Texture of the Ore Minerals from the Shimokawa Mine

Abstract

Ores of the Shimokawa mine are divided into two types, banded and massive sulfide ores; the former predominate in Northern orebody, while the latter in Central and Hangingwall orebody, though in some cases both types coexist in the same orebody with a sharp or gradual boundary. Banded ore consists of sulfide bands, several millimeters wide, in parallel alternation with bands of quartz-chloritic tu ffaceous material. Massive sulfide ore is compact, fine-textured and usually homogeneous, but where it is highly enriched with chalcopyrite fine banding of pyrrhotite is observed.
The ore is composed mainly of pyrite, chalcopyrite and pyrrhotite. Sphalerite also occurs in lesser amount which increases locally. Minor amounts of cubanite, valeriite cobalt pentlandite and magnetite are observed under the microscope.
Outstanding feature of the ore is the texture or crystallized gel as shown by colloform texture. Neither katagenic association of minerals from early to later mineralization stages, nor replacement texture of early association by later is observed in thorough underground and microscopic studies.
From these ore textures as well as from other geological facts, the genesis of the ore is concluded as sedimentary-exhalative.