Geologic descriptionAn unpublished National Park Service map and accompanying database identify this locality as a porphyry gold prospect. Bedrock in this part of Monte Cristo Creek is marine and subaerial volcanic and volcaniclastic rocks of the Lower Cretaceous, Chisana Formation (Richter, 1976). Nearly horizontal volcanic rocks of the upper Tertiary and Quaternary, Wrangell Lava unconformably overly the Chisana Formation. The Chisana Formation is extensively hydrothermally altered and is characteristically replaced by gypsum-quartz-sulfide assemblages (Richter, 1976). Tertiary hornblende-plagioclase porphyry crops out downstream in Monte Cristo Creek in the Nabesna A-4 quadrangle. A K/Ar age for this porphyry is 17 Ma (Richter, 1973). |
Geologic map unit |
(-143.023025336001, 62.2124095926742) |
Mineral deposit model |
Porphyry gold? |
Age of mineralization |
Tertiary? Hydrothermal alteration may be related to the emplacement of a hornblende-plagioclase porphyry downstream in the Nabesna A-4 quadrangle; the porphyry has a 17 Ma K/Ar age (Richter, 1973). |
Alteration of deposit |
Gypsum-quartz-sulfide (pyrite?) replacement of Chisana Formation volcanic rocks. Oxidation is shown by abundant iron-oxide staining. |