Paul F. Kerr

Giant Desiccation Polygons of Great Basin Playas

Several previous investigators have recognized giant polygonal fissure patterns in 6 playas of the Basin and Range Physiographic Province (Great Basin). This paper extends the study to 39 playas in Oregon, Nevada, California, Arizona, and New Mexico, with observations on the physical and mineralogical features of fissured and nonfissured areas. Fissures are often 5 m deep and the polygons may attain a width of 300 m. These giant mud cracks develop in clay playas and are attributed to desiccation phenomena. As dehydration proceeds from the surface downward and penetrates the capillary fringe above the water table, shrinkage occurs, which ultimately results in rupture at depth that extends upward to the surface. The mineral constituents of sediments in both the fissured and nonfissured areas are predominantly clay minerals, carbonates, salines, and analcite, with fine grains of quartz, feldspar, and ferro-magnesian silicates. Fissured playas possess significantly greater quantities of clay and carbonate minerals as compared to nonfissured playas. The clay minerals, carbonates, and analcite are primarily present in <2μ size fraction. This colloidal aggregate is believed to exert a major influence on the physical behavior of the sediments which contain the giant polygons. In particular, the dehydration to an almost dry condition of a clay mass, in which the water content may exceed the mineral content, results in a major loss of volume. The shrinkage leads to rupture with the formation of fissures. The fissures form orthogonal polygons characteristic of volume change in a largely uniform horizontal mass with one surface exposed.

Infrared Studies of Saline Sulfate Minerals

The cations Na, K, NH4, Ca, Mg, Mn, and, in certain instances, Ba, Sr, and Pb combine with the anion SO4 to form 58 mineral species. Slightly more than half are hydrous, and several contain Cl, F, or CO3. Infrared absorption spectra of most of the above sulfate s have been obtained with a split beam infrared spectrophotometer. The identity of each species examined has been verified optically and by means of X-ray diffraction for further confirmation. Where infrared curves have been previously published, the absorption bands obtained have been compared with data in the literature. Examination of the spectra indicates that the sulfates yield infrared curves that fall naturally into several groups. These groups are outlined, and the relative ranges in absorption characteristics are given for each. Structural analysis is beyond the scope of this paper, but attention is directed toward such structural features as may be compared with those of previous structural studies.

Mineralogic Nature and Origin of Phosphorite, Beaufort County, North Carolina

A large Miocene phosphorite deposit on the Atlantic Coastal Plain in Beaufort County, North Carolina, contains estimated reserves of 10 billion tons. The phosphorite zone, where examined, is 60 feet thick, and the P 2 O 5 content of the untreated ore is about 18 per cent. The sediment consists of phosphate pellets, sand-sized quartz grains, and clay, with thin beds of indurated coquina and phosphatic dolomite. The phosphate pellets contain quartz grains, glauconite, carbonaceous matter, and organic remains. Although most of the pellets are structureless, some show concentric layering around a nucleus. Chemical, X-ray-diffraction, infrared-spectral, and other data demonstrate that the phosphorite mineral is francolite, and that CO 2 is an integral part of the apatite structure. The clay fraction of the phosphorite includes montmorillonite, illite and clinoptilolite. The clay minerals and zeolite probably originated through alteration of volcanic detritus from an undetermined source. Studies indicate origin of the phosphorite to have been in a shallow marine basin characterized by a reducing environment, phosphate replacement of calcareous sediments, local reworking and alteration of certain of the pellets, and coincidence of phosphorite deposition with pyroclastic activity.

The clay minerals and their identity

ABSTRACT A study of the clay minerals is in progress and while not complete is yielding information about some of the fundamental minerals of sedimentary materials and the conditions that favor their formation. There are several kaolin minerals, but kaolinite is the only one that is likely to be found in sedimentary beds. Clays of the heidellite, montmorillonite, or other types are, however, more widespread in soils and shales than kaolinite. Calculations based on the assumption that kaolin is the typical clay-forming mineral are commonly in error. The relationship between geologic processes and the formation of different types of clays is outlined; and also the way in which geologic conditions may be reflected by base exchange.

Tungsten-bearing manganese deposit at Golconda, Nevada

The tungsten deposit lies just above the former high water level of Quaternary Lake Lahontan and a short distance east of Golconda, Nevada. Tungsten-bearing manganiferous and ocherous deposits underlie calcareous tufa. The tungsten ores lie blanketlike on an erosion surface which truncates tilted Triassic sediments. Beneath the blanket deposits are veins of similar mineralization which are thought to have provided the source of the overlying ores. The blanket deposits are sufficiently large and contain enough tungsten to justify economic development. The ore minerals are colloidal in origin, tungstic acid having been adsorbed in psilomelane and Iimonite while both were gels. Both the ore-bearing layers and the tufa are considered to be chiefly of hot spring origin rather than the result of precipitation from Lake Lahontan. A jarosite-bearing vein containing small amounts of tungsten crops out at a slightly higher elevation where the hot springs deposit has been removed by erosion. The vein cuts steeply inclined limestone which has been considerably altered to chert and highly silicified with the production of quartzose masses. This vein is thought to be indicative of a still lower level of mineralization than the veins immediately below the blanket deposits. It is believed mineralization started with chertification and silicification but ultimately resulted in precipitation of tungsten, iron, manganese, and tufa. The source of the tungsten is not exposed, but the existence of scheelite deposits in the vicinity suggests the possibility of underlying scheelite or perhaps wolframite-bearing veins.

Application of clay mineral technique to Illinois clay and shale

INTRODUCTION The method of analysis herein described is being used in Illinois in an investigation of the mineral constituents of various soils, clays, and shales. The results are to be published later, but sufficient progress has already been made to warrant a statement of the technique developed. The need for a method for the accurate identification and classification of mineral particles of colloidal size has long been a problem.[1][1] Various methods have been used in attempting to solve the problem, but in investigating the argillaceous sediments of Illinois, it was found that even the most recently described techniques do not entirely suffice when the colloidal particles contain several minerals. Although this inadequacy has not been entirely surmounted for all argillaceous materials, it is felt that the technique herein described permits a more complete and more accurate mineral identification than has been possible heretofore. A clay and a shale from Illinois . . . [1]: #fn-2

Breccia Pipe near Cameron, Arizona

Black Peak protrudes above a tableland of Navajo Sandstone on the Colorado Plateau just east of Echo Cliffs and 30 miles north of Cameron, Arizona. A breccia pipe on the west slope of the butte locally contains breccia fragments of sandstone, mudstone, shale, and altered dike rock believed to have been plucked from wall rocks and transported upward. Sources of uranium mineralization in the Cameron area may be inferred from the origin of the pipe. A vesicular, silicified collar several feet thick encloses the pipe on three sides. Minute micro-acicular quartz overgrowths on quartz crystals in the wall rock suggest that explosive penetration of superheated steam formed the pipe. Irregularly distributed argillic alteration, silicification, and mineralization suggest subsequent hydrothermal activity. Associated with the pipe are carbonates, alunite, gold, silver, iron, manganese, and possibly uranium and copper. Silica has been introduced in the largest quantities. The butte was probably formed by vertical penetration by fluids of magmatic origin from below; this suggests a possible original source and one phase in the mechanism of introduction of mineralization in the Cameron area.

URANO-ORGANIC ORE AT TEMPLE MOUNTAIN, UTAH

Urano-organic substances form essential constituents of the uranium ore at Temple Mountain, Utah. These occur in the vicinity of highly altered collapse structures associated with carbonaceous and petroliferous materials. Chemically, the ore is similar to low-rank coals. Geological conditions, the uranium distribution, texture, physical properties, and microscopic characteristics are indicative of a petroliferous origin. The ore is considered a uranium analogue corresponding to thucolite, the thorium and rare-earth radioactive mineral. The writers believe that induration resulted from polymerization and oxidation-devolatilization of hydrocarbons, caused by the interaction of ore solutions and organic materials at elevated temperatures. The limits of temperature postulated are a minimum of 100° C. and a maximum possibly as high as 350° C. A characteristic group of metallic elements is present in the ore, as shown by the X-ray spectrograph. A rough zonal relation exists. Arsenic, cobalt, and selenium are concentrated near the collapse, whereas uranium, zinc, and vanadium appear more abundant in the mining area away from the collapse. Small particles of uraninite and sphalerite are disseminated throughout the ore, but the zonal relation is emphasized by the occurrence of native arsenic near the collapse and by the occurrence of montroseite, the primary vanadium oxide, in the mining area. The distribution of supergene oxidation minerals of vanadium and arsenic is further confirmation. Ore textures suggest the emplacement of uranium-bearing organic material by the flocculation and subsequent accretion of hydrocarbons immiscible in aqueous ore solutions. Replacement of the sediments took place under the corrosive influence of the ore and pre-ore solutions. Contemporaneously, metallic elements were extracted from the solutions by the organic material. During emplacement and induration, dispersed particles of metallic minerals were formed. Banded nodules of the organic material and associated metallic minerals developed as the intensity, composition, and quantity of the solutions varied through time. A change in the character of the ore solutions is indicated in the vicinity of the collapse by the presence of large replacement masses of dolomite and siderite above the ore horizon, abundant late hydrothermal jarosite in the Chinle, marcasite below the ore horizon, and the replacement of carbonate at depth. Slightly acidic conditions prevailed at depth, and neutral to slightly alkaline conditions prevailed above the ore horizon. Collapse features provided channels for the migration of organic materials and for the penetration of hydrothermal solutions. The occurrence of native arsenic, 2M 1 mica clay, and large masses of dolomite, and the character of the urano-organic ore indicate heating in excess of the effects ordinarily attributed to ground water. The distribution and character of the alteration, the ore-mineral suite, and the presence of collapse structures suggest an epithermal hot-spring origin for the uranium mineralization. The features at Temple Mountain are significant in the delineation of centers of uranium mineralization elsewhere on the Colorado Plateau.

Mud Volcano Clay, Trinidad, West Indies

Laboratory studies of clay-mineral samples have been made from two mud volcanoes on the island of Trinidad--Moruga Bouffe and Palo Seco. The mineral content and physical properties have been compared with clay samples from the lower Cruse and Nariva Formations, through which the throats of the mud volcanoes are believed to have penetrated. The clay minerals are mixed-layer illite-montmorillonite and kaolinite. In the formational samples, illite forms the larger part of the mixed-layer clay. Montmorillonite is preponderant in the clay from the mud volcanoes. The kaolinite in the formational clay is more ordered in crystal structure than that of the mud volcanoes. These slight differences produce interesting variations in the behavior of these clays. The formation samples contain 55-69 percent Higgins and Saunders suggested that the mud-volcanoes have formed either as a result of tectonic movement, accumulated gas pressure, or a combination of the two mechanisms. It is suggested herein that the thixotropic character of the clay may have greatly accelerated either mechanism. Thixotropic clay saturated with water becomes a highly mobile fluid with great transporting power. Where such a mobile mass accumulates along a partly broken anticlinal structure, any release of pressure will occur upward. A gas pocket, tectonic squeeze, or both will provide pressure to maintain upward motion. In this way the clay would be extruded to form a mud volcano. Although moving vertically and supported by gas and tectonic pressure, the clay flowage has characteristics comparable to horizontal cl y movement in landslides where motion is maintained by gravity.

Observations on Quick Clay

Certain glacial and postglacial clay strata, long static in almost flat terrain, with little or no warning may flow spontaneously with destructive consequences. Samples of such clays, known as “quick clays,” have been examined from Scandinavia, Canada, and the northeastern United States. These have been compared with similar clays in areas where quick-clay movement has not been reported. The principal minerals in the clay-size fraction of the quick clays observed are sheet-layer silicates. Illite (hydromica) and chlorite occur most frequently, interlayered illite-montmorillonite is common, interlayered chlorite-montmorillonite occurs occasionally, and interlayered illite-vermiculite was found in one sample. Quartz, feldspar, hornblende, and calcite predominate in the coarser-size fractions and are found to some extent in the clay-size fractions. Most of the clays examined are of marine origin, but one of established fresh-water origin was included. The quick clays contain an average by weight of 57.3 per cent less than 2-μ. material, and the nonquick clays average 31.6 per cent less than 2-μ material. Chlorinity tests indicate that pore-water salinity of marine quick clays, about 35 g per 1 when deposited, becomes 0.2–15 g per 1 at flowage. The pore-water content of quick clays noted exceeds 44 per cent and in some clays may be as high as 80 per cent. Major critical conditions which contribute to quick-clay movement appear to be: substantial quantities of layer-lattice silicates of colloidal size (about 40 per cent or more by dry weight), substantial pore water (44 per cent), a reduction in electrolyte concentration below 5 g of salt per 1, and the addition of a dispersant. Under such conditions a clay becomes critically sensitive and may flow spontaneously or as the result of a shock. In quick clay of marine origin it has been suggested that a random orientation of clay particles is probably induced by coagulation during deposition. This orientation appears to provide stability to such clay strata. Removal of an electrolyte by natural leaching with fresh water appears to render the clay unstable. When the clay structure undergoes collapse, flowage is believed to result. Field conditions suggest that flowage of non-marine quick clay may be attributed to the action of a dispersant such as humic acid.