Hill 1870

Prospect, Active

Alternative names

Shorty Creek

Commodities and mineralogy

Main commodities Ag; As; Au; Cu; Mo
Other commodities Bi; Pb; Sb; Sn; W; Zn
Ore minerals arsenopyrite; bornite; chalcopyrite; gold; molybdenite; pyrite; pyrrhotite; stibnite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale LG
Quadrangle map, 1:63,360-scale B-4
Latitude 65.4169
Longitude -148.5326
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Hill 1870 prospect is on hill 1870 about 0.5 mile southwest of the head of Shorty Creek. It is about 7.3 miles south of Livengood, about 0.5 mile west-southwest of the center of section 23, T. 7 N., R. 5 W., and about 0.2 miles west of the Alyeska Pipeline service road.

Geologic setting

Geologic description

There is a long history of exploration by industry and government at and around this prospect on large blocks of claims that cover much of the area south of the Tolovana River in the Shorty Creek-Ranney Hollow-Steel Creek- Wilbur Creek area. Freeman (2010) describes the extensive mapping, sampling, and geophysical and geochemical surveys in this area. The exact chronology of this prospect is unclear but it known by 1985 and probably was discovered, mapped and sampled in conjunction with work at the Hill 1835 prospect (LG209) (Freeman, 2010). At the Hill 1870 prospect, hornfelsed flysch of the Wilbur unit, iron-oxide cemented breccia, and strongly altered crackle breccia were found on the flanks of hill 1870. Samples contain less than 69 to 1,063 parts per billion gold, 0.7 to 5.8 parts per million (ppm) silver, and 160 to more than 1,000 ppm arsenic. The mineralization is probably the same as that at the better known Hill 1835 prospect (LG209) prospect about a mile to the northeast. The Hill 1835 prospect was drilled in 1989 and 1990. The core from that drilling shows disseminated and fracture controlled pyrite, pyrrhotite, chalcopyrite, arsenopyrite, and bornite. The most intense hydrothermal alteration in this area is at the nearby Hill 1835 prospect (LG209). In addition to widespread biotite-diopside hornfels, late vein and flood silicification 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 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 include several other prospects including this, the original Shorty Creek prospect (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.
The hills south of the Tolovana River in this area are covered with sub-Arctic forest and loess; outcrop is sparse. The rocks in the area are mainly the Lower Cretaceous Wilbur Creek sequence of folded black carbonaceous siltstone, gray feldspathic sandstone and silty sandstone, black shale, and polymictic conglomerate (Albanese, 1983 [Bedrock geology]; 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 crop are sparse, the widespread hornfels suggests large intrusions nearby or at depth. The structure of the area is dominated by northwest-directed, northeast-trending thrust faults and northeast-trending, open to recumbent isoclinal folds.
Freeman (2010) notes that others consider the prospects in the Shorty Creek area to be intrusive-related gold (IRG) deposits. However, he concludes that the Shorty Creek mineralization is more likely a large copper-gold-molybdenum porphyry system about 8 miles in diameter. This system is manifested in three main types of deposits: 1) proximal copper-gold-molybdenum mineralization as seen in the old Shorty Creek deposit (HG203); 2) high-sulfidation epithermal gold-arsenic-bismuth-tungsten+/-copper+/-silver mineralization as seen at the Hill 1835 prospect (HG209); and 3) intermediate sulfidation epithermal gold-silver-lead-zinc+/-arsenic+/-antimony+/-manganese mineralization as seen on the ridge south of Wilbur Creek.
Geologic map unit (-148.535097007688, 65.4164640545891)
Mineral deposit model Part of a copper-gold-molybdenum porphyry system (Cox and Singer, 1986; model 20c or 21a).
Mineral deposit model number 20c or 21a
Age of mineralization Probably related to intermediate plutons, one of which has been dated at 63 Ma. A white mica from a drill hole at the nearby Hill 1835 prospect (HG New H1004) gave a Ar40/Ar39 age of 65-70 Ma.
Alteration of deposit The most intense hydrothermal alteration in the area occurs at the nearby Hill 1835 prospect (HG New H1004). In addition to widespread biotite-diopside hornfels, late vein and flood silicification 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.

Production and reserves

Workings or exploration There is a long history of exploration by industry and government at and around this prospect on large blocks of claims that cover much of the area south of the Tolovana River in the Shorty Creek-Ranney Hollow-Steel Creek- Wilbur Creek area. Freeman (2010) describes the extensive mapping, sampling, and geophysical and geochemical surveys in this area. The exact chronology of this prospect is unclear but it known by 1985 and probably was discovered, mapped and sampled in conjunction with work at the Hill 1835 prospect (LG209) (Freeman, 2010). 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 include several other prospects including this, the original Shorty Creek prospect (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.
Indication of production None
Reserve estimates None.
Production notes None.

References

References

Freeman, C.J., 2010, Geology and mineralization of the Shorty Creek project, Livengood-Tolovana mining district, Alaska: Unpublished NI43-101 report for Select Resources Corporation, 88 p. (posted on www.sedar.com, May 20, 2010).
Robinson, M.S. and Metz, P.A., 1979, Evaluation of Mineral resources in the pipeline corridor, Phases I and II: Mineral Industry Research Laboratory, University of Alaska Open File Report 79-2, 77 p.
Reporters D.J. Grybeck (Contractor, USGS)
Last report date 2/28/2011