Magmatism And Lead-zinc Mineralization In The Southern Great Xing'an Range,NE China

The Southern Great Xing'an Range(SGXR),located in the eastern segment of the Central Asian Orogenic Belt,is an important Pb-Zn-Ag-Cu-Mo metallogenic belt in northern China.It was influenced by the subduction and closure of the Paleo-Asian Ocean to the north in the Paleozoic,the subduction of the Mongol-Okhotsk Ocean to the northwest,and the subduction of the Paleo-Pacific Ocean to the east in the Mesozoic.However,in some issues,such as magma source,tectonic setting and metallogenetic materials,the question still remain controversial.In this paper,typical Baiyinnuoer Zn-Pb-Ag polymetallic deposit,Bairendaba Zn-Pb-Ag polymetallic deposit,Weilasituo Zn-Cu polymetallic deposit,and Bianj iadyuan Pb-Zn-Ag polymetallic deposit were studied.We also carried out detailed petrological,whole-rock geochemical,Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry(LA-ICP-MS)zircon U-Pb geochronological,and Sr-Nd-Pb isotopic analysis on the Late Paleozoic-Mesozoic magmatic rocks in the SGXR,which were also associated with the lead-zinc mineralization,with the aim of understanding the genetic relationship between the magmatism and mineralization and clarifying the tectonic evolution of the SGXR.We can get the following conclusions:(1)Three magmatic stages are identified in the SGXR:Variscan magmatic rocks consisting of gabbro and quartz diorite with ages from 379 to 325 Ma;Indosinian magmatic rocks consisting of gabbro,diorite,and granodiorite with ages from 273 to 248 Ma;Yanshanian granitoids consisting of diorite with the age of 133 Ma.(2)The gabbro,in the Weilasituo Zn-Cu polymetallic deposit,was emplaced at 379±3.3 Ma.Geochemical and Sr-Nd-Pb isotopic data indicate that the gabbro might result from the subduction of the Paleo-Asian Ocean.The quartz diorite(326-325 Ma),in the Bairendaba Zn-Pb-Ag polymetallic deposit,are characterized by high SiO2 and K2O+Na2O,and low MgO contents,and belong to calc-alkaline to high K calc-alkaline series,showing similar geochemical features with I-type granites.Geochemical and Sr-Nd-Pb isotopic data show that the quartz diorite might have been derived from parial melting of lower crustal materials,and small amount of ancient crustal materials were added in their origin.(3)The ore-bearing granodiorite(251-248 Ma),in the Baiyinnuoer Zn-Pb-Ag polymetallic deposit,belong to calc-alkaline to high K calc-alkaline series,and show similar geochemical features with I-type granites.Geochemical and Sr-Nd-Pb isotopic data indicate that the ore-bearing granodiorite might be related with the mixing magmas of both mantle and crust sources.The closure of the Paleo-Asian Ocean occurred in Late Permian,and led to plate extension in the SGXR.(4)The ore-bearing diorite(133±1.0 Ma),in the Bianjiadayuan Pb-Zn-Ag polymetallic deposit,have positive ENd(t)value and old crustal model age(TDM2),indicating that crustal contamination might happen during the magma uplift.The SGXR might be influenced by the subduction of the Mongol-Okhotsk Ocean to the northwest and the subduction of the Paleo-Pacific Ocean in Early Cretaceous.(5)Pb-S isotopic compositions show that the metallogenetic materials might have been derived from deep-seated magmas.Indosinian and Yanshanian granitoids have genetic relationship with lead-zinc mineralization in the SGXR,and the magmas also provide metallogenetic materials.(6)The processes of lead-zinc mineralization in the SGXR were dominantly influenced by Permian strata,NE-trending faults,and Mesozoic magmatic rocks.The granitoids,which are related with lead-zinc mineralization,belong to high K calc-alkaline series and might have been derived from both mantle and crust sources.