Kougarok prospect, Serpentine Mining District, Nome Census Area, Alaska, USAi

Regional Level Types
Kougarok prospect	Prospect
Serpentine Mining District	Mining District
Nome Census Area	Census Area
Alaska	State
USA	Country

Location: The Kougarok prospect is a 1.5 square mile area centered 2 miles N of the summit of Kougarok Mountain (2,870 feet elevation), the highest area in the Teller quadrangle outside the York Mountains. The prospect area is on the west flank of the north-south trending ridge crest from near the Kougarok Mountain summit downslope to elevations of about 1,000 feet in the southeast headwaters of Star Creek. Star Creek is a north-flowing headwater tributary to the south fork of the Serpentine River.

Geology: A Late Cretaceous composite granite complex intrudes metapelitic schist in the Kougarok prospect area. The metapelitic schist is a highly deformed mica-quartz schist characterized by isoclinally folded quartz boudins and segregations that may be Precambrian in age (Gardner and Hudson, 1984). It is thermally metamorphosed to biotite-bearing hornfels within several hundred feet of the granite contact. Boron-rich metasomatism has altered metapelitic schist and hornfels to tourmaline-axinite-sulfide rocks throughout the main prospect area. Most of the granite complex is only present in the subsurface but a few granite dikes and a highly altered plug are exposed at the surface. Diamond drilling shows the subsurface granite to have porphyritic and equigranular phases (Puchner, 1986) . Equigranular leucocratic phases were intruded later than the porphyritic phases and are associated with extensive alteration of the country rocks, exogreisen development in peripheral dikes and plug, and roof greisen development in the subsurface pluton. Local and regional gravity surveys (Puchner, 1986; Barnes and Hudson, 1977) show that the Kougarok granites are part of a much larger batholithic complex at depth. Puchner (1986) reports Rb/Sr and K/Ar data that indicate that the granite and associated mineralized rocks are Late Cretaceous in age (72 +/- 2 and 70.2 +/- 2.2 Ma respectively). These ages are consistent with that of other tin granite complexes on the western Seward Peninsula (Hudson and Arth, 1983). A greisen-altered granite dike, Chuck's dike, and the Main plug are the principal exogreisen deposits (Puchner, 1984; Apel, 1984). The equigranular zinnwaldite granite dike is offset locally by normal faults and is almost 3,000 feet long in the prospect area (Puchner, 1986, figure 3). This dike dips steeply east, and varies in thickness from one to 15 feet although it commonly is 6 to 8 feet thick. It is variably altered over most of its length but complete greisenization is present at five places at the surface (Puchner, 1986, p. 1787). The longest exposed greisen segment is 500 feet in strike length and greisen development in it continues down dip in the subsurface about 500 feet where it merges with a roof greisen in the subsurface pluton (Puchner, 1986, p. 1786). Tin grades in the Chuck's dike greisen are commonly 1 percent. Two surface trenches and 9 diamond drill holes in this part of the dike indicate a resource of 240,000 tons of 1.3 percent tin ( with a 0.1 percent tin cutoff grade (Puchner, 1984). This resource includes a higher grade portion of 110,000 tons averaging 2.3 percent tin. The Main plug area that is exposed up slope to the east of Chuck's dike at an elevation of about 2,100 feet is a nearly vertical composite intrusive center that is extensively altered and contains two greisen pipes. These pipes, each about 100 feet across at the surface, appear to merge at depth and extend to deep levels in the intrusive center (Puchner, 1986, p. 1786). The Main plug is a complex body but surface trenches and diamond drilling suggest a combined resource of 1.4 million tons averaging 0.45 percent (no cutoff); tantalum and niobium are each present in the 0.1 to 0.03 percent range (Puchner, 1984). A high grade resource within this plug (0.5 percent tin cutoff) is estimated to contain 100,000 tons averaging 2.1 percent tin. The zinnwaldite granite that forms Chuck's dike at the surface becomes a subhorizontal granite intrusion at depth whose irregular upper part is a greisen (Puchner, 1986, p. 1786). Alteration throughout this intrusion increases upward to quartz-tourmaline-topaz greisen in which tin grades can exceed 1 percent. Limited diamond drilling suggests a resource of 1.3 million tons or more averaging 0.36 percent tin (0.1 percent cutoff) including a portion where 140,000 tons averages 1.0 percent tin (0.5 percent cutoff) (Puchner, 1984). One of the diamond drill intercepts in the roof greisen was 53 feet of 0.23 percent tin (0.1 percent cutoff) including 13 feet of 0.93 percent tin (0.5 percent cutoff). In general, tin grade increases to as much as 3.4 percent upwards through the altered zinnwaldite intrusion to the roof greisen. Upward from the base to the roof greisen, silver increases to 17 parts per million (ppm) and lead to 1,340 ppm; tantalum increases from 20 ppm to as high as 845 ppm from the base to the roof greisen. The zinnwaldite granite contains 1 to 2 percent fluorite and arsenic may be as high as 1,000 ppm locally in the upper part of the intrusion (Puchner, 1986, p. 1791). Kougarok is a boron-rich tin system characterized by abundant tourmaline and axinite replacement in the host schist and by tourmaline disseminations in altered granite. Its elevated tantalum and niobium, present in discrete tantalite/columbite grains, is also notable. Anaconda's 1980's exploration showed that parts of the roof greisen and main plug zones contained elevated tantalum contents in the few to several hundred ppm range. (The following information has not previously been made public; it comes from the personal involvement in the work by the compiler, Travis Hudson.) Navigator Exploration Corp. and Chapleau Resources, Ltd. optioned this prospect from Greatland Exploration Ltd. in 2001 and 2002 to evaluate its tantalum potential. This exploration included surface prospecting and sampling, examination and sampling of core from Anaconda's 1980's drilling, analysis of gravity and magnetic data, and drilling of 7 vertical diamond drill holes totaling 2,438.2 m (8,000 feet). Their descriptions follow: 1) Drill hole 2002-1 was located near the summit of Kougarok Mountain (489457 mE, 7284312 mN). This 237.6 m (813 foot) hole encountered a few felsic dikes intruding Kougarok Schist. The highest tantalum value was 32 ppm and the highest tin value was 310 ppm; 2) Drill hole 2002-2 was located near the north end of Chuck's dike and about 650 meters northwest of the main plug (489222 mE, 7287955 mN). This 237.6 meter (780 feet) hole encountered 70.8 meters (232 feet) of zinnwaldite granite with tantalum values to 87 ppm and tin values to 337 ppm; 3) Drill hole 2002-3 was located between 2002-2 and the main plug (489494 mE, 7287718 mN). Its total length was 368.4 meters (1,209 feet) and it encountered 114.4 meters (375 feet) of zinnwaldite granite and related intrusive breccias. The highest tantalum value was 57 ppm and the highest tin value was 408 ppm; 4) Drill hole 2002-4 was located about 40 meters east of the main plug (489683 mE, 7287497 mN). This 328.6 meter (1,078 feet) hole encountered 198 meters (649 feet) of variously altered zinnwaldite granite and related intrusive breccias. Tantalum values reached 353 ppm; one 31.5 meter (103 feet) interval averaged 233 ppm Ta. Tin values reached 3.6 percent.; 5) Drill hole 2002-5 was located about 250 meters east of 2002-4 (389916 mE, 7287460 mN). This 408.6 meter (1,340 foot) hole encountered 172 meters (564 feet) of Kougarok Schist above 237 meters (778 feet) of Paleozoic quartzite and marble. No samples were submitted for assay from this hole.; 6) Drill hole 2002-6 was located on Tourmaline Ridge about 1,200 meters southwest of the main plug and near the south end of Chuck's dike (489453 mE, 7826435 mN). This 473.1 meter (1,552 foot) hole encountered a zone of zinnwaldite granite intrusives between 393 and 470 meters (1,289 and 1,542 feet). The hole bottomed in porphyritic biotite granite. The highest Ta value in the hole was 13 ppm and the highest Sn value was 59 ppm; 7) Drill hole 2002-7 was located about 900 meters (2,950 feet) north of the main plug (489700 mE, 7288447 mN) This 264.6 meter (868 foot) hole encountered several felsic dikes and brecciated intrusives in Kougarok Schist. One dike contained 119 ppm tantalum.

Workings: Surface bulldozer trenching has been completed on a part of Chuck's dike and in the Main plug area. Twenty nine larger diameter diamond drill holes and 32 smaller diamond drill (Winkie) holes were done in the early 1980's (Puchner, 1984). Most of these have been in the north Chuck's dike and Main plug area. Anaconda's 1980's exploration showed that parts of the roof greisen and main plug zones contained elevated tantalum contents in the few to several hundred ppm range. Navigator Exploration Corp. and Chapleau Resources, Ltd. optioned this prospect from Greatland Exploration Ltd. in 2001 and 2002 to evaluate its tantalum potential. This exploration included surface prospecting and sampling, examination and sampling of core from Anaconda's 1980's drilling, analysis of gravity and magnetic data, and drilling of 7 vertical diamond drill holes totaling 2,438.2 meters (8,000 feet).

Age: Late Cretaceous; the radiometric ages referenced by Puchner (1986) include an Rb/Sr age of 72 +/- 2 Ma for porphyritic biotite granite and a K/Ar age of 70.2 +/- 2.6 Ma for zinnwaldite granite from the Main plug.

Alteration: Hydrothermal alteration is extensive in the Kougarok prospect area. The country rock metapelitic schist and hornfels is extensively veined and replaced by tourmaline, axinite, and sulfide minerals (dominantly pyrrhotite but including arsenopyrite and chalcopyrite) over a roughly circular area with a diameter of 3,700 feet at the surface and to a depth of almost 800 feet in the area above the zinnwaldite granite and between Chuck's dike and the Main plug (Puchner, 1986). Tin is commonly anomalous in these rocks and in places exceeds 0.1%. Sericite and tourmaline development is ubiquitous in granite intrusions of the prospect area. Puchner (1986) recognizes increasing degrees of alteration from weak sericite-tourmaline replacement to assemblages with increasing zinnwaldite contents to quartz-tourmaline-topaz greisen. Zinnwaldite-rich alteration zones peripheral to roof greisen are common.

Reserves: Preliminary resource estimates have been made for a part of the exogreisen deposit in Chuck's dike, the exogreisen deposit in the Main plug, and the roof greisen in buried zinnwaldite granite (Puchner, 1984). The resource estimate for exogreisen in Chuck's dike is 240,000 tons averaging 1.3 percent tin (including a part that is 110,00 tons averaging 2.3 percent tin). The Main plug exogreisen resource estimate is 1.4 million tons averaging 0.45 percent tin and 0.1 to 0.3 percent of both tantalum and niobium; this includes a part that has 100,000 tons of 2.1 percent tin. The roof greisen estimate is 1.3 million tons of 0.36 percent tin including a part that is 140,000 tons of 1.0 percent tin. Puchner (1984) emphasized that these estimates are preliminary and that more exploration is needed to constrain them. (No reserves have been published from the drilling in 2001 and 2002).

Commodities: (Major) - Nb, Sn, Ta.

Development Status: None.

Deposit Model: Tin greisen including exogreisen and endogreisen (roof) deposits (Cox and Singe).

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Link to USGS - Alaska:	TE072

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References