ABSTRACT

NVI Mining’s Myra Falls Operation is a 4,000 mtpd copper/zinc flotation circuit with by product
gold of ~28,000 ounces per year. Gold recovery has historically averaged 40-55%, however, a
portion of this was recovered in the zinc concentrate and received poor payment. Two Knelson
CD-30 Concentrators have been operating in the grinding circuit since 1992, with gravity
recovery averaging about 2-5% over that time period.

The Myra Falls gravity circuit was one of the very first hard rock mining installations operating
in the world with automated Knelsons. The mine has employed a unique and unusual upgrading
method for the Knelson concentrate that had never been evaluated as to its efficiency. Recent
Gravity Recoverable Gold Testing by McGill University, and mathematical modelling of the
Gravity Circuit by Knelson Gravity Solutions indicated the gravity circuit was not living up to its
potential. The upgrade system operating regime was changed by Myra Falls Personnel, and a
complete gravity audit of the grinding circuit was carried out, with the results confirming the
initial suspicions. Gravity recovery increased from 5% to 15%, with overall gold recovery
improving by 5%.

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