RARE EARTH ELEMENTS (REE) IN PROTEROZOIC PERALKALINE IGNEOUS ROCKS (PAJARITO MOUNTAIN) AND PEGMATITES IN NEW MEXICO

摘要

Three types of Proterozoic deposits have economic potential for REE in New Mexico: peralkaline igneous rocks, granites, and pegmatites. The Pajarito Mountain pluton on the Mescalero Indian Reservation, south-central New Mexico is a layered, peralkaline syenitic and pegmatitic intrusion, where REE, Y and Zr predominantly occurs in magmatic eudialyte group minerals. One sample contained 6869 ppm total REE. In 1990, Molycorp, Inc. reported historic resources of 2.7 million short tons grading 0.18% Y_2O_3 and 1.2% ZrO_2. Additional areas of Proterozoic granite in New Mexico may have potential for REE deposits (Tajo Granite in Socorro County, La Cueva Granite in Taos County, and Tusas Granite in Rio Arriba County), but additional geochemical studies and ultimately drilling are needed to determine the economic potential of these areas. Pegmatites are coarse-grained igneous rocks, lenses, or veins of granitic composition that contain essential quartz and feldspar, and represent the last, most hydrous phase of crystallizing magmas. Pegmatites can contain a variety of economic commodities, including, mica, feldspar, quartz, Li, REE, Cs, Ta, Nb, Rb, Y, Sc, U, Th, Sn, B, Be and other critical minerals. Recent exploration for REE and Li has occurred in New Mexico Proterozoic pegmatites and possible nearby placer deposits in the Petaca, Ojo Caliente No. 1, and Rociada districts in northern New Mexico. Many pegmatites in New Mexico have yielded past REE production, but the REE minerals are generally scattered throughout the pegmatite and are difficult to selectively mine and process, and probably will not constitute an economic resource because of low grade, small size, and the expensive hand-sorting techniques required in order to recover any of the commodities.