How much gold is in Brolga alone?

Not many dusters at Brolga (please correct me if I'm wrong) and I fully expect the infill drilling to confirm more of the same.
They say 1g/t is needed for an economic open pit mine.
Brolga itself is larger than a square km but lets just take a look at a central Brolga square km.
We have transported cover of around 40 metres, so let's go to a depth of 340 metres (300m actual).
One cubic metre of rock weighs 2.5 to 3 tonnes. But lets be super conservative and use 1.75 tonnes (which puts us in crushed rock weight range).
Let's be super conservative and just say there is only 1 g/t overall.
1 troy oz = 31.1 grams.

1000m x 1000m x 300m = 300Mill cubic metres
x 1.75 = 525 Mill tonnes @ 1g/t
/ 31.1 = 16.88 Mill oz's

So the maths tells me there is all this gold in just this central part of Brolga let alone all of hemi.
So what am I NOT taking into account?????
I must be missing something or doing the math wrong?
Help required please!!!!