West Rigg opencut is an old working for iron ore, near Westgate in Weardale. 

This abandoned quarry is unique and is designated a Site of Special Scientific Interest. Nineteenth-century quarrying for iron ore here has exposed a lead vein. Before men dug the quarry the vein was hidden under the ground. This is now one of the best places in the North Pennines to appreciate the structure of a mineral vein.

Around 290 million years ago a crack formed in the limestone which makes up much of the hillside around you. Water, heated by buried granite and containing dissolved minerals, rose up the crack. Like a central heating pipe furring up, the crack gradually filled with minerals deposited as the water cooled. This formed the vein we see today. Some of the hot water leaked out sideways, attacking the limestone and altering it to form iron ore. The vein itself is composed mostly of quartz and some f luorite, with lead ore (galena) in the middle. The lead miners called it Slitt Vein and dug into it underground searching for lead ore. You can see their excavations in the middle of the vein. Later, the vein was exposed when the iron ore beside it was quarried away in the second half of the nineteenth century. Of no value, the vein was left as a wide rib of rock in the centre of the quarry. Slitt Vein is the longest vein in this part of the North Pennines. It extends for 13.5 miles (21.6 kilometres) from Wearhead to Frosterley.