Yamana went public in 2003, and started producing the same year. the only way they could have done that was to be a private company with deep pockets for a number of years. Minera Yamana the original company started in 1994.
There are a lot of companies that start out as private companies with exploration funded by the principals and their friends. An example is Canico, which went public @ $7 a share and was bought out by CVRD less than 2 years later. That same group has started another private company and so it goes on.