PETROLOGY AND CHEMISTRY OF SOME EXOTIC ROCK FRAGMENTS FROM JABAL SANAM, BASRAH, IRAQ

S. Al-Bassam, Khaldoun

	PETROLOGY AND CHEMISTRY OF SOME EXOTIC ROCK FRAGMENTS FROM JABAL SANAM, BASRAH, IRAQ
Iraqi Bulletin of Geology and Mining
Article 1, Volume 7, Issue 1, 2011, Pages 39-53
Author
Khaldoun S. Al-Bassam
Abstract
Petrologic and chemical analyses of 16 exotic rock samples collected from Sanam salt plug in southern Iraq showed igneous and sedimentary rocks of various types and origins. Highly magnesian igneous rock samples with forsterite composition of (Fo 90 – 92) mole% are the only igneous rock type found in this study. They are highly serpentinized and the alteration minerals are antigorite and talc. This is a mantle-derived subvolcanic rock, fragmented and brought to surface with the rising salt diapir. Dark gray dolomite with possible stromatolitic structures is one of the common rock types at the Sanam plug. It is fine crystalline and partly silicified. It was probably precipitated in reducing environment on the flanks of the salt basin. Some pure recrystallized calcitic limestones were also recognized and seem to be of chemogenic origin; as parts of vein fillings. Shale, with illite, as dominant clay mineral, and quartz with minor kaolinite and montmorillonite may represent ancient fluvial deposits. One sample was identified as silicified ferruginous mudstone with peculiar mineral composition of orthoclase, quartz, illite, hematite, goethite, gypsum and jarosite. The origin of this rock may be volcanic and include initial mud rich in feldspar, which was indurated and altered by microbial Fe precipitation and enrichment via colloidal state, gypsum cement was introduced later and silicification followed.

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