Geomorphology applied to glacial regions
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the greatest damages were related to graben areas in the upper part and in the push ridges
of the frontal part (Hansen, 1965).
5. Placer deposits in glacial environments
Placers are accumulations of heavy metals that have been extracted from the rock substrate
by weathering, water, wind, and glacial processes. They are important economic resources
and are ores of gold, diamonds, platinum, tin, and other minerals. Placers subject to ice
action are exploited in northern Asia, Canada, and Alaska, though most of these
exploitations are in environments not affected by glacial activity (Boyle, 1979).
Placer deposits (Figure 6.15) are located in a wide range of sedimentary situations,
such as alluvial, colluvial, glacial, fluvioglacial, coastal, and marine environments (Levson
and Morison, 1996). Alluvial placers are located in active or abandoned streams, such as
gullies, braided and meandering rivers, alluvial fans, and fan-deltas. Gold concentrates
essentially together with loose blocks and gravels and in a conglomeratic facies (Fayzullin,
1969).
Fluvial placers are the most frequent type and are located in recent alluvial deposits and
in lower terraces. In meandering rivers they locate in point bars and in the internal curve of
the meanders. In braided rivers the distribution of heavy metals is discontinuous; they
locate in transverse bars, curves of the channel, junctions of channels and stretches with
convergent flow (Smith and Minter, 1980).
In alluvial fans, placers locate in interbedded gravels and in debris-flow sediments.
These develop after glacial retreat, when the absence of plant cover facilitates slope
instability. Once they fail, they are subject to erosion by glacial meltwaters.
141
the greatest damages were related to graben areas in the upper part and in the push ridges
of the frontal part (Hansen, 1965).
5. Placer deposits in glacial environments
Placers are accumulations of heavy metals that have been extracted from the rock substrate
by weathering, water, wind, and glacial processes. They are important economic resources
and are ores of gold, diamonds, platinum, tin, and other minerals. Placers subject to ice
action are exploited in northern Asia, Canada, and Alaska, though most of these
exploitations are in environments not affected by glacial activity (Boyle, 1979).
Placer deposits (Figure 6.15) are located in a wide range of sedimentary situations,
such as alluvial, colluvial, glacial, fluvioglacial, coastal, and marine environments (Levson
and Morison, 1996). Alluvial placers are located in active or abandoned streams, such as
gullies, braided and meandering rivers, alluvial fans, and fan-deltas. Gold concentrates
essentially together with loose blocks and gravels and in a conglomeratic facies (Fayzullin,
1969).
Fluvial placers are the most frequent type and are located in recent alluvial deposits and
in lower terraces. In meandering rivers they locate in point bars and in the internal curve of
the meanders. In braided rivers the distribution of heavy metals is discontinuous; they
locate in transverse bars, curves of the channel, junctions of channels and stretches with
convergent flow (Smith and Minter, 1980).
In alluvial fans, placers locate in interbedded gravels and in debris-flow sediments.
These develop after glacial retreat, when the absence of plant cover facilitates slope
instability. Once they fail, they are subject to erosion by glacial meltwaters.