A Study On Metallogenic Regularity Of The Mengnuo Lead-Zinc Deposit In Longling Yunnan

The Mengnuo lead-zinc deposit in western Yunnan is located on the east flank of the Mengnuo syncline in the Baoshan-Zhenkang block and is an important large-scale lead-zinc deposit in the Sanjiang metallogenic belt.The mining area is relatively weak in isotope geochemistry research.Based on the summary of previous data and a large number of field geological surveys,this paper uses the C,O,S,Pb,Sr isotope characteristics,trace element characteristics and rare earth element characteristics of the deposits.Several metal deposits?Luziyuan,Jinchanghe,Shuitoushan,Xiyi,Fangyangshan?of the plot were compared,and the ore-forming fluids and source of ore-forming materials of the Mengnuo lead-zinc deposit were discussed.Metallogenic regularity,metallogenic mechanism,deposit genesis and ore control factors.The thesis mainly obtains the following points:1.The distribution of the ore body of the Mengnuo lead-zinc deposit is controlled by the secondary Mengnuo syncline in the southern section of the Baoshan-Shidian compound syncline?S₂¹?.It is the main output part of the ore body,which is near SN direction,and the ore belt is about 10km long.2.Through field geological survey in the study area,grinding the collected samples into light film and observing under the microscope through a microscope,combined with previous studies,the mineralization stage can be roughly divided into:?1?sedimentation period:It mainly forms pyrite with associated calcite.?2?Hydrothermal metallogenic period?can be divided into three stages?:stage I,mainly forming pyrite with a small amount of barite;stage II,the main mineralizing stage,mainly forming galena and sphalerite Often light yellow-red-red-brown fine-grained strips,lumps,disseminated or colloidal output;stage III,mainly formed galena and sphalerite brown-light yellow coarse grain,cross-cut stage II Lead ore.?3?Supergene period:mainly formed secondary oxidized minerals such as limonite.3.Characteristics of trace elements,the migration law of Pb and Zn elements in crystalline limestone and other surrounding rocks relatively far from the ore body is obvious,and there is a clear correlation;then comparing the abundance of Chinese sedimentary rocks and the background value of the mining area,the main mineralization of the mining area The elemental background values are much higher than the abundance of sedimentary rocks in China,and also higher than other surrounding rocks except crystalline limestone in the mine area.It indicates the crystalline limestone in the lower section?S₂¹?of the Upper Silenheqiao Formation of the Middle Silurian in the indicated mining area,providing part of the material source.The crystalline limestone and lead-zinc ore in the study area have very similar rare earth distribution curves,both of which represent the properties of ore-forming fluids.The lead-zinc ore?REE is slightly lower than that of crystalline limestone,and also has Eu negative anomalies,no Ce anomalies or weak positive anomalies.,Indicating its inheritance of the rare earth elements of the surrounding rock.4.Isotope characteristics:?1?C and O isotopes,and the?¹³C_PDB value analysis of hydrothermal calcite shows that hydrothermal fluid reacts with surrounding rocks,resulting in the dissolution of carbonate rocks providing a source of C and O isotopes for ore-forming fluids.The reaction with the water rock of the surrounding rock makes the hydrothermal calcite precipitate in the carbonate rock surrounding rock in this area.It indicates that the ore-forming fluid is derived from the degassing of carbonate rocks or the interaction between salty brine and sedimentary rocks;the sedimentary environment of the study area is the shallow sea-open platform subtidal zone,and there are also a large number of organisms in the bioclastic limestone Fossils indicate that a large number of microorganisms provide some material sources for mineralization;?2?S isotopes,?³⁴S values are all positive values and the change range is not large,the heavy sulfur isotope is enriched,and the composition is relatively stable,indicating that the physical and chemical environment has not changed significantly during the mineralization process.The?³⁴S value is generally characterized as pyrite>sphalerite>galena,and the?³⁴S value of sphalerite and galena partially overlaps,indicating that the S between sphalerite and galena in this mineralization stage It is precipitated under the condition of isotope equilibrium,and it also shows that the sulfide in the ore-forming hydrothermal fluid is a mineral combination formed under equilibrium symbiotic conditions and precipitated in the same physical-chemical system.It is also similar to the?³⁴S value of typical hydrothermal deposits?Luziyuan,Jinchanghe,Shuitoushan,Xiyi,Fangyangshan?in Baoshan block.A comprehensive analysis of the?³⁴S change interval in the study area revealed that S mainly originated from the seawater sulfur during the same period;the conditions for the occurrence of TSR and BSR and the effect on the?³⁴S fractionation.It is believed that the evolution of sulfate is closely related to the TSR model.Transported under high temperature conditions,leaching,extracting and activating the sulfur produced in the thermochemical reduction reaction of the Silurian-rich crystalline limestone rich in sulfate;?3?Pb isotope,the projection shows that it is derived from the upper crust.The absolute age reflects that the ore lead was formed during the transition period between the exchange of the Middle Silurian?S₂?and the early Devonian,which is consistent with the age of the ore-bearing horizon,combined with macro-geological inference,indicating that the mineral source is the same period?syngeneic?source layer,And may be contaminated by mantle-derived materials;?4?Sr isotope,with obvious high radiogenic strontium,is probably formed by the selective leaching of hot water on the clastic rocks in ore-bearing formations.At the same time,the average value of the Sr isotope ratio is 0.71878,indicating that the sulfide mineralization material originates from the mixing of shell sources.5.Comprehensive isotope data and previous research results,the metallogenic mechanism of the Mengnuo zinc deposit has brought deep magma emplacement to the mineralization structure,providing minerals and heat energy for deep circulation atmospheric precipitation,atmospheric precipitation and magmatic ore-bearing heat The ore-forming fluid mixed with fluid extracts the minerals in the basement layer under the action of the fold-fracture-interlayer fracture zone and the fissure structure system,and unloads and deposits the deposits in favorable geology and structural parts.The deposit has the characteristics of low temperature and post-genetic ore.It is speculated that the Mengnuo lead-zinc deposit is MVT type.