Magnetic Minerals Research Articles

An Overview of Late Quaternary Studies and Status of Mineral Magnetism from the Konkan Coast: Constrains on Degradation of the West Coast of India

We present here an overview of textural, sedimentological, magnetic, and remote sensing studies from different sectors of the west coast along with new mineral magnetic results. The emerging coastal erosion and growing incidences of extreme events with an increase in cyclones in the Arabian Sea are affecting these beaches at higher rates of dynamics. The sand characteristics, textures, sorting and clast composition have been studied to correlate them with energy conditions and interpret the transportation dynamics. Heavy mineral analyses delineated provenances and detrital pathways, the morphological and volumetric vicissitudes of beaches helped characterize western coast beaches into stable, eroding or depositing regimes aided by time elapsed satellite images. The multi-parametric studies unravel the relationship of hydrodynamics over a range of geomorphic features. The predominant controls of longshore and rip currents in altering the land-sea interfaces at less than decadal scales were observed. New mineral magnetic results from the Vengurla Beach of the Sindhudurg district are evaluated in above context and to establish semiquantitative relations amongst depositional and erosional patterns that can be further linked to the effects of degree and intensity of local monsoon. The beaches record systematic changes in the concentration of magnetite, haematite, maghaemite, and goethite as a result of a combination of the above beach processes. The studies from Vengurla beach successfully demonstrate mineral magnetism as a suitable quantitative approach to depict the quasi-decadal effects of long shore currents that are further governed by the shoreline changes resultant of increasing competitiveness between coastal erosion and depositional conditions in recent years. The status of studies over the west coast depicted an alarming increase in the rates of erosion at several beaches demanding quantitative monitoring using the integrative approach of mineral magnetism and satellite data. Keywords: West Coast, Magnetic Susceptibility, Curie Temperature, Provenance, Sindhudurg.

Analysis of Isothermal Remanent Magnetization (IRM) data of Brantas river sediments using IRMITS program

Pollution is one of the big problems of continuous pollution in the Brantas River. The type of pollution that occurs in the sediment of a river is associated with the characteristics of its magnetic mineral. This study aims to determine the types of magnetic minerals in the Brantas River sediments. IRM data was taken from the measurement results in the Brantas River sediments. In this study, the IRMITS program is used to provides a deeper and better analysis and interpretation. From the processing results, IRMITS produces 3 graphs, namely the Linear Acquisition Plot (LAP) curve (b) the Gradient Acquisition Plot (GAP) curve; (c) Standardized Acquisition Plot (SAP) curve. From this study that has been done, it shows that magnetic minerals in the Brantas River are saturated in magnetic fields above 800mT with permanent coercivity occurring in the range 12-13 x 10−3 and z value 0 before saturation occurs. This indicates that most of the Brantas River sediments is dominated by magnetite minerals (Fe3O4).

Differential Thermal Analysis Using High Temperature Susceptibility Instruments

AbstractMeasurements of susceptibility as a function of temperature are an important, standard method of quantifying a sample's magnetic mineralogy. These measurements are used to identify the Curie/Néel temperatures of constituent minerals and show evidence of thermally induced oxidation and formation of magnetic minerals. For these reasons, the High Temperature Susceptibility Bridge (HTSB) is a common instrument in paleomagnetism laboratories around the world. Here, we argue that HTSBs can be used to perform simple differential thermal analysis, a technique used to identify phase transitions and exo‐/endothermic reactions by measuring deviations in temperature from a steady heating rate. Because HTSBs are designed to heat samples at a relatively constant rate, the standard susceptibility measurement can be used to obtain similar information, albeit crude, about the phase transitions taking place. For standard samples of vivianite, goethite, and maghemite, we compare the heating curves of the sample and a blank run, to identify DTA‐analogous information. In the case of goethite and vivianite, the reactions identified do not have a corresponding expression in susceptibility, demonstrating that this approach expands the utility of this common piece of equipment. We estimate the minimum enthalpy of reactions detectable and their mass dependence. Additionally, we show that this approach is successful in detecting the dehydration of vivianite in a mixed mineralogy natural sample.

Irregular Magnetic Susceptibility Pattern of Iron Sand from Pasia Jambak Beach, Pasia Nan Tigo, Padang, Indonesia

West Sumatra has the potential of abundant natural resources in the form of iron sand, one of which is located in the Pasia Jambak Beach area, Pasia Nan Tigo, Padang. Basically iron sands have magnetite (Fe3O 4), hematite (α-Fe2O 3), and maghemite (γ-Fe2O 3) which can be used as a mineral of high economic value. However, the iron sand of Pasia Jambak Beach, Pasia Nan Tigo, has no known magnetic mineral. This study aims to investigate the magnetic mineral content of the iron sand of Pasia Jambak Beach, Pasia Nan Tigo, Padang based on its magnetic susceptibility. The variation of the investigated susceptibility value is based on depth. Magnetic susceptibility measurements were carried out using a Bartington Magnetic Susceptibility Meter with a MS2B sensor dual frequency. The results showed that the magnetic susceptibility value of the iron sand of Pasia Jambak Beach, Pasia Nan Tigo, Padang varied based on the depth from 291.1 x 10−8 m3/kg to 12445.5 x 10−8 m3/kg with an average value of 2016.35 x 10−8 m3/kg. Variations in the susceptibility value of iron sand obtained at each depth have changes or variations in the susceptibility value that are irregular or do not have a certain pattern.

Analysis of Vibrating Sample Magnetometer (VSM) data of Brantas river sediments using HYSITS

Several vital activities in East Java are supported by the Brantas River, ranging from irrigation, supply of water raw materials, to industry. Along with the growing population, has the potential to increase the pollution that occurs in the Brantas River. VSM data was taken from the measurement results in Brantas River sediments. The aim of this study is to analyze the VSM measurement data in the Brantas River using the HYSITS script. The analysis was carried out to determine the type of magnetic domain contained in the Brantas river sediment. HYSITS program is used to provides a deeper and better analysis and interpretation. The results show that HYSITS produces 2 curves besides hysteresis loop graphic, that is 1st derivative of ΔM curve and ΔM curve. From the Hysteresis curve of sample, it is known that the Saturation Magnetization (Ms ) value are 5.3262 - 5.998587 emu/g, the Saturation Remanent Magnetization (Mrs ) value are 1.1537 - 1.545586 emu/g, the Magnetic Coercivity (Bc ) value are 0.0188 - 0.020784 T, and Magnetic Remanent Coercivity (Bcr ) are 0.059891 - 0.0815. Result of the analysis indicates that the magnetic minerals in Brantas River are strongly suspected to represent ferrimagnetic minerals with Pseudo-Single Domain (PSD).

Application of K-Means Cluster Analysis for Magnetic Susceptibility Zoning of Urban Topsoil in Bandung City

Bandung is one of the metropolitan cities in Indonesia which has a dense population. As a result, the number of vehicles is increasing, which causes an abundance of particulates on the urban topsoil. Motor vehicle particulates can be identified through the value of magnetic susceptibility. The greater the magnetic susceptibility value on the topsoil, the more magnetic minerals are associated with the number of particulates produced by vehicles. To zone the value of magnetic susceptibility in an area, a clustering method is needed. In this study, magnetic susceptibility zoning analysis was conducted using the K-mean cluster method. The data processing results on 38 samples divided into three clusters showed that 12 samples were in cluster 1, 23 samples were in cluster 2, and 3 samples were in cluster 3. The samples in each cluster were influenced by the magnetic susceptibility value between the sample centre and the neighbouring samples. The validation of the clustering results is shown through the F test, which shows that the calculated F is greater than the F table at a significance level of 0.05. Thus, it can be said that there is an association between the magnetic susceptibility values in a cluster.

PyTherNal: A python program for analyzing curie temperature from thermomagnetic data

Thermomagnetic analysis is performed by bringing subject materials into its cooled and heated state, followed by analyzing the magnetic moment change. Performing these would result in obtaining the Curie Temperature of the materials, which is essential in estimating magnetic minerals contained in material samples. PyTherNal (Python Thermomagnetic Analyzer) is a thermomagnetic analysis tool in Python environment meant to assist in analyzing thermomagnetic data. The advantages of Python in its functionality and flexibility of being used in any operating system (OS) became the main reason for the program to be written in Python. PyTherNal is designed to assist in estimating Curie temperature of materials through thermomagnetic method, by locating the maximum curvature of the highest value of second (2nd) derivative of both cooling and heating data. To facilitate these, PyTherNal generates three figures, which are the curves for the thermomagnetic data, its 1st derivative, and its 2nd derivative. An advantage of the program is that it performs smoothing to increase the accuracy in estimating the Curie temperature as doing so would significantly minimize the variability of the derivative curve. Since the program is written in Python, it is open-source and therefore free to use. It is also capable of cross-platforming.

Identification of Rock Types from Iron Sand at Pasia Jambak Beach, Padang, West Sumatra

West Sumatera is a region that has an abundance of natural resources in the form of iron sand, one of which is in the area of Pasia Jambak Beach, Padang. Pasia Jambak Beach is one type of beach in rumps and sandy beaches, which has grayish-brown sand and rough grains on its surface. Iron sand could be formed due to weathering of rocks and materials found around the coast, such as old ships and others. This study aims to see the type rock of origin and the composition of the magnetic mineral elements found in the iron sand of Pasia Jambak Beach. The composition of iron sand-forming elements can be seen using XRF. The analysis results using XRF showed that the most dominant element in the samples was Si (Silica) and Fe (Ferrum). Based on the SiO2 vs K2O diagram, it can be seen that the iron sand in the Pasia jambak Beach area comes from weathering of Basalt, Dacite, and Latite rocks. So, it could be concluded that the original rock group from iron sand at Pasia Jambak Beach is the Calc-Alkaline group (medium Potassium content) and High K Calc-Alkaline (high Potassium content).

Mathematical Model of Ilmenite Separation Efficiency Using a High Gradient Plate Magnetic Separator

High gradient magnetic separation is widely used in magnetic minerals upgrading, and its separation performance is significant depending on the parameters. In this investigation, the Mathematical model of the plate high gradient magnetic separator is established, the magnetic induction and the flow field distribution are investigated based on the COMSOL multi-physical simulation, and then the separation efficiency and TiO2 grade are analyzed using the plate high gradient magnetic separator. Additionally, the key factors affecting the efficiency of mineral separation are detailed in the experimental separation, the separation efficiency is demonstrated and its feasibility is verified by experiments. It is founded that the mathematical model and simulation results are basically validated by the experimental separation process, and the TiO2 grade can be effectively upgraded from 5.2% to 11.5% with the rinsing water consumption 9.5 L/min and the belt rotating speed 2 r/min. It is thus concluded that plate high gradient magnetic separator has provided an effective way in upgrading ilmenite quality.

New Rock Magnetic Analysis of Ultramafic Cores From the Oman Drilling Project and Its Implications for Alteration of Lower Crust and Upper Mantle

AbstractDetailed magnetic analyses of ultramafic rock samples recovered from the Wadi Tayin massif as part of the Oman Drilling Project provide a unique opportunity to understand the magnetic properties of oceanic lithosphere and its alteration since obduction. We examined 300‐ to 400‐m‐long cores from 3 sites (BA1B, BA3A, and BA4A) that transected the crust‐mantle boundary. Serpentinization that produces a small amount of magnetite from olivine alteration plays an important role in shaping the magnetic signature of the rocks recovered from these holes. Our investigation reveals new features, which have not been reported in previous studies of ophiolite largely based on surface rock samples. It appears that when serpentinization reaches a certain point (65%), a sharp increase in magnetic susceptibility occurs. Such pattern opens the possibility of additional production of magnetic minerals induced by various reactions (e.g., further hydration of Fe‐rich serpentine minerals), which may have occurred, while the rocks were being serpentinized. In general, the uppermost section (0–40 m) shows higher susceptibility than the deeper part. Also, higher susceptibility is found in dunite‐dominated sections than those composed of harzburgite. Overall, our observations suggest that mantle rocks of Semail ophiolite have undergone multiple stages of serpentinization over different time periods.

Mapping magnetism: Geophysical modelling of stratigraphic features by using in situ magnetic susceptibility measurements at Pinnacle Point 5‐6 North, South Africa

AbstractThis study utilizes geostatistical modelling of magnetic susceptibility (MS) for geophysical prospection of archaeological stratigraphy at the Middle Stone Age rock shelter site of Pinnacle Point 5‐6 North. These models are overlaid onto high‐resolution photography of the stratigraphic sequence to study the lateral and vertical changes within the magnetic signature of the archaeological sequence and correlate these changes to micromorphological interpretations previously made at the site. In situ analysis is reinforced by laboratory magnetic mineralogical analysis utilizing MS; frequency‐dependent susceptibility (χFD); isothermal remanent magnetization; and anhysteric remanent magnetization to understand the composition of the magnetic minerals creating the in situ signature. This study shows that there is consistent variation in the magnetic signatures of the sequence that can be mapped with in situ MS; there is a correlation with laboratory analysis of magnetic mineralogy, which provides insight into changes in human behaviour; and our models correlate well with micromorphological interpretations of the site.

Sedimentary Rock Magnetic Response to Holocene Environmental Instability in the Pearl River Delta

Located on the northern coast of the South China Sea, the densely populated Pearl River Delta has experienced the combined effects of sea-level change, monsoon-driven discharge, and especially human activity, since the late Holocene. However, how these factors have regulated the regional environmental and sedimentary evolution remains unclear. To better understand these processes, we conducted a high-resolution rock magnetic investigation of the Holocene sediments of core DS01, drilled in the vicinity of the West River channel in the head area of the Pearl River deltaic plain. The magnetic grain-size proxy of the ARM/κlf ratio (the ratio of anhysteretic remanent magnetization to low-field magnetic susceptibility) indicates a long-term fining trend of the magnetite grain size, which may be a response to an increase in the weathering intensity in the Asian monsoon region during the Holocene. An interval with an enhanced concentration of magnetic minerals (mainly magnetite and hematite) occurred during 7.7–4.8 kyr BP (calendar years before 1950), coinciding with a period of delta progradation. During the marine transgression in the early Holocene, two similar intervals of magnetic enrichment may reflect regional hydrodynamic shifts associated with cooling events at ∼9.5–9.3 kyr BP and 8.2 kyr BP. The subsequent 4.2 kyr BP cooling event possibly induced a cold and dry environment in the sediment source area. From ∼800 yr BP onward, there was a major increase in the sedimentary magnetic mineral content, likely in response to intensified agricultural and industrial activities.

Magnetic Susceptibility of Volcanic Soil on the Surface of Mount Singgalang, Sumatra Barat

Volcanic soil is a part of interest for physical, chemical, and morphology studies of soil derived from volcanic ash, which is known to be fertile and is one of the most productive soils in the world. They are also known to have a high environmental carrying capacity, as evidenced by the dense population in the area around the volcano. The soil contains many minerals, one of which is magnetic minerals. However, there is no document so far that records the value of the magnetic susceptibility of volcanic soil on the surface of Mount Singgalang. This study aims to determine the abundance of magnetic minerals based on their magnetic susceptibility values. To achieve this goal, the rock magnetism method is applied with the Bartington magnetic susceptibility meter type MS2B sensor instrument. Magnetic susceptibility values can be used as initial characteristics to understand past volcanic processes and explain environmental changes. This method is very effective, inexpensive, sensitive, fast, and non-destructive. The results showed that the value of the magnetic susceptibility of volcanic soils varied with a value range of 93.3 - 352.5 (x10 −8 m 3 /kg). Based on this value, it is assumed that the magnetic mineral properties are antiferromagnetic. The average frequency dependent susceptibility (χ fd ) (%) ranges from 0.831 - 2.090 %, indicating that the measured volcanic soil contains almost no superparamagnetic grains and is generally dominated by multi-domain grains.

Locating skarns with magnetic survey data, Geyer, Erzgebirge: optimizing data acquisition procedures

ABSTRACTMagnetic data can be acquired from a number of different platforms (e.g., ground, drone, helicopter) using a variety of sensors (e.g., caesium vapour‐type optically pumped magnetometers, fluxgate, superconducting quantum interference devices) with different flight line configurations. To detect a magnetic anomaly associated with a mineral commodity that is not exposed but is thought to be associated with the anomalous magnetic mineral content, it is necessary to optimize the survey parameters through a complete data integration process. Prior petrophysical measurements provide insight into the physical contrast that might be expected between adjacent lithologic units and between the ore zone and the encompassing lithology. Oriented rock samples provide access to magnetic remanence data through palaeomagnetic laboratory measurements. Knowing the typical morphology of the ore zone one can compute a forward model of the expected anomalous response and determine which combination of survey parameters provides the highest probability of detecting the commodity being sought. In this study, we analyse magnetic patterns associated with thin dipping skarn bodies from the Geyer mining district in Erzgebirge, Germany. Petrophysical measurements indicate that the skarns are more magnetic than the surrounding host rock. Partially oriented samples from a bore core record a Variscan age metamorphic remanence. Forward modelling indicates that clusters of skarn bodies are required to produce a reliably detectable magnetic signal. Ground, or low elevation drone surveys are needed to detect these anomalies with standard scalar‐type optically pumped magnetometer or fluxgate magnetic surveys. The enhanced spatial resolution and long‐wavelength rejection of a superconducting quantum interference device based full‐tensor magnetic gradiometer provide an improvement over optically pumped magnetometers for an aircraft‐based survey platform.

A comparative study on adsorption and catalytic degradation of tetracycline by five magnetic mineral functional materials prepared from steel pickling waste liquor

Palygorskite (Pal), bentonite (Bent), sepiolite (Sep), zeolite (Zeol), and kaolin (Kaol) were used with steel pickling waste liquor to synthesize magnetic palygorskite (Pal@Fe3O4), magnetic bentonite (Bent@Fe3O4), magnetic sepiolite (Sep@Fe3O4), magnetic zeolite (Zeol@Fe3O4), and magnetic kaolin (Kaol@Fe3O4), for adsorption and catalytic degradation of tetracycline (TC), respectively. Through the study of adsorption kinetics and adsorption isotherms, the maximum adsorption capacity of Pal@Fe3O4 to TC was 149.439mg/g, which was 1.239 times, 2.260 times, 3.161 times, and 3.448 times of Bent@Fe3O4, Zeol@Fe3O4, Kaol@Fe3O4, and Sep@Fe3O4, respectively. The kinetic study of tetracycline degradation demonstrated that the maximum reaction rate constant of Bent@Fe3O4/H2O2 system was K(obs) = 2.12 × 10-2min-1, which was close to that of Pal@Fe3O4/H2O2, Kaol@Fe3O4/H2O2 system, and was 2.000 times, 2.356 times, 2.650 times, and 4.711 times of Fe3O4/H2O2, Zeol@Fe3O4/H2O2, Sep@Fe3O4/H2O2, and H2O2 system, respectively. The results showed that Pal@Fe3O4 and Bent@Fe3O4 were more advantageous in the treatment of wastewater containing tetracycline, and efficient reuse of exhausted magnetic minerals and deep mineralization of organic pollutants were achieved by constructing an advanced oxidation system. The BET, VSM, SEM, XPS, XRD, and FTIR were used to characterize the five clay minerals before and after magnetic modification. It was speculated that the surface structure - OH groups of clay minerals might be significant factors influencing the adsorption performance of magnetic minerals on TC, and reduction ability of clay minerals to Fe3+ importantly affected the catalytic performance of magnetic minerals. The specific surface area and morphological structure of clay minerals both affected the adsorption and catalytic degradation of TC by the five magnetic minerals.

MagNet: Automated Magnetic Mineral Grain Morphometry Using Convolutional Neural Network

AbstractMorphometry (i.e., the quantitative determination of grain size and shape information) is an essential component of all rock and environmental magnetic studies. Electron microscopy is often used to image magnetic mineral grains, but the current lack of systematic image processing tools makes it challenging to quantify key morphological features of magnetic minerals in natural samples. Here, we present an easy‐to‐use machine learning framework MagNet for automated morphological recognition of magnetic mineral grains in microscopic images. This framework, based on a convolutional neural network, performs well in the recognition and classification of magnetofossil nanoparticles in transmission electron microscopy images after training and testing. MagNet is open‐source and can easily be extended to process different types of mineral images. This tool has the potential, therefore, to extract key quantitative information of magnetic mineral populations within heterogeneous terrestrial and meteoritic samples for the interpretations of Earth and planetary processes.

Rock magnetic fingerprint of Mt Etna volcanic ash

SUMMARYA detailed rock magnetic study was conducted on ash samples collected from different products erupted during explosive activity of Mount Etna, Italy, in order to test the use of magnetic properties as discriminating factors among them, and their explosive character in particular. Samples include tephra emplaced during the last 18 ka: the benmoreitic Plinian eruptions of the Pleistocene Ellittico activity from marine core ET97-70 (Ionian Sea) and the basaltic Holocene FG eruption (122 BC), the Strombolian/Phreatomagmatic/sub-Plinian eruptions (namely, the Holocene TV, FS, FL, ETP products and the 1990, 1998 eruptions) collected from the slope of the volcano, and the Recent explosive activity (lava fountains referred to as ‘Ash Rich Jets and Plumes’, or ARJP) that occurred in the 2001–2002 period, related to flank eruptions. Mössbauer spectrometry informs that a single magnetic mineral dominates the three groups, which are characterized by variable magnetic grain sizes and composition. Detailed rock-magnetic investigations, ranging from low temperature to high temperature remanence and susceptibility experiments, indicate that the more explosive products of the Plinian eruptions and ARJP activity tephra, are characterized by oxidized Ti-rich titanomagnetites, with dominant Curie Temperatures between 230 and 330 °C. The FG and ARJP tephra are also characterized by contrasting, yet overall higher, coercivity distributions and higher magnetizations and susceptibilities, including below room temperature. In contrast, most of the Strombolian/sub-Plinian eruptions have a magnetic signature dominated by less coercive magnetite and/or Ti-poor titanomagnetite. Magnetic differences observed between the Late Pleistocene and Holocene FG Plinian eruptions can be attributed to the different composition of the former eruptions, which were fed by more evolved magmas, whereas geochemical variations characterizing the products erupted in the last few decades can be responsible for the differences between the Holocene and recent Strombolian/sub-Plinian products. Importantly, detailed magnetic investigation of sideromelane and tachylite clasts, the two end members of the juvenile fraction extracted from the ash of the most explosive products, determines that the tachylite fraction is responsible for the magnetic signature of the Plinian FG and ARJP tephra, and is attributed to the intense fragmentation that characterizes these activities, likely resulting from undercooling processes. Moreover, the abundant superparamagnetic grains associated with these eruptive styles are believed to represent the nanolite fraction responsible for the increasing viscosity of these magmas, and to be responsible for their explosive character. The distinctive magnetic properties that characterize the tachylite-bearing tephra, representative of the fragmentation process that distinguishes the most explosive activities, provides a useful magnetic tool that can complement traditional volcanological investigations.

Variation in humidity and the forcing mechanism in Asian monsoon-influenced regions indicated by hematite/goethite from Baxian Lake, southern China, since AD 800

Understanding the potential mechanisms driving the precipitation pattern in the Asian summer monsoon (ASM) area is significant to reconstructing the environmental and hydrological conditions over the past 2000 years. However, robust and consistent conclusions have been hampered by the complex processes controlling the dynamics and diverse interconnected linkage of the Asian monsoon. Here, we present a reconstruction of variations in humidity since AD 800, based on the ratio of hematite to goethite (Hem/Goe) and other magnetic parameters in the sediments of Baxian Lake, southern China. The record indicates that a dramatic transition from dry to humid climate occurred during AD 800–950 and then returned to extreme drought during the second half of the Medieval Warm Period. The fluctuations between a relatively wet climate and weak drought were also demonstrated during the Little Ice Age (AD 1450–1800). Climate-influenced vegetation coverage may influence the flux of weathered detrital magnetic minerals in sediments, as it hinders the input of coarser detritus into Baxian Lake. The magnetic minerals in the sediments were not significantly altered during the post-depositional processes. Additionally, the Hem/Goe record indicates that an opposite precipitation pattern occurred in southern China when compared with precipitation records in northern China and India. We ascribe this result to the superimposition of land-ocean-atmosphere dynamics on the traditional model of the intertropical convergence zone (ITCZ) movement forced by the Atlantic Meridional Overturning Circulation. This is significant for enhancing our understanding of the relationship among the continent-ocean thermal gradient, ASM variation, ITCZ movement, El Niño Southern Oscillation-like events, and extreme climates in areas influenced by the ASM.

The low-temperature heat capacity and thermodynamic properties of greigite (Fe3S4)

Heat capacity measurements provide important insights into the energetic, thermodynamic, and magnetic properties of materials. Herein we report the heat capacity of greigite (Fe3S4) from 1.8 to 300 K. Greigite is a magnetic spinel mineral and through a ferromagnetic magnon term, Cfsw = BfswT3/2, ferrimagnetic ordering is observed in the low-temperature heat capacity. Using a set of theoretical fits of the experimental data, we calculate the thermodynamic functions, including the standard entropy (Δ0TSm°). Greigite is important in iron sulfide formation and reaction pathways in environmental, ore-forming, and technological settings and previous work has measured enthalpies (ΔHr°) of formation and decomposition to neighboring phases. In this work, the stability of greigite relative to the elements is demonstrated with a negative Gibbs energy (ΔGr°) of formation and the stability relative to decomposition products of pyrrhotite (FeS1.092) and pyrite (FeS2) is demonstrated with a positive Gibbs energy (ΔGr°) of decomposition. Values of the standard thermodynamic functions Cp,m°, Δ0TSm°, Δ0THm°, andΦm° are tabulated.

Magnetic anomaly patterns and volcano-tectonic features associated with geothermal prospect areas in the Ziway-Shala Lakes Basin, Central Main Ethiopian Rift

The Ziway-Shala Lakes Basin is a structural depression within the Main Ethiopian rift that is associated with Cenozoic volcanism, faulting and sedimentation. The Aluto-Langano volcano complex contains a geothermal field within this basin that is currently being exploited for geothermal power production. Recent magnetotelluric analyzes did not reveal a heat source beneath the Aluto-Langano geothermal field but found an electrical conductor that may be the magmatic heat source near the Silti Debre Zeyet Fault Zone (SDFZ) northwest of the Aluto- Langano geothermal field. To investigate the subsurface structure of the Ziway-Shala Lakes Basin and especially the Aluto-Langano geothermal field, a ground based magnetic survey was performed. Volcano-tectonic features were identified using a differentially reduced to the pole total magnetic field anomaly and a variety of map transformations including upward continuation, first vertical derivatives and tilt derivatives, to map the regional and residual magnetic fields. To identify subsurface magnetic susceptibility sources between the SDFZ and the Aluto-Shala geothermal field, a power spectral analysis, 2D-Werner Deconvolution, and 2D forward modeling were applied. The integrated interpretation of the maps and models, indicates that magnetic maxima occurred over the SDFZ and the Wonji Fault Zone and the minima over the Aluto-Langano geothermal field. The magnetic maxima may be caused by shallow (< 5 km) igneous intrusions that are related to deeper magma movement. The magnetic minima may be caused by warm geothermal waters causing thermal alteration of the magnetic minerals under the Aluto-Langano volcanic complex. The residual and derivative magnetic anomaly maps suggest the existence of lineations that may transfer geothermal fluids suggested by the magnetotelluric models from the SDFZ to the Aluto-Langano geothermal field. The upward movement of the fluids is evident by the magnetic minimum in the Aluto-Langano geothermal field and agrees with a recent earthquake analysis. Additionally, a majority of the magnetic lineaments are oriented parallel to pre-existing Mesozoic structures related to the opening of the Ogaden Basin.