County Geological Site

Site reference no. WSX47SW1_A-B Name: Wheal Anna Maria (Devon Great Consols)

District: West Devon Parish: Gulworthy

National grid ref: SX42677367 OS sheets: 1:50k 201 1:25k 108 1:10k SX47SWGS 1:50k 337

GridRef x y Lat Long SX426736 242600 73600 50.540932 -4.2226894

Locality description (address): The site comprises two distinct sections, close to Wheal Anna Maria, Houses, Gulworthy (Tamar-Tavy Geodiversity Audit, Site 110): (A) Mine dumps around former Engine Shaft, 130 m north of Wheal Anna Maria House (Site 110.1), (B) Mine dumps adjacent to arsenic works, 200 m south-west and up to c. 200 m south of Wheal Anna Maria Cottages (Site 110.5, pad). Both sections lie within the Wheal Anna Maria sett of the former Devon Great Consols Mine.

Nature of site: The CGS represents two distinct areas of mine dumps in which a significant quantity of original, unprocessed mineralised rock remains. Adjacent areas of mine waste are dominated by fine-grained burnt or leached waste material in which little or no original mineralogy survives.

Geological / geomorphological features:

The main workings at Wheal Anna Maria were on the Devon Great Consols Main Lode, the largest sulphide deposit in south-west England. The lode was 2 m to 10 m wide, with a centre dominated by chalcopyrite, with pyrite, quartz, chlorite ‘peach’ and more locally fluorite and siderite. The margins of the copper-rich lode were dominated by arsenopyrite. There appears to have been little development of secondary copper minerals. At least two other lodes were worked in the Wheal Anna Maria sett, at least one of which, South Lode, was a branch of Main Lode. Site (A) admirably represents the generally mineralogy of Main Lode and has remarkably survived later reprocessing (see below) - the tip yields common chalcopyrite, with associated pyrite and arsenopyrite, often in a quartz or quartz- chlorite veinstone. Localised blue and green crusts represent the development of secondary copper minerals within the spoil, and not the original mineralogy of the lode, however. Area (B) in contrast, is dominated by large rock fragments, typically with brownish weathered surfaces, and yielding common samples of arsenopyrite-rich veinstone - thereby apparently providing a contrasting mineralisation phase. Additional minerals recorded in Area (B) include quartz, massive fluorite, siderite, chalcopyrite and scorodite. Mineralogical analysis of samples from boreholes in the Wheal Anna Maria Sett, probably also from within area (B) at 4276733 - and not therefore on Main Lode - identified arsenopyrite, chalcopyrite, pyrite, galena and sphalerite in quartz-chlorite gangue, with a vuggy centre to the lode containing quartz, fluorite, dolomite, siderite and rare childrenite. Matildite and bravoite also are recorded from ‘Devon Great Consols’ and brochantite and ‘iron sulphate’ have been noted forming in dump material. Notably, some underground workings have survived and are being surveyed by specialist groups. The country rock belongs to the Tavy Formation (Upper Devonian), and lies within the metamorphic aureole of granite mass.

Reasons for registration as a County Geological Site:

Devon Great Consols was at one time the world's largest copper producer and was established through the amalgamation of several smaller mines - Wheal Maria, Wheal Fanny, Wheal Mary Anne, Wheal Josiah and Wheal Emma, all exploiting the exceedingly rich deposits of ‘Main Lode’. Later production included arsenic, the ore coming from the margins of Main Lode, and ultimately also from earlier mine dumps. As the result of the latter activities, large volumes of the waste tips were reprocessed, thus destroying evidence of the mineralisation present. At Wheal Anna Maria, however, a significant quantity of mineralised material survives. In particular, dumps around Engine Shaft (Area (A)) show abundant evidence of chalcopyrite, the primary copper ore, and are possibly therefore the only significant surviving, unprocessed surface record of the mineralogy of Main Lode. In addition Area (B) contains abundant arsenopyrite, representing the mine’s other main product (although they probably also include material from other lodes worked on the mine). Crucially, the small Devon Great Consols SSSI, represents workings on another lode, New South Lode (in the Wheal Josiah sett), and not Main Lode - it is not therefore representative of the most famous copper-bearing deposit in the region.

Site sensitivity: Area (A) is sensitive to unregulated mineral collecting as the dump is very limited in extent. ln addition, disturbance of ‘in-situ’ dumps should be avoided, and only permitted for bone-fide scientific studies, to maintain the natural weathering processes that are leading to the formation of new mineral types. Area (B), however, is more extensive and therefore less sensitive. The greatest historical threat, however, has been removal for reprocessing or for use as fill or surfacing material.

Safety: The site contains hazards typical of disused mine sites, including a major shaft in area (A) and a potentially contaminated arsenic works in area (B). Appropriate pre-visit risk-assessment and caution during visits are therefore essential.

Interest groups: Schools. Years 5-11: Years 12-16: Years 17-18. University. Undergraduate - Research Professional geologists - Amateur geologists - General public.

Access and Parking: All areas lie within the Woodlands Estate and permission is required for access. Area (B), in particular, is restricted, although area (A) is adjacent to tracks used for local residential access.

Date of assessment (V = visited) : V Aug 2004

Site owner :

References: BULL. B.W. 1982. Geology and Mineralogy of an area around Tavistock, SW England. Unpublished PhD thesis, University of Exeter, pp.49, 120-121, 171, 178; DINES, H.G. 1956. The metalliterous mining region of South-West England —Volume 2, Memoirs of the Geological Sun/ey of Great Britain. England and Wales. HMSO. London, pp.657-658; STEWART, R.J. (Ed) 2003. Devon Great Consols: A collection of contemporary articles and reports . Tamar Mining Press. , 60pp; SPARROW, C. and WILKINS, J. 2001. Devon Great Consols & Bedford United — Mineralogical Report . A Report to County Council. Cornwall Environmental Consultants Ltd., CEC 1447 (11pp + Appendices).