The Qinglongshan Xigeda profile in Panzhihua was studied,and the variation of trace element content as well as their ratio was analyzed.The results show that in addition to Ba,Sr,the content of other elements are all higher than the upper crust.The ratios of w(Sr)/w(Cu) is 1.81 ~ 4.50,and δ Ce appeared weak negative anomalies,which reflect in the deposition process of the whole profile,climate mainly warm and moist.The ratio of w(Th)/w(U) is high,and δEu is moderate negative anomaly,which reflect the profile depositional environment overall bias reducing.LREE enrichment in the sample,LREE content and REE content has a significant positive correlation.This indicates that the characteristics of REE are controlled by the activity of LREE,the profile sediment have land-based sources characteristics.
Accurately constraining the age and source of primary U mineralization is commonly difficult as diverse U minerals are affected by α-recoils and subjected to overprints of multi-stage fluids. Titanite has a good potential in revealing rock-forming and metallogenic information, and widely occurs in magmatic, metamorphic, and hydrothermal U deposits. However, the textural and chemical characteristics of titanite from most U deposits are poorly documented and little is known about the relationship between titanite and U mineralization. At the western margin of the Yangtze Block, a series of uranium occurrences and high-grade uraninite-predominant ores are hosted in the leucogranitic dykes, e.g., fine-grained albitite, monzogranite, and pegmatitic quartz vein. The genesis of U mineralization remains unclear largely because of the uncertainties as to the timing of mineralization and the origin of metals.Here, we present comprehensive U-Pb and Sm-Nd isotopic data, and major and trace element compositions for metamorphic (Ttn-I) and magmatic/hydrothermal (Ttn-II) titanites from the leucogranitic dykes and/or amphibolitic wall rocks. Ttn-I is in direct contact with metamorphic hornblende and plagioclase or occurs as irregular relics captured by the leucogranites, and is thus inferred to be the product of amphibolite facies metamorphism. Chemically, Ttn-I is characterized by low Fe/Al ratios, LREE-depleted patterns and weakly negative to positive Eu anomalies. By contrast, magmatic/hydrothermal Ttn-II crystals intergrown with uraninite in the leucogranites generally display flatter REE patterns, more negative Eu anomalies, higher Fe/Al ratios, and U, Nb, REE and Y contents, which could be applied as an indicator for U exploration. LA-ICP-MS U-Pb dating on Ttn-I yielded ages of ~860 Ma for amphibolite facies metamorphism. Instead, U-Pb dating on syn-ore Ttn-II yielded ages of ~786–779 Ma for U mineralization, which is coeval with the emplacement of leucogranitic dykes. Uraninite and intergrown Ttn-II have uniform, negative εNd(t) values (–5.7 to –15.5), indicating the initial melts were predominantly sourced from the old crustal materials (T DM2 = ~1.9–2.7 Ga). Considering the dyke-shape occurrences, feldspar-quartz-dominant lithologies, and wide textural and compositional variations of leucogranitic dykes, and obviously negative Eu anomalies in uraninite and titanite, we suggest that low-degree partial melting of U-rich protolith, subsequent fractional crystallization of plagioclase and assimilation of wall rocks may have contributed to uranium mineralization.
The thin but widely distributed sandstones in the shallow-water deltas have the potential to hold large deposits of natural gas. The fluvial sand bodies formed from river channels with different sedimentary facies and sandstone architectures have remarkable heterogeneities. The results of this investigation suggest that the sandstone architectures of river channels have a significant impact on the hydrocarbon accumulation and production of sandstone reservoirs. Information regarding the sandstone origin and architecture of shallow-water deltas, especially of the fingered bar type, is still very limited. This investigation focused on the channel sandstones in the shallow-water delta of the Jurassic Shaximiao Formation on the eastern slope of the western Sichuan Basin in China. Based on data from cores and logs of sandstones, seven types of lithofacies and four sedimentary facies were identified. Sand-rich sedimentary facies, including distributary channels, mouth bars, and overbanks, have merged to form four types of compound sandbodies corresponding to the fourth-order architectural unit in the architectural classification. Four types of compound sand bodies were classified, including CS1 (variable distributary channel sand body), CS2 (diverting channel and residual overbank sand body), CS3 (diverting channel and residual mouth bar sand body), and CS4 (terminal channel and residual mouth bar sand body). Relatively good physical properties occur in the sandstone architectures of types CS3 and CS4, with an average porosity of 11.06% and an average permeability of 0.97 mD. Sandstone architectures from the Jurassic Shaximiao Formation of the study area were controlled by water depth and climate, tectonic subsidence, distance from provenance, erosion effect, and channel sinuosity and discharge. With strong lateral erosion, a shallow-water delta would have more sandstone architectures of types CS3 and CS4 in the high sinuosity of channels far from the provenance. Furthermore, sandstone architectures of types CS3 and CS4 are prone to form in connected channel sandbodies with relatively high contents of natural gas of approximately 4.48 × 104 m3/d. The results of this investigation are beneficial to improve the understanding of the characteristics of sandstone distributions in shallow-water deltas, especially in fingered bar types, and to guide oil and gas explorations in shallow-water delta systems.
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