Study On Polymetallic Mineralization Of Pb-Zn-Ag And Cu-Mo In The Southern Part Of The Derbugan Metallogenic Belt,Inner Mongolia

The Deerbugan metallogenic belt in Inner Mongolia is located in the east part of the Central Asian orogenic belt and the south margin of the Mongolian okutsk orogenic belt,and its main body is located on the Erguna block.In the south part of Deerbugan metallogenic belt,the polymetallic deposits mainly consist of Jiawula Pb-Zn-Ag deposit,Chaganbulagen Pb-Zn-Ag deposit,Erentaolegai Ag deposit and Wunugetushan Cu-Mo deposit,etc.According to the geological,mineralization characteristics and genesis of the ore deposits,the polymetallic deposits in the south section of the Deerbugan metallogenic belt can be divided into three main types:porphyry type(Wunugetushan Cu-Mo deposit),hydrothermal vein-type(Jiawula Pb-Zn-(Ag)deposit,Chaganbulagen Pb-Zn-(Ag)deposit and epithermal-type(Erentaolegai Ag deposit).The Wunugetushan Cu-Mo deposit occurs in the early Jurassic monzogranite.The hydrothermal mineralization can be divided into four stages:pyrite quartz,molybdenite-quartz,chalcopyrite-quartz and carbonate-quartz;The Jiawula Pb-Zn-(Ag)deposit occurs in the volcanic rocks and sandstones of the Middle Jurassic.The hydrothermal mineralization can be divided into five stages:pyrite-quartz,molybdenite-quartz,pyrite-pyrrhotite-chalcopyrite-sphalerite-quartz,pyrite-sphalerite-galena-quartz and calcite-quartz;The Chaganbulagen Pb-Zn-(Ag)deposit occurs in the volcanic rocks and sandstones of the Middle Jurassic.The hydrothermal mineralization can be divided into four stages:pyrite-quartz,pyrite-pyrrhotite-chalcopyrite-sphalerite quartz,pyrite-sphalerite-galena-quartz and carbonate-quartz.The Erentaolegai Ag deposit occurs in the volcanic rocks of the Middle Jurassic.The hydrothermal mineralization can be divided into four stages:pyrite-quartz,polymetallic sulfide-quartz,quartz-manganese carbonate stage and calcite-quartz.The comprehensive study of geochemistry of ore deposits shows that the ore-forming fluids and materials of each typical deposit in the study area are closely related to regional magmatism.The ore-forming fluid of Wunugetushan deposit is a middle-high temperature and middle-high salinity Na Cl-H₂O system hydrothermal fluid,which is derived from magmatic water and meteoric water.And the ore-forming fluid is mainly crustal fluid.The sulfur in ore-forming materials is derived from magmatic sulfur,and the lead is derived from crust-mantle mixed lead.Fluid boiling may be the key genetic mechanism leading to the precipitation of metallic minerals.The ore-forming fluid of vein-type deposits(Pb-Zn-(Ag)deposit and Chaganbulagen Pb-Zn-(Ag)deposit)is a middle temperature and middle salinity Na Cl-H₂O system hydrothermal fluid.The ore-forming fluid mainly comes from meteoric water mixed with a small amount of magmatic water.And the ore-forming fluid is mainly crustal fluid;The sulfur in ore-forming materials is derived from magmatic sulfur,and the lead is derived from crust-mantle mixed lead.Fluid boiling may be the key genetic mechanism leading to the precipitation of metallic minerals.The ore-forming fluid of epithermal-type deposit(Erentaolegai Ag deposit)is a low temperature and low salinity Na Cl-H₂O system hydrothermal fluid.The ore-forming fluid is magmatic water in the early stage and a large amount of meteoric water in the later stage;And the ore-forming fluid is mainly crustal fluid.The sulfur in ore-forming materials is derived from magmatic sulfur,and the lead is derived from crust-mantle mixed lead.The temperature drop and Water/Rock(W/R)reaction may be the key mechanism leading to the precipitation of metallic minerals in the deposit.According to the study of diagenesis and geochemistry of typical ore deposits,the Wunugetushan Cu-Mo deposit was formed in the early Jurassic(178-180Ma),and the Jiawula Pb-Zn-(Ag)deposit,Chaganbulagen Pb-Zn-(Ag)deposit and Erentaolegai Ag deposit were formed in the early Cretaceous(134-138Ma).Therefore,there are two periods of early Jurassic and early Cretaceous polymetallic mineralization in the southern part of the Deerbugan metallogenic belt.According to the comprehensive analysis of regional tectonic evolution-magmatism-hydrothermal mineralization,the regional metallogenic model is established as follows:1)During the early Jurassic,the Mongolia Okhotsk ocean continued to subduct southward,and the thickened lower crust was partially melted to form the parent magma of Wunugetushan monzonitic granite porphyry.The differentiated magmatic hydrothermal solution gradually developed into Wunugetushan Cu Mo deposit;2)In the late the Early Triassic,the Mongolia Okhotsk ocean has been closed.At this time,the study area is in an extensional environment.The lower crust undergoes partial melting(A-type granite),and the crust mantle materials are mixed to form the parent magma of quartz monzonite porphyry in the Jiawula-Chaganbulagen deposit and and quartz porphyry in the Erentaolegai deposit.Magmatic hydrothermal solution differentiated from magma gradually developed and mixed with atmospheric precipitation to form Jiawula Pb-Zn-(Ag)deposit,Chaganbulagen Pb Zn-(Ag)deposit and Erentaolegai Ag deposit.