Redetermination of the Depositional Age of the Haerdaban Group in the Northern Margin of the Yili Block, Western Tianshan, NW China: Implications for Regional Tectonics and Pb‐Zn Mineralization

Abstract

AbstractThe Yili Block in the Western Tianshan orogen is a key area for understanding the early crustal formation and evolution of the Central Asian orogenic belt, due to the widely‐distributed Precambrian rocks. Also, it hosts a lot of medium– to large‐scale sedimentary exhalative (SEDEX) Pb‐Zn deposits that mainly occur in Proterozoic metamorphosed clastic‐carbonate rocks. In this study, LA‐ICP‐MS U‐Pb analyses were carried out on detrital zircons in siltstones of the Precambrian Haerdaban Group in the Haerdaban Pb‐Zn deposit and magmatic zircons in the diorite dyke that cuts through the strata and orebodies. The maximum depositional age of the siltstones was determined to be about 604 Ma, the diorite having formed at approximately 500 Ma. As such, the Haerdaban Group was most likely formed in the Neoproterozoic Sinian, rather than the previously considered Mesoproterozoic Changchengian. Detrital materials of the Haerdaban Group were mostly derived from the Nanhua–Sinian mafic dykes and granitic rocks around Lake Sayram at the northern margin of the Yili Block. It is proposed that the Yili Block, together with the Kazakhstan and Central Tianshan blocks and the Tarim Craton, might all pertain to the same Rodinia supercontinent, which has great potential for targeting large to super‐large SEDEX Pb‐Zn deposits.