Pliocene intrusive rocks and mineralization near Rico, Colorado

Fission-track and potassium-argon studies of intrusive rocks in the vicinity of Rico, Colorado, have shown that at least two periods of igneous activity occurred and that significant ore mineralization is associated with alaskites and latites that are 3 to 5 million years old. Discordant fission-track ages of apatite and zircon in the older rocks reveal a major heat source, centered under the mineralized rocks near the townsite of Rico, that cooled in late Miocene or early Pliocene time. This heat source may indicate the presence of a buried stock that is related to the mineralization.