Diamonds

Diamonds remain without question the worlds most sought after gemstone. The world jewellery market is demanding increasing numbers of high grade diamonds and the production of lower quality diamonds used in the industrial market remains robust. Given the profitability of diamond mining it is unsurprising that the exploration sector continues to have a strong focus on diamonds.

Diamonds in Northern Ireland

To date no bedrock diamond source has been identified in Northern Ireland and at present no companies are exploring for diamonds in the country. However, because diamonds have proved so difficult to locate, most discoveries in virgin territory have had a great deal to do with luck. This was the case in South Africa where the chance discovery provided the catalyst to the development of the world’s most successful diamondmining economy. In 1995 the British Geological Survey reported that the potential for a diamond discovery in Northern Ireland is good. Two reports from the Journal of the Royal Geological Society of Ireland refer to the 1816 discovery of the Brookeborough diamond in the Colebrooke River of Co. Fermanagh. The stone was presented to Lady Brooke and inspected by several jewellers in Dublin, who confirmed the stone to be a diamond.

The Carboniferous

Inspired by the above accounts, a Canadian company licenced large tracts of Counties Tyrone and Fermanagh in 1996 to locate the source of the Brookeborough diamond. The work was concentrated on the Carboniferous and older rocks which may be underlain by Proterozoic/Archaean basement. The company identified a number of target areas which which were the subject of regional large volume stream sediment sampling. In total, 158 samples were collected, comprising 30kg of sediment screened to minus 1.7mm on site. The results of this programme revealed over 400 potentially kimberlitic minerals in 28 of the samples. In summary, two garnets were found and rated as highmedium diamond interest, 364 chromite grains were classified as kimberlitic - one being rated as high interest and 273 rated as medium interest and one ilmenite analysis was also classified as being kimberlitic. Independent consultants interpreted these results as suggesting the possible occurrence of high interest kimberlites within the area drained by the streams from which the samples were recovered. In 2000 the company surrendered its Northern Ireland licence block without conducting any further work.

The Dalradian

The Inishowen Peninsula of Co. Donegal in the Republic of Ireland is underlain by similar Dalradian metasediments to north Co. Londonderry. In 1996 an exploration company began work on the peninsula. Airborne magnetic surveys were completed over the entire licence block and followed up by ground surveys over anomalous areas. In addition, a regional stream sediment survey collected 96 samples for heavy mineral analysis. This led to the identification in 2000 of a potential bedrock source believed by the company to be a lamproite and a short drilling programme was completed. The possibility for other gemstones in the area has also been confirmed with the discovery of micro and macro rubies and sapphires in Co. Donegal.