|
Geological Survey Professional Paper 215
Geology of the Southern Guadalupe Mountains, Texas |
ECONOMIC GEOLOGY
The southern Guadalupe Mountains are not rich in natural resources. It seems unlikely that their rocks will ever be productive of oil or metals, however much scientific treasure they may yield to the geologist and paleontologist. The resource most worthy of investigation and conservation is ground water, as it makes life possible in a land that is otherwise barren.
ORE DEPOSITS
The almost complete absence of igneous rocks in the area has already been noted (pp. 102-103). There is a corresponding lack of mineralization, except at a few localities. One of these localities is at the prospect known as the Calumet and Texas mine, in the headwaters of Dog Canyon about a mile northeast of Lost Peak (pl. 3), where veins in the Carlsbad limestone contain copper minerals. The minerals have been prospected from time to time since about 1900, but the workings are small and had been abandoned before our visit in 1934. A brief examination of the locality was made, and a small collection of specimens was taken from material on the dumps. These specimens were submitted to Mr. Charles Milton, of the Geological Survey, who reports as follows:
There are three varieties of material:
1. Fine-grained, chocolate-brown, siliceous rock, impregnated with iron and copper oxides, the former more or less hydrous.
2. Buff to brown, clayey, bedded rock, with coatings of green and blue copper minerals. The blue mineral is azurite. The green mineral, which has a spheruilitic structure, is either aurichalcite 2 (Zn, Cu) CO, 3 (Zn, Cu) (OH), or zinc-bearing malachite (Cu,Zn)CO3. (Cu,Zn) (OH)2. The clayey rock itself has an appreciable content of zinc and may be a zinciferous clay, such as has been described from other western localities.
3. Siliceous rock, carrying a heavy coating of yellow, powdery substance. This mineral is beaverite, CuO.PbO.Fe2O3.2SO3.4H2O, As viewed under the microscope, it consists of minute grains, of high [refractive] index (greater than 1.78), with zero birefringence, in part with hexagonal, in part with cuboid shapes. An analysis of the grains showed the following composition:
Percent Insoluble 20.82 PbO 23.56 CuO 8.85 Fe2O3 19.45 SO2 18.32 H2O 7.09 CaO .86 MgO .15 Al2O3 and P2O5 .30
99.40
Field examination indicates that the deposit is not extensive, and the valuable minerals seem too diffusely spread through the rock to give economic value to the deposit. Moreover, the prospect is so far from any road that development would be expensive and difficult.
Two other smaller mineralized areas have been reported in the southern Guadalupe Mountains, but were not visited during the present investigation. According to Wallace Pratt,80
There are two other openings (shallow shafts) on mineralized limestone in the area; one is about a mile west of Bell Spring on the mountain flank, the prospector having camped at Bell Spring; the other opening is on the edge of the high plateau, a couple of hundred yards northeast of the trail from the Grisham-Hunter Lodge on South McKittrick Canyon to Grisham-Hunter Camp, at a point about a mile as the crow flies west of Grisham-Hunter Lodge. Both these openings uncover concentrated black iron oxides, with a trace of copper. Local tradition claims that silver also is present. The first described opening is in the upper part of the Bell Canyon formation and the second is in the Carlsbad limestone, at the base of a sandstone phase.
80Wallace Pratt, letter of January 1945.
FLUORSPAR
In the vicinity of the Pratt Lodge, and forming ledges at the bottom of McKittrick Canyon, are beds of dark limestone that probably belong to the Hegler limestone member of the Bell Canyon formation (section E—E', pl. 17). Here and there these beds contain vugs filled with a blue, crystalline substance, which, according to Charles Milton of the Geological Survey, is fluorite. He states that "in order to distinguish this positively from the similar-appearing and optically similar yttrocerite and yttrofluorite, tests were made for rare earths, but with negative results." The fluorite is too dispersed in the rock to be of any value. Its origin is unknown.
SALT
A few miles southwest of the southwest corner of the area of this report are some salt workings which represent the first mineral deposit opened near the southern Guadalupe Mountains, and the only one producing today. The workings were described by Richardson 81 in 1904, and were visited by John C. Dunlap of the Geological Survey in May 1946. Most of the data given below are taken from an unpublished report by Dunlap.
81Richardson, G. B., Report of a reconnaissance in trans-Pecos Texas north of the Texas and Pacific Railway: Texas Univ. Bull. 23, pp. 61-64, 1904.
The salt deposits are in small alkali flats or salt lakes lying a little west of the main alkali flats on the floor of the Salt Basin. The present workings are in the Zimpleman Salt Lake, which lies about a mile southwest of the southwest corner of the area studied, and a mile south of United States Highway No. 62. The lake is about half a mile long and a quarter of a mile wide. It is owned in part by Mrs. W. Z. Copprell, of New York, N. Y., and in part by the Texas and Pacific Railroad. At present it is under lease to Arthur Grable, of Van Horn, Tex. Older workings are in the Maverick Salt Lake, about two miles south of the Zimpleman lake. This lake is about a mile long and a quarter of a mile wide. It is owned by the heirs of S. A. Maverick. It was apparently the first deposit to be opened, but is not known to have produced any salt since about 1900.
The salt deposits were first opened about 1863, when Mexican residents of the El Paso area, in Texas and adjacent parts of Chihuahua, Mexico, opened roads to the deposits and began extraction of salt for household and other uses. Shortly thereafter, various attempts were made by individuals to file claims to the land, with the intention of obtaining a monopoly of the deposits. This resulted in bad feeling among the Mexican population, and much local political strife, and culminated in the so-called "Salt War" in 1877, when some claim holders and Texas Rangers were killed by a mob at San Elizario.82
82El Paso troubles in Texas: 45th Cong. 2d sess., H. Ex. Doc. 93, 1878. Raht, C. G., The romance of Davis Mountains and Big Bend country, pp. 208-214, El Paso, 1919.
When the area was visited by Richardson in 1903, the Zimpleman Salt Lake was in production, the salt being extensively used by ranchmen, and also by the amalgamation works at the Shafter silver mine, 150 miles to the south. "No careful records are kept of the amount of salt hauled away, but certainly immense quantities have been used, and apparently there is as much in sight as there was forty years ago [1863]."83
83Richardson, G. B., op. cit., p. 64.
According to Dunlap, records indicate almost continuous production from the Zimpleman lake by various lessees from 1911 to 1946. He states that Arthur Grable, the present lessee, believes that more salt has been produced since 1932 than in all the previous period. Dunlap estimates that the total production from the lake has been between 5,000 and 15,000 tons. The salt is now being used by ranchmen in the surrounding area for livestock, and is also being used in El Paso for various industrial purposes.
The Zimpleman Salt Lake occupies a shallow depression in one of the lower parts of the Salt Basin. The low, gently sloping banks that surround it are composed of sand, clay, and some gypsum. A dike one to two feet high has been built around the entire lake about 100 feet from the shore. A dike of equal height extends across the lake about 350 feet from the north end. In addition to these long dikes, shorter ones have been constructed at the north end and at the southwest corner to form brine vats. Corduroy roads with a gravel surface lead into most of the brine vats, thus providing access for trucks that are used to haul the salt.
On May 26, 1946, the entire surface of the lake, inside the outer dike, was covered with a crust of salt that averaged about half an inch thick. This crust was nearly free of wind-blown sand and clay and so must have formed since the heaviest sand storms in March. To judge by taste and appearance, the crust is mainly sodium chloride, although the somewhat bitter taste of sulfates can be detected in it. Brine is present immediately below the surface crust and this, in turn, is underlain by the next solid material, which is salt mixed with clay and fine sand. This layer of clayey salt is about six inches thick, according to Mr. Grable, and forms a "hardpan" that will support a loaded truck. Beneath the "hardpan" the salt, clay, and sand is soft, porous, and permeable.
Richardson84 gives various analyses of salt crusts, salt crystals, and brines from this vicinity. He gives the following analysis of salt from the crust on the Zimpleman lake:
| Percent | |
| Silica | 0.6 |
| Alumina | 0.0 |
| Iron | Trace |
| Magnesia | Trace |
| Lime | Trace |
| Potash | None |
| Sodium sulfate | 1.4 |
| Sodium chloride | 97.3 |
99.9 |
84Richardson, G. B., op. cit., pp. 62-64.
He also describes a test hole a few feet deep that was dug in the surface of the salt lake and states that analysis of the material penetrated "shows the presence of silica, lime, magnesia, soda, sulfur trioxide, carbon dioxide, and traces of potash and lithium, but no borax. Borax, however, occurs in at least one locality nearby."
During the period between 1929 and 1932, a shallow sump was put in and a centrifugal pump was installed with a capacity of at least 1,000 gallons per minute. The dikes now present in the lake were built at this time to confine the brine that was pumped to the surface. Greater production of salt was obtained by pumping brine, but resulted in a lower-grade product that consumers claimed contained "alkali." With the above exception, all salt harvested from the lake has formed as a result of natural evaporation of surface and subsurface waters that left their contained salts as a surface crust. During the period that brine was being pumped, a crust was allowed to form on the brine ponds about once each month and was harvested by means of forks, the tines of which are closely enough spaced to support the salt crust. The salt crust produced by natural rise and evaporation of brine is harvested in the same manner. After being stripped from the lake surface, the salt is either hauled directly to the consumer or is hauled to stock piles near the lake. It is not refined in any way to remove objectionable impurities.
Demand for salt from this deposit has fallen off in recent years because of competition from other sources, notably the salt mines in Kansas and the potash mines near Carlsbad, N. Mex., where salt is produced as a byproduct. The reserves of salt at the deposit are apparently adequate for continued production at the present scale of operations, and there will probably continue to be a small local market for the product.
OIL AND GAS
The southern Guadalupe Mountains are of interest to petroleum geologists because features there exposed at the surface are analogous to features known only from drilling in the oil fields to the east. However, within the area itself the chances of obtaining commercial quantities of oil or gas are probably small. There are no surface indications of oil in the region, nor have any noteworthy showings been found in the four wells that have been drilled in or near it. The positions of these wells are indicated on figure 2, and they are listed below.
Test wells drilled in or near the Guadalupe Mountains
N. B. Updike, Williams No. 1. Located within area of this report, 3 miles south of El Capitan, section 24, block 121, Public School Land. Total depth, 3,400 feet. Starts near top of Bone Spring limestone, and was probably drilled into Pennsylvanian rocks (pl. 8).
Anderson and Prichard, Borders No. 1. Located 14 miles south of El Capitan, section 34, block 69, Public School Land. Total depth, 4,728 feet. Starts 435 feet below top of Bone Spring limestone, and was probably drilled into Pennsylvanian rocks (pl. 8).
Pure Oil Co., Quaid No. 1. Located 20 miles east of El Capitan, section 12, block 63, township 2, Texas and Pacific Railroad survey. Total depth, 3,419 feet. Starts a little below top of Delaware Mountain group, and was drilled into Bone Spring limestone.
Niehaus et al., Caldwell No. 1. Located 35 miles east-southeast of El Capitan, section 15, block 109, Public School Land. Total depth, 5,008 feet. Starts in Castile formation, and was drilled through Delaware Mountain group into Bone Spring limestone (pl. 6).
In the region east of the Pecos River, oil and gas are produced from horizons in the Capitan and Carlsbad limestones, which there lie buried beneath several thousand feet of younger rocks. In the Guadalupe Mountains, these formations form the mountain summits, and any oil or gas that they once may have contained has long since escaped.
There is a possibility that oil may occur in the deeper formations, which lie beneath the surface of the mountains. As noted in the stratigraphic descriptions, black limestones of the Bone Spring are impregnated by bituminous material, although chemical analyses show that this bituminous material forms less than one per cent of the rock. Occasional small pockets in the limestone contain some free oil. Parts of the formation might therefore serve as source beds, and oil derived from them may have accumulated in interbedded sandstones in the Bone Spring, or in the overlying Delaware Mountain group. As the Delaware Mountain group, however, is predominantly a sandstone, any oil escaping into it from the Bone Spring limestone would likely be diffused and lost, unless local variations in porosity or structural conditions were such as to permit accumulation. There is a possibility that oil may be trapped in the northwestward tapering sandstone wedges of the Delaware Mountain group, where they are under a cover of younger rocks.
The possibilities of oil in the underlying, pre-Permian formations are largely unknown, as only their top has been reached by the Updike and the Anderson and Prichard wells. Beds of Middle Ordovician age produce oil east of the Pecos River, but exposures in the Sierra Diablo southwest of the Guadalupe Mountains show the Upper Ordovician resting on the Lower Ordovician with the producing beds absent. As the two wells in the Guadalupe Mountain region indicate that the Pennsylvanian series underlies the Permian, the Guadalupe Mountain region was probably much lower structurally in pre-Permian time than either the Sierra Diablo or the producing areas (fig. 16, B).
Most of the present tectonic features of the region are of Cenozoic age (pl. 21 and fig. 15, A). As a result of the Cenozoic movements, the region is broken into tilted fault blocks, some of which, along the crest of the uplift, might enclose sands that would serve as traps for oil and gas. Moreover, the easternmost faults, which form the terminus of a long westward rise of the strata, might seal off porous beds on their updip sides, and thus cause them to collect oil and gas that had been generated over an extensive area and had migrated up the dip. The wells listed above have been located on Cenozoic tectonic features.
Many petroleum geologists believe that oil and gas are likely to be generated shortly after the source rocks are deposited, and thus to accumulate mainly in such structural traps as are developed in them within a short time after deposition. if so, the tectonic features imposed on the region in Cenozoic time probably had little or no influence on petroleum accumulation in Permian or older source beds.
GROUND WATER
The ground-water resources of the region received little attention in this investigation. The best account of the water resources of the area is that of Richardson,85 published in 1904. These resources deserve further study because, aside from water supplies that can be collected in surface storage tanks, ground waters constitute the only source of water for the inhabitants of the area.
85Richardson, G. B., Reconnaissance in trans-Pecos Texas north of the Texas and Pacific Railway: Texas Univ. Bull. 23, pp. 86-92, 1904.
Ground water is fairly abundant along the southeast base of the Guadalupe Mountains, and comes to the surface in numerous springs. The largest and most numerous lie within a mile or so of the southeastern base of the Guadalupe Mountains and issue from sandstones of the Delaware Mountain group or the gravels that cover them. They include Pine Spring, Upper Pine Spring, Manzanita Spring, and many smaller ones. Their water is derived from the high Guadalupe Mountains to the northwest, where the rainfall is greater than in surrounding areas. Migration of the water from the mountains to the points where the springs issue is accomplished in several ways. Some of it probably moved down through joints in the limestone and sandstone, for the north-northwesterly joint set is prominently developed near the springs and extends toward them down the slope of the mountains.
Other springs some miles to the southeast of the Guadalupe Mountains issue from the base of the gravel sheet that overlies the sandstone, and their water may have traveled through the gravel from the foot of the Guadalupe Mountains. The largest of them is Independence Spring, about 5 miles east of the mountains and near the southeast edge of the gravel sheet. Only a few wells have been put down in this area, and it is not known whether additional supplies can be obtained by more wells.
Several springs issue from the west side of the Guadalupe Mountains, whose water is derived also from the mountains. The largest of them is Bone Spring, west of Guadalupe Peak. It issues from sandstone a little above the Bone Spring limestone, and its water is no doubt brought to the surface by following the top of this impervious limestone bed.
Ground water is relatively more abundant in the Salt Basin than in the mountains to the east but is of poor quality, most of it being rather strongly saline and gypseous. Over most of the basin floor it is reached at depths of 30 feet or less, and is being taken out in numerous wells. Many more wells probably can be sunk without depleting the supply. It is unlikely that water of better quality can be discovered in the basin, for the central part of the basin has doubtless been an area of concentration of mineral salts throughout its history as a topographic feature.
Water of better quality probably occurs in the fanglomerates that form bajada slopes along the edges of the basin, especially at the foot of the Guadalupe Mountains. The bajadas stand much higher than the basin floor, and water contained in the deposits is derived from nearby mountains; hence it is unlikely that much concentration of mineral salts has taken place. Abundant supplies of water of this type are found at Van Horn,86 but they are probably derived from the broad drainage area of Ryan Flat to the south. Nothing comparable to this drainage area exists near the Guadalupe Mountains. Limited supplies might be obtained from the two large areas of alluvial fans at the north and south ends of the Patterson Hills, where rock ridges have caused the drainage to converge. In these areas the rock floor on which the fanglomerates rest is irregular. It is probable that on the mountainward side of the buried rock ridges water has accumulated in the fanglomerates in local reservoirs.
86Richardson, G. B., U. S. Geol. Survey Geol. Atlas, Van Horn folio (No. 194), p. 9, 1914.
BUILDING STONE
The sedimentary rocks of the southern Guadalupe Mountains include several sorts of stone that are used locally for building purposes. Of them the most distinctive and useful are the even-bedded, flaggy limestones and sandstones that occur in the Delaware Mountain group. These rocks are used in building houses, and in making fences and other structures along the highway. The bed most extensively used is the flaggy limestone that lies between the Rader and Lamar limestone members of the Bell Canyon formation southeast of the mouth of McKittrick Canyon. This bed is about 10 feet thick and crops out over an extensive area. Numerous small quarries have been opened in it by the local residents. At Frijole some of the buildings have been constructed of cobbles of Capitan limestone obtained from the gravels washed out from the mountains.
ROAD METAL
Abundant supplies of road metal are available near the highway that crosses the region. In many places the highway extends across patches of older and younger gravel deposits, but some of them are too coarse to use as road metal and require much screening to remove the large stones. In places the gravels and other alluvial deposits are strongly impregnated by caliche. The caliche also has been used for surfacing the highway.
| <<< Previous | <<< Contents >>> | Next >>> |
pp/215/sec7.htm
Last Updated: 28-Dec-2007