Environmental Engineering Reference
In-Depth Information
(a)
(b)
v
90
E
102
v
River
Norilsk
v
v
68
N
v
v
v
Crater-lake sediments
Magnetite-rich breccia
Sediment breccia
Sill
Turukhansk
v
v
v
500 m
V
Borehole
64
N
(c)
400
200
0
200
Pipes with magnetite
Lava
60
400
Te p h r a
Sill
Tunguska Basin sediments
250 km
v
v
Sill
600
v
v
v
96
E
108
800
Figure 12.3
flood basalts,
sills and explosion pipes that formed during the end-Permian. (b) Map view of
two pipes located about 100 km west of Bratsk in the southern parts of the
Tunguska Basin (Benedyuk,
1987
). The central parts of the pipes are occupied
by crater-lake sediments. The eastern pipe is mineralized with strontium
carbonate, the eastern pipe (the October pipe) with magnetite. (c) Cross section
through the October pipe based on numerous, fully cored boreholes drilled during
mineral prospecting in the 1980s. The grey area within the pipe is a magnetite-rich
breccia. A black and white version of this
(a) Geological map of East Siberia showing exposed
figure will appear in some formats.
For
atmosphere (Von der Flaass and Naumov,
1995
; Von der Flaass,
1997
; Svensen
et al
.,
2009
). Various parts of the Tunguska Basin are characterized by different
volume of sills, volcaniclastics and lava
flows (Vasil
'
ev
et al
.,
2000
). In the
Tunguska Basin, spectacular pipes with up to 1.6-km-wide subaerial explosion
craters formed during the end-Permian (
Figure 12.3b
,
c
). The pipes are rooted in
metasomatic aureole zones 2
-
4 km down in the basin and are filled by breccias
with a compositional range reflecting the underlying country rock, commonly
designated as either
magnetite
'
pipes (Von der Flaass,
1997
).
Magnetite-rich pipes are most common in the southern halite-rich region of the
basin where hydrothermal brines rose to the surface through the pipes, leaving
massive deposits rich in iron, strontium, copper and other ores. Borehole explor-
ation has revealed twelve pipes containing explosion craters hosting lacustrine
deposits (Von der Flaass and Naumov,
1995
; Fristad,
2012
). The mineral and
'
basalt
'
or
'
