The Kollur Mine, in present-day Andhra Pradesh on the south bank of the Krishna River, is one of the most historically important diamond-producing localities in the world. It is the source from which a substantial fraction of the great historical diamonds of South Asia, including the Koh-i-Noor, the Hope, the Regent, the Great Mogul, the Orlov and others traditionally attributed to the Golconda field, are believed to have been recovered. The mine was active from at least the sixteenth century through the early eighteenth, after which the deposits were progressively exhausted and the workings effectively abandoned.

Geological setting

The Kollur deposits are alluvial workings on the Krishna River and its tributaries, set in conglomerates and gravel beds derived from the erosion of older diamondiferous source rocks higher in the drainage basin. The diamond population of the Krishna alluvials is distinguished by an unusually high proportion of large, type IIa and type IaB stones, the chemically purest of the natural diamond varieties, which present as exceptionally colourless when well cut. The trade term Golconda diamond now refers, in technical usage, specifically to type IIa diamonds with the historical inclusion fingerprint and trace-element pattern of the Krishna alluvials, regardless of the specific Krishna-basin locality from which the stone was recovered.

Historical operation

The Kollur workings were the principal supplier of the diamond trade of the Sultanate of Golconda, the Qutb Shahi dynasty whose capital lay near present-day Hyderabad. The French jeweller Jean-Baptiste Tavernier visited the Kollur mine on his travels in India between 1640 and 1668 and provided the first detailed European account of its operation in his Six Voyages of 1676. He reports a workforce of around 60,000 miners working through alluvial gravels with hand tools, sluicing the gravel through a sequence of ponds and sieves. The Kollur production at its peak supported the Golconda court's substantial trade in cut and uncut diamonds with the Mughal court at Delhi, the Safavid court at Isfahan, and the European merchant network running through Goa, Hormuz and Aleppo.

Decline

The Kollur deposits were progressively worked out through the late seventeenth and early eighteenth centuries. By the time of the Mughal collapse in the mid-eighteenth century, production had reduced to a trickle, and after the British annexation of the broader region the mine was effectively closed. Modern exploration in the area has confirmed that the alluvial deposits are exhausted of their original economic content, although small-scale informal collecting continues. The kimberlite or lamproite source rocks of the Krishna alluvial diamonds have not been definitively identified, although the Wajrakarur kimberlite field of Andhra Pradesh is one of the candidate primary sources.

Trade and gemmological relevance

The Kollur Mine is significant in the contemporary trade primarily as the historical source of Golconda diamonds. Type IIa stones with documented or confidently inferred Krishna-basin origin command substantial premiums at auction, often two to four times the equivalent African or Russian stone of comparable size, colour and clarity. Provenance research for stones claimed to be Golconda relies on a combination of trace-element analysis, spectroscopic identification of type IIa character, and historical documentation. The auction market for confirmed Golconda stones is dominated by Christie's, Sotheby's and Bonhams, with notable sales including the Beau Sancy, the Princie Diamond and several stones from European royal estates.