The survey on wall rocks alteration has been less accepted for the technology of the ore prospecting in Japan, because of its rather scanty knowledge. Recent rapid advancements on clay mineralogy particularly, however, made possible to get some important informations from it concerned to fixing of maximum area for prospecting, structural characteristics of deposits, as well as to ore forming environments. Late hydrothermal alterations superposed on skarn ore deposits, and Mg-enrichment along bedded pyritic deposits are very common. Development of montmorillonite, chlorite, sericite, kaolin minerals, silica minerals, allunite, pyrophyllite, diaspore, corundum and andalusite are also characteristic respectively to the main groups of the ore deposits of epithermal origin in Japan.
