Unnamed Occurrence (ARDF - NL006; east of hill 2120), Kaiyuh Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Unnamed Occurrence (ARDF - NL006; east of hill 2120)	- not defined -
Kaiyuh Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Location: This occurrence is in the southern Kaiyuh Hills, 36 miles south of Galena. It is in a body of dunite exposed in a 6-square-mile area between the Yuki River and the East Fork Yuki River. The occurrence is at an elevation of approximately 1500 feet, about 1.7 miles east of hill 2120. It corresponds to occurrence 21 of Foley and others (1984). The location is accurate within 500 feet.
Geology: Chromite occurrences in the Kaiyuh Hills were first documented in 1980 by C.C. Hawley and Associates, Inc., during their investigations for Armco Mineral Exploration, Ltd. The Bureau of Mines examined four of the occurrences in 1982, and published a report in 1984 (Foley and others, 1984). Twenty-one occurrences were located within a northeast-trending, approximately 6-mile-long body of dunite and pyroxene peridotite in the Kaiyuh Hills. The largest 4 occurrences are described in this record and in records NL003, 004, and 005. These four occurrences are estimated to contain a combined total of between 17,000 and 37,000 tons of chromic oxide (Foley and others, 1984). The Kaiyuh Hills are underlain by a portion of the Rampart ophiolite belt that is offset along the Kaltag fault from the remainder of the belt. The belt comprises two tectonic units: an upper unit of ultramafic and gabbroic rocks and a lower unit of mafic volcanic rocks, diabase, and chert (Patton and others, 1977). Ultramafic rocks of the upper unit, which contain the chromite occurrences, are exposed along a 24-mile-long, northeast-striking belt in the Kaiyuh Hills (Foley and others, 1984). At the southwestern end of the belt is a 6-square-mile area underlain mostly by a body of dunite. This dunite contains more than 90% olivine, sparsely disseminated chromite, and locally banded segregations of disseminated to massive chromite. Nodular chromite was observed at one location. At the northeastern end of this body, the dunite grades into pyroxene peridotite interlayered with dunite. This part of the body also contains chromite bands ranging in thickness from less than 1 inch to 3 feet. The dunite layers range from a few inches to several hundred feet thick. The pyroxene peridotite is mostly harzburgite. Minor amounts of wehrlite and lherzoliteare also present (Foley and others, 1984). This occurrence consists of a 75- by 300-foot zone of discontinuous bands of chromite up to 2.5 inches thick and 1.5 feet long. The chromite occurs as highly fractured, subhedral to anhedral crystals disseminated in serpentinized dunite. Fractures in the chromite are filled with pale green serpentine. Chalky white to pale blue magnesite coats weathered surfaces (Foley and others, 1984). This zone contains approximately 3% chromite, and is estimated to contain between 3,000 and 6,000 tons of chromic oxide (Foley and others, 1984).
Workings: Chromite occurrences within the Kaiyuh Hills were first documented in 1980 by C.C. Hawley and Associates, Inc., during their investigations for Armco Mineral Exploration, Ltd. The U.S. Bureau of Mines examined four of the occurrences in 1982 and published a report in 1984 (Foley and others, 1984).
Age: Jurassic, the age of the ultramafic hostrocks (Patton and others, 1977).
Reserves: This occurrence is estimated to contain between 3,000 and 6,000 tons of chromic oxide. This occurrence and three others nearby (NL003, 004, and 005) contain a combined total of between 17,000 and 37,000 tons of chromic oxide.

Commodities (Major) - Cr
Development Status: No
Deposit Model: Podiform chromite (Cox and Singer, 1986; model 8a)

Other Databases

Link to USGS - Alaska:	NL006

Other Regions, Features and Areas containing this locality

References