Once ordinary chondrites fall on Earth, Fe–Ni minerals and troilite they contain oxidize and transform into iron oxyhydroxides and/or iron oxides, which is expected to modify their magnetic properties. In this study, the effect of long-term terrestrial weathering on the magnetic properties (magnetic susceptibility and hysteresis parameters) of 117 H and L ordinary chondrites from the Atacama Desert (Chile), a region hosting the oldest meteorite collection in the world, was investigated. The measurements revealed a consistent weathering-induced decrease in the saturation magnetization and magnetic susceptibility of both H and L chondrites. The observed trends indicate a faster initial weathering of Fe–Ni minerals compared to troilite, their transformation into mostly paramagnetic iron oxyhydroxides, as well as the formation of magnetite in the later weathering stages.

Aim. To compare the results of studying the magnetic properties and concentration of heavy metals in the soils of the Dubravniy Forest recreational zone of Kazan to justify the use of the petromagnetic method in conducting ecological and geochemical studies in urbanised areas.Material and Methods. The object of the study is the soil cover in the "Dubravniy Forest", using petromagnetic methods (magnetic susceptibility, differential thermomagnetic analysis) and atomic absorption spectrometry.Results. According to the results of the studies conducted into the lightgray forest soil, the measurements of magnetic susceptibility and concentration of mobile forms of heavy metals do not contradict each other and indicate the absence of magnetic minerals and heavy metals of technogenic origin.Conclusions. The results of magnetic susceptibility studies indicate the absence of soil contamination with heavy metal compounds, which was confirmed by the results of the determination of mobile forms of heavy metals by the atomic absorption method.

В статье приведены некоторые результаты сейсмоакустического профилирования бассейна и исследования магнитных свойств донных отложений озера Тургояк (Южный Урал). Толща озерных осадков в восточных впадинах достигает 8 м. Радиоуглеродное датирование образцов позволяет говорить о возрасте озера, составляющем не менее 25 тыс. лет. По данным сейсмоакустики нижняя часть разреза, представленная плотными осадками неоплейстоцена, накапливалась при более низком уровне воды. Голоценовые осадки представлены толщей слабоконсолидированных илов мощностью до 4 м. Показано, что магнитные свойства осадков характеризуют условия окружающей среды и колебания уровня озера. Скалярные магнитные величины в осадках показывают высокоамплитудные вариации, отражающие частую смену условий осадконакопления. Осадки с самыми высокими значениями магнитной восприимчивости (χ), естественной остаточной намагниченности (NRM), коэрцитивной силы намагниченности насыщения за вычетом влияния парамагнитной компоненты (B_c), коэрцитивной силы остаточной намагниченности насыщения (B_cr), намагниченности насыщения за вычетом парамагнитной компоненты (M_s), нормальной остаточной намагниченности насыщения (M_sr) вероятно формировались в периоды ледового переноса осадочного материала со значительным участием эолового агента.

Summary: In-situ combustion (ISC) has been proven as a promising technique for the extraction of heavy oils. It has been used in oil fields since the 1920s; however, it is still not as widely used as steam injection. One of the difficulties limiting its wide application is monitoring and controlling the movement of the combustion front. This work is aimed at studying the change in the properties of rock during the ISC process, which is expected to be used for developing an effective monitoring method of the combustion front movement. Rock samples before and after the ISC process were obtained from the Xinjiang Oil field (China) where an ISC industrial pilot has been implemented. In the temperature range of lower than 500℃, the minerals may only alter slightly. Therefore, it is difficult to determine whether the rock was heated or not during the ISC processes using general mineralogical or geochemical methods, for example, X-ray diffraction. This work takes a comprehensive approach to study the variation of rock properties. Magnetic analysis was chosen as the primary method since a very tiny change in the mineral composition during heating leads to profound changes in the magnetic properties. We analyzed magnetic susceptibility (MS), natural remanent magnetization (NRM), hysteresis parameters and thermomagnetic data. In addition, we performed differential thermomagnetic analysis (DTMA) for tracing magnetic minerals based on their Curie temperatures as well as for monitoring transformations in magnetic minerals during heating. Simultaneously, X-ray diffractometer (XRD), optical microscope for thin-sections, and organic content measurements were used as assistive methods to get a comprehensive evaluation on the variation of rock. We found that there is a big difference in magnetic minerals between the initial samples (not subjected to the ISC process) and burned samples from different wells and depths in the ISC pilot. Several magnetic clusters with different coercive force and domain structure were found in these samples. Based on the difference in magnetic properties, we found that the burned samples were heated to different temperatures during the ISC process. In addition, for some rock samples, the heating temperature during the ISC process was determined, and an analysis was made of the propagation of the combustion front. The thermal magnetic properties variation of rock during the ISC process is obvious, which makes it promising to be used for monitoring the propagation direction of the combustion front. Theoretical calculations of magnetic anomalies that occur due to changes in the magnetic properties of rocks during the ISC process indicate the possibility of the detection of such anomalies from the Earth’s surface through high-precision magnetic surveys. The findings in this work provide a theoretical base and direction for developing combustion front monitoring technologies.

Петрофизические таксоны месторождения алмазов кимберлитовой трубки «Комсомольская» (Якутская алмазоносная провинция)