Okeltor Mine

Overview

Okeltor's arsenic works, expanded through the 1870s with an especially rare surviving shaft kiln, processed not only its own ore but pyrites barged upriver from another mine entirely -- making the Tamar itself part of its production line.

History

Okeltor Mine occupies the north bank of a loop in the River Tamar east of Calstock, worked through the 19th century for arsenic and copper, with significant quantities of tin and some lead. The earliest recorded working was an adit dug from near the riverbank around 1845; renewed activity from 1850 extended this adit and began a vertical engine shaft that would eventually reach at least 166 metres deep, remaining the mine's chief pumping, winding and access route for most of its working life. A pumping engine house built in 1853 to house a 50-foot steam engine survives fairly intact despite the collapse of its west wall, its boiler house chimney rising to full height beside it -- both listed Grade II. For much of the 1850s arsenic and lead were the chief products, but cross-cuts from the shaft reached copper-bearing lodes from 1859, more than doubling the mine's copper output between 1864 and 1870 and prompting further investment in machinery. The early 1870s brought major growth in arsenic refining and tin processing: by around 1870 a Brunton calciner, in which arsenic ore was roasted on a rotating hearth, had been built, with a second added around 1872, both surviving today with their brick-arched power vaults intact. To the south of the calciners, a rare shaft kiln survives with the remains of six cylindrical, brick-lined shafts, each about a metre across, used with fuel to roast coarser arsenic ore -- a nationally rare survival. By 1872, around 450 metres of arsenic flues linked the ore-heating sites to condensing chambers, most surviving intact though largely roofless. A stamps and dressing-floor complex, built in 1872-3 to process newly discovered tin ore, retains a stamps engine house with walls surviving almost to roof height and fine original detail including timber lintels and window glazing bars. Falling ore prices forced the mine's closure and the sale of its machinery in September 1873, though work soon restarted, with only arsenic production significant between 1876 and 1881. A new company brought renewed investment from 1881, sinking two further shafts in 1882 to work newly discovered arsenic/copper and tin lodes, and enlarging the stamps and dressing floor; from this period, the mine also processed arsenical pyrites barged up the Tamar from the Danescoombe Valley Mine further west. Tailings from the dressing floor were carefully diverted through channels and settling ponds to control pollution before reaching the river -- an early example of such measures. Despite a peak in arsenic production, tin and copper output remained poor against falling prices; the mine was wound up in 1885, restarted under new ownership in 1886, and finally closed in 1887, though its company remained in operation until 1889.

Geology

Arsenic-, copper- and tin-bearing lodes worked from a vertical engine shaft reaching at least 166m deep, on a loop of the River Tamar.

Workings

A pumping engine house and chimney (1853), two Brunton calciners, a rare six-shaft arsenic roasting kiln, about 450m of arsenic flues, and a stamps/dressing floor complex (1872-3, enlarged 1882) with pollution-control settling ponds.

Closure

Closed and machinery sold in 1873; work restarted but only arsenic was significant 1876-81; renewed investment from 1881 under a new company; final production 1887, company operated until 1889.

What remains

Scheduled as a nationally important monument; the pumping engine house, boiler house chimney, count house and smithy are separately listed Grade II. The arsenic refining works are considered among the best-preserved of their date nationally.

A pumping engine house and chimney, two Brunton calciners, a rare shaft kiln, extensive arsenic flues, a stamps engine house with fine surviving detail, a count house, smithy, and pollution-control settling ponds survive.

Nearby mines

• Gawton Mine — 0.7 km E, Devon
• George and Charlotte Copper Mine — 0.8 km N, Devon
• Bere Alston Silver-Lead Mines — 1.6 km S, Devon
• Danescombe Mine — 2.3 km W
• Hingston Down Quarry — 3.6 km NW

Straight-line distance, within 15 km. Show on the map.

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• In 1853, a pumping engine house was built by the north of the shaft to house a 50ft steam engine; it survives fairly intact except for extensive collapse of its west wall, and the pumping engine house and its boiler house chimney are Listed Buildings Grade II. ¹
• By 1872, the ore-heating sites were served by about 450m of arsenic flues which survive mostly intact, but largely roofless; remains of six shaft-kiln shafts survive, three to each side of a partly collapsed central brick-arched vault, an especially rare survival among 19th-century arsenic works. ¹
• The engine house had a 50 inch cylinder draught engine, operating 75 fathoms of 12 inch plunger lifts and 15 fathoms of 12 inch drawing lifts, the date of installation being 1864; the main engine shaft reached 80 fathoms below the level of the Tamar, and the main copper lode passes under the river into Gawton mine on the Devon side. ²

Photographs & further reading

Sources

1. (primary) Okeltor 19th century arsenic, copper and tin mine, Calstock, Cornwall — AncientMonuments.uk (mirroring the Historic England scheduling record)
2. (primary) Okeltor Mine Buildings, Calstock, Cornwall — British Listed Buildings (Historic England listed building record)

Record created: 17 September 2026 · Last researched: 17 September 2026