Геохимический состав циркона из различных магматических пород, ассоциирующих с разными типами оруденения (Восточное Забайкалье): разработка инновационных методов прогноза и поисков месторождений металлов

The magnetic susceptibility of granitic rocks as a proxy for geochemical composition: Example from the Saruhan granitoids, NE Turkey

Magnetic susceptibility and petrographic studies of drilled rock cuttings from two geothermal wells (Az-26 and Az-49) of the important electricity-generating geothermal system, Los Azufres, Mexico, were carried out to determine the relation between the magnetic susceptibility of rocks, the concentration of magnetic minerals and hydrothermal alteration. For this purpose, low-frequency magnetic susceptibility (χlf) was measured and compared its distribution trends with those of magnetic and Fe–Mg silicate minerals, and with the extent of hydrothermal alteration in rocks of the two geothermal wells. The study indicates a decrease in χlf values with depth in the two geothermal wells corresponding with: (1) an increase in the reservoir temperature and hydrothermal alteration; and (2) a decrease in the concentrations of Fe–Mg silicates and opaque minerals. The data suggest that ferromagnesian minerals and opaque minerals like ilmenite are the main contributors to the χlf of rocks. The decrease in χlf, ilmenite, and Fe–Mg mineral contents with an increase in the hydrothermal alteration degree, pyrite and haematite contents suggests the hydrothermal alteration of ilmenite and Fe–Mg minerals (characteristic of high χlf values) to pyrite, haematite and other opaque minerals (with low χlf values). The interaction of hydrothermal fluids with rocks results in the hydrothermal alteration of primary minerals. In a geothermal area, an anomaly of low magnetic susceptibility values of rocks in a homogenous litho unit characterized by high magnetic susceptibility may suggest hydrothermal alteration. Magnetic susceptibility can be a useful parameter, during the initial stages of geothermal exploration, in identifying hydrothermally altered rocks and zones of hydrothermal alteration both at the surface and from drilled wells in geothermal systems.

Twenty-seven areas of basement outcrop in California were systematically examined in an attempt to correlate rock type and magnetic susceptibility with observed magnetic response. The investigation was performed by traversing selected areas of basement outcrop with a portable total intensity magnetometer, mapping lithologic contacts along the traverses, and sampling the different rock types for later petrographic identification and susceptibility determination in an inductance bridge. In general, results from 275 samples support the established relationships between magnetic susceptibility and rock composition; i.e., acidic igneous rocks and metasediments are less susceptible than basic igneous rocks. However, magnetic susceptibility is primarily a function of magnetite and ilmenite content, and susceptibilities of individual samples within a given rock type were found to vary widely and in direct relation to the percentages of these minerals. Good over-all correlation is shown between magnetic response and rock magnetic susceptibility, but theoretical susceptibility contrasts calculated from the magnetometer profile gradients are usually very much higher than the laboratory measured susceptibilities. This discrepancy is most probably due either to weathering effects on the surface rocks or to an insufficient number of samples. Serpentinite yielded the highest mean susceptibilities both by laboratory measurement and analysis of gradients measured in the field. End_of_Article - Last_Page 1770------------

Summary Gravity- Magnetic Potential Field Survey for Hydro-Carbon Exploration, in Azerbaycan Onland Summary Deep geological structures studied by gravity and magnetic exploration, based on Earth’s potential fields. Detailed mapping oil and gas deposits in gravity and magnetic fields were resolved. Decrease in density and magnetic susceptibility of rocks in oil fields, are proved by studying physical parameters in Middle Kura Depression, author quantitatively evaluated the change in magnetic susceptibility, temperature and density of rocks above and below the reservoir, on basis of which physical and geological model of the Muradkhanly Reservoir was compiled. New technique was developed to identify weak local gravity and magnetic anomaly associated with oil and gas deposits. A regional background field was constructed, so that it adjoins curves from side of the lowest value potential fields, which makes it possible to identify anomalies caused by structural constructions of deep geological environment. Depending on zones of gradient changes, characteristic local minima are distinguished against their background due to presence of HC deposits in section which is diagnostic sign of reservoir type anomalies. Successful results obtained by GM Exploration in Muradkhanly, Jafarly and Bozgobu Fields of the Middle Kura Depression.

Based on the volume magnetic susceptibility and specific gravity measurements and mineral and lithologic identification results for 540 samples, the rock type, density, and magnetic susceptibility of rocks from northern Borneo were analyzed, and the applicability of gravity and magnetic data to the lithologic identification of the Mesozoic strata in the southern South China Sea was assessed accordingly. The results show that there are 3 types and 25 subtypes of rocks in northern Borneo, mainly intermediate‐mafic igneous rocks and exogenous clastic sedimentary rocks, with small amounts of endogenous sedimentary rocks, felsic igneous rocks, and metamorphic rocks. The rocks that are very strongly–strongly magnetic and have high–medium densities are mostly igneous rocks, tuffaceous sandstones, and their metamorphic equivalents. The rocks that are weakly magnetic‐non‐magnetic and have medium–very low densities are mostly conglomerates, sandstones, siltstones, mudstones, and coal. The rocks that are weakly magnetic‐diamagnetic and have high‐medium densities are mostly limestones and siliceous rocks. The Cenozoic rocks are characterized by low densities and medium susceptibilities; the Mesozoic rocks are characterized by medium densities and medium–high susceptibilities; and the pre‐Mesozoic rocks are characterized by high densities and low magnetism. Based on these results and the distribution characteristics of the various rock types, it was found that the pre‐Mesozoic rocks produce weak regional gravity anomalies; the Mesozoic sedimentary rocks produce negative regional gravity anomalies; whereas the Mesozoic igneous rocks produce positive regional gravity anomalies; and the Cenozoic igneous rocks produce positive regional gravity anomalies. The regional high magnetic anomalies in the southern part of the South China Sea originate from the Mesozoic mafic igneous rocks and their metamorphic equivalents; and the regional medium magnetic anomalies may be produced by the felsic igneous rocks and their metamorphic equivalents. Accordingly, the identification of the Mesozoic lithology in the southern South China Sea shows that the Mesozoic sedimentary rocks are distributed over a large area of the southern South China Sea. Thus, it is concluded that the Mesozoic strata in this area have the potential for oil and gas exploration.

Lake Maninjau was formed after a caldera forming eruption ∼50,000 years ago. Eventhough this eruption is one of the biggest Quarternary eruptions on Sumatra, it is not studied in detail so far. Only few attempts to study the volcanic processes have been carried out, mainly focusing on stratigraphy, physical volcanologoical parameters and geochemical characterization of volcanic rocks around the lake but the magnetic susceptibility of the pre- and post caldera lava have not been studied. Identification of the magnetic susceptibility of rocks can be done by using Bartington Magnetic Susceptibility Meter type MS2B. This study aims to determine the concentration of magnetic minerals based on the value of magnetic susceptibility in rocks. The Magnetic susceptibility data can be used as initial characteristics to understand the volcanic processes in the past and explain the environmental changes processes. The magnetic susceptibility values obtained ranged from 967.8 × 10−8 m3/kg - 2187.0 × 10−8 m3/kg. This Range indicates that the sample is estimated to be dominated by ilmenite (FeTiO3). Further frequency dependent susceptibility (χfds%) defined as ratio of magnetic susceptibility measured with difference frequency ranges less than 1%. Our results show all the samples are virtually no superparamagnetic and generally dominated by multi-domain (MD) grains.

Upper Cretaceous volcanic rocks were collected at 24 sites along the Pontides, N-NE Turkey, for rock magnetic and geochemical studies. Rock magnetic and petrographic methods showed that the lavas are characterized predominantly by titanomagnetites with a mixture of pseudo-single and multi-domain grains, whereas in tephrite single domain titanohematite was dominant. Measurements of magnetic susceptibility and the geochemical properties on different volcanic rock types provide important knowledge about the magnetic stability of the rocks. The magnetic properties are interpreted in terms of the composition, concentration, magma generation. Tephrite and phonotephrites with the highest intensities (5200 mA/m) and high magnetic susceptibility values (2585 × 10−5), largest grain sizes and Fe/Ti values, showing minor or no alteration are the most magnetic stable samples in contrast to dacites with the lowest intensity-magnetic susceptibility (520 mA/m − 573 × 10−5) and high alteration degree. The basanite samples show very low NRM (48–165 mA/m) but very high magnetic susceptibility (2906–3100 × 10−5) values suggesting the alteration of Fe-Ti minerals. It is shown that the magnetic properties of the basic to acidic rocks show a systematic variation with magma differentiation and could be related to fractional crystallization. Major and trace elements revealed that the lavas are compatible with complex magma evolution, with mineral phases of olivine+magnetite+clinopyroxene in basic series, amphibole+ +clinopyroxene in intermediate rocks and plagioclase+clinopyroxene+biotite in acidic series.

Recent advances in environmental magnetism have led to new applications in understanding soil pollutions from anthropogenic sources. The utility of environmental magnetic techniques varies widely depending on biological, chemical and physical processes that create and transform soils and sediments. Researchers in some European and Asian countries have successfully studied heavy metals in top soils using magnetic susceptibility technique. Accelerated urbanization in the past two decades has significantly altered the environmental landscape of Madinah. A famous wadi Aqiq in the heart of Madinah, an important conduit for groundwater recharge, is one of the most affected. This study thus focuses on magnetic susceptibility application as environmental magnetic technique to map heavy metal concentrations in top soils along wadi Aqiq, northwestern part of Madinah. Higher values of magnetic susceptibility from soil cover than those from parent igneous rocks indicate anthropogenic origin metallic contamination in the study area. The trucks/tankers parking area reveal highest values of magnetic susceptibility. The areas close to heavy vehicular traffic along two major roads also indicate higher magnetic susceptibilities because of enhanced metallic contaminations. The areas covered by residential and commercial buildings reveal medium level of magnetic susceptibilities. The left over asphalted materials at various places in the area is another source of high magnetic susceptibilities. Widely distributed metallic objects in the area, such as hangers, cans, and construction materials also contribute to enhanced soil contamination as evident from high magnetic susceptibilities.

The purpose of the article: obtain new data of magnetic fields, magnetization, and magnetic susceptibility of rocks at large depths under conditions of their natural location. Solve technological problems associated with the detection of metal in the walls of wells and near borehole space. Methods: for magneto metric studies, magnetometers-inclinometers have been developed at the Institute of Geophysics of the Ural Branch of the Russian Academy of Sciences, which allow continuous measurements of the magnetic susceptibility of rocks (χ), the vertical component (Za) and whole vector of the horizontal component (Ha) of the geomagnetic field; magnetic azimuth (Am) and zenith angle (φ) of the well. Results: the capabilities of the well magnetometry method for studying the magnetic properties of rocks and the refinement of the litho logical and stratigraphic characteristics of the Kola SG-3, Krivoy Rog SG-8, Ural SG-4, Muruntau SG-10, Saatlinsk SG-1, Timan-Pechora SG-5, Kolvin, Vorotilov, Tyumen SG-6, Novo-Elkhovsk, Tyrnyauzsk super deep wells. Conclusions: it was showed the interrelation of magnetic characteristics with depth, age and litho logical composition of rocks was studied. Analysis of well magnetometer and MEP data allowed establishing the boundary of pyrite-pyrrhotine transition in the gold ore zone. It is shown the possibility of borehole magnetometry for solving paleomagnetic problems for determining the magnetization of rocks.

This study evaluated the magnetic properties, magnetic susceptibility and isothermal remanent magnetization (IRM) of tissue samples from the brain, liver, spleen, pancreas, heart and lungs, resected from human corpses, with the aim of identifying the magnetic mineral structures and understanding their possible connection to diseases, professional activity, age and gender of the individual, smoking habits and the environment. The heart was the organ with the highest values of magnetic susceptibility and the pancreas showed the lowest values. No relationship was found between magnetic susceptibility, IRM values and ages of the individuals. However the samples obtained in females showed lower values of magnetic susceptibility than those resected from males. The samples collected from the lungs of smokers have higher values of magnetic susceptibility and IRM indicating the presence of magnetic particles with an anthropic origin. Moreover, the complexity of the magnetic behaviour of these tissues may suggest a contribution of both biogenic and anthropogenic magnetic particles also due to some professional activities. In the brain a heterogeneous distribution of the magnetic susceptibility values was found, which might be related mainly to the diamagnetic behaviour of myelin-rich structures. This study suggests that although the diamagnetic and paramagnetic behaviour is common to all structures, magnetite-type structures are always present in the tissues and hematite-type structures may also contribute to the magnetic signal of the sample. IRM values are only dependent on the presence of magnetite or hematite-type magnetic structures and so this technique seems more suitable to achieve the characterization of biomagnetic structures than magnetic susceptibility.

Magnetic survey of topsoils in Windsor–Essex County, Canada

Complex studies of the mineral composition and petromagnetic properties of the rocks which compose an edifice of the Minami–Khiosi submarine volcano located in the Mariana island arc are carried out for the first time. The Minami–Khiosi Volcano is a part of the Khiosi volcanic complex within the alkaline province of the Idzu–Bonin and Mariana island arcs. All of the rocks analyzed are enriched in K2O (1.34–3.30%), Ba (370–806 ppm), and Sr (204–748 ppm). The basalt has a porhyric texture and contains mosTy olivine phenocrysts as individual crystals and growths with a size up to 2 cm; the groundmass is finecrystalline. The samples studied contain at least three Fe-bearing oxide minerals. These are predominant magnetite and less abundant ilmenite and Fe hydroxides. It is established that the samples studied are magnetically isotropic and have high values of natural remanent magnetization and Königsberger ratio. Similarly to the other island-arc Late Cenozoic submarine volcanoes in the western part of the Pacific Ocean, the samples studied are strongly differentiated by the value of natural remanent magnetization and magnetic susceptibility. The low-coercivity magnetic minerals (titanomagnetite and magnetite) of the pseudo-single-domain structure, as well as high-coercivity minerals (hematite) are the main carriers of magnetization. The high values of natural remanent magnetization are explained by the pseudo-single-domain structure of the titanomagnetite grains, whereas the high values of magnetic susceptibility result from the high concentration of ferromagnetic grains.

A landslide is one type of natural disaster due to the movement of masses of soil or rock moving down the slope. There is a place in Cihanjuang Village, Sumedang Regency that has experienced a landslide disaster. A landslide is a form of natural disaster resulting from the descent of large quantities of soil or rock down a slope. Cihanjuang Village in Sumedang Regency is one area that has been affected by such a landslide. The rock magnetism is one of the methods that can be used to analyze the characteristics of soil in potential landslide areas. Regarding the landslide and its soil properties, this research aims to distinguish the soil characteristics between non-landslide and landslide-prone areas in Cihanjuang Village, Sumedang Regency. The soil characteristics will be analyzed using magnetic susceptibility by low-frequency magnetic susceptibility (χLF) and frequency-dependent magnetic susceptibility (χFD%) values along with the morphology and mineralogy of magnetic grains by scanning electron microscopeenergy dispersive x-ray (SEM-EDX) and x-ray diffractometer (XRD). The χLF values of soil samples from non-landslide areas (outcrop) ranged from 327,21 – 409,34 × 10−8 m3/kg, whereas in the landslide-prone ranged from 202,87 – 408,56 × 10−8 m3/kg. The cFD% value in non-landslide and landslide areas ranged between 3,32 – 7,53% and 1,46 – 6,30%, respectively. The soil from non-landslide areas tends to have higher magnetic susceptibility values than landslide areas. Both soil samples have an abundance of superparamagnetic (SP) [ine grain. However, the morphology of non-landslide and landslide areas can be distinguished by grain size. This differentiation is based on the size of magnetite minerals present in the soil samples, as identi[ied by XRD analysis. Based on SEM-EDX analysis, the lower magnetic susceptibility values in landslide areas were identi[ied due to the low abundance of superparamagnetic or the high abundance of multi-domain (MD) particles that have a bigger size of magnetic grains than non-landslide areas.

Relationship between magnetic susceptibility and sediment grain size since the last glacial period in the Southern Ocean off the northern Antarctic Peninsula – Linkages between the cryosphere and atmospheric circulation

BackgroundA QSM template of the older‐adult brain is not yet available. This study constructed a high resolution QSM template of the older‐adult brain for the MITRA atlas using data from a large, diverse, community cohort of non‐demented older‐adults.MethodMagnetic susceptibility maps were generated for the 400 older‐adult paricipants used in the construction of MIITRA using the Morphology Enabled Dipole Inversion(MEDI) on the 3D 5‐echo GRE data(0.7×0.7×1.3mm3) and upsampled to 0.7×0.7×0.65mm3 using nonlocal upsampling. The first GRE echo of each participant were N4 bias field corrected, then upsampled to 0.7×0.7×0.65mm3 using non‐local upsampling and converted to synthetic T1w images using mri_synthsr. The original 3D T1w MPRAGE(1×1×1mm3) data were upsampled to 0.5×0.5×0.5mm3. The synthetic T1w images were linearly registered to the upsampled T1w data and the resulting transformations were used to forward‐map magnetic susceptibility values from the native space of each participant to exact physical locations in MIITRA space. A sparse representation based data‐fusion approach was used on the transformed signals to generate the final 0.5×0.5×0.5mm3 resolution template, denoted as MIITRA_QSM(Fig.1). Since no other magnetic susceptibility template of the older‐adult brain is currently available, we compared MIITRA_QSM to a young adult template named MuSus‐100(1×1×1mm3,100 participants,mean age 24 years) in terms of image quality and magnetic susceptibility properties.ResultVisual showed that MIITRA_QSM template includes fine details, has the expected QSM contrast, highest values in subcortical, brainstem, and cerebellar structures known for their high magnetic susceptibility(especially in older adults), lower values in the white compared to gray matter, and higher values in white matter of the frontal lobe compared to parietal and occipital lobes. When compared to MuSus‐100, MIITRA_QSM showed better delineation of cortical structures and higher image sharpness(Fig.2), as well as higher magnetic susceptibility values in most subcortical brain structures(Fig.3A), Cortical structures from the two templates exhibited more similar magnetic susceptibility values(Fig.3B).ConclusionMagnetic susceptibility values in specific subcortical, brainstem and cerebellar structures are higher in the MIITRA_QSM template compared to a young adult template, probably due to increased metal deposition in these structures with aging. The new template is expected to greatly enhance the accuracy of voxel‐wise and atlas‐based QSM studies on older‐adults.