Reserve vs resourceA gold resource is all the gold known to exist on a property.
A gold reserve is that fraction of the resource which is currently economical to mine.
Both resource and reserve expand with drilling and mine development. Fosterville maintains 2 million ozs reserves even though it mines out 600,000 ozs every year. I have not read a resource estimate.
The first figures published are resource estimates. Reserve estimates come much later. In both cases drilling defines volumes/blocks of rock and the average grade of the block is an average of the drill holes in the corners of the block. Coarse grained systems like Keates require a much tighter drill hole pattern than fine grained systems.
We are still a long way from an official resource estimate at Keates and I'm not expecting one until the deposit is defined in terms of length and depth. In the mean time it just gets bigger and bigger!