ارتباط شورابه هاي تبخيري كامبرين آغازين با ژئوشيمي و ژنز كانسار آهن آنومالي شمالي در شمال بافق (ايران مركزي)

Role of Cambrian evaporitic fluids in geochemistry and genesis of Nord Anomaly iron ore deposit, North Bafq(Central Iran)

Nord Anomaly deposit is an iron ore deposit in Bafq district. It contains 250 Mt iron ore with average grade of Fe=28 %. The host rocks of the mineralization in Nord Anomaly deposit are granitic and microgranitic rocks with probably Early Paleozoic age. Petrographic investigations reveal that sodic and calcic alterations are related to iron mineralization. Other alterations such as silisic, chloritic, epidotic and sericitic alterations are insignificant and post date the iron mineralization. Sodic and calcic alterations are characterized by formation of chessboard albite and actinolite -termolite respectively. Widespread sodic and calcic alterations are contemporaneous with the feldspar-magnetite and magnetite-amphibole ore respectively. Magnetite-amphibole ore is high grade and low tonage while magnetite-feldspar ore is low grade and high tonage. Geochemical studies show that alkaline cations (Na, K) concentration were increased and immobile elements (Fe, V, Ni) decreased during sodic alteration. In calcic alteration case, immobile elements (Fe, V, Ni) shows a distinct increase in their concentration. Sulfur isotope studies showed that fluid source could be mainly from evaporatic sources with minor contribution of magmatic fluids. At the Late Precambrian, granitoid magmatism occurred with subduction of Proto-Tethys under Central Iranian Plate. As a result, pull-apart basins have formed in the magmatic back arcs, caused deposition of Rizu and Dezu evaporatic sequences. Iron ore mineralization in Nord Anomaly could be related to the Central Iran evaporatic salts and Cambrian granitoid magmatism.