Abstract
Clay minerals are found associated with the Kuroko ores at the Shakanai mine as alteration products of tuffaceous sediments formed by submarine volcanic activities. Core samples from the Shakanai No.11 deposit contain illite and chlorite. The present investigation was undertaken to reveal the variation of the nature on illite and chlorite with depth and lithology of the Shakanai Formation at the Shakanai No.11 deposit and following results were obtained.
(1) On the basis of X-ray powder diffraction, infra-red analysis and electron micrograph, illite can be grouped into three types A, B, C in the core.
Type A is found with chlorite and has properties of a 1M polymorph. It shows characteristic elongated-tabular habit like needle. Its particle size measured by the Jones' method is 170-200A.
Type B is appeared in and/or near the Kuroko ore body and has properties of a 2M polymorph. Its morphorogy is very thin plate habit from irregular to hexagonal form and their aggregated parts are ambiguous under electron micrograph. This type clearly contains a small amount of expandable layers.
Type C is associated with calcite in the Kuroko ore body and shows a very strong (001) reflection in comparison to a (002) one and it is 1M polymorph. It shows very fine (0.1-0.5 micron) regular hexagonal thin plate.
(2) Fe content in chlorite gradually decreases in the structure with depth of the core, but Al value of the replacement of Si is not changed in the core. Therefore, the chlorite is changed from pycnochlorite to clinochlorite with depth of the core. Fe in chlorite is occupied selectively its structural position in the silicate layer rather than in the brucite layer. But chlorite in the tuff of the bottom of the core contained more Fe in the brucite layer than in the silicate layer.
