| Basis for focus area |
Permissive tract PC12 for Massive sulfide, Sierran Kuroko-type deposits polygons extracted and merged from the 1995 National Assessment (U.S. Geological Survey National Mineral Resource Assessment Team, 2002). Also PC16 from the ICBEMP (Box and others, 1996). |
| Identified resources |
Identified resources and historical production of copper, gold, silver, and zinc. |
| Production |
Holden mine (1938-1957): 9.1 Mt averaging 1.06% Cu, 0.2% Zn, 6.8 g/t Ag, and 2 g/t Au (McWilliams, 1958). |
| Status |
Past mining and post-mining exploration. |
| Estimated resources |
Holden mine resources: 5.6 t Au, 9.7 t Ag, 29.946 t Cu, and 8,167 t Zn; Alder mine resources: Indicated 388,000 mt, Demonstrated 388,000 mt, Inferred 2,268,000 mt with grades of 1.8% Zn, 0.5% Cu, 2.92 g/mt Au, and 15.18g/mt Ag. |
| Geologic maps |
Tabor and others (1993, 2002), scale 1:100,000; Tabor, Booth and others (2006), scale 1:100,000; Tabor, Frizzell and others (2006), scale 1:100,000. |
| Geophysical data |
Northern 2/3 of the focus area has inadequate aeromagnetic data; southern part is covered by Rank 2 data. Inadequate, Rank 5 aeroradiometric data. |
| Favorable rocks and structures |
Focus area includes all map units containing sequences of submarine volcanic rocks in the Northern Cascades. |
| Deposits |
Holden mine (MRDS dep_id: 10180545), Alder mine (MRDS dep_id: 10055964). |
| Evidence from mineral occurrences |
MRDS. |
| Geochemical evidence |
Unknown. |
| Geophysical evidence |
Unknown. |
| Evidence from other sources |
Unknown. |
| Comments |
Holden mine closed in 1957 because of high operating costs; an unknown amount of reserves/resources remain. Mostly disseminated ore, local massive ore. Stratigraphy is overturned. A significant exploration effort in the 1970s and 1980s failed to generate any prospects that warranted further exploration efforts. However the host rock unit extends under cover of the Miocene Columbia River Basalt on the east, allowing for a significant unevaluated area for undiscovered deposits. (Box and others, 1996). |
| Cover thickness and description |
Colombia River basalt covers host rocks on apart of the focus area. |
| Authors |
Allen K. Andersen, Deborah A. Briggs. |
| New data needs |
Mapping, geophysics, lidar, geochemistry, and structural analysis. |
| Geologic mapping and modeling needs |
Complete mapping at a scale of 1:100,000 scale, probably less than 25% mapped at any finer scale. Significant areas could use finer resolution mapping. |
| Geophysical survey and modeling needs |
High-resolution, Rank 1 aeromagnetic and aeroradiometric surveys. |
| Digital elevation data needs |
Lidar variable across a large focus area. |
