Gold Mineralization And Comprehensive Information Prospecting Prediction In Balong-Gouli Area,East Kunlun Orogen

The Balong-Gouli area is located in the eastern of the East Kunlun Orogenic Belt.Affected by the two phases of Tethys evolution,the Caledonian and Indosinian intrusive rocks are widely distributed in the area,and are controlled by the Middle Kunlun Fault and its secondary faults,providing a superior metallogenic geological background for gold polymetallic mineralization.The Gouli area is an important gold polymetallic ore concentration area in the East Kunlun orogenic belt.In recent years,new deposits have been discovered and reported,and the amount of gold metal currently controlled exceeds125 tons.The Balong area is located about 40km west of the Gouli area.Although the metallogenic geological background is similar to that of the Gouli area,there is a lack of in-depth research on the genesis and patterns of gold deposits,and there have been no breakthroughs in prospecting for many years.Therefore,this article takes the Balong gold deposit as the research object and based on data collection and fieldwork,using various research methods such as petrography,petrogeochemistry,ore deposit geochemistry,isotope geochemistry,etc.,analyze the petrogenesis and tectonic background of the Middle-Late Triassic intrusive rocks in the study area,summarize the evolution process of the Paleo-Tethys Ocean,and provide a basis for the study of gold mineralization.Rb-Sr isotope chronology,fluid inclusion analysis,H-O-S-Pb isotope geochemistry,sulfide LA-ICP-MS trace elements,and in-situ S isotope analysis were carried out to explore the mineralizing fluids and mineralizing material sources of the Balong gold deposits,and to discuss the genesis and mineralization mode of gold deposits.Based on the above research,analyze the key ore-controlling factors of gold deposits in the Balong-Gouli area,and construct a conceptual model of comprehensive prospecting for gold polymetallic deposits in the Balong-Gouli area.Taking the Gouli area as the model area,extract geophysical and remote favorable prospecting information,construct a comprehensive prospecting model,apply the model to the Balong area and carry out mineralization prediction,and provide a reference for subsequent prospecting work.The main achievements and understandings of the thesis are as follows:(1)The zircon U-Pb ages of granodiorite,quartz diorite,and diorite in the Balong area are 238.2 Ma,229.5 Ma,and 223.0 Ma,respectively.The above three intrusions have similar main and trace characteristics.Sr-Nd-Hf isotopic composition.The high K2O content and low Rittman Index indicate that they are all high K Calc-alkaline rocks,and the high Al2O3 content indicates that they are all quasi-aluminous.All samples showed obvious fractionation of light rare earth elements,and relatively weak fractionation of heavy rare earth elements.And they have the characteristics of enriching the large ion lithophile elements(Rb,Th,U,and K),and significantly depleting the high field strength elements(Nb,P,and Ti).The three above-mentioned rocks in the Balong area are all I-type granites.The quartz diorite has the characteristics of high Sr and low Y,which can be judged as Adakite rocks.The whole-rock(⁸⁷Sr/⁸⁶Sr)i values(0.70819?0.70896)and?_Nd(t)values(-6.05?-4.79)are more concentrated,and the zircon?_Hf(t)values are-5.2?-1.1.The Middle-Late Triassic pluton in the Balong area has a similar source of magma,which mainly originated from the partial melting of the lower crust in the Mesoproterozoic.The mantle source was affected by the mantle-derived basaltic magma,resulting in crust-mantle magma mixing.The magma rapidly rises and cools,without experiencing strong separation and crystallization.Combining the analysis of the tectonic background and previous studies,the granodiorite in the Balong area was formed in the subduction stage of the Paleo-Tethys Ocean.The slab and lithospheric mantle melted during the subduction process,forming the upwelling and under-invasion of mafic magma.The lower crust was partially melted and mixed with magma.At the beginning of the post-collision phase,the thickening of the lower crust during the subduction process caused the asthenospheric material to rise up,and part of the asthenospheric material was in contact with the lower crust and mixed with magma to form Balong quartz diorite intrusions with deep diagenesis depth and characteristics of adakitic rocks.The continuous upwelling of asthenospheric materials also induces partial melting of the relatively shallow lower crust,resulting in the formation of the Balong diorite with the characteristics of ordinary I-type granite.The study of the petrogenesis and tectonic background of the intermediate-acid rock bodies in the Balong area provides more sufficient evidence for the discussion of the transition time of the Paleo-Tethys Ocean.This article believes that the subduction of the Paleo-Tethys Ocean occurred from 278 to238 Ma,after a brief syn-collision.After the stage,it enters the post-collision stage at about 230 Ma.(2)The Balong gold deposit was developed in the Indosinian intermediate-acid quartz diorite.The structure of the mining area is mainly composed of nearly east-west,northwest-west,and northwest-trending faults.Most of the ore bodies are located in the fractured alteration zone,and the orientation is mainly NWW.The ore is mainly disseminated,vein-shaped,massive,and breccia-shaped.The main structure of ore minerals is euhedral-semi-automorphic-heteromorphic granular structure,package structure,interstitial structure,crushed structure,metasomatic dissolution structure,inclusion Structure,etc.Common metal minerals include pyrite,arsenopyrite and a small amount of sphalerite,chalcopyrite,galena and natural gold.The wall rock alterations related to mineralization mainly include sericitization,silicification,and carbonation.Salinization,pyrite mineralization,jarosite,kaolinization.According to the type of ore and the interspersed sequence of veins,the metallogenesis of the Balong gold deposit can be divided into two metallogenic periods:the hydrothermal metallogenic period and the epigenetic period.The hydrothermal metallogenic period can be divided into the quartz-pyrite period,Quartz-pyrite arsenopyrite stage,quartz-polymetallic sulfide stage,quartz-calcite stage.By comparing with the Golongwa gold deposit and Asha gold deposit,which are hosted in stratigraphic and rock bodies,respectively.It is found that both deposits are strictly controlled by tectonics,among which the deposit in stratigraphy is mainly controlled by near EW faults,and arsenopyrite is almost absent in ore minerals;the deposit in rock body is controlled by near NE and near NW faults,and arsenopyrite is an important ore mineral.(3)Ore deposit geochemistry studies were conducted on the Balong gold deposit in terms of metallogenic age,metallogenic fluids,gold precipitation mechanism,and the source of mineralized material.The pyrite Rb-Sr isotope chronology shows that the metallogenic time of the Balong gold deposit was 227 Ma.The tectonic setting of this period was the post-collision extension stage of the Paleo-Tethys ocean subduction.The extensional tectonic background provided sufficient space for mineralization.The magmatic activity of the Late Triassic also provided material,fluid and heat sources for mineralization.The characteristics of fluid inclusions and H-O isotopes show that the ore-forming fluid is magmatic water,which is added by atmospheric precipitation in the later period.In the main mineralization period,two-phase inclusions with different gas-liquid ratios and three-phase inclusions containing CO2 can be seen.Different types of inclusions at the same stage have similar uniform temperatures,indicating the occurrence of fluid immiscibility.The ore-forming fluid has the characteristics of medium-low temperature,medium-low salinity and relatively low density.Due to the addition of atmospheric precipitation,the temperature and salinity of the ore-forming fluid in the fourth ore-forming stage decreased,and the density increased slightly.The pyrite in the four metallogenic stages can be divided into 9 different generations,among which there are 2 generations each of the quartz-pyrite stage,the quartz-pyrite arsenopyrite stage,and the polymetallic sulfide stage.The quartz-carbonate stage Stage three generations.Electron probe analysis shows that the edges of pyrite in all mineralization stages have higher As and lower S than the core,and As and S have a relatively obvious negative correlation.Micro-analysis of trace elements shows that most of the Au elements exist in pyrite in the form of solid solutions.Pb elements have a good positive correlation with Bi and Ag elements,which may indicate that there is a certain degree of substitution relationship between Ag,Bi elements and Pb elements.Almost all pyrites have rings of specific elements such as As and Au.The single mineral sulfur isotope?³⁴S value is 0.7?4.1‰,showing the characteristics of magmatic sulfur.The results of in-situ sulfur isotope analysis showed that the sulfur isotope distribution of pyrite in each mineralization stage was relatively stable,and all showed that the internal sulfur isotope value of the pyrite grain was lower than the grain edge,and in the second to fourth metallogenic stages,the S isotope content The overall value has an upward trend.The lead isotope analysis results of single minerals of pyrite are similar to rock lead,and its distribution characteristics indicate that the source of lead is related to the deep mantle,and it may be contaminated by crust-derived lead during the mineralization process.Taken together,the Au in the ore-forming fluid migrates in the form of gold-sulfur complexes,and fluid immiscibility occurs during the migration process,which leads to the precipitation of Au.The ore-forming material mainly comes from the crust-mantle mixed magma.During the formation of pyrite,due to the continuous water-rock reaction with the surrounding rock,boiling effect and intermittent changes in structure,the pyrite in almost all ore-forming stages is homogeneous.It has Au-As-rich zoning,and foreign Au-As-rich fluids are added during the mineralization process,which may be derived from deep-source magma extracted from metamorphic rock specific elements.(4)The temporal and spatial distribution and metallogenic process of gold deposits in the Balong-Gouli area are closely related to tectonic magmatism.In terms of space,almost all gold deposits are distributed on the north side of the Middle Kunlun Fault.In terms of time,the age of gold deposits is consistent with the intermediate-acid magmatic rocks in the area,and belongs to the post-collision stage of the Paleo-Tethys Ocean.In terms of ore-forming fluids and material sources,the ore-forming fluids and materials of the Balong gold deposit are all derived from multiple injections of crust-mantle mixed magma.Under the background of the subduction of the Paleo-Tethys Ocean,the Middle Kunlun Fault was activated and generated a large number of secondary faults,forming a structural framework before metallogenesis,and the expansion of the fault structure in the post-collision extension stage provided a guide for the upwelling of ore-forming fluids.Mine and ore-holding space.After the ore-forming fluid enters the ore-containing space,fluid immiscibility occurs due to changes in temperature and pressure,and gold precipitates and forms ore.(5)Summarized the main ore-controlling factors in the Balong-Gouli area.The spatial distribution of gold polymetallic deposits in the study area is strictly controlled by the tertiary structure of the area.Most of the gold polymetallic deposits are distributed to the north of the Middle Kunlun Fault.The deposits are distributed near the field-scale structure,and the ore bodies are produced in the ore fields.In the secondary fault of the scale structure.Most of the mineral deposits are located in the Caledonian and Indosinian intrusive rocks or near the contact zone with the strata,and the magmatic rocks and the deposits have a contemporaneous and genetic relationship.The metallogenic geological backgrounds of Balong and Gouli are similar.In order to promote new breakthroughs in prospecting in Balong,under the guidance of similar analogy theory,this thesis extracts the favorable information of mineralization in Gouli and constructs a comprehensive prospecting for the area.The model is applied to the Balong area,and the beneficial information of the Balong area is extracted and the model is applied.It delineates 3 first-level favorable mineralization areas,7 second-level favorable mineralization areas,and 5third-level mineralization areas.