Model Answer
0 min readIntroduction
Diamonds, renowned for their exceptional hardness and brilliance, are formed under extreme pressure and temperature conditions deep within the Earth's mantle. These precious gemstones are brought to the surface through volcanic eruptions, often associated with kimberlite and lamproite pipes. In India, diamond occurrences are primarily linked to ancient geological formations, particularly the Proterozoic rocks, and more specifically, the Gondwana sediments. Historically, India was a major source of diamonds until the 18th century, with Golconda being a globally recognized diamond trading center. Today, while production has decreased, India still holds significant diamondiferous strata.
Geological Context of Diamond Formation
Diamonds are primarily composed of carbon atoms arranged in a specific crystal structure. Their formation requires pressures exceeding 4.5 GPa and temperatures above 1050°C, typically found at depths of 150-200 km within the Earth’s mantle. These diamonds are then transported to the surface via kimberlite and lamproite volcanic pipes, which act as conduits for magma originating from the mantle. The age of diamonds can range from ancient Archean times (over 2.5 billion years) to more recent periods.
Diamondiferous Strata in India
1. Gondwana Rocks
The most significant diamondiferous strata in India are found within the Gondwana sedimentary formations. These rocks, dating back to the Permian and Jurassic periods (approximately 300-145 million years ago), are characterized by fluvial and lacustrine sediments. Diamonds are found as detrital grains within these sediments, having been eroded from their primary kimberlite sources and transported by rivers and streams. Key areas include:
- Panna, Madhya Pradesh: This is the most famous diamond-producing region in India. Diamonds are found in conglomerate beds within the Vindhyan Supergroup, which overlies the Gondwana sediments. The diamonds are typically of alluvial origin, having been reworked from kimberlite pipes.
- Golconda, Andhra Pradesh & Telangana: Historically significant, Golconda’s diamonds were sourced from both primary kimberlite pipes and alluvial deposits within the Krishna River basin. The Kollur mine is a notable example.
- Raigarh, Chhattisgarh: Diamond occurrences are associated with the Mahakoshal Gondwana basin.
2. Kimberlite Pipes
While Gondwana sediments are the primary source, India also has several kimberlite pipes, though many are economically unviable. These pipes are the primary source of diamonds, but erosion and weathering have often dispersed the diamonds into surrounding sediments.
- Majhgawan, Panna: One of the first kimberlite pipes discovered in India, it has yielded significant diamond production.
- Raigarh Kimberlites: Several kimberlite pipes have been identified in the Raigarh area, but their economic potential is still being evaluated.
3. Lamproite Pipes
Lamproite pipes, though less common than kimberlites, are also potential diamond hosts. The Argyle mine in Australia is a famous example of a lamproite-hosted diamond deposit. India has a few identified lamproite occurrences, but their diamondiferous nature is still under investigation.
Types of Diamonds Found
Indian diamonds are known for their variety in color and clarity. Historically, Golconda diamonds were famous for their exceptional quality and included renowned gems like the Koh-i-Noor and the Hope Diamond. The diamonds found in Panna are generally of lower quality but still contribute to the domestic diamond market. The color range includes colorless, yellow, brown, and occasionally, fancy colored diamonds.
| Region | Host Rock | Diamond Characteristics |
|---|---|---|
| Panna | Gondwana Conglomerates & Kimberlites | Alluvial, varying quality, mostly yellow/brown |
| Golconda | Alluvial & Kimberlites | Historically high quality, colorless & fancy colors |
| Raigarh | Gondwana Sediments & Kimberlites | Potential for economic deposits, under exploration |
Conclusion
India’s diamondiferous strata, primarily within the Gondwana formations and associated kimberlite pipes, represent a significant geological heritage. While historical production has declined, ongoing exploration and advancements in mining technology offer potential for revitalizing the Indian diamond industry. Understanding the geological context of diamond formation and distribution is crucial for sustainable resource management and economic development in these regions. Further research into lamproite occurrences could also unlock new diamond resources.
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.