The nameplate of the system is 50MW. This is arrived at by...

The nameplate of the system is 50MW. This is arrived at by multiplying the rating of the panels by the number of panels. I don't know what the panels are rated at, but for argument's sake, let's say each one is 300W. This would mean that there are ~166,666 panels. Crucially, the rating of the panels is based upon lab conditions, 'Standard Test Conditions', known as STC. Under these conditions the panels will produce 300W. These conditions are light intensity of 1000W/m^2 and a cell temperature of 25 degrees C. If the light is lower or the temperature higher, the panels will yield less (they will also yield more than 300W with lower cell temperatures and light intensity higher than 1000W/m^2)

There are things that affect the output of a panel. Primarily, temperature, but also voltage drops in the cables. GNX are using thin film technology, which is less sensitive to temperature, which is good. With the following losses, I would expect the system to lose 10% capacity:
Temperature losses
Volt drops
inverter losses
transmission losses
dirt/soiling
note: this doesn't even factor in cloud cover

So the effective rating is 45MW. Remember, that is only 45MW @ 1000W/m^2
If you look at the BOM data:
http://www.bom.gov.au/jsp/awap/solar/index.jsp

You'll see that for Kidston, yesterday, the irradiation was 30MJ/m^2. That's energy, we want power. Firstly, that's converted to kWh by multiplying by 277, to give 8.333 kWh/m^2. Now, making a big assumption, I'm going to assume there were 12 hours of effective sunlight. This would mean that the power was 8.333 / 12 = 694W/m^2

I am also going to assume that, even though the panels are single-axis tracking, they only capture 10 hours of sun.

So, based upon this, if the whole system was commissioned and the above data/assumptions correct, the energy produced would be:

45,000 KW x 0.694W/m^2 x 10 hours = 312,300 kWh, or 312.30 MWh

My assumptions are conservative (and likely very wrong). Please take these figures with a pinch of salt. This is to show the effect of system losses and less than perfect temperatures and irradiance