Apatite Fission-Track Thermochronology in the Tamusu Area,Bayingobi Basin,NW China,and its Geological Significance

The Bayingobi basin is located in the middle of Central Asia Orogenic Belt,at the intersection of Paleo-Asian Ocean and Tethys Ocean,as well as the junction of multiple tectonic plates.This unique tectonic setting underpins the basin's intricate history of tectonic activity.To unravel the multifaceted tectono-thermal evolution within the southwestern region of the basin and to elucidate the implications of sandstone-hosted uranium mineralization,granitic and clastic rock samples were collected from the Zongnai Mts.uplift and Yingejing depression,and apatite fission track(AFT)dating and thermal history simulation analysis were performed.AFT dating findings reveal that the apparent ages of all samples fall within the range of 244 Ma to 112 Ma.In particular,the bedrock of the Zongnai Mts.and Jurassic detrital apatite fission tracks have undergone complete annealing,capturing the uplift-cooling age.Meanwhile,the AFT ages of Cretaceous detrital rocks are either equivalent to or notably exceed the age of sedimentary strata,signifying the cooling age of the provenance.A comprehensive examination of AFT ages and palaeocurrent direction analyses suggests that the Cretaceous source in the Tamusu area predominantly originated from the central and southern sectors of the Zongnai Mts.uplift.However,at a certain juncture during the Late Early Cretaceous,the Cretaceous provenance expanded to include the northern part of the Zongnai Mts.uplift.Based on the results of thermal history simulations and previous studies,it is considered that the Tamusu area has undergone four distinct tectonic uplift events since the Late Paleozoic.The first is the Late Permian to Early Triassic(260-240 Ma),which is associated with the closure of the Paleo-Asian Ocean and the accretionary orogeny within the Alxa region.The second uplift event took place in the Early Jurassic(190-175 Ma)and corresponded to intraplate orogeny following the closure of the Paleo-Asian Ocean.The third uplift event is the Late Jurassic to Early Cretaceous(160-120 Ma),which is linked to the East Asia's position as the convergence center of multiple tectonic plates during this period.The fourth uplift event is linked to the Late Early Cretaceous(112-100 Ma),driven either by the westward subduction of the eastern Pacific plate or the mantle upwelling resulting from the Bangong-Nujiang oceanic lithosphere subduction and slab break-off.The primary stress orientation for the first three tectonic uplift phases approximated a nearly SN direction,while the fourth stage featured a principal stress direction of NW.The fourth tectonic uplift event of the Late Early Cretaceous and basaltic eruption thermal event during this period likely exerted a significant influence on the formation of the Tamusu sandstone-hosted uranium deposit.

The Relationship between Jurassic Coal Measures and Sandstone-type Uranium Deposits in the Northeastern Ordos Basin,China

Outcrop and drill hole data show that the Jurassic coal measures in the northeastern Ordos Basin are composed mainly of the Yan’an Formation and the lowstand system tract of the Zhiluo Formation, and there is a regional unconformity between them. The Dongsheng uranium deposit is associated with the Jurassic coal measures. Research data indicate that the Jurassic coal measures in the study area have a certain hydrocarbon-generating capacity, although the metamorphic grade is low （Ro=0.40%–0.58%）. In the Dongsheng region alone, the accumulative amount of generated coalbed methane （CBM） is about 2028.29 × 108 –2218.72 × 108 m3; the residual amount is about 50.92 × 108 m3, and the lost amount is about 1977 × 108 m3. Analysis of the burial history of the host rocks and the evolutionary history of the Dongsheng uranium deposit suggests that the Jurassic coal measures generated hydrocarbon mainly from Middle Jurassic to Early Crataceous, which is the main mineralization phase of the Dongsheng uranium deposit. By the Late Cretaceous, a mass of CBM dissipated due to the strong tectonic uplift, and the Dongsheng uranium deposit stepped into the preservation phase. Therefore, the low-mature hydrocarbon-containing fluid in the Jurassic coal measures not only served as a reducing agent for the formation of sandstone-type uranium deposits, but also rendered the second reduction of paleo-interlayer oxidation zone and become the primary reducing agent for ore conservation. Regional strata correlation reveals that the sandstone-type uranium reservoir at the bottom of the Zhiluo Formation is in contact with the underlying industrial coal seams in the Yan’an Formation through incision or in the form of an unconformity surface. In the Dongsheng region with poorly developed fault systems, the unconformity surface and scour surface served as the main migration pathways for low-mature hydrocarbon-containing fluid migrating to the uranium reservoir.

Outline of Uranium Resources Characteristics and Metallogenetic Regularity in China

Uranium,as one of twenty-six kinds of important minerals in China,is strategic resource and energy mineral,which has been thoroughly investigated in the project of National Potential Evaluation of Uranium Resource.During the implementation of this project,the authors summarized the metallogenic regularity of uranium resource in China systematically,through the researches of geological characteristics of uranium resource,uranium deposits type（genetic and prediction type）,temporal and spatial distribution,and metallogenic series.Based on the investigation of present situation and progress in uranium exploration,this paper proposes the uranium deposits in China should be divided into 4 classes,9 types,21 subtypes in genetic,and 50 types in prediction;suggests to divide China into 29 uranium metallogenic belts and 20 uranium prospective area,and constructs 20uranium-polymetallic metallogenic series,through summarizing temporal and spatial distribution characteristics and metallogenic regularity of uranium deposits in China.The above research is beneficial to the comprehensive understanding of regional uranium metallogenic regularity,and will direct the uranium exploration in the future.

Effects of hydrocarbon generation on fluid flow in the Ordos Basin and its relationship to uranium mineralization

The Ordos Basin of North China is not only an important uranium mineralization province, but also a major producer of oil, gas and coal in China. The genetic relationship between uranium mineralization and hydrocarbons has been recognized by a number of previous studies, but it has not been well understood in terms of the hydrodynamics of basin fluid flow. We have demonstrated in a previous study that the preferential localization of Cretaceous uranium mineralization in the upper part of the Ordos Jurassic section may have been related to the interface between an upward flowing, reducing fluid and a downward flowing, oxidizing fluid. This interface may have been controlled by the interplay between fluid overpressure related to disequilibrium sediment compaction and which drove the upward flow, and topographic relief, which drove the downward flow. In this study, we carried out numerical modeling for the contribution of oil and gas generation to the development of fluid overpressure, in addition to sedi- ment compaction and heating. Our results indicate that when hydrocarbon generation is taken into account, fluid overpressure during the Cretaceous was more than doubled in comparison with the simu- lation when hydrocarbon generation was not considered. Furthermore, fluid overpressure dissipation at the end of sedimentation slowed down relative to the no-hydrocarbon generation case. These results suggest that hydrocarbon generation may have played an important role in uranium mineralization, not only in providing reducing agents required for the mineralization, but also in contributing to the driving force to maintain the upward flow.

Origin and Superposition Metallogenic Model of the Sandstone-type Uranium Deposit in the Northeastern Ordos Basin,China

This paper deals with the metallogenic model of the sandstone type uranium deposit in the northeastern Ordos Basin from aspects of uranium source, migration and deposition. A superposition metallogenic model has been established due to complex uranium mineralization processes with superposition of oil-gas reduction and thermal reformation.

The Discovery of Natural Native Uranium and Its Significance

This study analyzed the composition and uranium valence of pitchblendes sampled from the hydrothermal Guidong and Zhuguang uranium deposits of the middle Nanling metallogenic belt, Southern China using X-ray photoelectron spectroscopy（XPS）.A revolutionary discovery is that the uranium not only exists in the forms of tetravalent and hexavalent uranium oxides, but also occurs in the form of native uranium.This is the first discovery of the existence of native uranium in nature.It greatly helps to reveal the origin of hydrothermal mineralization of uranium, and also has great significance for studying the thermal energy, formation and evolution of the earth.

Uranium Provinces in China

Three uranium provinces are recognized in China, the Southeast China uranium province, the Northeast China-Inner Mongolia uranium province and the Northwest China (Xinjiang) uranium province. The latter two promise good potential for uranium resources and are major exploration target areas in recent years. There are two major types of uranium deposits: the Phanerozoic hydrothermal type (vein type) and the Meso-Cenozoic sandstone type in different proportions in the three uranium provinces. The most important reason or prerequisite for the formation of these uranium provinces is that Precambrian uranium-enriched old basement or its broken parts (median massifs) exists or once existed in these regions, and underwent strong tectonomagmatic activation during Phanerozoic time. Uranium was mobilized from the old basement and migrated upwards to the upper structural level together with the acidic magma originating from anatexis and the primary fluids, which were then mixed with meteoric water and resulted in the formation of Phanerozoic hydrothermal uranium deposits under extensional tectonic environments. Erosion of uraniferous rocks and pre-existing uranium deposits during the Meso-Cenozoic brought about the removal of uranium into young sedimentary basins. When those basins were uplifted and slightly deformed by later tectonic activity, roll-type uranium deposits were formed as a result of redox in permeable sandstone strata.

Evolution of Tectonic Uplift, Hydrocarbon Migration, and Uranium Mineralization in the NW Junggar Basin： An Apatite Fission-Track Thermochronology Study

The Mesozoic–Cenozoic tectonic movement largely controls the northwest region of the Junggar Basin（NWJB）, which is a significant area for the exploration of petroleum and sandstone-type uranium deposits in China. This work collected six samples from this sedimentary basin and surrounding mountains to conduct apatite fission track（AFT） dating, and utilized the dating results for thermochronological modeling to reconstruct the uplift history of the NWJB and its response to hydrocarbon migration and uranium mineralization. The results indicate that a single continuous uplift event has occurred since the Early Cretaceous, showing spatiotemporal variation in the uplift and exhumation patterns throughout the NWJB. Uplift and exhumation initiated in the northwest and then proceeded to the southeast, suggesting that the fault system induced a post spread-thrust nappe into the basin during the Late Yanshanian. Modeling results indicate that the NWJB mountains have undergone three distinct stages of rapid cooling： Early Cretaceous（ca. 140–115 Ma）, Late Cretaceous（ca. 80–60 Ma）, and Miocene–present（since ca. 20 Ma）. These three stages regionally correspond to the LhasaEurasian collision during the Late Jurassic–Early Cretaceous（ca. 140–125 Ma）, the Lhasa-Gandise collision during the Late Cretaceous（ca. 80–70 Ma）, and a remote response to the India-Asian collision since ca. 55 Ma, respectively. These tectonic events also resulted in several regional unconformities between the J3/K1, K2/E, and E/N, and three large-scale hydrocarbon injection events in the Piedmont Thrust Belt（PTB）. Particularly, the hydrocarbon charge event during the Early Cretaceous resulted in the initial inundation and protection of paleo-uranium ore bodies that were formed during the Middle–Late Jurassic. The uplift and denudation of the PTB was extremely slow from 40 Ma onward due to a slight influence from the Himalayan orogeny. However, the uplift of the PTB was faster after the Miocene, which led to re-uplift and exposure at the surface during the Quaternary, resulting in its oxidation and the formation of small uranium ore bodies.

Biomineralization of Uranium: A Simulated Experiment and Its Significance

A simulated experimental reduction of and the synthesis of uraninite by a sulfate-reducing bacteria, Desulfovibrio desulfuricans DSM 642, are first reported. The simulated physicochemical experimental conditions were: 35°C, pH=7.0-7.4, corresponding to the environments of formation of the sandstone-hosted interlayer oxidation-zone type uranium deposits in Xinjiang, NW China. Uraninite was formed on the surface of the host bacteria after a one-week's incubation. Therefore, sulfate-reducing bacteria, which existed extensively in Jurassic sandstone-producing environments, might have participated in the biomineralization of this uranium deposit. There is an important difference in the order- disorder of the crystalline structure between the uraninite produced by Desulfovibrio desulfuricans and naturally occurring uraninite. Long time and slow precipitation and growth of uraninite in the geological environment might have resulted in larger uraninite crystals, with uraninite nanocrystals arranged in order, whereas the experimentally produced uraninite is composed of unordered uraninite nanocrystals which, in contrast, result from the short time span of formation and rapid precipitation and growth of uraninite. The discovery has important implications for understanding genetic significance in mineralogy, and also indicates that in-situ bioremediation of U-contaminated environments and use of biotechnology in the treatment of radioactive liquid waste is being contemplated.

New Evidence for Genesis of the Zoige Carbonate-Siliceous-Pelitic Rock Type Uranium Deposit in Southern Qinling:Discovery and Significance of the 64 Ma Intrusions

The carbonaceous-siliceous-argillitic rock type uranium deposit in the Zoige area is located in the northeastern margin of the Tibetan Plateau, and has gained much attention of many geologists and ore deposit experts due to its scale, high grade and abundant associated ores. Because of the insufficient reliable dating of intrusive rocks, the relationship between mineralization and the magmatic activities is still unknown. In order to study this key scientific issue and the ore-forming processes of the Zoige uranium ore field, the LA-ICP-MS zircon U-Pb dating of magmatic rocks was obtained：64.08±0.59 Ma for the granite-prophyry and ~200 Ma for the dolerite. U-Pb dating results of uraninite from the Zoige uranium ore field are mainly concentrated on ~90 Ma and ~60 Ma. According to LA-ICP-MS U-Pb zircon dating, the ages for the dolerite, porphyry granite and granodiorite are 200 Ma, 64.08 Ma approximately and 226.5-200.88 Ma, respectively. This indicates that the mineralization has close relationship with activities of the intermediate-acidic magma. The ages of the granite porphyry are consistent with those uraninite U-Pb dating results achieved by previous studies, which reflects the magmatic and ore-forming event during the later Yanshanian. Based on the data from previous researches, the ore bodies in the Zoige uranium ore field can be divided into two categories：the single uranium type and the uranium with polymetal mineralization type. The former formed at late Cretaceous（about 90 Ma）, while the latter, closely related to the granite porphyry, formed at early Paleogene（about 60 Ma）. And apart from ore forming elemental uranium, the latter is often associated with polymetallic elements, such as molybdenum, nickel, zinc, etc.

Elemental Geochemistry of the Interlayer Oxidation Zonein the Shihongtan Sandstone Type Uranium Deposit, Xinjiang

According to the oxidation intensity of ore-hosting sandstone, the interlayer oxidation zone of the Shihongtan sandstone-type uranium deposit in the Turpan-Hami basin can be divided into 4 geochemical subzones, namely, intenselyoxidized, weakly-oxidized, redox and unoxidized primary subzones. The elemental geochemical characteristics of the four subzones have been studied in detail, and the results show that U, together with other elements such as Re, Mo, Se, Sr, S, REE, Corganic etc., is enriched in the redox subzone. Re and U have similar geochemical properties in the reductionoxidation process. The geochemical properties of Mo and Se are similar to those of U in the reduction condition, but different from those of U in the oxidation condition. It is proposed that the ore-hosting layers can provide a curtain mount of uranium for uranium mineralization.

Mineralogy,Fluid Inclusion and H-O-C-S Stable Isotopes of Mengqiguer Uranium Deposit in the Southern Yili Basin,Xinjiang:Implication for Ore Formation

The Mengqiguer deposit in the southern Yili basin Ili Basin is a large interlayer-oxidation-zone type uranium deposit.In this paper,we applied multiple methods including microscopic observation,scanning electron microscope and electronic probe,to analyze the systematical alteration characteristics of the ore-bearing sandstone layer.Fluid inclusion and stable isotope studies on the ore-bearing sandstone have also been carried out to discuss the internal relations between fluid activities,epigenetic alteration and the uranium mineralization.Major epigenetic alteration include clay alteration,carbonatization and pyritization,of which biogenetic pyritization is most closely related to the uranium mineralization.This suggests the existence of microorganism during the uranium mineralization process.The mineralization fluids of low temperature,medium density but varied salinities are suggested to be derived from multi-source,including the meteoric water and organic acidic vapor components from coal-bearing strata.Uranium mineralization,grain-dispersed kaolinite,limonite,colloidal pyrite,and the carbonate cements associated with sulfate-reducing bacteria were formed by meteoric water and vermicular-shaped kaolinite,autologous pyrite,and the carbonate cementation associated with the dehydroxylation of organic matter was formed by organic acidic.Based on these results,we consider that the uranium mineralization and epigenetic alteration both resulted from the reciprocity of organic–inorganic fluid and fluid–rock during the formation of the interlayer oxidation zone.

Genesis of green sandstone/mudstone from Middle Jurassic Zhiluo Formation in the Dongsheng Uranium Orefield, Ordos Basin and its enlightenment for uranium mineralization

The middle Jurassic Zhiluo Formation in the Dongsheng is comprised of a big set of green sandstone/mudstone with most of uranium orebodies occurring in close proximity to its footwall.By synthesizing field observations,region analysis,data collected from previous coal and uranium borehole,a regional north-south geological profile across the entire orefield is conducted.Experiments on sandstone/mudstone including rock mineral identification,clastic micromorphology and element geochemistry were carried out.Information from the geological profile indicates that green sandstone/mudstone is widely present in a stable horizon with clear boundaries to the country rock.Microscopic observations and geochemical data on sandstone/mudstone exhibit similar mineral composition with almost identical slightly flat,minor Eu enriched,Ce depleted chondrite-normalized REE patterns.Furthermore,the green clay membrane of the clasts has a complex composition containing chlorite/smectite,green smectite,chlorite,and green kaolinite,with elements including Fe,Mg,Si,and Al.These above results indicate that the green sandstone/mudstone underwent resemble sedimentary diagenetic processes as the country rock without transformation by large-scale regional fluid,while the existence of Fe2+-rich membrane is the main factor to the green sandstone/mudstone.Further concentration of the pre-enrichment uranium during diagenetic process led to the final formation for uranium deposits.The above studies are conducive to enrich the metallogenic mechanism of sandstone type uranium deposits and could provide certain reference for uranium exploration and deployment.

Types of uranium deposits in central Zhuguang Mountains in Hunan Province,South China and their metallogenic regularity and prospecting directions

The central Zhuguang Mountains in Hunan Province is located at the junction of the three provinces,namely Hunan,Jiangxi,and Guangdong,where the famous Lujing uranium ore field lies.The uranium deposits occurring in this area are all granite-related and they can be divided into three types,namely endogranitic ones,perigranitic ones,and contact zone types.The endogranitic uranium deposits are mainly controlled by the structural alteration zones developing within granites,with fragmentation,hematitization,and alkali metasomatism as their main mineralization characteristics.The perigranitic uranium deposits are mainly produced in the carbonaceous,siliceous,and argillaceous composite layers of epimetamorphic rocks and are controlled by fractured zones formed due to interlayer compression.The contact zone type uranium deposits mainly occur in the contact parts between the granites and favorable horizons.They have developed in favorable sections where multiple sets of structures are combined and intersected.The main metallogenic regularities of uranium in the central Zhuguang Mountains are as follows.The basic conditions for the uranium mineralization in this area include the framework consisting of regional deep large faults and their associated multi-set multi-direction favorable metallogenic structures,multi-cycle and multi-stage uranium-rich rock masses,and uranium-rich folded basement.Meanwhile,the uranium deposits in this area are closely related to granites in terms of genesis and space and they are formed in different structural parts subject to the same metallization.Furthermore,based on the summary of the characteristics and regularities of uranium mineralization in this area,the controlling factors of different types of uranium deposits in the area were explored and six metallogenic target areas were predicted.All these will provide references for the exploration of uranium deposits in this area.

Uranium Metallogenic Regionalization and Resource Potential in China

This paper is comprehensively involved in main types of uranium deposits and their general metallogenic characteristics, metallogenic fields, provinces, regions and belts, and uranium resources potential evaluation. Generally speaking, there are favorable conditions and good uranium resources potential for uranium mineralization in China.

Zircon U-Pb ages and provenance characteristics of the Zhiluo Formation sandstones and the formation background of the uranium deposit in Huangling area,Ordos Basin,China

The newly discovered medium-scale Huangling uranium deposit is located in the Shuanlong area of the southeast Ordos Basin.This paper presents the systematic geochemical and zircon U-Pb studies on the Zhiluo Formation sandstones in the Huanling area.The data obtained play an important role in deducing the provenance and tectonic setting of the source rocks.The results show that the lower part of the Zhiluo Formation is mainly composed of felsic sedimentary rocks.The source rocks originated from a continental island arc environment in terms of tectonic setting.U-Pb ages of detrital zircons obtained can be roughly divided into three groups:170‒500 Ma,1600‒2050 Ma,and 2100‒2650 Ma.Based on the characteristics of trace elements and rare earth elements(REE)and the zircon U-Pb dating results,it is considered that the Cryptozoic Edo provenance of the Zhiluo Formation mainly includes magmatic rocks(such as granodioritic intrusions)and metamorphic rocks(such as gneiss and granulite)in the orogenic belts on the northern margin of the North China Plate and in the Alxa Block.Based on sedimentological and petrological results,it can be concluded that the provenance of clastic sediments in the Zhiluo Formation was in north-south direction.The preconcentration of uranium is relatively low in the Lower Zhiluo Formation in the Huangling area.Meanwhile,the paleocurrent system in the sedimentary period is inconsistent with the ore-bearing flow field in the mineralization period,which restricts the formation of large-scale and super-large-scale uranium deposits and ore zones in the southeast Ordos Basin.The understanding of provenance directions will provide crucial references for the Jurassic prototype recovery and paleo-geomorphology of the Ordos Basin and the prediction of potential uranium reservoirs of the basin.

In-situ Chemical Age of the Sandstone-hosted Uranium Deposit in Ningdong Area on the Western Margin of the Ordos Basin, North China

Objective The Ordos Basin located in the westem part of the North China Craton bears various energy resources such as oil, gas, coal and uranium. It is one of the richest uranium-bearing basins in China. Since the discovery of the large-scale Dongsheng, Hangjinqi and Daying uranium deposits in the north of the Ordos Basin, a new breakthrough of uranium exploration has been achieved in the Ningdong area （eastern Ningxia） on the western margin of the Ordos Basin （WMOB） in the past two years （Wang Feifei et al., 2017）.

Sequence Stratigraphy of the Lower Cretaceous Uraniferous Measures and Mineralization of the Sandstone-hosted Tamusu Large Uranium Deposit,North China

The Bayingobi basin is the Mesozoic-Cenozoic basin in North China in which the Tamusu uranium deposit is located.The ore-target layer of the deposit is the Lower Cretaceous Bayingobi Formation,which developed as a fan deltashallow lacustrine deposit.The distributary channel sand body of the fan delta plain and the underwater distributary channel sand body of the fan delta front formed a favorable uranium reservoir,so the study of sequence stratigraphy is extremely important to understanding the genesis of uranium deposits.On the basis of field investigation and a large number of borehole logs,the high resolution sequence stratigraphy of the Lower Cretaceous is divided and the system tracts of different periods are established.The relationship between deposition,interlayer oxidation and uranium enrichment is discussed.The Lower Cretaceous Bayingobi Formation can be divided into two fourth-order sequences(Sq1 and Sq2).The lower member of the Bayingobi Formation is referred to as Sq1,which is composed of a falling-stage system tract(FSST)on top.On the other hand,the upper member of the Bayingobi Formation is referred to as Sq2,which is composed of a lowstand system tract(LST),transgressive system tract(TST)and highstand system tract(HST).The lowstand system tract forms a favorable stratigraphic structure(mud-sand-mud formation)with the lacustrine mudstone of the overlying transgressive system tract,that is conducive for the migration of uranium-bearing oxygen water.The organic matter and pyrite in the fan delta sand body,as well as the dark mudstone in the distributary bay,provided a reducing medium for uranium mineralization.The ore body mainly occurs in the distributary channel,underwater distributary channel or the mouth bar of the fan delta.As a result of the moderate thickness,high permeability,favorable barrier and rich reducing medium,the rich ore body mainly occurs in the underwater distributary channel and mouth bar sand body of the delta front.Based on study of the sequence stratigraphy,the model of the sequence,sedimentation and mineralization of the uranium deposit is established,which enriches uranium metallogenic theory and provides a reference for exploration of the same type of uranium deposits.

Multistage Enrichment of the Sawafuqi Uranium Deposit: New Insights into Sandstone-hosted Uranium Deposits in the Intramontane Basins of Tian Shan, China

Meso-Cenozoic intracontinental orogenic processes in the Tian Shan orogenic belt have significant effect on the sandstone-hosted uranium deposits in the intramontane basins and those adjacent to the orogen. The Sawafuqi uranium deposit, which is located in the South Tian Shan orogenic belt, is investigated to reveal the relationships between uranium mineralization and orogenies. Recent exploration results show that the Sawafuqi uranium deposit has tabular, stratiform, quasi-stratiform, and lens-like orebodies and various geological characteristics different from typical interlayer oxidation zone sandstone-hosted uranium deposits. Systematic studies of ore samples from the Sawafuqi uranium deposit using a variety of techniques, including thin section observation, a-track radiograph, electron microprobe and scanning electron microscope, suggest that uranium mineralization is closely related to pyrite and organic matter. Mineralization-related alterations in the host rocks are mainly silicification and argillation including kaolinite, illite （and illite-smectite mixed layer） and chlorite. Tree stages of mineralization were identified in the Sawafuqi uranium deposit： （i） uranium-bearing detritus and synsedimentary initial pre-enrichment; （ii） interlayer oxidization zone uranium mineralization; and （iii） vein-type uranium mineralization. The synsedimentary uranium pre-enrichment represents an early uranium enrichment in the Sawafuqi uranium deposit, and interlayer oxidation zone uranium mineralization formed the main orebodies, which are superimposed by the vein-type uranium mineralization. Combining the results of this study with previous studies on the Meso-Cenozoic orogenies of South Tian Shan, it is proposed that the synsedimentary uranium pre-enrichment of the Sawafuqi uranium deposit was caused by Triassic Tian Shan uplift, and the interlayer oxidation zone uranium mineralization occurred during the Eocence-Oligocene period, when tectonism was relatively quiet, whereas the vein-type uranium mineralization took place in relation to the strong orogeny of South Tian Shan since Miocene.

Constraints on granite-related uranium mineralization in the Sanjiu uranium ore field,SE China provided by pyrite mineralogy,major and trace elements,S-He-Ar isotopes

The Sanjiu uranium ore field,located in the central of Zhuguangshan granitic batholith,is a newly discovered granite-related uranium ore field in South China.The main sulfide in the ore field is pyrite,which is closely related to uranium mineralization.The textures major and trace elements,S-He-Ar isotopes compositions of pyrites in ores of different grade were observed and/or analyzed by optical microscope,scanning electron microscope,electron microprobe,laser ablation inductively coupled plasma mass spectrometry,and noble gas mass spectrometer(Helix-SFT).It is observed that these U-related pyrites are generally euhedral-subhedral with dissolution textures,anhedral variety with colloform texture veinlet and fine particles,and the color of the associated minerals is mostly dark hue,such as purple-black fluorite dark-red hematite,and dark-green chlorite,etc.The analytical results show that the average compositions of major elements in pyrite are FeS1.944.Pyrites are characterized by S-deficiency,low content of Co and Th,and Co/Ni>1which indicate that these ores are of low-temperature hydrothermal origin.We found that the higher the grade of ore,the more deficient in S,the more obvious negative δ^34S,and the higher REE content(close to U-rich granitic pluton)of pyrite.The S-He-Ar isotopic compositions of various varieties of pyrites indicate that the ore-forming fluids mainly come from crust-derived fluids and mixed with mantle-derived fluids.