I think you're in the right ballpark. Atlas seems to run the other mines at around 3Mtpa so if they replicate that model at Corunna it gives GDA a royalty stream of 3m x $1.13 or $3.39m per year.
Pretty good news for a bunch of chancers (GDA I mean, not you).
All of which adds to Watso's question: why didn't they announce Atlas' assay results?