|Quadrangle map, 1:250,000-scale||LG|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This prospect is on hill 1835 about 0.5 mile northeast of the head of Shorty Creek and about 7 miles south-southeast of Livengood. Since 2005, it is one of several prospects often referred to as part of the Shorty Creek project which covers a large area and several other prospects. It is southeast quarter of section 14, T. 7 N., R. 5 W of the Fairbanks Meridian. The location is accurate with a quarter mile.|
The hills south of the Tolovana River in this area are covered with sub-Arctic forest and loess; outcrop is sparse; however at the Hill 1835 prospect there is an absence of vegetation which is attributed to acidic soils and metal toxicity (Abrams, 2015). The rocks in the area are mainly the Lower Cretaceous Wilber Creek sequence of folded black carbonaceous siltstone, gray feldspathic sandstone and silty sandstone, black shale, and polymictic conglomerate (Albanese, 1983a; Weber and others, 1992). The sequence disconformably overlies Lower Paleozoic carbonate, volcanic, and pelitic rocks. Several small plutons, mostly of granodiorite composition, are in the Shorty Creek area. Biotite hornfels and lesser diopside hornfels is widespread. Although outcrops of the plutonic rocks are sparse, the widespread hornfels suggests large intrusions nearby or at depth.The most intense hydrothermal alteration occurs at the Hill 1835 prospect. In addition to widespread biotite-diopside hornfels, late vein and silica flooding is accompanied by variable crackled to matrix-supported brecciation. Widespread pervasive sericite (?) or clay (?) alteration overprints all other alteration and mineralization giving the rocks a pale yellow to tan bleached appearance. The area is dominated by northwest-directed, northeast-trending thrust faults and northeast-trending, open to recumbent isoclinal folds (Freeman, 2010). Mineralization at the Hill 1835 prospect appears to be bound by northeast striking faults and part of the same structural zone exposed over one mile to the southwest on the Alyeska Pipeline access road where a shear zone several hundred feet wide contains intense brecciation, silicification, and gold-sulfide mineralization, including arsenopyrite, stibnite, galena, and chalcopyrite. Rubble and outcrop at Hill 1835 contain hornfels with large (1 centimeter) cubic molds of pyrite, often partially filled with limonite. Drill chips contain disseminated and fracture-controlled pyrite, pyrrhotite, chalcopyrite, arsenopyrite, and bornite. Vuggy, barren, stockwork quartz veins cut grain-supported and matrix-supported breccias and appear to be the last phase of silicification (Abrams, 2015). Gold values from drill holes at Hill 1835 drilled in 1989 were higher in the hornfels in the upper 100 to 150 feet of drilling while copper values were higher outside the hornfels particularly near the bottom of some holes.
|Geologic map unit||(-148.516098379037, 65.430464579928)|
|Mineral deposit model||Copper-gold porphyry system (Cox and Singer, 1986; model 20c).|
|Mineral deposit model number||20c|
|Age of mineralization||Probably related to intermediate plutons, one of which has been dated at 63 Ma. A white mica from a drill hole gave a 40Ar/39Ar age of 65 to 70 Ma (Albanese, 1983a).|
|Alteration of deposit||The most intense hydrothermal alteration in the area occurs at this prospect. In addition to widespread biotite-diopside hornfels, late vein and silica flooding is accompanied by variable crackled to matrix-supported brecciation. Widespread pervasive sericite (?) or clay (?) alteration overprints all other alteration and mineralization giving the rocks a pale yellow to tan bleached appearance (Freeman, 2010).|
|Workings or exploration||
There is a long history of exploration by industry and government at and around this prospect. Freeman (2010) describes the extensive mapping, sampling, and geophysical and geochemical surveys in this area. In 1979, massive sulfide as much as 5 inches thick were found in roadcuts along the Alyeska Pipeline service road about a half mile southwest of Hill 1835 (Robinson and Metz, 1979). This led to extensive soil and rock sampling in the area by Fairbanks Exploration Inc. (FEI).
In 1989 and 1990, FEI and Asarco Ltd. drilled 20 reverse-circulation holes that totaled 6,843 feet at this prospect. Numerous intercepts of up to 500 feet were cut that contained more than 0.1 part per million (ppm) gold; some notable intercepts were 125 feet that contained 1.776 ppm gold and 25 feet that contained 4.577 ppm gold (Freeman, 2010). The core from the 1989 to 1990 drilling shows disseminated and fracture controlled pyrite, pyrrhotite, chalcopyrite, arsenopyrite, and bornite.
The area was largely dormant from 1990 to 2005. In 2005, Select Resources leased a large block of claims, staked more, and as of 2010 they held several large blocks that totaled more than 300 claims and included several other prospects (Freeman, 2010). In 2005, they did considerable rock and soil sampling on their claims which they collectively call the Shorty Creek project or just Shorty Creek.
Freegold Ventures Limited (Freegold) completed 28.6 kilometers of induced polarization (IP) surveying and collected 354 soil samples in 2014 covering the prospect areas of Hill 1835 and Hill 1710 (LG203). A resistivity high at Hill 1835 represents the silicified hornfels and is associated with a gold-arsenic-bismuth-copper soil anomaly (Abrams, 2015).Freegold Ventures Limited’s 2016 drilling program at their intrusion-related Shorty Creek property included 7 holes totaling 3,038 m; 2 holes were drilled in the ‘Hill 1835’ area, and 5 holes were drilled in the ‘1710’ area to test copper-molybdenum targets. ‘Hill 1835’ mineralization is spatially associated with a magnetic high defined by airborne- (Burns and others, 2015) and ground-based surveys, as well as magnetic highs in inverted profiles. Drilling highlights include 434.5 meters averaging 0.57 percent copper-equivalent, and 409.6 meters averaging 0.41 percent copper-equivalent. In the ‘1710’ area, 5 drill holes totaling 2,019.8 m, tested a copper-molybdenum soil anomaly and magnetic high. Drill hole SC 16-07 intersected 0.11 percent copper and 0.011 percent molybdenum from 0-159 m, including 0.15 percent copper and 0.009 percent molybdenum from 0-70.8 meters within quartz-feldspar porphyry. The entire 396-meter-long drill hole averaged 0.08 percent copper and 0.006 percent molybdenum. Additionally, Freegold conducted new ground-based geochemical sampling, geophysical surveys, and claim staking in 2016, and identified the new Quarry and Steel Creek target areas (Athey and Werdon, 2017).
|Indication of production||None|
Additional commentsThe new Steel Creek geophysically defined target does not correspond to ARDF description LG027 (Steel Creek).
|Reporters||D.J. Grybeck (Contractor, USGS); N.V. King (Alaska Earth Sciences); M.B. Werdon (DGGS)|
|Last report date||8/26/2017|