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BACKGROUND The Changjiang uranium ore field in the southern margin of the Zhuguangshan complex pluton is a typical granite-type uranium ore field in China. Zircon U-Pb dating has been used to date ore-bearing granites. However, due to the high content of uranium in the whole rock and zircon mineral, some zircons tend to be decrystallized, which may lead to scattered zircon U-Pb data and may affect the reliability of zircon U-Pb dating. Monazite is a widespread accessory mineral in granite, and it is an ideal mineral for U-Pb dating due to its high U and Th contents (up to 10000×10-6), and low common Pb content of about 100×10-6-1000×10-6. OBJECTIVES In order to constrain the age of the ore-bearing granite and discuss the tectonic setting. METHODS LA-ICP-MS U-Pb dating method was used to constrain the formation age of monazite from the Youdong and Changjiang plutons. The monazite standard materials USGS44069 and Trebilcock were selected as external standard samples and monitoring standard samples, respectively. RESULTS The 206Pb/238U age of monazite in the Youdong pluton is 228.0±1.5Ma (MSWD=0.82, n=23), and that of monazite in the Changjiang pluton is 156.8±1.7Ma (MSWD=0.76, n=14). These ages are consistent with the SHRIMP zircon ages of 232±4Ma and 160±2Ma, respectively, which further confirms that the Youdong pluton is the product of Late Indosinian magmatism, and the Yangtze River pluton is the product of early Yanshanian magmatism. CONCLUSIONS This study demonstrates that the U-Pb age of monazite in high-uranium granites can effectively constrain their formation age.

BACKGROUND The carbonatite-type molybdenum metallogenic belt in East Qinling is the largest molybdenum metallogenic belt in the world. The Huanglongpu deposit is one of the earliest discovered carbonatite-type molybdenum deposits in China. Our field survey found that the uranium grade of ores in this deposit was higher than the industrial uranium grade, being similar to the Huayangchuan U-Nb-Pb-REE deposit in the Qinling Orogenic Belt. However, the occurrences and mineralogical characteristics of radioactive elements are still unclear. OBJECTIVES To explore the main mineral assemblages, U occurrences and other characteristics of uranium ores in the Huanglongpu deposit. METHODS The detailed geological survey, μ-XRF, SEM and EDS analyses were carried out on the high-radioactivity ore from the Huanglongpu deposit. RESULTS The results showed that major uranium minerals in the Huanglongpu deposit were brannerite, betafite and uraninite, which were associated with calcite, feldspar, pyrite, molybdenite and chalcopyrite. Significant alteration and replacement of uranium minerals were observed in the studied ore sample. The betafite was transformed into Nb-rich Ti-Fe oxides after alteration. After alteration of brannerite and uraninite, a large number of cavities were formed within those minerals. The post-ore fluids were possible from meteoric water. The textural differences of altered brannerite and uraninite on BSE images suggested the variable chemical composition. CONCLUSIONS μ-XRF technology has a great application prospect in the future research of uranium deposit genesis and prospecting prediction.

BACKGROUND The Huayangchua polymetallic deposit is a super-large mineral deposit that has economic endowments of uranium and rare earth resources. The deposit is characterized by the unique ore types and complex mineral assemblage. Systematic mineralogical studies can reveal the main rare-earth minerals and the occurrence of REE, providing an important reference for the comprehensive utilization and metallurgical technology of rare earth elements. OBJECTIVES To provide new insight for mineralogy using the in-situ observation and analysis technology. METHODS The field emission scanning electron microscope (SEM), electron microprobe analysis (EMPA) and energy dispersive X-ray spectrometer (EDS) were used to systematically study ore minerals of the Huayangchuan deposit. RESULTS The rare earth elements in the Huayangchuan deposit mainly occurred in two states. Independent rare-earth minerals included allanite (La2O3 6.49%-7.61%, Ce2O3 11.50%-14.00%), monazite (La2O3 16.30%-21.21%, Ce2O3 32.06%-39.18%), bastnasite (La2O3 12.86%-14.20%, Ce2O3 36.67%-39.90%), fergusonite (La2O3 1.19%-2.11%, Ce2O3 1.29%-2.30%, Y2O3 22.67%-25.88%), and xenotime (La2O3 2.29%-3.58%, Ce2O3 1.89%-2.37%, Y2O3 39.77%-42.80%). REE also occurred as isomorphism in apatite, pyrochlore and sphene. CONCLUSIONS REE occurs as rare-earth minerals in the Huayangchuan deposit, including allanite, monazite, bastnasite, fergusonite and xenotime, as well as isomorphism in apatite, pyrochlore and sphene. The REEs in the Huayangchuan deposit are dominated by light rare earth elements, such as La and Ce, with minor heavy rare earth element Y.

BACKGROUND The Shijiaowei uranium deposit (No.339 deposit) in the Eastern Guidong granite complex of Nanling region, is one of the large type deposits in the Xiazhuang uranium ore field. Uraninite, the main ore mineral of the Shijiaowei deposit, is the ideal mineral for geochronology. Previous studies show that the uranium mineralize ages of Shijiaowei deposit is 38-138Ma acquired by ID-TIMS and EMPA. OBJECTIVES To provide new insight for uranium metallogenic mechanism and background of the Shijiaowei deposit by a new reliable uranium mineralization age determination method. METHODS In situ LA-ICP-MS U-Pb dating method was used to constrain the formation age of uraninite from the Shijiaowei deposit. RESULTS The 206Pb/238U age of uraninite was 52.46-56.89Ma with the weighted average age of 54.68±0.53Ma (MSWD=1.19, n=18). The in situ U-Pb dating of the uraninite avoids the influence of mineral inclusions, secondary changes and micro-cracks on dating. CONCLUSIONS Therefore, the in situ U-Pb isotopic age of the uraninite determined by LA-ICP-MS represents the ore-forming age of the deposit. The ore-forming age (about 55Ma) is consistent with the main metallogenic period (about 50Ma) of the South China granite-type uranium deposit, indicating that the uranium mineralization of the Shijiao ore deposit is closely related to fault tectonic activity induced by the local extension of the lithosphere in South China.

Quantitative analysis of sandstone clastic composition can provide important basis for provenance and sedimentary basin investigation. Based on the observation and description of sandstone macroscopic characteristics in the field, the ore-bearing sandstones from the Mengqiuer uranium deposit in Xinjiang were studied by optical Microscope and Electron Microprobe. Petrological characteristics of sandstone and occurrences of uranium minerals are discussed. Results show that the compositional maturity index of the sandstone is 0.56-1.08 with an average index of 0.78, indicating low compositional maturity and low structural maturity. The source rock is derived from a mixed recycled orogenic belt transition to the orogenic belt, and finally to the evolution of lithic and orogenic belt transition. The source rocks originated mainly from the Carboniferous-Permian intermediate acid volcanics in the southern margin of the basin and the northern margin of the Nalati, Keguqin, and Bonukenu mountains, as well as the late Devonian-early Carboniferous Dahalajunshan volcanic rocks and Paleozoic granites. Uranium minerals are mainly pitchblende, coffinite, and brannerite with minor adsorbed uranium. The back-scattering image shows that the distribution of uranium minerals is closely related to charcoal, pyrite and rutile.

The Yangtze Platform preserves relatively thick carbonate successions and excellent fossil records across the Ediacaran-Cambrian boundary interval. The intensely studied Meishucun section in East Yunnan was one of the Global Stratotype Section candidates for the Precambrian-Cambrian boundary. However, depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified. The Laolin section located in NE Yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the Precambrian-Cambrian boundary. However, the stratigraphic framework and correlations were controversial. We studied and systematically sampled the Laolin section and present here new carbon isotope data for this section. The Laolin section consists of, in ascending order, the Baiyanshao dolostone of the Dengying Formation, the Daibu siliceous dolostone, Zhongyicun dolomitic phosphorite, lower Dahai dolostone and upper Dahai limestone of the Zhujiaqing Formation, and the black siltstone of the Shiyantou Formation. Our data reveal a large negative [delta][sup.13]C excursion (-7.2 [per thousand], L1') in the Daibu Member, which matches the previously published data for the Laolin section, and a large positive excursion (+3.5 [per thousand], L4) in the Dahai Member, which was not shown in the published data. The excursion Ll' correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in Siberia and Mongolia. Similar magnitude excursions are also known from Morocco and Oman, for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 Ma, thus confirming a global biogeochemical event near the Ediacaran-Cambrian boundary. Our data also indicate that deposition was more continuous at the Laolin section compared with the Meishucun section, where there are no records of a comparable negative excursion near the Ediacaran-Cambrian boundary, nor any comparable positive excursion in the Dahai Member. Therefore, the Laolin section has proven potential to be a supplementary Global Stratotype Section for the Ediacaran-Cambrian boundary on the Yangtze Platform. Keywords: C-isotope stratigraphy, Ediacaran-Cambrian boundary, Laolin section, Yangtze Platform.

Changtian Basin is one of significant energy basins in Guangdong Province. To learn the geological structure, sedimentary material characteristics and tracer sandstone provenance in detail, microscopic identification, electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) are used to systematically study the typical sandstones of Nanxiong Group in Changtian Basin on the basis of field geological survey. The results show that the Upper Cretaceous Nanxiong Upper Subgroup is mainly composed of (carbonaceous) lithic quartz sandstone, followed by calcareous sandstone, (argillaceous) siltstone, fine sandstone, conglomerate and greywacke, generally developed with obvious secondary changes and metallization. The analysis of detrital zircons from Nanxiong Group reveals that most of the zircons in the samples have perfect oscillatory bands with Th/U values usually greater than 0.4, indicating the zircons are mainly of magmatic crystallization origin, with a few metamorphic zircons of complex origin. The U-Pb concordant ages can be roughly divided into five groups: 2506-1666 Ma, 1815-941 Ma, 510-434 Ma, 308-234 Ma, and 172-99 Ma, which correspond to the known tectonic events in northeast Guangdong, reflecting that the tectono-magmatic activities in the study area are mainly controlled by the magmatic activities in eastern China, with the characteristics of episodic development and evolution. Based on the systematic analysis of lithography, zircon U-Pb age and REE characteristics of clastic rocks from Nanxiong Group, and comparison with the possible provenance, it is concluded that the detrital materials were mainly derived from Mesozoic magmatic intrusions in the western margin of Changtian Basin. [ABSTRACT FROM AUTHOR]

The Late Mesozoic Pucheng granitic complex in northern Fujian Province is composed of the Chengbu and Shipi peralkaline A‐type granitoids, the Pucheng A‐type granitoid, and the Yongxing I‐type granitoid. The Chengbu and Shipi peralkaline granitoids were dated at 160 and 130 Ma, respectively, and are explained by the melting of meta‐igneous rocks with TDM2 of 1.70 Ga and 2.01 to 2.05 Ga. The Pucheng A‐type granitoid was emplaced at 110 and 102 Ma and is divided into two groups. Group 1 comprises the extremely felsic A‐type granite (SiO2 > 73 wt.%), high FeOT/MgO (>16), and low Ga/Al ratios and Zr + Nb + Ce + Y content. Group 2 contains a less‐evolved A‐type granite with high Zr + Nb + Ce + Y content. Both groups can be explained by dehydration melting of meta‐igneous rocks at low pressure. The diversity between the two groups was caused by different physicochemical environments. The Yongxing I‐type granite, which is abundant in mafic microgranular enclaves, was emplaced at 106 ± 1 Ma. It can be explained by the mingling of mantle‐derived and crustal‐derived magmas. Our data along with previously published data demonstrate that the northern Fujian Province was under an extensional environment from 160 to 100 Ma. This was caused by the NW‐trending subduction of the palaeo‐Pacific Plate. The Jurassic peralkaline granitoids were probably generated in a rift environment as a result of the reactivation of pre‐existing faults caused by the initial subduction of the palaeo‐Pacific Plate. The Early Cretaceous peralkaline granitoids may represent a rift environment as a tectonic response from low‐angle subduction to an increasing subduction dip angle. The 100 Ma granitoids derive from an intraplate extensional environment caused by the roll‐back of the palaeo‐Pacific Plate. [ABSTRACT FROM AUTHOR]