大兴安岭成矿省南段布敦乌拉中硫型银矿床的成矿与找矿模型OA

In the southern metallogenic province of the Great Xing'an range,a series of superlarge and even world-class silver and tin deposits,including the Bairendaba,Shuangjianzishan,Fuxingtun,Baiyinchagan and Weila-si-tuo deposits,have been discovered in recent years.Nevertheless,research on genetic types,metallogenic models and exploration models of deposits in this region remains at a relatively low level,and fierce controversies exist over several key scientific issues,which restricts further breakthroughs in regional mineral exploration.To tack-le this bottleneck,this paper carries out a typical deposit study on the Budunwula superlarge silver deposit.Based on systematic geological logging,1∶5000 unmanned aerial vehicle(UAV)aeromagnetic survey,1∶10 000 induced polarization(IP)geophysical survey and rock-chip geochemical survey,the following understandings are summarized:① Orebodies mainly occur as pod-like and lenticular bodies within breccia-bearing rhyolite of the Baiyingaolao Formation,with disseminated,brecciated and veinlet ore structures developed.Metallic miner-als are characterized by an assemblage of complex silver-bearing minerals and base-metal sulfides;② Altera-tions closely associated with mineralization include silicification,illitization,sericitization,kaolinization and epi-dotization;③ Aeromagnetic anomalies are represented by a combination of northeast-trending high magnetic anomalies,multiple isolated moderate magnetic anomalies and ring-shaped low magnetic anomalies;④ Five moderate apparent chargeability anomalies and three northeast-trending moderate apparent resistivity anomaly zones are delineated;⑤ One Ag-As-Sb-Pb-Zn composite anomaly(corresponding to the Budunwula minera-lized area)and one Ag-As-Sb-Pb-Zn-Bi-W composite anomaly are identified.On the basis of summarizing and analyzing the geological features of the deposit as well as the origins of geophysical and geochemical anoma-lies,a metallogenic model and explorational model for the deposit are established in this paper,and the follow-ing viewpoints are proposed:① The Budunwula deposit is a typical intermediate-sulfidation epithermal silver deposit;② The detachment zone between rhyolite and sandstone-slate provides critical migration pathways for ore-forming hydrothermal fluids,whereas the breccia-bearing rhyolite,acting as a paleo-permeable zone,offers favorable host space for hydrothermal fluid localization;③ Ring-shaped low magnetic anomaly zones(with magnetic anomaly △T ranging from+5 to-20 nT)can effectively predict the distribution range of epithermal argillic alteration zones;④ Zones with moderate apparent chargeability and apparent resistivity anomalies(ap-parent chargeability:4～9 ms;apparent resistivity:150～250 Ω·m)exhibit high spatial coincidence with orebod-ies and are ore-related anomalies;⑤ Ag-As-Sb-Pb-Zn composite anomalies can be used for preliminary pros-pecting target selection,yet their applicability is limited due to thick regional quaternary overburden.Therefore,the optimal scheme for delineating target areas of intermediate-sulfidation epithermal silver deposits in covered areas is dominated by highly permeable volcanic rocks+ring-shaped low magnetic anomaly zones+zones with moderate apparent chargeability and apparent resistivity anomalies,supplemented by Ag-As-Sb-Pb-Zn element anomaly zones.