Quarry Operations © Dr. B. C. Paul Summer 2003

Specialized Open Pit Simple Quarries operate on thick tabular limestone deposits with limited soil cover Simple Quarries operate on thick tabular limestone deposits with limited soil cover Quarry will be developed as a true open pit 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 Areal extent of quarry operations limited

Unique Procedures of Quarry Usually no grade guide to dictate elaborate push-backs from central cone 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) 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 Either working down dip Or not planning at all Or not planning at all

More Unique Features Slopes stand at high angles of repose Slopes stand at high angles of repose –Favors almost vertical walls to limit SR Working slope constraint could still dictate slope Working slope constraint could still dictate slope –Often work around this

Working Around a Working Slope Grade control usually less critical (whole similar layers) 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 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 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 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 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 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 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 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) Can lead to steepness problems that raise trucking wear and tear (often not checked closely enough)

Quarry Waste Problems Overburden is often relatively minor Overburden is often relatively minor May be significant internal waste problems May be significant internal waste problems –Once in the rock layers may find things can’t be marketed Weathered fracture zones Weathered fracture zones Shale partings in horizontal layers Shale partings in horizontal layers In more complex settings can have dikes intrusives as well as faults and fractures full of gunk In more complex settings can have dikes intrusives as well as faults and fractures full of gunk Processing Waste Processing Waste –Crushing tends to produce excess fines Can lead to almost 10% of process tonnage waste Can lead to almost 10% of process tonnage waste

Where Does the Waste Go Stripping waste often goes into little piles by the side Stripping waste often goes into little piles by the side Processing Waste Processing Waste –Big headache when washing involved (about 5% solids slurry) Try to settle it out in incised ponds or old small quarry pits Try to settle it out in incised ponds or old small quarry pits –May have to try dredging and drying Internal Waste Internal Waste –Piles or backfill –Some of processing waste may go the same places