Model Answer
0 min readIntroduction
Kimberlites are the primary source of diamonds globally, representing volatile-rich potassic igneous rocks originating from deep within the Earth’s mantle. Their formation is intrinsically linked to the transport of diamonds, formed under extreme pressure and temperature conditions in the Earth’s mantle, to the surface. These rocks are named after the town of Kimberley in South Africa, where the first significant diamond-bearing kimberlite was discovered in 1869. India, while not a major producer currently, possesses several kimberlite fields, notably in the Bundelkhand region and Andhra Pradesh, holding potential for future diamond exploration. This answer will detail the formation of diamond-bearing kimberlites and provide a note on the Majhgawan and Wajrakarur kimberlite fields.
Kimberlite Formation: A Deep Earth Process
Kimberlite magmas are generated in the mantle, typically at depths of 150-250 km, though some may originate even deeper. The process is complex and not fully understood, but several key factors are believed to be involved:
- Mantle Plumes: Many kimberlites are associated with mantle plumes – upwellings of abnormally hot rock from the deep mantle. These plumes cause partial melting of the surrounding mantle rocks.
- Partial Melting: The melting process doesn't involve complete fusion; instead, specific minerals melt while others remain solid. This results in a magma rich in potassium (K), magnesium (Mg), and volatile components like water (H2O) and carbon dioxide (CO2).
- Ascent Mechanism: The volatile-rich nature of kimberlite magma is crucial for its rapid ascent. These volatiles lower the magma's viscosity and create a powerful driving force, allowing it to travel through the lithosphere at exceptionally high speeds (estimated at 30-60 km/hr). This rapid ascent is vital for preserving diamonds, as slow ascent would allow them to convert to graphite.
- Kimberlite Pipes & Dykes: Kimberlite magmas typically form vertical, carrot-shaped intrusions known as kimberlite pipes. They also occur as dykes (tabular intrusions). These structures are formed by explosive volcanism, creating breccias (fragmented rock) and volcanic ash.
- Diamond Entrainment: Diamonds are not formed *within* the kimberlite magma itself. Instead, they are pre-existing crystals residing in the mantle rocks (xenoliths) that are picked up and transported to the surface by the ascending kimberlite magma.
Majhgawan Kimberlite Field (Bundelkhand, Madhya Pradesh)
The Majhgawan kimberlite field, located in the Panna district of Madhya Pradesh, is the only producing diamond mine in India as of 2024 (knowledge cutoff). It’s part of the Bundelkhand Craton, a stable continental block.
- Geological Setting: The kimberlites intrude Archaean granite and gneiss rocks of the Bundelkhand Craton. The Majhgawan kimberlite is a typical potassic kimberlite, characterized by olivine, phlogopite, and serpentine.
- Diamond Content: The diamonds found in Majhgawan are predominantly of gem quality, though the overall concentration is relatively low. The diamonds are typically yellow and brown in color.
- Exploration History: Diamond exploration in the area began in the 1960s by the Geological Survey of India (GSI). Commercial mining commenced in 2005 by Rio Tinto (later transferred to National Mineral Development Corporation - NMDC).
- Current Status: The mine has faced challenges related to declining diamond grades and operational difficulties. NMDC is actively involved in exploration to identify new kimberlite bodies in the region.
Wajrakarur Kimberlite Field (Andhra Pradesh)
The Wajrakarur kimberlite field, located in the Anantapur district of Andhra Pradesh, represents a significant, though currently non-producing, kimberlite occurrence in India.
- Geological Setting: The Wajrakarur kimberlites intrude Proterozoic granite and sedimentary rocks of the Eastern Dharwar Craton. The kimberlites are characterized by a higher groundmass content compared to Majhgawan.
- Diamond Content: Microdiamonds have been recovered from the Wajrakarur kimberlites, indicating the potential for diamondiferousity. However, gem-quality diamonds have not been found in commercially viable quantities.
- Exploration History: Exploration activities were initiated by the GSI in the 1980s and continued with private sector involvement in the 1990s and 2000s. Extensive drilling and geophysical surveys have been conducted.
- Challenges: The Wajrakarur kimberlites are smaller in size and have a lower diamond grade compared to Majhgawan. The presence of alteration and weathering also poses challenges for diamond recovery.
| Feature | Majhgawan Kimberlite | Wajrakarur Kimberlite |
|---|---|---|
| Location | Panna, Madhya Pradesh | Anantapur, Andhra Pradesh |
| Craton | Bundelkhand Craton | Eastern Dharwar Craton |
| Diamond Grade | Low, but commercially viable | Very low, primarily microdiamonds |
| Production Status | Currently Producing | Non-Producing |
| Diamond Quality | Gem quality (yellow, brown) | Not yet established (microdiamonds) |
Conclusion
In conclusion, diamond-bearing kimberlites form through a complex interplay of mantle plume activity, partial melting, and rapid volatile-driven ascent. The Majhgawan kimberlite field represents India’s only current diamond production, while the Wajrakarur field holds potential, though requires further exploration and technological advancements to overcome challenges related to diamond grade and size. Continued research into kimberlite genesis and advanced exploration techniques are crucial for unlocking India’s diamond potential and contributing to the global diamond supply.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.