Luna County, New Mexico
One of the last counties to be officially created in the state of New Mexico, Luna County is located in the far southwest corner of the state, abutting Mexico along its southern border. Once part of Grant County, rivalries between Silver City (now in Grant County) and Deming (now county seat of Luna County) resulted in the creation of Luna County in 1901, named for the politician who actively sought its creation.
This description from the website of Rock Hound State Park, located in the Little Florida Mountains (11 miles southeast of Deming) captures the feel of this region:
The remote southwest corner of New Mexico, south of I-10, is one of the least-visited parts of the state - there are few roads or villages, just lifeless mountain ranges separated by desert basins, dry lake beds and lava deposits
The Luna County seat, Deming, is about the size of Taos, and nothing like a ghost town. In addition to an impressive courthouse, it has several museums and national historic sites, adding to its charm. Some of these relate to the Mexican-American Border War, when Mexican revolutionary Pancho Villa led a raid on Columbus (a small town close to Deming) in 1916.
As in many other New Mexico counties, economic mining operations began in the late 1800s with the advent of railroads. The first recorded American mining operations began in 1876. Although gold and silver were primary attractions for prospectors, economic deposits of lead, zinc, manganese, copper and fluorospar (fluorite) were also developed in the 20thcentury.
Present-day mining in Luna County mines focuses on lead, zinc and silver. According to data from the USGS, about 60 mines are currently in production in Luna County of about 88 identified. There are almost 6000 closed mining claims. For more information, visit HERE (Mindat.org) and HERE (the Diggings). The major mining districts of Luna County are shown in the map below from Griswold (1961).
Overview of Luna County Geologic Setting
Luna County is part of what geologists term the Basin-and-Range region, an area of the southwestern US characterized by extensional (pull-apart) faulting. The extensional stresses result in series of fault block mountains related to adjacent fault basins. Millions of years before the active faulting near Earth’s surface occurred, higher heat flows generated magmatic intrusions at depth, resulting in the emplacement of granitic and granodioritic plutons. Magmatism occurred throughout the region into the Tertiary and Quaternary periods.
In Luna County the fault block mountains expose sequences of rocks ranging from Precambrian through Mesozoic in age, mostly sedimentary rocks like shales, limestones, and sandstones. Alluvial (stream-related) sediments have infilled the fault basins, burying the fault block mountains in a sea of sand.
Economically valuable mineral deposits occur where these older rocks were intruded by granitic magma, and hot, aqueous solutions rich in elements such as gold, silver, copper, lead and manganese flowed around the bodies, and were injected into cracks and veins where they later crystallized. Mineralized rocks are visible only in the fault block mountains that outcrop above the surrounding sediments.
Other interesting but less economically valuable mineral deposits occur where surface waters percolate into the older volcanic and sedimentary rocks, dissolving silica and reprecipitating it as quartz, chalcedony and agate, either in seams or as nodules (geodes) in a host rock.
Although many economic minerals (lead, silver, tungsten, manganese minerals) have been found in Luna County, most mineral and rock collectors have focused on the beautiful “thunder eggs” found at the Baker Ranch site. Taos Rockers has an extensive collection of Baker Ranch agate geodes, all legally obtained and cut and polished in the state of New Mexico. Pink chalcedony and Cooks Peak fluorite from Luna County are also available.
Cooks Peak Fluorite
Cooks Peak fluorite (photo above) is from the Cooks Peak mining district. The formation of fluorite appears to post-date the earlier silicic magmatism, and to be temporally related to Quaternary basaltic volcanism. Fluorite deposits occur in veins related to faulting, often accompanied by quartz and other silica deposits.
Chalcedony is one of several microcrystalline forms of silica. Others include agate and jasper. In chalcedony, the quartz crystals develop in parallel, forming fibrous aggregates, often growing radially from the nuclei. Read more about chalcedony HERE.
The Luna County pink chalcedony (photo above) looks almost exactly like ribbons of soft-serve ice cream – think DQ strawberry!
Are you a rock hound wandering through southeast New Mexico? Then a must-visit site is the Basin Range Volcanics Geolapidary Museum located on Stirrup Road SE, in Deming, New Mexico, in the Carrizialillo mining district. This is the home of the Baker Egg Ranch “thundereggs” (photo above), lovingly and meticulously documented by owner Robert Colburn, aka “Paul the Geode Kid.” You might want to give them a call to make sure they’re open (505) 546-4021.
Robert Colburn has painstakingly documented his studies of these beautiful agate geodes in his book The Formation of Thundereggs, available on his website and as a CD. Mindat.org also has information on the Baker geodes, click HERE.
Luna County Mining Districts
Please note that the minerals listed for each mining district do not necessarily occur as large, specimen-quality, collectible pieces. Many are fine-grained and observable only by microscopic or x-ray study.
argentite, chalcocite, chlorargyrite, gold, silver, stephanite, stromeyerite
Cooks Peak district
actinolite, alunogen, andesine, anglesite, ankerite, apatite, aragonite, argentite, augite, barite, biotite, calcite, cerussite, chalcedony, chlorargyrite, chlorite, chrysocolla, copper, cuprite, dolomite, epidote, fluorite, galena, glauconite, gypsum, hematite, hemimorphite, hypersthene, iddingsite, limonite, magnetite, microcline, sericite, natrojarosite, nitratine, olivine, orthoclase, plattnerite, plumbojarosite, pyrite, quartz, sanidine, smithsonite, sphalerite, tenorite, titanite, vanadinite, zoisite
Florida Mountains district
albite, anorthoclase, argentite, augite, azurite, bismuthinite, cerussite, chalcopyrite, chlorargyrite, coronadite, fluorite, galena, glauconite, hollandite, ilmenite, labradorite, magnetite, malachite, muscovite, psilomelane, pyrite, quartz, smithsonite, sphalerite
Fluorite Ridge district
albite, biotite, calcite, fluorite, glauconite, sericite, orthoclase, pyrite, quartz
Little Florida Mountains district
apatite, barite, calcite, cryptomelane, fluorite, forsterite, hematite, manganite, opal, psilomelane, pyrolusite, quartz, stibiconite, thomsonite, zircon
Tres Hermanas district
anglesite, antigorite, aragonite, argentite, arsenopyrite, azurite, biotite, bromargyrite, calcite, cerussite, chalcopyrite, chlorargyrite, chlorite, conichalcite, cordierite, cummingtonite, diopside, dumortierite, epidote, fluorite, fornacite, galena, gehlenite, gold, grossular, hematite, hemimorphite, hydrogrossular, hydrozincite, magnetite, malachite, merwinite, mimetite, molybdofornacite, monticellite, muscovite, oligoclase, orthoclase, prehnite, pyrite, pyrolusite, quartz, scapolite, silver, smithsonite, sphalerite, spurrite, titanite, vesuvianite, willemite, wollastonite, wulfenite, zincite, zoisite
anglesite, argentite, augite, aurichalcite, beryl, beyerite, bismutite, calcite, cerussite, chlorargyrite, conichalcite, descloizite, erythrite, fluorite, galena, gehlenite, gold, grossular, helvite, hematite, hemimorphite, hubnerite, kettnerite, limonite, mimetite, muscovite, psilomelane, pyrite, pyromorphite, quartz, scheelite, serpentine, siderite, silver, smithsonite, spessartine, stephanite, stolzite, talc, tremolite, vanadinite, vesuvianite, wolframite, wulfenite
For more in-depth geological information about Luna County, check out these resources. Many additional scholarly articles are available through the New Mexico Bureau of Mines and Mineral Resources.