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USGS1961

Distribution of uranium ore deposits in the elk ridge area, San Juan County, Utah

The Elk Ridge area of southeastern Utah contains uranium ore deposits in two lower members of the Chinle formation of Late Triassic age. Each member is mineralized in different parts of the area , and where both are present only the lower contains ore . Across the Elk Ridge area from southwest to northeast, successively younger beds lap onto the unconformity that separates the Chinle from the underlying Moenkopi formation of Triassic(?), Early and Middle(?) Triassic age. Important uranium deposits have been found only in sandstone beds of the Chinle that are in contact with the Moenkopi. Sandstone of the Chinle formation lies on the Moenkopi (or is separated from it by gray mudstone of the Chinle no thicker than the depths of most of the known paleostream channel scours) in two separate parts of the Elk Ridge area . These "favorable areas" contain all the mines and important prospects. The ore deposits are flat-lying tabular to lenticular bodies in fluvial sandstone beds of the Chinle with fine-grained black uranium minerals chiefly interstitial to sand grains and as replacement of carbonaceous material. Most of the ore -bearing sandstone beds are discontinuous lenses intertonguing with and overlain by relatively impermeable mudstone. Contact of the host sandstone with the underlying Moenkopi seems to be a prerequisite for ore as the ore bodies are generally within a few feet of such contact areas and sandstone lenses separated from the Moenkopi by gray mudstone are generally not ore bearing. The consistent association of ore deposits with the Chinle-Moenkopi contact suggests that mineralizing solutions were introduced into the host beds from their areas of contact with the Moenkopi formation. Impermeable barriers overlying ore -bearing parts of the host sandstones were probably an important control on the deposition of ore minerals from solution. Hypofiltration of metallic constituents from ascending ore solutions may have been important. It is also possible that the overlying barriers formed traps for H2S gas or fluid hydrocarbons and thus localized a reducing chemical environment in which ore minerals were later precipitated.

Utah↗
USGS1961

Tephroite in California manganese deposits

Recent studies of manganese deposits and mineral specimens in the Sierran belt of sedimentary rocks as well as in the Klamath Mountains to the north and in the Rand Mountains to the south, have shown the presence of tephroite , the orthosilicate of manganese (Mn2Si04), at numerous localities. Earlier studies of these deposits have shown that the original layered deposits of carbonate and hydrous silicates of manganese have been widely altered by metamorphism to spessartite (Mn3Al2-(SiO.),), rhodonite (MnSi03), and piedmontite (Ca2(Al,Mn"',Fe"')3-Si3Oi2(OH)). Recent work shows that layered manganese oxides also were present in the original sedimentary rocks. It shows also, that tephroite has formed widely in the original assemblage of carbonate, silicate, and oxide of manganese ; in several localities, a little alleghanyite (2Mn2-S1O4 - Mn(OH,F)2) has been formed. Rhodonite, spessartite, and piedmontite uniformly follow the tephroite ; in places, bementite and neotocite are present. In one deposit a little pyroxmangite ( (Mn,Fe,Ca)Si03) has been noted and in another, some crystals that are probably pyrophanite (MnTi03), not yet recorded in the United States. By contrast, the restudy of large collections of material from deposits in sedimentary rocks of the Franciscan formation in the Coast Ranges indicates the tephroite is very uncommon; it has been recognized with assurance at only one locality-Alum Rock Park, Santa Clara County. In the Coast Ranges, rhodonite and spessartite, the high manganese garnet, are very uncommon. The assemblages of manganese silicates indicate that the layered deposits of manganese minerals in the Sierra belt have been metamorphosed to a higher degree than those of the Coast Ranges. This review also shows the presence of axinite, the boro-silicate of aluminum, calcium, and manganese , in three deposits .

California↗
USGS1961

Ground-water control in the Neyveli lignite field, South Arcot district, Madras State, India

Unconsolidated deposits of the Cuddalore series of Miocene age underlie much of the coastal plain of southern Madras . Several lignite seams occur in a thick sequence of sand, gravel, and clay that dips seaward about 40 to 100 feet per mile. The principal seam of lignite mapped in the Neyveli area averages more than 50 feet in thickness, underlies at least 80 square miles, and occurs at a minimum depth of 165 feet near Neyveli , where deposits totalling 230 million tons have been proved in an area of 4J square miles. The lignite seam is immediately underlain, throughout its area of occurrence, by a thick bed of sand and gravel that contains artesian water, the head of which is more than 100 feet above the top of the lignite at Neyveli . The sand and gravel aquifer is exposed to recharge in and near its outcrop area, 6 to 10 miles northwest of Neyveli , where the average annual rainfall is 41 inches. Hydraulic tests of the aquifer indicate that ground-water control for mining by opencast from a pit 6,000 feet long and 1,200 feet wide will require continuous withdrawal of about 40,000 gallons (Imperial) per minute from wells in and adjacent to the mine. The well field , including 50 to 65 large-capacity wells, must move with the open cut; and no appreciable decrease in the withdrawal rate can be expected throughout the life of the mine, which is designed to produce about 3j million tons of raw lignite per year.

Madras State↗
USGS1961

Late pleistocene and recent accumulation of uranium in ground water saturated sandstone deposits

Protactinium-231 and thorium-230 relations in several ground water saturated sandstones containing uranium ore indicate that much of the uranium has been accumulating in very recent times. Samples from the Hauber mine, Crook County, Wyoming, were selected to illustrate the concept of recent accumulation and the methods of calculation of the estimated minimum and maximum dates of the start of the uranium accumulation . The radiochemical results of eight samples from this mine show extremely consistent radioactive daughter product distribution, and a close correlation between the estimated dates of the start of uranium accumulation and the uranium content of the ore. The results for mill pulp samples, representing large tonnages of ore, indicate that the major part of uranium deposition started between 40,000 and 130,000 years ago and the rate of deposition has increased approaching the present time.

Wyoming↗
USGS1961

A comparison of analytical methods used in geochemical prospecting for copper

Analytical methods used in geochemical prospecting for copper were compared by analysis of samples of residual soil collected in duplicate near a copper -bearing vein at the Malachite mine, Jefferson County, Colo. In this area barren or "background" samples have a mean copper content of 58 ppm (parts per million) and anomalous samples containing copper derived from the vein have a mean copper content of 216 ppm. Most anomalous samples are above 100 ppm and most barren samples are below. Geochemical prospecting tests, such as the spectrographic, biquinoline, dithizone and chromograph tests for copper and the citrate soluble and acid-soluble tests for total heavy metal, are almost as sensitive but are less precise and less accurate than standard quantitative trace analysis. Statistical techniques based chiefly upon the coefficient of variation show that the geochemical prospecting tests differ considerably among themselves in sensitivity, precision, and accuracy. This study indicates that the dithizone and the biquinoline tests for copper are the best for geochemical prospecting in this area.

Colorado↗
USGS1961

Beryllium-bearing tuff in the Thomas Range, Juab County, Utah

Recently discovered beryllium deposits in the Thomas Range , Utah , are along the periphery of the fluorspar district at Spor Mountain. The beryllium is in altered rhyolite tuff of Tertiary age and is associated with genetically related fluorite, quartz, chalcedony, opal, calcite, and mont-morillonite and with residual quartz, feldspar, and biotite. Nodules of silica and fluorite contain more beryllium than the enclosing tuff . The ores probably were formed by fluorine-rich solutions derived from rhyo-litic magma related to a second period of volcanic activity.The district promises to be an important source of beryllium.

Utah↗
USGS1961

Sandstone-type uranium deposits at Ambrosia Lake, New Mexico-An interim report

The Ambrosia Lake district in northwestern New Mexico is the most important uranium mining and milling district in the United States. Together with the nearby Laguna district it contains more than 50 percent of the nation's reserves.Most of the ore occurs in the Morrison formation of Late Jurassic age as elongate, tabular, mantolike bodies principally in the upper half of the Westwater Canyon sandstone member and near the base of the Poison Canyon sandstone tongue (9). Individual deposits are distributed along two easterly trending belts 2 to 3 miles apart. The ore bodies are as much as 3,000 feet long, several hundred feet wide, and 100 feet thick. Depths to the ore range from 0 to 2,200 feet. Some ore is also mined from the Todilto limestone of Late Jurassic age and from the Dakota sandstone of Early (?) and Late Cretaceous age.Two types of unoxidized ore are recognized: prefault ore, which is considered to be primary, and postfault ore, which may be redistributed. The prefault ore shows no obvious relationship to tectonic structures but appears to be controlled by a variety of sedimentary structures. Postfault ore is controlled by a combination of sedimentary and tectonic structures. Disseminated carbonaceous matter, believed to be plant derived, appears to be the dominant control in the localization of the uranium .The ore mineralogy is comparatively simple, and coffinite is by far the most abundant ore mineral. Molybdenum, selenium, vanadium, and iron occur in anomalous quantities in the deposits in both oxidized and unoxidized minerals.U/eU ratios and radioisotope distribution indicate almost universal disequilibrium and fairly recent migration of radioisotopes in all deposits that have been sampled.Further studies on the organic carbonaceous matter, sandstone alteration, age determinations, and sulfur isotope composition are required to obtain a better understanding of the source, transportation, and deposition of uranium and other elements in the deposits .

New Mexico↗
USGS1961

Some aspects of the geochemistry of sphalerite, Central City District, Colorado

Detailed studies of sphalerite , as a part of a larger study of the Central City district , Colorado , have been undertaken to learn something of the physico-chemical environment of ore deposition. More than 90 samples have been analyzed by chemical and spectrochemical methods and these data are interpreted in the light of experimental information. Sphalerite is a widespread and moderately abundant constituent of the gold- and silver-rich veins of the district . It was deposited during one stage of mineralization, in all environments of the concentrically zoned district except in the core. On a district -wide basis it occurs in three mineral assemblages: sphalerite -pyrite- chalcopyrite-tennantite-galena, sphalerite -pyrite-tennantite-galena, and sphalerite -pyrite-enargite-tennan-tite-galena. Quartz and, locally, other gangues are present.The sphalerite samples contain from 12 to 0.05 weight percent iron and detectable amounts of a restricted suite of minor elements, principally manganese, cadmium, copper, and lead. Manganese correlates directly with iron content, but the other minor elements have random correlations.The iron content of Central City sphalerite is interpreted to be mainly a function of activity of sulfur and temperature. Total pressure and minor elements that may enter the structure of either sphalerite or coexisting pyrite are thought to have negligible effects on the amount of iron in the sphalerite .The iron content of the sphalerite and fluid inclusion studies indicate that mineralization occurred over a temperature range from at least 620° C to about 150° C. In general, the temperatures tended to decrease from the vicinity of the central zone outward toward the peripheral zone. The thermal pattern, however, was complex, and marked by local irregularities.The activity of sulfur decreased with temperature, but to an extent such that more sulfur-rich mineral assemblages could form toward the margins of the district .The minor-element content of the sphalerite is governed by the activities of the various components and by the ability of the host mineral to accomodate it. Manganese varies widely because (1) it is geochemically much more abundant than is zinc and (2) it can also enter other minerals on a large scale. Conversely, because the amount of cadmium is small relative to that of zinc and because it enters only sphalerite in quantitatively significant amounts in hydrothermal environments, the cadmium content of sphalerite is constant. The copper content of the sphalerites is low and in good agreement with recent experimental data of Priestley Toulmin 3d.

Colorado↗
USGS1961

Uranium migration and geochemistry of uranium deposits in sandstone above, at, and below the water table; Part 1, Calculation of apparent dates of uranium migration in deposits above and at the water table

The migration of U may be studied by the distribution of the radioactive daughter products, which serve as natural tracers in the migration of U. The distribution of the daughter products is determined by radiochemical analyses of samples from ore deposits in sandstone, and the apparent minimum and maximum dates of U introduction or redistribution may be calculated from the Pa 231 /Th 230 ratio. The primary assumption required is that the Pa and Th do not migrate in measurable quantities from the place where they were produced by the decay of the parent U isotopes. The upper limit of age determination is about 250,000 years, based on the half-lives of Pa 231 and Th 230 . The difference in the half-lives of these isotopes is reflected in their differential rates of growth and decay corresponding to migrations of the parent U during the time range considered. The growth and decay patterns, analyzed mathematically, are used to determine the apparent date of U migration. Calculations based on analyses of samples from the Hulett Creek area, Wyoming, illustrate the results for typical sandstone ore deposits that are above and at the water table.

Economic Geology↗
USGS1962

Metallogenetic provinces of Chile, S. A

The metalliferous deposits of Chile tend to be restricted to well denned metallogenetic provinces, each characterized by a dominant mineral or mineral assemblage. The most important ore deposits are those of copper, iron, silver, gold, and manganese. The primary minerals are few in number and most are simple sulfides and oxides; more complex sulfosalts are scarce. Secondary minerals in great variety are important constituents of the ores. Many of the ore deposits are situated along well defined structural lines, several hundred kilometers long, that parallel the structural grain of the Andes.The deposits, with few exceptions, are found in sedimentary or volcanic rocks that range in age from Jurassic to Late Cretaceous or in intrusive rocks of Late Jurassic to Late Cretaceous age. Most deposits are genetically related to intrusive bodies, which have an average composition within the range of granite-diorite.The metalliferous deposits can be classed as hydrothermal, sedimentary, contact-metasomatic and magmatic. Copper deposits are typically hydro-thermal, manganese deposits are sedimentary, and most of the iron ore deposits are contact-metasomatic. A unique group of iron ore deposits apparently formed by near-surface intrusion and surface flows of a magma consisting of iron oxides. Hydrothermal deposits, the most abundant and most important economically, were formed under conditions ranging from low to high temperature and pressure. © 1962 Society of Economic Geologists, Inc.

Economic Geology↗
USGS1962

Diffusion features of uranium-vanadium deposits in Montezuma Canyon, Utah

Uranium-vanadium deposits in the Salt Wash Member of the Morrison Formation in Montezuma Canyon , San Juan County, Utah , exhibit zoning that is interpreted as a result of metal transport by diffusion . The concentric zones consist of a brown nonmineralized core, an olive-gray mineralized shell, and a gray nonmineralized outer zone. The brown zone is iron-stained, porous sandstone commonly containing abundant carbonaceous material. The curved mineralized layer completely encloses the brown zone, and is composed of oxidized uranium-vanadium minerals that impregnate sandstone. The gray zone is light-gray sandstone tightly cemented with calcite and commonly freckled with limonitic specks.Formation of the deposits most likely took place during Late Cretaceous or early Tertiary time when the ore-bearing sandstones were deeply buried and saturated with connate waters. The concentration of organic material in the brown zone suggests that this zone was once saturated with a reducing solution containing soluble organic compounds like alcohols and aldehydes derived from the organic material. The gray zone, on the other hand, was probably saturated with an oxidizing solution containing uranium and vanadium. Where these two solutions were in contact, oxidation-reduction reactions took place that caused the precipitation of low-valent uranium and vanadium minerals.The ellipsoidal shape of the ore layer and the lack of any exit or entrance for flowing solutions indicates that the dissolved metals moved through the gray zone by diffusion and were precipitated at the periphery of the reducing zone. Recent weathering and oxidation have altered the primary low-valent minerals to high-valent forms without noticeable leaching of the ore metals.

Utah↗
USGS1962

The origin of jasperoid in limestone

The name jasperoid has been applied to rocks that consist mainly of silica and that have formed by replacement. This paper considers only those jasperoids formed by replacement of limestone . Major problems involved in the origin of such jasperoid include: source of the silica; nature of solutions that dissolve, transport, and precipitate silica; and the mechanism of replacement of limestone by silica. The answers to these problems are of practical as well as scientific interest because many jasperoid bodies are closely related to mineralization. Silica may be derived from: juvenile silica of magmatic origin ; silica leached from underlying rocks by hydrothermal solutions; silica locally derived from enclosing rocks by circulating solutions; and silica carried downward in ground water from the weathering of overlying rocks. The nature and the concentration of other substances in solutions influence, in a complex manner, the ability of these solutions to dissolve, transport, and precipitate silica. Nevertheless, the following generalizations can be made. The solubility and rate of solution of silica in water at moderate pressure increase slowly with temperature up to 200 degrees C.; from 200 degrees to 360 degrees C. they increase rapidly; above 360 degrees C. solubility is pressure dependent, increasing steadily at high pressure and decreasing slightly at moderate pressure due to the formation of a vapor phase. The pH has slight effect on the ionic solubility of silica in the range from pH 1 to ph 9 at low temperature. The effect of other components on the solubility of silica is probably subordinate to that of temperature above 200 degrees C., but becomes increasingly important as the temperature falls below that point. Most jasperoid bodies form by both replacement and silica deposition in voids, with replacement dominant during the early phase, and precipitation dominant during later phases. Replacement of limestone by silica is favored by relatively low temperature acid solutions, and the presence of CO 2 . As limestone dissolves, Ca ions are released to promote the precipitation of colloidal silica. Acid solutions then diffuse through this gelatinous film to continue dissolving limestone behind it; the Ca ions diffusing outward cause the precipitation of more colloidal silica at the solution-gel interface. As the gel mass ages, it shrinks, hardens, and ruptures. More silica is then deposited in the fractures. Eventually the gel crystallizes to a dense mass of aphanitic quartz and chalcedony, with shrinkage cracks and vugs filled or coated with younger coarse-grained quartz and other minerals that have been deposited directly from solution. The theory that relatively low temperature favors the formation of jasperoid replacement bodies in carbonate rocks, and high temperature inhibits their formation, offers an explanation for the gap that is observed in some districts between contact metasomatic lime silicates and siliceous replacement of limestone . This gap is characterized by the lack of any reaction between limestone and silica-bearing solutions moving through it.

Economic Geology↗
USGS1962

Studies of fluid inclusions I: Low temperature application of a dual-purpose freezing and heating stage

The design and operation of a microscope freezing stage developed for use at magnifications up to 500X are described. It makes possible studies of low - temperature phase changes such as the freezing of a saline water phase, and hence an estimate of the total salt concentration, in fluid inclusions as small as 10 microns (10-6 milligram in weight). The crystal or polished mineral plate containing the inclusions is viewed while immersed in a thermostated heat exchange medium (acetone) circulating rapidly in order to minimize thermal gradients. The stage permits easy operation at temperatures down to -35° C, with electrical control to ±0.05° C, and to much lower temperatures with manual control. With substitution of silicone oil for acetone, the same stage can be used for heating experiments up to +250° C. Calibration points in the low range indicate the accuracy of freezing temperature determinations on optimum material to be better than ±0.1° C. The low relief of ice crystals in water solution places considerable importance on sample selection, preparation, and lighting. As a result of almost ubiquitous and drastic supercooling (meta-stability), -35° C is inadequate to freeze most inclusions . Holding at -78.5° C (acetone + solid CO 2 ) for thirty minutes is generally adequate, although a few samples require extended immersion in liquid nitrogen at -196° C to cause freezing of even a part of their inclusions . Such extensive supercooling is not possible with most surface waters owing to the presence of abundant extraneous solid nuclei for the crystallization of ice.

Economic Geology↗
USGS1962

Trace element distribution in the searchlight, Nevada quartz monzonite stock

Gold, silver, copper, and lead-bearing veins, non-radially zoned, occur just beyond the southern and western margins of the Searchlight , Nevada , quartz monzonite stock . Seven samples of the quartz monzonite and purified individual constituent minerals of the rock, representing apophyses and marginal and interior parts of the intrusive mass, were analyzed petrographically and spectrographically. A semiquantitative total-energy spectrographic method proved satisfactory for Cu, Pb, Ni, Co, Ga, Mo, Mn, Ti, V, Cr, Sr, and Zr, but too insensitive for Zn, Ag, and Au. A synthetic silicate base was used for preparation of standards and working curves. The modal trace element content of unaltered (hypothetical) quartz monzonite samples was determined from the trace element content of the purified minerals. Ferromagnesian minerals contain concentrations of Cu, Pb, Ni, Co, Mn, and Cr. Felsic minerals are low in these but high in Sr and Ga. Cu appears to have been partly released during chloritization of the mafic minerals. Ni, Cr, Zr show little difference between the unaltered (hypothetical) and actual rock. Ga, V, Mn, Sr are in lesser quantities in the altered rock. Pb and Cu also show a loss, especially nearest largest Pb and Cu producers. Pb, Cu, V occur in the spatially related veins, but Sr or Ga have not been reported to date. Pb/Cu in unaltered rock compared to altered rock is 1.6/1; past mining production ratio of Pb/Cu is 2.6/1. While further work is needed, the trace element pattern suggests a possible means of identifying a "productive" intrusive body.

Economic Geology↗
USGS1962

Observations on the pyrite deposits of the huelva district, Spain, and their relation to volcanism

The felsitic porphyritic rocks that occur with Lower Carboniferous shale or slate in the Huelva district , Spain , were examined at the Rio Tinto, Tharsis, and La Zarza mines. Most of the bodies of porphyry are not intrusive into the shale, but instead consist of rhyolite flows overlain by variable thicknesses of coarse and fine pyroclastic rhyolite. These lie conformably beneath the shale. The pyroclastic beds are the ore horizon, and the ore bodies are confined to this stratigraphic zone. Various modes of formation have been postulated for the ore bodies of the Huelva district . The apparent limitation of ore to one strati-graphic horizon for more than 100 kilometers seems to favor a modified syngenetic origin with metallic elements derived from volcanic emanations.

Economic Geology↗
USGS1962

The ore knob massive sulfide copper deposit, North Carolina: An example of recrystallized ore

Massive and disseminated pyrrhotite-chalcopyrite-pyrite ore replaced a fault zone in Precambrian Carolina Gneiss of Keith (1). Closely following sulfide deposition, vein sulfides and silicates in the wall rock were recrystallized under a rising temperature gradient to coarse-grained unoriented aggregates that contain late pyrite porphyroblasts in pyrrhotite. Boudinage, dilation, and flow structures are common.

North Carolina↗
USGS1962

Temperature of crystallization of pyrrhotite and sphalerite from the Highland-Surprise Mine, Coeur d'Alene district, Idaho

The ore bodies of the Highland-Surprise Mine are replacements along shear zones in quartzose slate, quartzite, and phyllite of the Prichard Formation of the Belt series (Precambrian). Pyrite, arsenopyrite, pyrrhotite, sphalerite, chalcopyrite, and galena are the chief metallic minerals and were probably deposited in that order. Temperatures of formation were estimated for pyrrhotite-pyrite and sphalerite-pyrrhotite assemblages contained in the steeply dipping vein system. Measurements on 62 pyrrhotites indicate a range in temperature of crystallization between 370 degrees and 492 degrees C. (no correction required for confining pressures <2000 bars below 670 degrees C.), and measurements on 14 sphalerites indicate crystallization temperatures between 375 degrees and 460 degrees C. (uncorrected for confining pressure). No systematic temperature gradients were recognized. Minor elements in 23 pyrrhotite, 8 pyrite, 13 sphalerite, and 2 galena samples were determined. Partition ratios of Ni and Co in pyrrhotite-pyrite and sphalerite-pyrrhotite pairs are erratic. This suggests a dis-equilibrium distribution of these elements between the phases of each mineral pair and/or b) crystallization of the mineral pairs under different physical conditions.

Idaho↗
USGS1963

The peg claims spodumene pegmatites, Maine

The Peg Claims pegmatites are located southwest of Rockland in the towns of Warren and Cushing, Knox County, Maine . These pegmatites are representative of a group of zoned, granitic, lithium-bearing pegmatites in which spodumene is present nearly from wall to wall. The pegmatites are discordant, steeply dipping, tabular bodies in the Penobscot quartz-mica schist near the Waldoboro granite. A narrow quartz-tourmaline-muscovite-apatite aureole is commonly developed around each of the pegmatites and around inclusions of country rock in the pegmatites . The pegmatites are zoned, and each may be subdivided into: (1) a narrow quartz-muscovite border zone; (2) a narrow albite-quartz-muscovite wall zone; (3) and an albite-quartz- spodumene -perthite core that constitutes most of the pegmatite . Cross-cutting, fine-grained, quartz-albite- spodumene -muscovite lenses are found within pegmatite cores. The bulk mineralogy and variations in the mineralogy from zone to zone of the largest body (Dike 1) were determined by megascopic mineral point-counts. There is a decrease of albite, quartz, and muscovite and an increase of spodumene and perthite from the border and wall zones into the core. The alkali contents of Dike 1 and of each of its zones were determined by flame photometer and X-ray fluorescence analyses. The amount of Na20 decreases and the amounts of K 2 O, Li 2 0, Rb 2 0, and CS 2 O increase from the border and wall zones into the core. Estimated bulk compositions of Dike 1 and of each of its zones were computed. It is concluded that the distribution, structural features, bulk chemistry, and the mineralogical, chemical, and textural zoning of the pegmatites are consistent with development by fractional crystallization of a pegma-titic fluid in a restricted system.

Maine↗