Navigator Resources (ASX: NAV) has updated progress on the first ore processing trial completed in April from its 100% owned Leonora Gold Project (LGP) in Western Australia, with gold recovery of over 98% from the 8,918 tonnes milled from the Bruno open pit ore.
The company said the first parcel of ore in the 75,000 tonne trial mining and milling program was milled through St Barbara Limited’s Gwalia processing plant during the period 13th to 19th April 2010.
Significant rain during ore haulage resulted in damp supergene clay ore from Bruno being delivered to the mill. This resulted in lower throughput rates than would normally be expected from oxide material.
Mill throughput averaged less than 100 tonnes per hour, which is below the optimal throughput level of the plant and less than St Barbara’s throughput on underground hardrock ore.
Due to the soft nature of the ore and the slow feed rate, the grind was very fine with 100% passing 75 microns with a mean of ~20 microns. This led to low levels of gold reporting to the gravity circuit and the majority reporting to the leaching circuit.
Despite the low amount of gravity gold, recovery through the plant was very high at 98.2% which confirmed that the ore is amenable to normal CIL treatment methods.
The average grade of the Bruno ore from within the pit design had been estimated at 1.7g/t gold. The final plant reconciliation head grade was 2.83g/t gold, thus indicating an overcall of 66% for the gold grade of the processed ore.
David Hatch, managing director, said "the overcall is significant and whilst the company believes this first parcel of ore was representative of the ore mined to date from the Bruno pit, the next milling campaign will add further information on whether this grade uplift could reasonably be expected over the entire Bruno pit."
The second milling campaign commenced yesterday (13 May) and the company intends to treat approximately 25,000 tonnes of material which will comprise a blend of Mert 2 hard rock and Bruno soft supergene ore types.
This mix has been selected to provide a better flow of material through the plant which will result in less hang-ups and therefore better throughput rates.
Navigator continues to gain valuable information and remove mining and processing uncertainties, thereby obtaining greater confidence in its decision making aimed at the LGP becoming its second producing gold operation.