RE: Pre-feasibility and feasibility studiesactually a good question
think of it as a series of steps on a journey
at each step you ask if it is worthwhile to continue
each step builds on the last and takes you further on your journey
a prefeasibility puts together enough information to say is it worthwhile to go further?
And what areas am I weak in where I need to gather more info
I have attached links to 3 prefeasibility reports
read them and learn
https://www.detourgold.com/i/pdf/NI43-10_Technical_Report_Sedar_2F.pdf
there is a hell of a lot more to it than a geo say so,
geology plays a part, metallurgy is important, type of physical plant and cost power, water, environment, labor, social implications
the bottom line question is - IS THE RATE OF RETURN POSITIVE?
you keep working on it till a no go or a 95% confidence level is reached at a suitable RoR