Gunnis

A narrow, linear excavation left where a near-vertical, rich ore-bearing lode has been worked out completely -- most often used where the resulting void is open to the surface.

Historical usage

The word derives from the Cornish gonis, meaning 'working', and William Pryce recorded it as early as 1778, when it was also used as a unit of measurement -- a single gunnis being reckoned at three feet.

How it worked

Where a lode was rich enough, narrow enough and steep enough, miners could work it out entirely from top to bottom rather than leaving pillars or working selectively, leaving behind a long, narrow chasm following the exact line the ore had taken through the rock. Where such a void reaches the surface it is more often called a coffen or goffen; a broader excavation of the same kind, taking in a wide band of small parallel lodes rather than one narrow one, is a stockworks instead.

Why it was used

Working a lode out completely, rather than leaving supporting pillars, recovered the maximum possible ore from a deposit rich enough to justify it -- appropriate for a narrow, well-defined, high-grade vertical lode where the ground on either side held little worth returning for.

Risks & limitations

A large, deep gunnis left standing open was a serious hazard to later mine development, and remains one today at surviving sites: sheer drops of many metres with no barrier beyond a modern fence, exactly the case at the already-published Wheal Frementor.

Regional variation

A specifically Cornish term, tied to the Cornish language and to Cornwall and west Devon's characteristic narrow, steeply dipping tin and copper lodes; the word is not generally used outside this district's mining vocabulary.

Mines associated with this term

Included only where MineArchive's own research gives a reasonable evidential basis — not every mine where this might plausibly apply.

• Wheal Frementor — Devon (well documented example)
  Named 6 times in this record, first in the summary: “…worked-out vertical deposit left an exceptional open void known as a gunnis.”

Sources

1. (secondary) A Cornish mining glossary — Cornish Mining World Heritage Site (UNESCO)
2. (secondary) Gunnies — Wikipedia

Record created: 31 August 2026 · Last researched: 31 August 2026