Cerniau

A landscape image of part of the former Gorseddau Slate Quarry, at Cwmsystradllyn. Taken from part of the former tramway, that linked it to Ynys-Y-Pandy Slate Mill. The former tramway path this side of the gate, local stone built retaining wall. Providing a lead in to the image, and view of the remaining slate waste beyond.

The path down the south-west ridge of Rhobell Fawr follows this wall to Bwlch Goriwared. Here on the lower slopes, the wall divides the hillside into the colourful heather on the eastern side and coarse grasses to the west. The Cadair ridge is in the background.

The old drove road climbs up to the pass. Waun Oer is the highest of the hills on the horizon.

A mixture of heather-covered hillside and better grazing, through which the old drove road to Bwlch Goriwared climbs.

Looking down the lower part of the long western approach to Rhobell Fawr in the direction of Bwlch Goriwared. The distinctive rocky knoll on the left can be seen from below in SH7624 : Hillside east of Bwlch Goriwared. The Rhinogydd form the horizon.

The road downstream along the east side of the Afon Wen, heading for Dolgellau, is one of many narrow lanes in this part of Wales

Rivers were pretty dry in the spring of 2011.

Rivers in this part of Wales were pretty low in the spring of 2011.

This path climbs gently away from the Afon Wen.

Set against the churchyard wall is this 11kV electricity substation where in time past the hearse was kept. The plate on the door has the legend 'Ty Hers 10 7522 013'. 10 represents the district according to the old MANWEB designation, 7522 tells you that you are in that grid square and 013 is the substation number.

Part of the poorly exposed orebody. This is sited in the highly altered host volcanics and sediments. There are some overlap into the stock. Green copper supergene minerals stain the rock, molybdenite (MoS2) can be seen in hand samples. Magmatic fluid pressures created hairline cracks, when the pressure dropped suddenly metals were deposited. This is often in a stockwork tenture. The sudden pressure drop causes phenocryst formation in the stock. This resource is 200Mt of Cu at 0.3% with 1ppm of Au and some Mo. However, opencasting would be required so it is only a curiosity.

Part of the poorly exposed orebody. This is sited in the highly altered host volcanics and sediments. There is some overlap into the stock. Green copper supergene minerals stain the rock, molybdenite (MoS2) can be seen in hand samples. Magmatic fluid pressures created hairline cracks, when the pressure dropped suddenly metals were deposited. This is often in a stockwork tenture. The sudden pressure drop causes phenocryst formation in the stock. This resource is 200Mt of Cu at 0.3% with 1ppm of Au and some Mo. However, opencasting would be required so it is only a curiosity.

Part of the poorly exposed orebody. This is sited in the highly altered host volcanics and sediments. There is some overlap into the stock. Green copper supergene minerals stain the rock, molybdenite (MoS2) can be seen in hand samples. Magmatic fluid pressures created hairline cracks, when the pressure dropped suddenly metals were deposited. This is often in a stockwork tenture. The sudden pressure drop causes phenocryst formation in the stock. This resource is 200Mt of Cu at 0.3% with 1ppm of Au and some Mo. However. opencasting would be required so it is only a curiosity.

Porphyry copper deposits are of a major economic importance due to the high tonnage (but often low grades) of copper, molybdenum and gold. This deposit contains 200Mt of ore at 0.3% Cu with some Mo and Au. It would be economic only through opencasting, which I can't see happening any time soon! A process that made PCDs economic was developed in the area, at Glasdir copper mine SE of here. SH7422 : Glasdir Copper Mine Link Hydrothermal and magmatic fluids circulate to create alteration zones. The ore is usually hosted in the outer edge of the stock. Potassic zone, usually an igneous stock (volcanic magma chamber). Can be rich in secondary orthoclase, quartz, biotite and chlorite/sericite. Phyllic zone, altered host rocks. In this case volcanics and sediments. Pyrite rich (10-15%), quartz, sericite, chlorite and illite. +/- Argillic zone. Varies in size, clay alteration. Propylitic zone, always present. Lightly altered with pyrite, chlorite, quartz, carbonates and epidote. This shows the phyllic zone. The pyrite has oxidised to produce the red stained colour.