Snailbeach Lead Mine Geology

The main rock in which the minerals have been deposited at the Snailbeach Mine is called Mytton Flags. These are grit/shale sedimentary rocks laid down in the early Ordovician times, approximately 450 million years ago, and now make up most of the rock types that lay at the base of the Stiperstones range of hills.

The Mytton Flags consist of fine silts and grits deposited onto the beds of ancient estuaries from rivers eroding away even more ancient mountains, over a long period of geological time. These sediments built up in layers and now attain a present day thickness of over 2,000ft.

As geological time progressed, these sediments were subject to major earth movements causing them to fold and fault. At a later stage, there was deep seated Igneous activity, possible in the Devonian period approximately 380 million years ago. Super-heated brine waters, containing dissolved chemical elements, ascended from the Igneous mass and found their way along the faults. In doing so, they slowly cooled and released minerals which filled the voids of the faults and became the mineral veins that we know today.

Minerals were deposited at different cooling temperatures within the faults, Barite, Witherite and Calcite in the upper parts of the veins, Galena, Calcite and Quartz deeper, and still deeper the minerals Sphalerite, Calcite and Quartz. In theory, Copper and Tin minerals should be found at depth but this has not been proven!

You can see good surface exposures of the Mytton Flags at three locations :-

§ side of the old railway line, close to Crows Nest Dingle (NGR370014)

§ right side of the lane leading up to the Lords Hill Chapel (NGR378022)

§ behind the bungalow to the left of the Stiperstones Inn (NGR363005).

All of these exposures can be seen to dip at approximately 50 degrees due to ancient earth movements.

The other rock type encountered underground at the Snailbeach Mine is Stiperstones Quartzite. This is very hard rock, consisting of almost pure fine silica sand laid down in the shallow tropical seas of the early Ordovician period. However, although these rocks have been subjected to folding and faulting in a similar way to the Mytton Flags, for some reason they never laid themselves open to mineral deposition. They almost acted as a cap rock, halting migrating mineral fluids from the Mytton Flags. This was found to be the case, and to the detriment of the mine owners, when they drove levels in an easterly direction from Chapel Shaft and met with the Stiperstones Quartzite at the112 Yard Level and below.

Today the Stiperstones Quartzite can easily be recognised on the surface, they are the rocks that make up the famous Stiperstones Ridge which includes The Devil’s Chair, Cranberry Rock and Nipstone Rock.

The minerals found in the veins at Snailbeach Mine are :-

Common

Barite - barium sulphate (BaS04)

Calcite - calcium carbonate (CaCO3)

Galena - lead sulphide (PbS)

Iron Pyrites - iron sulphide (FeS)

Quartz - silicon dioxide (SiO2)

Sphalerite - zinc sulphide (ZnS)

Witherite - barium carbonate (BaCO3)

Rare

Cerussite - lead carbonate (PbCO3)

Copper Pyrites - copper sulphide (CuS)

Pyromorphite - chloro-phosphate of lead (3Pb3P2O8.PbCl2)

Recorded but not seen

Fluorspar - calcium fluoride (CaF2)

Lead production peaked about 1860, examples of production for 50 years up to the First World War were :-

Lead -132,000 tons

Barytes - 42,000 tons

Zinc - 4,000 tons

Fluorspar - 900 tons

There is no mineralisation to be seen in Day Level as this was cut in barren rock for access only. In Perkins Level, however, there is a prominent barite vein with localised traces of galena. There is no geological collecting allowed underground at any time but an area of the tips has been left uncovered for visitors to pick through.

Last revised: 18 July 2008