Geological Characteristics And Prospecting Signs Of The Fuxingtun Ag-Pb-Zn Polymetallic Ore Deposit In Inner Mongolia

In this paper,the Ag-Pb-Zn polymetallic ore deposits in Fuxingtun,Horqin Right Wing Front,Inner Mongolia were selected as the research object.Based on long-term field survey and systematic data research,the features of geochemistry,geophysics,geology and ore bodies were analyzed,and the genesis and prospecting signs of ore deposits were summarized.This study provided guiding significance for the prospecting of Mesozoic continental volcanic Ag-Pb-Zn polymetallic ore deposits in both the areas around Fuxingtun and the central-southern Great Xing'an Range.The study area was tectonically located in the Zhalantun-Duobaoshan island arc of the Tianshan-Xingmeng orogenic system.The ore bodies were mainly hosted in the Jurassic volcanic rocks.The ore-bearing rocks were generally characterized by pyrophyllitiazation,chloritization,kaolinization and carbonation.The tuff in drill holes was regarded as a marker layer,reflecting the volcano intervals.The upper part of the tuff was dominated by an overflow phase,and the lower part was an eruption phase.The geochemical anomalies were composed of Ag,Pb,Zn,Cu,Sb,Mn,W,and Sn.The main ore-forming elements,Ag,Pb,and Zn,had obviously concentrated centers,and highly anomalous intensity.They have element combination features for Ag-Pb-Zn polymetallic ore of the medium-low temperature hydrothermal type.The primary halo anomalies of the drill holes showed that the high-medium-low temperature elements superimposed on each other in the near surface and the depth of the ore body,indicating that the ore body was vertically characterized by the superimposition of the ore tail halo-ore middle halo-ore head halo.The magnetic anomaly in the study area was in a secondary superposition state,composed of multiple secondary anomalies.Each secondary anomaly had a large intensity and a steep variation gradient of field values.An ordered distribution of positive and negative scattered arrays was observed.The anomalous characteristics of the induced voltage were low resistance and high polarization.In the study area the volcanic edifice was developed.The volcanic edifice provided early migration channels for the ore-forming hydrothermal sources,and the produced caldera or sub-crater provided the main metallogenic space.At the same time,the volcanic activity had the characteristics of the synchronous diagenesis and mineralization.A grid-like structural form was developed along the northeastward and northwestward tectonic structures,which defined the ore-bearing range.During the Late Jurassic,extensive continental volcanic activity occurred in the Fuxingtun area of the central-southern Great Xing'an Range,forming the volcanic-clastic rock formations of the Manketou Ebo Formation,the Manitu Formation and the Baiyingaolao Formation.During the intermittent and/or late stages of volcanic activity,especially in the late stage of the volcanic eruption of the Baiyingaokao Formation,multiple subvolcanic rock intrusions were formed.These intrusions were in the lower part of the volcanic sequence,forming a metallogenic structural system consisting of volcanic sequence and subvolcanic intrusions.Awide-scale hydrothermal cycle system was formed centering on the sub-volcanic rock intrusions.The metallogenic materials were extracted from the volcanic rocks by the cycle system.The cycling meteoric water and the hydrothermal fluid from the deep sub-volcanic rocks consisted of the ore-bearing hydrothermal fluids.There was a close genetic relationship between the mineralization of the Ag-Pb-Zn polymetallic ore deposits in Fuxingtun and the volcanic-subvolcanic hydrothermal activity.