INVESTORS in Greater Bendigo Gold Mines will be buoyed by independent test results showing gold grades up to 13kg per tonne in some concentrate from the Maxwell mine at Inglewood.
Managing director John Cahill said the exceptionally high result might have been influenced by the presence of some free gold.
"It's early days yet," Mr Cahill said.
"The results are significant, but the ongoing recovery of these high concentrate grades can't be guaranteed.
"We will not be in a position to reassess our resource statements or review our financial forecasts until larger volumes of the tailings feeds and the rich underground feeds have been processed and sampled.
"The challenge is to recover the gold from these concentrates in a bar form for sale."
Processing during the first two weeks of shakedown operations included about 500 tonnes of the 30,000 tonnes of tailings left by the mine's previous operator and stockpiled by GBGM as initial feed for the plant.
This yielded about 100kg per 100 tonnes (0.1 per cent) of sulphide concentrate, in which visual analysis revealed free gold as well as gold contained in arsenopyrite and pyrite crystals.
The distribution of sulphide concentrates in the tailings is unknown.
Continued processing at current distribution rates suggests that a tonne of concentrate will be possible for every two days of operation.
The amount of gold that can be recovered as bullion is yet to be established.
To enable recovery of gold from the concentrate, a testing regime to determine the optimum grind size and potential leaching requirements will be carried out.
Proposals from several laboratories are being assessed.
Much of the higher yield is attributed to the improved efficiency of the newly refurbished Maxwell plant.
The plant's enhanced gravity concentrators capture microscopic gold particles down to 10 microns, allowing GBGM to recover gold that other gravity recovery systems cannot.