Two drill holes revealed the extension, intersecting "well-developed pipe alteration below the sulphide mineralization suggesting the hydrothermal system is robust in the area", the company said in a statement.
Drilling at McLeod Deep continues with four drills, it added.
Exploration drilling is also in progress between the Bracemac and McLeod zones, with six widely-spaced holes completed to date targeting the Key Tuffite horizon.
Donner said it found anomalous base metal values to the east of the Bracemac-KT zone.
Drilling 7 kilometres north-west of the Matagami mill meanwhile returned the first discovery of semi-massive copper-rich sulphides within a 1.2 kilometre-wide zone of chlorite-silica-pyrite alteration.
Glencore Xstrata operates the mine and owns 65%, while Donner has the remaining 35%.
The deposit contains proven and probable mineral reserves of 3.7mln tonnes grading 9.6% zinc, 1.26% copper, 28.25 grams per tonne silver and 0.43 grams per tonne gold.
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