While I prefer conservatism generally I'd err on the lower 40%...

While I prefer conservatism generally I'd err on the lower 40% increase in capex side of the equation if the resource doubled. Regardless of the resource size:
- any contribution to the access road is fixed,
- capex associated with power also has a large fixed component
- Processing will of course need to be scaled, but the central admin/office facilities associated with it will be 'largely' fixed.
- Workforce accommodation will need to scale, but I'm not sure a doubling of resource equates to a doubling of workers, even if mine throughput doubled as there are 'back office' roles on site that arguably aren't one-for-one.
- As a corollary, the other central facilities - recreation, mess halls, should probably be scaled for efficiency across a range of workforce sizes, even with a starter pit, and may not need to be 'doubled'.
- With a bigger facility, there is the greater potential for economy of scale in purchasing.

All just speculative of course and ignores the potential for continued inflation.