MINERALOGY AND GEOCHEMISTRY OF GYPSIFEROUS SOIL EAST RAZAZA LAKE - CENTRAL Iraq

Abstract

This work aims investigating the gypsiferous soils texture, mineralogy and to interpret their geotechnical characteristics in east Razazza Lake area –Central Iraq. A total of twelve (12) soil samples were taken of gypsiferous soils distributed on three (3) sites. The results of grain-size analysis show that sand size grains are dominant with variable percentages of clay fraction and the silt fraction. The soil profile in site 1 reflect that thesilty clayey sandfacies is existed within the upper 1.9 m., whereas theclayey silty sandis within thelower 2 m. Concerning the soil profiles in site 2 and 3 is representing clayey silty sand. The soils within the three sites are fine-grained, yellowish light brown, moderately to highly gypsum, ranging from friable to hard gypsiferous soil. The microscopic examination are indicating that gypsum content between 12.0 – 29.2 %; clay comprise 12.4 – 23.3 %, while calcite and dolomite are from 8.8-21.2 %. Quartz and Chert grains are ranging from 10.1-28.0 %. Feldspar is ranging between 6.0-15.0 %, while rock fragments is ranging from 9.2 – 19.0%, with heavy minerals ranging from 0.7-1.4%. The X-ray diffraction analysis showsgypsum, calcite, quartz, feldsparand dolomite as light minerals withsmectite, illite, chlorite, palygorskite and kaolinite as clay minerals. The geotechnical properties results reflect that six samples (1a, 1c, 2a, 2c, 2d, 3b) are classified as gypsiferous soil with less than 25% gypsum content and with less values of uniformity coefficient, coefficient of curvature, initial void ratio, collapse potential %, compression strength, plasticity index % and cohesion, while the other six samples (1b,1d,2b,2e,3a,3c) are classified as highly gypsiferous soil with more than 25% gypsum content and with relatively higher values of coefficient of curvature, initial void ratio, uniformity coefficient, collapse potential %, compression strength, plasticity index % and cohesion.