Geochemical Characteristics, Source Of Ore-forming Materials And Metallogenic Prediction For The Lianhuashan Ag-Cu Deposit In Middle-south Segment Of Da Hinggan Mountains

The Lianhuashan Ag-Cu deposit is a hydrothermal vien-type deposit located at the east along middle-south segment of Da Hinggan Mountains.Based on a detailed analysis of predecessor research results and field geological survey,this paper has deep analysis of the deposits geological feature,S-Pb isotope,trace elements of pyrite and the main trace elements of surrounding rock,we explored the geochemical characteristics of rock,source of ore-forming materials,ore-forming fluid characteristics and the rock mass formation age about the Lianhuashan Ag-Cu deposit,established the mineralization model,provided theoretical basis for the future metallogenic prediction and prospecting direction,the main results and conclusions obtained were as follows:1)The ore-forming geological body of Lianhuashan Ag-Cu deposit are plagioclase granite porphyry and intermediate-acid volcanic subvolcanic rocks.The plagioclase granite porphyry are Ca-alkaline I-typed granite,originating from the depleted mantle,and in the process of emplacement affected by the earth's crust or lithosphere mantle contamination;Its formed from lithosphere extension environment after the closure of north China plate and Siberia plate.2)The diorite porphyrite of Lianhuashan Ag-Cu deposit origination from a metasomatized mantle wedge or depleted mantle,which had been modified during the previous subcontinental/oceanic subduction.The intermediate-acid rocks were derived from the differentiated crystallization of basaltic magmas.They are formed in ocean-land subduction orogenic or post-tectonic stage during the closure of Old Asian Ocean,relating to the extension of lithosphere resulting from the up-welling of asthenosphere.3)The?³⁴S_VCDT of metal sulfides from the Lianhuashan Ag-Cu deposit vary from 0.0‰to3.0‰,varying in a narrow range and have obvious characteristics of tower-type distribution,which implies that the sulfur was mainly derived from the deep-seated magma.The results of lead isotopes suggesting that the lead of the ore is mainly derived from mixture of crust-mantle materials and affected by the orogeny.4)REE composition and trace element characteristics of pyrite in the Lianhuashan Ag-Cu deposit show that:ore forming fluid strong enrichment in LREE,depleted high field strength element?HFSE?and its Hf/Sm,Th/La,Nb/La ratios are almostly less than 1,infeing that the ore forming fluid of Lianhuashan Ag-Cu deposit is mainly originated from the Cl rich mineralization hydrothermal.They are similarity to the intermediate-acid volcanic subvolcanic rocks in the mining area show that ore-forming materials mainly comes from intermediate-acid volcanic subvolcanic rocks,and extracting the composition from surrounding rock in a certain extent.5)The Zr-Hf,Nb-Ta,Y-Ho ratios indicated that ore-forming hydrothermal in the Lianhuashan Ag-Cu deposit has affected by the late volcanic hydrothermal activity.The Co/Ni elemental ratios suggested that the Lianhuashan Ag-Cu deposit is volcanic hydrothermal origin.