| Basis for focus area |
Alkaline/peralkaline igneous rocks Tertiary-age REE-U-Th veins in alkaline rocks. Focus area is based on outlines of the following districts and areas in McLemore (2014, 2015b, fig. 1, 2017): Gallinas-Red Cloud Mining District, Ojo Caliente No. 2, Salinas Peak, Capitan Mountains, Three Rivers, and San Simon. |
| Identified resources |
Identified REE resources; historical production of barite, fluorite, and REE (bastnaesite). |
| Production |
Gallinas Mountains (1954-1956) produced 146,000 lbs bastnaesite concentrate from fluorite veins. San Andres Mountains had minor fluorite +/- barite production. |
| Status |
Past mining. Exploration in Gallinas and Cornudas Mountains; no activity in other areas. |
| Estimated resources |
Gallinas-Red Cloud area: 537,000 (short) tons at a grade of 2.95% ΣREE (not NI-43-101-compliant estimate), attributed to Schreiner (1993 in McLemore (2014, p. 2). |
| Geologic maps |
McLemore (2010c), scale: ~1:100,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
Porphyritic trachyte (Tertiary), porphyritic latite (Tertiary), rhyolite (Tertiary), Pennsylvanian and Permian limestone; differentiated plutons such as Capitan Mountains pluton. Intrusives in the Cornuda and Hueco Mountains in southern Otero County ranges are the northernmost rocks of the Trans-Pecos magmatic belt; they include both alkalic types (syenites) to the east and calc-alkaline types to the west. At the temporal transition from calc-alkaline to alkalic further south in the Trans-Pecos, the Round Top Mountain rhyolite was intruded between present-day Sierra Blanca and Ft. Hancock, Texas. Round Top Mountain is considered a gigantic tonnage, low-grade resource of heavy REE and some additional rare elements (Hulse and others, 2012). |
| Deposits |
Gallinas: Red Cloud mine (MRDS deposit_id: 10150086), Conqueror No. 4 and Hilltop prospect (MRDS dep_id: 10013652), Eagle Nest prospect (MRDS dep_id: 10013644), Hilltop occurrence (MRDS dep_id: 10296515), Old Hickory mine (MRDS dep_id: 10013653); San Andres Mountains: Baso Four Claims (MRDS dep_id: 10011715). |
| Evidence from mineral occurrences |
MRDS. |
| Geochemical evidence |
Geochemical work has been specific to mineral occurrences. Grab samples from San Andres Mountains district yielded 86% fluorite and 8.4% barite. The Mina Tiro Estrella deposit in south flank of Capitan Mountains pluton, yielded samples with >8,133 ppm REE (7 REE measured) and identified allanite (McLemore and Phillips, 1991, p. 296). From this and several other veins in or marginal to the Capitan Mountains, Campbell and others (1995) concluded that fluids were unequivocally magmatic in origin, possibly also with assimilation of evaporites. REE measured in streambed sediments in Salinas Peak area. |
| Geophysical evidence |
Unknown. |
| Evidence from other sources |
None. |
| Comments |
In 1980-81, Molycorp, Inc., explored the Gallinas district, and chose to drill a ground magnetic survey high, drilling near the Old Hickory mine (MRDS dep_id: 10013653) and inclining a core hole S 30°W at 53° from the horizontal (Schreiner, 1993, p. 24) The magnetic anomaly proved to be a Precambrian diorite intrusive body. Schreiner (1993, p. 7), however, also states that, "Drilling by Molycorp Inc. has shown that high-grade REE-bearing-fluorite mineralized rock (greater than 5% REO) is present at depths over 400 ft and there is no reason to believe that the grade of the deposits decreases with depth." The "greater than 5%" statement may refer to just a single sample from 538 to 545 ft drilled depth in the core hole that graded 5.20% REO in fluorite-rich brecciated diorite. Gallinas-Red Cloud area has limited tonnages of fluorspar-barite-bastnaesite ore in place, known from US Bureau of Mines underground and surface sampling. |
| Cover thickness and description |
Covered rhyolite intrusive in areas between the known and outcropped intrusive bodies are to be sought using geophysics. The known mountains are isolated from one another, and additional intrusions are probably between, beneath shallow cover. None of the outcropped intrusions has the desired geochemistry and petrology, namely that of an end-member evolved peraluminous fluorine-rich rhyolite analogous with Round Top Mountain rhyolite. |
| Authors |
Lukas Zurcher, Timothy S. Hayes, Mark E. Gettings, Virginia T. McLemore, Joshua M. Rosera. |
| New data needs |
Geophysics, geologic mapping. |
| Geologic mapping and modeling needs |
Updated geologic mapping. |
| Geophysical survey and modeling needs |
Magnetic data together with local gravity measurement has potential to discover a buried body analogous to Round Top Mountain Rhyolite (see Pingitore and others, 2014; Hulse and others, 2012). |
| Digital elevation data needs |
Lidar complete or in progress. |
