New Mexico Geological Society · Socorro, NM

(575) 835-5410

Eric L. Ruggles1, Nicole Hurtig1, Alexander Gysi2 and Virginia McLemore2

1New Mexico Institute of Mining and Technology, PO Box: 2305, Socorro, NM, 87801, United States, eric.ruggles@student.nmt.edu
2New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM, 87801, United States

The Lemitar Carbonatite, located in the Lemitar Mountains, NM, comprises 516.7±0.7 Ma old dikes intruded into Proterozoic mafic rocks [1,2]. This area comprises of more than one hundred surface exposures of carbonatite dikes with grades of up to 1.1% total rare earth element (REE) concentrations that show variable degrees of hydrothermal overprinting. Hydrothermal processes have been shown to be critical for REE mobilization and enrichment to economic levels [3]. This study aims to determine a mineral paragenesis and study fluid inclusions to highlight REE mobility and enrichment at the magmatic-hydrothermal transition in the Lemitar Carbonatite.

Magmatic minerals comprise of calcite, dolomite, phlogopite, magnetite, and apatite [1] overprinted by hydrothermal veins comprising of calcite, fluorite, and quartz. Alteration surrounding carbonatites includes potassic fenitization, hematization, F-Ca-metasomatism, chloritization, and silicification [4]. Cathodoluminescence imaging shows three distinct calcite generations of which calcite-1 is early and likely magmatic, calcite-2 is the early hydrothermal vein calcite and calcite-3 is the latest hydrothermal calcite generation. Apatite occurs in the fine-grained carbonate matrix, exhibits dissolution textures, and is cross-cut by calcite-3. Calcite-2 occurs as euhedral crystals growing on hydrothermal vein walls overgrown and crosscut by calcite-3 and subsequently by quartz and fluorite. Four fluid inclusion types have been observed including: type-1 vapor-poor (5-15 vol% vapor) and type-2 vapor-rich (>30 vol% vapor) liquid-vapor inclusions, type-3 vapor-poor (5-15 vol% vapor) and type-4 vapor-rich (>30 vol% vapor) multiphase inclusions. Apatite displays inclusion types 1, 2, and 4, as well as melt inclusions. Type-1 and 3 inclusions occur in calcite-1, type-1, 2, and 3 inclusions occur in calcite-2, and type-2 and 3 inclusions occur in calcite-3, type 1 and 3 inclusions occur in quartz, and fluorite exclusively exhibits type-1 inclusions. Microthermometric data of fluorite-hosted type-1 inclusions show ice melting temperatures at -1.2±0.1°C, and calcite-3 type-1 inclusions yielding -2.5±0.08°C. Apatite-hosted type-2 and 4 inclusions show melting temperatures from -5.8±0.2°C to -8.6±0.15°C. Salinities are 2.07 wt% NaCl equivalent in type-1 fluorite-hosted inclusions, 4.18 wt% in type-1 calcite-3 hosted inclusions and 8.95 to 12.4 wt.% in apatite-hosted type-2 and 4, respectively. Preliminary data indicate a decrease in salinity and homogenization temperatures for fluid inclusions between apatite and fluorite from early to late in the paragenetic sequence.

References:

  1. [1] McLemore, 1987, The Journal of Geology, Issue 2, pg. 255-270.
  2. [2] Haft et al., 2022, New Mexico Geological Society, 72nd Annual Fall Field Conference, pg. 365-373.
  3. [3] Perry, E.P., Gysi, A.P., 2018. Rare Earth Elements in Mineral Deposits: Speciation in Hydrothermal Fluids and Partitioning in Calcite. Geofluids 2018, 1–19.
  4. [4] Perry, E.P., 2019. Rare earth element signatures in hydrothermal calcite: insights from numerical modelling, experimental geochemistry, and mineral deposits in New Mexico. PhD. Thesis, 125.

2023 New Mexico Geological Society Annual Spring Meeting April 21, 2023, Macey Center, Socorro, NM Online ISSN: 2834-5800

Pages: 90-91