Other thing to keep in mind is "Payback", often companies review payback in years.

For example if mine cost is 200M, and acquistion cost for zen is $600M, and cash flow is $400m/year, then payback is only 2 years, after which for a 25 yr mine, the next 23 years cash flow is pure gravy.

DEFINITION OF 'PAYBACK PERIOD'

The length of time required to recover the cost of an investment. The payback period of a given investment or project is an important determinant of whether to undertake the position or project, as longer payback periods are typically not desirable for investment positions.

Calculated as:

Payback Period = Cost of Project / Annual Cash Inflows