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Granduc -
Engineering and Planning cont...
The other major
aspect studied at this time was the feasibility of trans- verse and/ or
longitudinal sub-level caving. In the narrower sections of the ore zone,
up to a 50-ft. width, the longitudinal method was used and those
sections exceeding that thickness woulds be mined by the transverse
method. Crosscuts 11 ft. by 16 ft. are driven on 30-ft. horizontal
intervals and a 3% slope was maintained to assure drainage. On the
retreat from the hangingwall, a diamond-shape zone resulting from the
staggering of the crosscuts would be blasted from each crosscut.
 In
those ore zones less than 50 feet in thickness the longitudinal method
was being used to minimize waste. The longitudinal workings were driven
along the footwall on 60-ft. vertical spacing, the headings being
advanced to the end of the orebody and the ore extracted on retreat.
The blastholes
are 2-1/8 in. in diameter and are drilled upward in a standard ring
pattern using six Gardner- Denver two-boom "Fan-DriI" Mark-1 and Mark 2
jumbos. Maximum hole length is 60 feet in the transverse areas and 80
feet in the longitudinal zones. In addition, seven three-boom Mark 3
jumbos by the same manufacturer are being used in development work.
The holes are
loaded with I Y2-in. by 16-in. Cilgel "B", 70%; Forcite Xactex was used
for perimeter blasting. The ex- plosives are inserted into plastic
liners. Major mine access to the working levels between the 2,600 and 3,
720 levels is by a ramp system. Studies of the alternative methods of
access indicated the economic advantages of the ramp layouts, although
at the time no known project, mining a steeply- dipping orebody,
operated solely with a ramp system. It was noted during the visit to
Sweden that the mines at Kiruna and Malmberget operated their ramps in
conjunction with a shaft.
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