Kilolitna River

Prospect, Active

Commodities and mineralogy

Main commodities Sn
Other commodities Nb; REE; Ta; Ti; W; Zr
Ore minerals cassiterite; ilmenite; monazite; scheelite; wolframite (ferberite end-member); xenotime; yttroflourite; zircon

Geographic location

Quadrangle map, 1:250,000-scale TN
Quadrangle map, 1:63,360-scale D-3
Latitude 65.9526
Longitude -151.204
Nearby scientific data Find additional scientific data near this location
Location and accuracy This record represents occurrences of anomalous heavy minerals in samples from the Kilolitna River basin and several unnamed tributaries (Barker, 1983, 1991a, 2012; Barker and Foley, 1986; Ucore, Incorporated, 2012, 2014; Freeman, et al., 2014). For this record, the site is a gravel bar where two bulk samples of surface river bar gravel were collected in 2014 by Ucore subsidiary Landmark Alaska, LLP. The site location is accurate within 500 feet and is located in T. 13 N., R. 17 W., section 17 NW¼SW¼, Fairbanks Meridian. The general subject area of this report is a distinct lowland about 3 to 5 miles wide and up to 10 miles north-south on the north side of the Ray Mountains. The site, as described extends into the adjacent Bettles quadrangle.

Geologic setting

Geologic description

The Kilolitna River basin is a prominent, north trending and gently north-sloping basin feature about 10 miles long and up to 5 miles wide. The basin developed at the margin of the northern foothills of the Ray Mountains, and has been in-filled by sedimentation off the Ray Mountains pluton. Granitic rocks border the basin on the south, east, and north. The Kilolitna River basin lies between the Sithylemenkat pluton to the north-northeast and the Ray Mountains pluton to the south. The granitic rocks are all considered part of the broad northeast-trending peraluminous Ruby Batholith of central Alaska (Chapman and others, 1982; Barker and Foley, 1986; Herreid, 1969; Patton and Miller, 1970, 1973; Tuzzolino and others, 2013). Generally the granitic rocks are coarse-grained, equigranular to porphyritic orthoclase-biotite-quartz monzonite varying to granite with subordinate phases of aplite, biotite aplite, tourmaline aplite, and fine-grained quartz monzonite. Tourmaline pegmatite phases have been recognized locally. The granitic rocks cut Paleozoic schist, phyllite, quartzite, and lesser greenstone and limestone. The granitic plutons, especially the Sithylemenkat pluton, are multi-phased intrusions with trace element signatures comparable to tin-rare earth element granites elsewhere (Patton and Miller, 1973; Barker and Foley, 1986). Placer gold is not present in heavy mineral samples as it is in the Ray River alluvium to the east suggesting the gold-bearing source rocks are farther east (Barker, 1991a) of the Kilolitna drainage.
Schist and quartzite, generally silicified due to the regional plutonic intrusions, outcrop and abut the basin on the west. Satellite imagery indicates the river has progressively occupied and later successively abandoned a series of northeast-flowing channels beginning on the west and progressing to the east across the basin. The present Kilolitna River occupies the eastern-most channel along the east margin of the basin. Regional tilting due to the Porcupine-Kaltag fault system is suspected to be the cause. Consequently there is little evidence of basin downcutting; however, the present river is reworking the flood plains created by the earlier river channels along the east of the basin (T. 13 N., R. 17 W., sections 17-21, 27-33). This area appears to be associated with the better heavy mineral concentrations, ranging from 100 up to 333 grams per cubic meter (rare earth elements plus tin), (Ucore Rare Metals Inc., 2012). The area of higher grade rare earth elements plus tin is also in agreement with heavy mineral sample results reported by Freeman and others, 2014, in a sampling campaign by the Alaska Division of Geological and Geophysical Surveys [ADGGS] (Bachmann, and others, 2013). Depth of the unconsolidated sediments in the basin is unknown and both the river gravel bed and the cut banks are particularly poorly consolidated and mostly covered by transient silt and vegetation.
In 2011 to 2013, ADGGS collected rock, stream sediment, as well as heavy mineral concentrates from the Kilolitna Basin area and reported numerous samples were anomalous for rare earth elements, tin and tungsten in rock and stream sediments. The work was part of a mineral resource evaluation of rare metals on State lands and land selections (Bachmann, et. al., 2013).
Geologic map unit (, )
Mineral deposit model Alluvial tin placer (Cox and Singer, 1986; model 39e).
Mineral deposit model number 39e
Age of mineralization Quaternary.
Alteration of deposit Thermal alteration from the Ruby Batholith is widespread. Locally extensive, tourmalization, potassic, carbonate, and argillic styles of advanced alteration can be mapped and generally are associated with regional-scale northeast trending faults. Such zones of altered and weakened rock give rise to locally intense large-scale disintegration of the bedrock granite, which has released the contained interstitial heavy minerals. Local sources of the placer tin and rare earth element minerals also include areas of argillic alteration, and chloritic greisen vein-like occurrences apparently from source areas in the Ray Mountains pluton to the south and east. Such alteration is also particularly evident in the better exposed Sithylemenkat pluton to the north (Barker and Foley, 1986). Greisen samples will generally contain 100 to as much as 2500 ppm tin and contain elevated rare earth elements. Cassiterite has also been found associated with quartz veins at a few locations, for example, the high ridge to the east of the Kilolitna basin (Bachmann, et. al., 2013).

Production and reserves

Workings or exploration
Sample results from field investigations in the 1970s (Barker, 1983); in the 1980s (Barker and Foley, 1986); Ucore, (Ucore Rare Metals Inc., 2012; 2014); and 2014, by ADGGS (Bachmann, et. al., 2013) indicate potential economic-grade alluvial concentrations of rare earth elements and tin in the upper Kilolitna River basin. Sampling of the large area remains relatively sparse; however, as many areas are covered by soil and vegetation. Surface exposures of alluvial gravel and sand containing a threshold value of about 0.15 kilograms per cubic meter (0.25 pounds per cubic yard) of combined rare earth elements and/or tin are found along the present channel of the river. Mineral concentrates also contain by-product concentrations of tungsten, zirconium, niobium, and tantalum. Samples containing near or exceeding this threshold value are mostly concentrated in the east and southeast of the Kilolitna basin where the lower segments of older channels of the Kilolitna are being reworked by the modern river channel. Sample details for 15 heavy mineral sample sites by Landmark Alaska, LLP, including original volumes, the recovered weight of heavy mineral, rare metal analyses, and the calculated grams of total rare earth elements and tin per cubic meter can be accessed at http://ucore.com/projects/ray-mountains-alaska. Details for 10 heavy mineral sites by ADGGS are in Bachmann and others, 2013, and data for 12 Kilolitna basin area samples by USBM are in Barker, 1983. All samples after 2010 were analyzed by ALS Minerals, Incorporated, in Vancouver, British Columbia, using lithium metaborate fusion followed by ICP-MS analyses.
Most samples were one standard gold pan in volume. Samples by Landmark Alaska, Ltd., consisted of one or more 5-gallon buckets (0.0133 cubic meter per 5-gallon bucket) of material that was later concentrated on a standard shaking table or processed by hand panning. Either procedure achieves an estimated 75 to 85 percent recovery of the heavy mineral suite, including rare earth element-bearing minerals such as monazite and xenotime, thus demonstrates amenability to physical separation in a full scale mine plant. This simple gravity separation method uses only water as the separation medium. Furthermore, extraction technology for rare earth elements from a monazite-xenotime matrix and tin from cassiterite in concentrates is well known and does not present new metallurgical challenges. Cassiterite, monazite, xenotime, wolframite (ferberite end-member), scheelite, ilmenite, and zircon have been identified in heavy mineral concentrates. A few grains of yttroflourite were reported by Barker and Foley, 1986. The total rare earth element composition includes 15 to 20 percent heavy rare earth elements gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium in the majority of samples.
Indication of production None

Additional comments

The land in the Kilolitna Basin is held by the U.S. Bureau of Land Management. The State of Alaska has selected the area under provisions of the 1959 Statehood Act and nominated it as a priority selection. Ucore, through its local subsidiary Landmark Alaska, LLP, has located State mining claims according to the provisions provided by Alaska for locating claims on State Selected land. No surface disturbance activities, including ground-transported drilling equipment, can be permitted until Alaska receives tentative approval of the land transfer from the BLM. Ucore’s subsidiary (Landmark Alaska, LLP) is planning expanded exploration once title transfer is tentatively approved by the federal government.

References