It is a red flag when a development-stage mining company makes plans for a mine with expansion stages. Why? There is one mine size that maximizes the net present value (NPV) of the deposit. Usually this size results in a mine life of 6-15 years. A bigger mine exploits the resource faster, making the future revenues happen earlier. Because there is a time value to money, mining faster increases the present value of the future cash flows. A larger mine also enjoys economies of scale that lower operating costs. Of course, all of this has to be balanced against the capital costs of a bigger mine. Underground mines tend to have higher capital costs so they tend to be designed with longer lives. Open pit mines tend to have low capital costs so they tend to be designed with short lives.
If the estimated mine life is over 20 years, then there is probably something fishy going on. Usually, it would make more sense to build a bigger mine with a shorter life.
