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Wales has over 1000 workings wrought in search of metals. Some just consist of a tunnel driven 5 paces and abandoned. But others were major producers. Mining, since Bronze Age times, has produced copper, lead, silver, gold, zinc, iron, manganese, antimony, arsenic and barite. The mines therefore constitute an important scientific resource for the study of the mineralisation that they worked. Many are also of great archaeological importance, although one can have archaeologically-important but mineralogically-disappointing sites - and vice-versa.

Mines represent a particularly threatened group of sites. They often end up as unofficial rubbish-dumps. Sometimes, it is necessary to take action to prevent the spread of harmful pollutants and this can threaten areas of mineralogical interest. Spoil may be taken for hardcore or the tips may become completely overgrown. Minescan ensured that a representative selection will not share this fate! Here are some examples:

This is part of a spoil-heap at Cefn Coch gold mine near Dolgellau. The mine is on National Trust land and the buildings have been carefully looked after. The site has been a SSSI for some years.

It is a great site for the study of the Gold-belt lode textures. This tip is composed of lode fragments consisting of white quartz and black Clogau Shale.
This is a polished slab cut from a block of lode material from the tip above. The field of view is about 20cm high. The lodes typically have the ribboned appearance as seen here, a feature which indicates repeated fracture reopening and vein mineralisation.
Close to the Dolgellau Gold-belt, there outcrops a bed of sedimentary manganese-ore which has been worked extensively around the flanks of the Rhinogau. There are a plethora of sites at which the geology and mineralogy are visible, but those high in the northern Rhinogau are particularly spectacular, combining geology, archaeology and stunning mountain scenery. This cut and polished sample shows the layered appearance of the very fine-grained ore, which consists chiefly of manganese-bearing carbonates and silicates. The various pinks and yellows are typical of the unweathered ore: at some sites it has weathered to a chocolate-brown colour.
This is a view of the eastern section of Darren mine in Central Wales. Darren was, with other nearby mines, a celebrated 16th-17th century silver producer. The silver grades of the ores were much higher in these mines than at most other Central Wales localities.

The lower tip is derived from a shaft (Francis' Shaft) and a level (Level Y Coed) driven into the hillside. The upper tips are from the great opencast which crosses the hill, and which is another potential Bronze Age working. An Iron Age hill-fort sits on the hilltop and blocks of lode material have been found built into its walls during archaeological excavations.

An excellent historical account of these mines has been written:

Hughes, S.J.S. (1990) The Darren Mines. British Mining No. 40. Northern Mine Research Society, 131-141.
The mineral responsible for the high silver grades at Darren mine was discovered (or should I say rediscovered after 300 years?) in the mid-1980s when I was doing the research for my M.Phil. In this image, the grey, grainy-looking mineral above the blue-grey galena is the copper-silver-antimony sulphide, tetrahedrite. The aggregate is about 3cm across: they range from this size down to a few tens of microns. The occurrence of this important ore of silver, combined with the site's historical importance, make the Darren mine a prime candidate for preservation.
In the wilds of Plynlimon, close to the source of the River Wye (Afon Gwy), lies the Nantiago mine. Due to its remote situation and a careful landowner, the mine has not suffered the damage that has occurred at some others. It is also of importance as the best locality to study the Central Wales A2-c assemblage (calcite-sphalerite-galena; open fissure-filling). It is part of a much larger SSSI and permission to visit must be obtained from the landowner and from the Countryside Council for Wales.
Another remote site, Ceulan Mine in NW Powys, reveals an excellent lode outcrop with much sulphide (galena has weathered grey-white in the image).
The study of mineralisation involves a number of techniques. Hand-specimens may reveal much of interest to the naked eye: in this block of quartz-cemented breccia from Brynyrafr mine, metallic gold-coloured spots of chalcopyrite are visible.
Under the binocular microscope, another sample from Brynyrafr mine shows metallic needles associated with the chalcopyrite. These are the nickel sulphide, millerite, a widespread mineral in Central Wales in small amounts.
To study ore minerals at higher magnification, small fragments are mounted in epoxy resin and ground flat then polished to an optical mirror-finish. It is then possible to see mineral grains only a few microns across. The prepared samples are studied using a petrological microscope using reflected light. Here, in a sample from Esgairfraith mine, millerite (bright yellow) forms veins in the cobalt-nickel sulphide siegenite (pinkish-grey), the whole lot overgrown by yellow chalcopyrite. For more of these mineral images go to my Central Wales page via the Mineralogy page!
Wales also boasts a large number of secondary minerals, formed by the weathering of the primary sulphides by oxidising groundwaters. Some were formed long ago in situ underground, while others have formed within the mine-tips since mining ceased. The latter group include some very colourful species like the dark blue lead-copper sulphate linarite (left). The crystals are 1-2mm long so again the best study method is a binocular microscope.
This is one of Wales' rarities - bottle-green crystals of the copper-zinc sulphate mineral ramsbeckite. The mineral was only discovered and named in 1987, from a locality in Germany. This sample was found at Penrhiw Mine in Central Wales in 1992 and the crystals are up to 1mm across. Some mines are under protection because of their rare secondary mineral assemblages. Understanding the chemical processes leading to their formation is of considerable interest as they act as reservoirs for otherwise mobile heavy metals which cause environmental damage.