On copper ore deposit of Kagenosawa mine, Iburi province, Hokkaido. (I)

Abstract

The Kaaenosawa mine is located about 5km northwest of Horobetsu station, Iburi province, Hokkido. The hollocrystalline rock, intruded into the Neogene formations, is found in the neighbourhood of this mine. Especially, the relationship between this plutonic rock and metallic ore deposit, which has been discussed, is clear at this mine. The geological complex, developed in the adjacent area of this mine, belong to the Neogene Tertiary, various kindes of volcanic, and Quarternary sediments. The Neogene Tertiary consists of the lower green tuff, quartz-diorite intrusived into the former rock (Fg. 3 showing its intruded relation), conglomerate and, upper green tuff in ascending order. The conglomerate is composed chiefy of chert and slate derived from the so-called Palaeozoic, and subordinately of diorite and green tuff derived from the Tertiary member. Its traced distance is very short, the thickness being about 60cm. Covering the Tertiary formations descrived above, the Quarternary sediments and volcanic, are widely developed through the elevated plateau of this district. They are mainly composed of the Noboribetsu mud lava and pumice bed in ascending order. The ore deposits are embraced in the lowei green tuff, diorite and upper green tuff. Especially, the deposits which are now under mining are a vein-like type in the fault zone striking in N 80°E and in the brecciated none of diorite striking N 10°E. On the other hand, the network type deposits, which had produced. the higher trade ore of Au, Ag in the earlier development of these mine, are embraced in the clayed zone of Lower green tuff. Furthermore, the deposits showing the same mineral assemblage as in diorite, also exsist in the upper green tuff, covering the dicrite and the lower green tuff. It is clear, accordingly, that the mineralization began after the deposition of the upper green tuff, and then the ore depcsiton here was. ultimately unrelated to the intrusion of quartz diorite. As covered by the Quarternary rocks, the accurate age of mineralization is unclear, but it is doubtlessly younger than the later Kunnui stage.