The Behaviour of Gold In Hemlo Mine Ltd. Grinding Circuit

S. Banisi, A.R. Laplante; McGill University, Montreal J. Marois; Hemlo Gold Mines Ltd.

December 12th, 1999

This paper compares the behaviour of gold and ore in the grinding circuit of Hemlo Mines Ltd.; Golden Giant Mine in North Central Ontario. Particular attention is given to grinding kinetics, classification and liberation. Discussion focuses on golds' malleability and the consequences of this characteristic. These consequences often result in high circulating gold loads within the grinding circuit, the occurrence of "smearing" resulting in "un-liberation" of free gold.

The topics of lab and plant scale test work are discussed and the paper documents results of this test work on a number of feed streams within the Hemlo grinding circuit. Results yielded recoveries ranging from 27.1% for primary mill discharge to 91.8% secondary mill discharge.

"When gravity recovery is not used, gold's malleability and long residence time in the circuit is conducive to interaction with other minerals. Although embedding of harder minerals into gold particle is common and can be readily detected, the reverse phenomenon of smearing is potentially more deleterious ahead of flotation, as liberated gold can become "unliberated" when smeared onto other minerals. Other potential losses of gold can occur when gold is pounded into grinding medium or liners, and these are rejected because of excessive wear."

"The recycled streams, cyclone underflow and secondary mill discharges are then the better candidates for recovery. High gold circulating loads make it unnecessary to process the full streams. Rather, part of the streams can be bled and presented to the gold recovery unit."
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