Thursday, November 15, 2012
It may be time to re-examine the potential for rare earth elements (REE) in Arizona. The conventional wisdom is that we have only minor amounts in a few pegmatites. But Virginia McLemore from the New Mexico Bureau of Geology and Mineral Resources may have dispelled that as a myth, with her talk at the Arizona Geological Society monthly dinner meeting on Tuesday.
Ginger’s talk addressed REEs in New Mexico, but she started off with an overview of known deposits worldwide, consideration of economic and political factors, and the challenges facing development of new mines. Her map of REE deposits in the U.S. showed an big concentration of deposits in New Mexico. She characterized these into half a dozen different types of deposits and regional geologic trends, including carbonatites, sills, plugs, and laccoliths and smaller dikes and plugs of phonolite, syenite, and other alkaline igneous rock, disseminated deposits in syenite, Cretaceous heavy mineral, beach-placer sandstone deposits, and marine phosphates. [Right, REE deposits in the Southwest. Credit, USGS]
As she spoke one question became obvious – couldn’t there be similar deposits here?. We have many of the same types of rocks in Arizona, some part of the same belt as REE-bearing rocks in New Mexico. Well, before we had a chance to raise that question, Ginger made the point herself.
After her talk, I asked why there is such a big difference between the New Mexico and Arizona maps showing REEs. Her response was that she had led a state-wide REE assessment starting in the 1980s while Arizona has not done similar.
To emphasize that, Jim Briscoe reminded us that an announcement by Liberty Star Uranium & Metals Corp. (August 13, 2012) described the company’s Hay Mountain block of their Tombstone project in Cochise County, which consists of 57 unpatented federal lode mining claims in addition to Arizona State land leases (Mineral Exploration Permits, “MEPs”). They state that their “land position covers geologically, geophysically, geochemically indicated completely covered porphyry copper- moly-silver-gold, and rare earth element (REE) mineral center.”
“Liberty Star has recently discovered a large intrusion indicated by an aerially extensive low flight level magnetic survey under and partially exposed in and around the Tombstone caldera. Mineralization is clearly associated with this intrusive body.”
Could Arizona have a lot more REEs than we think? It’s a possibility.