Abstract:The Yangchang phosphate deposit in the northwest Zhenxiong County is located at the area of Qingba Village in Wanchang Town to Liaoyeba Village in Yanyuan Town (also called Yangchang). The deposit has the characteristics of large reserves of resources, excellent ore quality and concentrated distribution of resources, and is currently the largest concealed monomeric phosphorus-rich deposit in Asia, ranking fifth in the world. The genetic type of the deposit is the shallow marine sedimentary type phosphorite deposit in the Lower Cambrian Meishucun Formation (∈₁ms). The ore body is stratified and concealed in the Yangchang anticline. Generally, the ore body develop from east to west, and the mineralization tends to be richer. To date, the Yangchang phosphate deposit has made a major breakthrough in deep mining, revealing 3 layers of phosphorite depositions, and the inferred phosphorus ore resources of grade Ⅰ+Ⅱ+Ⅲ have been discovered in 3 survey areas (Zhujiachang, Fengjiagou and Qingba Village) has a cumulative mineral thickness of 36.77 m and an average P₂O₅ grade of 22.94%. The potential phosphorite resources estimated as 132.0×10⁸ t, which effectively improves the capacity of phosphorus resources in the country, achieves the deep prospecting breakthrough of strategic minerals in short supply in the country, and has huge potential economic value and social benefits. In this paper, the formation mechanism and enrichment of the early Cambrian Meishucun phosphorus deposit is summarized systematically through the prospecting project results, and an effective deep phosphorite prospecting technology is established, which is helpful to further improve the ore-forming theory of early Cambrian phosphorus deposit, and with important guiding significance for the exploration and development of concealed phosphorus deposits in northeast Yunnan. The discovery of the super large phosphorus deposit in Yangchang has achieved a major breakthrough in deep concealed phosphorus deposit prospecting technology, greatly expanded the amount of phosphorus resources available in Yunnan Province, and laid a solid resource foundation for strengthening the storage and production of important energy and mineral resources, punning the resource economy of Yunnan Province, and building a national important phosphorus chemical industry base of 100 billion. It also provides a strong resource guarantee for the maintenance of energy and resources security of the nation.

Abstract:The recently discovered Yangchang deposit in Zhenxiong County, Zhaotong City, Yunnan Province is an ultra-large-scaled buried phosphate deposit. Previous research on this deposit mainly focused on the metallogeny, while the study of sedimentary geochemistry and the paleoenvironment is lacked. More importantly, the inorganic (δ¹³C_carb) and organic (δ¹³C_org) carbon isotopes as well as their relationships in the early Cambrian were rarely reported. In this study, three drill cores (ZK001, ZK0701, ZK1512) in Yangchang phosphate deposit were selected for high-resolution investigations of δ¹³C_carb and δ¹³C_org. Both δ¹³C_carb and δ¹³C_org show negative shifts in the top Precambrian Dengying Formation and the bottom of its overlying Zhujiaqing Formation, which is consistent with the global Basal Cambrian Carbon Isotopic Excursion (BACE), likely due to the oxidation of organic carbon reservoir. However, we did not find significant positive shifts in the overlying strata (i.e., Zhujiaqing Carbon Isotopic Excursion, ZHUCE), which may be caused by sedimentary hiatus given that the Yangchang phosphate deposit is mostly intra-clastic phosphorus-rich deposits. Nevertheless, we propose that this phosphate deposit was mainly formed during the Fortunian according to the comparison between the δ¹³C_carb in the three drill cores and the composite profile of δ¹³C_carb in South China. The comparisons for the δ¹³C_carb and δ¹³C_org values in the drill cores ZK001 and ZK0701, show that the average value of the ΔC_carb-org (difference between δ¹³C_carb and δ¹³C_org) is 28.8‰ and 22.2‰ in the Dengying Formation, and these values change to 31.7‰ and 31.7‰ at the bottom of the Zhujiaqing Formation, and 29.6‰ and 29.8‰, in the middle and upper of the Zhujiaqing Formation, respectively. We propose that the decoupled δ¹³C_carb and δ¹³C_org occurring in the middle of the Zhujiaqing Formation may be caused by the increased primary productivity or buried organic carbon. In summary, the high-resolution paired inorganic and organic carbon isotopes in this work indicate the formation time of Yangchang phosphate deposit and shed light on associated paleoenvironmental changes, which also support the regional stratigraphic correlation.

Abstract:The Yangchang phosphate deposit is a large-buried shallow marine carbonate stratified phosphorite deposit discovered in the Meishucun Formation (∈₁ms) of the Lower Cambrian recently. The understanding of its sedimentary environment and enrichment mechanism is still limited. Representative borehole cores were selected to carry out systematic sedimentary facies cataloguing. By means of sedimentary (microfacies) analysis, mineralogy and mineral chemistry tracing, the characteristics of rock and mineral (assemblage), sedimentary (microfacies) types, sedimentary environment and spatial and temporal distribution of each lithologic section of the Meishucun Formation are analyzed. We also studied the sedimentary environment evolution, the source, migration and enrichment mechanism of phosphorus, and its metallogenic model. The comparative analysis shows that the ore-bearing strata exhibits the nearshore tidal flat facies sedimentary environment with transgression-regressive sequence vertically, 6 microfacies types in 3 subfacies namely supratidic flat, intertidal flat and subtidal flat are identified. Supratidic flat is divided into supratidic flat and supratidic carbonate flat. The intertidal flat is divided into intertidal carbonate flat, intertidal flat and storm current. The subtidal flat developed a low energy subtidal flat. The favorable phosphorus formation environment is the high energy intertidal flat in intertidal flat. Repeated action of tides and waves in the shallow water environment for a long time is conducive to the winnowing, enrichment and reconstruction of phosphorous rich particles, thus forming a phosphorous rock deposit with rich and thick beds in the northwest and poor and thin beds in the southeast of the mining area. To sum up, the ore forming process of the Yangchang phosphate deposit can be divided into three stages, namely: ① initial accumulation and precipitation mineralization stage (phosphorus source carried by upwelling ocean current); ② biochemical deposition and accretion mineralization stage (migration and enrichment driven by microbial decomposition, transformation and compound); ③ winnowing enrichment and re-enrichment mineralization stage (precipitation and enrichment driven by multi-stage wave and tidal action). This new points provides an important basis for prospecting and exploration in the mining area and peripheral areas.

Abstract:The Cambrian life explosion is closely related to the redox environment of plaeoocean, and the Lower Cambrian phosphorite in the Upper Yangtze Block has recorded a relatively complete information of the Early Cambrian. The Yangchang phosphate deposit in western margin of the Yangtze Block is a super-large phosphate deposit occurring in the Meishucun Formation of the Lower Cambrian, which can reconstruct the paleomarine environment of this period. In this paper, ICP-MS and other techniques were used to analyze the elemental geochemical composition characteristics of the phosphorite and its surrounding rocks and explore the geological environment of the Yangchang phosphate deposit. The results show that the CIA value of phosphorite is 46.40~65.60, with an average of 57.43, indicating that the weathering degree is low, the total amount of rare earth element (ΣREE) in phosphorites in this deposit is relatively low (140.0×l0^-6~237.4×l0^-6), but yttrium is relatively rich (87.0×l0^-6~183.2×l0^-6). The North American standardized rare earth distribution pattern is relatively flat, the LREE/HREE is of 4.22~7.50, shows that the diffrernce of light and heavy rare earth elements is not obvious, with obvious Ce negative anomaly (0.22~0.42), Eu anomaly is not obvious with δEu of 0.90~1.21, and U/ Th ratio of 2.55~27.68, which reflect that the phosphorite was affected by a certain influx of hydrothermal fluid during the sedimentary of phosphorites. Combined with the analysis of δCe, V/Cr, Y/Ho, Sr/Cu and other elements, it is indicate that from the bottom of Dengying Formation in the Sinian Period, to the phosphate-bearing layer Cambrian Meishucun Formation, to the upper cover Niutitang Formation, the ancient ocean redox environment changes from the relative reduction environment at the bottom to the oxidation environment upward until the top becomes the relative reduction environment. The paleoclimatic environment is cold and dry-warm and moist alternatively appear. The salinity of ancient seawater is the evolution process of salt water to semi-salt water to salt water to fresh water. The above analysis shows that the phosphorite deposit in a relatively oxidized saline water and arid climatic environment, and the climatic environment is relatively arid during sedimentation, and may be affected by the influx of hydrothermal fluid.

Abstract:Marine sedimentary phosphorites usually contain high rare earth elements (REEs) content, especially the heavy REEs (HREEs), which account for over 30% of the total REEs. The phosphorites may became another important source for HREEs in the future. Phosphorite deposits are widely distributed in China and most of them are found in Yunnan, Guizhou, Sichuan Provinces, etc. High REEs abundances are confirmed in the Zhijin phosphorite deposit in Guizhou Province and with total REEs resource over 3 Mt. The collophanite and apatite are the main host phase for both REEs and P, and the collophanite has complex chemical composition. There are still controversies for the mineral and chemical composition of collophanite. Based on detailed petrological, mineralogical, SEM/EDS, XRD, FIB-TEM and LA-ICP-MS results of phosphorites in Zhijin deposit, this paper discuss the mineral composition of phosphorites and the origin of the complex chemical composition of collophanite. The results show that the most phosphorites in the deposit show the pelletal texture,which is composed of phosphorous pellets and carbonate cement. The mineral composition of the phosphorous pellet is very complex, including mainly fluorapatite and dolomite, and with minor quartz, dolomite, pyrite (some oxidized into limonite), muscovite, solid bitumen and barite. The mineral composition of the cement is mainly dolomite, with minor quartz, pyrite, barite, and trace amounts of zircon, rutile, and liebigite (possibly formed by oxidation of other uranium minerals). The FIB-TEM results show that the cryptocrystalline part of the outer layer of phosphorus pellet is composed of nanoscale mineral aggregates including mainly nanoscale fluorapatite, and small amount of nanoscale dolomite, pyrite and organic matter. The mineral composition of collophanite is similar to that of phosphorus pellet. The discovery of nanoscale fluorapatite, dolomite, pyrite, and organic matter in phosphorite provides reliable evidence for explaining the chemical complexity of collophanite. The discovery of solid bitumen and liebigite in phosphorites, as well as high REEs content in organic matter, also provides new evidence for an alternative occurrence of U and REEs in phosphorites.

Abstract:Phosphate ore is an important strategic mineral resource, and its guarantee degree is related to national resources, energy and food security. Phosphate ore resources in Yunnan Province occupy an important position in the country, with the characteristics of concentrated distribution, simple deposit types, large and medium-sized deposit are abundant, good ore quality and easy mining. With the major breakthrough in mineral prospecting of the Yangchang phosphate deposit in Zhenxiong area in recent years, phosphate ore in Yunnan Province has become one of the hot spots in mineral deposit research. This paper systematically sorted out the types and resource reserves of phosphate ore deposits in Yunnan Province, selected typical deposits of different deposit types for detailed dissections, systematically summarized the metallogenic laws from the aspects of spatial and temporal distribution charac- teristics, ore-bearing rock series characteristics, etc., improved the sedimentary phosphate ore mineralization model in Yunnan Province on the basis of the Yangchang phosphate deposit research, and combined with the results of potential evaluation, delineated 8 key prospecting potential areas. It provides the direction for phosphate rock prospecting in Yunnan Province in the future.

Abstract:Shifang-type phosphorite deposit is an important type of phosphorite deposit in China, which is characterized by large scale, high phosphorus grade, and enrichment in rare earth elements (REEs). However, the enrichment regularity and resource potential of REEs in this type of deposit are not studied in detail. This study takes the typical Shifang-type phosphorite deposit in Mianzhu, Sichuan Province, as the research object. Based on field geological investigation, the distribution and enrichment characteristics of REEs in the deposit are explored through microscopic petrographic observation, scanning electron microscope/energy disperse spectroscopy imaging, and whole-rock geochemical analysis for the phosphorus-bearing layers (phosphorite layer, dark grey and maroon S-P-Al-Sr-rich layers) and their roof and floor rocks (dolomite) in the mining area. In turn, the potential resource of REEs in Shifang-type phosphorite deposits in Sichuan Province is discussed. The results showed that the total REEs (La-Lu+Y) contents in the roof and floor dolomites of the phosphorus-bearing layers are very low (13.6×10^-6 on average), the REEs contents in the phosphorite are medium (280.0×10^-6 on average), while the REEs contents in the S-P-Al-Sr-rich layers are extremely high (2 053.9×10^-6 on average), especially the maroon S-P-Al-Sr-rich layer (up to 3 257.2×10^-6). Together with previously published REEs content data from adjacent phosphorite deposit, the average REEs content in S-P-Al-Sr-rich layers in the Shifang-type phosphorite deposits in Sichuan Province is 2 259.4×10^-6 with the maximum up to 3 286.8×10^-6, of which the average concentration of medium and heavy REEs (Sm～Lu+Y) is 1 276.9×10^-6 with the maximum up to 2 213.0×10^-6, accounting for 55.1% of the total REEs. REEs contents in the Shifang-type phosphorite deposits in Sichuan Province are much higher than those in ion adsorption-type REEs deposits in southern China, Zhijin REEs-bearing phosphorite deposit, and REEs-rich deep-sea sediments. According to preliminary estimates, the total potential REEs resources associated with the Shifang-type phosphorite deposits in Sichuan Province can reach 252 000 tons, 156 000 tons of which are medium and heavy REEs. The potential medium and heavy REEs resources in the S-P-Al-Sr-rich layer alone can reach 96 000 tons. Therefore, the Shifang-type phosphorite deposits in Sichuan Province have important economic and social value, and the development and utilization of REEs in these deposits are expected to alleviate the current shortage of medium and heavy REEs in China.

Abstract:The Yangchang phosphate deposit in Zhenxiong County, Yunnan Province is a super large sedimentary phosphate deposit evaluated in recent years in the Early Cambrian period. It is characterized by large resource reserves, excellent ore quality, and concentrated resource distribution, and is currently the largest hidden single rich phosphate deposit in Asia. This article mainly uses different analysis methods to conduct systematic mineralogical research on the chemical composition, mineral composition, embedding characteristics, embedding particle size and intergrowth relationship, dissociation degree of the phosphate ore in the deposit. The grinding fineness and ore sorting process methods are also preliminarily explored. Our results show that the samples in this study are high-grade silicon calcium carbonate phosphate ore, with a P₂O₅ content of 29.34%. The main P-bearing mineral in the ore is fluorapatite which commonly distribute as hidden crystal microcrystal aggregates (commonly known as collophane). The main gangue minerals are quartz, calcite, dolomite, and a small amount of pyrite. The ore is characterized by low magnesium and low silicon, and can be processed using the direct-reverse flotation method. The ore has fine particle size and complex interrelationships, making it difficult to dissociate. During the beneficiation, fine grinding is required to increase the degree of monomer dissociation, but the impact of mechanical entrainment and mud formation caused by excessive grinding on flotation indicators should be paid special attention. The ore has reached the phosphate concentrate index and can be directly processed and utilized. If beneficiation is required, it is recommended to focus on studying the grinding process and exploring joint beneficiation methods to achieve the desired beneficiation effect.

Abstract:Phosphorite deposit is a kind of marine sedimentary phosphate deposit with the francolite as the main ore mineral. These deposits were formed in the upwelling areas during six historical periods after Paleoproterozoic, and are generally related to the biological activity and the intensity of continental weathering. The formation of phosphorite deposits is controlled by marine transgressions and regressions, microbial activities and physical and chemical conditions of sediment pore water. The key factors for the formation of phosphorite deposits with high rare earth elements (REEs) content are low sedimentation rate and periodic submarine storms. Some phosphorite deposits are rich in medium and heavy REEs, which are potential important REE resources. The main host mineral of REEs in phosphorite is francolite. The REEs in francolite are mainly derived from seawater in sedimentary period and sediment pore water in early diagenetic period, and are incorporated into francolite via adsorption or lattice substitution. REEs can be adsorbed on the surface of marine particles by forming as REEs-carbonate complex and released by the marine particles decomposing that is induced by the change of redox conditions in the sediment pore water. Through the previous research, it is found that different marine particles preferentially adsorb different REEs, which results in the formation of different REEs patterns of pore water and then affects the patterns of francolite in phosphorite deposits. The enrichment of REEs in francolite is equal for light, medium and heavy REEs and different REEs patterns in francolite are derived from contrasting fluid sources. In general, seawater can produce a HREEs-enriched pattern, and pore water might yield a MREEs-bulge pattern (enrichment of medium REEs). As the phosphorite deposits with significant REEs contents are characterized by MREEs-bulge patterns that are consistent with Fe-Mn (oxyhydr)oxides input by the submarine hydrothermal process and the pore water in the early diagenetic process, which may indicates the influence of the submarine hydrothermal activities and the early diagenetic process on the REEs enrichment mechanism of phosphorite deposits. In this paper, the metallogenic process of phosphorite deposits is summarized from the characteristics, spatiotemporal distribution and metallogenic control factors of phosphorite deposits; the enrichment behavior and differentiation behavior of REEs in the process of phosphorite mineralization are analyzed from the content and anomaly of REEs in phosphorite deposits; and the possible enrichment mechanism of REEs in phosphorite rocks with abnormal enrichment of REEs is revealed. The study of metallogenic process and REEs enrichment mechanism of phosphorite deposits is of great significance for the prospecting and exploitation of phosphorite deposits that are highly enriched in REEs.

Abstract:The Aruhan granodiorite intrusion in Xiwuqi, Inner Mongolia, is exposed along the central and eastern parts of the Hegenshan suture zone. LA-ICP-MS zircon U-Pb dating shows that the ages of the granodiorite are ranging from 332±3 to 327 ±1 Ma, suggesting emplacement during the Early Carboniferous. The Aruhan granodiorite is characterized by high contents of SiO₂ (65.20% to 68.27%), Al₂O₃ (15.61% to 17.35%), Sr (472 ×10^-6 to 552×10^-6) and low contents of MgO (1.16% to 1.61%), Yb (0.86×10^-6 to 1.13×10^-6), Y (7.29×10^-6 to 11.42×10^-6, with Na₂O/K₂O and Sr/Y ratios ranging from 2.56 to 4.35 and 43.45 to 75.68, respectively. The total REE is low (44.73×10^-6 to 88.11×10^-6), the fractionation of REE is significant , and the anomaly of Eu (δEu=0.79 to 1.07) is not obvious. The geochemical characteristics of the whole-rock indicate that the Aruhan granodiorite belongs to typical high-SiO₂ island arc adakites (O-type) series, formed in an environment of active continental marginal arc. The source of the maga might be the product of partial melting of subducting oceanic crust with oceanic sediments, which reacts with overlying mantle peridotite. Crystallization differentiation and contamination by crustal materials might occurre during its emplacement. This discovery may support the fact that the central and eastern parts of the Hegenshan Ocean was not yet closed during the Early Carboniferous. Combined with the regional research, we preliminarily believe that the Hegenshan Ocean may have undergone bidirectional subduction and abatement during the Early Carboniferous, which is different from the previous view that the Hegenshan Ocean underwent unidirectional subduction and abatement northward only.

Abstract:The Proterozoic Eon is a critical period of the Earth’s evolution, and the study of its rock records in this period is important for understanding the Earth’s evolution in the Precambrian. The correct interpretation of rock genesis is the basis of the study of rock geotectonics and the premise of revealing the change of earth environment based on rock records. A set of silicon-rich layered rocks generally developed at the bottom of the Changcheng System in the North China Craton, which is considered to be a set of marine quartz sandstones and siliceous rocks formed by shallow metamorphism in rift valley deposition. This paper focuses on the silica-rich layered rocks of Changzhougou Formation at the bottom of the Great Wall System exposed in Huyugou, Changping, Beijing. Through detailed field geological observations, petrological and mineral analysis of typical samples, SEM/EDS (Scanning Electron Microscopy/X-ray Spectroscopy), CL (Cathodoluminescence) imaging, in-situ LA-ICP-MS (Laser Ablation-inductively Coupled Plasma Mass Spectrometry) analysis of quartz, and petrological, micro-thermometry, muffle furnace heating-quenching experiments, and SEM/EDS, EPMA (Electron Probe Microanalysis), LRM (Laser Raman Microscopy) analysis of melt inclusions in quartz, a new understanding of the volcanic origin of the silicon-rich stratified rocks at the bottom of the Great Wall System has been proposed. The results indicate that the silicon-rich stratified rocks at the bottom of the Great Wall System include two types: clastic structures (previously defined as quartz "sandstone") and mosaic structures (previously defined as "quartzite"). The main mineral compositions are quartz and K-feldspar, with minor amounts of zircon, rutile, and other minerals. In the clastic structure rocks, quartz and K-feldspar clasts exhibit angular to subangular shapes, and K-feldspar shows no signs of clay alteration at the edges. The CL of quartz in the two types of rocks mostly shows blue-purple luminous characteristics. Additionally, the formation temperature estimated by the quartz titanium saturation thermometer is concentrated between 550~650℃, indicating characteristics of high-temperature quartz. Both types of rocks contain iron-titanium-rich two-phase melt inclusions in quartz and K-feldspar. Micro-thermometry results of the melt inclusions show that during the heating process to 1 000℃, the composition of the two-phase immiscible melt inclusions changes continuously, when the temperature reaches 1 000℃, with a color reversal occurring at about 1 050℃, and critical homogenization around 1 350℃. Muffle furnace heating-quenching experiments also confirmed that the two-phase melt inclusions in the samples quenched after heating to 1 350℃ became homogeneous. SEM/EDS and EPMA results indicate that the main components of the melt inclusions are iron and titanium oxides, with the dark part being relatively rich in iron and the light part being relatively rich in titanium, and the Fe/Ti ratio of the two phases of the melt inclusions varies greatly. LRM analysis results show that both phases of the melt inclusions are amorphous. Integrating the structural characteristics of the rocks, the CL luminescence characteristics of quartz, the formation temperature estimation of quartz, and the micro-thermometry results of the melt inclusions in quartz, it is believed that the siliceous strata at bottom of the Changcheng System should be siliceous volcanic rocks and volcaniclastic rocks. This indicates that there was a large-scale siliceous volcanic activity in the North China Craton during the Paleoproterozoic, which is related to the rifting of the Columbia Supercontinent. It provides new evidence for the geological evolution of the North China Craton in the Proterozoic. The discovery of iron-titanium-rich melt inclusions in quartz also offers new perspectives on the formation of Precambrian magmatic iron and titanium deposits, particularly the enrichment mechanism of iron and titanium during the magmatic process.

Abstract:The Mesozoic and Cenozoic tectonic magmatic activity in the Lhasa block has always been one of the research hotspots in the basic geology of the Qinghai-Xizang Plateau. There are many Cenozoic, especially Miocene magmatic rocks developed in the western part of the Lhasa block. This article takes the newly discovered Miocene granite in the Anglonggangri area of the western Lhasa block as the research object, and explores its rock types, rock genesis, and tectonic background. The Miocene granites in the Anglonggangri area are composed of fine-grained muscovite monzonitic granite and medium-fine-grained monzonitic granite, with a small amount of dark inclusions developed internally. The zircon U-Pb age of fine-grained muscovite monzonitic granite is 9.95±0.14 Ma, and the zircon U-Pb age of medium-fine-grained monzonitic granite is 10.68±0.2 Ma, both from the Miocene. Both of them have the characteristics of high silicon (SiO₂=72.35%~74.74%), rich potassium (K₂O/Na₂O=1.15~1.45, all greater than 1), high aluminum (Al₂O₃=14. 35%~14.83%), and weak peraluminum peraluminum (A/CNK=1.08~1.14). The number of CIPW corundum molecules is greater than 1%. The differentiation of light and heavy rare earth elements is very obvious, with a moderate negative Eu anomaly, enriched in large ion lithophile elements such as Rb, Th, K, and depleted in high field strength elements such as Nb, relatively enriched in high field strength elements such as Hf and Zr, Sr, Ba, P, Ti, etc. These characteristics indicate that it is a high potassium calcium alkaline series of peraluminous S-type granite. Both of them have relatively low Sr, high Sr/Y, La/Yb ratios, and extremely low Y and Yb contents. The granite in the research area originated from a thickened lower crustal environment and underwent a certain degree of magma mixing. Based on the comprehensive regional research results, the formation of Miocene granites in the Anglonggangri area may be related to the northward subduction of the Indian plate into the north Lhasa block, where plate tearing occurred and high-temperature asthenosphere material flowed through the plate fragments, causing partial melting of the lower crust.

Abstract:In recent years, the exploration of sandstone-type uranium deposits in the northern part of China has made breakthroughs in the Mesozoic and Cenozoic red-colored sedimentary formations. However, there is a great controversy about the mechanism of uranium mineralization in red beds, which has become a hot topic of current research. A large amount of uranium mineralization outcrop information is developed in the Neogene red layer in the Kuqa Depression. Carrying out relevant research is very helpful in analyzing the uranium enrichment mechanism in the red variegated layer. Through systematic sedimentology, petrology and mineralogy, the uranium mineralization spots in the red variegated layer of the Jidike Formation were dissected, and a relatively special type of uranium mineralization was discovered: the mineralized layer was located in a lacustrine sedimentary environment under an arid background. It is produced in a large set of red mudstone in the shape of a thin layer of lens. The mineralization lithology is gray-green marl and develops a large number of reddened siliceous masses. The mineralization has layer-controlled characteristics and is closely related to the siliceous masses. The siliceous mass has a combination of reddish microcrystalline quartz, fluorite, uranite, calcite and a small amount of natural arsenic, chalcopyrite and barite intergrowth minerals. The siliceous mass is very similar to the granite-type siliceous vein uranium mineralization in South China, showing the characteristics of deep hydrothermal origin. It is comprehensively judged that this mineralized layer has dual effects of sedimentation and hydrothermal fluid, and is a special hot water deposition type uranium mineralization. This type of uranium mineralization discovery provides direct and strong evidence that deep hydrothermal fluids could carry uranium into sedimentary basins to undergo uranium mineralization, and improve the theory of sedimentary uranium mineralization in continental basins.

Abstract:In this study, the whole-rock geochemistry and zircon U-Pb ages are reported for the meta-basic rocks of the Li’eryu Formation of the South Liaohe Group from the cobalt exploration area in Kuandian. These data provide a significant insight into the tectonic background, as well as the source of cobalt. Geochemical features of the meta-basic rocks in boreholes show that they are orthorhombic amphibolite, and have similar rare-earth elements (REEs) patterns, with slightly negative Eu anomalies. REEs and trace elements compositions have affinity to those of E-MORB. Based on the mineral compositional analyses and p-t estimates using conventional geothermobarometers, the clinopyroxene-bearing amphibolite (ZK2-1) records p-t conditions of p=0.82~1.00 GPa and t= 712~751℃, which probably constrained the peak high amphibolites-facies stage. The metamorphic p-t conditions of (clinopyroxene-bearing) amphibolite (ZK1-1 and ZK3-1) are p= 0.42~0.81 GPa, t= 688~759℃ and p=0.59~0.85 GPa, t=703~739℃, respectively, which represent the conditions of the retrograde stage. The metamorphic zircon from the meta-basic rocks yield the SHRIMP U-Pb ages of 1 857~1 850 Ma. The integrated study of geochemistry and zircon U-Pb dating reveals that their protoliths of the meta-basic rocks are mid-Paleoproterozoic tholeiitic basalt and formed in an extended tectonic environment. Their protoliths underwent significant crustal assimilation imply that the scale of the mid-Paleoproterozoic oceanic basin may be limited. By comparing the geochemical characteristics of meta-basic rocks in the North and South Liaohe groups, it is believed that meta-basic rocks in the Kuandian area are not the main source of cobalt mineralization. The material sources of cobalt mineralization still needs further research.

Abstract:The Maevatanana gold deposit in Madagascar is a quartz-vein type gold deposit hosted in a greenstone belt, and its genesis is highly controversial. This article conducts elemental geochemical analysis and dating of the Maevatanana gold deposit, and explores the mineralization age and process of the Maevatanana gold deposit in Madagascar. The gold content of gneiss is 1.11×10^-9~80.8 ×10^-9, with an average of 19.55×10^-9; pyrite is the main gold-bearing mineral in gneiss, with a Re-Os isotopic age of 752±27 Ma. The gold grade of the gold-bearing quartz vein is 26.44×10^-6~132.22×10^-6, and pyrite is the main gold-bearing mineral. The Re-Os isotopic age of pyrite in the gold-bearing quartz vein is 535±26 Ma, representing the mineralization age of the Maevatanana gold deposit. The Re-Os isotope isochron ages of two phases of pyrite correspond to the time of two collisions during the Pan Afri- can orogeny event. The gold content in gneiss is much higher than the average grade of the crust, and encapsulated gold can be seen in pyrite. The Re-Os isotopic age of pyrite indicates intrusion of granite and gabbro at 752±27 Ma. The Madagascar terrane underwent extensive metamorphism from greenschist to amphibolite facies, and gold in volcanic sedimentary rocks was activated, migrated, and enriched to form a source layer. The mineralization age of the gold-bearing quartz vein is 535 ± 26 Ma, which is consistent with the age of the Cambrian post collisional A-type granite in central northern Madagascar. Field evidence and geochemical data indicate a close genetic relationship between the Maevatanana gold deposit and the Cambrian post collisional A-type granite. During the process of magma ascending, the high-Si melts entered the magma and gradually evolved into ore-forming fluids, which enter the host structures and enrich mineralization.

Abstract:Chloritization is a typical middle-low temperature hydrothermal alteration type of early ore-forming stage in Shulouqiu deposit of Changjiang rock mass in southern Zhuguang. In this paper, the chlorite in the horizontal alteration zone around the ore body are studied comprehensively by optical microscopy, electron probe and scanning electron microscopy. Based on the lithological characteristics and genesis of chlorite, they are divided into five types: fissure filling chlorite, biotite altered chlorite, feldspar altered chlorite, dolomite altered chlorite and spherical chlorite. The five types of chlorite are all trioctahedral iron-rich chlorite with the same structure type, belonging to three species: vermicular chlorite, ferromagnesian chlorite and uraninite chlorite. Then, the five types of chlorite may have formed in the same period of fluid action in the early ore-forming period, with the formation temperature between 219~282℃ and log f_O2 between -47.74~-43.69. Combined with previous research results in the region, the early ore-forming fluid may be a crust-mantle mixed fluid dominated by mantle-derived materials, with strong reducibility. Its formation is related to the intrusion of regional basic veins, which provides a reducing field for the mineralization system, resulting in the reduction and precipitation of U⁶⁺ in the ore-forming fluid.

Abstract:The Lijiagou pegmatite-type lithium spodumene deposit is one of the typical deposits in the Ke’eryin ore field, located in the central part of the Songpan-Ganzi fold belt in Sichuan Province, China. Through recent exploration and assessment, the Lijiagou deposit has been identified as a super-large spodumene deposit, drawing significant attention from domestic and international scholars. The mineral processing characteristics of the Lijiagou deposit vary with elevation, necessitating an accurate evaluation of the industrial value of the ore. Based on detailed microscopic and hand specimen observations, this study employs various methods and techniques, including X-ray powder diffraction (XRD), electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), chemical element analysis, chemical phase analysis, and the mineral liberation analyzer system (MLA). These methods and techniques are used to determine the composition of the ore, identify the types and occurrence states of beneficial and harmful elements, and clarify the ore’s processing properties. The results will provide theoretical and technical support for the comprehensive utilization of rare metal resources in the region. The average grade of lithium ore is 0.94%, with approximately 84.7% of Li derived from spodumene. The average grade of Rb₂O is 0.13%, meeting the industrial-grade requirements for comprehensive recovery of associated elements. The spodumene exhibits a wide range of grain sizes and is highly heterogeneous, requiring multiple stages of grinding. Based on the liberation characteristics, it is recommended to grind the material to -0.075 mm before entering the final flotation process.