Quartz Hill

Prospect, Active

Commodities and mineralogy

Main commodities Mo
Ore minerals molybdenite; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale B-2
Latitude 55.403
Longitude -130.483
Nearby scientific data Find additional scientific data near this location
Location and accuracy The surface expression of the Quartz Hill deposit occupies a mile-square area that encompasses Quartz Hill and parts of the upper drainages of White and Beaver Creeks (sections 1, 2, 26, 34, 35, and 36, T. 74 and 75 S., R. 98 E., of the Copper River Meridian.). The map site is at the summit of Quartz Hill and is accurate within a few hundred feet. The site corresponds to loc. 105 in Elliott and others (1978).

Geologic setting

Geologic description

The country rocks in the general area of the Quartz Hill deposit include: Cretaceous or Tertiary quartz diorite, granodiorite, and quartz monzonite of the Coast Range batholith; hypabyssal stocks and associated dikes of Miocene or Oligocene granite and gabbro; Tertiary lamprophyre dikes that postdate the stocks; and Tertiary and Quaternary basalt and andesite lava flows and cinder cones (Berg and others, 1988).
The Quartz Hill deposit consists of a molybdenite-quartz stockwork and molybdenite fracture coatings in a hypabyssal, Miocene or Oligocene, composite stock and associated apophyses of porphyritic, aplitic, and aphanitic quartz monzonite and quartz latite (Elliott and others, 1976; Hudson and others, 1977, 1978, 1979). Molybdenite-quartz veinlets and fracture coatings also occur in the country rocks near the stock. Pyrite is common, chiefly as disseminated grains and small veinlets in the porphyritic rocks, and in the country rocks near the stock.
The Quartz Hill deposit was discovered in 1974. Since then, the orebody has been defined by more than 450 drill holes totalling about 265,000 feet (Maas and others, 1995, p. 265). Two test adits, totalling nearly 5,000 feet of underground workings, were driven in 1981 to better define the deposit and to collect metallurgical test samples. The orebody is generally tabular and subhorizontal. Assuming a cutoff grade of 0.05% molybdenum sulfide (MoS2), the orebody has a surface area of about 5,000 feet by 10,000 feet, and extends to a depth of up to 1,700 feet. Resource estimates vary, depending on cutoff grades. In 1992, the property owners reported a 'probable resource' of 210 million metric tons (mt) averaging 0.22% MoS2, and an additional 'possible resource' of 1.2 billion mt averaging 0.12% MoS2. A more widely publicized estimate is a probable resource of 444 million mt containing 0.219% MoS2, and a possible resource of 1.36 billion mt averaging 0.136% MoS2 (Maas and others, 1995, p. 265).
Geologic map unit (-130.484694588651, 55.4026743900842)
Mineral deposit model Porphyry Mo, Low-F (Cox and Singer, 1986; model 21b)
Mineral deposit model number 21b
Age of mineralization Miocene or Oligocene.
Alteration of deposit Pyritization, silicification.

Production and reserves

Workings or exploration The Quartz Hill deposit was discovered in 1974. Since then, the orebody has been defined by more than 450 drill holes totalling about 265,000 feet (Maas and others, 1995, p. 265). Two test adits, totalling nearly 5,000 feet of underground workings, were driven in 1981 to better define the deposit and to collect metallurgical test samples.
Indication of production None
Reserve estimates The orebody is generally tabular and subhorizontal. Assuming a cutoff grade of 0.05% molybdenum sulfide (MoS2), the orebody has a surface area of about 5,000 feet by 10,000 feet, and extends to a depth of up to 1,700 feet. Resource estimates vary, depending on cutoff grades. In 1992, the property owners reported a 'probable resource' of 210 million metric tons (mt) averaging 0.22% MoS2, and an additional 'possible resource' of 1.2 billion mt averaging 0.12% MoS2. A more widely publicized estimate is a probable resource of 444 million mt containing 0.219% MoS2, and a possible resource of 1.36 billion mt averaging 0.136% MoS2 (Maas and others, 1995, p. 265).

Additional comments

This world-class deposit is estimated to contain 10% of the free world's known reserves of molybdenum.

References

MRDS Number A012355

References

Hudson, T.L., Smith, J.G., and Elliott, R.L., 1979, Petrology, chemistry, and age of intrusive rocks associated with the Quartz Hill molybdenite deposit, southeastern Alaska: Canadian Journal of Earth Sciences, v. 16, no. 9, p. 1805-1822.
Reporters H.C. Berg, USGS
Last report date 7/5/1999