Kody

Prospect, Inactive

Commodities and mineralogy

Main commodities Ag; Cu; Sn
Other commodities As; Au
Ore minerals arsenopyrite; chalcopyrite; pyrite; pyrrhotite
Gangue minerals quartz; sericite; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale LC
Quadrangle map, 1:63,360-scale B-6
Latitude 60.3968
Longitude -154.9043
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Kody prospect is located in the hills between the Koksetna and Chilikadrotna Rivers approximately 20 miles northwest of Lake Clark. It lies in a saddle northwest of hill 3084 at the headwaters of a tributary of the Koksetna River. The northwest 1/4 of section 31 in T. 4 N., R. 32 W. of the Seward Meridian is the approximate center of a 4 square mile prospect area. The location is accurate within 200 meters.

Geologic setting

Geologic description

The area between the Koksetna and Chilikadrotna Rivers is underlain by undivided Kuskokwim Group sedimentary rocks and the Koksetna River sequence of Wallace and others (1989) that have been intruded by Cretaceous to Tertiary quartz monzonite plutons and rhyolite to dacite plugs, sills, dikes and flows (Wilson and others, 2006).
The Kody prospect is a 1 square kilometer intrusive/subvolcanic complex that has been pervasively greisenized. An exposed, steep-sided, late Cretaceous quartz monzonite plug has intruded and hornfelsed siliceous clastic sedimentary rocks that strike northeast and dip to the northwest (Ellis and others, 1985) correlating with the Jurassic-Cretaceous Koksetna River sequence of Wallice and others (1989). The quartz monzonite and adjacent hornfelsed sedimentary rocks form a 4 square kilometer topographic knob which rises greater than 1,100 feet above the surrounding lowlands. The eastern edge of the quartz monzonite and the hornfelsed sedimentary rocks has been cut by numerous rhyolite apophyses of Tertiary (?) age (Scott and Ellis, 1982).
Greisenization of the quartz monzonite is widespread. Smaller non-greisenized areas exist adjacent to the faulted northwestern hornfels contact, and these areas are chloritized and locally sericitized. The greisen varies from a white to tan to gray, fine- to medium-grained, granular, quartz-white mica rock with abundant voids. The white mica occurs as tiny 1 to 3 millimeter sprays that appear interstitial to the fine-grained secondary quartz. Incipient tourmalinization is associated with the white mica (Ellis and others, 1985).
Sulfide mineralization is distinctly localized in greisenized areas implying a genetic relationship between greisenization and introduction of the sulfides. Locally abundant sulfides were deposited in open spaces in the greisens, in fractures, in quartz-flooded zones, and in hornfelsed zones (Scott and Ellis, 1982). The greisen locally grades into a banded, fine-grained, and white to black tourmaline-quartz rock. In these flooded zones, the rock is extremely fine-grained, and open-space filling by arsenopyrite and chalcopyrite is locally common. The rock is very hard, forming irregulary shaped cobbles with a patina of intense iron-oxide stain. Where this 'flooding' occurs in the hornfels, the sedimentary rocks are also iron-stained (Ellis and others, 1985).
Pyrrhotite (up to 30 percent), arsenopyrite (up to 10 percent), chalcopyrite (up to 3 percent) and silver from 0.5 to 11 ounces per ton is present in scattered zones within the altered intrusive. A 100 by 300 meter zone near the eastern margin of the of the greisenized quartz monzonite averaged over 1 ounce per ton silver and exceeded 100 parts per million (ppm) tin (Ellis and others, 1985).
Geologic map unit (, )
Mineral deposit model Porphyry Sn (Cox and Singer, 1986; model 20a).
Mineral deposit model number 20a
Age of mineralization Mineralization is probably related to 60.5 to 61.6 Ma intrusions dated in the area (Eakins and others, 1978).
Alteration of deposit A quartz-white mica-tourmaline greisen has replaced the majority of the exposed quartz monzonite at the Kody prospect. Ungreisenized areas in the quartz monzonite show local chloritization of biotite and hornblende and clay alteration of feldspars. The rhyolite which intrudes both the quartz monzonite and hornfelsed sediments is locally tourmalinized. Relict feldspar phenocrysts in the rhyolite are intensely sericitized (Ellis and others, 1985).

Production and reserves

Workings or exploration The Kody prospect was discovered by Anaconda Minerals Company in 1982. Exploration work included geologic mapping, grid rock sampling, a one kilometer induced polarization (IP)-resistivity line and a 10 square kilometer gravity survey. A Bouguer gravity map based on 39 surveyed stations and a gravity profile show an 8 milligal low that is best depicted as a 2.5 kilometer northwest dipping slab that broadens slightly with depth. The top of this anomaly is coincident with mapped quartz monzonite, greisen, and rhyolite intrusive rock (Scott and Ellis, 1982). Pyrrhotite (up to 30 percent), arsenopyrite (up to 10 percent), chalcopyrite (up to 3 percent), silver from 0.5 to 11 ounces per ton, and gold from 100 to 800 parts per billion is present in scattered zones within the altered intrusive. A 100 by 300 meter zone near the eastern margin of the of the greisenized quartz monzonite averaged over 1 ounce per ton silver and from 100 to 400 parts per million tin (Ellis and others, 1985).
Indication of production None

References

References

Reporters W.T. Ellis (Alaska Earth Sciences)
Last report date 3/15/2016