Mining at Gwynfynydd Mines Royal
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An extract from Welsh Gold, The story of Gwynfynydd.
copyright : Aur Cymru Ccc, not to be reproduced without written consent.
The Welsh Gold Rush
The existence of gold in the Dolgellau area has probably been known for centuries, possibly to the early Celts. In their charter of 1198, the monks of Cymer Abbey at Llanelltyd were given
" the right in digging or carrying away metals and treasure free from all secular exaction".
Despite this, it was not until 1844 that the existence of this precious metal was made known to the world at large by Arthur Dean in a paper to the British Association. By that time a number of small mines were already established including the Beddcoedwr Mine at Gwynfynydd, following a local discovery in around 1836.
A period of intense mining speculation followed and there were many discoveries including a find at Gwynfynydd in 1863.
Pritchard Morgan was one of the early owners of Gwynfynydd, having acquired the mine from the original discoverer, Readwin in 1887, as the result of a legal dispute. No sooner had he started the mine up again than he found a very large pocket of gold. He initially tried to keep the find quiet as ther was a question as to whether he owned the lease to extract gold. This question came about because the Crown has prerogative rights over gold and silver in most areas of the UK. Even though an individual may own the freehold land and the mineral rights to a property, the gold and silver is most often vested in the Crown and requires a Crown Mineral License to extract it. Such leases are not granted lightly and require royalties to be paid.The Gwynfynydd find was so rich it was impossible to keep quiet and special police had to be drafted in to guard it.
On the strength of this find, Morgan floated the Morgan Gld Mining Company, employing extravagant publicity methods. Morgan did well, he retained 70% of the shares and received £45,000 in cash, an enormous sum in those days. The mine ran, in several ownerships, until 1917, when it closed.
Modern Mining at Gwynfynydd
In 1981, Sir Mark Weinberg re-opened the mine. It was closed for two years at the end of the 80's, when it changed hands. Passing into the hands of Welsh Gold plc, mining was carried out using the Shrinkage Stoping technique. In this method the sub-vertical vein is drilled and blasted above ones head. The broken vein falls into the stope and is drawn off by means of chutes (called "Cousin Jacks") below to provide sufficient headroom to work. When the vertical interval of vein is worked out, the stope (or shrink) is drawn empty. The method is very good in terms of ground support as the broken ore supports the stope walls and prevents collapse. The broken ore was transported to the mill via an internal shaft and rail system. Gwynfynydd ceased mining underground in 1998, production moving over to the re-processing of old mine dumps. Recoveries of gold since 1980 totals in excess of 2,000 ounces of gold. Re-processing of dumps continues today but is expected to last only until 2005.
The gold at Gwynfynydd is not chemically combined with other minerals present in the rock. The technical term for this is "free", a misnoma since it is probably the most expensive gold worked anywhere in the world. This lack of chemical association, coupled with Gwynfynydd gold's unusually large grain size, means that it can be extracted making use of its high density or weight / volume . Gwynfynydd's gold separation plant was probably the most efficient gravity separation plant anywhere in the world. The surface plant currently used is a little different from that used underground but key to the underground plant was the Knelson concentrator, a high speed centrifuge spiral with a fluidised bed. After the ore has been crushed and ground to a fine sand, the Knelson, combined with a conventional shaking table, separates the gold from the rock without the use of cyanide. Cyanide is one of the most common chemicals used in gold extraction but is not used at Gwynfynydd. The surface plant currently installed is smaller than that previously used but used essentially the same principles.
Environmental Considerations at Gwynfynydd.
Welsh Gold plc has always looked at its operations very carefully from an environmental standpoint. It has received environmental awards from the Campaign for the Protection of Rural Wales and plaudits from the Environment Agency. The EA stated that "the current effective management of the mining operations and the treatment plant should ensure that the environmental impact of the mine is kept to a minimum and well within the environmentally protective conditions imposed". The mine is located adjacent to the Mawddach River and the famous Rhaeddr Mawddach (waterfalls) are upon mine property. The river has good Salmon and Sea Trout fishing which could be adversely affected by any pollution in the catchment area.
In common with many mines in where iron pyrites is plentiful and where is a lack of calcium carbonate in the wall rocks, Gwynfynydd has the ability to produce acidified mine waters. One particular area of the mine, worked by others in the past, was a source of the acidification. Research was undertaken to discover a means by which acidification could be slowed or halted. It was found that filling the area with clean tailings sand, produced during the gold extraction operation, with intervening layers of clays from external settling tanks, has reduced acid production significantly.
On closure of the underground workings, two large concrete dams were built in the main adits of the mine. This enables flows from the mine to be halted if at any time the quality of water from the mine is found to be below an acceptable standard. The dams are designed to withstand the full hydrostatic head of water that can build up inside the mine. Stratification of mine waters ensures that acid waters will be very diluted on exit from upper levels. In over 12 months of constant monitoring, water quality remains satisfactory.
The re-processing of surface dumps is an environmentally positive activity as the ground surface is being restored. Care is being taken to ensure stream borne sediment loads are not increased.
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