Prospecting for phosphate deposits in the southeastern portion of the Kopeh Daq-Hezarmasjed structural zone
The study area is located between 59 25' to 61 20' eastern longitudes and 36 15' to 37 15' northern latitudes. The Kopeh Daq structural zone that is NW-trending is a tectonically active zone with Jurassic to Paleocene-Eocene rock units. Kashafrud, Chamanbid, Mozduran, Shurijeh, Tirgan, Sarcheshmeh, Sanganeh, Atamir, Abderaz, Abtalkh, Neyzar, Kalat, Pesteliq, Chehelkaman and Khangiran are the main formations of the zone. All of these formations have conformable contact with each other. Toward northwest, there is a series of anticlines and synclines that are partly eroded. Main lithology includes shale, limestone, marl, sandstone, and little conglomerate. Because of geological setting, this zone is not permissible for hydrothermal or metamorphic ore deposits. Expected deposits in the zone include oil, gas, and phosphate.
After gathering the primary information, several formations were selected for exploration project that include upper Kashafrud formation, Chamanbid, Sarcheshmeh, Sanganeh, Khangiran in addition to Atamir and Chehelkaman that were previously suggested for phosphate exploration by BRGM. At first, all formations were studied carefully. By progress, the Atamir and Khangiran formations that showed more potential were selected for detailed study. First time, phosphate layers are reported from Khangiran formation as interlayer with sandstone and a thin layer within a conglomerate. Our study shows that phosphate grade in the mentioned formations ranges between 0.11% in Beyzar, 0.57% in Chehelkaman, 1% in Atamir, and 2.5% in Khangiran. A sample at south of Sarakhs contained 6.3% phosphate. The phosphate in the Khangiran and Atamir formations has occurred as broken apatite minerals, honey-colored to green. In the base of Khangrian formation, the apatite is mixed with quartz. The evidence shows that most of phosphate in this formation was transported from other places and plate-shaped and coprolite phosphate minerals are rare.