Penberthy Croft Mine, St Hilary, Mount's Bay District, Cornwall, England, UK
|Latitude & Longitude (WGS84):||50° 8' 25'' North , 5° 25' 19'' West|
|Latitude & Longitude (decimal):||50.14028,-5.42222|
|UK National Grid Reference:||SW555324|
|Other regions containing this locality:||Devon and Cornwall metalliferous mining district, England, UK|
|Köppen climate type:||Cfb : Temperate oceanic climate|
Penberthy Croft mine is situated approximately one mile northeast of the village of Goldsithney in the parish of St. Hilary, Cornwall, England (NGR SW 555 324). The locality is a prolific source of rare and unusual secondary minerals of which the Cu-Pb-Fe-Al arsenates are the best known. Penberthy Croft is the type locality for the following species: the copper lead arsenate bayldonite and the aluminium arsenates bettertonite and penberthycroftite.
Penberthy Croft is the first, or joint first recorded site for the tin hydroxide minerals jeanbandyite and natanite in the British Isles. Segnitite is also first recorded at this location.
The land is owned by the St. Aubyn Estate. Permission for site visits and bona fide research must be made prior to any visit through the Agent for the St. Aubyn Estates. The address is Manor Office, Marazion, Cornwall, TR17 0EF, England. Telephone: +44 (0) 1736 710507.
The mine is quite ancient and records of output give approximately 3000 tons of copper ore toward the end of the 18th century. Mixed copper and tin mining took place at depth at a later date, the lodes being stoped out to a depth of 53 fathoms below adit level. The mine closed around 1840. There being no further activity until recent years when at a time of high tin prices the dumps were sampled to evaluate their cassiterite content. The mine became listed as a SSSI by English Nature for its mineralisation in 1993.
The sett is situated in Devonian metasediments consisting of lower-grade-greenschist facies (killas) slates between the Land's End and Godolphin granite masses. The slates belong to the Mylor Slates Formation and are a series of dark coloured rocks with a slaty cleavage and well-developed foliation. They are generally characterised by a series of siltstones and mudstones, with occasional impersistent sandstone sequences. A series of interbedded metabasic rocks strikes east-west within the sett. The main Penberthy lode strikes east-west and dips to the south. The lode is associated with a rhyolite porphyry elvan dyke and cross course structures and is probably related to a shear zone. There are in addition five other named lodes within the sett.
The mineralisation is of a multi-stage, polymetallic and hydrothermal character. The deposit consists of several, but distinct overlapping assemblages: Minor, burial-related quartz-albite-anatase-monazite veins of a pre-tectonic, metamorphic origin; main-stage high-temperature hypothermal-mesothermal Sn-Cu-As-W veins; later lower-temperature epithermal Pb-Zn sulphide mineralisation; and a late-stage, low-temperature Fe-Mn mineralisation. Subsequent supergene oxidation and weathering of lodes resulted in the formation of complex gossans with oxide and supergene enrichment zones. Post-mining formation of other minerals both underground and on the dumps has resulted in a very large variety of mineral species in a small area. These in order of approximate abundance include arsenates, arsenate-sulphates and phosphates. The greatest diversity in terms of species has been located in five main areas of the old dumps: Three in the western and two in the eastern section of the workings. Most minerals here are found as good quality subhedral to euhedral microcrystals with occasional miniature specimens. Brecciation, fracturing, silicification, chloritization and carbonatization are abundant. The mineralisation formed over a very wide period of time extending from the Upper Palaeozoic through to the Cenozoic.
A major comprehensive mineralogical study was recently completed on this important locality by Betterton (2000) and was published in the UK Journal of Mines & Minerals, 20, 7-37.
Note on the mineral list:
Reference to adamite at Penberthy Croft is from Kingsbury. Given the doubts about the provenance of other Kingsbury specimens (Ryback et al. 1998, 2001), investigated this and discredited the occurrence.
Unknowns (UK PC = Unknown Penberthy Croft) from the John Betterton Collection under investigations:
UK PC2 ? MnxOx
UK PC3 ? Cu+Zn+As+Mn+Fe+Co??+La???+O
Additional work is required on these unknowns.
Mineral ListMineral list contains entries from the region specified including sub-localities
112 valid minerals. 3 (TL) - type locality of valid minerals. 8 erroneous literature entries.
|Geologic Time||Rocks, Minerals and Events|
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
323.2 - 358.9 Ma
|Paleozoic sedimentary rocks|
Age: Mississippian (323.2 - 358.9 Ma)
Lithology: Sedimentary rocks
Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. 
358.9 - 382.7 Ma
|Upper Devonian Rocks (Undifferentiated)|
358.9 - 382.7 Ma
|Late Devonian claystone|
Localities in this Region
- Mount's Bay District
- St Hilary
- Penberthy Croft Mine
- St Hilary
- Mount's Bay District