Elk Creek

Location: Nebraska, United States (40.300, -96.200 approx.)

Commodities: niobium; scandium; titanium; rare earth elements

Deposit model: carbonatite · carbonatite deposits

Geology

“Deposit type and basic geology: A buried, rare earth elements (REE)- and niobium (Nb)-rich carbonatite mass, referred to as the Elk Creek carbonatite, lies in the subsurface about 1.6 km (1 mi) southwest of the small town of Elk Creek in southeastern Nebraska. On the basis of exploration drilling and the extent of magnetic and gravity anomalies, the carbonatite mass at depth appears to have its center beneath section 33, township 4 north, range 11 east. The entire oval-shaped, subsurface body, which is recognized by a geophysical anomaly caused by the carbonatite and associated intrusive rocks, is about 7 km (4.3 mi) in diameter. Analyses of drill core showed the intrusion at depth comprised mostly massive to brecciated, apatite- and pyrochlore-bearing dolomitic carbonatite (89 percent), along with fenitized basalt, lamprophyre, and syenite (totaling 11 percent). Major-element analyses suggest that the carbonate mass is a magnesian carbonatite (dolomitic), generally similar in gross chemical composition to the Iron Hill (Powderhorn) carbonatite stock in southwestern Colorado. The REE are hosted principally by the minerals bastnasite, parisite, and synchisite and by smaller amounts of monazite (Xu, 1996). Niobium was deposited in pyrochlore. The U.S. Geological Survey obtained a potassium-argon age on biotite in the carbonatite of 544±7 million years old (Xu, 1996).” (Long and others (2010)) “From 1973 to 1986, Molycorp undertook both regional and local exploration of the Elk Creek gravity anomaly. Molycorp conducted airborne geophysical surveys as well as a comprehensive regional drill program. In May 1978, Molycorp made their discovery of the Elk Creek Nb-REE deposit with drill hole EC-11. EC-11 is located on Section 33, Township 4N, and Range 11. The Elk Creek Nb-REE deposit was intersected at a depth of 203.61 m (668 ft) in the Elk Creek Carbonatite.” (Daigle (2011)) “The Elk Creek Property is comprised of the Elk Creek Carbonatite that has intruded into the older Precambrian granitic and metamorphic basement rocks. The Elk Creek Carbonatite and Precambrian rocks are unconformably overlain by layer of roughly 200 m of Paleozoic marine sedimentary rocks of Pennsylvanian age (approximately 299 – 318 Ma)....There are no surface expressions of the Elk Creek Carbonatite on the property.” (Daigle (2011))

Published resource estimates

As compiled by USGS USMIN from the cited studies. Resource classes follow the source; "approximate" flags values USMIN reports as approximations. These are not current company reserve statements.

Exploration and site history

• Discovery — In May 1978, Molycorp made their discovery of the Elk Creek Nb-REE deposit with drill hole EC-11; The Elk Creek Nb-REE deposit was intersected at a depth of 203.61 m (668 ft) in the Elk Creek Carbonatite, 1978 (Daigle (2011))
• Evaluation — NI 43-101 technical report; Resource estimate, 2011 (Daigle (2011))
• Exploration — Molycorp undertakes regional and local exploration; Airborne geophysical surveys; Drilling; A total of 106 drill holes for a total of approximately 46,797 m (153,532 ft), 1973–1986 (Daigle (2011))

Record imported from USGS USMIN ver. 4.0 (June 2019). Developments after that date appear on facility records, not here; see the methodology.