590
Climatic Geomorphology
....................
"~ "l'~f
..........
~~ .......
J
r
.
o
km
"
, .
Equatorial Scale
,
~,
OD
o
3000
Placer deposits
Weathering deposits
o Gold, silver, lead, zinc, copper
9 Lateritic bauxite
Tin
C' Karstic bauxite
v Titanium
9 Lateritic nickel
O Diamonds
9 Residual manganese
9 Kaolin
v Lateritic Iron
Figure 22.4. Major mineral weathering deposits and placers formed under humid tropical conditions
(Reading et al., 1995).
carbonates gave rise to minerals of secondary iron (Figure 22.5) (Fernfindez-Nieto et al.,
1981).
Nearly 10% of the world's aluminium production proceeds from karstic bauxites
(Caribbean region and southeast Asia). They mainly appear filling karst depressions that
have been slowly lowering at the same time that the bauxite deposit increased. They are
recognised from the Cambrian through the Quaternary, always related to warm climates
(Bardossy, 1981).
In the Malayan tower karst, staniferous alluvium penetrates the endokarst and fill voids
and fissures. It constitutes an important tin ore where processes of previous karstification
and later placer infillings are involved (Sweeting, 1972).
Placers originate by mechanical concentration due to the gravity separation of heavy
minerals (denser than quartz), by water, or by wind (Bateman, 1950). For this process to
occur, it is required that minerals be released from the altered rock and become
concentrated. Most placers are generated in fluvial and littoral environments. The most
important exploitable minerals are gold, diamond, ilmenite, rutile, cassiterite, zircon,
monazite, gemstones, and others. Although placers have a wide distribution all over the
world (Figure 22.4), humid and subhumid tropical environments present optimum
conditions for their formation (Thomas, 1994). Most placers result from the activity of
present (Figure 22.6) or recent geomorphological processes, such as diamonds in the
Central African Republic or cassiterite in Indonesia. Other deposits were generated in
former geological times, such as the Tertiary auriferous placers of Las Mrdulas in Le6n
Climatic Geomorphology
....................
"~ "l'~f
..........
~~ .......
J
r
.
o
km
"
, .
Equatorial Scale
,
~,
OD
o
3000
Placer deposits
Weathering deposits
o Gold, silver, lead, zinc, copper
9 Lateritic bauxite
Tin
C' Karstic bauxite
v Titanium
9 Lateritic nickel
O Diamonds
9 Residual manganese
9 Kaolin
v Lateritic Iron
Figure 22.4. Major mineral weathering deposits and placers formed under humid tropical conditions
(Reading et al., 1995).
carbonates gave rise to minerals of secondary iron (Figure 22.5) (Fernfindez-Nieto et al.,
1981).
Nearly 10% of the world's aluminium production proceeds from karstic bauxites
(Caribbean region and southeast Asia). They mainly appear filling karst depressions that
have been slowly lowering at the same time that the bauxite deposit increased. They are
recognised from the Cambrian through the Quaternary, always related to warm climates
(Bardossy, 1981).
In the Malayan tower karst, staniferous alluvium penetrates the endokarst and fill voids
and fissures. It constitutes an important tin ore where processes of previous karstification
and later placer infillings are involved (Sweeting, 1972).
Placers originate by mechanical concentration due to the gravity separation of heavy
minerals (denser than quartz), by water, or by wind (Bateman, 1950). For this process to
occur, it is required that minerals be released from the altered rock and become
concentrated. Most placers are generated in fluvial and littoral environments. The most
important exploitable minerals are gold, diamond, ilmenite, rutile, cassiterite, zircon,
monazite, gemstones, and others. Although placers have a wide distribution all over the
world (Figure 22.4), humid and subhumid tropical environments present optimum
conditions for their formation (Thomas, 1994). Most placers result from the activity of
present (Figure 22.6) or recent geomorphological processes, such as diamonds in the
Central African Republic or cassiterite in Indonesia. Other deposits were generated in
former geological times, such as the Tertiary auriferous placers of Las Mrdulas in Le6n