Field Geochemistry Research Articles

GEOCHEMICAL ANOMALIES IN THE BOTTOM WATERS OF THE TADJOURA RIFT ZONE, GULF OF ADEN

The study of geochemical fields and geochemical anomalies is a necessary part of exploration for ore deposits on the ocean floor. Geochemical processes related to hydrothermal activity occurring at the boundary between different media are of special interest. About 10 years ago, concentrations of suspended iron 20 times greater than those in the overlying waters were found in the bottom waters of the Mid-Atlantic Rift near 26/sup 0/N. A number of reports then appeared, showing that in other rift zones as well, the bottom/water interface is characterized by elevated concentrations of iron, manganese, zinc, copper, nickel, and other elements. Thus the present writers were persuaded that the minor elements in bottom waters can serve as indicators of hydrothermal flux to the ocean floor. In carrying out investigations of this kind, one must study the distribution of the metals not only in the bottom waters, but through the entire depth of the sea, so that anomalies can be detected and localized against the level of the background concentrations. In addition, to obtain information on the sources of the metals, one must determine not just the total contents, but also distinguish the metals in solution and in suspension. Results are discussed. Themore » observations clarify the relations between dissolved and suspended forms of metals in weakly mineralized waters above oceanic rifts. 13 references, 5 figures, 5 tables.« less

The concept of geochemical potential field exemplified by ore formation field

Geochemical potential field is defined as the scope within the earth’s space where a given component in a certain phase of a certain material system is acted upon by a diffusion force, depending on its spatial coordinatesX, Y andZ. The three coordinates follow the relations: $$NF_{ix} = - \frac{{\partial \mu }}{{\partial x}}, NF_{iy} = - \frac{{\partial \mu }}{{\partial y}}, NF_{iz} = - \frac{{\partial \mu }}{{\partial z}}$$

Geothermal resources assessment in Hawaii

Report prepared for Western States Cooperative Direct Heat Resource Assessment under grant No. DOE DE-ACO3-80SF10819, Feb. 1985.

Formation of geochemical fields of concentration in the thermal gradient fields of intrusive bodies

The concentration of metals and ores in thermal fields of intrusive bodies can be analyzed by numerical simulation (modelling) of the heat-mass transfer process. A knowledge of the dynamics and the movement of the temperature and crystallization fronts, as well as an understanding of the characteristics of the thermal gradients, heat flows, energy, and thermal stresses which result in the formation of fracture zones, are necessary for an estimation of the spacial and temporal aspects of the mass balance calculations and the ore concentration processes. The application of the method is illustrated by observing the changes in the rare earth element concentration in a vein-type apatite orebody in limestone which has been intruded by a post-ore dike. The method has potential value in exploring for hidden mineralization.

GEOCHEMICAL AND GEOPHYSICAL PREREQUISITES FOR PREDICTING THE TYPE OF OIL AND GAS TRAPS

The use of traditional geophysical and geochemical methods for local oil and gas predictions is complicated by the effect of regional intraformational barriers such as traprock bodies, coal measures, and evaporites. Traprock intrusives often generate false structures, coal measures generate false hydrocarbon anomalies, and evaporites selectively control migration. A review is presented of the processes generating hydrocarbon accumulations based on paragenesis of subvertical, zonal-annual geophysical, geochemical, and biogeochemical fields within the sedimentary mantle and on hydrocarbon evolution modes in light of the regional geologic structure. In general, application of remote and direct geophysical and geochemical methods based on genetic analysis, will increase the number of exploration objects and raise the effectiveness of geologic explorations for petroleum and natural gas. 9 references.

Calorimetric measurements of the low-temperature heat capacity, standard molar enthalpy of formation at 298.15 K, and high-temperature molar enthalpy increments relative to 298.15 K of tungsten disulfide (WS 2), and the thermodynamic properties to 1500 K

Low-temperature (5 to 350 K) heat capacity, fluorine combustion, and high-temperature (350 to 1500 K) drop-calorimetric measurements have been performed on a pure synthetic specimen of tungsten disulfide, WS 2. The following molar thermodynamic quantities are reported at T o = 298.15 K: the standard enthalpy of formation, Δ f H m o( T o), −(240.8±3.1) kJ·mol −1; the heat capacity, C p,m o( T o), (63.82±0.32) J·K −1·mol −1; the standard entropy, S m o( T o), (67.78±0.34) J·K −1·mol −1; and the standard Gibbs energy of formation, Δ f G m o( T o), −(232.1±3.1) kJ·mol −1. The thermodynamic quantities have been calculated to 1500 K. Standard enthalpies of formation deduced from high-temperature equilibrium and e.m.f. studies in the literature are, in general, not in good agreement with one another or the present result. There have been no previous measurements of the low-temperature heat capacity, but the high-temperature enthalpy increments are in fair agreement with results published for WS 1.97. There is some indication of a γT ( i.e. conduction electrontribution to the heat capacity at low temperatures, but the evidence for this is not strong. The present thermodynamic quantities are consistent with geochemical field observations that molybdenite (MoS 2) and not tungstenite (WS 2) but tungstates and not molybdates are formed in hydrothermal deposits.

Controls on pore-fluid concentration of 4He and 222Rn and the calculation of 4He/222Rn ages

Abstract Controls governing the production of 4He and 222Rn in the solid phase as well as parameters and processes contributing to their transport into the pore fluid are discussed. 222Rn activity is used to quantify the uranium sources for 4He and the result is a simplified pore-fluid age equation which is virtually independent of the porosity, the water/rock ratio, the rock density and the uranium concentration, but does require a Th/U estimate. The crucial parameter is the ratio of the release factors for the two species, /GLRn//GLHe, which is discussed in terms of three possible release mechanisms: (1) recoil; (2) recoil followed by diffusion; and (3) weathering release of accumulated 4He. It was found that /GLRn//GLHe can vary over several orders of magnitude, but can be expressed in terms of the effective grain size r, and the diffusive half-length for 222Rn decay, re. 4He measurements are used to “date” gases from known gas fields and the agreement with the assumed source-rock age is good. Application of 4He/ 222Rn measurements to continental freshwater springs indicates that the weathering release of accumulated 4He dominates the input and results in a large overestimate of groundwater age. Measurement in the Lardarello geothermal field indicates that the 4He/222Rn method can indicate relative transport direction. Other possible applications in various geochemical fields are suggested.

Theory of geochemical prospecting for oil and gas (mathematical modeling of the process of transformation of organic matter)

Construction of a theory of the geochemical field is not only extremely important to improve current geochemical prospecting, but is extremely necessary for creating new methods of determining the predicted reserves based on mathematical models of the processes of oil and gas formation. Only a systematic analysis of the formation of concentration fields will allow construction of a model which accounts for all aspects of the relations of hydrocarbons to the mineral components of the surrounding medium. 1 figure.

Distribution and dispersion of lead and zinc in anomalous soils and stream sediments, Mount Hermon area, Israel

Geochemical field and laboratory tests of soils and stream sediments in an area of weak surficial lead-zinc mineralization resulted in the delineation of two anomalous zones. Lead-zinc values are exceptionally high, but downslope and downstream mobility is low. The metals occur in base-exchangeable positions (∼5%), with iron oxides (∼45–60%), in clay lattice positions (∼15–30%), as resistant minerals (∼2–5%), and in organic matter (up to 20%). Intense dissolution and redeposition of metals occurred probably close to their point of origin in residual soils.

北蒲原平野における石油・ガスの移動，集積機構に関する１考察

During the last decade, many arguments have arisen about the generation, migration and accumulation of hydrocarbons. Improvement of geochemical field and the study of physical properties of hydrocarbons contribute to solve the above subject.The writers studied Kitakanbara area, northern part of Niigata prefecture, where active hydrocarbon exploration and development have been made. As a result of the exploration and development of the hydrocarbon in this area, many kinds of the data on the subsurface petroleum geology were collected, and published. In this paper the subject is discussed as follows: 1. distribution and deposional mechanism of reservoir facies, 2. a change of chemical composition of hydrocarbon at each producing oil and gas field and thermal effects.Paleodeposional system of reservoir facies is different at each geological stage. The sands of the Teradomari and Shiiya formation are transported lateraly from local source area. On the contrary, the sands of Nishiyama formation are widely derived from Kushigata mountain range area. Their distribution indicate a close relationship between the migration mechanism and the forming of accumulation of hydrocarbon. A significant change of chemical composition of hydrocarbon reflects the migration distance (mobility) and a grade of water washing. These data show that the Shiiya formation generates hydrocarbon in surrounding Shintainai area, which then migrated to Hirakida gas field with oil and gas segregation facies, and then medium gravity crude oil is transfered to Echigo-Kurokawa under the controls of differential entrapment. These migrations occured between the Nishiyama stage and Haizume stage that is simultaneous developing and forming this basin. This oil varied to the heavy oil after accumulation by water washing effect.

Geochemical field kit for the determination of trace amounts of molybdenum [reply to 1968 discussion by Bloom of 1967 paper

At sufficient temperature, potassium pyrosulfate fusion should generate enough sulfuric acid to attack molybdenite and make the field test valid for samples with this sulfide. 9Nearly total9 is preferred to 9total9 for actual amount of Mo extracted from rocks and soils (original paper, ibid., v. 62, no. 5, p. 732-736, 1967).

Geochemical field kit for the determination of trace amounts of molybdenum

Geochemical field kit for the determination of trace amounts of molybdenum

General Patterns in the World Geography of Soils

The author, head of the Department of Soil Science and Landscape Geochemistry at Moscow University's Geography Faculty, notes that the traditional zonal concept based on heat belts of the earth no longer accounts satisfactorily for the world distribution of soils. She proposes a typology of geographic soil units based on soil characteristics rather than soil-formation factors: major geochemical fields based on soil reaction and oxidation-reduction potential; and soil sectors within fields, defined in terms of soil classes and families, the history of soil formation, and the energy level of soil processes.

A geochemical field method for determining tungsten in soils and stream sediments

A geochemical field method for determining tungsten in soils and stream sediments

Geochemical Exploration Techniques in U.S.S.R.: ABSTRACT

Geochemistry is widely used in field operations, and represents about 25 per cent of the petroleum exploration research in the U.S.S.R. Three approaches are used: (1) subsurface prospecting which included mudlogging, End_Page 381------------------------------ hydrocarbon distributions in sediments, and geochemical criteria for indicating oil such as the presence of organic compounds in waters; (2) surface prospecting which is concerned with rates of diffusion and filtration of hydrocarbons through sedimentary rocks, micro-biological detection of hydrocarbons, and the evaluation of radiometric, organic, and inorganic anomalies of the surface; (3) studies on the origin of petroleum and the recognition of favorable oil forming environments. About 90 per cent of the 300 geochemical field parties are doing subsurface prospecting. The other 10 per cent are engaged in surface surveys, and these are on a research basis. They are limited to arid areas of shallow young sediments such as around Volgograd, Baku, and Turkmenia. In contrast, about half of the geochemical research at 30 institutes or more in the U.S.S.R. involves surface prospecting techniques. The Soviets hope to develop a practical surface method that can be combined with geology for use in stratigraphic prospecting. In general, the Soviet scientists seem to be using more manpower and developing more geochemical parameters for field use than U. S. oil companies. The established facts of petroleum geochemistry, such as the organic nature of source beds and the detection of hydrocarbons in sediments and subsurface waters, are understood and taken into account in exploration programs. Thus the practical application of geochemistry in exploration is more widespread than in the U. S. End_of_Article - Last_Page 382------------

Origin of the bedded magnesite deposits of Manchuria

On the basis of available geochemical evidence and field and laboratory observations, concludes that extensive deposits of crystalline magnesite interbedded with dolomite of the Precambrian Wutai system in southwest Manchuria were formed by direct precipitation in a lagoon or shallow sea.

Geochemical field methods for the determination of tungsten and molybdenum in soils

Geochemical field methods for the determination of tungsten and molybdenum in soils

Geochemical Field Method for Determination of Nickel in Plants

Geochemical Field Method for Determination of Nickel in Plants