Discussion and communications: "Band", "Layer," and some kindred terms
No abstract available.
Economic Geology↗
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Comments on the origin and major structural control of igneous rocks and related mineral deposits
No abstract available.
Economic Geology↗
Notes on the early history of water-well drilling in the United States
The standard cable-tool drilling rig was invented and developed in drilling salt wells in the West Virginia-Ohio-Pennsylvania region during the twenty years following the successful completion of the first drilled well in 1808 by the Ruffnet brothers at the Great Buffalo Lick near Charleston, West Virginia. Some time previous to 1823, Levi Disbrow studied the drilling methods used in the western salt industry and came east to become the first professional water well driller in the states north of the Potomac River. Possibly the first artesian water well in the United States was constructed in 1820 in Charleston, South Carolina, by sinking an iron pipe through a clay bed. Auger boring for artesian water appears to have been first used in Charleston, South Carolina, in 1823; however, the first successful auger-bored well was not completed in that city until after 1825. The drilling methods and tools were copied from a description of a well bored in London, England. Between 1821 and 1833 auger boring of artesian wells began in the Black Belt of Alabama and possibly in Mississippi. The process of jetting wells, invented in 1884, became the chief method of sinking artesian wells in the Atlantic and Gulf Coastal Plain by the end of the century. The first successful artesian wells in Georgia and Florida were put down during the period 1880-1882. © 1943 Society of Economic Geologists, Inc.
Economic Geology↗
The manganese oxide minerals, a preliminary report
This paper summarizes the results obtained thus far in an intensive study of the manganese oxide minerals. X-ray powder photographs, supplemented by chemical tests, have proved to be the best means for identifying these minerals. Formulas are suggested. Physical properties and X-ray data are listed for the commoner minerals and those for which new data have been obtained. Rules of nomenclature for these minerals are suggested.
Economic Geology↗
Structural determinations from diamond drilling
Several problems may arise in the geometrical determinations of strike and dip from core drilling. If the stratigraphic or structural surfaces are plane, as the bedding planes of a homocline, two problems may exist, depending upon whether the drill cores do or do not penetrate to some recognizable horizon. The first of these is solved by a simple graphic interpolation, and is not discussed in this paper. The second, however, is solved for the most general case of three non-parallel drill holes, no one of which is necessarily vertical. Errors are necessarily present in this solution, due to: 1. Inaccuracies in the measurement of the initial directions and dips of the drill holes. 2. Deviations of the drill holes from their initial directions. 3. Inaccuracies in the measurement of the angles between the axes of the drill cores, and the stratigraphic or structural planes. The second and third of these causes result in initial errors in the measurement of the core angles. Hence, for this simplest case, error formulm are developed for finding the final errors in the angles of strike and dip, under certain specified assumptions. To illustrate the solution, a problem is stated and solved. This problem is of a general nature, selected to show the necessary operations when the three drill holes occur in different octants. The error formulae are subsequently applied. For curved surfaces, as where folded beds are present, the same two problems arise, depending upon whether the drill holes do or do not penetrate to some recognizable horizon. Only the first of these problems is considered. It is shown, in this case, that 9 drill holes are required to obtain a satisfactory solution. The method consists essentially in fitting nine known points to a ternary quadric surface; and in determining the equations of the planes tangent to this surface at any of the nine points, or at any other points on the surface. The strikes and dips are then derived from these equations. © 1943 Society of Economic Geologists, Inc.
Economic Geology↗
The hydrothermal solubility of silica
The solubility of silica glass in water has been determined through the temperature range 200 degrees C. to 420 degrees C. at a pressure of 300 atmospheres. Some previous investigations of solubility of silica in water, it is believed, have indicated a too great solubility as a result of failure to distinguish true solubility from colloidal dispersion. The solubility is essentially zero at temperatures below 200 degrees C. and increases to a maximum of 0.20 part silica per 100 parts water at 360 degrees C. Solubility falls off beyond 360 degrees C., but is only slightly less at the critical temperature of water. Solubility in the vapor phase of water appears to be a function of the density of the vapor phase, as well as of temperature. At high pressures, as the density of the vapor phase approaches that of the liquid, its ability to act as a solvent will approach that of the liquid.
Economic Geology↗
The fluorspar deposits of Saint Lawrence, Newfoundland
Fluorspar from Newfoundland, eighth ranking producer of the world, comes entirely from the St. Lawrence district. Here pre-Cambrian lavas and pyroclastics, Cambrian sedimentary rocks, Ordovician (?) volcanic and sedimentary rocks, and a Paleozoic alaskite-granite comprise the bedrock.Epithermal fluorite veins occupy steeply dipping fault fissures in granite, rhyolite porphyry, and lamprophyre. Eleven veins show walls bearing nearly horizontal striations; one vein bears only vertical striations; and the walls of three veins show both horizontal and vertical striations. The strikes of nearly all veins are within 45 degrees of the normal to the walls of the elongated granite mass. Some veins are more than a mile long and contain numerous workable lenses. Veins are of two types: high-grade containing over 95 per cent CaF 2 and averaging about 5 feet thick, and lower grade containing about 75 per cent CaF 2 and averaging between 15 and 20 feet thick.Sulphides, present in small quantities, include pyrite, chalcopyrite, sphalerite, and argentiferous galena. Non-metallic gangue minerals are quartz, calcite, and rarely barite. "Blastonite," a local name for material composed of microcrystalline quartz and brecciated fluorite, in some places forms as much as 10 per cent of a vein. A nodular type of fluorspar probably formed by alternate rotation of fragments of breccia and deposition of fluorite.Regional zoning is shown by the distribution of barite and green fluorite. Barite shows a distinct zone of localization, and green fluorite predominates in veins both near the granite margins and farther from the granite body.This district will undoubtedly occupy a still more prominent position among producers of fluorspar.
Newfoundland↗
The differentiation of magnesite from dolomite in concentrates and tailings
A new method is presented here for differentiating magnesite from dolomite in crushed materials. This method is based on the essentially different temperatures at which these minerals undergo thermal decomposition. The resulting lowly birefringent periclase is easily distinguished microscopically from the highly birefringent dolomite. This method is based on the ease of recognition of the periclase which permits rapid counting and gives reliable quantitative data on mineral composition. A method is given for staining thermally treated specimens for the determination of the distribution of these minerals in rock fragments.
Economic Geology↗
"Ribbon rock", an unusual beryllium-bearing tactite
The beryllium deposits at Iron Mountain, near the northern end of the Sierra Cuchillo in Sierra and Socorro Counties, New Mexico, are unusual products of contact metamorphism. They occur in irregular bodies of tactile formed by replacement of Paleozoic limestone, generally at or near contacts with small intrusive masses of rhyolite, aplite, and fine-grained granite. The metamorphism took place in mid-Tertiary time. Beryllium is present chiefly in the complex silicate minerals helvite and danalite, and is a minor constituent of the garnet grossularite, a boron-bearing idocrase, and chlorite. These minerals are known to occur in noteworthy concentrations in only one type of rock, a peculiar rhythmically layered variety of tactile to which the name "ribbon rock" is given. The structure of such tactite is very conspicuous, and appears in section as thin, finely crenulated bands of magnetite alternating with similar bands of silicate minerals and finely crystalline fluorite. Concentric banding about fluorite-rich pod-like masses is common. Bodies of "ribbon rock" range in size from inch-thick lenses to large masses amounting to thousands of tons; most appear to have been formed along contacts between re-crystallized limestone and massive magnetite-andradite tactite, chiefly by replacing fluids penetrating the limestone from fractures. The layered structure is interpreted as a diffusion effect.The formation of massive and "ribbon rock" tactites can be traced through a range of falling temperature from a stage characterized by deposition from iron-rich vapors to a stage in which hydrothermal solutions were dominant. Both vapors and liquids appear to have been acid. Reducing conditions undoubtedly existed during the latter part of the hydrothermal stage. The occurrence of beryllium in "ribbon rock," but not in typical massive tactite, may signify that its compounds in deposits at or near intrusive contacts are confined to rocks of hydrothermal origin. The occurrence of "ribbon rock" is suggested as a potentially useful clue for recognition of beryllium-bearing contact deposits elsewhere; at least two other occurrences of what apparently is "ribbon rock" have been described in the literature.
New Mexico↗
Celestite in Buffalo Cove, Fentress County, Tennessee
Mineral aggregates consisting of celestite, dolomite, calcite, and very small amounts of sphalerite, anhydrite, and pyrite occur in the uppermost beds of the Glen Dean limestone, of upper Mississippian age, which crops out along the slopes of Buffalo Cove. Proportions of minerals range widely in adjacent aggregates; maximum content of strontium sulphate is about 96 per cent. The aggregates are spherical to nearly flat, and are regular to irregular in outline; a few coalesce. The maximum dimensions of those examined range from 0.04 to 1.35 feet, and their known vertical range in the Glen Dean limestone is from 7 to 20 feet or more downward from the contact with the overlying Pennington shale. The aggregates in the uppermost beds commonly contain chert and are somewhat hollowed as a result of weathering. Those in the lower beds contain no chert, and, where unweathered, no cavities. Celestite also occurs as isolated crystals and groups of crystals embedded in the limestone. The limetone is fine-grained, brownish gray, argillaceous, and un-fractured. The isolated crystals probably were precipitated from connate water as the limestone consolidated. During subsequent erosion of the Pennington shale to a level only 200 feet above the Glen Dean limestone, meteoric water probably gained access to the upper Glen Dean beds and dissolved cavities in them. The dense, unjointed limestone prevented downward percolation of the water, which became saturated with strontium sulphate and calcium carbonate, and deposited celestite and calcite in the solution cavities. As the dolomite in the aggregates has no apparent local source, it is believed to have been introduced from depth, probably with the small amounts of sphalerite and pyrite, by hydrothermal solutions in post-Mississippian time. Although no veins were seen in the few exposures examined around the cove, it is inferred by analogy with other mineralized areas that the solutions rose along fissures and were deflected by the overlying shale, spreading laterally through the partly filled cavities in the limestone without impregnating the limestone itself. Meteoric water still present in the cavities probably promoted deposition without attack on the limestone by lowering the temperature of the solutions.The celestite zone is being developed at the Youngs quarry. Reserves in the block of ground that contains the quarry are estimated to be 2,822 tons of the mineral aggregates, or strontium ore, containing 2,148 tons of celestite. The celestite constitutes 5.89 per cent by weight of the combined rock and aggregates in the block. Four out of seven exposures examined elsewhere in the ore zone suggest that other roughly comparable blocks may be developed. Underground quarrying is not practicable because of the overlying shale, but a dozen or more similar open quarry sites might be found on the divides between the numerous ravines that drain the sides of the cove.
Tennessee↗
Variations in chemical composition of Los Angeles Basin ground waters
No abstract available.
California↗
Manganese content of the Shady dolomite in Bumpass Cove, Tennessee
The Shady dolomite in Bumpass Cove, Tennessee, contains deposits of hydrothermal sulphide minerals, and its residual clay contains oxidized manganese deposits. New chemical evidence bearing on the source of this manganese is presented.Chemical analyses of isolated components of sulphide-bearing dolomite show that the percentage of manganese is highest in country-rock dolomite unaffected by hydrothermal action, and that the manganese is present as carbonate. Manganese determinations on samples from a drill hole show that 43 feet of beds, about 100 feet above the base of the Shady dolomite, average 0.6 per cent manganese oxide, and that adjacent beds carry smaller amounts. Manganese carbonate, deposited with the original carbonate rock, is therefore considered to be the source of the manganese deposits of Bumpass Cove
Tennessee↗
The preparation of polished thin sections
The relations in ores between opaque and translucent minerals can not be determined satisfactorily by independent examination of either polished surfaces or thin sections. Previous attempts to prepare polished thin sections by Tolman and Rogers, and thinned polished sections by Donnay, appear not to have been entirely successful. Canada balsam, the cementing medium used, is not sufficiently tenacious to overcome the stresses imparted to the surface of the polished grain by the polishing process, which cause the grains to crackle and curl away from the glass slide. This paper describes two mounting media which largely overcome these stresses. These media are the thermoplastics glycol phthalate and Gelva V 7. Glycol phthalate is best suited to the polishing of thin sections on a cloth lap. Gelva V 7 is preferable if sections are to be polished on a Graton-Vanderwilt polishing machine. Photomicrographs of the results are appended.
Economic Geology↗
A portable differential thermal analysis unit for bauxite exploration
A small differential thermal analysis unit that embodies the fundamental features of larger laboratory models is designed for field exploration for bauxite and related materials. The apparatus, requiring only a source of electrical power, combines portability with ease of operation and rapid analysis. The portable unit is suitable for quantitative work and has been successfully applied in bauxite exploration on the island of Hispaniola.
Economic Geology↗
Stages and epochs of mineralization in the San Juan Mountains, Colorado, as shown at the Dunmore Mine, Ouray County, Colorado
The Dunmore lode is localized along a persistent fissure zone over two miles long and averaging nearly 100 feet in width along the length of the Dunmore claim. The fault in which the lode is located offset the pre-Cambrian quartzite and slate walls about 4,500 feet prior to deposition of the overlying thick San Juan tuff. Late Tertiary faulting extended the fissure into the San Juan tuff, dropping the south side about 80 feet. Although most of the lode crops out in the pre-Cambrian rocks, it extends upward across the profound unconformity into the tuff. The lode is complex, containing sharply marked fissure veins, sheared slate dragged into the fault zone, a sheared dike, breccia chimneys, and pebble dikes. An assemblage consisting of quartz, sericite, kaolin, and pyrite appears to be of early Tertiary age. The more productive part of the lode, however, is late Tertiary and consists of a hematite chimney inclosing a copper shoot, a tungsten chimney, and compound base-metal fissure veins. These chimneys and veins are mostly localized along early Tertiary structures, but their mineral sequences correlate them with the second stage of late Tertiary deposition recognized by Burbank in the adjoining Red Mountain and other districts. The Dunmore lode, however, is believed to have been deposited at greater depth and higher temperature and nearer to a source of supply than the lodes of these districts. In structure as well as mineral assemblages the Dunmore lode shows a connection between the chimneys and veins of the region.
Colorado↗