A Mineral Store/muse
117
are turning increasigly to coastal marine deposits as those on the
land become depleted or too expensive to
In 1966 over 6, per
cent of this country’s gravel came from the seabed. «In the United
States the value of gravel and sand accounts for 20 per cent or m0re
of the total value of all non—metallic minerals, other than fuels. And
of course some sands and gravels also contain other constituents
which are worth extracting. The Japanese have been obtaining iron
from gravel dredged up from the sea for many years; the iron can be
Separated magnetically, thus lendihg to the economy of the prbcess.
However, the low grade of the ore and the interference With the
sheries caused by the dredging arereducing the size ofthis industry.
Apart from their direct use in the conStructional industry, sand
and gravel taken from the sea also play a part in land reclamation;
Masters of this art are, of course, the Dutch who have dev‘ised
several systems for raising sand and gravel by continuous dredging
—:either conventionally or by suction—and transportin'g it to
site selected for the new land. The important thing is «to devisea
system by Which they can deposit material faster than the
,,
sea
currents can sweep it away. Certainly the sucCess of the DutChin
winning back a considerable area of ”land from the sea must have
been at least. partly responsible —for the British suggestion to build
a third airport on landrecl‘aimed from the shallow Mapin—sands
at the inouth of the Thames. Dock facilities are included in the
scheme. Land reclamation often :hasthe added benets of deep—:
water channels created by the dredging operations;
newport
of
Rotterdam—called Europoort—is a typical example.
;p…3
.
…
AS in so many marine operationsthe—decisive«factor in {dredgin3r
_
is the depth of the deposit.
that are
-
shallow Ïby sea standards has already»been acquired
operations but, beyondthisg kn0wledge
the » deepest= «Operations i's S‘till‘A,l_ittle more
the
designer’s drawing—board… In the ïshallowest— werkings;:ard£dœdgè
armed with a continuous belt carrying ;_scoOpsùis;quite :adcquate.
“
.
These…ladder;bucketdredges
however;liinited
by which the‘-laddercan extend andstill
Beyond this, the hydraulicdredges comes :intô
; €Xp crien_cc
With:3ucti0n ïdredges in inlaind waters…suggésts;äthat they should be
abléî to pump up »loose
:;sahd :fro‘mä d‘ept‘hs: up to 200 feet.
A‘èthird
air lift:
been …_used " m
,
the diamond Operations o” the west coast—of Africa. -è This creates
117
are turning increasigly to coastal marine deposits as those on the
land become depleted or too expensive to
In 1966 over 6, per
cent of this country’s gravel came from the seabed. «In the United
States the value of gravel and sand accounts for 20 per cent or m0re
of the total value of all non—metallic minerals, other than fuels. And
of course some sands and gravels also contain other constituents
which are worth extracting. The Japanese have been obtaining iron
from gravel dredged up from the sea for many years; the iron can be
Separated magnetically, thus lendihg to the economy of the prbcess.
However, the low grade of the ore and the interference With the
sheries caused by the dredging arereducing the size ofthis industry.
Apart from their direct use in the conStructional industry, sand
and gravel taken from the sea also play a part in land reclamation;
Masters of this art are, of course, the Dutch who have dev‘ised
several systems for raising sand and gravel by continuous dredging
—:either conventionally or by suction—and transportin'g it to
site selected for the new land. The important thing is «to devisea
system by Which they can deposit material faster than the
,,
sea
currents can sweep it away. Certainly the sucCess of the DutChin
winning back a considerable area of ”land from the sea must have
been at least. partly responsible —for the British suggestion to build
a third airport on landrecl‘aimed from the shallow Mapin—sands
at the inouth of the Thames. Dock facilities are included in the
scheme. Land reclamation often :hasthe added benets of deep—:
water channels created by the dredging operations;
newport
of
Rotterdam—called Europoort—is a typical example.
;p…3
.
…
AS in so many marine operationsthe—decisive«factor in {dredgin3r
_
is the depth of the deposit.
that are
-
shallow Ïby sea standards has already»been acquired
operations but, beyondthisg kn0wledge
the » deepest= «Operations i's S‘till‘A,l_ittle more
the
designer’s drawing—board… In the ïshallowest— werkings;:ard£dœdgè
armed with a continuous belt carrying ;_scoOpsùis;quite :adcquate.
“
.
These…ladder;bucketdredges
however;liinited
by which the‘-laddercan extend andstill
Beyond this, the hydraulicdredges comes :intô
; €Xp crien_cc
With:3ucti0n ïdredges in inlaind waters…suggésts;äthat they should be
abléî to pump up »loose
:;sahd :fro‘mä d‘ept‘hs: up to 200 feet.
A‘èthird
air lift:
been …_used " m
,
the diamond Operations o” the west coast—of Africa. -è This creates