Richards gives the average amount of water used in 21 mills as 2 77 gallons per stamp per minute or 6 68 tons of water per ton of ore crushed The average duty of a miner s inch in a gold stamp mill is given by P M Randall as 12 tons of quartz if the head under which the water is supplied is 4 inches and 15 88 tons if the head is 7 inches