Dataset of Thermomagnetic Curves, Hysteresis parameters and Sample Coordinates from Soil Studies in Eastern Botswana
Description
This study hypothesizes that the magnetic properties of soils and rocks in eastern Botswana—specifically thermomagnetic and hysteresis parameters—can reveal mineralogy, geological history, and environmental conditions. Parameters like Curie temperature, magnetic susceptibility, and hysteresis traits help identify minerals such as magnetite, hematite, pyrrhotite, and titanomagnetite, and their grain sizes. These signatures enable mapping of geological units, boundaries, and mineral formation processes influenced by tectonics and past environments. Samples were collected from soils (5–30 cm depth) along roads during the dry season, stored in plastic containers to prevent contamination. Rocks came from outcrops and quarries. Laboratory analysis involved heating samples up to 700 °C in nitrogen to identify Curie temperatures, and measuring hysteresis parameters (Mrs, Ms, Hcr, Hc) to assess mineral grain size and domain states. Results show most samples contain magnetite-like minerals with Curie temperatures near 585 °C. Some exhibit secondary features like Hopkinson peaks, indicating mineral mixes such as hematite and pyrrhotite. Mineral alterations, like magnetite oxidation to hematite, are evident from susceptibility changes. Hysteresis data reveal a range of grain sizes and magnetic domain states, reflecting geological processes like weathering and neoformation. Non-reversible heating/cooling behavior suggests metastable minerals or alteration during thermal treatment. Geologically, magnetic variations support mapping of features like the Kaapvaal and Zimbabwe Cratons and the Limpopo Belt. The data confirm regions dominated by magnetite minerals, useful for mineral exploration, paleoenvironmental reconstruction, and regional tectonic mapping. Overall, combining thermomagnetic and hysteresis measurements provides insights into mineralogy, alteration pathways, and geological structures essential for exploration and environmental assessments.
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Steps to reproduce
Samples were collected from specific locations across eastern Botswana, with precise GPS coordinates recorded for each site. Soil samples were obtained from the surface layer (5–30 cm depth) along roads using clean plastic shovels, approximately 500 grams per site, and stored in labeled, non-magnetic plastic containers. Rock samples were extracted from outcrops, excavations, or quarries using a hammer and chisel, with 1–2 kg collected and stored in plastic bags. All samples were kept in airtight, dry conditions, away from sunlight, until laboratory analysis. In the lab, samples were air-dried at approximately 25 °C for 48 hours and then gently crushed and sieved through a 2 mm mesh to achieve uniform powder. A representative aliquot (~10 mg) of each powdered sample was prepared for magnetic measurements. Thermomagnetic curves were generated using a high-temperature magnetic susceptibility instrument capable of heating up to 700 °C in a nitrogen atmosphere to prevent oxidation. Approximately 100 mg of sample powder was placed in a non-magnetic sample holder, then heated from room temperature to 700 °C at a rate of 20 °C/min, with susceptibility measurements recorded continuously during heating. After reaching the maximum temperature, samples were cooled back to room temperature at the same rate, with susceptibility measured throughout cooling. The data were then processed to identify peaks and inflection points corresponding to Curie temperatures, using a tangent or inflection point method. For hysteresis measurements, approximately 10 mg of powdered sample was mounted on a non-magnetic holder with minimal adhesive or wax. The samples were subjected to increasing and decreasing magnetic fields up to 1 Tesla using a vibrating sample magnetometer. Hysteresis loops were recorded at room temperature, and parameters such as Ms, Mrs, Hc, and Hcr were extracted from the loops via the instrument’s software. Ratios like Mrs/Ms and Hcr/Hc were calculated to classify magnetic domain states. All equipment was calibrated prior to measurements following manufacturer instructions, and sample handling was conducted carefully to prevent contamination or oxidation.