Abstract
Aluminous clay minerals such as pyrophyllite, dickite, sudoite, tosudite, rectorite, and sericite were found in a drillhole which was sunk near the Kamikita mine, Aomori Prefecture, Japan. These minerals display a zonal arrangement as follows: pyrophyllite (±diaspore±dickite)→sudoite (±sericite)→tosudite (±sudoite±rectorite)→rectorite (±tosudite±sudoite) from the central part of alteration envelopes to the marginal part in the Miocene Wadagawa formation.
The structure formula of sudoite was calculated as (Mg1.76Al2.88Fe2+0.16Mn0.01Ti0.04Na0.06K0.01Ca0.01) 4.93 (Si3.26Al0.74) O10 (OH) 8from electron microprobe analysis, though it contains a small amount of expandable layer. The material has a IIb polytype and 1.507 Å of d (060) value. Tosudite intergrew intimately with sudoite. Two kinds of interstratified mica/smectites (M/S) containing 30 and 40% of expandable layers (%Sm) were identified; they showed large intergrain chemical variation. The interlayer cation composition of rectorite is variable with respect to different depths of a drillhole and to different drillholes. K-rectorite occurs interrelatedly with M/S having 30 and 40%Sm, pyrophyllite, sericite, and sudoite. The spatial and chemical relations of these minerals indicated that the reaction series, pyrophyllite→M/S (30-40%Sm) +pyrophyllite→K-rectorite±sericite, proceeded from pyrophyllite zone to the out-ward as the result of increase in activities of Na, Ca, and K in hydrothermal solution. At the same time, elemental distribution reaction took place with the formation of the above minerals; Fe, Mg, and K were selectively accomodated in sericite and Na, Ca, and Al were in rectorite.
