Abstract
The Misano and Utozaka uranium deposits in the eastern part of the Kani Basin, Gifu, occur within Miocene non-marine sediments which unconformably overlie Paleozoic-Mesozoic sediments and Cretaceous-Paleogene granites. These deposits are classified as sandstone-type deposits structually controlled by palaeo-channel structures formed on the pre-Miocene basement rocks.
The host rock is the Kani Lignite-bearing Formation which is the lowermost sequence of the Kani Group. The age of the formation is estimated to be 20-19 Ma on the basis of fission-track dating and is correlated to that of the Toki Lignite-bearing Formation which hosts the Tsukiyoshi uranium deposits in the Toki Basin. The mineralized host sediments consist of conglomerates, arkosic sandstones, tuffaceous sandstones and carbonaceous sandstones. Abundant organic material is associated with the mineralization in many cases and calcite cementation and/or veinlets are often observed as well. Pyrite is also an important mineral coexisting with the mineralization. Although no primary uranium minerals are identified to date, uramium is considered to be present as the uranous form.
The mineralization is strongly controlled by a fault structure within the basement granites as well as channel structures formed on the basement rocks especially on the granites. The enriched ore zone of the Misano deposit is distributed within the basal part of the Kani Lignite-bearing Formation above the basement fault structure and in the polaeo-channel downward from the fault structure. The basement granites is also mineralized along the fault structure.
The evidence indicates that groundwater leached uranium from the basement granites which then migrated along the fault structure into the host sediments to form the deposit.
