North Fork Snoqualmie River

Porphyry copper deposit in Washington, United States

Names and other identifiers

Alternate names Condor Hemlock
Tract name Cascade Arc (003pCu9014)
Site status deposit

Geographic location

Country United States
State or province Washington
Geographic location -121.636388889, 47.6775
Geologic map unit -121.636388889, 47.6775
Nearby data

Geologic information

Deposit type Porphyry copper
Age (Ma) 18Ma
Age determination method unknown
Age range 18 Ma
Age reference Singer and others (2008)
Minerals azurite/malachite, biotite, bornite, brochantite, chalcopyrite, chlorite, digenite, epidote, goethite/limonite, gold, magnetite, molybdenite, pyrite, pyrrhotite, scheelite, sericite, sphalerite
Associated rocks breccia, lamprophyre, quartz feldspar porphyry, quartz latite porphyry, granodiorite, metasedimentary rocks, andesite, andesite volcaniclastics, quartz diorite
Tectonic setting continental margin
Stratigraphic age Miocene

Commodity and development information

Development status Occurrence
Major commodities Cu
Tonnage (Mt) 128Mt
Cu grade (%) 0.68%
Mo grade (%) 0.0082%
Au grade (g/t) 0.1g/t
Contained copper 870,000t
Gold-Moly ratio 10

Reference information

Study area name United States
References Lasmanis (1995); Long and others (1998); Herdrick and others (1995); Hollister and Bauman (1978); Singer and others (2008)
Site reference U.S. Geological Survey National Mineral Resource Assessment Team (2002)
Herdrick, M.A., Newport, G.R., and Heinemeyer, G.R., 1995, Geology of the North Fork Snoqualmie porphyry copper deposit, King County, Washington, in Pierce, F.W., and Bolm, J.G., eds., Porphyry copper deposits of the American Cordillera: Tucson, Arizona Geological Society Digest 20, p. 243–250.
Hollister, V.F., and Bauman, F.W., 1978, The North Fork porphyry copper deposit of the Washington Cascades: Mineralium Deposita, v. 13, p. 191–199. (Also available at
Lasmanis, Raymond, 1995, Regional geological and tectonic setting of porphyry deposits in Washington State, in Schroeter, T.G., ed., Porphyry deposits of the northwestern Cordillera of North America: Canadian Institute of Mining, Metallurgy and Petroleum Special Volume 46, p. 77–102.
Long, K.R., De Young, J.H., Jr., and Ludington, S.D., 1998, Database of significant deposits of gold, silver, copper, lead, and zinc in the United States—Part A, Database description and analysis; Part B, Digital database: U.S. Geological Survey Open-File Report 98-206, 33 p., one 3.5-inch diskette. (Also available at, D.A., Berger, V.I., and Moring, B.C., 2008, Porphyry copper deposits of the world—Database and grade and tonnage models, 2008: U.S. Geological Survey Open-File Report 2008-1155, [45] p. and digital data, accessed December 31, 2013, at