Great Dowgas Mine (St Stephen Tin and Copper Mines), Downderry, St Stephen-in-Brannel, Cornwall, England, UKi

Regional Level Types
Great Dowgas Mine (St Stephen Tin and Copper Mines)	Mine
Downderry	Census-designated Place
St Stephen-in-Brannel	Civil Parish
Cornwall	County
England	Constituent Country
UK	Country

A tin and copper mine which also produced pyrite, some cobalt and nickel ores and a considerable amount of ochre. It was first worked around 1719, when it sold some black tin, and reworked many times until 1913, but it was never very successful. In 1865, Thomas Spargo states that it "was always a poor mine, and the works have wholly ceased, at least underground, but the sett, I believe, has not been surrendered."

The mine worked five SE-trending lodes within a transverse distance of 130 fms, from north to south Woodhead's Lode, New North Lode, Copper Lode, Goffins Lode (or Coffins Lode, also known as Great Stopes Lode) and South Lode. It was drained by a deep adit, which commences near Coombe and follows the valley northeastwards to Brannel farm, where it turns to the southeast and continues into the sett of St Austell Consols, a distance of more than a mile. A cross-cut driven to the southwest below Dowgas farm connects to Engine Shaft, which was sunk on New North Lode, at 46 fms below surface. The grid reference marks the approximate position of this shaft. The engine house has not survived, but the stack is still standing.

Main lode was Goffins Lode, which was developed from several shafts on a length of 300 fms along strike. It occupied a crush zone and was composed of killas fragments and a filling of mainly quartz and pyrite. Cassiterite only occurred sporadically, except in the eastern part where the lode intersected an elvan before it passed into killas and died out. In the 18th century, the lode had already been worked from open gunnises, but they were abandoned at shallow depth, probably because the tin grades became poor.

The mine is reported to have sold some tin in 1719, but early production figures are not known. Up to 1832, it produced copper ores worth at least £12,000, and tin worth more than £9,000 is reported for the years 1828-1832. Official records give an output of 120 tons of black tin for 1856-1860, and another 47 tons for 1907-1913. In 1857, it also raised 4 tons of cobalt ores, but their mode of occurrence is not known. When it was worked for the last time, it mainly raised pyrite, which came from the upper levels. It finally closed in 1913.

During its last period of working, Great Dowgas Mine was amalgamated with Ventonwyn Mine. For some time during the 18th century, it also included Wheal Unanimity, which adjoined the sett on the east (not on the south, as suggested by Hamilton Jenkin; Beer, in: Dines, 1994). In 1873, it was worked for a short period of time together with parts of St Austell Consols under the name St Stephen Tin and Copper Mines.

Geochronology

Geologic Time				Rocks, Minerals and Events
Phanerozoic
	Paleozoic
		Permian
			Guadalupian	ⓘ Major polymetallic mineralization ~270 Ma Cornwall, England, UK
			Cisuralian	ⓘ Porphyry dikes intruded (latest age) ~275 Ma Cornwall, England, UK ⓘ Greisenization (latest age) ~280 Ma Cornwall, England, UK ⓘ Porphyry dikes intruded (earliest age) ~280 Ma Cornwall, England, UK ⓘ Formation of metallized pegmatites ~285 Ma Cornwall, England, UK ⓘ Greisenization (earliest age) ~285 Ma Cornwall, England, UK ⓘ Emplacement of major plutons ~295 Ma Cornwall, England, UK

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References