Quarry Operations
© Dr. B. C. Paul Summer 2003
Specialized Open Pit
• Simple Quarries operate on thick tabular
limestone deposits with limited soil cover
• Quarry will be developed as a true open
pit
– Large amount of material extracted relative to
OB usually will preclude backfill options
– Soil horizons are often handled somewhat
carelessly
• Areal extent of quarry operations limited
Unique Procedures of Quarry
• Usually no grade guide to dictate
elaborate push-backs from central cone
– Common to strip the soil horizons over most
of planned area of pit from the start
• Cost of different types of materials operations
spread over time may be greater than biting the
bullet once (soil OB stripping ratio is usually very
low)
– If entire planned pit is not stripped initially
• Either working down dip
• Or not planning at all
More Unique Features
• Slopes stand at high angles of repose
– Favors almost vertical walls to limit SR
• Working slope constraint could still dictate
slope
– Often work around this
Working Around a Working Slope
• Grade control usually less critical (whole similar
layers)
– Need to limit bench height to maintain grade control
is not there
• Could still have bench height limited by digging
depth of shovels
– Quarries modify blasting technique to collapse the
blasting face into a muck pile rather than loosen it for
easy digging
• Now bench height is controlled by drilling
accuracy or safety considerations on how tall a
single vertical cliff can be
– High near vertical cliffs favor very steep over-all
slopes
The Collapsed Face Problem
• To get around digging height limits quarries
blast to collapse face
– This spreads out muck pile and could cause very wide
benches that cause gentle working slopes
• Quarries tend to slice down by layers
– Grade issues are not really there
– Horizons are often level so quality is controlled by
horizontal layers
– Means that quarries need run only a few benches at a
time
• Geometry spreads out on layers rather than dives down as
cone
General Quarry Image
• Almost verticals going down to one or two
very wide benches that spread-out across
the deposit
• Roads get stashed back on the side as
ramps between levels
– There is a tendency to have short ramps to
take up less space
• Can lead to steepness problems that raise trucking
wear and tear (often not checked closely enough)
Quarry Waste Problems
• Overburden is often relatively minor
• May be significant internal waste problems
– Once in the rock layers may find things can’t
be marketed
• Weathered fracture zones
• Shale partings in horizontal layers
• In more complex settings can have dikes intrusives
as well as faults and fractures full of gunk
• Processing Waste
– Crushing tends to produce excess fines
• Can lead to almost 10% of process tonnage waste
Where Does the Waste Go
• Stripping waste often goes into little piles by the
•
side
Processing Waste
– Big headache when washing involved (about 5%
solids slurry)
• Try to settle it out in incised ponds or old small quarry pits
– May have to try dredging and drying
• Internal Waste
– Piles or backfill
– Some of processing waste may go the same places