For more than 2,000 years, the Golconda mines on the banks of the Krishna River in southern India produced virtually all the world's fine diamonds.

Many of history's most famous diamonds claimed a Golconda origin, and these included the 105-carat Koh-i-noor (replica, above), 45-carat Hope Diamond, 140-carat Regent Diamond, 189-carat Orlov and the 70-carat Idol's Eye.

During peak production between the 1600s and the 1800s, the Golconda mines supported a massive operation that employed 30,000 people at a time.

Golconda's mines produced an estimated 10 million carats of diamonds before the resources became exhausted in 1830. There were no more diamonds, but the legend carried on.

In the diamond trade, "Golconda" became synonymous with "superb quality." The Indian diamonds from that region had very few inclusions and contained little or no nitrogen. Today, those diamonds would be classified as Type IIa — the best of the best.

It was widely assumed that Golconda's alluvial diamonds originated in kimberlite pipes and were deposited downstream by ancient rivers. Until recently, the primary source of the gemstones remained a mystery.

Geoscientists at Savitribai Phule Pune University, near Mumbai, now believe the true origin of the Golconda diamonds is a volcanic outcrop nearly 200 miles upstream from the alluvial mines. Their findings were published recently in the Journal of Earth System Science.

The researchers utilized field geological studies and remote sensing tools to locate a long-dry ancient river channel that they believe was primarily responsible for the transportation of diamonds from the source rocks at the kimberlite fields of Wajrakarur to their final sites of recovery on the banks of the Krishna River.

The researchers noted that the movement of the precious stones in India is similar to the way the Orange River ferried precious diamonds from the center of South Africa westward all the way to the Atlantic coast in the Republic of Namibia.

That country currently produces more than 2.3 million carats each year. Most of those diamonds are extracted from the ocean floor by giant vacuum systems attached to massive production vessels.

Credit: Photo of Koh-i-Noor replica by aiva., CC BY 2.0, via Wikimedia Commons.