عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The Dalir phosphate deposit is located in ~57 km of southwest of Chalous city, Mazandaran Province.This deposit is part of the Marand-Damavand phosphate belt and has developed as a stratiform horizon within upper shale member of Soltanieh Formation (Neoproterozoic- Lower Cambrian). Mineralogical studies show that phosphatization process in the Dalir area was accompanied by development of various minerals such as dolomite, fluor-apatite, calcite, quartz, pyrite, illite and muscovite. Distribution patterns of major, minor and trace elements normalized to PAAS display depletion of elements such as Si, Fe, Al, K, Na, Ti, Th, Zr, Co, Cu, Ni, and Nb, and enrichment of elements such as Ca, P, Sr, and Y during phosphatization. Depletion of REEs ratio to average of world phosphorites indicates that this deposit was formed in a closed environment. Geochemical indices such as ratios of V/V+Ni (0.59-0.73), Th/U (0.10-0.89), Ce/Ce* (0.22-0.55), Mn* (–0.75 to –1.87) and Y/Ho (42.63-57.84) suggest that deposit was developed in an anoxic-suboxic condition. Distribution pattern of elements such as Al, Mn, Fe, Mg and Sr reveal that biogenic processes have played vital role in development of deposit. According to values of Eu/Eu* (0.88-1.12) and Sr/Ba (0.45-4.86) in the studied samples, it seems that phosphatization process in the Dalir area occurred in slightly acidic to neutal pH and normal salinity. Combination of the obtained results from field observations, mineralogical studies and geochemical data indicate that formation of studied deposit was controlled by marine upwellings.