Reconnaissance sampling of high calcium (HC) limestones in New Mexico has been reported by Siemers (1982), Jicha (1956), and Kottlowski (1962). Numerous articles describe the limestone units in and near the state, such as Armstrong (1958) for west-central New Mexico, Mississippian and Pennsylvanian Systems in the state (Armstrong, and others, 1979), Pennsylvanian units in south-central New Mexico (Wilson, 1989), Pennsylvanian strata in southwestern New Mexico and southeastern Arizona (Kottlowski, 1960), Pennsylvanian section in Big Hatchet Mountains (Thompson and Jacka, (1981), Paleozoic strata in Big Hatchet Mountains (Zeller, 1965), Mississippian in southwestern New Mexico and southeastern Arizona (Armstrong, 1962, 1978), Mississippian in San Juan Mountains (Armstrong, 1978), Mississippian and Pennsylvanian rocks in Sangre de Cristo Mountains (Sutherland, 1963), Pennsylvanian System in New Mexico (Bachman, 1975), Pennsylvanian and Wolfcampian rocks in southeastern New Mexico (Meyer, 1966), Paleozoic rocks in Manzano Mountains (Myers, 1973), and Paleozoic strata in the Sacramento Mountains (Pray, 1961). Other shorter articles report on Paleozoic outcrops of individual quadrangles, and numerous reports detail the thick Permian strata in southeastern New Mexico in the Guadalupe Mountains; many of these carbonate rocks are dolomite or dolomitic

HC limestones best serve for usage in sulfur removal, either directly or converted to lime. The latter is an important basic chemical utilized also in production of glass, paper, alkalies, metallurgical flux, calcium carbide, and for water purification plants. The copper smelters in southwestern New Mexico are heavy users of lime for flux. HC limestone may meet the requirements of dimension stone and can be used as crushed stone for aggregate, to make cement, and as “lime” for soil conditioning, although less pure limestone can be quarried for these purposes.

HC limestone contains at least 95 percent calcium carbonate (about 53.22 % CaO) and less than three to five percent magnesium carbonate; limits for other impurities are alumina, one percent; silica, two percent; sulfur, 0.05 percent; phosphorous, 0.02 percent; and iron oxide, about one percent. The chemical and physical requirements differ slightly depending upon the ultimate use.

Quick and hydrated lime, obtained by calcination of HC limestone, are low cost, flammable, perishable products. Safe transportation is expensive and, with the low price of the bulk material, makes shipping over long distances uneconomical. New Mexico, with only two large metropolitan centers (Albuquerque and El Paso) in or close to the state and a relatively sparse number of industries, is unfavorably located for most large usage of chemical- and industrial-grade lime, except for cement plants. However, the lack of a lime-producing plant in New Mexico has resulted in long-distance shipping from Arizona to a powerplant in the Four-Corners region of northwest New Mexico.

Usage for Flue-Gas Desulfurizaton

The Clean Air Act of 1990 established requirements for electric utilities requiring SO2 emissions to be halved by flue-gas cleaning systems and fuel modifications. These apply to all powerplants, even those fired by low-sulfur (one percent or less sulfur) coal. Using limestone in scrubber systems can remove 95 percent of the sulfur, and lime (CaO) can remove 98 percent. General estimates are that to remove a ton of sulfur takes four tons of limestone and can result in 14 tons of waste material consisting largely of impure gypsum. In regions where landfill sites are costly (perhaps as much as $250,000 per 4,000 m²), production of byproduct gypsum may be a financial alternative to throwaway solid waste (Ellison and Kantze, 1993).

Most limestone used for scrubbers should be 93 to 96 percent calcium carbonate, have less than three to six percent magnesium carbonate, and be free of fluorine, selenium, and mercury.

New Mexico has numerous large deposits of gypsum (Weber and Kottlowski, 1959), therefore flue-gas desulfurization byproduct gypsum, mainly to produce gypsum board and portland cement, probably would not be competitive.

New Mexico has three large coal-fueled powerplants. Two in the northwestern corner of the state west of Farmington, are the Arizona Public Service Co. Four Corners Plant and the Public Service Co. of New Mexico San Juan Plant. The Escalante Plant of Plains Electric Coop, is in west-central New Mexico, between Grants and Gallup.

The Four Corners Plant can produce 2,269 megawatts of electricity and uses about 7,711,111 t of coal per year from the adjoining Navajo Mine of BHP-Utah International Inc. The coal averages about 4,864 kcal/kg, 0.78 percent sulfur, and 22.2 percent ash. To reduce the sulfur emissions, the plant uses lime from Tucson, Arizona. The lime is shipped by railroad to Gallup, New Mexico, then hauled by truck to the powerplant. Waste from the scrubbers is thickened to almost solid calcium sulfate, fly ash is added, then trucked to the Navajo Mine and deposited in the stripped pits.

The San Juan Plant is rated at 1,710 megawatts and uses about 5,443,108 t of coal per year from the adjoining San Juan Mine and the nearby La Plata Mine, both operated by BHP-Utah International, Inc. The coal contains about 5,303 k cal/kg, 0.74 percent sulfur, and 21.3 percent ash. Soda ash trucked from Wyoming is used in the scrubbers to produce sulfuric acid. Waste ash is placed in the stripped pits of the San Juan Mine.

The Escalante Plant, rated at 235 megawatts, uses about 807,394 t of coal per year, shipped by rail from the Lee Ranch Mine of Hanson Natural Resources Co. The coal yields about 5,237 kcal/kg, 0.7 percent sulfur and 15.7 percent ash. Limestone (Permian, San Andres Limestone) for the plant is quarried on the southwest side of the Zuni Mountains, trucked to the plant, and added to the scrubber system; the waste sludge of calcium sulfate, is placed in a landfill, and covered by soil and vegetation. All of the ash is shipped via railroad and truck to the Tijeras cement plant of Holnam, Inc. east of Albuquerque.

In eastern Arizona, three powerplants near New Mexico are supplied with New Mexico coal. These are the Cholla Plant of Arizona Public Service Co. at Joseph City; the Coronado Plant of Salt River Project near St. John, and the Apache Station Plant of Arizona Electric Power Cooperative near Cochise.

Distribution of Limestones

Limestones crop out or are near the surface in about one-fourth of the state; they range in age from the thin dolomitic limestone lenses in the Cambrian part of the Bliss Sandstone to Cenozoic travertine, calcareous tufa, and caliche. Some of the HC limestones of Mississippian, Pennsylvanian, Permian, and Early Cretaceous Ages exceed 30 m, and locally even 305 m, in thickness. The purity ranges from almost pure calcite to calcareous tufa and caliche, which in places contain as much as 40 percent insoluble residues.

Locating outcrops of HC limestone is no problem, but the most economical deposits should fulfill three requirements: (1) be easily mined by open-pit methods; i.e., should cap extensive mesas and underlie thin overburden; (2) be within 12.4 km of a railroad and accessible by good trucking roads; and (3) be within short distance of a gas pipeline. The intersections of highways, railroads, and gas pipelines with limestone outcrop areas determine most of the deposits investigated. Some limestones in relatively inaccessible area were sampled to obtain a fairly complete stratigraphic coverage of limestones in the State.

Limestones checked and sampled as possible economic HC deposits include Cenozoic travertine of the Lucero Mesa, Mesa del Oro, and Ladron Mountains areas; the caliche “caprock” of the Llano Estacado; the Tertiary algal limestone of Apache Valley, limestone beds in the northern and central New Mexico Upper Cretaceous sequence; the Lower Cretaceous limestones of southwestern New Mexico; the Jurassic Todilto limestone southeast of Grants and east of Santa Rosa; favorable Permian, Pennsylvanian, Mississippian limestones in the Robledo, Guadalupe, Sacramento, Peloncillo, Florida, Tres Hermanas, Oscura, Sandia, Manzano, Sangre de Cristo, Ladron, and Magdalena mountains, Border Hills, Cerros de Amado, and near Luna; and the El Paso Limestone in the Victorio Mountains. The samples collected are merely a partial testing of the limestones in these areas and are only a rough guide to commercial possibilities.

Pre-Mississippian Limestones

Small lenses of carbonate rocks, dolomitic in most places, are present amid rocks of Precambrian age in widely scattered areas of southern New Mexico, as in the Redrock area and near Hembrillo Canyon in the central San Andres Mountains. Thick Precambrian quartzite and schist sequences of the central and northern parts of the state lack appreciable amounts of limestone.

Fossiliferous pre-Mississippian post-Precambrian strata crop out only in southwestern and south-central New Mexico, the northeastern-most outcrops being in the northern San Andres and southern Oscura mountains. The oldest unit is the Bliss Sandstone, of Cambrian and Ordovician Ages; locally, a few limy beds are present near the top of the sandstone, sensu stricto. The overlying El Paso and Montoya formations of Ordovician Age are chiefly of dolomite and magnesium limestone. The El Paso Limestone may contain some local HC limestone beds; it thickens, under a pre-Montoya erosion surface, from a knife-edge at the northern sections (in the northern San Andres Mountains) to more than 459 m near El Paso, and is about 262 m thick in the latitudes of Las Cruces and Deming. Analyses of limestones of the El Paso Group from scattered localities (Kottlowski, 1957) show more than ten percent magnesium carbonate, and in most samples at least 5 to 10 percent insoluble residues, chiefly of quartz silt. Selected limestones from the El Paso Limestone in the Victorio Mountains, however, contain almost 94 percent calcium carbonate.

Except for a few beds of impure limestone in the upper Cutter Formation, the Montoya Dolomite is entirely of dolomite or dolomitic limestone (except for basal dolomitic sandstones), although locally some beds are magnesium limestone. Limestones in the Montoya from the Cooks Peak and other areas contain more than five percent magnesium carbonate.

The Silurian Fusselman Dolomite is more than 262 m thick in the triangular area from the Victorio Mountains southeast to the Franklin Mountains, but it thins rapidly northward and westward as a result of erosion during early Devonian and (or) late Silurian time. Some of its carbonate-rock beds are as calcic as dolomitic limestone, but all its units appear to be high in magnesium (Kottlowski, 1957), with dolomite dominating. Devonian rocks typically are calcareous shales and calcareous siltstones; the only limestone beds are impure, thin, and lenticular. Silty dolomites, however, are present in the Onate Formation. Pre-Mississippian limestones are not likely sources of HC lime in New Mexico.

Mississippian Limestones

Mississippian strata in northern and central New Mexico crop out as discontinuous remnants beneath an erosion surface of late Mississippian and early Pennsylvanian Ages (Armstrong, 1955, 1958). Some of the crinoidal calcarenites in the Sandia, Ladron, Magdalena, Nacimiento, and Sangre de Cristo mountains appear to be relatively HC limestone, except for sparse to abundant chert lenses and nodules. Locally, these encrinites are thick (6.6 to 16.4 m) and cap low benches below ledges and slopes eroded on the shaly lower Pennsylvanian strata. Samples from cherty Mississippian limestones near Bishop’s Lodge (Kottlowski, 1962) in the southwestern Sangre de Cristo Mountains and along Las Huertas Creek Canyon in the northeastern Sandia Mountains contained only 91 percent calcium carbonate, 2 to 6 percent magnesium carbonate, and 1.5 to 5.6 percent silica. These samples are representative of the total thickness of Mississippian limestones at these localities; selected purer samples have insoluble residues (quartz and clay) of 0.3 to 0.7 percent. In the southeastern Sangre de Cristo Mountains along Gallinas Canyon east of Montezuma, as reported by Baltz and Read (1960), the Cowles Member of the Tererro Formation (upper unit of the Mississippian) is as much as 13.1 m thick and consists of a crinoidal calcarenite with insoluble residue (grab sample) of about 0.6 percent.

The Mississippian Lake Valley Formation exceeds 32.8 m in thickness in the Sacramento Mountains (Pray, 1961), southern San Andres Mountains (Kottlowski and others, 1956), Cooks Peak-Lake Valley area (Jicha, 1954), and Silver City-Santa Rita district. Similar limestones, partly correlative with the Lake Valley Formation, are placed in the Escabrosa Group by Armstrong (1962). This group includes as much as 328 m of carbonate rocks in the Big Hatchet and Animas mountains (Figure 1) and Klondike Hills, and locally it may exceed 164 m in the Peloncillo and Tres Hermanas mountains. Analyses of these crinoidal strata show them to be HC; near Alamogordo millions of tons are available a short distance from a gas line and railroad.

The Mississippian strata in the Franklin Mountains are mainly siliceous impure limestone of the Rancheria Formation. To the north along the Rio Grande, the Mississippian section is thin or absent in the Robledo and Caballo Mountains.

Pennsylvanian Limestones

The sedimentary beds of Pennsylvanian Age are thick, though variable, in New Mexico (Thompson, 1942; Kottlowski, 1960; Read and Wood, 1947; Armstrong, and others, 1979) and crop out in most of the major mountain ranges. The majority of the formations include HC limestones, and in many areas these limestones underlie dip-slope mesas where they could be quarried from open pits after removal of only thin overburden. Extensive outcrops of Pennsylvanian limestones are found in the Sangre de Cristo, Nacimiento, Sandia, Manzano, Los Pinos, Ladron, Magdalena, Oscura, San Andres, Sacramento, Franklin, Robledo, Big Hatchet, and Peloncillo Mountains, the Cerro de Amado, and the Silver City-Santa Rita area. Smaller outcrop areas are scattered in many other mountain ranges. An average section of the Pennsylvanian strata would be 328 to 984 m thick and consist of a basal clastic unit in which most of the limestones are arenaceous, a thick medial unit of cherty to HC limestones, and an upper unit of interbedded marine limestones and shale-sandstones beds (i.e., siliciclastic beds). The medial unit makes ledgy cliffs in many mountain ranges. Dip slopes of the tilted fault-block ranges are, in many places, of massive limestones in the upper unit. The best locations for quarries (such as that of the Tijeras Cement Plant east of Albuquerque) are in HC limestones of the middle Pennsylvanian, where the interbedded, shaly, clastic strata have been removed by erosion, leaving thick, pure limestones near the surface covered by only thin overburden. Such possible quarry locations are present in most of the mountain ranges listed.

Permian Limestones

The basal Permian strata in many parts of south-central New Mexico are the interbedded red beds and marine limestones of the Bursum Formation (Wilpolt and Wanek, 1952; Thompson, 1954). Southward from the Oscura Mountains, this formation and correlative units include some massive HC limestones that are near transportation facilities in the northern Sacramento Mountains (Otte, 1959) and Robledo Mountains (Kottlowski, 1960). The upper part of the Horquilla Limestone, containing hundreds of meters of massive limestone, is of early Permian Age in the Big Hatchet (Zeller, 1958) and Peloncillo mountains.

The basal Permian in most of north-central New Mexico is within the Abo Redbeds, the Sangre de Cristo Formation, or the Cutler Redbeds. The Abo Redbeds grade southward into the Hueco Formation, which includes thick HC limestones in the San Andres (Kottlowski and others, 1956), Franklin (Harbour, 1960), Robledo, Dona Ana (Kottlowski 1960), Florida, and Tres Hermanas Mountains.

The Yeso Formation, conformable on the Abo Redbeds, consists of interbedded gypsum, brown sandstone, pinkish shale, and thin, impure limestone. The amount and thickness of the limestone units increases southward. In most areas, however, the limestones of the Yeso appear to be dolomitic and silty. Outcrops of the Yeso Formation locally may contain HC limestone. In the central part of the New Mexico, the Yeso is overlain by the Glorieta Sandstone and it in turn by the San Andres Limestone. In south-central New Mexico, however, the Yeso grades up into the San Andres Limestone. Several thin, lenticular, arenaceous beds in the upper Yeso and lower San Andres are called the Glorieta or Hondo Sandstone.

The San Andres Limestone and uppermost beds of the Yeso crop out over extensive areas in the central, south- central, and southeastern parts of the state. The formation is the surface bedrock of Chupadera and Jumanes Mesas, the higher mesas east of Socorro, and on the southeast slope of the Los Pinos Mountains; the wide plateau (on the west edge of the High Plains) extending south from near Vaughn onto the east slopes of the Jicarilla, Capitan, White, and Sacramento Mountains; and much of the Otero Mesa-western Guadalupe Mountains area of southeastern Otero County. The San Andres Limestone caps dip-slope cuestas or hogback ridges in or bordering the Zuni, Nacimiento, Sandia, San Andres, Fra Cristobal, and Caballo Mountains, Lucero Mesa, Sierra Cuchillo, and the Phillips Hills. The formation crops out on the Glorieta Mesa escarpment and is present in small outcrop patches along Nogal Canyon in the volcanic San Mateo Mountains and on the south side of Horse Mountain amid the volcanic rocks of the Datil Plateau.

Descriptions of the carbonate-rock beds of the San Andres Limestone indicate that most individual beds are dolomitic limestone or magnesium limestone (i.e., more than five percent magnesium carbonate). Beds quarried near Gallinas in central New Mexico, for example, have (Vincent C. Kelley, 1957, written communication) 20.2 percent magnesium oxide, 32.20 percent lime, and 3.26 percent silica. In the central Guadalupe Mountains, Boyd reported that samples typical of the San Andres Formation contain 1.1 to 0.5 percent SiO2, 40.6 to 45.7 percent MgCO3 and 53.1 to 58.8 percent CaCO3- nearly pure dolomites. In contrast, however, samples from the type section of the San Andres Limestone, in Rhodes Canyon of the San Andres Mountains, gave (Kottlowski, 1957) analyses high in SiO2 (13.2 percent) quartz sand and silt for the basal 31 m of dolomitic limestones, but an average CaO content of 53.5 percent for the overlying 72 m of relatively pure limestone containing insoluble residue 1.3 percent. By contrast the upper 84 m of the formation contains 20.3 to 28.7 percent MgCO3. On the eastern slopes of the Sacramento Mountains, and in oil tests drilled in that area, the lower part of the San Andres Limestone is reported as chiefly limestone, whereas the upper beds are mainly dolomite. Extensive sampling of the widespread San Andres Limestone outcrops should locate some HC limestones in places where they could be quarried economically.
Northward from the type section (Lee and Girty, 1909; Needham and Bates, 1943; Kottlowski and others, 1956), the San Andres Limestone thins from the 197 to 246 m in the northern San Andres Mountains to 36 m in the southeastern Zuni Mountains (Figure 2) and 4.9 m on northern Glorieta Mesa. Interbeds of gypsum are exposed in such areas as Mesa del Oro (Jicha, 1958), Lucero Mesa (Kelley and Wood, 1946), and southeast Chupadera Mesa (Wilpolt and Wanek, 1952), suggesting deposition in nearshore lagoonal evaporite basins. Toward the southeast, the San Andres Limestone thickens in the Guadalupe Mountains to about 394 m (Hayes, 1959; Boyd, 1958). Triassic or younger strata overlie eroded parts of the San Andres Limestone except in the eastern part of the state, where the Guadalupian Bernal Formation or Artesia Group rests upon the San Andres.

The interbedded red beds, gypsum, and dolomitic rocks of the Artesia Group and Bemal Formation crop out along the Pecos River Valley from Carlsbad northward, and in the Guadalupe Mountains. The carbonate-rock beds are thin, lenticular, impure, and dolomitic. Correlative basinal beds of the Cherry Canyon and Bell Canyon Formations crop out in the state only along the Texas stateline in the southern Guadalupe Mountains. The limestone members of these formations locally are as much as 30 m thick. The carbonate rocks of the Cherry Canyon Formation are impure or dolomitic (Newell and others, 1953); the Rader and Lamar Limestone Members of the Bell Canyon Formation, however, include HC limestones (Kottlowski, 1962). that crop out on the southeastern side of the Guadalupe Mountains. The basinal Yeso equivalent, the Bone Spring Limestone, crops out in the Brokeoff Mountains of the western part of the Guadalupe Mountains, a relatively inaccessible area. Analyses of the upper part of the Victorio Peak Member of the Bone Spring Limestone show that it is a HC limestone.

The massive Capitan reef limestone crops out along the southeast Guadalupe Mountains escarpment and is 492 to 656 m thick if measured vertically without regard to the dip of the reef-flank beds. This limestone, according to Newell and others (1953), is mainly unstratified calcific limestone, whereas the bordering reef-talus beds contain high percentages of dolomite. They listed 11 analyses of the Capitan reef rock that average 98.2 percent CaCO3, 1.3 percent MgCO3, and 0.4 percent SiO. The reef appears to be a huge mass of HC limestone that is, near gas fields, a railroad, and U. S. highways. Much of the outcrop area is within Carlsbad Caverns National Park, but the outcrop belt extends for about 6 km northeast of the Park and from the Park southwestward to the Texas stateline. Cursory sampling of the Capitan Limestone, however, suggests that the limestone and dolomite facies are complexly mingled. Whereas most of the reef-flank beds to appear to be dolomitic, or at least magnesium-rich, some of the reef-core beds also contain appreciable amounts of MgCO3. A chip-channel sample (Kottlowski, 1962) of the reef core in Dark Canyon yielded 16 percent MgCO3. Where the reef-core facies is overlain by sandstone tongues of the Yates and Tansill Formations, the core appears to be dolomitic and siliceous, as along North Slaughter Canyon. Along parts of McKittrick, Rattlesnake, and West Slaughter canyons, the reef-flank beds, especially the more massive ones, appear to be chiefly limestone, as determined by dilute HCl and by specific gravity tests (in heavy liquids).

The Ochoan Castile and Rustler Formations crop out above the Guadalupian rocks in the Delaware basin, forming low hills between the valleys of Black River and the Pecos River south of Carlsbad. The Rustler Formation is of dolomite, gypsum, and siltstone, whereas the underlying Castile Formation consists of gypsum, interlaminated gypsum and limestone, and some thin beds of limestone. In the subsurface, both formations include much anhydrite and some halite. Oddly, an analysis of basal limestone from the Castile Formation, as given by King, (1948), shows a HC limestone containing 96.63 percent CaCO3. Most of the Castile limestones are too thin and too intimately interlaminated with gypsum to be of commercial use.

In the southwestern corner of New Mexico, Permian rocks younger than the Hueco Formation crop out in the Big Hatchet, Peloncillo, and Animas Mountains. The section, as described in detail by Zeller (1958), consists of the Horquilla Limestone (of Pennsylvanian and Permian Ages), Earp redbeds, Colina Limestone, Epitaph Dolomite, Scherrer Sandstone, and Concha Limestone. Fusulinids date the upper Horquilla as Wolfcampian and the Concha Limestone as Leonardian. Yochelson (1956) identified Wolfcampian gastropods in the Colina Limestone from southeastern Arizona; the upper Horquilla Limestone, Earp redbeds, and the overlying Colina Limestone appear to be a sequence similar to that in the Robledo Mountains (Kottlowski, 1960), where the Hueco Limestone includes a tongue of the Abo redbeds. Both the Horquilla and Colina Limestones probably contain HC limestone beds but crop out in relatively inaccessible areas. A chip-channel sample from the Colina Limestone in the Peloncillo Mountains (Kottlowski, 1962) has large amounts of SiO2 and MgCO3, but the sample was collected in a metamorphosed zone near a granitic body.

The Epitaph Dolomite includes gypsum and siltstone interbeds and may be a southwestern correlative of the Yeso and Bone Spring Formations; no appreciable amount of HC limestone is known from the Epitaph Dolomite.

Likewise, the Concha Limestone appears, from the scant data available, to be too cherty and too dolomitic to contain high-calcium limestones.

Mesozoic Limestones

Limestones in Triassic rocks are limited to thin, lenticular, arenaceous to conglomeratic, limy beds in the Chinle and Moenkopi Formations of northwestern New Mexico and the Dockum/Chinle Group in the eastern part of the State.
In Jurassic strata, limestones are found in the Todilto Formation in northern New Mexico. Where typically developed, this formation consists of a lower limestone and an upper gypsum. The limestone, locally as much as 13.1 m thick, is dark, laminated, thin- to massive-bedded, fetid, and contains laminae of gypsum near the top. Near the western edge of limestone deposition, in Todilto Park close to the New Mexico-Arizona border, the limestone grades laterally from a 4.6-m-thick limestone bed into limy sandstone and siltstone. North of Todilto Park near Beautiful Mountain, Allen and Balk (1954) noted an extensive mesa capped by 2.3 to 4.6 m of Todilto limestone and estimated the reserves at 32.6 million t. These samples average 12.27 percent SiO2. Allen and Balk believed the silica is present as an arenaceous laminate in the lower foot of the limestone. They suggested that if this lower foot were discarded, the upper beds would be a HC limestone averaging 97.5 percent calcium carbonate.

Limestone of the Todilto Formation crops out along the northern edge of the Zuni Mountains from near Wingate to east of Grants. The limestone is 2.3 to 9.8 m thick in this area (average thickness of about 4.6 m) and has numerous laminae of sandstone, siltstone, and gypsum, as well as pods of uranium ore. Farther to the southeast, the limestone crops out along the north valley wall of Rio San Jose from near Mesita to north of Suwanee and in several isolated outcrops on the flanks of Mesa Redonda and Lucero Mesa. Thicknesses range from 1.6 to 5.2 m. Similar thicknesses are northeast of Acoma.

Along the north wall of the broad valley of Arroyo Colorado, limestone of the Todilto Formation is thick and caps extensive benches extending from Mesita southeast to Petoch Butte, which is near its southwest wedge-edge. Silver (1948) reported local thicknesses of 13.1 m. A chip-channel sample contained about 94.3 percent CaCO3 selective mining may yield a HC limestone.

East of the Rio Grande Valley, small patches and more extensive outcrops of the Todilto Formation are present northeast and east of the Sandia Mountains, near Lamy and Rosario Siding, and south of Galisteo. The limestone member is thin (1 to 2.6 m thick) and impure. Steeply dipping beds of the Todilto crop out along the west side of Sierra Nacimiento south of Cuba to White Mesa near San Ysidro; here the limestone member, a thin-bedded shaly unit, is 2.0 to 3.9 m thick and is overlain by interlaminated limestone and gypsum that grade up into the thick, massive gypsum member (Weber and Kottlowski, 1959). The Todilto is exposed north of Gallina in a northward structural extension of the hogback ridges near Cuba as well as to the east along the canyon of Rio Chama and two of its tributaries, Rio Puerco and El Rito. Outcrops of the Todilto Formation encircle Mesa Prieta in the Rio Chama area; the limestone member is lenticular, ranging from 0.3 to 5.9 m in thickness, and consists of lower dark shale grading upward from thin-bedded gray limestone into massive gray limestone; this in turn grades up into the gypsum member. Typically, the Todilto caps benches above cliffs of the Entrada Sandstone and below slopes cut in the Morrison Formation.

The Todilto Formation crops out in the hogback ridges along the southeast edge of the Sangre de Cristo Mountains near Las Vegas but is thin. On the south edge of Louisiana Mesa near the west border of Quay County east of Ima (sec. 18, T. 8 N., R. 27 E.), the eastern pinchout of the limestone member borders the valley of Alamogordo Creek. The limestone is 0.7 to 3.3 m thick and is a thinly laminated, platy to fissile bed containing paper-thin laminae of siltstone and gypsum. Amazingly, however, a channel sample shows almost 95 percent CaCO3 and only slightly more than one percent SiO2. The Todilto crops out as a ledge, capping the soft, brown to light-gray Wingate Sandstone, and is overlain by the slope-forming shales and sandstones of the Morrison Formation.

Cretaceous strata in New Mexico change abruptly from the sandstone-shale-coal, chiefly of Late Cretaceous Age, in northern and central areas southward to the marine limestones, cobble conglomerates, and reddish clastic rocks of Early Cretaceous Age in southwestern areas. Limy beds above the Dakota Sandstone are in the Mancos Shale, Mesaverde Group, and Lewis Shale in northwestern New Mexico, the Mancos Shale in central New Mexico, and the Graneros Shale, Greenhorn Limestone, Carlile Shale, Niobrara Formation, and Pierre Shale of the northeastern part of the State. These formations tend to contain more and thicker limestones from the west to the northeast.

Along the west edge of the San Juan Basin, limy beds in the Cretaceous section are thin, argillaceous limestone lenses or concretionary strata in the lower part of the Mancos Shale or in the Lewis Shale (Beaumont, 1954, 1955; Allen and Balk, 1954). In the Gallup-Zuni Basin, a 3.3 m-thick bed of fossiliferous impure limestone occurs near the base of the Mancos. Eastward into the Mount Taylor region and to the southeast edge of the San Juan Basin, the limy beds are only calcareous, fossiliferous sandstone and zones of limestone concretions. Along the northeast edge of the San Juan Basin, and in the eastward adjoining Chama basin, equivalents of the Graneros, Greenhorn, Carlile, and Niobrara are recognized (Dane, 1948). The Greenhorn Limestone member of the Mancos Shale consists of interbedded, gray, dense limestone and dark-gray calcareous shale; the limestone beds are as much as 0.8 m thick (Dane, 1960) and are described as a limonkic Globigerina biomicrite by Muehlberger and others (1960). Dane (1960) also noted some thin, gray, shaly limestones in the Niobrara calcareous shale member. None of the Cretaceous limestones of northwestern New Mexico are HC limestone. Burchard (1913) reported a lime kiln active near Kirtland; limy lenses in the Lewis Shale were quarried for this operation as well as coquina oyster beds at the top of the Pictured Cliffs Sandstone.

Only thin, impure limestones are found in the Cretaceous of the Carthage coal field (Wilpolt and Wanek, 1952), Caballo Mountains (Kelley and Silver, 1952), southern San Andres Mountains (Kottlowski and others, 1956), Cooks Range (Jicha, 1954), and Silver City area. Near the Capitan coal field in south-central Lincoln County on the east side of the Sierra Blanca volcanic complex, is a 19.7-m-thick sequence of dark-gray limestone is in the lower part of the Mancos Shale. Shale interbeds make up much of the sequence, and the limestone beds are impure.

Cretaceous strata near the border with Mexico include thick fossiliferous limestones, chiefly of Early Cretaceous Age. These limestones, and interbedded clastic units such as limestone-cobble conglomerate, sandstone, and tuff-breccia, range from hundred to thousands of meters in thickness in the East Potrillo (Bowers, 1960), Big Hatchet (Zeller, 1965), Little Hatchet, Animas, Peloncillo and Victorio Mountains, and in small outcrop areas on Cerro del Muleros, on the west edge of the West Potrillo Mountains, and in faulted areas of Sierra Rica and the Apache Hills. Large masses of Cretaceous relatively HC limestone are in remote localities, except the somewhat marly beds that encircle Cerro de Muleros near El Paso. The limestone used by the Southwestern Portland Cement Company from quarries near Cerro del Muleros is almost HC limestone, being barely too high in SiO2 (3.2 percent) and with considerable MgCO3 (2.1 percent). Higher, thick- bedded limestone from the Buda Formation, collected on the outskirts of Sunland Park Village, is similar in composition containing several percent too much SiO2 (3.7 percent) and clay (alumina 0.7 percent).

Cenozoic Limestones

Most of the Cenozoic sedimentary strata of New Mexico are of clastic rocks that are highly calcareous because of their derivation, in part, from pre-Cenozoic limestones. The calcareous rocks of Cenozoic age are classified as follows: (1) fresh-water lacustrine limestones, (2) spring deposits, calcareous tufa, and travertine, and (3) caliche blankets. With few exceptions, these nonmarine calcium carbonate deposits do not qualify as HC limestone because of their high content of clay and noncarbonate-rock sand and silt. Impure limestones are found in many of the Tertiary sedimentary units. For example, thin beds (several inches thick) and laminae of tuffaceous limestone and limy tuff are in the basal Tertiary beds of Robledo Mountains, a unit of interbedded red siltstones, gypsum, and tuff. Travertine and calcareous tufa spring deposits are extensive in the state: some of the larger deposits are those around Lucero Mesa and Mesa del Oro. The banded porous travertine of the northeast Lucero Mesa area has been quarried as travertine “marble” and makes an attractive ornamental stone. Jicha (1956) described similar spring deposits from the Mesa del Oro area and gave an analysis showing the CaCO3 content as 96.5 percent. The three samples that he combined for the analyses yielded insoluble residues of 0.3, 1.3, and 3.0 percent.

The travertine deposits on the northeast end of Lucero Mesa near South Garcia station were sampled extensively; only a few samples have less than 10 percent insoluble residues. The higher grade travertines are in thin lenticular beds. A representative chip-channel sample of a 5.6-m- thick “bed” (Kottlowski, 1962) shows about 85 percent CaCO3, 11 percent SiO2 and Al2O3, and almost 1 percent combined iron oxide and sulfur.

West of the Ladron Mountains, and overlooking Rio Salado to the south, massive-bedded and laminated travertine caps the Santa Fe Group and older beds, occurring along a north-south belt about 1.9 km wide and about 5.6 km long, underlying about 52 (km)² of upland plains. A chip-channel sample of the laminated limestone shows 99 percent CaCO3. Grab samples from other localities contain scattered to abundant grains of quartz silt.

The banded travertine deposits described by Jicha (1956) at the north tip of Mesa del Oro are in a rather anomalous situation for spring deposits. They cap the easily eroded Triassic red beds high above valleys carved in these red beds, and locally are overlain by Quaternary basalt flows. Apparently the travertine is not related to faults. Being erosional remnants, their original extent is not known, but they form continuous north-south belt about 3.1 km long and 1.2 km wide. About 4.3 to 6.2 km to the northeast of Mesa del Oro, and 0.6 to 3.1 km west of Lucero Mesa, high, isolated buttes are capped by a really small remnants of similar travertine. If these travertine deposits were a single continuous sheet during the late Tertiary, they covered an area of at least 91 (km)² and may be playa lake deposits, or relatively pure caliche capping an old erosion surface.

Several lenticular (reefoid?) stromatolitic limestones, locally in lenses as much as 13.1 m thick, are present in the Tertiary Palm Park Formation of the southwestern Caballo Mountains. In the valleys of Apache and Green Creeks, the Palm Park Formation, about 295 m thick, is unconformable on Paleozoic rocks and consists of three units: (1) a basal one-third of interbedded red siltstones and pebble to boulder conglomerates with clasts of Precambrian and Paleozoic rocks as well as of andesitic lavas, (2) a middle one-third of light blue-gray to purple porphyritic latite tuff, and (3) an upper one-third of pinkish tuffaceous sandstones and lenticular stromatolitic limestones. The mound-like masses of stromatolitic limestone appear to be high in calcium, with one chip- channel sample of a 13.1-m-thick mass yielding 97 percent CaCO3.

Caliche, widely used for road metal in the intermontane plateaus and the High Plains parts of New Mexico, is the only monolithologic calcium-carbonate rock inexpensively available. Finely banded (algal-like) and pisolitic travertine lenses are found in many localities in the caliche (Bretz and Horberg, 1949), especially in the “caprock” of the High Plains in eastern New Mexico. In most areas the relatively pure “limestone” is thin, 0.3 to 0.6 m, and lenticular. Bretz and Horberg reported an average of only three percent insoluble residues from 12 samples of the caprock caliche. Samples of the top 2½ zones (banded caprock, brecciated caprock, and upper chalky concretionary caliche) from three widely separated localities in southeastern New Mexico have an average insoluble residue of more than 31 percent. Selected fragments of the upper caprock may contain only 3 to 10 percent insoluble residues, but any appreciable thickness or lateral mass of the caprock appears to be high in siliceous impurities.

Thick (thicker than 0.66 m), extensive, and relatively HC caliche appears confined, except for localized deposits, to surfaces bordering the valley of the Rio Grande and its tributaries and to the Llano Estacado of eastern New Mexico and its isolated western remnants. The caliche of eastern New Mexico is more important economically, as it provides road metal and aggregate.

San Juan Mountains Southwest Colorado

The San Juan Mountains (Figure 3) are a dissected dome more than 62 km across. The mountains are primarily of Tertiary volcanic rocks, but Paleozoic rocks are exposed in the western and northern parts. The Paleozoic limestone outcrops bordering the Animas River are 37 to 44 km northeast of the Four Corners power plants. The Cambrian Ignacio Quartzite (33 to 49 m thick) rest unconformable on Proterozoic rocks. The Devonian Elbert Formation (6.6-23 m thick) is composed of calcareous shales and thin sandy limestones with salt casts. The Devonian Ouray Limestone (33-67 m thick) is a relatively pure, massive limestone. The Mississippian Leadville Limestone (33-49 m thick) is composed of crinoidal and dolomitic limestones.

The Pennsylvanian Hermosa Formation is a 656-m- thick series of alternating limestones, shales, siltstones and conglomerates. The limestones are generally massive, of marine origin, and commonly contain bituminous matter. Limestone beds range from 3.3 to 16 m in thickness.

Although the limestones along the Animas River north of Durango are the closest carbonate rocks to the two powerplants west of Farmington, it is doubtful that they could be utilized because the outcrop areas are environmentally sensitive forest lands, the highway for transporta¬tion goes through the scenic tourist city of Durango, and in many places the highway would be dangerous because of traffic from large trucks.

Acknowledgments

The writers thank George S. Austin, James M. Barker, and Gretchen K. Hoffman, New Mexico Bureau of Mines and Mineral Resources, and Chester Wrucke, U.S. Geological Survey for helpful comments, data, and corrections. Terry Telles typed the manuscript and Becky Titus drafted the figures.

Conclusions

New Mexico has ample amounts of HC limestone but no large quantities near the two present-day powerplants west of Farmington. The Escalente powerplant in west-central New Mexico does use Permian limestones for its flue-gas desulfurization.