Petrography and Geochemistry of Dolerite Exotic Rocks at Sanam Salt Dome, Southern Iraq

Four samples of dolerite rocks are selected to conduct their petrography and geochemical properties. Dolerite rocks exist as large blocks and fragments exposed at the southeastern part of Sanam salt dome, Basrah, Iraq. The petrography reveals that their characteristic ophitic texture is dominant. Anorthite and augite are the main minerals of dolerite, whereas, hornblende, quartz, chlorite, sericite and epidote are secondary minerals formed as a result of chloritization, sericitization, and epidotization, due to low grade hydrothermal alteration. The presence of hematite in some samples reflects the oxidization condition and high oxygen activity during the late alteration processes. The major geochemical analysis shows that the studied dolerite rocks are of saturated and over saturated basalt-type, where the composition ranges from basaltic andesite to basaltic trachyandesite falling in both alkaline and tholeiitic basalt fields. It is worth noting that the high percentage of L.O.I, as well as, relatively high silica content indicate that the dolerite rocks have been affected by low-grade hydrothermal alteration. This is associated by metasomatism followed by weathering processes. The pattern of REE in the studied dolerite rocks combined with other chemical analyses suggests that the present dolerite rocks are of within plate tholeiites.