Hf-O isotope characteristics for ore-related intrusions of typical iron deposits in Zhonggu ore field, Ningwu basin

Abstract

Zhonggu iron ore field is located in south part of Ningwu basin. The ore filed occurred diorite and monzonite intrusions (132 ～ 129Ma) which are related to iron deposits. The origin and evolution of these intrusions still need to be further studied. Here, we conduct LA-ICP-MS zircon Hf isotope and SHRIMP zircon O isotope test focus on the Gushan porphyritic gabbrodiorite, the Longshan gabbrodiorite, the Baixingshan diorite, the Zhongjiu diorite and the Taipingshan monzonite. 176 Hf/ 177 Hf ratios of these intrusions are 0.282425 ～ 0.282695 (t DM2 = - 1.26 ? 1.86Ga). The range of zircons have ～ 18 O ranging from 3.34 to 8.05 and ～ Hf (t) ranging from - 12.3 to -3.9. 176 Hf/ 177 Hf ratios of inherited zircons in Taipingshan monzonite are 0.282324 ～ 0.282487 (t DM2 = 1.72 ? 20.8 Ga). The range of inherited zircons have ～ 18 O ranging from 5.90 to 6.51 and ～ Hf (t) ranging from - 15.8 to -10.1. Zhonggu magmatic rocks are derived from enriched lithospheric mantle. Hf-O isotope imply the magma in this area are consistent with the Early Cretaceous period of lithospheric thinning and extension influenced by the subduction of the Paleo-Pacific Plate. Magmatic rocks in Middle and Lower Yangtze Metalloic Belt include Ningwu have the same origin, magmatic rocks in iron districts such as Ningwu and Luzong are mainly directely framed by enriched lithospheric mantle, while magmatic rocks in copper-polymetallic districts represented by Tongling and Fancang contaminated with more Paleoproterozoic and neoproterozoic earth crust.