Geological-Geochemical Characteristics And Prospecting Significance Of Gold Deposits In Xixia-Tongbai District,Western Henan

The Qinling-Dabie orogenic belt is one of the most important polymetallic metallogenic belts in China.But affected by the thinning/destruction of the lithosphere of the North China Craton,the gold deposits in Henan Province are concentrated in the Xiaoqinling area.Xixia-Tongbai area in western Henan,located at the center of the Qinling-Dabie orogenic belt in central China.The area is not only in the evolution of Qinling-Dabie orogenic belt,but also involved in the extension process of North China Craton lithosphere.The complex geological background and tectonomagmatic activities provide superior conditions for metal mineralization.In recent years,great progress has been made in gold prospecting in the East Qinling-Dabie region,and phased breakthroughs have been made in the prospecting of many gold deposits(points).The Laowan gold deposit in Tongbai is a typical gold deposit in the area at the eastern end of the region.At present,the deposit has controlled resources of nearly 150t and estimated reserves of 208t.It is the largest gold deposit discovered so far in Henan Province,but the degree of exploration is high and the degree of research is low.The divergence on metallogenic mechanism,material source and occurrence form of gold directly affect the potential prospecting in deep and surrounding areas.The Yindongpo gold deposit in Tongbai also has similar problems.There are many metal deposits distributed along Zhuyangguan-Xiaguan fault in Xixia-Neixiang area of East Qinling,and the research degree of deposits is relatively weak.As one of the representative deposits in Zhu-Xia fault zone,the research degree of Henanzhuang Gold Deposit and Xingshuping gold deposit is much lower than that of several gold deposits in Tongbai area.There is no specific conclusion on the source of ore-forming materials,ore-forming fluid,the genesis of the deposit and the relationship between them,which seriously restricts the prospecting work.Moreover,Xixia-Neixiang area and Tongbai area are separated by Nanyang Basin,and most prospecting and exploration work has not been connected carry out.The two regions are located in the middle of the Qinling-Dabie orogenic belt,and the regional geological background and structural conditions are similar.Therefore,this research takes the two regions as an overall study area,and selects four typical gold deposits(Tongbai Laowan gold deposit,Tongbai Yindongpo gold deposit,Xixia Henanzhuang Gold Deposit and Neixiang Xingshuping gold deposit)as the research object.On the basis of detailed field geological investigation,using mineralogy,Trace-element geochemistry,fluid inclusion research,in-situ analysis of gold bearing mineral micro areas,isotope geochemistry and other technical methods are used to detect the geological characteristics,special mineral genesis,enrichment mechanism of ore-forming elements,source of ore-forming fluid and ore-forming material and metallogenic process of four gold deposits,and to explore the evolutionary relationship between gold mineralization and regional tectonic magmatic mineralization.Based on the above understanding,the key ore controlling factors are screened and evaluated,which provides reference information for the deployment of ore prospecting in the study area.The main understanding obtained in this thesis is as follows:(1)Tellurides were widespread in the Laowan gold deposit,consisting of petzite,calaverite,tellurobismuthite,tetradymite,volynskite,and hessite.The vertical zonation of different telluride combinations indicates that mineral distribution shows the vertical zoning characteristics of upper Ag and lower Bi.From 250°C to 200°C,logf Te₂ and logf S₂decreased from(-13.0?-8.3)and(-14.7?-8.6)to(-15.2?-11.2)and(-16.7?-10.5),respectively.Temperature,S and Te fugacity were the conditions controlling variations in the telluride combination.(2)Five types of pyrite(Py1,Py2,Py3,Py4,Py5)were identified in Laowan gold deposit.Pyrite contains As,but Au has little correlation with As.Py1 and Py2 are poor in Au,while Py3 and Py4 are rich in Au,Ag,Te and Bi.There is a significant positive correlation between Au and Ag,Te,Bi.The trace element data show that there is a positive correlation between Au and Te under the condition of high tellurium fugacity,and the enrichment of Au was unrelated to As.Te is an important scavenger of Au,the effect of As is not obvious.Visible gold mostly occurs in high fineness fissure gold,while invisible gold mainly occurs in pyrite in the form of micro Au-Ag-Te-Bi mineral inclusions.Au and Te-Bi minerals migrate,enrich and precipitate in the form of molten particulate solid solution.Enrichment of metallogenic materials indicate the ore-forming fluids and metals of the Laowangold deposit stemmed directly from the regional mantle-derived magmatic system,which could have provided materials,sufficient heat energy,volatiles,and components for the gold mineralisation.The consistent characteristics of C-H-O-S-Pb isotopic composition show that the ore-forming fluid and material of Laowan gold deposit come from mantle derived magmatic hydrothermal solution.There is the mixing of atmospheric precipitation and crust derived materials in the late stage of mineralization.The role of Laowan granite and Guishanyan formation on mineralization is not obvious.(3)Three types of pyrite were identified in Yindongpo gold deposit,two of which are related to mineralization,and there is a positive correlation between Au and As in auriferous pyrites.Visible gold mostly occurs in the form of fissure gold,while invisible gold occurs in pyrite in the form of micro inclusion and lattice gold.The characteristics of trace element data show that pyrite is of magmatic hydrothermal origin,combined with the characteristics of in-situ sulfur isotope,it is proved that magmatism has an impact on mineralization.The early ore bearing calcite is selected and the C-O isotopes are used to analyse that the ore-forming fluid has the characteristics of magmatic water source.The C-H-O-S-Pb isotopic data show that the ore-forming fluid of Yindongpo gold deposit comes from the mixing of magmatic water and metamorphic water.The ore-forming material is provided by the mixed magma of crust and mantle and the strata of Waitoushan formation of Erlangping group.The role of intrusive rock(Taoyuan granite and Liangwan granite)is not obvious,there may be concealed rock mass.(4)The Henanzhuang gold deposit is significantly controlled by structure,and the ore body occurs in the fracture zone between fault layers and the contact zone between stratum and intrusive rock.Two types of pyrite were identified,and there was a positive correlation between Au and As in auriferous pyrites.Visible gold mostly occurs independently in the fissure of gangue minerals in the form of fissure gold,mostly electrum.A small amount of invisible gold occurs in pyrite in the form of micro inclusions and lattice gold.The widespread of pyrrhotite in ore sulfide indicates the reduction property of low oxygen fugacity of ore-forming fluid.The characteristics of trace element data show that pyrite is of magmatic hydrothermal origin,and the metallogenic environment is poor in Zn and Pb elements.Three types of inclusions are developed in the ore-forming fluid.The early,middle and late homogenization temperatures are concentrated at 290?310°C,270?290°C and 170?200°C,respectively;the salinity is9.14?12.73 wt%,1.40?12.13 wt%and 0.40?10.10 wt%,respectively;the homogenization temperatures of the three stages are 300°C,280°C and 180°C,respectively.The gas phase composition of ore-forming fluid is mainly CO₂,CH₄,SO₂,N₂and H₂S,of which the characteristic peak of CH₄ is much higher than that of other gases,indicating that the fluid is a deep source reducing fluid.The C-H-O-S-Pb isotopic data show that the ore-forming fluid of Henanzhuang gold deposit comes from deep magmatic water mixed with stratigraphic carbon and sulfur sources;the source of ore-forming material is provided by deep magma and Yanlinggou formation of Qinling group.It has no obvious relationship with the known Yanshanian granite in North Qinling and Erlangping granite,and there may be concealed rock mass.(5)The Xingshuping gold deposit is significantly controlled by structure,and the ore body occurs in the interlayer fault in the contact zone between intrusive rock and stratum.Two types of pyrite were identified.There was a positive correlation between Au and As in auriferous pyrites,and chalcopyrite and sphalerite also had a certain gold bearing property.Visible gold mostly coexists with chalcopyrite,sphalerite and galena in the form of fissure gold,or occurs between fissures.The fineness of gold varies widely,and native gold,electrum,kustelite and argentite have been found.Invisible gold occurs in pyrite and chalcopyrite in the form of micro inclusions.Trace element data show that pyrite is of magmatic hydrothermal origin and has strong water rock reaction.The metallogenic environment is rich in Ag,Pb and Zn elements.Three types of inclusions are developed in the ore-forming fluid.The early,middle and late homogenization temperatures are concentrated at 310?350°C,260?300°C and 180?200°C,respectively;The salinity is8.92?12.93 wt%,1.34?10.99 wt%and 0.31?9.23 wt%,respectively;the homogenization temperatures of the three stages are 330°C,280°C and 190°C,respectively.The gas phase composition of ore-forming fluid is mainly CO₂,CH₄,SO₂,H₂Sand C₃H₈,indicating that the fluid is also a deep source reducing fluid.The C-H-O-S-Pb isotopic data show that the ore-forming fluid of Xingshuping gold deposit comes from deep-source magmatic water,and the ore-forming material source may be jointly provided by deep-source magma and Wuduoshan granite,while the Yanlinggou formation of Qinling group provides less material.(6)The typical gold deposits in Zhu-Xia fault zone in Xixia-Neixiang area(Henanzhuang gold deposit and Xingshuping gold deposit)are derived from magmatic water,and the ore-forming materials are derived from the mixing of deep source and shallow layer,which reveals that the enrichment,migration and release of ore-forming materials are controlled by the deep.Combined with the conclusions of Laowan gold deposit and Yindongpo gold deposit,the metallogenic processes of the four gold deposits are closely related to magmatism.Magmatic hydrothermal solution provides the necessary conditions for the metallogenic process,such as metallogenic fluid,material source,heat energy and volatiles.The reason may be that the research area was affected by large-scale magmatism caused by lithospheric delamination and destruction of the North China Craton(NCC)in the early Cretaceous,the magmatic hydrothermal solution moved up along the regional deep fault and produced mineralization in different layers and sections.Therefore,Xixia-Neixiang-Tongbai area is in the same tectonic geological background,which is involved in the evolution of Qinling-Dabie orogenic belt and the extension of North China Craton(NCC)lithosphere.(7)The formation of magma related gold deposits in Xixia-Neixiang-Tongbai area of western Henan is closely related to the thinning and overall destruction of the lithosphere of the North China Craton(NCC)in the early Cretaceous.According to the work results of Laowan gold deposit in Tongbai area and the previous research on telluride of Gaozhuang gold deposit in Xixia area,it is proved that mantle derived magmatism in Xixia-Neixiang-Tongbai area can also affect the gold mineralization process,it extends the influence range of lithospheric thinning of the North China Craton(NCC)in the early Cretaceous.The gold deposits related to magmatism and affected by deep faults in the East Qinling-Dabie orogenic belt are the regional geological response to this tectonic magmatism.At the same time,it provides support for comprehensively considering the early Cretaceous magmatism and mineralization of the North China Craton(NCC)and the mineralization of the Qinling-Dabie orogenic belt as a whole.(8)The existence of faults leads to the upward movement of mantle-derived magma along the fault channel,and the gold content of gold bearing pyrite affected by mantle-derived magma is many orders of magnitude higher than that of other pyrite bearing pyrite.The NWW faults control the evolution of regional tectonic-magmatic-mineralization,and the development intensity of the deep faults directly affects the scale of ore body occurrence.The large-scale magmatic activity in the early Cretaceous led to large-scale mineralization in the southern margin of the North China Craton and the East Qinling-Dabie orogenic belt,and most of the deposits were closely related to magmatism.Most ore deposits are concentrated in some strata.These strata or rocks are dense and hard,and are prone to fracture cambium fracture zone,which is conducive to ore fluid migration.Or high carbon content,which is conducive to the adsorption of ore-forming metal elements in the ore liquid,so that the enrichment and precipitation mineralization.The local fold structure and the existence of brittle-ductile shear zone provide migration channel and ore-hosting space for ore-forming hydrothermal.