A press release about this:
Nebraska's Elk Creek Carbonatite Promises
Large Rare Earth Elements Resource
http://evworld.com/news.cfm?newsid=23277
Some references,
Brookins, D. G., S. B. Trevesb and S. L. Bolivara,
1975, Elk Creek, Nebraska, carbonatite: Strontium
geochemistry. Earth and Planetary Science Letters
vol. 28, no 1, pp. 79-82
http://www.sciencedirect.com/science/article/pii/0012821X7590076X
Carlson, M. P., and S. B. Treves, 2005, The Elk
Creek Carbonatite, Southeast Nebraska–An Overview.
Natural Resource Research. vol. 14, no. 1, pp. 39-45.
http://www.springerlink.com/content/xqm033615r2251g3/
Xu, A., 1996, Mineralogy, petrology, geochemistry
and origin of the Elk Creek Carbonatite, Nebraska.
Unpublished PhD. Dissertation, University of
Nebraska, Lincoln.
http://digitalcommons.unl.edu/dissertations/AAI9628256/
A Couple More PDF Files - Elk Creek Related:
Long+(2010)
Palacass(1997)
Best wishes,
Paul
