I am not experienced in mining directly, only indirectly through...

I am not experienced in mining directly, only indirectly through owning shares. Not an accountant either.
But, I never take much notice of NTA with mining stocks, especially smaller ones ( Regis is not small and is multi mine which helps). But assumptions to calculate NTA are so dependent on head grade, gold price, recovery etc as to be pretty risky to be devalued......and costs also determine what can be mined or classed as reserves etc...these can blow out if you have ground stability issues or such like, but moreso when running into grade issues , especially as mines age.