Porphyry Knob

The Porphyry Knob is a gold and silver mine located in Alaska.

About the MRDS Data:

All mine locations were obtained from the USGS Mineral Resources Data System. The locations and other information in this database have not been verified for accuracy. It should be assumed that all mines are on private property.

Mine Info

Satelite View

MRDS mine locations are often very general, and in some cases are incorrect. Some mine remains have been covered or removed by modern industrial activity or by development of things like housing. The satellite view offers a quick glimpse as to whether the MRDS location corresponds to visible mine remains.

Site Name

Primary: Porphyry Knob

Commodity

Primary: Gold
Primary: Silver

Location

State: Alaska
District: Innoko

Land Status

Not available

Holdings

Not available

Workings

Not available

Ownership

Not available

Production

Not available

Deposit

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

Physiography

Not available

Mineral Deposit Model

Model Name: Epithermal vein, Creede
Model Name: Epithermal vein, Comstock

Orebody

Not available

Structure

Not available

Alterations

Alteration Type: L
Alteration Text: The igneous rocks display intense levels of phyllic, silicic, and carbonate alteration. The sedimentary rocks exhibit local sericitic, silicic, carbonate, hornfels, and skarn alteration (Avalon Development, 1998; Duncan, 1999).

Rocks

Not available

Analytical Data

Not available

Materials

Ore: Chalcopyrite
Ore: Arsenopyrite
Ore: Stibnite
Ore: Pyrite
Ore: Gold
Gangue: Quartz

Comments

Comment (Exploration): Status = Active

Comment (Deposit): Model Name = Epithermal gold (quartz-adularia) (Cox and Singer, 1986; model 25b, 25c?).

Comment (Geology): Geologic Description = The rocks in the vicinity of the Porphyry Knob prospect consist of highly altered, intermediate to mafic, volcanic, volcaniclastic, and flow-layered rocks interbedded with black shale, graywacke, and minor conglomerate of the Cretaceous Kuskokwim group (McGinnis, 1997). In the Colorado Creek area, high-angle, northeast-trending faults are cut by later, northwest-trending faults. Gold at the Porphyry Knob prospect occurs in a gently-dipping sequence of intermediate to mafic volcanic, volcaniclastic, and marine sedimentary rocks. The principal country rock at the prospect is altered andesite. Dacite porphyry is also an important hostrock, but petrographic work by Placer Dome Exploration demonstrates that the light-colored, porphyritic rocks characteristic of this prospect are in fact altered andesite and basalt, despite their leucocratic appearance in hand specimen (McGinnis, 1997). The altered volcanic rocks contain abundant disseminated pryite and arsenopyrite and are cut by quartz and limonite veins up to 2 centimeters thick. The dacite porphyry contains veins and veinlets of quartz + adularia + pyrite +/- apatite +/- ankerite +/- calcite. The andesite contains veins and veinlets of quartz +/- albite + ankerite +/- calcite + pyrite + arsenopyrite (McGinnis, 1997). Fine colorws of native gold can be panned from soil on the southeast margin of the prospect area (Avalon Development, 1998). Ten core holes were drilled into the prospect by Placer Dome Exploration in 1997. The most significant intercept averaged 1.9 grams of gold per ton over 19.2 meters, and includes an intercept 2 meters long of 7.5 grams of gold per ton (McGinnis, 1997). The most abundant sulfides in the core included arsenopyrite, chalcopyrite, pyrite, and stibnite (Duncan, 2000). The gold:silver ratio at Porphyry Knob is generally low and ranges from 1:1 to 1:10 (Duncan, 1999). The prospect is marked by soil samples containing up to 3610 ppb gold, anomalous amounts of arsenic, antimony, and mercury, and minor bismuth (Avalon Development, 1998). The igneous rocks display intense levels of phyllic, silicic, and carbonate alteration. The sedimentary rocks exhibit local sericitic, silicic, carbonate, hornfels, and skarn alteration (Avalon Development, 1998; Duncan, 1999). The Porphyry Knob prospect may be part of a gold-bearing, quartz-adularia- type epithermal system (Avalon Development, 1998; Duncan, 1999; Dashevsky, 2000). Also see the Moose Jaw prospect (OP032), and Eldorado Creek (OP033).

Comment (Deposit): Other Comments = For more information, contact Ron Rosander in McGrath, AK.

Comment (Deposit): Model Number = 25b, 25c?

Comment (Reference): Primary Reference = McGinnis, 1997

Comment (Geology): Age = Cretaceous or younger. Mineralized sills intrude Cretaceous sedimentary rocks of the Kuskokwim Group.

Comment (Workings): Workings / Exploration = Gold mineralization was identified on Porphyry Knob by S. Nerod during the 1970's at the Nerod trench in the southern part of the prospect area. In 1994, 1995, and 1996, Ron Rosander, the claim owner, contracted James Barker to evaluate lode sources of placer gold in the Colorado Creek area. Barker (1966) collected 254 soil samples, 93 rock samples, and 12 samples of placer gold for scanning-electron microscope and trace element analysis. Barker also conducted geologic mapping and a ground-based magnetometer survey. In 1996, the Alaska Division of Geological and Geophysical Surveys conducted geologic mapping in the Cripple Creek Mountains, and Placer Dome Exploration flew an east-west-oriented aeromagnetic survey over the Cripple Creek Mountains (Avalon Development, 1998). Placer Dome Exploration drilled 10 core holes totaling 1372 meters in the Porphyry Knob prospect during 1997, soil sampled along a large grid, and conducted geologic mapping, trenching, and road construction (McGinnis, 1997). Nova Gold explored the Porphyry Knob prospect in 1998 and conducted further geologic mapping, rock sampling, and soil sampling (Avalon Development, 1998). During 1999, Northern Associates, Inc., was contracted by Poisedon Minerals, Ltd. to conduct further soil sampling in the Colorado Creek area, including Porphyry Knob.

References

Reference (Deposit): Dashevsky, S.S., 2000, Colorado Creek project (Au) Innoko district, Alaska: unpublished report for Rosander Mining Company, 7 p.

Reference (Deposit): Duncan, R.G., 1999, Colorado Creek project, Alaska, interim report: unpublished report for Poseidon Minerals Ltd., 22 p.

Reference (Deposit): Avalon Development Corp., 1998, Colorado Creek project, Ophir and Medfra quadrangles, southwest Alaska: report prepared for NovaGold Resources Inc., 9 p.

Reference (Deposit): McGinnis, M.F., McCoy, M.E., Nerup, M.R., and Barnett, D., 1997, Colorado Creek project Alaska, 1997 summary report: unpublished Placer Dome Exploration Inc. report, 37 p.

The Top Ten Gold Producing States

These ten states contributed the most to the gold production that built the West from 1848 through the 1930s. The Top Ten Gold Producing States.