A 10mtpa operation scenario will likely only ever run with a...

A 10mtpa operation scenario will likely only ever run with a carbonate plant. I'd dare say the same for 5mtpa also. With the massive export volumes, the Capex begins to become quite insignificant in comparison to the cost of transport. 

It is however good practice to kick start money flow asap  on the lowest possible Capex and is why the 2mtpa option is so critical. Carbonate plant is a no brainer as consistent positive cash flow kicks into place

Note also, power is an additional hold back to the carbonate plant and probably best the mine isn't constrained by external developments to progress