Cobalt mineralisation in Cornwall - A new discovery at Porthtowan

Although cobalt mineralisation has been noted in Cornwall and Devon in the mining literature, there are limited details of its production and paragenesis; detailed mineral studies of cobalt are almost non-existent. This paper describes in detail previously unrecorded cobalt mineralisation discovered at Porthtowan, Cornwall, in the vicinity of old workings which are part of the Wheal Lushington group of mines, immediately west of the village. A small number of massive sulphide/gangue samples (taken from a larger sample suite) were chosen to be as representative as possible. Analysis was carried out using a QEMSCAN® automated mineral SEM-EDS system, which found that samples contained up to 50% cobaltite, along with chalcopyrite, bornite, galena, sphalerite, acanthite, erythrite, matildite, chlorargyite and other primary and secondary mineral species. This assemblage is typical of a sub-type of crosscourse mineralisation, with secondary species a result of significant weathering and supergene alteration, complicated by seawater infiltration due to the coastal location. While the number of samples is limited, the detail of the mineralogical assemblage is significant, as it is the first time such an assemblage has been subjected to this level of scientific scrutiny in Cornwall.