Studies on the magnetic properties of the Shinyama ore body of Kamaishi iron and copper ore deposits, Iwate Prefecture (I)

Abstract

Recently rock magnetism is contributing to solve many geological problems. There are several types of remanent magnetization. In case of igneous rocks, magnetism arises from thermo-remanent magnetization. When the ferromagnetic mineral grows or changes chemically in the magnetic field under its curie point, it gets chemical or crystalline magnetization. In this paper, application of rock magnetism arising from chemical or crystalline remanent magnetization to economic geology was attempted. In order to achieve this purpose, the Shinyama ore body of Kamaishi iron and copper ore deposits was selected, because it is a typical contact metasomatic ore deposit and is a well exploited one. The Shinyama ore body consists of two iron ore bodies that contain magnetite and several copper ore bodies that contain pyrrhotite. Oriented samples were collected from many localities of the ore deposits systimatically. The direction and intensity of remanent magnetization, the magnetic susceptibility and other magnetic properties of ores were measured. The direction of remanent magnetization of each ore body is as follows. the iron ore…………………………Inclination 90°Down The 2nd copper ore body (closed to the iron ore body)……………{Declination 12°E INclination 48°Down The 4th copper ore body (200m distant from the iron ore body)…{Declination 333°E Inclination 53°Down From the view point of mechanism of magnetization, it is sure that the iron ore body gets the remanent magnetization which, roughly speaking, agrees with the direction of elongation of the ore body; and the 2nd copper ore body gets the remanent magnetization in the direction compounding geomagnetic field and magnetic flux of the iron ore body. By means of remanent magnetization together with other magnetic properties of ores, the direction of elongation of an ore body and the order of mineralization can be predicated.