Basical characteristics of fluid geologic process of interlayer oxidation zone sandstone-type uranium deposit

This paper reveals the physicochemical properties such as component, formulation, genesis, tem-perature, pH, Eh, salinity and pressure of all main alteration fluid of interlayer oxidation zone sand-stone-type uranium deposits after studying the geologic process and geochemistry of internal typical sandstone-type uranium deposits such as Shihongtan deposit in the Turpan-Hami basin, 512 deposit in the Yili basin, Dongsheng deposit in the Ordos basin. The composition of fluid can be divided into two parts based on the analysis of inclusion: one can be affirmed as atmospheric water with ordinary temperature epigenesist according to the character of hydrogen and oxygen isotope of inclusion, the other is natural gas containing gaseous hydrocarbon like CH₄, and CO₂ as well as a little H₂S, CO, H₂, N₂ and so on, it always contains a small quantity of hydrocarbon liquid in petroliferous basins. The fluid property of oxidation alteration zone is always oxidation alkaline, and neutrality or weak acid-weak alkaline and reducibility during the metallizing process, but at secondary reduction or deoxidization zone it becomes strong reduction alkaline. Oxygenic groundwater in the fluid is the activate and mig-ratory medium of uranium element, but the gaseous hydrocarbon like CH₄ as well as H₂, H₂S, CO from natural gas is the important sedimentary reducer of uranium mineral; the transformation of pH,Eh in fluid environment is the main reason for the formation of uranium metallization.     

Fluid mixing as the mechanism of formation of the Dajing Cu-Sn-Ag-Pb-Zn ore deposit,Inner Mongolia ——Fluid inclusion and stable isotope evidence

Since the 1990s, interest in the magmatic fluids and their relation to mineralization has been re-aroused[1—6]. Studies on stable isotopes of low-sulfidation deposits commonly show the predominance of meteoric water[7]. Paradoxically, the evidence for me…     

Development characteristics of interlayer oxidation zone type of sandstone uranium deposits in the southwestern Turfan-Hami basin

The known uranium ore and anomaly occur-rences are distributed mainly in the southwestern part of the Turfan-Hami basin. The focus of current explo-ration is placed on the leachable interlayered oxidation zone type of sandstone uranium deposits. Uranium deposits in the sedimentary basin can be classified into three types in accordance with their host rock types, i.e. the sandstone-type uranium deposits, the coal rock-type uranium deposits and the mud-stone-type uranium deposits. The sandstone…     

Origin of gray-green sandstone in ore bed of sandstone type uranium deposit in north Ordos Basin

Dongsheng sandstone-type uranium deposit is located in the northern part of Ordos Basin, occurring in the transitional zones between gray-green and gray sandstones of Jurassic Zhiluo Formation. Sandstones in oxidized zone of the ore bed look gray-green, being of unique signature and different from one of ordinary inter-layered oxidation zone of sandstone-type uranium deposits. The character and origin of gray-green sandstones are systematically studied through their petrology, mineralogy and geochemistry. It is pointed out that this color of sandstones is originated from secondary oil-gas reduction processes after paleo-oxidation, being due to acicular-leaf chlorite covering surfaces of the sandstone grains. To find out the origin of gray-green sandstone and recognize paleo-oxidation zones in the ore bed are of not only theoretical significance for understanding metallogenesis of this kind of sandstone-type uranium deposit, but also very importantly practical significance for prospecting for similar kind of sandstone-type uranium deposit.     

Origin of gray-green sandstone in ore bed of sandstone type uranium deposit in north Ordos Basin

Dongsheng sandstone-type uranium deposit is located in the northern part of Ordos Basin, occurring in the transitional zones between gray-green and gray sandstones of Jurassic Zhiluo Formation. Sandstones in oxidized zone of the ore bed look gray-green, being of unique signature and different from one of ordinary inter-layered oxidation zone of sandstone-type uranium deposits. The character and origin of gray-green sandstones are systematically studied through their petrology, mineralogy and geochemistry. It is pointed out that this color of sandstones is originated from secondary oil-gas reduction processes after paleo-oxidation, being due to acicular-leaf chlorite covering surfaces of the sandstone grains. To find out the origin of gray-green sandstone and recognize paleo-oxidation zones in the ore bed are of not only theoretical significance for understanding metallogenesis of this kind of sandstone-type uranium deposit, but also very importantly practical significance for prospecting for similar kind of sandstone-type uranium deposit.     

Sources of ore-forming fluids and metallic materials in the Jinwozi lode gold deposit, eastern Tianshan Mountains of China

This paper presents gas compositions and H-, O-isotope compositions of sulfide- and quartz-hosted fluid inclusions, and S-, Pb-isotope compositions of sulfide separates collected from the principal Stage 2 ores in Veins 3 and 210 of the Jinwozi lode gold deposit, eastern Tianshan Mountains of China. Fluid inclusions trapped in quartz and sphalerite are dominantly primary. H- and O-isotopic compositions of pyrite-hosted fluid inclusions indicate two major contributions to the ore-forming fluid that include the degassed magma and the meteoric-derived but rock 18O-buffered groundwater. However, H- and O-isotopic compositions of quartz-hosted fluid inclusions essentially suggest the presence of groundwater. Sulfide-hosted fluid inclusions show considerably higher abundances of gaseous species CO2, N2, H2S, etc. Than quartz-hosted ones. The linear trends among inclusion gaseous species reflect the mixing tendency between the gas-rich magmatic fluid and the groundwater. The relative enrichment of gaseous species in sulfide-hosted fluid inclusions, coupled with the banded ore structure indicating alternate precipitation of quartz with sulfide minerals, suggests that the magmatic fluid has been inputted to the ore-forming fluid in pulsation. Sulfur and lead isotope compositions of pyrite and galena separates indicate an essential magma derivation for sulfur but the multiple sources for metallic materials from the mantle to the bulk crust.     

Geological and geochemical characteristics of the Baogudi Carlintype gold district(Southwest Guizhou,China) and their geological implications

The newly discovered Baogudi gold district is located in the southwestern Guizhou Province,China,where there are numerous Carlin-type gold deposits.To better understand the geological and geochemical characteristics of the Baogudi gold district,we carried out petrographic observations,elemental analyses,and fluid inclusion and isotopic composition studies.We also compared the results with those of typical Carlin-type gold deposits in southwestern Guizhou.Three mineralization stages,namely,the sedimentation diagenesis,hydrothermal(main-ore and late-ore substages),and supergene stages,were identified based on field and petrographic observations.The main-ore and late-ore stages correspond to Au and Sb mineralization,respectively,which are similar to typical Carlin-type mineralization.The mass transfer associated with alteration and mineralization shows that a significant amount of Au,As,Sb,Hg,Tl,Mo,and S were added to mineralized rocks during the main-ore stage.Remarkably,arsenic,Sb,and S were added to the mineralized rocks during the late-ore stage.Element migration indicates that the sulfidation process was responsible for ore formation.Four types of fluid inclusions were identified in ore-related quartz and fluorite.The main-ore stage fluids are characterized by an H2O–NaCl–CO2–CH4±N2system,with medium to low temperatures(180–260℃)and low salinity(0–9.08%NaCl equivalent).The late-ore stage fluids featured H2O–NaCl±CO2±CH4,with low temperature(120–200℃)and low salinity(0–7.48%Na Cl equivalent).The temperature,salinity,and CO2and CH4concentrations of ore-forming fluids decreased from the main-ore stage to the late-ore stage.The calculated δ^13C,d D,and δ^18O values of the ore-forming fluids range from-14.3 to-7.0%,-76 to-55.7%,and 4.5–15.0%,respectively.Late-ore-stage stibnite had δ^34S values ranging from-0.6 to 1.9%.These stable isotopic compositions indicate that the ore-forming fluids originated mainly from deep magmatic hydrothermal fluids,with minor contributions from strata.Collectively,the Baogudi metallogenic district has geological and geochemical characteristics that are typical of Carlin-type gold deposits in southwest Guizhou.It is likely that the Baogudi gold district,together with other Carlin-type gold deposits in southwestern Guizhou,was formed in response to a single widespread metallogenic event.     

Hydrodynamic regime as a major control on localization of uranium mineralization in sedimentary basins

Uranium deposits in sedimentary basins can be formed at various depths,from near surface to the basement.While many factors may have played a role in controlling the location of mineralization,examination of various examples in the world,coupled with numerical modeling of fluid flow,indicates that the hydrodynamic regime of a basin may have exerted a major control on the localization of uranium deposits.If a basin is strongly overpressured,due to rapid sedimentation,abundance of low-permeability sediments or generation of hydrocarbons,fluid flow is dominantly upward and uranium mineralization is likely limited at shallow depths.If a basin is moderately overpressured,upward moving fluids carrying reducing agents may meet downward moving,oxidizing,uranium-bearing fluids in the middle of the basin,forming uranium deposits at moderate depths.If a basin is weakly or not overpressured,either due to slow sedimentation or dominance of high-permeability lithologies,minor topographic disturbance or density variation may drive oxidizing fluids to the bottom of the basin,leaching uranium either from the basin or the basement,forming unconformity-type uranium deposits.It is therefore important to analyze the hydrodynamic regime of a basin in order to predict the most likely type and location of uranium deposits in the basin.     

S,C, O,H, and Pb isotopic studies for the Shuiyindong Carlin-type gold deposit,Southwest Guizhou,China: constraints for ore genesis

The Shuiyindong gold deposit is one of the most famous and largest Carlin-type gold deposits in China and is located in southwest Guizhou, in the eastern part of the Huijiabao anticline. The Shuiyindong's gold mineralization occurred in bioclastic limestone of the Permian Longtan Formation. Sulfur, carbon, hydrogen, oxygen, and lead isotopic compositions are reported in this paper. The properties and sources of ore-forming fluid have been discussed and a metallogenic model for the Shuiyindong gold deposit has been proposed. The d34 S values of stibnite, realgar, orpiment, pyrite from orebodies, and pyrite from quartz veins are similar to or slightly higher than the d34 S values of mantle sulfur. It is suggested that the sulfur of hydrothermal sulfides was likely of magmatic origin with minor heavy sulfur contributed from the country rocks. The measured d D values and calculated d18OH2 O values of inclusion fluid in quartz plotted within or below a magmatic hydrothermal fluid field far from the meteoric water line. This indicates that the ore-forming fluid for the main-stage gold mineralization could have been derived mainly from a magmatic source and mixed with a small amount of meteoric water. The carbon and oxygen isotopic compositions of calcites in the d18 O vs. d13 C diagram suggest that the CO2 in ore-forming fluid was derived from dissolution of bioclastic limestone and oxidation of sedimentary organic carbon in limestone. However, the d13 C values of ore-related calcites, which contain intergrown realgar and/or orpiment, are similar to those of mantle carbon. Although no igneous intrusive rock has been observed in the vicinity of the gold deposits, the possibility of mantle fluid integrated into the ore-forming fluid cannot be eliminated based on the d13 C values of ore-related calcites. The lead isotopes of sulfides are distributed near the growth curves of upper crust and orogenic belt in the plumbotectonic diagram. Their calculated Dc and Db values plotted within the magmatism field of crust-mantle subduction zone in the Dc- Db diagram. This suggests that the lead of sulfides has an intimate connection with magmatism. Our S, H, O, C, and Pb isotopic studies for the Shuiyindong Carlin-type gold deposit in Guizhou manifest a concordant possibility that the ore-forming fluid was mainly derived from magmatic fluid with minor contribution from the surrounding strata. With the integration of comprehensive geology and isotopic geochemistry, we have proposed a magmatic hydrothermal model for the origin of the Shuiyindong gold deposit.     

松辽盆地深部地壳构造特征与无机油气生成模式

松辽盆地中地壳有一低速-高导层(也称塑性层),中地壳的塑性层与松辽盆地的成因以及盆山耦合系统有关.盆地地幔流体活动有下列表现:(1)高热流、高地温场;(2)深大断裂与火山岩喷溢;(3)碱交代作用(如钠长石化、伊利石化);(4)Mg2 交代作用(如白云石化)等等.地球化学省与地球化学急变带控制了大油气田的分布并显示了盆地发生的壳-幔相互作用.中地壳的低速-高导层不是岩浆岩,而是一充满地幔流体的地质体,它们富含氢、碱金属(K 、Na )、卤素(F-、Cl-)、碳(甲烷、CO、CO2)、氮、硫等.在中地壳的温度压力条件下,在Fe、Ni等催化荆的参与下,H2与CO(CO2)可发生费-托合成烃的反应.实验表明:这个反应不仅可生成气态烃还可生成液态烃,并将发生碳同位素分馏作用.松辽盆地的U形运移模型受到质疑.按照石油无机生成的模型,松辽盆地的深部将会有更多的石油与天然气,庆深气田的发现便是一个明证.     

Effects of uranium on hydrocarbon generation of hydrocarbon source rocks with type-Ⅲ kerogen

Organic-inorganic interaction exists universally and is important in the process of mineral resources formation.It is the essential reason why organic oil,gas,coal and inorganic uranium coexist,accumulate,and mineralize in the same sedimentary basins.Hydrocarbon-generating simulation experiment was conducted using low-mature hydrocarbon source rock containing kerogen type III with uranium(UO2CO3 solution)added to study the effects of uranium on the hydrocarbon generation of hydrocarbon source rocks.Experiment results show that uranium can enhance the yield of gas hydrocarbon,promote the total gas output,and increase the total hydrocarbon production(mass or volume).Uranium may lower the hydrocarbon generation threshold temperature and lead to the generation of liquid hydrocarbon in the relative low temperature of hydrocarbon source rock.Uranium can enhance the yield of saturated hydrocarbon,promote the low molecular weight hydrocarbons generating,and in turn increase the content of CH4 and the content of dry gas of the generated hydrocarbons.Uranium is one of the potential inorganic accelerating factors of the immature hydrocarbons.     

Skarn mineralogy and its geological significance for the Tayuan(Cu-Mo)-Pb-Zn deposit,northern Daxinganling metallogenic belt

The Tayuan(Cu-Mo)-Pb-Zn deposit is located in the northern part of Daxinganling,NE China.Lenticular ore body occurs in the skarn zone.The skarn minerals mainly include garnet,pyroxene,epidote and wollastonite.Electron microprobe analysis shows that the end member of garnet is mainly andradite(Ad_(62-97)Gr_(11-45),the pyroxene is mainly diopside,and epidote is mainly clinozoisite.These characteristics indicate that the Tayuan polymetallic skarn deposit is mainly calcareous skarn.Sometimes the content zonation can be observed in garnets.With one garnet crystal,content is shifty from the core to the rim.In general,the iron content in the core is higher than in the edge.The content in the garnet shows that the garnet in the Tayuan deposit formed from weak oxidation in alkaline environment with the oxygen fugacity increasing,suggesting that the hydrothermal fluid evolved from an acidic to a slight alkaline state.In the Tayuan polymetallic deposit,the ratio of Mn/Fe in pyroxene is about 1.3,and of Mg/Fe,it is about 2.The components of garnet in the Tayuan deposit plot in the field of the typical skarn Zn,Cu,Mo deposits in the world.     

粤北下庄矿田小水铀矿床地球化学特征分析

粤北小水矿床是下庄矿田典型的交点型铀矿床。通过对矿床内发育的花岗岩、辉绿岩及铀矿石采样分析．发现小水矿床矿石具有轻稀土富集的稀土元素特征和富集大离子亲石元素Rb、Th的微量元素特征。与辉绿岩的相应特征十分吻合,与花岗岩的相应特征差异很大,推测其成矿物质来源于深部地幔流体（富含U、F、CO2）,且交点型矿石的形成很有可能伴有幔源成矿流体对与花岗岩有关的早期红化矿石的叠加改造作用。     

Thermal simulation experiments of saturated hydrocarbons with calcium sulfate and element sulfur: Implications on origin of H<Subscript>2</Subscript>S

Temperature-programmed simulation experiments of saturated hydrocarbons with calcium sulfate and element sulfur were compared in this study. Based on the variation analysis of the yields and evolvement features of gaseous hydrocarbon (C1-C5) and inorganic gaseous CO2, H2 and H2S, the reaction mechanisms were analyzed and discussed. In the calcium sulfate-saturated hydrocarbon system, H2S was produced by a small quantity, which indicates this reaction belongs to the low-degreed thermal sulfate reduction (TSR...     

PATTERN SPACE OF SEISMIC ANOMALIES ASSOCIATED WITH HYDROCARBON DEPOSITS*

The quantitative estimate of the anomalies in the seismic signal associated with a realistic subsurface hydrocarbon bearing anticline is discussed. This estimate is derived by the calculation of synthetic seismograms for a dissipative media. The reflection amplitude anomaly associated with gas deposit are as much as three times the background level. However, oil deposits give rise to much weaker anomalies. A decrease of the reflection amplitude by about fifty percent occurs for horizons lying below the gas bearing zone, causing a shadow zone. Time sag anomaly is dependent chiefly on the thickness of the gas bearing zone. The appearance of the anomaly on the time section is modified by the structure, and flat reflectors may be seen over the structure owing to the mutual cancellation of the structural rise and the time sag. Flat spots corresponding to the horizontal fluid interfaces may be expected at the edges of the pool only. The presence of hydrocarbon bearing layers causes a diagnostic character in the composite reflection signal which is very clearly seen in the spectra, the cross correlation functions, and the cross-spectra in profiles crossing the hydrocarbon bearing structures. These are potential diagnostic tools for locating hydrocarbon deposits, particularly when entrapped in thin layers.     

The scientific connotation of oil and gas formations under deep fluids and organic-inorganic interaction

As a relatively stable craton block in the earth system, the petroliferous basin is influenced by the evolution of the earth system from the early development environment of source rocks, hydrocarbon formation, and reservoir dissolution to hydrocarbon accumulation or destruction. As a link between the internal and external factors of the basin, deep fluids run through the whole process of hydrocarbon formation and accumulation through organic-inorganic interaction. The nutrients carried by deep fluids promote the bloom of hydrocarbon-generating organisms and extra addition of carbon and hydrogen source, which are beneficial to the development of high-quality source rock and enhancement of the hydrocarbon generation potential. The energy carried by the deep fluid promotes the early maturation of the source rock and facilitates the hydrocarbon generation by activation and hydrogenation in high-mature hydrocarbon sources. The dissolution alteration of carbonate rocks and clastic reservoirs by CO_2-rich deep fluids improves the deep reservoir space, thus extending the oil and gas reservoir space into greater depth. The extraction of deeply retained crude oil by deep supercritical CO_2 and the displacement of CH_4 in shale have both improved the hydrocarbon fluidity in deep and tight reservoirs. Simultaneously, the energy and material carried by deep fluids(C, H, and catalytic substances) not only induce inorganic CH_4 formation by Fischer-Tropsch(F-T) synthesis and "hydrothermal petroleum" generation from organic matter by thermal activity but also cause the hydrothermal alteration of crude oil from organic sources. Therefore, from the perspective of the interaction of the earth's sphere, deep fluids not only input a significant amount of exogenous C and H into sedimentary basins but also improve the reservoir space for oil and gas, as well as their enrichment and accumulation efficiencies.     

Origin of Mesozoic gold mineralization in South Korea

Abstract   The Mesozoic gold–silver deposits in South Korea are closely associated with the Mesozoic granitoids. The Jurassic gold–silver deposits can be distinguished from the Cretaceous ones in terms of occurrence, alteration style, gold fineness, associated mineral assemblage, fluid inclusion and stable isotopic compositions. The Jurassic deposits were formed in mesozonal environments related to deep-seated granitoids, whereas the Cretaceous ones were formed in epizonal environments related to shallow-level granitoids. The Jurassic auriferous deposits (about 165–145 Ma) show fluid characteristics typical of an orogenic-type gold deposit, and were probably generated in a compressional regime caused by an orthogonal convergence of the Izanagi oceanic plate into the Asiatic margin. However, strike-slip faults and caldera-related fractures, together with subvolcanic to volcanic activity, may have played an important role in the formation of Cretaceous gold–silver lode deposits (about 110–45 Ma) under a continental arc setting.     

浙江大桥坞铀矿床铅、氢、氧同位素研究

浙江大桥坞矿床是赣杭火山岩铀成矿带重要的铀矿床之一。本文通过对大桥坞铀矿床铅、氢和氧同位素及前人资料的综合研究,探讨了矿床成矿流体和成矿物质来源。结果表明花岗斑岩、凝灰岩、辉绿岩、矿石中黄铁矿、蚀变围岩中黄铁矿的Ph同位素组成变化较小,可能指示它们具有相似的源区。在铅同位素构造环境判别图解中,铅同位素投影点分布范围较广,但多数集中于地幔和造山带演化线之间,偏向造山带,反映了铅的来源与岩浆活动有关。氢、氧同位素组成显示,成矿流体主要来自大气降水。成矿物质来源于壳幔混合源。     

Detection of alteration at the Millennium uranium deposit in the Athabasca Basin: a comparison of data from two airborne electromagnetic systems with ground resistivity data

The Millennium uranium deposit is located within the Athabasca Basin of northern Saskatchewan. The basement rocks, comprised primarily of paleo‐Proterozoic gneisses, are electrically resistive. However, the deposit is associated with highly conductive graphitic metasediments that are intercalated with the gneisses. An unconformity separates the basement rocks from the overlying, horizontally stratified, Proterozoic sandstones of the Athabasca Group (which are also highly resistive). The strike extents of the graphitic metasedimenary packages are extensive and therefore electromagnetic (EM) survey techniques are successful at identifying these zones but do not identify the specific locations where they are enriched in uranium. Through drilling it has been noted that hydrothermal processes associated with mineralization has altered the rocks in the vicinity of the deposits, which should in theory result in a resistivity low. A significant resistivity low has been mapped coincident with the Millennium deposit using ground resistivity survey techniques. However, a comparison of the airborne EM and ground resistivity results reveals that the two data sets have imaged different features. The resistive‐limit (on‐time) windows of the MEGATEM data show conductive features corresponding to lakes located to the west and south of the deposit. The late‐time windows show a feature to the east of the deposit, interpreted as being associated with the east‐dipping graphitic basement conductors (similar to that observed in historical ground EM data collected in this area). The early‐time TEMPEST windows (delay times less than 0.2 ms) show a broad resistivity low located at approximately the same location as where the alteration has been identified through drilling. Modelling the data is not easy but a response that decays prior to 0.3 ms is consistent with 500 Ωm material in the sandstone, a resistivity value close to the lower limit with respect to the hydrothermally altered Athabasca group sediments in this area. The MEGATEM system does not see a conductive zone over the alteration as clearly but the high signal‐to‐noise ratio in the late‐time MEGATEM data means that the conductive material at a greater depth is more coherently imaged.     

Salinity variation of formation water and diagenesis reaction in abnormal pressure environments

~~Salinity variation of formation water and diagenesis reaction in abnormal pressure environments@解习农 @焦赳赳 @李思田 @成建梅~~~~