埼玉県吉見丘陵の凝灰質岩表面における胆礬の形成

抄録

Bluish precipitates in association with white precipitates are found on the surface of cave wall at the Yoshimi Hills, Saitama Prefecture, Japan. In the inner part of cave, Neogene Tertiary tuffaceous rocks are exposed without vegetation because the sunlight does not reach. These blue and white precipitates are identified as chalcanthite and gypsum, respectively, using the X-ray powder diffraction. An SEM-EDS analysis shows that the chalcanthites are aggregates of euhedral crystals with nearly pure composition. Thermodynamic calculations indicate that chalcanthite precipitates under oxic copper- and sulfate-rich acidic environment. Taking the topographical and geological settings into consideration, these precipitates are regarded as evaporitic products of copper- and sulfate-rich groundwater which would be formed by the reaction of original vein-type chalcopyrite ore and permeated oxic groundwater of rainwater origin in near-surface shallow groundwater flow system.