Haytor Iron Mine [SX 773 772] is situated within the metamorphic aureole of the Dartmoor Granite, with the contact lying some 500m to the east. The ores are hosted conformably in metapelite probably of Lower Carboniferous age. The ore consists of finely intergrown magnetite and green-brown amphibole (ferro-edenite) which may be massive, or show banding marked by varying proportions of the two minerals. Coarse crystals of magnetite are present on some joint surfaces and the amphibole forms coarse fibro-radiate aggregates in places.
The deposit also hosts coarse garnet (andradite), axinite, siderite, calcite and apatite. Additionally, pseudomorphs of chalcedony after datolite, originally termed 'Haytorite', have been recorded. Traces of sulphides are present in the ore beds and include arsenopyrite, pyrite, sphalerite and chalcopyrite (tarnished crystals of chalcopyrite mantled by magnetite are visible in the thin section).
The paragenesis of this deposit is typical of infiltration exoskarns elsewhere in the region, with an early thermal metamorphic phase of silicate growth succeeded by the development of ore minerals from high temperature hydrothermal fluids.
Many thanks to Richard Scrivener for providing this sample.
The United Kingdom Virtual Microscope (UKVM) collection consists of igneous, sedimentary and metamorphic rocks from around the UK.
It is intended as a teaching resource, helping to tell the story of the common rock types and how they form, and reflecting the history of the UK at the margins of the continent of Europe. The collection is a series of teaching sets, for example igneous rocks from the North Atlantic Igneous province, and SW England; high temperature metamorphic rocks from Scotland and low temperature metamorphic rocks from Wales; and sedimentary rocks including English limestones and sandstones.