Sodic-calcic alteration in the host rocks of the Esfordi magnetite-apatite deposit

The host rocks of the Esfordi deposit consist of rhyolitic tuff lower Camrianand rhyolite along with dolomites of the Rizu series which are widely affected by sodic-calcic hydrothermal alteration in the north and the east. Typical mineral assemblage in the alteration zone is amphibole، albite، hematite، calcite and chlorite based on petrographic studies. The amphiboles in the Na-Ca alteration zone are within the calcic amphibole group with edenite and actinolite compositions. The average (Na+K) A content of the edenite and actinolite is 0. 67 and 0. 11 respectively. Chemically، edenite in comparison with actinolite is enriched in TiO2 (0. 93)، Al2O3 (11. 34)، FeO (13. 55)، Na2O (2. 09) and Cl (1. 05). Whole rock analysis reveal appreciable enrichment of FeOt، MgO، CaO، Na2O، P2O5 and Y2O3 in the Na-Ca altered rocks relative to unaltered host rocks. The calcite and quartz veins crosscut the Na-Ca altered rocks. The Na-Ca altered rocks and calcite veins δ18O values (relative to SMOW) vary between 10. 5 to 12 ‰ and between 14. 1 to 18. 1 ‰ respectively، while their δ13C values (relative to PDB) vary from -3. 8 to -4. 2 ‰ and -5. 5 to -6. 3 ‰ correspondingly. On the basis of O and C isotopic data on the host rocks، Na-Ca alteration occurred at 300-400 °C and the calcite veins formed at temperatures lower than 300 °C. According to available data، alteration is interpreted to develop by mixing of meteoric waters with magmatic fluids in Esfordi mine.