Pajarito Mountain, Otero County, New Mexico1

PAJARITO MOUNTAIN, OTERO COUNTY, NEW MEXICO1

Virginia T. McLemore, New Mexico Bureau of Geology and Mineral Resources, New Mexico Tech, Socorro, NM 87801

May 18, 2010

Pajarito Mountain (DIS130) lies in the northeastern part of the Mescalero Apache Indian Reservation, south of Ruidoso in Otero County, NM (Fig. 1). In 1984, Molycorp, Inc. (a subsidiary of Unocal Corp. at that time) began exploration in the area and announced the discovery of a yttrium and zirconium deposit at Pajarito Mountain on May 31, 1989 (Sherer, 1990; McLemore, 1990, 1991b). A joint leasing–operating agreement was reached between Molycorp, Inc. and the Mescalero Apache Tribe and a recoverable resource of 2.7 million short tons grading 0.18% Y2O3 and 1.2% ZrO2 (historic resources, not NI 43-101 compliant) as disseminated eudialyte was reported (Sherer, 1990). However, before mining began a market slump in the yttrium and zirconium markets occurred and Molycorp, Inc. dropped the project, which also was undergoing corporate financial difficulties. The Pajarito Mountain deposit would have been the first and only deposit in the world mined solely for yttrium and zirconium, which are typically produced as co-products or by–products of mining other commodities. Disseminated Y-Zr deposits in alkaline rocks are found at Pajarito Mountain (Kelley, 1968; Sherer, 1990; McLemore, 1990, 1991). Crystalline rocks of Proterozoic age at Pajarito Mountain were first reported by Kelley (1968), although previous workers (Thompson, 1942, p. 12; Lloyd, 1949, pl. 1) recognized that these rocks were Proterozoic. Motts and Gaul (1960), after detailed mapping and petrographic studies, presented compelling arguments for a Tertiary age of the complex, but subsequent dating by Kelley (1968) and the U.S. Geological Survey (Moore et al., 1988a, b) confirm a Proterozoic age of about 1100-1200 Ma. This deposit is associated with a period (1260-1000 Ma) of mafic, volcanic, and A-type granitic intrusions in Texas and Arizona, coincident with the Grenville orogeny and perhaps extension (Barnes et al., 1999; McLemore et al., 2000; Bickford et al., 2000). The Parajito Mountain complex consists of an unusual lithologic assemblage for Proterozoic rocks in New Mexico, in that the complex is predominantly alkaline. Several varieties of syenite, quartz syenite, alkali granite, and gabbro are exposed at Pajarito Mountain and are intruded by pegmatite and gabbroic dikes (Kelley, 1968; Condie and Budding, 1979; Moore et al., 1988a; Sherer, 1990). Such rocks, although present locally, are not common lithologies in most Proterozoic terranes in New Mexico. Paleozoic sedimentary rocks unconformably overlie the Proterozoic rocks. The mineralogy of the alkaline rocks is complex consisting of various amounts of essential K-feldspar, plagioclase, arfvedsonite and accessory riebeckite, quartz, eudialtye, fluorite, monazite, apatite, biotite, rutile(?), titanite, aegirine-augite, ziconium silicates, lanthanide and yttrium minerals and zircon (Moore et al., 1988a; Sherer, 1990). No feldspathoids have been observed at Parajito Mountain (Sherer, 1990; McLemore, 1991b), although Moore et al. (1988a) reports the presence of nepheline syenite. The origin of the Parajito Mountain complex is speculative at present, due to the lack of detailed petrographic and geochemical studies. The complex lies in the southern portion of anorogenic, middle Proterozoic, plutonic magmatism that extends across North America (Anderson, 1983; Woolley, 1987; McLemore, 1996b). The alkaline rocks within this belt were probably a result of complex magmatic differentiation and fractionation of an upper-mantle or lower-crustal source as indicated by alkaline lithologies and enriched REE geochemistry (Fig. 2). Eudialyte is the major ore mineral at Parajito Mountain and is disseminated throughout the syenite, quartz syenite, and alkali granite. Eudialyte, (Na,Ca)5(Zr,Fe,Mn) (Si6O17)(O,Oh,Cl), is a zirconium silicate containing yttrium and is generally amenable to heap-leach recovery after crushing, similar to the process used in recovering gold and silver. The deposit is at shallow depths and open pit mining was planned (Sherer, 1990). Future Development of this resource is dependent upon the ever changing market and demand for yttrium and zirconium. The presence of the alkaline lithologies suggests the potential for uranium and light-REE deposits (Fig. 2; McLemore, 1983; McLemore et al., 1988a, b). Selected chemical analyses indicate the Proterozoic rocks are anonymously high in light-REE (Fig. 1; La as high as 1500 ppm, Ce as high as 3910 ppm; McLemore, 1991b; Moore et al., 1988a), zinc (700 ppm; Moore et al., 1988a), and niobium (200 ppm; Moore et al., 1988a). NURE stream sediments in the arroyos draining the Proterozoic rocks (Fig. 1) are high in Zr (as much as 707 ppm), Y (as much as 106 ppm), and Ce (as much as 138 ppm). Detailed petrographic and geochemical work, along with confirmation drilling, is needed to determine if some of these commodities can be economic in the future.

FIGURE 1. Zr geochemical map showing NURE stream-sediment locations and mineral prospects in the Pajarito district (blue), Otero County, New Mexico. Concentrations greater than 350 ppm Zr (mean plus 1 standard deviation) are anomalously high. Samples also are high in Y (as much as 106 ppm) and Ce (as much as 138 ppm). 3000 e t i

r 1000 d n o h C

1 C / e l p m a S

100 70 L a P r E u H o T m L u Ce Nd Sm G d Dy E r Yb

FIGURE 2. REE chondrite-normalized plot of syenites samples from the Pajarito Mountain deposit, Otero County. Note the enriched light REE pattern.

REFERENCES Foord, E. E., Moore, S. L., Marvin, R. F., and Taggart, J. E., Jr., 1983, Petrology of the Proterozoic syenites at Pajarito Mountain and the Tertiary igneous complex of the Sierra Blanca region, Otero County, New Mexico: Mineralogical Society of America, Symposium on Alkaline Complexes, abstracts, 6 p. Kelley, V. C., 1968, Geology of the alkaline Precambrian rocks at Pajarito Mountain, Otero County, New Mexico: Geological Society of America Bulletin, 79, p. 1565-1572. McLemore, V. T., North, R. M., and Leppert, S . , 1988, Rare-earth elements (REE) in New Mexico: New Mexico Geology, v. 10, p. 33-38. McLemore, V. T., North, R. M., and Leppert, S., 1988a, REE, niobium, and thorium districts and occurrences in New Mexico: New Mexico Bureau of Mines and Mineral Resources, Open-file Report 324, 27 p. McLemore, V. T., 1990, Background and perspectives on the Pajarito Mountains yttrium - zirconium deposit, Mescalero Apache Indian Reservation, Otero County, New Mexico: New Mexico Geology, v. 12, p. 22. McLemore, V. T., 1991a, Base- and precious-metal deposits in Lincoln and Otero Counties, New Mexico; in Barker, J. M., Kues, B. S, Austin, G. S., and Lucas, S. G., eds., Geology of the Sierra Blanca, Sacramento, and Capitan Ranges, New Mexico: New Mexico Geological Society, Guidebook 42, pp. 305-309. McLemore, V. T., 1991b, Pajarito Mountain yttrium - zirconium deposit, Mescalero Indian Reservation, Otero County, New Mexico: New Mexico Geological Society, Guidebook to the 42nd field conference, p. 30-32. Moore, S. L., and Foord, E. E., 1986, Roadlog from Inn of the Mountain Gods to the Ruidoso ski area on Sierra Blanca Peak: Southwest section of American Association of Petroleum Geologists, Transactions and Guidebook of 1986 Convention, Ruidoso, New Mexico, New Mexico Bureau of Mines and Mineral Resources, p. 29-36. Moore, S. M., Foord, E. E., Meyer, G. A., and Smith, G. W., 1985, Mineral resources of the Mescalero Apache Indian Reservation, Otero County, New Mexico: U. S. Geological Survey, Administrative Report, 78 p. Moore, S. M., Foord, E. E., Meyer, G. A., and Smith, G. W., 1988, Geologic map of the northwestern part of the Mescalero Apache Indian Reservation, Otero County, New Mexico: U.S. Geological Survey, Misc. Investigations Map I-1895, 1:24,000 scale. Roeder, P. L., McArthur, D., Ma, Xin-Pei, Palmer, G. R., and Mariano, A. N., 1987, Cathodoluminescence and microprope study of rare-earth elements in apatite: American Mineralogist, v. 72, p. 801-811. Sherer, R.L., 1990, Pajarito yttrium-zirconium deposit, Otero County, New Mexico: New Mexico Geology, v. 12, p. 21.

1 This information is preliminary and has not been reviewed according to New Mexico Bureau of Geology and Mineral Resources standards. The content of this report should not be considered final and is subject to revision based upon new information.