Mineral Geochemical Characteristics Of Celestites And Their Genesis At The Supergiant Jinding Zn-Pb Deposit In Lanping Basin,western Yunnan Province

The Lanping Jinding super-large Pb-Zn deposit in western Yunnan is one of the typical MVT deposits in the Tethys-Himalaya tectonic metallogenic domain with sedimentary rocks as the host rock.Among them,the Baicaoping section is an independently produced large-scale celestite deposit,including many Pb-Zn deposits（body）in Beichang,Fengzishan,Paomaping and Jiayashan sections,which are also related to celestite deposits（body）.The mineralization framework of"symbiosis"or"coexistence of heterogeneity"shows that it has a certain genetic relationship with Pb-Zn mineralization and development mechanism.These two deposit types may respectively represent a unified ore-forming fluid differential metallogenic endmember type.For this reason,this time,the celestite deposit（body）in the Baicaoping ore section was selected as the research object,and compared with the Beichang ore section,the geological characteristics and mineral geochemical characteristics of celestite were compared and studied,and its mineralization was traced.The fluid evolution sequence clarifies the genesis of celestite,and provides a basis for in-depth understanding of the genetic connection between celestite deposits（bodies）and Pb-Zn mineralization in the area.The main results of this study are as follows:1.The celestite ore body in the Baicaoping ore section is mainly layered and lenticular,and occurs in the purplish red/brick red argillaceous siltstone of the Oliocene-Miocene Jinding Group（E₃N1j）,mostly interbedded with（anhydrite）gypsum.,and a small amount of（net）veins occur in the limestone"blocks"of the Upper Triassic Sanhedong Formation（T₃s）;while the Pb-Zn-Sr orebodies in the northeast part of the Beichang ore section mainly occur in the Upper Triassic Among the breccia limestones of the Sanhedong Formation（T₃s）,a small amount of lenticular and patchy limestones occur in the gray-green/purple argilaceous siltstones of the Oligocene-Miocene Jinding Group（E₃N1j）.2.In the north-eastern part of the Beichang ore section,celestite and Pb-Zn and other metal sulfides co-produce（accompanied）,and the types of mineralization alteration and mineral assemblages are diverse,showing that the hydrothermal ore-forming fluids fill the open space along with ore-forming fluids and episodic fluids.The characteristics of mixed mineralization are highly consistent with the Pb-Zn mineralized strata,unconformities and faults that control the mineralization.Except for a small amount of red crystal cave-like celestite with gray-green-purple argillaceous siltstone as the host rock,it belongs to the early sedimentary products of the Jinding Group,indicating that this type of celestite belongs to sedimentary origin（sedimentary type）,and the rest of the celestite are Hydrothermal ore-forming by-products（hydrothermal type）,and the general development of Ba-rich celestite-Sr-rich barite in the form of incomplete isomorphic substitution of solid solution exsolution phenomenon,can be divided into geodes according to their production status Shaped,reticulated celestite,etc.Among them,the tectonic transformation of the unconformity between the Jingxing Formation and the Sanhedong Formation,the Jinding Group and the Sanhedong Formation resulted in the spatial coexistence of hydrothermal and sedimentary celestite,and the former dominated.3.In the Baicaoping section,the Pb-Zn mineralization is very weak and unevenly distributed,and does not constitute an industrial ore body.The output location of the generally developed celestite ore（chemical）body is controlled by the specific stratum and lithology of the Jinding Group..The rock assemblage of the Jinding Group presents the multi-cycle sedimentary characteristics of clastic rock+carbonate rock+celestite rock+gypsum rock.The celestite ore（chemical）body can be divided into four types according to its production status:celestified calcareous cemented breccia,limestone-bearing breccia calcite-celestite,thick-layered massive celestite,and celestified quartz sandstone.Its strontium minerals are mainly celestite,with a small amount of strontium ore and（strontium）barite,which are closely associated with（anhydrite）gypsum,and the dissolution of celestite from solid solution is extremely rare.Among them,the celestified calcareous cemented breccias show the obvious characteristics of hydrothermal metasomatism,and generally develop metasomatic residual structures and breccia and network vein structures,which are of hydrothermal type;the rest are of sedimentary origin（sedimentary type）).In addition,there are two types of limestones in the Jinding Group strata,one is the sedimentary calcite in the Jinding Group,and the calcite and celestite mostly have a co-edge structure,showing the characteristics of contemporaneous sedimentary mineralization,and the other is sedimentary celestite;The species are limestone breccias and rock blocks（chips）of the Sanhedong Formation in the Jinding Group.Among them,hydrothermal metasomatism with uneven strength and weakness is often seen in celestite,associated with hydrothermal calcite and gypsum,showing the characteristics of post-hydrothermal metasomatism.,for the hydrothermal celestite.These features reveal that the different mineralized types of celestite in the area are the products of strontium-bearing hot brine fluids with different depositional rhythms deposited in different mineralized layers.It can be seen that the celestite in the Baicaoping section is mainly a hot water sedimentary deposit.4.The XRD results show that the phase composition of celestite in the northeastern part of the Beichang ore section is quite different from that of the Baicaopang ore section,and Sr and Ba,Sr and Ca generally undergo isomorphic substitution,and their hydrothermal type and sedimentary The structures of celestites show regular differences,reflecting the differences in the composition of major and trace elements.This indicates that the properties and elements of the ore-forming fluid changed significantly during its crystallization and precipitation.5.The characteristics of mineral geochemical composition show that the sulfur main body of sedimentary celestite originates from H₂S in the Upper Triassic marine carbonate rocks and the contribution of sulfate in the Jinding stage brine,and partly from the preformed sulfate thermochemistry Reduction（TSR）;while the sulfur of hydrothermal celestite originates from bacterial sulfate reduction（BSR）and organic matter thermal cracking（ODM）.6.The formation of celestite in the Baicaoping ore section is synchronized with the stratigraphic deposition,while the formation of celestite in the northeast of the Beichang ore section is co-existent with lead-zinc mineralization,which occurs synchronously in time,and there are differences in space sexual changes.Therefore,the temporal and spatial evolution of the oxidizing brine rich in strontium and metal ions at low temperature and high salinity,and the reducing fluids in medium-low temperature,low salinity,high porosity and permeability fractured limestone blocks and sandy limestone breccias are different in time and space.It may be an important mechanism for the difference between celestite and Pb-Zn mineralization in the area.