HYDROGEOCHEMISTRY AND GEOMICROBIOLOGY OF DARZILA SPRING IN SANGAW, SULAIMANIYAH, NE IRAQ

A. Al-Manmi, Diary; A. Khanaqa, Polla

	HYDROGEOCHEMISTRY AND GEOMICROBIOLOGY OF DARZILA SPRING IN SANGAW, SULAIMANIYAH, NE IRAQ
Iraqi Bulletin of Geology and Mining
Article 1, Volume 7, Issue 3, 2011, Pages 63-79
Authors
Diary A. Al-Manmi; Polla A. Khanaqa
Abstract
Darzila is a hypogenic cave located in Sangaw near Sulaimaniyah; Northeast of Iraq, offers a remarkable opportunity to observe microbial interactions within environment, which is related to the karst aquifers. Both water and atmosphere in the cave are rich in hydrogen sulphide. The predominant cation in the cave's water sample is Ca2+ and anion is SO42. The chemical speciation shows that samples 1 and 3 are supersaturated with gypsum. The high ionic ratio values of Ca/ Mg and Ca/ SO4 indicates further dissolution of anhydrite and calcite. While the high ratio value of Na/ Cl, in sample 4 is attributed to ionic exchange inside the cave. Redox reactions in the cave appear to be microbially mediated. Bacteriological analysis of water samples shows that there are three Thiobacilli species, a genus that often obtains its energy from the oxidation of sulphur compounds. Oxidation of hydrogen sulphide to sulphuric acid, and hence the cave enlargement, is probably enhanced by these bacteria. Two cave-enlargement processes were identified: i) Sulphuric acid derived from oxidation of the hydrogen sulphide converts subaerial limestone surfaces to gypsum. The gypsum falls into the cave stream and dissolves. ii) Strongly acidic droplets form on the gypsum and on microbial filaments, dissolving the limestone, where they drip onto the cave floors. The possible source of organic matter is from deep oil-rich reservoirs (or bitumen occurrences within the limestone), the presence of organic matter at the bank of Awa Spi stream support this idea.

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