Kimberlites are a unique type of igneous rock known for their potential to host diamonds, and they exhibit distinct magnetic properties that are crucial for their exploration and identification. Understanding the magnetic characteristics of kimberlites is essential for geophysicists, geologists, and mining professionals involved in diamond exploration and extraction. In this comprehensive guide, we will delve into the intricate details of the magnetic properties of kimberlites, providing a valuable resource for physics students and enthusiasts.
Remanent Magnetization in Kimberlites
Kimberlites often possess strong remanent magnetization, which is the magnetization that a rock retains even after the removal of an external magnetic field. This remanent magnetization is a crucial factor in the interpretation of magnetic data and can significantly impact the analysis process.
The remanent magnetization in kimberlites is primarily influenced by the presence of magnetic minerals, such as titanomagnetite and magnetite, which can acquire a stable magnetic moment during the rock’s formation and cooling. The intensity and direction of the remanent magnetization can vary depending on factors like the composition of the kimberlite, the conditions during its emplacement, and the subsequent geological history.
To quantify the remanent magnetization, researchers often use the Königsberger ratio (Q-ratio), which is the ratio of the remanent magnetization to the induced magnetization. Kimberlites typically exhibit Q-ratios ranging from 0.1 to 10, indicating a significant contribution of remanent magnetization to their overall magnetic properties.
Magnetic Susceptibility of Kimberlites
Kimberlites have relatively low magnetic susceptibility compared to other igneous rocks, making them less responsive to external magnetic fields. This low susceptibility is primarily due to the absence of highly magnetic minerals, such as magnetite, in the kimberlite composition.
However, the presence of magnetic indicator minerals, like titanomagnetite and ilmenite, can enhance the magnetic response of kimberlites, particularly in fresh and unaltered samples. These magnetic minerals can contribute to the overall magnetic susceptibility of the kimberlite, which can be measured using laboratory techniques or in-situ geophysical surveys.
The magnetic susceptibility of kimberlites is typically in the range of 0.001 to 0.1 SI units, which is significantly lower than the susceptibility of other mafic and ultramafic igneous rocks. This low susceptibility can pose challenges in the detection and identification of kimberlite pipes using conventional magnetic exploration methods.
Magnetic Anomalies Associated with Kimberlites
Despite their relatively low magnetic susceptibility, kimberlites can create distinct magnetic anomalies due to their remanent magnetization and the presence of magnetic indicator minerals. These magnetic anomalies can provide valuable information about the location, size, and depth of kimberlite pipes, which is crucial for targeted exploration and mining activities.
The magnetic anomalies associated with kimberlites can be detected and analyzed using various geophysical techniques, such as airborne or ground-based magnetometry. The shape, amplitude, and spatial distribution of these anomalies can be used to infer the geometry and physical properties of the kimberlite pipes.
For example, the Regis kimberlite pipe in Brazil exhibits a strong magnetic anomaly, which was interpreted using high-resolution ground magnetic data to reveal its subsurface structure and dimensions. By analyzing the magnetic data, researchers were able to determine the depth, size, and orientation of the Regis kimberlite pipe, providing valuable insights for further exploration and mining activities.
Joint Parametric Inversion of Magnetic Data
In the presence of strong remanent magnetization, the interpretation of magnetic data can be challenging, as the remanent magnetization can significantly influence the observed magnetic anomalies. To address this challenge, researchers have developed a novel method called joint parametric inversion, which combines the analysis of total-field magnetic data and its analytic signal.
The joint parametric inversion method, based on the Gauss-Newton algorithm, allows for the simultaneous determination of the magnetic and geometric properties of kimberlite pipes. This approach is more stable and accurate than separate inversion methods, as it can recover the total magnetization and geometric properties of the magnetic anomalies with a good data fit and stable convergence.
By using the joint parametric inversion method, geophysicists can obtain a more comprehensive understanding of the subsurface architecture of kimberlite pipes, including their depth, size, and orientation. This information is crucial for targeted exploration and efficient diamond mining operations.
Depth of Investigation and Kimberlite Exploration
Comprehensive magnetic data analysis can offer a unique cross-sectional view of the subsurface, reaching depths up to 60 km, as demonstrated in the Wajrakarur Kimberlite Field in India. This depth of investigation is particularly important for kimberlite exploration, as kimberlite pipes can extend deep into the Earth’s crust.
By combining magnetic data with other geophysical and geological information, researchers can develop a more complete understanding of the subsurface structure and the potential for diamond-bearing kimberlites. This integrated approach, which may include seismic, gravity, and remote sensing data, can help identify and prioritize potential kimberlite targets for further exploration and evaluation.
Conclusion
Kimberlites exhibit a range of measurable and quantifiable magnetic properties, including remanent magnetization, magnetic susceptibility, and magnetic anomalies. These properties are crucial for the exploration, identification, and interpretation of kimberlite pipes, which are essential for the discovery and extraction of diamonds.
By understanding the intricacies of kimberlite magnetism, physics students and professionals can contribute to the advancement of diamond exploration and mining techniques, ultimately leading to more efficient and sustainable resource extraction.
References
- Alva-Valdivia, L. M., Urrutia-Fucugauchi, J., & Rivas-Sánchez, M. L. (2003). 3D magnetic interpretation of the Regis kimberlite pipe, Minas Gerais, Brazil. Geofísica Internacional, 42(4), 575-586.
- Kjarsgaard, B. A. (2007). Kimberlite pipe models: Significance for exploration. Mineralogical Association of Canada Short Course, 37, 1-40.
- Dentith, M. C., & Mudge, S. T. (2014). Geophysics for the Mineral Exploration Geoscientist. Cambridge University Press.
- Lelièvre, P. G., & Oldenburg, D. W. (2009). A comprehensive study of including structural orientation information in geophysical inversions. Geophysical Journal International, 178(2), 623-637.
- Pilkington, M., & Keating, P. (2004). Geophysical signatures of kimberlite pipes. Lithos, 77(1-4), 579-588.
Hi, I’m Akshita Mapari. I have done M.Sc. in Physics. I have worked on projects like Numerical modeling of winds and waves during cyclone, Physics of toys and mechanized thrill machines in amusement park based on Classical Mechanics. I have pursued a course on Arduino and have accomplished some mini projects on Arduino UNO. I always like to explore new zones in the field of science. I personally believe that learning is more enthusiastic when learnt with creativity. Apart from this, I like to read, travel, strumming on guitar, identifying rocks and strata, photography and playing chess.