Unnamed (west of Monte Cristo Creek) (ARDF #NB035) Au

Unnamed (west of Monte Cristo Creek)

Occurrence, Inactive

Commodities and mineralogy

Main commodities	Au
Ore minerals	gold; pyrite
Gangue minerals	gypsum; quartz

Geographic location

Quadrangle map, 1:250,000-scale	NB
Quadrangle map, 1:63,360-scale	A-5
Latitude	62.2128
Longitude	-143.0209
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	This occurrence is at an elevation of about 4,900 feet on the north valley-wall of Monte Cristo Creek valley near the point that the creek crosses the east boundary of the Nabesna A-5 quadrangle. The site coincides with one shown on an unpublished National Park Service map; it is near the center of the SW1/4 of section 9, T. 5 N., R. 13 E. of the Copper River Meridian. This is National Park Service locality WRST-19 (unpublished data) and the coordinates for this occurrence were provided by the National Park Service.

Geologic setting

Geologic description An unpublished National Park Service map and accompanying database identify this locality as a porphyry gold prospect.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.

Production and reserves

Indication of production	None
Additional comments The prospect is in the Wrangell-St. Elias National Preserve.

References

References Richter, D.H., 1976, Geologic map of the Nabesna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-932, 1 sheet, scale 1:250,000.
Reporters	Travis L. Hudson (Applied Geology)
Last report date	11/24/2002