Investing in a commodity such as gold, silver or platinum and the mining of it is possible through purchasing shares in companies that are involved in the sourcing of them. A company will initially do a preliminary exploration to find a mineral reserve, then the cost of extracting these will be worked out to determine feasibility - this will tell you whether it is potentially worthwhile as an investment or not.

Aside from investing in shares in these companies is the actual purchase of the mineral, such as a gold sovereign coin, etc.