| Title | Geology and Hydrothermal Alteration of Makushin Geothermal Area, Unalaska Island, Alaska |
|---|---|
| Authors | Parmentier, Paul P.; Reeder, John W.; Henning, Mitchell W. |
| Year | 1983 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Exploration; USA; Alaska; Unalaska; Geology; Alteration; Volcanics |
| Abstract | The oldest rocks exposed in the Makushin geothermal area are of Miocene Age, and include Unalaska Formation metasediments and metavolcanics, and a dioritic pluton. These rocks have been locally covered by Pliocene to Recent Makushin volcanics, consisting mostly of andesitic to basaltic lavas, and by Recent pyroclastic flows and cinder cones. Abundant hydrothermal alteration zones mostly associated with the Makushin diorite reflect both the early stages of alteration related to the diorite emplacement, and the alteration related to the the presently active geothermal system. Most of the active fumarolic areas have mineralogic assemblages which suggest acidic alteration conditions probably caused by ascending steam. |