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Waterpump Creek; Last Hurrah Prospects, Kaiyuh District, Yukon-Koyukuk Borough, Alaska, USA

Latitude: 64°4'12"N
Longitude: 157°48'0"W
Location: The Waterpump Creek prospect is in the southern Kaiyuh Mountians, approximately 7 miles southeast of the summit of Khotol Mountain. The coordinates are for the approximate center of mineralization at Waterpump Creek, just south of the center of sec. 26, T. 16 S., R. 5 E., Kateel River Meridian. The location is accurate within 500 feet. This site also includes the Last Hurrah prospect, which is on the same mineral trend as the Waterpump Creek prospect. The Last Hurrah prospect is centered about 1.4 miles southwest of the Waterpump Creek prospect.
Geology: The Waterpump Creek deposit is in dolomitic quartzite and metadolostone. There are two ore zones: 1) a body about 200 meters long and 9 by 30 meters in section that consists of oxidized ore (gossan); and 2) a body of sulfide-siderite ore about 120 meters below the gossan that is about 120 meters long and 20 by 15 meters in section (Flanigan, 1998). Initially, the Waterpump Creek deposit was considered to be syngenetic. However, Flanigan (1998) demonstrates that it probably is a plutonic-related, epigenetic deposit, based on its relationship to the 113 Ma Khotol pluton, the presence of stannite and boulangerite, and a depositional temperature of 300-350 degrees C. The oxide (gossan) zone and the deeper, unoxidized sulfide-siderite zone strike S40E and dip 30SE. The mineralization pinches, swells, and bifurcates, suggesting that it comprises several different zones. Most of the mineralization is in quartzite with minor dolostone layers. The ore zones cross-cut quartzite-dolostone contacts (Flanigan, 1998). The gossan consists of soft masses and veins with many voids and masses of loose breccia. Breccia clasts range from clay size to small cobbles, and include rare, unoxidized mineral grains that range up to sand size. The minerals in the gossan zone include anglesite, argentojarosite, beudantite, carminite, cerussite, gypsum, fraipontite, hemimorphite, hopeite, jarosite, massicot, mimetite, platternite, plumbjarosite, pyrolusite, schultenite, and scorodite (Flanigan, 1998). The oxidized zone also contains galena that occurs as remnants rimmed with lead oxide or carbonate minerals, including anglesite or cerussite. Zinc-rich areas of the gossan consist primarily of limonite, along with hemimorphite and hydrozincite (Flanigan, 1998). In the unoxidized, sulfide-siderite zone, siderite gangue replaces dolostone along irregular contacts. Major sulfide minerals include sphalerite, galena, and pyrite, within manganosiderite gangue. Radiating clusters of acicular calcite crystals coat fracture surfaces and line vugs near mineralization. Calcite and dolomite veins also occur. Sphalerite and galena commonly are intergrown and may form large pods, veins, bands, and rare vug fillings. Minor disseminated galena, pyrite, and manganosiderite occur throughout massive sphalerite. Pyrite commonly is subordinate, but it locally may form as much as 70% of the sulfide body (Flanigan, 1998). Boulangerite occurs as small, wire-like grains in siderite or as inclusions in pyrite. Stannite forms inclusions in pyrite. Teller and Wilson (in Flanigan, 1998) also identified acanthite, bornite, chalcopyrite, diopside, rosenhahnite, and tremolite in the sulfide zones, suggesting a possible skarn affinity (Flanigan, 1998). Alteration consists of calcite and dolomite veining, manganosiderite alteration of wallrock, and replacement of dolostone wallrock by siderite. Estimated reserves at the Waterpump Creek prospect are 166,000 metric tons of ore averaging 9.5 ounces of silver per ton, 16.1% lead, and 5.5% zinc (Flanigan, 1998). The Waterpump Creek deposit lies along a lineament that also crosses the Illinois Creek (NL023) and Round Top (NL011) deposits. This lineament is parallel to the Kaltag fault. The Last Hurrah occurrence is marked by elevated concentrations of lead and zinc along two perpendicular soil lines. Soil-sample assays range up to 525 ppm lead and 903 ppm zinc. This soil anomaly is along an air-photo lineament (fault) that also crosses the Waterpump Creek (NL023) and Illinois Creek (NL023) deposits.
Workings: The Waterpump Creek prospect was first located by Anaconda Minerals Company in 1980. Since then, the prospect has been trenched, drilled, geologically mapped, and soil and rock sampled.
Age: The nearby Khotol pluton has been dated by K/Ar and Ar/Ar methods at 108-112 Ma (Flanigan, 1998). Flanigan (1998) links the mineralization at this deposit to magmatic fluids from this pluton. His interpretation is supported by a K/Ar date of about 113 Ma on sericite from a mineralized vein at the Waterpump Creek prospect (Flanigan, 1998).
Alteration: Calcite and dolomite veining, manganosiderite alteration of wallrock, and replacement of dolostone wallrock by siderite.
Reserves: The estimated reserves at the Waterpump Creek prospect are 166,000 metric tons of ore averaging 9.5 ounces of silver per ton, 16.1% lead, and 5.5% zinc (Flanigan, 1998).

Commodities (Major) - Ag, Pb, Zn
Development Status: No
Deposit Model: Plutonic-related, epigenetic, lode Ag-Pb-Zn; Polymetallic veins? (Cox and Singe

Mineral List

Acanthite
Anglesite
Argentojarosite
Beudantite
Bornite
Boulangerite
Calcite
Carminite
Cerussite
Chalcopyrite
Dolomite
Fluorite
Galena
Gypsum
Hemimorphite
Hopeite
Hydrozincite
Limonite
Massicot
Mimetite
Pyrite
Pyrolusite
Quartz
Schultenite
Scorodite
Siderite
var: Manganoan Siderite
Sphalerite
Stannite


29 entries listed. 27 valid minerals.

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References

Flanigan, B., 1998, Genesis and mineralization of ore deposits in the Illinois Creek region, west central Alaska: University of Alaska, Fairbanks, M.Sc. thesis, 125 p., 2 plates. Gillerman, V.S., Brewer, N.H., Millholland, M.A., and Wyman, W.F., 1986, Oxidized polymetallic gold mineralization, Illinois Creek, Alaska [abs.], in Chater, A.M., ed., Gold '86, an international symposium on the geology of gold deposits; poster paper abstracts: Geological Association of Canada, p. 51-53.

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