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 there are at least two periods of igneous activity and that significant ore mineralization is associated with alaskites and latites that are 3 to 5 m.y. old. Discordant fission track ages of apatite and zircon in the older rocks reveal a major heat source that cooled in late Miocene or early Pliocene and is centered under the mineralized rocks near the townsite of Rico. This heating may indicate the presence of a buried stock that is related to the mineralization.