Geology of the Jicarilla mining district, Lincoln County, New Mexico — Summary
The Jicarilla mining district is one of several mining districts associated with alkaline igneous rocks in the Lincoln County porphyry belt in central New Mexico. The Lincoln County porphyry belt (LCPB) is part of the North American Cordilleran alkaline-igneous belt (Fig. 1) and, in New Mexico, the North American Cordilleran alkaline-igneous belt extends from the Sangre de Cristo Mountains near Raton, southward to the Cornudas Mountains, east of El Paso, Texas (McLemore, 2018a). Significant mineral production, especially gold, has come from deposits spatially associated with Tertiary alkaline-igneous rocks in the New Mexico alkaline-igneous belt (McLemore, 2001, 2015). These mineral deposits in New Mexico have been referred to as Great Plains Margin (GPM) deposits by North and McLemore (1986, 1988) and McLemore (1996, 2001, 2015). Alternative classifications by other workers include Au-Ag-Te veins (Cox and Bagby, 1986; Bliss et al., 1992; Kelley, 1995; Kelley et al., 1995, 1998), alkalic-gold or alkaline-igneous related gold deposits (Fulp and Woodward, 1991a; Thompson, 1991; Bonham, 1988; Mutschler et al., 1985, 1991; Richards, 1995), porphyry gold deposits, and Rocky Mountain gold province.
The Jicarilla district (also known as the Ancho district) is in the Jicarilla Mountains in Lincoln County (Fig. 2). The district is accessed via U.S. Highway 54, approximately 20 miles northeast of Carrizozo on Jicarilla Road, a gravel county road. The area is rural, part of the Lincoln National Forest, and a few ranches are located within several miles of the district. The Jicarilla Mountains consist of rough terrain with steep slopes, narrow canyons and mountain peaks. Elevations in the district range from 6800 to 7800 ft.
The geology and mineralization of the Jicarilla mining district has been described in several reports (Ryberg, 1968; Johnson, 1972; Seagerstrom and Ryberg, 1974; North and McLemore, 1986; McLemore et al., 1992). The area is currently being mapped and sampled by the author and results reported here are preliminary. The purpose of this project is to (1) update McLemore et al. (1992), (2) describe the magmatic activity and gold resources within the Jicarilla district, (3) present some hypotheses on the origins of these mineral deposits, (4) present new age dates of the igneous rocks, (5) understand the relationship of the placer gold deposits to the vein deposits, and (6) understand the relationship of the Jicarilla district with magmatic activity and mineralization in the North American Cordilleran alkaline-igneous belt.
The predominant intrusive rock in the district is a porphyritic dacite and granodiorite to monzonite, intruded by a variety of dikes, sills, and laccoliths. Mafic xenoliths are common locally in the intrusive coarse-grained granodiorite. New, unpublished ages of igneous rocks from the Jicarilla Mountains in the northern Lincoln County porphyry belt range from 39.45±0.02 and 40.72±0.04 Ma, which is one of the oldest GPM districts (40Ar/39Ar, V.T. McLemore, report in progress).
The igneous rocks in the Jicarilla Mountains are subalkaline to alkaline, metaluminous to peraluminous. The samples plot as I or S type granites and plot within the VAG and active continental margin. The samples have linear, slightly enriched LREE chondrite-normalized patterns, with no europium anomaly. Initial strontium isotopes and neodymium isotopes are similar to other GPM districts (0.70565-0.70578, Allen and Foord, 1991).
Three types of deposits have been identified in the Jicarilla Mountains, as defined by McLemore (1996, 2015, 2018a) and McLemore and Lueth (2017):
- GPM polymetallic, epithermal to mesothermal veins
- GPM iron skarns and replacement deposits
- Placer gold deposits.
GPM polymetallic, epithermal to mesothermal veins are mostly fissure pyrite-gold veins, narrow (less than 2 m wide), north- to northeast-trending, with variable gold and low amounts of copper, lead, and zinc sulfides. Quartz and calcite are rare in most veins, although silicification and clay alteration are common.
The GPM iron skarns and replacement deposits are found throughout the Jicarilla Mountains replacing Yeso and San Andres limestone and siltstone and are spatially associated with the igneous rocks. These deposits typically consist of magnetite, hematite, limonite, and martite in a gangue of calcite, quartz, fluorite, tremolite, actinolite, pyrite, phlogopite, and locally malachite, azurite, and chalcopyrite. The iron ore grade is typically less than 50%.
The Jicarilla district contains large resources of residual, alluvial, and stream placer gold deposits. These placers formed by weathering of the lode gold deposits and the dacite and granodiorite to monzonite porphyry, which underlies much of the area. The dacite and granodiorite to monzonite porphyry apparently contains fine-grained gold disseminated within the matrix. In the placers, gold appears to be controlled by reddish soil streaks within the alluvium above white clay lenses. The alluvium is very poorly sorted and consists of angular to rounded boulders, cobbles, and grains of the dacite and granodiorite to monzonite as well as pieces of magnetite-hematite derived from nearby iron-replacement deposits. Many active streams in the Jicarilla Mountains also contain small placer gold deposits. Recovery of the placer gold is difficult because of the fine grain size of the gold, abundance of clay, and lack of water.
The Jicarilla district has future mineral-resource potential for gold in veins, as described by McLemore et al. (1991) and McLemore (2018b). It is concluded that the mineral-resource potential is very high with a high level of certainty for placer gold and high with a moderate level of certainty for lode gold in the Jicarilla district. The mineral-resource potential is moderate with a high level of certainty for iron and low with a low level of certainty for molybdenum and tellurium in the Jicarilla district (McLemore, 2018b).
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- McLemore, V.T., 2017, Mining districts and prospect areas of New Mexico: New Mexico Bureau of Geology and Mineral Resources, Resource Map 24, 65 p., scale 1:1,000,000.
- McLemore, V.T., 2018a, Rare Earth Elements (REE) Deposits Associated with Great Plain Margin Deposits (Alkaline-Related), Southwestern United States and Eastern Mexico: Resources, 7(1), 8; 44 p., doi:10.3390/resources7010008; http://www.mdpi.com/2079-9276/7/1/8 link http://www.mdpi.com/2079-9276/7/1/8
- McLemore, V.T., 2018b, Mineral-resource Potential of proposed U.S. Bureau of Land Management exchange of lands with New Mexico State Land Office: New Mexico Bureau of Geology and Mineral Resources, Open-file Report OF-598, 152 p., https://geoinfo.nmt.edu/publications/openfile/details.cfml?Volume=598
- McLemore, V.T. and Lueth, V., 2017, Metallic Mineral Deposits; in McLemore, V.T., Timmons, S., and Wilks, M., eds., Energy and Mineral deposits in New Mexico: New Mexico Bureau of Geology and Mineral Resources Memoir 50 and New Mexico Geological Society Special Publication 13, 79 p.
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Updated June 24, 2019