Valdez Creek; Valdez Creek Mining Co. Mines, Valdez Creek District, Matanuska-Susitna Borough, Alaska, USA
|Latitude & Longitude (WGS84):||63° 10' 48'' North , 147° 27' 36'' West|
|Latitude & Longitude (decimal):||63.18, -147.46|
Location: This site represents an area of placer gold mining on lower Valdez Creek and on adjacent parts of some of its tributaries. The map site is on the northbank of lower Valdez Creek, at the northeast end of the historic mining town of Denali. The site is in the SE1/4 of sec. 13, T. 20 S., R 1 E., of the Fairbanks Meridian. This location is accurate to within a quarter mile.
Geology: The following description inpart duplicates, and in part supplements, the information in record HE194. Valdez Creek drains an area underlain by pelitic metasedimentary rocks of probable Jurassic age, and several small intrusions of intermediate composition (Smith, 1981). The sedimentary sequence was regionally metamorphosed during the Cretaceous pumpellyite-prehnite grade on the southeast, through greenschist grade, to amphibolite grade on the northwest. The metamorphic sequence appears to be telescoped, possibly by northward-dipping thrust faults. An east-trending strike-slip fault zone south of, and sub-parallel to, Valdez Creek forms a distinct topographic break from upper Timberline Creek, across the upper end of Rusty and White creeks, and on eastward along the east-west portion of the Pass Creek drainage. This zone is important to the distribution of the origin of the placer gold because it has controlled the emplacement of several of the intermediate composition intrusions as well of as quartz vein swarms, some of which are auriferous. None of the northern tributaries of Valdez Creek are significant sources of placer gold. The genesis and distribution of the placer gold deposits are also linked to the complex glacial history of the drainage. Near the lower end of the valley, at least three superimposed, gold-bearing paleochannels were cut into bedrock (Reger and Bundtzen, 1990), probably during valley deglaciation. From youngest to oldest, the paleochannels are designated Tammany paleochannel, A paleochannel, and B paleochannel. Portions of other paleochannels were also identified by drilling. Each paleochannel is at a specific elevation and gradient, and the younger paleochannels cut the older paleochannels, thereby redistributing and reconcentrating the gold. Gold concentrations are highest in the lowest portions of the paleochannels. The gravels and cobbles in these channels indicate that the channels were a very high energy depositional environment. The paleochannels served as natural giant sluiceboxes to concentrate the gold. The cracks and crevices in the bedrock in the bottom of the paleochannel also collected gold to depths of at least five feet below the bedrock surface (D.L. Stevens, personal observation). The paleochannels become less incised upstream and eventually are not found. The pay streaks merge into a large volume of lower grade auriferous gravel from the upper limit of mining by Valdez Creek Mining Company, apparently up into the White Creek drainage, and in Valdez Creek upstream from White Creek. These auriferous gravels are fluvial and glacial in origin. The fineness of the gold runs about 852 with only minor variations. The gold itself showed several different varieties. Most of the gold is 'oatmeal' sized and shaped; other varieties include well-polished and rounded grains, rough, angular, and quartz-rich grains, and rough, angular, and oxide-coated grains.
Workings: Lower Valdez Creek was mined by hand methods after discovery in 1903. The Tammany Channel was mined by underground methods for a distance of about 3,500 feet from the confluence of the channel with Valdez Creek. The lower portion of the Tammany Channel was hydraulicked. The Dry Creek Cut was mined by hand methods and then by hydraulick methods. From 1984 through 1994, Channels A and B were mined by large-scale, open-pit methods for a distance of several miles upstream after have been thoroughly explored by reverse-circulation drilling. During this period, this mine was the largest placer mine in North America. The highest single year's production was nearly 102,000 ounces of gold.
Age: Paleochannel A is probably Sangamon in age, the Tammany channel is probably mid-Wisconsin in age, and Paleochannel B was probably deposited during the late Illinoian interstade (Reger and Bundtzen, 1990). The pay streaks and low-grade gravels in the White Creek drainage and Lucky Gulch are probably younger.
Production: Recorded production for all of Valdez Creek exceeds 600,000 ounces.
Reserves: The large volume of low-grade material upstream from the upper limit of mining by Valdez Creek Mining Company has been extensively drilled, but is not economic to mine at this time (1999). No definitive efforts have been made to classify this large resource.
Commodities (Major) - Au
Development Status: Yes; large
Deposit Model: Placer Au-PGE (Cox and Singer, 1986; model 39a)
5 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
0 - 2.588 Ma
|Unconsolidated surficial deposits, undivided|
Age: Pleistocene (0 - 2.588 Ma)
Reference: Wilson, F.H., Hults, C.P., Mull, C.G, and Karl, S.M. (compilers). Geologic map of Alaska. doi: 10.3133/sim3340. U.S. Geological Survey Scientific Investigations Map 3340, pamphlet 196. 
2.588 - 23.03 Ma
|Supracrustal; Sedimentary and/or volcanic: undivided|
Age: Neogene (2.588 - 23.03 Ma)
Description: Okhotsk, Bering Sea, Pacific Alaska, Alaska Range
Comments: Orogen, magmatic arc/suite; Wilson & Hults, unpublished compilation, 2007-08
Reference: J.C. Harrison, M.R. St-Onge, O.V. Petrov, S.I. Strelnikov, B.G. Lopatin, F.H. Wilson, S. Tella, D. Paul, T. Lynds, S.P. Shokalsky, C.K. Hults, S. Bergman, H.F. Jepsen, and A. Solli. Geological map of the Arctic. doi:10.4095/287868. Geological Survey of Canada Map 2159A.