The geological structures on both banks of the Yarlung Zangbo river and the Niyang river are active,and landslides occur frequently.The landslide susceptibility assessment can effectively reduce the damage to hu-man life and property caused by disasters.This paper studies the performances of Weighted Random Forests,XGBoost and LightGBM algorithms based on Gini coefficient in landslide susceptibility.Select 188 landslide samples and 7 influencing factors,and use the 50-fold cross-validation method to train the model.During the training process,the feature selection algorithm is considered at the same time,and the Bayesian method is used to optimize the hyperparameters.Analysis of forecast results at the level.The results show that landslide is most likely to occur within the elevation of 32～1544 m and 2722～3752 m,the gradient of 30°～40°,and the dis-tance of 200 m from the fault zone,river and road.The extremely high and high landslide prone areas account for 12.14%and 12.41%respectively,and the low and extremely low landslide prone areas account for 26.47%and 29.55%respectively.More than half of the areas in Nyingchi prefecture are not prone to landslide disasters.Among all models,LightGBM model performs best,with AUC value of 0.8432,accuracy of 0.8531,and F1 score of 0.8345.Damu township and Bangxin township in Motuo county,Danniang,Lilong,Zhaxi Raodeng township in Linzhi county,Long village in Lang county,and Jiangda township in Gongbujiangda county are po-sitioned in extraordinarily high-risk areas,with a excessive likelihood of landslides.Corresponding prevention and control measures should be taken in these areas.
As a major component of the western segment of the Central Orogenic System, the East Kunlun Orogeny is characterized by the largely exposed of Triassic magmatic rocks. Based on the collected zircon U–Pb geochronological data of 96 Triassic magmatic rocks in the eastern segment of the East Kunlun orogeny, the Triassic magmatic activity is limited to 212～252 Ma, and can be further divided into three stages: early– (238～252 Ma), middle– (226～238 Ma) and late–stage (212～226 Ma). Among them, the peak magmatic period is the early stage (238～252 Ma). The statistical results of 106 Nd isotopes of Triassic magmatite in the eastern segment of the East Kunlun Orogeny show that εNd(t) values range from –9.4 to –1.7, mainly concentrated between –6.5 and –3.0, and the Nd model ages (TDM(Nd)) range from 0.72 to 1.88 Ga, mainly concentrated between 1.00 and 1.80 Ga. The statistical results of 41 Hf isotopes (whole rock, zircon) of Triassic magmatite show that εHf(t) values vary greatly (–8.4 to +12.4), mainly concentrated between –4.5 and +2.0, and the crustal model ages (TDMC(Hf)) range from 0.49 to 1.80 Ga, mainly concentrated between 1.15 and 1.55 Ga. Overall, the Triassic magmatic rocks are mainly derived from the reworking of Mesoproterozoic crustal materials, with minor involvement of juvenile crust (＜ 1.0 Ga) and Paleoproterozoic crustal materials. From the early stage (237～250 Ma) to middle stage (226～238 Ma) and then to late stage (212～226 Ma), the Nd–Hf isotopic parameters seems exhibit a certain evolutionary trend. In the early stage especially in the early Triassic, the εNd(t) values are higher, and positive εHf(t) values occupy a large proportion, indicating the presence of more juvenile material in the source. In the middle stage, lower εNd(t) values and negative εHf(t) values dominate the major proportion, and Hf model ages (TDMC(Hf)) reveals the presence of Paleoproterozoic crustal material. In the late stage, the Nd–Hf model ages reveal an increase in older crustal source components. This magmatic source evolutionary trend is consistent with the tectonic evolution setting of subduction to collision and then to post–collision in the eastern segment of the East Kunlun orogeny in Triassic period.
Aqiyin gold deposit is a newly discovered gold deposit in the western section of East Kunlun in recent years.In order to explore the genesis of the deposit, the characteristics of ore−forming fluid and the source of ore−forming materials, and establish the metallogenic model, the fluid inclusion analysis of pyrite bearing quartz fine mesh vein type gold ore in the metallogenic period was carried out, and the isotopic analysis of fluid H−O, pyrite and arsenopyrite S−Pb in quartz vein was carried out. The results show that the homogenization temperature of inclusions is 167～356.9℃, the salinity is mainly concentrated between 3.21～9.99 wt% NaCleqv, and the density is 0.65～0.94 g/cm3. The ore-forming fluid has the characteristics of medium temperature, low salinity and low density. The fluid inclusions in ore bearing quartz vein have δDv-smow values of −90.3‰～−98.7‰, δ18O of 9.4‰～11.3‰ and δ34S of 11.6 ‰～13.9 ‰. The Pb isotopes of Au−bearing pyrite vary from 38.067 to 38.651, from 15.598 to 15.681, and from 18.122 to 18.533 for 208Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb ratios, respectively. The values of μ are from 9.49 to 9.61. Combined with the geological background of the Aqiyin gold deposit, the author hold that the ore–bearing hydrothermal fluid is a mixture of metamorphic water and meteoric water, sulfur is mainly derived from dynamic metamorphism, and lead shows the characteristics of lead source in orogenic belt. The genetic type is orogenic (tectonic altered rock type) gold deposit.
Ordos Basin is rich in geothermal energy at moderate and low temperature. By studying the occurrence state of geothermal resources in Yanchang oil and gas area, it is found that there are mainly two sets of thermal reservoirs: Cretaceous clastic rocks in the west and Carboniferous and Jurassic clastic rocks in the east; The thermal conductivity of rock is closely related to the degree of diagenesis and porosity of formation rock; The geothermal gradient is 2.73–3.50 ℃/100 m, which is higher in the north and lower in the south; The earth heat flow value is 57.28–86.18 mW/m2, with obvious east–west distribution characteristics. The comprehensive analysis shows that the geothermal resources in the eastern part of the region are better than those in the western part, and can be divided into three types: shallow low temperature favorable area, middle–low temperature favorable area and middle-deep medium temperature favorable area. Combined with the exploitation and utilization examples of geothermal resources in oil fields, it is considered that the transformation and utilization of abandoned Wells in these favorable areas can reduce the cost of geothermal development projects and realize the stepwise utilization of geothermal resources in geothermal power generation, industrial utilization and three–production and aquaculture, it is expected to establish an energy internet framework of "Source network load storage integration".
The subduction−collision (accretion)−post−collision stages in the ocean−continent transition process have different magmatisms, among which the slab subduction and lithosphere delamination−thinning mechanisms have received special attention. The East Kunlun orogenic belt is located in the northern part of the Qinghai−Tibet Plateau, and is an important part of the Qin−Qi−Kun central orogenic belt, which has experienced the transformation process of the Proto−Tethys Ocean and Continent in the Early Paleozoic. Based on the geochronology, whole−rock geochemistry and Sr−Nd−Hf isotope studies of the Paleozoic granites in the Dulan area, eastern Kunlun, this paper suggests that the Langmuri Middle Silurian (429±4 Ma) granites were formed in the subduction stage of the oceanic crust. It has the property of adakitic island arc magma, which is related to the partial melting of oceanic crust under the mechanism of thermal subduction. The Xiwanggou and Harizha Early Devonian (416 ~ 403 Ma) granites were formed in the post−collision stage, showing the characteristics of I−type and A−type granites, respectively, which are related to the partial melting of the young lower crust and thinning of the lithosphere. The comprehensive regional Paleozoic granite geochemical data indicate that the difference of magmatic rocks in the east and west of East Kunlun may be caused by ocean ridge subduction.
The Cambrian System in the Ordos basin is a set of marine sedimentary formations dominated by carbonate rocks and interbedded with a small amount of clastic rocks. In recent years, the Cambrian System in this area has been considered to have great exploration potential, but so far no large reservoirs have been discovered. Previous research has mainly focused on the eastern, western, and southern parts, while research on the central part has been severely lacking, which has hindered breakthroughs in oil and gas exploration in the region. In this study, single–well divisions were conducted on 56 drill cores and 13 outcrop sections, and based on the characteristics of 120 thin sections and rock combinations, two sedimentary facies were identified: slope facies and platform facies. Based on this, inter–well comparisons were carried out, and two cross–well sections running through the east-west and north-south of the basin were delineated with the center of the basin as the focus, to explore the sedimentary thickness and facies changes in different periods. The study suggests that the Cambrian in the Ordos basin was formed under a transgression background, and after the Xijian period, seawater advanced from the western and southern parts of the basin towards the interior. By the Zhangxia period, the sea had reached its peak and most of the basin was submerged by seawater, leaving only sporadic low–lying ancient land. During the sedimentation period of the Sanshanzi Formation, the sea transgressed to regress. This study also reconstructed the paleogeographic pattern of “one uplift and four depressions” and restored the tectonic and sedimentary evolution process of the Cambrian period in the central part of the basin.
Sanyu area is located in the Yawan−Daqiao gold−antimony ore belt of Gansu Province, which belongs to the national integrated exploration, and has the metallogenic conditions and prospecting potential of gold, antimony, copper and other polymetals. In order to further improve the geological prospecting work, 1∶25000 soil geochemical survey was carried out in the research area. Based on the original data of Au, Ag, Cu, Pb, Zn, Ni, Sb, Bi and Hg elements, fractal characteristics, coefficient of variation, coefficient of concentration and other methods, The basic data of 9 elements were statistically analyzed, and the spatial enrichment status and distribution trend of elements were analyzed. The results showed that Pb, Zn, Sb and Au had certain prospecting indexes, SPSS 25 was used for clustering and factor analysis of 9 elements, and three combination elements were divided into F1 (Ag−Pb−Zn−Sb), F2 (Au−Cu−Ni−Bi) and F3 (Hg). The lower limit of element combination anomaly was obtained by contrast anomaly method, and according to software Sufer. The factor score anomaly map of 13 combination elements was made, and a total of 4 prospecting prospects were delineated, which provided a basis for further geological prospecting and reduction of prospective areas.
The influence and control factors of the regional geomorphic patterns, such as the plane shape and the flow directions of the mainstream and tributaries of the river system, in the middle reaches of the Yellow River, and the effects of the regional geomorphic patterns on soil and water loss, ecological and economic development, have long been one of the hot debates that have received much attention. In this study, we select the Huangfuchuan, Gushanchuan and Zhujiachuan–Xianchuan drainage in the northern reaches of the middle Yellow River as the research objects. Based on high–precision DEM extraction of the drainage system, statistics of flow direction, as well as systematic investigation and measurement of the structural styles and attitudes of the joints and/or faults in bedrock and loess, combined with the tectonic background of the study area since the Cenozoic, it is proposed that the series of vertical joints and faults formed by regional extension in the northern reaches of the middle Yellow River are key factors that influence or control the development and spreading characteristics of the drainage patterns.
Zircon is widespread and compositionally stable in intermediate–acid magmatic rocks and is resistant to later hydrothermal activities. Therefore, its composition can more accurately record information about mineralizing magmas. Among them, zircon features (such as Ce4+/Ce3+, Ce/Ce*, Eu/Eu*, and Ce/Nd) have been widely used in evaluating the mineralization potential of granitoids, because they have been found to reflect ore−forming information, such as magmatic oxygen fugacity and water content. However, further studies have revealed that the universality of these geochemical indicators has been questioned. In addition, the proposed methods for discriminating mineralization capacity are all based on the current “limited understanding” of mineralized rocks, and considering the complexity of the mineralization process, much geochemical information reflecting the capacity of magmatic mineralization may not have been revealed yet. Therefore, in the paper, taking the Qimantagh mineralized zone of the East Kunlun as an example, and with the help of one of the most widely used machine learning algorithms today (Support Vector Machine), the authors trained machine learning on zircon data from porphyry skarn Cu−Fe−Pb−Zn mineralized rock bodies in the region and zircon data from non−mineralized rock bodies around the world, and the aim is to excavate zircon trace element signatures that reflect magmatic mineralization capacity, so as to construct a new discriminative schema for granite mineralization potential. The results of the model training show that among 21 common zircon trace element features, five element features, Gd, Dy, Yb, Y and Tm are the most important for identifying the magmatic mineralization ability; based on this, 10 binary discriminant diagrams are established in this paper, and their accuracy rates in identifying mineralized and non−mineralized rock bodies are close to 1. The present study show that the use of machine learning methods and geological big data can be used to explore the potential of granite mineralization which is difficult to study with traditional research methods. The study demonstrates that machine learning methods and geological big data can be used to mine new geochemical indicators and diagrams that are difficult to discover by traditional research methods, which is of great significance to deeply understand the genesis of mineral deposits and guide the prospecting and exploration of minerals.
The continental sedimentary strata of the Jiulongshan Formation in the Xuanhua basin in Northwest Hebei are well developed, but the age of the strata is lacking in evidence from fossils and isotope dating data. In the Yangjiaying−Xiangshuipu area of the study area, rhyolitic tuff interlayers develop in the middle and lower parts of the Jiulongshan Formation. In order to accurately determine the age and formation environment of the Jiulongshan Formation in the Xuanhua Basin, the author collected zircon U−Pb isotope dating samples from the rhyolitic tuff and rock geochemical analysis samples. The 206Pb/238U weighted average age (LA−ICP−MS method) of (161.9±0.8) Ma was obtained, which is the early Late Jurassic. The petrochemical characteristics show that the rhyolitic tuff is a high−silicon, high−potassium calc−alkaline peraluminous rock; the distribution pattern curve of rare earth elements is right−dipping, with strong enrichment of light rare earths and no obvious negative Eu anomaly; the enrichment of large ions is lithophilic elements (Rb, K, Th, U), depleted Sr and high field strength elements (Nb, Ti). The geochemical characteristics of the rocks show that it was formed in a compressional tectonic setting. The zircon Hf isotope εHf(t) value is between −33.79～−2.71, and the second−stage depletion model age (tDM2) is between 1179～3323 Ma, indicating that the rhyolitic tuff magma is mostly Paleoproterozoic−Mesoproterozoic thickened lower crust Melted to form. According to comprehensive analysis, the Jiulongshan Formation in Xuanhua basin was formed in the late Middle Jurassic−early Late Jurassic compressional structural setting. The research results provide new data for the study of the age attribution and formation environment of the Jiulongshan Formation.
The Daomuti intrusive rocks is located in the eastern section of the East Kunlun orogenic belt, and mainly includes monzogranite, granodiorite and diorite. In this paper, zircon U–Pb dating and petrogeochemical tests are performed on newly discovered diorite to determine its crystalline age and petrogenesis. Comprehensively analyse the petrogeochemical characteristics of monzogranite and granodiorite, and discuss the emplacement age, rock genesis and tectonic evolution of the Daomuti intrusive rocks. LA–ICP–MS zircon U–Pb dating analysis shows that the 206Pb/238U weighted average age of diorite is (244.6±1.8) Ma, and the crystallization age of the diorite is Early Triassic. The geochemical characteristics of the monzogranite and granodiorite show that the Ritman index is greater than 3.3 and has the characteristics of calcium alkalinity–high potassium calcium alkalinity; the aluminum saturation index A/CNK values are less than 1.1; the P2O5 content in the rocks is low, and its has a negative correlation with SiO2 content; It is enriched with LILE such as K, Rb, La, and loses HFSE such as Nb, Ta, Ti and P. The above characteristics indicate that the Daomuti intrusive rocks belongs to type I granite. Based on the research results of this paper, it can be considered that the Daomuti intrusive rocks is a volcanic arc granite, its formed by partial melting of the lower crust rocks, and the Animaqing Ocean subduction continued to the Early–Middle Triassic The mantle magma underplating during the subduction process is the heat source that causes the melting of the lower crust, and the mantle source magma is mixed into the Daomuti intrusive rocks’ magma evolution, and during the Daomuti intrusive rocks’ magma evolution occurred fractional crystallization.
The industrial value of the Xiarihamu giant Ni–Co sulfide deposit in the East Kunlun orogenic belt, is not only depends on the content of Co and Ni elements in the minerals, but also on the occurrence state and spatial distribution pattern of Co and Ni elements. In this study, Borehole samples were analyzed by TESCAN Integrated Mineral Analyzer . It was determined that Co and Ni elements occur as isolated minerals and sulfur-arsenic mineral compositions. In-situ analysis of major and trace element analysis of the metal minerals in the Xiarihamu Ni–Co deposit have been carried out. The contents of Co in the minerals from high to low are as follows: cobaltine ＞ maucherite, bravoite, pentlandite ＞ niccolite, magnetite ＞ pyrrhotite, chalcopyrite; the contents of Ni in the minerals from high to low are as follows: maucherite, niccolite＞ bismuthite, bravoite, pentlandite ＞ cobaltine ＞ magnetite, pyrrhotite and chalcopyrite. Pyrrhotite, pentlandite and chalcopyrite were chosen for LA–ICP–MS trace elements and elements mapping analysis, the Co and Ni were uniform in pentlandite and chalcopyrite in the single particle mineral scales, and there are no obvious changes observed in Co/Ni ratios, these indicating that hydrothermal process did not affect the Co and Ni contents of pentlandites and chalcopyrites. However, Ni is heterogeneous in pyrrhotite, and the Co/Ni ratios varies from 0.01 to 0.63, indicating that the pyrrhotite is more sensitive to hydrothermal processes. In situ major and trace element analysis show that the contents of Co and Ni in pentlandite are close to that of isolated Co–Ni minerals, and far exceeds that of pyrrhotites and chalcopyrites. Therefore, the ore containing pentlandite has the most potential for Co and Ni resource exploretion.
The exploitation of Ningdong coal base has become an important engine for industrial economic development in Ningxia. Surface subsidence, which caused by coal mining has become the main geological environmental problem in the area. This study monitored regional surface subsidence characteristics of Ningdong coal base by utilizing Differential Interferometry Synthetic Aperture Radar (DinSAR) and Sentinel-1A dataset from 2015 to 2019. The results indicated that the characteristics of subsidence vary widely in different regions and years, subsidence in the north is larger than that in the south, which maximum reached 0.13 m. In the past four years, the subsidence from 2015 to 2016 is most serious and however its from 2016 to 2017 is lest. During 2015～2019, the area with subsidence value more than 0.1 m were 578 km². The subsidence area is consistent with the mining activity area, which means that the surface subsidence is mainly caused by coal mining. Other slight surface subsidence, on the one hand, could caused by coherent distortion of radar image and be related to the surface deformation such as wind-sand erosion on the other hand. DinSAR technique has distinct advantage in monitoring large-scale land subsidence, but there is a loss of coherent phenomenon due to the long time baseline.
The exploration in the Tianming Mining Area, Anhua, Hunan, has uncovered the concealed mica−plagioclase lamprophyre. In order to study the relationship between the dike and mineralization, we conducted various studies including petrographic, LA−ICP−MS zircon U−Pb chronology, whole−rock major and trace elements and Sr−Nd isotope composition analyses on the mica-plagioclase lamprophyre. The results indicate that the mica−plagioclase lamprophyre underwent significant carbonate alteration. The diagenesis age is estimated to be no earlier than 104 Ma and may be a response to the Late Yanshanian tectonic−magmatic events in South China Block. The concordant ages of (418.79±1.57) Ma and (2506±14 )Ma document the events of Silurian arc−crust collision of the Yangtze plate and the Cathaysia island arc, and Archaean crustal accretion, respectively, indicating the crystal basement material source. The mica−plagioclase lamprophyre belongs to a high−K calcium−alkaline series with an enriched light rare−earth element (LREE) and depleted heavy rare−earth element (HREE), with Eu negative anomalies and Ce positive anomalies. The rock also has large ionic lithophile and high−field strength elements depleted and high compatible element content. Whole−rock εNd(t) values ranging from −8.28 to −7.61 suggest crust−mantle mixing. Our findings suggest that the mica−plagioclase lamprophyre was formed by mantle magma in the source area with residual hornblende, ilmenite, and/or rutile. It underwent fractional crystallization dominant of plagioclase, was mixed by crust, and finally intruded in near−EW faulting tectonics. Comparison of the Au and Sb contents of dikes in central Hunan, ore−bearing formation, and crust, implies that the dikes and antimony may have deep homology. These findings suggest that the Tianming deposit has antimony mineralization potential. Overall, the study highlights the complex geological processes that lead to the formation of mineral deposits. By using a multidisciplinary approach, it is able to unravel the complex history of the mica−plagioclase lamprophyre and its association with mineralization. These findings can provide valuable insights for future exploration activities in the region.
In order to protect the Qilitang geothermal hot spring in Weihai City, this paper discusses the elements of the Qilitang geothermal field, such as water source, heat source, geothermal field, heat accumulation model, and water and heat migration channel, through the methods of geothermal geological survey, geophysical exploration and geochemical exploration, and establishes the genetic conceptual model of the geothermal field and reveals its genetic mechanism. The research shows that: ① The chemical types of geothermal water are mainly SO4·HCO3−Ca·Na and HCO3−Na·Ca type water, and the water quality dynamics are relatively stable. ② The main source of hot water recharge is meteoric water, which circulates to about 2276 m underground along the Hengkou−Yanggezhuang deep fracture and is heated to about 114.39 ℃. At the intersection of the faults, springs emerge along the fracture zone. ③ The infiltrated groundwater continuously absorbs heat from surrounding rocks during its deep migration along the fault tectonic belt. The genetic type of hot spring in geothermal field is deep circulation−convection type. ④ Jiaodong hot spring geothermal fields such as Qilitang are controlled by faults. The area of geothermal anomaly is small and the scale of geothermal field is small. Although Jiaodong hot spring geothermal has good market prospects for development, exploitation must be controlled to avoid resource exhaustion and temperature drop of hot water caused by excessive exploitation. The research results have certain guiding significance for the development and utilization of geothermal resources in Weihai area.
The downstream area of the Nalingguole river is predominantly covered by Quaternary sediments. Several polymetallic ore deposits, primarily composed of iron, have been discovered in this region. However, the presence of sediment cover has increased the difficulty of prospecting activities. In this study, the author analysied of the distribution characteristics gravity and magnetic anomalies, and inferred the fault structure of the study area in the downstream structures of the Nalingguole river, focusing on 1∶50,000 aeromagnetic anomaly data and 1∶200,000 regional gravity data. Based on the relationship between strata, rock mass, gravity and magnetic field in the southern bedrock outcropping area, deduced and divided the distribution of strata and intrusive rocks under the overlying area. Moreover, the mineral occurrences are predominantly found near inferred fault lines, indicating a clear influence of fault control. Two prospective mining targets were identified, providing favorable evidence for future ore exploration and target selection in the (partially) covered areas surrounding the Qaidam basin.
The Qimantagh area of East Kunlun orogeninc belt is an important skarn–type polymetallic mineralization belt in Qinghai, and the Niukutou deposit is located in the central–western part of this area, which is one of the middle–large Pb–Zn skarn deposits in Qimantagh area. In view of the controversy about the diagenetic and metallogenic age and the source of the metal ore–forming materials of Niukutou ore district, the zircon and pyrite chronology has been studied by LA–ICP–MS and thermal surface ionization mass spectrometry Re–Os isotope testing technology in this paper. The results show that the ages of the ore-forming granite bodies at the bottom of the 10 line drill hole in the M1 ore block of Niukutou ore district are (362.2±2.7) Ma and (361.8±3.4) Ma respectively, and the Re–Os isochron age of the pyrite closely associated with the sphalerite in the main mineralization stage is (359.2±6.3) Ma. This shows that the diagenesis and mineralization age of the skarn Pb–Zn polymetallic deposit in Niukutou ore district are coupled at (362.2±2.7)～(359.2±6.3) Ma, which further indicates that the skarn Pb–Zn polymetallic deposit was formed in the late Devonian of Variscan. The initial 187OS/188Os of pyrite is 0.13±0.24, which indicates that the metal ore–forming materials of Niukutou Pb–Zn deposit are of crust mantle mixed source, and formed under the extensional background of collision–post collision in the tectonic magmatic cycle from Early Paleozoic to early Late Paleozoic at Late Devonian.
Magmatic nickel–cobalt sulfide deposits are the main source of nickel–cobalt resources in China, and the Jinchuan deposit is the main supplier of nickel–cobalt sulfide ores in China. However, with the rapid development of emerging industries and the advent of a low–carbon era, China’s dependence on the external supply of nickel–cobalt resources continues to rise, which is a serious threat. Deep exploration is the only way to increase the storage and production of nickel–cobalt resources. Based on the systematic study of the distribution patterns of the ore bodies of the Jinchuan magmatic sulfide deposit and the gravity, magnetic, and electrical data, a geological–geophysical three–dimensional model for the deep ore exploration was established. The ore–bearing evaluation indicators were summarized, and the possible locations of hidden ore bodies were inferred. This work supports the deep exploration of the Jinchuan magmatic nickel cobalt sulfide deposit and improves China’s self–supply capacity for nickel–cobalt resources.
The Tongchanggou skarn−porphyry Mo−Cu deposit, located in the northwest Yunnan Province, is one of the newly−discovered large molybdenum−copper deposits in the western margin of the Yangtze Block. Skarn is widely exposed in the Tongchanggou deposit and is the most important ore−bearing body in the deposit. In this paper, both EPMA and LA−ICP−MS technology have been used to analyze the major and trace element compositions and U−Pb isotopes of garnet grains from the Tongchanggou skarn. Based on microscopic observation, the garnet in the Tongchanggou deposit can be divided into two generations: the early, light yellow to yellowish white, zoning−free to weakly zoning garnet (Grt I) and the late, brown to reddish brown, strongly zoning garnet (Grt II). The results of EPMA show that the two-generation garnet samples have SiO2 contents of 34.41%～38.45%, CaO contents of 32.7%～35.25%, Al2O3 contents of 6.64%～12.57% and FeO contents of 12.03%～22.63%, indicating both the two generations belong to the andradite−grossularite series (And34-64Gro34-58). Both Grt I and Grt II have similar “hump−type” rare earth element (REE) pattern with enrichments in middle REE and depletions in light and heavy REE. Relative to Grt I, Grt II have lower U concentrations and more obvious δEu anomalies, indicating it formed under higher oxygen fugacity (fO2) and more variable pH conditions. Meanwhile, stronger oscillatory zoning within Grt II than Grt I, together with more variable major elements, indicate more intensive water/rock interaction. The two-generation garnet of the Tongchanggou deposit record its an evolving hydrothermal system, accompanying with increasing oxygen fugacity and water/rock interaction degrees. In addition, LA−ICP−MS U−Pb dating results of Grt I yield an age of (85.4±5.6) Ma (MSWD= 0.91), which directly constrains the Tongchanggou mineralization age. Within uncertainties, this age is coeval with emplacement of porphyry intrusions and timing of Mo mineralization in the Tongchanggou area, indicating that the Tongchanggou skarn mineralization consists of an important part of the porphyry−hydrothermal mineralization system. Combined with regional tectonic evolution, it's proposed that the late Cretaceous Tongchanggou and regional coeval Cu−Mo−W deposits are products of post−collisional porphyry−hydrothermal system.
The Qimantagh Orogenic Belt in the East Kunlun is an important Cu−Mo−Fe−Pb−Zn polymetallic mineralization belt in the northwest of China, and many porphyry-skarn deposits that are genetically related to granitoids are founded, such as Kaerqueka, Yemaquan, Weibao, and Wulanwuzhuer. With the development of a new round of strategic action to find mineral breakthroughs, further strengthening the study of granite mineralization potential in the Qimantagh Orogenic Belt has become an important breakthrough to promote the growth of metal mineral reserves in the region. In this paper, based on the systematic collection of whole−rock major and trace element data of mineralized and barren magmatic rocks of typical porphyry−skarn polymetallic deposits in the Qimantagh Orogenic Belt, 28 common whole-rock geochemical features are selected, and the machine learning algorithm (Random Forest) is used for the training of the machine learning model to establish a machine learning model capable of identifying the mineralized and barren magmatic rocks of porphyry−skarn polymetallic deposits in the region. A new method is developed to identify the mineralized and barren magmatic rocks in the porphyry−skarn polymetallic deposits in this area. According to the model evaluation metric, the accuracy of the Random Forest classification model trained in this paper is 0.90, which proves that the method can effectively recognize mineralized and barren magmatic rocks. This study provides a new idea for the prospecting and exploration of porphyry−skarn polymetallic deposits in the Qimantagh Orogenic Belt, which will greatly improve the efficiency of prospecting, reduce the economic and labor costs of prospecting, and thus better serve the new round of strategic action of prospecting and breakthrough. The machine learning code has been uploaded to GitHub at https://github.com/ShihuaZhong/2023-Qimantagh-RF-whole-rock-classifier.
