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Granduc - Milling cont...
The crushed product was delivered to a discharge conveyor which
was, concurrently, picking up the minus 6-in. ore that by-passed the
grizzly as noted above and delivered, after passing under a tramp-iron
magnet, via a 48-in. transfer conveyor, inclined at 16 degrees, either
directly to No.3, 2,000- ton waste bin in the case of waste or, through
a system of feed conveyors and transfer chutes to Nos. 1 and 2 bins,
each with a capacity of 3,000 tons.
 From these bins, ore
was drawn through undercut arc-loading gates
which use the railroad car as a volumetric hopper so that flow ceases
when the ore level builds up to the loading-chute lip. The car, one of
20 having a capacity of 50 tons used in the haulage through the tunnel
to Tide, was slowly drawn through the loading position until full at
which point the gate was closed by upward rotation. Chance of spillage
had been found to be slight.
The cars were open hoppers with individual air cylinders and
were
arranged for side-dumping in either direction. At
the end of the run to Tide, the ore was dumped into a 3,000-ton pocket in
rock about 1,100 feet inside the portal on a spur track. Another spur
track, leaving the snowshed just outside the portal, went to a
dump area for disposal of the mine waste.
During observation of these various crushing, conveying, storage,
haulage, and dumping operations, it became obvious that a great deal of
attention had been paid to level controls and alarms for extraordinary
conditions such as over-loading. While too detailed to describe here,
it can be said that the system in effect provided for a smooth flow of
the ore from the crushing unit underground to the underground pocket
from which it was removed and conveyed over a 42-in. belt 2400 feet long
first through a concrete tunnel and then a steel pipe to the top of the
concentrator building in preparation for further reduction and
treatment.
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