زمین‌شناسی و ژئوشیمی نهشته‌های فسفات در منطقه لردگان، جنوب استان چهارمحال و بختیاری

Abstract
Lordegan phosphate deposites are located in the Amirabad, Shirmardi and Sateh, in the south of Chaharmahal and Bakhtiari province, and in the folded Zagros zone. These areas are include marl and limestone marl pabdeh formations, limestone Kahzdoms formation and shale marl, and gluconite sandstone gurpi formation. Mineralogy studies show, ther are calcite, fluoropatite, dolomite, quartz, muscovite, illite along with gluconite as main minerals. Phosphote was formed often as autogenetic and replacmet as oolite, pelitic, fossil pezodomorhphic and cement.The normalize pattern of rare earth elements with PAAS pattern indicates to poor differentiation of LREE compared to HREE and negative anomalies of Ce and Eu. The Ce anegetive anomaly indicated to reduction condition during phosphate diagenesis.The combination of the field study, petrographic and geochemical data indicates to formed phosphate by the interference of diagenesis, adsorption, degradation of organic matter, oxidation and reduction conditions and the performance of pore water in these area.

Introduction
Phosphorus, a chemical element with symbol P and atomic number 15, is very necessary for life. This element forms the major part of the DNA molecule, which is necessary for energy transfer in cells (Föllmi, 2011, Filippelli, 1996). In the phosphorus industry, it is one of the main materials for the preparation and production of fertilizers, feed additives, water purification, and metals. It is very useful in the preparation and production of detergents and toothpastes, the processing of meat products, cheeses, beverages in the food industry and the production of batteries for electric vehicles. Considering the importance of this element in various industries and its shortages with population growth, the production of this element with The use of recycling from wastewater and agricultural runoff has been suggested (Cordell et al, 2009; Cordell and White, 2011). This element is obtained by extracting minerals containing phosphate ions such as apatites. The main sources of phosphate include phosphate from marine sediments, deposits They are igneous, metamorphic, biological sources and weathering products (Guimaraes and Araujo, 2005). Rocks that contain amounts higher than 12% of phosphate are economically valuable and affordable (Sengul et al., 2006). The most important sources Phosphates in the world are made up of sedimentary deposits. These sediments include 1: Chemical sediments (corresponding to the coastal to shallow environment) which are in the form of olitic and pelitic and are seen in the shale and marl series (such as the concentration of phosphates in the Soltanieh Formation and the phosphate deposits of the Tertiary period of the Zagros, which extends to the north of Iraq) or The chemical sediments of the platform which include alternating layers of thin-layered chert, black shale, thin-layered dolomite with phosphate formations. 2: Biogenic sediments include fragments of bones and teeth of fishes and phosphatic shells along with olitic and pelitic chemical sediments (such as Soltanieh Formation in Delir region). 3: Clastic sediments that are observed from the destruction of previous phosphate formations along with mineralogical erosion and the size and progress of the sea. The formation environment of phosphates is often alkaline and acidic environment leads to their dissolution. For the first time, the theory of the geochemical cycle of phosphorus from the main sources, i.e. igneous rocks, to stabilization in oceanic sediments was introduced by Blackwelder in 1916. Kazakov 1937 considers the cause of phosphate sedimentation in such a way that during the Cenozoic, phosphate-bearing sediments were formed in warm areas and geographical latitudes of 40 degrees north and south and on the western coasts of the continents. These phosphate-bearing facies are accompanied by marine limestone, sandstone, and glauconite-carbon shale. The amount of P2O5 in phosphate facies increases with increasing depth. Phosphates are often seen with the advance of the sea and are formed in connection with the continental plateau and the continental slope in a large basin connected to the ocean. The amount of P2O5 is minimum in the photosynthesis area and maximum at a depth of 500 meters. He believes that apatite is formed due to the presence of a saline basin with higher pH and temperature than sea water and due to the presence of small amounts of destructive substances. In this basin, there should be sufficient amounts of phosphorus and water should be in circulation so that the environment is almost aerobic. According to him, the phenomenon of upflows of phosphorus-rich waters from deep to shallow parts leads to an increase in pH and a decrease in CO2, and phosphorus enters the sedimentary basin in the form of a solution, combined with organic substances, absorbed by aluminum hydroxide, iron, and detrital minerals. It will be The data shows that phosphorus is saturated in oceanic waters in a non-uniform manner, and usually cold waters have higher amounts of phosphorus. According to the classification done by (Riggs, 1979), phosphates include orthochemical, allochemical, olitic, pliitic and intraclastic.
The studied areas are located in the south of Chaharmahal and Bakhtiari province and in the folded Zagros structural zone. These areas are in the southern part (near the villages of Shirmardi, Amirabad) in the geological sheet of 1.100000 Dana (Sedaghat et al., 1378) and in the central part of the sheet 1.100000 Cheng (near the village of Sateh) (Bakhshkermani et al., 1374). The stratigraphic units of the region extend with a northwest-southeast trend in the region, which sometimes folds and faults can be seen in the stratigraphic units of the region. Also, simple, regular and low-span anticlis and navdis buildings are spread in the northwest-southeast direction

Methodology
Following geological and field studies, 3 sections were surveyed in the areas near the villages of Shirmardi, Sateh and Amirabad and 46 samples were taken from the formations of Kazhdomi, Gurpi and Pabdeh. Then 30 thin sections were prepared and studied. There were 10 samples selected to ICp MS, AES analysis by Tehran's Binaloud Company. Finally, by combining field, microscopic and geochemical data, an analysis was made regarding the investigation of phosphate in the studied areas and its genesis.

Conclusion
Field studies, microscopy and chemical analysis of Gurpi, Pabdeh and Kazhdami formations in the south of Lordegan in Chaharmahal and Bakhtiari provinces indicate the presence of phosphate horizons. These horizons are outcropped in the northern side of Taghdis Zard Mountain, Bakhtiari border of Pabdeh-Asmari Formation. Petrographic data indicating a simple mineralogical composition is seen as a collection of calcite, quartz, clay minerals, glauconite, phosphate with paxton to wackestone texture. The formation of phosphate is autogenic and replacement, that is, the creation of a suitable environment and the settling of phosphate directly due to regeneration conditions and suitable oxidants, as well as the phosphatization of primary carbonate minerals due to replacement. The variety of macrofossils indicates the different facies of shallow to deep parts. High-energy environment, with oxidizing-reduction boundary condition, saturated with phosphate and full of light are among the characteristics of phosphate formation environments in the region. The extent of outcrops of phosphate formations in the region, the lack of mineralogical diversity, the results of chemical analysis and the values of up to 7.8% p2O5 in the studied areas point to the importance of these horizons for accurate economic exploration studies. The negative anomaly of Eu and Ce in the studied samples confirms the presence of an oxygen-free sedimentary environment or a diagenesis (stimulating) environment for the formation of phosphates..