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The Penberthy Croft mine is approximately 1 mile (1.61 km) northeast of the village of Goldsithney in the parish of St. Hilary, Cornwall, England (NGR SW 555 324). The Wheal Fancy mine is now represented by shafts in the field NE of Trewhellan Farm. An old tithe map ( https://en.wikipedia.org/wiki/Tithe_map ) dated 1842 shows the name Penberthy Crofts Mine, it seems likely the 's' was dropped in later writings.

The locality is a prolific source of rare and unusual secondary minerals, of which the Cu-Pb-Fe-Al arsenates are the best known. New additions to the minerals from PCM are still being made to this day.

Penberthy Croft is the type locality for the copper lead arsenate bayldonite and the aluminium arsenates bettertonite and penberthycroftite. However, there is some dispute that Penberthy Croft is the type locality for bayldonite. The specimens supplied to A.H. Church (who named the species) by Richard Talling (mineral dealer) for the description only had the locality as "Cornwall".

It is also visually not possible to say that the yellow colour in the series mimetite-pyromorphite occurring here is always pyromorphite. It is quite likely that pyromorphite is not the pure PO₄ end member from this mine, but this needs further investigation. Specimens have to be analysed to confirm either mimetite or pyromorphite or written as mimetite-pyromorphite series.
Jeanbandyite and natanite from PCM have been analysed as mixed crystals containing both minerals and should be labelled as jeanbandyite-natanite.

Penberthy Croft is the first, or joint first, recorded site for jeanbandyite and natanite and also the first occurrence of neustädtelite, galeaclolusite, atelestite, bulachite, pharmacoalumite, schoenfliesite, perite, and zipserite in the British Isles. It is also the first recorded occurrence of bayldonite, bettertonite and penberthycroftite in the world.

The land is owned by the St. Aubyn Estate. Permission for site visits and bona fide research must be made before 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.

History:

Penberthy Croft is quite old, maybe pre-1700 (Beer, 1988 (unsubstantiated)). The mine is recorded as producing copper ore in the 1780s and again in the 1790s, producing £281 (period value) worth of Cu ore in 1798. Copper and tin were produced from 1800 to 1804, producing 3,230 tonnes of Cu ore and from 1819 to 1825, with a recorded output of 7,318 tonnes of Cu ore. The next recorded output of ore was from 1834 to 1840; output is unknown from this period — having not been found — although it is recorded that regular sales were made. The mine was again at work from 1871 to 1876 and from 1905 to 1907, producing 130 tonnes of black tin, 130 tonnes of tin ore, and some lead ore. When the tin price hit a high in 1993, the dumps were sampled. Judging from the output figures, the ore shoots may have been of limited tonnage.

Geology:

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 lodes are associated with a rhyolite porphyry elvan dike mapped about 50 m south of the Main Lode. Only one cross-course structure is possibly indicated on an old plan on the west side of the mine and is probably related to a shear zone, an old plan may indicate two low-angle structures underlining to the west, cutting the main lode. There are, in addition, five other named lodes within the sett.

Mineralisation:

The mineralisation is of a multi-stage, polymetallic-hydrothermal character. The deposit consists of several distinct overlapping assemblages:

— minor, burial-related quartz-apatite-albite-anatase-monazite veins of a pre-tectonic, metamorphic origin;
— main-stage high-temperature hypothermal-mesothermal Sn-Cu-As-W veins are said to have been emplaced over a 20 million-year period;
— later lower-temperature epithermal Fe-Pb-Zn-sulphide with a small Bi, Co, and Ni component and later carbonate mineralisation, ankerite, calcite, dolomite.
— and a late-stage, low-temperature Fe-Mn mineralisation, although the Mn mineralisation is unclear from this mine and may relate to Mn oxides; maybe a generic statement for the ore field in general needs clarification specific to PCM.

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. These include — in order of approximate abundance — 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, although other dumps also produce specimens but are sporadic. Most minerals here are found as good-quality subhedral to euhedral microcrystals, with occasional miniature specimens. Sir Arthur Russell collected hand-sized bayldonite underground between 1903 and 1905; it is now in the NHM London. Brecciation, fracturing, silicification, chloritization, and carbonatization are abundant. The mineralisation formed over a very long time, extending from the Upper Palaeozoic through to the Cenozoic.

The lode structures are recorded as:

— Main Lode (East-West);
— Longclose Lode (ENE-WSW);
— Canart Lode (ENE-WSW), which crosses Main Lode east of Long Lane.
The Main Lode then splits into three going east before and after Long Lane dissects the sett and becomes:

— Main Lode (East-West);
— Kings Lode (E by N-W by S) splits from the Main Lode before crossing Long Lane according to the old plans.
— Tellam's Lode (E by N-W by S) — with a branch off this lode, the location of this branch is unknown — splits from Canart Lode (ENE-WSW) on the east side of Long Lane.
— Cocks Lode and Wheal Fancy Lode on the old plans show these to be both parallel, approximately NW counter-lodes. Dines (1956) says the Wheal Fancy lode is a continuation of the Main Lode; the old plans appear to show the Main Lode tracking to the south to connect with the Wheal Fancy lode.

The mine has a record of 23 shafts on the sett, including adit/air shafts and working shafts. The deepest shaft sunk to a depth of 110 fathoms (ca. 201 m) below adit, approximately 25 fathoms (ca. 48 m), was at Minach's, immediately west of Long Lane, sunk on Canart Lode.

At some time, Wheal Fancy and Wheal Mundic were incorporated into the Penberthy Croft mine sett; the location of Wheal Mundic is unknown.

A major comprehensive mineralogical study was completed on this important locality by Betterton (2000) and was published in the UK Journal of Mines & Minerals, 20, 7-37.

Notes on the mineral list:

The references to adamite, arseniosiderite, beraunite, bieberite, ceruleite, hornblende, plumbojarosite, rosasite, serpierite, tyrolite, vanadinite, and zálesíite at Penberthy Croft are from Kingsbury. Atacamite, beaverite-Cu and paratacamite may also be fraudulent. Given the doubts about the provenance of other Kingsbury specimens (Ryback et al., 1998, 2001), investigated this and discredited the occurrence. The fraudulent adamite specimen was used to prove that this specimen was zincolivenite and not adamite. A true zincolivenite was found on the Daws Shaft dump. Plumbojarosite has now been confirmed from the mine (Steve Rust, June 2025). Specimens of hidalgoite should be analysed, as most have turned out to be philipsbornite. An inquiry to the NHM London (Rust, March 2026) regarding the specimen of smithsonite recorded from PCM has indicated the specimen on fluorite is maybe from the north of England.

Unknowns (UK PC = Unknown Penberthy Croft) from the John Betterton Collection under investigation:
UK PC2? MnxOx
UK PC3? Cu+Zn+As+Mn+Fe+Co??+La???+O
Additional work is required on these unknowns.
Investigations are also continuing on specimens from the Steve A. Rust collection, who is also compiling a book on the minerals from the mine, a long-term project. The last update was published in 2000 by John Betterton.
An unnamed lead iron arsenite may be related to a tsumcorite group mineral (NHM London XRD, EDX), Rust #34 and #35 (SEM-EDS, Raman and XRD, Mineral Analytik Germany).
A new potential Cu,Pb,S,Si,Cl mineral, Rust #71 (SEM-EDX, Raman, and XRD Mineral Analytik Germany). The specimen is now with the NHM London for further investigation. Several further species have been confirmed recently, either new to the UK or first from the mine (Rust 2022-2026).
The alunite group of minerals (i.e., beudantite, corkite, segnitite) are a bit of a mess from PCM. There is a lot of substitution and overlap within this group. Attempts are in hand to throw some light on this group of minerals from the mine. It is also hoped to improve the knowledge of the primary metallic species found at PCM.
The mineralogy of Penberthy Croft mine is turning out to be more complex than previously believed.

Commodity List

This is a list of exploitable or exploited mineral commodities recorded from this region.

Mineral List

Mineral list contains entries from the region specified including sub-localities

139 valid minerals. 3 (TL) - type locality of valid minerals. 15 erroneous literature entries.