Ore forming processes

THE MINERAL DEPOSITS STUDIES GROUP held its third residential conference at Sheffield University from 10 to 14 December 1977. Following two days9 field excursions examining mineralization in northern Derbyshire twenty papers were presented by Group members. All but two were dominantly concerned with ore genesis and the majority of these dealt with deposits in the British Isles, four of them with Irish mineralization. A. M. Boast presented textural and isotopic evidence showing that much of the material, particularly the sulphur, of the Tynagh deposit was of synsedimentary origin. The weight of evidence for this and similar Irish ores undoubtedly suggests a very early time of deposition and M. J. Russell favoured a synsedimentary origin for all the larger Irish base metal deposits in the Lower Carboniferous. He discussed a mechanism whereby circulating sea water could have leached the metals from buried Lower Palaeozoic rocks. J. P. N. Badham put forward a fresh interpretation of the stratigraphy of the mineralized zones at Avoca and suggested that the stockwork feeder zone, a further possible orebody, has yet to be found. P. McArdle9s work on Donegal base metal mineralization also suggests a revision of exploration philosophy in that he demonstrated that deposits in the Dalradian were originally of stratiform type. Rock alteration processes in two very different environments and their relationship to mineralization were discussed by five workers. D. H. M. Alderton presented an excellent documentation of wall rock alteration assemblages developed in the Cornish granites. He made considerable use of isotopic and