Genesis of the Lower Ore Bodies, Kaminosawa Ore Deposit, Kamikita Mine, Aomori Prefecture

Abstract

The Kamikita mine is located in the central part of the Aomori Prefecture, about 36 km southwest of Aomori City. Ore deposits of the mine are well known as one of the representative ore deposits of "Kuroko" type. The mining area occupies a northern part of the Tohoku Green Tuff region where no exposure of the pre-Tertiary basements has been found. The area is composed of the Tsubokawa, the Okunosawa and the Kotsubogawa formations of the Miocene in ascending order, and Quaternary formations of the Old Hakkoda volcanics which unconformably cover the Miocene formations. The Okunosawa formation consists mainly of rhyolite domes and lavas with related tuff breccias. Rhyolitic volcanic activity of the Okunosawa formation is divided into two stages ; older and younger. Five ore deposits have been found only in the Okunosawa formation.
The Daisan Shitaban Hi ore bodies which belong to the lower ore body group of the Kaminosawa ore deposits are divided into two groups based on their modes of occurrences and geneses. The first group consists of the bedded compact sphalerite-rich ore body (so-called "Kuroko" ore body), the bedded compact chalcopyrite-rich ore body (so-called "Ohko" ore body), the massive pyrite ore body (so-called "Ryukako" ore body), and the stockwork ore body in descending order. Arrangement of these bodies show vertical zoning found in the "Kuroko" deposits. These are considered to be primary in origin. The second group is composed of the bedded fragmens bearing ore bodies with various. ores and lithic fragments. Judging from the lateral and vertical size grading, sole marking and orientated arrangement of elliptical boulders found in the ore bodies, and their texture and mineralogy, it is concluded that the second group was formed by the sedimentary deposition of the ores of the first group due to the submarine sliding or the mud flow caused by the volcanic explosion in the later stage of the Okunosawa volcanism.