Unnamed (in upper Slope Creek)

Site Name

Primary: Unnamed (in upper Slope Creek)

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Commodity

Primary: Copper
Primary: Gold
Secondary: Zinc
Secondary: Lead
Secondary: Iron

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Location

State: Alaska
District: Chistochina

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Prospect
Operation Type: Unknown
Years of Production:
Organization:
Significant:

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Physiography

Not available

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Mineral Deposit Model

Model Name: Porphyry Cu-Au

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Potassic alteration with the introduction of K-feldspar and biotite in the core of the system. Locally the rocks are sericitized and phyllically altered. Higher in the system, the rocks are silicified, altered to clay, and carbonatized. Bull and her co-authors (1997 and 1999) indicate that galena is more abundant distally.

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Rocks

Not available

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Analytical Data

Not available

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Materials

Ore: Sphalerite
Ore: Malachite
Ore: Magnetite
Ore: Galena
Ore: Chalcopyrite
Ore: Arsenopyrite
Gangue: Quartz

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Comments

Comment (Reference): Primary Reference = Bull, Freeman, and Schneider, 1999

Comment (Exploration): Status = Inactive

Comment (Commodity): Gangue = Carbonate

Comment (Commodity): Gangue = iron-carbonate

Comment (Geology): Age = the porphyry deposit is probably related to the emplacement of a Jurassic, diorite complex.

Comment (Deposit): Model Name = Porphyry Cu-Au (Cox and Singer, 1986; model 20c)

Comment (Deposit): Other Comments = Upper Slope Creek contains part of a copper-gold porphyry that has only been examined in reconnaissance. Additional information can be obtained from Ahtna Minerals in Anchorage, Alaska.

Comment (Geology): Geologic Description = The upper part of Slope Creek consists of highly altered volcanic rocks of the Pennsylvanian to Permian, Tetelna Formation. The Tetelna Formation is cut by by composite dikes and irregular bodies of a mid-Jurassic diorite to quartz diorite complex (Richter and Matson, 1968; Bull, Schneider, and Freeman, 1997; Bull, Freeman, and Schneider, 1999). Locally the diorite bodies trend north-northwest along the general regional trend. One diorite body is elongated east-northeast along a fault zone which appears to follow the north side of Slope Creek. The intensity of the mineralization and the distribution of the main masses of diorite indicate that a porphyry appears to underlie upper Slope Creek. Porphyry-type mineralization occurs mainly in the diorite complex and adjacent hornfels. Various subtypes occur: 1) propylitic altered zones with as much as 10% pyrite are cut by quartz-carbonate veins that contain pyrite, chalcopyrite and galena; 2) potassic altered zones containing secondary biotite and K-feldspar are cut by quartz-K feldspar veins, veinlets, and disseminated concentrations with up to 15% pyrite, chalcopyrite, arsenopyrite, and magnetite; and 3) sericite/phyllic altered zones locally stained with malachite contain 5-30 % sulfides. There are widespread local zones of argillic and iron-carbonate alteration. The hornfelsed Tetelna Formation within about 100 feet of diorite also has several subtypes of porphyry mineralization including: 1) silicified zones containing as much as 15% pyrite; 2) quartz-carbonate veins with pyrite, chalcopyrite, arsenopyrite, and galena; and 3) chloritic-magnetite or chloritic-pyrite breccia cut by quartz-pyrite-chalcopyrite veinlets. The hornfels adjacent to chloritic zones is typically bleached. The porphyry in upper Slope Creek has not been tested by drilling, but it has been mapped and sampled in reconnaissance by geologists affiliated with Homestake Mining Company. Soils collected by Homestake suggest that a broad area that covers both upper Grubstake and upper Slope Creeks contains more than 200 ppb gold. Eighty-four rock samples collected mostly in the Grubstake Creek-Slope Creek area contained a mean gold concentration of about 240 ppb gold. Rock samples collected in upper Slope Creek locally contained more than 2,000 ppb gold. Rock samples in the upper Slope Creek-upper Grubstake Creek area averaged about 350 ppm copper and locally exceeded 1%. The rocks in the area are so intensely deformed and altered that much more detailed work will be needed to accurately map the complex.

Comment (Workings): Workings / Exploration = Slope Creek has been explored since the discovery of placer deposits nearby in Grubstake Creek in 1934. That discovery led to prospecting and the location of small placer mines in Boulder Creek (GU017) and Slope Creek (GU021). Work by Richter and his associates appears to have triggered exploration in the 1960's and 1970's (Richter, 1964 and 1966; Richter and Matson, 1968). Kirk Stanley was active at this time in the Ahtell and Grubstake Creek-Slope Creek areas. In more recent years the area has been studied by Homestake Mining Company (Bull, Schneider and Freeman, 1997; and Bull, Freeman, and Schneider, 1999). Ahtna Minerals Company has recently consolidated the geologic data as much of the prospect area lies on Ahtna regional Native corporation land.

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References

Reference (Deposit): Bull, Katharine, Freeman, Larry, and Schneider, Craig, 1999, Slana property summary report for Homestake Mining Company: 11 p. and analytical appendices. (Report available, Ahtna Minerals Co., Anchorage, Alaska).

Reference (Deposit): Bull, Katharine, Schneider, Craig, and Freeman, Larry, 1997, Summary report for Ahtna Corporation: 12 p., appendices and maps. (Report available, Ahtna Minerals Co., Anchorage, Alaska).

Reference (Deposit): Richter, D.H., and Matson, N.A., 1968, Distribution of gold and some base metals in the Slana area, eastern Alaska Range, Alaska: U.S. Geological Survey Circular 593, 20 p.

Reference (Deposit): Richter, D.H., 1966, Geology of the Slana district on south-central Alaska: Alaska Division of Geological and Geophysical Surveys Geological Report 2l, 36b p., 3 sheets, scale 1:63,360.

Reference (Deposit): Richter, D.H., 1964, Geology and mineral deposits of the Ahtell Creek area, Slana District, south-central Alaska: Alaska Division of Geological and Geophysical Surveys Geologic Report 6, 17 p., 1 sheet, scale 1:31,680.

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