軽希土類元素に富むカーボナタイト鉱床:米国,マウンテンパス鉱床

抄録

Based on the latest research and newly obtained bulk chemical data of rare earth element (REE) for ores and intrusive rocks, we describe a summary of geology, mineralogy, and ore refining process of the Mountain Pass REE deposit, California, USA and briefly assess their potential and future issue. The Mountain Pass deposit is associated with carbonatite and alkaline intrusive rocks and has a tonnage of over 20Mt of 8.9% REO; which is represented by elevated LREE (La to Eu) contents such as La, Ce, and Nd owing to high bastnasite content. In addition to the Mountain Pass deposit, LREE-rich deposits such as Bayan Obo Fe-Nb-REE deposit, China, which occupied about 50% of global REO production in 2004, are also enriched in LREE. The bulk chemical data are revealed that ores from the Mountain Pass deposit record total HREE (Gd to Lu) contents ranging from 252 ppm to 1, 028 ppm with a maximum 2, 427 ppm for bastnasite concentrate, which indicates that LREE-rich deposits have potentially a significant economic contribution to HREE as well as LREE. For high-tech-nology industries with particular consumption of HREE resources, 1) a harmless and effective refining process extracting HREE from giant LREE-rich deposits even with a low-grade HREE (ex. Mountain Pass and Bayan Obo deposits) should be developed for the short-term demand, 2) an exploration for REE deposits which are primarily concentrated in HREE would be necessary for the approaching long-term shortage of HREE.