and other salt
minerals. Potassium chloride also forms a double salt
called Carnallite when combined with magnesium
chloride. Potassium sulphate (K SO ) forms Arcanite
2 4
and commonly occurs as a double salt combined
with calcium, magnesium and/or sodium.
Common extraction techniques include conventional
underground mining methods (room and pillar
for subhorizontal bodies or cut and fill stoping for
sub-vertical bodies) and solution mining, which
is typically applied to deep sylvite and rock salt
deposits where conventional underground mining
techniques are prohibitively expensive. Solution
mining consists of the in-situ dissolving of solid rock
salt or sylvite and forcing the resultant solution to
surface for processing. Solution mining does not