Flats

Sub-horizontal replacement ore bodies spreading sideways out of a vein where it meets a rock that will react with the mineralising fluid — most often a particular bed of limestone. Where a vein is a sheet standing on edge, a flat lies down along the bedding, and can be many times wider than the vein that fed it.

Historical usage

Flats were the making of the Derbyshire and Yorkshire orefields and of the Northern Pennines. In the South Pennine Orefield miners worked steeply inclined fissure veins — rakes, with thinner groups called scrins — and found that where those veins crossed receptive limestone beneath the impermeable shale cover, the ore spread out sideways into flats. In the North Pennines the Great Limestone was the great host: at Groverake the veins were at their widest and richest where they cut it, and at Boltsburn in Rookhope the flats were rich enough to keep the mine among the district's leading producers well into the 20th century.

How it worked

Miners rarely found a flat from the surface, because flats rarely reach it. The normal route was to follow a rake or a scrin sideways into the limestone and watch for the ore to open out. Once found, a flat was worked outward from the vein along the bed — a low, wide, spreading working rather than the tall narrow stope of vein mining, and one where the roof had to be held on pillars or timber because there was no natural arch to it.

Why it was used

Not a choice but a discovery: a flat is a shape ore takes, and the reason it mattered is that it concentrated far more mineral in one place than the feeding vein ever did. A mine that found a good flat could work profitably for years on ground the vein alone would not have justified.

Risks & limitations

Flats are unpredictable in extent, and no amount of driving guarantees finding one — a great deal of dead ground was cut in the search. Because they follow bedding rather than a fissure, they can also be cut off abruptly by faulting, and their wide, low workings need deliberate support: the roof of a flat is a bedding plane, which is exactly the surface most inclined to part.

Regional variation

'Flat' is Pennine and Peak District vocabulary. Derbyshire miners distinguished flats from pipes — irregular tubes or pockets filling older cavities in the rock — and both from the rakes and scrins that fed them. Cornish miners, working a granite-related orefield with a quite different chemistry, had little use for the word; the closest hard-rock equivalents there are the carbona bodies of the tin ground.

Related terminology

Fluorspar, Lead, Limestone, Rake, Stope, Vein

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.

• Good Luck Mine — Derbyshire (well documented example)
  A Derbyshire lead mine in the orefield where flats are part of the standard vocabulary of ore bodies.
• Groverake Mine — County Durham (well documented example)
  The veins were at their widest and richest where they cut the Great Limestone, which also hosts the flats of the Weardale orefield.
• Rookhope (Boltsburn Mine) — County Durham (well documented example)
  Boltsburn worked exceptionally rich flats in the Great Limestone.
• Milldam Mine — Derbyshire (historical documentary reference)
  Milldam works the Hucklow Edge vein in the same limestone that hosts the flats of the South Pennine orefield.

Sources

1. (primary) Mineral Resources report for the Peak District National Park — British Geological Survey / NERC
2. (secondary) Peak District Mineralisation — The Peak District

Record created: 25 August 2026 · Last researched: 25 August 2026