WillP -- Date:1999-03-06 12:05:49
Subject: Mining Under Lake
There was a recent question I ran across on SI
concerning mining under Snap Lake.
Mining of this deposit, should it come to pass would
most likely start as an open pit operation based on
land. Likely areas are the NW peninsula, the north
shore, and possibly the NE arm.
Beyond that...one would have to mine the portions of
the dyke under the lake by underground methods. It
appears that the depth of the dyke at shore's edge is
roughly 60-100 metres or significantly deeper...and
the cost effectiveness of open pit vs underground for
an 8 foot dyke at such a depth is highly debatable in
any case.
So...underground mining is pretty much called for
here. As to how that would be accomplished is still
open to much debate. It's not difficult...other than one
must keep in mind that there is a certain minimum
thickness that needs to be excavated in order to get
the equipment at depth. If the dyke is only 5 feet
thick...no matter...you're still going to have to
excavate a certain thickness. Much of that would be
waste rock. As to what the minimum thickness such a
mine would operate with...hard to say. I'm
comfortable with a dyke thickness of 2.4 metres...but
not one of 1.2 metres.
Another thing to be considered is the slope of said
dyke. Releases have called it a relatively uniform
12-15 degree slope, however that leaves questions
as to what the steepest slope is over short stretches.
Try to envision this dyke gently dipping (at 24
degrees) ... then running flat for a bit. Clearly, there is
a fair bit of waste rock that would have to be mined
as well.
These questions and concerns would, naturally, have
been addressed by the MRDI study in the limited
area they evaluated only. I assume the cost of
mining built in the minimum depth to be
excavated...and the amount of waste rock requiring
removal.
The underground operation would most likely be a
'room and pillar' one...where the dyke is removed,
save for supporting pillars. The waste and processed
kimberlite could be backfilled in mined areas, as well.
In the end this will all come down to cost
effectiveness, and much more needs to be done to
determine tonnage, and the shape of the ore before
such decisions are made.
Much has been guessed at as to how the kimberlite
will be mined. Most suggestions I've run across are
possible...workable...and probably a reasonable
guess under the circumstances. It's too early to get
wrapped up in the mechanics of it just yet, however.
Suffice it to say...mining under Snap Lake is not a
problem. At the worst...it's the sort of problem that
mining engineers get paid the big bucks for. :-)
Hope this helps.
WillP |
