I think your chart projection is a bit too steep in my opinion, glad to be proved wrong of course...
Otherwise potential risks to the SP are very low IMHO, mainly to the upside. GMM may just make 20M or so , then the following 2 years are very profitable indeed. I would not be surprised if they realise 44M+ a year over that 24mth period after most costs. (Factoring in the Tantalum offtake too). They also get 18M upfront soon with another 18M down the track JUL/AUG this year on a confirmed sale / delivery.
This is extremely good value for an initial 3 year outlay of 24M + the operating costs, initial restart/improvements over that 24mth period which have been factored in at 15% in the above figures. These are my back of the napkin figures anyway.
As always DYOR.