Uranium mining

Once an orebody has been delineated, general assumptions may be made as to methods of ore extraction. Before cost models can be applied to each method, an optimum mine life should be established for the deposit. Optimum production rate can be determined in many ways, but for uranium, probably the most important determinant is market analysis and supply/demand analysis. For pre-evaluation estimations, a very simple rule can be applied as a common estimating basis. Taylor's Rule (1978) is an empirical formula for calculating optimal mine life. The rule states:

Life (years) ~ 0.2 x ^Expected ore tonnage

4.6.3.2. Mine capital costs

General cost models are presented for open pit and underground mining operations. In situ leach mining operations are addressed in the beneficiation section. The models represent typical sedimentary-hosted uranium ore deposits within the United States. The models represent capital intensive operations, with associated US productivities, labour rates and burden. Ore production rates range from 900 to 5400 metric tonnes per day ore.

Typical open pit and underground capital costs are composed of 25-30% labour, 65-70%

equipment, and 5-10% supplies.

Open Pit Model

Open pit mines are limited by the stripping ratio which is directly related to depth. As a general rule, maximum depth is about 150 metres although the grade of the deposit will affect the economics and therefore the ultimate pit depth. The break-even stripping ratio, and ultimate pit depth, is determined when the costs of removing ore plus waste equals the value of the ore minus beneficiation costs.

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Two typical open pit methods are employed for overburden and waste removal; shovel and truck operations and scraper operations. Mining of ore, however, is usually by backhoe and truck or loader and truck. Shovel and truck operations are preferable when round-trip waste-hauls start to exceed 1.6 kilometres, or when digging conditions are difficult because of boulders or strongly cemented formations. Drilling and blasting may also be required when some of these conditions are encountered.

Scraper operations are preferable when digging unconsolidated or loosely consolidated material.

Bulldozers are often used in conjunction with scrapers and may contribute to a sizable percentage of material moved. They may also be used for ripping to eliminate the need for drilling and blasting.

When estimating capital requirements, it becomes readily apparent how many variables can affect the cost estimate. Type and combination of mining equipment, surface facilities, and infrastructure requirements (see Tables A-I.I and A-I.II of Appendix I) are items that need to be considered on a site specific basis. Despite all of the unknowns, a rough estimate can still be determined at this "pre-evaluation" stage. Excluding acquisition, exploration, and infrastructure costs, an estimate can be made using the following equation:

Capital Cost = 207.3 (tonnes) + 2 500 000

Where: The equation is of the form Y = Ax + B;

"Capital Cost" is on average 1990 US dollars;

207.3 is the constant "A";

"Tonnes" is the daily mine capacity of ore plus waste;

2 500 000 is the constant "B".

Underground Model

Underground mines are developed when the depth of the orebody generally exceeds 120 metres up to about 1400 metres. Underground mines typically produce higher grade ore than surface mines which offsets the higher capital and operating costs. Production rates are generally less, typically between 300 to 2300 metric tonnes of ore per day, and mining methods may include modified room-and-pillar, cut and fill, sublevel-open slope, and variations of each method.

General mine plant facilities would be similar to the open pit facilities with three notable exceptions: shafts and headframes, ventilation facilities, and a larger power substation. Excluding shafts and headframes, general surface facilities approximate 25% of total mine capital costs.

Shaft sinking is the largest capital cost item. Depending on depth and number of shafts required, the cost can range from 30 to 50% of total mine capital. Shaft sinking costs can be extremely variable due to rock conditions. Production shafts with 3.9 to 4.3 metre diameters will range from $16 300 to

$17 600 per metre. Ventilation shafts, commonly 1.8 metres in diameter, will cost approximately

$8800 per metre2. When poor ground conditions are encountered, costs can range from $30 000 to

$50 700 per metre.

Underground development costs depend on the type of mine plan, amount and type of development required, and mine equipment utilized. Typical development costs, excluding shafts, will include haulage drifts, cutouts, crosscuts, raises, manways, undercuts, and stope preparation.

Development costs account for approximately 20% of total mine capital costs.

Costs have been updated and converted to metric units.

Capital Cost per mt ore ($x!0⁶) = 0.002 (Depth'⁶¹ x Tonnes*¹)

Where: The equation is of the form Z = C(XAYB);

"Capital Cost" is on average 1990 US dollars;

0.002 is the constant "C";

"Depth" is the hoisting depth in metres;

"Tonnes" is the daily mine capacity of ore.

4.6.3.3. Mine operating costs

The following mine operating cost equations for the "pre-evaluation" stage of property evaluation may be used to roughly approximate costs.

Open Pit Model

The open pit model is based on a combination of scrapers and dozers for mining of overburden and waste, and loaders and trucks for ore and waste. The strip ratio is 40:1 and the pit depth is approximately 60 metres. Drilling and blasting is not required but ripping with dozers is required. The cost model equation is presented below:

Operating Cost = 0.004 (Tonnes) + 34.43

Where: The equation is of the form Y = Ax + B;

"Operating Cost" is on average 1990 US dollars;

0.004 is the constant "A";

"Tonnes" is the daily mine capacity of ore;

34.43 is the constant "B".

Adjustment factors: Labour: 55%, Equipment: 30%, Supplies: 15%

Underground Model

The underground cost model should approximate a modified room and pillar mining method with pillar extraction, a sublevel open stope mining method, and a cut and fill mining method. The model should also approximate a mining method which uses combinations of the above methods. The cost model equation is presented below:

Operating cost per mt ore = 75.4 (Depth,-** Tonnes'2)

Where: The equation is of the form Z = C(XAYB);

"Operating Cost" is on average 1990 US dollars;

75.4 is the constant "C";

"Depth" is the hoisting depth in metres;

"Tonnes" is the daily mine capacity of ore;

Adjustment factors: Labour: 65%, Equipment: 5%, Supplies: 30%

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4.6,3.4. Decommission/reclamation costs

Decommissioning the mine and mill facilities after the completion of mining are important considerations in this age of environmental awareness. Costs for these activities for a "typical" western United States, high-plains arid-region are in the order of $7500 per hectare on average 1990 US dollars.