United Kingdom’s gold potential

The momentum of gold exploration in Britain has been high since the discovery in 1979 by Consolidated Goldfields of gold-bearing strata-bound base-metal sulphides in the Archean at Gairloch, northwestern Scotland.

Targets subsequently drilled by Riofinex North and BP Minerals International lay in late Silurian to early Devonian igneous rocks offering possibilities for porphyry deposits at Comrie and Lagalochan (Report No. 9 in the British Geological Survey’s Mineral Reconnaissance Program series), and in southwestern Scotland at Hare Hill, Fore Burn (Report 55) and Moorbrock Hill. Geologically comparable targets at Glen Devon (Report 116) and Glenhead (Report 46) were also investigated under the Mineral Reconnaissance Program (MRP), funded by the Department of Trade and Industry (DTI). Much of the company work from the early 1970s to the mid-80s was carried out with support from the DTI-funded Mineral Exploration Grant Scheme and the information now lies in the public domain along with the reports, geochemical atlases and open-file reports of the British Geological Survey (BGS). More recently, Navan Resources, Cambridge Consultants, Doelcam-Echo Bay and Carnon Consolidated, as well as Ennex and Colby, have demonstrated interest in Scotland’s exploration potential.

The Crown Licence system for gold and silver exploration and development enables new entrants to see the current areas of activity and can give secure rights to precious metal exploration at reasonable cost. Information on how to undertake mineral exploration in Britain has been collated in the BGS booklet Exploration for metalliferous and related minerals in Britain: a guide.

Close interval drainage sampling for up to 30 elements has been completed over Scotland and northern England by the BGS’s Geochemical Survey Program (also DTI-funded) and further analyses for gold and pathfinder elements (arsenic, bismuth and antimony) are available for certain areas. Records of gold in panning concentrates from the Aberfeldy area, published by BGS, led to Colby Gold’s discovery of a swarm of thin but rich gold veins in Dalradian metamorphics at Calliachar Burn, about 5 km south of M-I GB’s bedded barite deposit at Foss (Report 40). These vein deposits are believed to be Lower Devonian, the same age as the gold occurrence in fossiliferous chert at Rhynie, Britain’s only known epithermal hot spring gold location. The principal gold deposit recently found in Britain is Ennex International’s Cononish vein structure, near Tyndrum, which cuts Dalradian (late Proterozoic) rocks. About 750,000 tonnes of ore, grading 10 grams gold (uncut) and 43 grams silver per tonne are indicated from drilling and underground development.

In the past, alluvial gold was extracted on a small scale, principally around Leadhills and Helmsdale. Leadhills gold was used to fashion the Scottish Regalia in the sixteenth century, and around 1860 the Helmsdale district was the scene of a minor gold rush with quite extensive diggings. Three mines in the Dolgellau gold belt of north Wales account for the bulk of Britain’s past gold production, perhaps 5 tonnes in all (mainly from 1870 to 1910). The gold occurs in quartz veins cutting Cambrian to Silurian sediments. There is no current production from these mines, two of which were open as tourist attractions until recently.

Polymetallic mineralization, including gold, has recently been located by BGS in several new areas of Wales. At Treffgarne in southwest Wales, highly pyritiferous dark mudstones containing enhanced gold levels (up to 2.5 ppm) are associated with Lower Ordovician acid volcanic rocks (Report 86). On Anglesey, a complex zone of Precambrian to Ordovician rocks, near the Parys Mountain volcanogenic massive sulphide deposit under investigation by Anglesey Mining (a subsidiary of Imperial Metals), was drilled on VLF-EM, IP and geochemical soil anomalies (Report 99); polyphase base metal mineralization was located, locally accompanied by gold.

The most recent gold discoveries have been made in

southwestern England. At Wadebridge in Cornwall, arsenopyrite-bearing quartz veins commonly contain up to 1 ppm gold in Middle Devonian volcanic and sedimentary rocks associated with basic igneous intrusions (Report 103). At Hope’s Nose in Devon, an occurrence of filligree palladium-gold in calcite veins was considered to be unique until gold, platinum and palladium-gold were shown to be widespread in streams in the surrounding South Hams district (Report 98).

This area of Lower to Middle Devonian sediments and acid to basic igneous rocks was sampled by drainage and overburden surveys which yielded not only abundant gold but also unusual dendritic, layered, precious metal grains (Report 111).

These layered grains usually contain gold, gold-palladium or gold-mercury cores with platinum-rich rims. The platinum in the rims is alloyed with gold or copper; mercury may also be present, or a combination of mercury, palladium, gold and platinum. Mercury is also found as cinnabar particularly in Middle Devonian mafic volcanics.

The gold is believed to have been concentrated in the weathered zone of the Devonian strata by circulating groundwaters during tropical weathering periods in the Permo-Trias or Tertiary. This deeply weathered zone has not been stripped off by the Pleistocene glaciation as the ice sheet never reached southwestern England.

It is also of interest to note that small-scale gold production was recorded as a byproduct of tin extraction from river alluvials in both Devon and Cornwall.

Further information regarding the MRP reports mentioned above and of a summary volume (Report 114), together with other BGS publications and open-file and company exploration reports, can be obtained from the writer, care of Minerals Group, British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K.