Here is a list of General Rules of Thumb often used in Mineral Processing and Metallurgy:

1. A concentrator (mill) requires up to 3 tons of water for each ton of ore processed. It is therefore important to operate with the maximum practical pulp density and minimum practical upward or horizontal movement. The basic philosophy requires movement over the shortest possible distances between processing units and makes use of gravity to save on power consumption. Source: Wayne Gould
2. In the arid climates, mills operate with less than one ton of new water for each ton of ore processed. The balance of the process water required is recovered from dewatering concentrate, thickening the tails, and re-circulation from tailing ponds. Source: Norman Weiss
3. A mill at the mine (and related facilities) accounts for approximately 85% of the total electrical power consumption for an open pit operation, but only about 45% for a typical underground mine. Source: Alan O’Hara
   Crushing Rules / Grinding Rules / Froth Flotation Rules of Thumb
   
4. For a typical underground mine, the cost for electrical power for the mill (concentrator) will be approximately 35% of the total electrical power cost for the mine. Source: Fred Nabb
5. The minimum slope of concrete floors in the mill is 3/8 inch/foot (3%), more around grinding mills where slurry spills can be frequent events. Source: Bob Shoemaker
6. Each hour of downtime in a mill is equivalent to a 4% decrease in recovery that day. Source: Bob Shoemaker
7. A mill built entirely of second-hand equipment and controls may be constructed for half the cost of one built “all new” with state-of-the-art automated monitoring and controls. Source: Bruce Cunningham-Dunlop
8. For gravity separation to be possible, the ratio of the difference in density of the heavy mineral and the medium and the difference between the light mineral and the medium must be greater than 1.25. Source: Arthur Taggart
9. If good gravity recoverable gold GRG is present, the gold assay of a grinding circuit’s cyclone Underflow CUF will be greater than 8 times the cyclone’s Overflow COF’s assay. Source:  Some metallurgist.
10. The actual cyanide consumption at a heap leach operation will be no more than one- third the rate indicated by column leach tests.  Source: Tim Arnold
11. The gold leaching recovery process requires dissolved oxygen in the leach solution to be efficient. This may be accomplished with air sparging when the oxygen uptake rate is 2 mg/liter/minute or less. Otherwise, oxygen injection is required. Source: Damian Connelly
12. Turbulence will be sufficient to ensure good mixing of a flocculating agent if the water velocity is at least 1m/s and maintained for 30 seconds in a feed pipe or channel.  Source: NMERI of South Africa
13. You estimate how much process water you need in a plant using:
    Cyanide Circuits ………………………………………….. 1 – 3 Tons per ton ore
    Flotation Circuits ………………………………………… 3 – 5 Tons per ton ore
    Table Circuits ……………………………………………… 5 – 7 Tons per ton ore
    Jig and Table Circuits ………………………………….. 6 – 10 Tons per ton ore
    Table and Amalgamation Circuits …………………. 8- 12 Tons per ton ore
14. You can approximate how much thickener capacity/area you need using:

Flotation Concentrates 5 to 12 sq. ft. per 24 hr. ton of solids
Slimes (Cyanide Plant) 3 to 10 sq. ft. per 24 hr. ton of solids
Easy Settling Ore 3 to 6 sq. ft. per 24 hr. ton of solids
Difficult Settling Ore 10 to 40 sq . ft . per 24 hr. ton of solids

Crushing Rule of Thumb
Grinding Rule of Thumb
Froth Flotation Rule of Thumb
Mineral Processing / Metallurgy Rule of Thumb

Hard Rock Miners Handbook – Edition 3 originally published by McIntosh Engineering in June 2003 now Stantec.