West Rigg Open Cutting is a

Site of Special Scientific Interest A Site of Special Scientific Interest (SSSI) in Great Britain, or an Area of Special Scientific Interest (ASSI) in the Isle of Man and Northern Ireland, is a conservation designation denoting a protected area in the United Kingdom and Isle ...

in the Wear Valley district of west

County Durham County Durham, officially simply Durham, is a ceremonial county in North East England.UK General Acts 1997 c. 23Lieutenancies Act 1997 Schedule 1(3). From legislation.gov.uk, retrieved 6 April 2022. The county borders Northumberland and Tyne an ...

, England. It is a disused

ironstone Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron ore compound from which iron (Fe) can be smelted commercially. Not to be c ...

quarry A quarry is a type of open-pit mining, open-pit mine in which dimension stone, rock (geology), rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some juri ...

, located just over 1 km north of the village of Westgate, in

Weardale Weardale is a dale, or valley, on the east side of the Pennines in County Durham, England. Large parts of Weardale fall within the North Pennines Area of Outstanding Natural Beauty (AONB) – the second-largest AONB in England and Wales. The u ...

. At West Rigg, the Slitt Vein, a 20 km-long quartz intrusion in the

Namurian The Namurian is a stage in the regional stratigraphy of northwest Europe, with an age between roughly 331 and 319 Ma (million years ago). It is a subdivision of the Carboniferous system or period, as well as the regional Silesian series. The Na ...

Great

Limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

, is exposed at the surface; the exposure is up to 5 m wide over a distance of some 200 m. During

Late Permian Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...

times, extensive mineralisation occurred in the vicinity of the Slitt Vein: high salinity fluids, rich in iron, permeated the Great Limestone which, throughout its full thickness, was mineralised, producing

siderite Siderite is a mineral composed of iron(II) carbonate (FeCO3). Its name comes from the Ancient Greek word (), meaning "iron". A valuable iron ore, it consists of 48% iron and lacks sulfur and phosphorus. Zinc, magnesium, and manganese commonly ...

and

ankerite Ankerite, also known as '' brown spar''礦物學名詞: (俄英中对照試用本) Mineralogical Terminology (Russian-English-Chinese version). — Beijing: 中國科学院. 編譯出版委員会 Compilation and Publication Committee of Chinese A ...

minerals which were subsequently oxidised, yielding a limonitic ore with an iron content of over 40 per cent. At West Rigg, the iron mineralisation extends up to 60 m on each side of the vein. The Slitt Vein is predominantly composed of

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

, with smaller amounts of

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs scal ...

and uneconomic amounts of

galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It crysta ...

lead ore. The earliest mining activity at the site was the extraction of fluorite and galena from the Slitt Vein itself: the miners worked from levels driven into the vein from the west. In the late 19th century, quarrying of the ironstone began, the Slitt Vein being left untouched so that today it protrudes as a vertical 'rib' along the centre of the quarry. The

Geological Conservation Review The Geological Conservation Review (GCR) is produced by the UK's Joint Nature Conservation Committee. It is designed to identify those sites of national and international importance needed to show all the key scientific elements of the geological ...

has identified the site as being of national importance because it provides an accessible illustration of the formation of iron ore by replacement and oxidation. The site also offers a rare surface view of the Slitt Vein.

References

{{SSSIs County Durham Sites of Special Scientific Interest in County Durham Quarries in County Durham Stanhope, County Durham

See also

References