Site Records

SiteName: Cae Coch Sulphur Mine

Trefriw
Caernarvonshire
OS Grid Ref: (No. 2 Adit) SH77536530

Sub Brit site visit 16th August 2003

GEOLOGY
The ore body at Cae Coch consists, in the main, of a two metre thick bed of massive quartzitic pyrites, sandwiched between the underlying Dolgarrog Volcanic Formation and the overlying Llanrhychwyn Mudstones, which are both Ordovician in age

This deposit is a major source of pyrites in Wales. Pyrites in its pure form contains 46.6% iron and 53.4% sulphur and it was for the sulphur that the Cae Coch deposit was worked, 70% iron content being found in the haematite ores worked extensively in Cumbria and Lancashire, which made them more attractive to the iron miner. The Cae Coch pyrites was not pure, typically containing 30% to 40% sulphur, with correspondingly less iron content.

The Cae Coch deposit consists of two separate ore bodies. The smaller northern body outcrops to the east of Blaen-y-wern, whilst the larger and more extensively worked lies immediately to the south.

The southern ore body has an average dip of thirty degrees to the south, with the superimposition of minor folding creating localised flattening or steepening of the pyrites which is clearly visible in the workings.

THE WORKINGS
The workings have been accessed by four main adits, No. 1 at the top of the hill, entering the northern ore body and Nos. 2, 3 & 4 entering the southern ore body. The No.2 adit provided access into the extensive pillar and stall workings of the main mine while the Nos. 3 & 4 were principally driven to drain the workings at depth.

The earliest workings are probably those of the linear quarry which follows the outcrop of the northern ore body to the east of Blaen-y-wern. The workings on the larger southern ore body also began as a quarrying exercise until continued removal of the overburden became impracticable after which the deposit was exploited by a series of adits; the most important of these being the No.2 adit.

TRIP REPORT The mine lies on Forestry Commission land and unlike many other mines in the Gwydyr Forest has not yet been gated. Access to this mine can be achieved via the forest road which leaves the B5016 Conwy to Trefriw road a short distance north of the Trefriw Spa. We decided to access the Mine from the upper road from Trefriw which eventually peters out to become a footpath at Tyddyn Wilym. In hindsight, might have been a mistake as the path down to the mine is steep, overgrown in places and badly signed. The footpath is clearly signed by a cattle grid in the road and surprisingly there was room to park our convoy of nine cars. The footpath heads in the direction of an occupied house but it isn't obvious that you have to walk up the drive of the house turning right as you pass it into a field that appears to be part of the garden. There is a gate at the eastern side of the field and this is the way on, descending steeply into a wooded area where a small open quarry is soon reached. This is the earliest upper working of the mine extracting ore from the northern ore body. At the bottom of the quarry No. 1 adit is clearly visible; this gives access to the upper underground workings but the adit was badly silted so we decided not to investigate as time was pressing.

A short distance down hill there are two further adits, one is dry and extends for about 20 yards to a blind end, the other has foot deep water at the portal and runs west for some fifty yards and then turns south for a further fifteen yards where the water deepens at the blind end; both were probably exploratory drivages.

From this point the footpath turns to the south and drops steeply down hill towards a fence line which has a number of notices fixed to it describing 'dangerous old mine workings' The footpath turns south west along the fence line and in a gully on the left hand side of the path the sheave wheel for the top of the 1917 aerial ropeway is still in place. On the opposite side of the footpath are the footings of a small building straddling the fence.

No. 2 adit is obscured by bushes at this point but by climbing over the fence and into the undergrowth it quickly becomes apparent. It is not an adit in the normal sense of the term but resembles a huge cave entrance thirty feet in height and as many wide. The adit opens immediately onto the steeply upward dipping pillar and stall workings in the lower ore body.

The pyrites bed was worked by leaving pillars from two to three yards in diameter, at
approximately eight to ten yard intervals. The pillars are irregular in shape and spacing, where the roof is stable a greater distance between pillars can be achieved without support. Where the roof is weaker the pillars are left closer together and are supplemented in some areas by a large timber pit props which are now doing little to support the roof, there are numerous roof falls, some apparently quite recent. In one area, up dip from the entrance the roof has fallen away around timber arching which is still left standing. Small electrical insulators fixed to the walls indicate that an electrical supply was taken deep into the mine.

There are many calcite formations and some spectacular colouring in the rock and in several places there are acid pools that leave permanent stains on boots and clothing. The lower levels of the mine are flooded up to the level of No. 2 adit and are no longer accessible.

At this point we had to retrace our steps but we will return to Cae Coch another day, there is plenty more to see underground and on the surface much remains including the inclines, drum house, storage bins, foundations of the processing mill, numerous other buildings and Nos. 3 & 4 blocked drainage adits.

The history and geology of Cae Coch Mine is an abridged version of Mines of the Gwyder Forest Part 7 by John Bennett & Robert Vernon pages 12 - 39. ISBN0 9514798 6 5. It is reproduced with permission from the author.

Published by Gwydyr Mines Publications 17 Field Lane, Appleton, Warrington, WA4 5JR

Mines of the Gwydyr Forest Parts 1 - 7 is available from Moore Books specialising in mining, caving and industrial archaeology.

For a gallery of photographs of cae Coch Mine click here

Home Page