International Geologiical Congress - Oslo 2008

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MRB-01 General contributions to industrial mineral deposits

 

Geology and exploration of shallow potash reserves

 

Reza Farhadi, Geological survey of Iran (Islamic Republic of Iran)
 

 

Iran is exceptionally rich in evaporate sediments which are classified to four groups according to the age and geological sitting: Hormuz salt in Zagros Fold-Thrust Belt, Miocene evaporate basins in the south of Alborz Belt, Ravar Basin in the east of Iran and recent basins in central Iran (playa).

The Zagros fold-thrust belt extends from East Anatolian fault in the northwest to Oman line in the southeast. The belt structurally is a prism of stacked thrust sheets composed of uppermost Neoproterozoic and Phanerozoic strata. Uppermost Neoproterozoic and Lower Cambrian part of these strata (Hormuz mega sequence) have deposited in an extensional pull-apart basin (Prototethys). Pohl and Khurgoo salt domes are fountain type extrusions of Cambrian Hormuz salt; large potash outcrops on the salt glaciers are iron rich type (erythrosiderite, rinneite, sylvite, halite) and also high grade yellow potash (sylvite, halite) which highly deformed by intrusion, extrusion and gravity spreading of salt. A rotary drilling machine was lifted by helicopter on Pohl salt glacier and according to the subsurface data the reserve of potash only for two small locations is more than two million tons.

Alborz belt extends for about 1000 kilometers from Aras Fault (west of the South Caspian Depression) to the south of Kopehdagh in north of Iran. Miocene sediments and evaporate deposits which called Upper Red Formation in foreland basins in the south of Alborz nappes is the host of numerous exposed or hidden salt domes and salt structures with magnesium rich potash reserves. Iljaq is a swollen structure which its topography in rims is higher than the center, dip of the strata near the rim is almost 90 degrees and a vertical gypsum layer around the structure in the top of ring shows the border of salt. According to the Bouguer anomalies the center bowel is lighter than the circular marginal rim. The origin of pure secondary picromerite and halite in the southern rim of structure is the primary potash beds or lenses, therefore an intersecting radial core drilling plan was designed and done. Under ground data provided a 3-D view of Iljaq salt dome; a conical structure is built by intrusion of salt into the crest of a double plunge inclined anticline. The potash reserve is more than 2 million tons and the average grade of kainite is 51.1%.

Geology of Ravar basin (Jurassic) show similarities with Zechstein basin in Germany then preliminary exploration is recommended. Potash reserves in recent basins such as Great Kavir playa is known in the form of brines, the average grade of potassium is 4 g/lit.

 

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