Geochemistry, petrogenesis and petrology of intrusive rocks in Shadan gold deposit, SW Birjand, Eastern Iran

Document Type : Research Paper


School of Geology, College of Science, University of Tehran, Tehran, Iran.


Shadan gold (+copper) deposit in the Lut block, east of Iran, comprises Eocene to Oligocene intrusive and subvolcanic rocks with intermediate to felsic composition, which have intruded into Eocene volcanic- pyroclastic rocks. Shadan intrusive rocks range from granodiorite, quartz monzonite, and diorite to micro-gabbrodiorite. Geochemical data indicate that Shadan intrusive rocks are I-type, metaluminous to peraluminous, belonging to the calc-alkaline to high-potassic calc-alkaline magmatic series. Rare earth elements (REE) and trace elements patterns of Shadan rocks display enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE) relative to heavy rare earth elements (HREE) and high field strength elements (HFSE). The main hydrothermal alteration types contain quartz-carbonate, propylitic, argillic, phyllic and potassic, which affected the rocks in varying degrees. According to tectonomagmatic discrimination diagrams, all rock samples display evidence of a volcanic arc, which was formed at an active continental margin. Based on Nb/Y vs. Rb/Y ratio, Shadan rock samples experienced subduction zone enrichment and crustal contamination. According to Nb/Zr vs. Nb/Ba ratio, source region of the Shadan intrusive and subvolcanic rocks are attributed to the subcontinental lithosphere source. Th/Yb versus Nb/Yb diagram shows a separation between Shadan samples and MORB-OIB arrays,possibly due to crustal contamination and the mobility of Th during subduction. La vs. La/Yb ratio reveals that partial melting played a significant role in the formation of Shadan rocks.


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