Geochronology and geochemistry of granitoid rocks from the Zhibo syngenetic volcanogenic iron ore deposit in the Western Tianshan Mountains (NW-China): Constraints on the age of mineralization and tectonic setting

Abstract

Several large syngenetic volcanogenic iron ore deposits including the Chagangnuoer Fe–Cu, the Zhibo Fe and the Beizhan Fe deposits occur in the Awulale Fe–Cu Metallogenetic Belt (AMB) which is located in the southeastern corner of the Yili block in the Western Tianshan Mountains (NW-China). In the present study, we report geochronological and geochemical data for granitoid rocks associated with the Zhibo iron ore deposit in order to constrain the age of the stratiform Fe mineralization and tectonic setting of this deposit. Laser ablation-ICPMS (LA-ICPMS) U–Pb zircon ages of 318.9±1.5Ma and 304.1±1.8Ma were obtained for a diorite and a granite pluton, respectively, both of which intruded the volcanic–volcaniclastic rocks of the Early Carboniferous Dahalajunshan Formation. Additional LA-ICPMS U–Pb zircon ages of 320.3±2.5Ma and 294.5±1.6Ma were obtained for two crosscutting granite dikes, respectively. The ca. 319Ma diorite has a high-potassium calc-alkaline, weakly peraluminous composition and is characterized by large ion lithophile element (LILE) and light rare earth element (LREE) enrichment and flat heavy rare earth element (HREE) patterns. It further shows distinct negative anomalies of Nb, Ta and Ti. In contrast, the ca. 304Ma granite classifies as A2 type granite and is characterized by an enrichment of LILE and LREE, flat HREEs and distinct negative anomalies of Ba, Nb, Ta and Ti. The ca. 320Ma granite dike has a low-potassium and weakly peraluminous composition and is characterized by LILE and LREE enrichment and a distinct depletion of Nb, Ta, Ti and HREE. The ca. 295Ma granite displays a high-potassium calc-alkaline and weakly peraluminous composition and is characterized by a slight enrichment of LILE and LREE, flat HREEs and a distinct depletion of Nb, Ta and Ti. The data presented here in conjunction with previously published data suggest a submarine, syngenetic volcanogenic mineralization age of ca. 320Ma for the Zhibo iron ore deposit. The Zhibo and other submarine volcanogenic iron ore deposits of the AMB are inferred to have formed in a continental arc-setting related to subduction tectonics. Furthermore, post-collisional granitic magmatism from 304 to 295Ma was superimposed on the entire AMB.