scholarly journals SIMS U-Pb Dating of Uraninite from the Guangshigou Uranium Deposit: Constraints on the Paleozoic Pegmatite-Type Uranium Mineralization in North Qinling Orogen, China

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 402
Author(s):  
Guolin Guo ◽  
Christophe Bonnetti ◽  
Zhanshi Zhang ◽  
Guanglai Li ◽  
Zhaobin Yan ◽  
...  
Keyword(s):  
Partial Melting ◽  
Fractional Crystallization ◽  
Secondary Ion Mass Spectrometry ◽  
Uranium Mineralization ◽  
Crustal Material ◽  
Early Devonian ◽  
The North ◽  
Low Degree ◽  
North Qinling ◽  
The One

Pegmatite-type uranium mineralization occurs in the Shangdan domain of the North Qinling Orogenic Belt, representing a significant uraniferous province. The Guangshigou deposit is the largest U deposit of the district. Within the North Qinling area, a series of Caledonian granitic igneous rocks intruded the Proterozoic metamorphic rocks of the Qinling Group in two magmatic stages: (i) the Early Silurian Huichizi granite that was derived from a low degree of partial melting of thickened lower basaltic crust combined with mantle-derived materials following the subduction of the Shangdan Ocean; and (ii) the Late Silurian–Early Devonian Damaogou granite and associated pegmatites derived from the same source but emplaced in a late tectonic post-collisional extension environment. In the Guangshigou deposit, the U mineralization mainly occurs as uraninite disseminated in U-rich granitic biotite pegmatites, which formed by assimilation-fractional crystallization magmatic processes. Petrographic observations showed evidence for coeval crystallization of uraninite and other rock-forming minerals of the host pegmatite including quartz, feldspar, biotite, zircon, monazite, apatite, and xenotime. In addition, the low U/Th ratios (~19) and Th, REE, and Y enrichments characterized a magmatic origin for uraninite, which was likely derived from fractionated high-K calc-alkaline pegmatitic magma that experienced various degrees of crustal material contamination. In situ U-Pb isotopic dating performed by Secondary-Ion Mass Spectrometry (SIMS) on uraninite from the Guangshigou deposit yielded a crystallization age of 412 ± 3 Ma, which is concomitant (within errors) with the emplacement age of the host pegmatite (415 ± 2 Ma) and constrained the U ore genesis to the Early Devonian, which corresponds to the late Caledonian post-collisional extension in the North Qinling area. Uraninite then experienced various degrees of metamictization and/or post-Caledonian hydrothermal alteration characterized by an alteration rim associated with coffinite, chlorite and limonite. Finally, the characteristics of the pegmatite-related Guangshigou deposit exhibiting Th-rich uraninite which was the product of assimilation-fractional crystallization of pegmatitic magma defined a model significantly different than the one established for the world-class Rössing deposit characterized by Th-poor uraninite hosted in alaskite dykes formed by low degree of partial melting of U-rich metasediments.

scholarly journals Final-Stage Magmatic Record of Paleo-Asian Oceanic Subduction? Insights from Late Permian to Early Triassic Intrusive Rocks in the Yanbian Area, Easternmost Central Asian Orogenic Belt

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 799
Author(s):  
Chao Zhang ◽  
Franz Neubauer ◽  
Zheng-Hong Liu ◽  
Fang-Hua Cui ◽  
Qing-Bin Guan
Keyword(s):  
Partial Melting ◽  
Granitic Rocks ◽  
Early Triassic ◽  
Crustal Material ◽  
Late Permian ◽  
The North ◽  
Wide Range ◽  
Intrusive Rocks ◽  
Subduction Setting ◽  
T Values

This paper reports new zircon LA–ICP–MS U–Pb and Hf isotope data, and whole-rock major and trace element data for Late Permian to Early Triassic intrusive rocks in the Yanbian area, NE China. These data provide new insights into the timing of the final subduction of the Paleo-Asian Ocean beneath the North China Craton. The zircon U–Pb age data indicate that a suite of Late Permian to Early Triassic intrusive rocks related to subduction is present within the Yanbian area. The Late Permian intrusive rocks consist of diorites while the Early Triassic granites and hornblende gabbros constitute a geochemically bimodal igneous rock association. Furthermore, the Early Triassic granites show the geochemical characteristics of shoshonitic rocks. All the rocks are characterized by enrichment in LILEs and LREEs, and depletion in HREEs and HFSEs, suggesting they formed in a subduction setting. Zircons from the Early Triassic gabbros have εHf(t) values and TDM2 ages of +7.6 to +10.7 and 735–1022 Ma, respectively, suggesting that they formed from a primary magma generated by the partial melting of lithospheric mantle material that had been previously modified by subduction-related fluids. The Late Permian diorites have εHf(t) values and TDM2 ages of +0.5 to +9.5 and 853 to 1669 Ma, respectively, while they have high contents of Al2O3, Fe2O3, and low contents of SiO2, Cr, and Ni, indicating Late Permian diorites should derive from the mantle and are influenced by some crustal material. Early Triassic granitic rocks have a wide range of εHf(t) values and TDM2 ages of −4.8 to +9.4 and 852 to 2136 Ma, respectively. Their zircons imply that the Early Triassic granites could be mainly derived from partial melting of the crust, with minor contribution of the crustal material of an ancient crust. The Early Triassic bimodal intrusive rocks in Yanbian area, combined with the regional geologic information; therefore, record a final post-subduction extensional environment due to the break-off of the previously subducted slab.

Petrogenesis of Ordovician granitoids in Western Kunlun, NW Tibetan Plateau: Insights into the evolution of the Proto-Tethys Ocean

2020 ◽  
Author(s):  
Peng Wang ◽  
Guochun Zhao ◽  
Yigui Han ◽  
Qian Liu ◽  
Jinlong Yao ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Partial Melting ◽  
Fractional Crystallization ◽  
Mantle Wedge ◽  
Saturation Index ◽  
Oceanic Lithosphere ◽  
Quartz Diorite ◽  
The North ◽  
Western Kunlun ◽  
Granitoid Intrusions

Granitoid rocks are universal in continental crust and are of special significance in understanding tectonic settings. This paper presents detailed zircon U-Pb dating, Hf isotope, whole-rock geochemistry, and Sr-Nd-Pb isotope analyses, and mineralogy of two Ordovician granitoid intrusions and one quartz diorite intrusion in Western Kunlun, NW Tibetan Plateau. The Yutian Complex is composed of diverse rock suites, including monzogabbros, quartz monzodiorites, monzogranites, and monzodioritic enclaves. These suites have similar rock formation ages (447−440 Ma) and minerals, e.g., amphibole grains from different suites belonging to pargasite. Moreover, they exhibit geochemical similarities, such as broadly parallel trace-element patterns characterized by enrichments in light rare earth elements and large ion lithophile elements, and depletions in high field strength elements, which are typical features of arc rocks. Furthermore, the studied samples display homogeneous zircon Hf values, e.g., εHf(t) = −1 to −3, and whole-rock isotopic compositions, e.g., εNd(t) = −4 to −6. Thus, they were most likely derived from a mantle wedge enriched by subducted sediments and fluids, which then evolved into different suites through fractional crystallization of hornblende and plagioclase. The ca. 440 Ma North Yutian quartz diorite intrusion, with an average of εHf(t) value of −6, was a product of the partial melting of mafic lower crust through slightly fractional crystallization of hornblende. In contrast, the ca. 470 Ma Aqiang granodiorite intrusion has εHf(t) values varying from −5 and −2, but it has heterogeneous petrological and geochemical features. It is considered to be a product of the partial melting of the overriding mantle wedge modified by fluids derived from the subducted Proto-Tethys slab and some mixed crustal materials. The Aqiang samples belong to the slightly fractionated I-type series, but they have variable alumina saturation index (ASI = molar Al2O3/[CaO − 3.33 × P2O5 + Na2O + K2O]) values (0.74−1.03) due to variable peraluminous biotite contents. The different suites in the Yutian Complex display low ASI values (<1) controlled by sources and fractional crystallization. The Yutian Complex and the North Yutian intrusion were emplaced during the southward subduction of the Proto-Tethys oceanic lithosphere, and the Aqiang intrusion was emplaced in response to the northward subduction.

scholarly journals Petrogenesis and Geochronology of Tianshui Granites from Western Qinling Orogen, Central China: Implications for Caledonian and Indosinian Orogenies on the Asian Plate

Minerals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 515
Author(s):  
Muhammad Saleem Mughal ◽  
Chengjun Zhang ◽  
Amjad Hussain ◽  
Hafiz Ur Rehman ◽  
Dingding Du ◽  
...  
Keyword(s):  
Partial Melting ◽  
Saturation Index ◽  
Central China ◽  
Qinling Orogen ◽  
North China Block ◽  
Western Qinling ◽  
The North ◽  
Western Segment ◽  
Indosinian Orogeny ◽  
North Qinling

The precise timing, petrogenesis, and geodynamic significance of three granitoid bodies (Beidao granite, Caochuanpu granite, Yuanlongzhen granite, and the Roche type rock) of the Tianshui area in the Western Qinling Orogen, central China, are poorly constrained. We performed an integrated study of petrology, geochemistry, and zircon U-Pb dating to constrain their genesis and tectonic implication. Petrographic investigation of the granites shows that the rocks are mainly monzogranites. The Al saturation index (A/CNK versus SiO2) of the granitoid samples indicates meta-aluminous to peraluminous I-type granites. Their magmas were likely generated by the partial melting of igneous protoliths during the syn-collisional tectonic regime. Rare-earth-elements data further support their origin from a magma that was formed by the partial melting of lower continental crust. The Beidao, Caochuanpu, and Yuanlongzhen granites yielded U-Pb zircon weighted mean ages of 417 ± 5 Ma, 216 ± 3 Ma, and 219 ± 3 Ma, respectively. This study shows that the Beidao granite possibly formed in syn- to post-collision tectonic settings due to the subduction of the Proto-Tethys under the North China Block, and can be linked to the generally reported Caledonian orogeny (440–400 Ma) in the western segment of the North Qinling belt, whereas Yuanlongzhen and Caochuanpu granites can be linked to the widely known Indosinian orogeny (255–210 Ma). These granitoids formed due to the subduction of the oceanic lithospheres of the Proto-Tethyan Qinling and Paleo-Tethyan Qinling. The Roche type rock, tourmaline-rich, was possibly formed from the hydrothermal fluids as indicated by the higher concentrations of boron leftover during the late-stages of magmatic crystallization of the granites.

scholarly journals Genesis of Megacrystalline Uraninite: A Case Study of the Haita Area of the Western Margin of the Yangtze Block, China

Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1173
Author(s):  
Zhengqi Xu ◽  
Minghui Yin ◽  
Youliang Chen ◽  
Lu Xiang ◽  
Hao Song ◽  
...  
Keyword(s):  
Partial Melting ◽  
Fractional Crystallization ◽  
Quartz Vein ◽  
Uranium Mineralization ◽  
Uranium Deposits ◽  
Yangtze Block ◽  
Western Margin ◽  
Quartz Veins ◽  
First Time

Megacrystalline uraninite (up to one centimeter in size) represents one of the most important discoveries in uranium mineralogy in the western margin of the Yangtze Block and even in China in recent years. However, the genesis of megacrystalline uraninite remains controversial. In this study, the megacrystalline uraninite found in the felsic and quartz veins in the Haita area is examined for the first time. The study examined the geochemical characteristics of uraninite in the two veins and resulted in two primary findings. (1) The genesis of the uraninite was likely intrusive and was closely related to partial melting. (2) The quartz vein and feldspar vein are cogenetic and have a simple differentiation evolution relationship. Therefore, the partial melting of felsic materials during migmatization may be the most important mechanism of uranium mineralization in the study area. Furthermore, further simple fractional crystallization may be another important mechanism for the formation of megacrystalline uraninite. This study enriches the REE database of uraninite in uranium deposits worldwide, which is meaningful for studying the genesis of megacrystalline uraninite.

scholarly journals Geochronology and Geochemistry of Uraninite and Coffinite: Insights into Ore-Forming Process in the Pegmatite-Hosted Uraniferous Province, North Qinling, Central China

Minerals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 552 ◽  
Author(s):  
Feng Yuan ◽  
Shao-Yong Jiang ◽  
Jiajun Liu ◽  
Shuai Zhang ◽  
Zhibin Xiao ◽  
...  
Keyword(s):  
Central China ◽  
Compositional Variation ◽  
Ionization Mass ◽  
Low Grade ◽  
Forming Process ◽  
Early Devonian ◽  
The North ◽  
North Qinling ◽  
Uranium Minerals

The biotite pegmatites in the Shangdan domain of the North Qinling orogenic belt contain economic concentrations of U, constituting a low-grade, large-tonnage pegmatite-hosted uraniferous province. Uraninite is predominant and ubiquitous ore mineral and coffinite is common alteration mineral after initial deposit formation. A comprehensive survey of the uraninite and coffinite assemblage of the Chenjiazhuang, Xiaohuacha, and Guangshigou biotite pegmatites in this uraniferous province reveal the primary magmatic U mineralization and its response during subsequent hydrothermal events. Integrating the ID-TIMS (Isotope Dilution Thermal Ionization Mass Spectrometry) 206Pb/238U ages and U-Th-Pb chemical ages for the uraninites with those reported from previous studies suggests that the timing of U mineralization in the uraniferous province was constrained at 407–415 Ma, confirming an Early Devonian magmatic ore-forming event. Based on microtextural relationships and compositional variation, three generations of uranium minerals can be identified: uaninite-A (high Th-low U-variable Y group), uranite-B (low Th-high U, Y group), and coffinite (high Si, Ca-low U, Pb group). Petrographic and microanalytical observations support a three-stage evolution model of uranium minerals from primary to subsequent generations as follows: (1) during the Early Devonian (stage 1), U derived from the hydrous silicate melt was mainly concentrated in primary magmatic uaninite-A by high-T (450–607 °C) precipitation; (2) during the Late Devonian (stage 2), U was mobilized and dissolved from pre-existing uraninite-A by U-bearing fluids and in situ reprecipitated as uraninite-B under reduced conditions. The in situ transformation of primary uraninite-A to second uraninite-B represent a local medium-T (250–450 °C) hydrothermal U-event; and (3) during the later low-T (100–140 °C) hydrothermal alteration (stage 3), U was remobilized and derived from the dissolution of pre-existing uraninite by CO2- and SiO2-rich fluids and interacted with reducing agent (e.g., pyrite) leading to reprecipitation of coffinite. This process represents a regional and extensive low-T hydrothermal U-event. In view of this, U minerals evolved from magmatic uraninite-A though fluid-induced recrystallized uraninite-B to coffinite, revealing three episodes of U circulation in the magmatic-hydrothermal system.

scholarly journals Uraninite from the Guangshigou Pegmatite-Type Uranium Deposit in the North Qinling Orogen, Central China: Its Occurrence, Alteration and Implications for Post-Caledonian Uranium Circulation

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 729
Author(s):  
Bin Wu ◽  
Christophe Bonnetti ◽  
Yue Liu ◽  
Zhan-Shi Zhang ◽  
Guo-Lin Guo ◽  
...  
Keyword(s):  
Uranium Deposit ◽  
Uranium Mineralization ◽  
Orogenic Belt ◽  
Central China ◽  
Qinling Orogen ◽  
Qinling Orogenic Belt ◽  
The North ◽  
Alteration Halo ◽  
North Qinling ◽  
Magmatic Event

The Guangshigou deposit is the largest pegmatite-type uranium deposit in the Shangdan domain of the North Qinling Orogenic Belt, which is characterized by the enrichment of uraninite hosted in biotite granitic pegmatites. At Guangshigou, uraninite commonly occurs as mineral inclusions in quartz, K-feldspar and biotite or in interstices of these rock-forming minerals with magmatic characteristics (e.g., U/Th < 100, high ThO2, Y2O3 and REE2O3 contents and low concentrations of CaO, FeO and SiO2). It crystallized at 407.6 ± 2.9 Ma from fractionated calc-alkaline high-K pegmatitic melts under conditions of 470–700 °C and 2.4–3.4 kbar as deduced by the compositions of coexisting peritectic biotite. The primary uranium mineralization took place during the Late Caledonian post-collisional extension in the North Qinling Orogen. After this magmatic event, uraninite has experienced multiple episodes of fluid-assisted metasomatism, which generated an alteration halo of mineral assemblages. The alteration halo (or radiohalo) was the result of the combined effects of metamictization and metasomatism characterized by an assemblage of goethite, coffinite and an unidentified aluminosilicate (probably clay minerals) around altered uraninite. This fluid-assisted alteration was concomitant with the albitization of K-feldspar subsequently followed by the coffinitization of uraninite during the major period of 84.9–143.6 Ma, as determined by U-Th-Pb chemical ages. Further investigations revealed that the metasomatic overprinting on uraninite initially and preferentially took place along microcracks or cavities induced by metamictization and promoted their amorphization, followed by the release of U and Pb from structure and the incorporation of K, Ca and Si from the fluids, finally resulting in various degrees of uraninite coffinitization. The released U and Pb were transported by alkali-rich, relatively oxidizing fluids and then re-precipitated locally as coffinite and an amorphous U-Pb-rich silicate under low to moderate temperature conditions (85–174 °C). The compositional changes in primary uraninite, its structure amorphization together with the paragenetic sequence of secondary phases, therefore, corroborate a combined result of intense metamictization of uraninite and an influx of alkali–metasomatic fluids during the Late Mesozoic Yanshanian magmatic event in the region. Hence, the remobilization and circulation of uranium in the North Qinling Orogen was most likely driven by post-Caledonian magmatism and hydrothermal activities related to large-scale tectonic events. In this regards, Paleozoic pegmatite-type uranium mineralization may represent a significant uranium source for Mesozoic hydrothermal mineralization identified in the Qinling Orogenic Belt.

Late Triassic porphyries in the Zhongdian arc, eastern Tibet: origin and implications for Cu mineralization

2019 ◽  
Vol 157 (2) ◽  
pp. 275-288
Author(s):  
Pengsheng Dong ◽  
Guochen Dong ◽  
Zhuanrong Sun ◽  
Huawei Li ◽  
Jiahui Tang ◽  
...  
Keyword(s):  
Partial Melting ◽  
Water Content ◽  
Fractional Crystallization ◽  
Lower Crust ◽  
Late Triassic ◽  
Magma Source ◽  
High Water Content ◽  
Asthenospheric Mantle ◽  
Low Degree ◽  
Eastern Tibet

AbstractWhole-rock and Sr–Nd–Pb isotopic composition data, zircon Hf isotopic data and zircon U–Pb ages were obtained for the Late Triassic porphyries in the Zhongdian arc, eastern Tibet. These porphyries are intermediate and metaluminous and are enriched in large ion lithophile elements and depleted in high field strength elements. Moreover, they have weak negative Eu anomalies, high Sr and Ba contents, and high Sr/Y ratios. Different mineral geothermobarometers suggest that the porphyries in the Zhongdian arc crystallized at c. 640–829 °C and pressures of 2.1–2.8 kbar at depths shallower than 8 km. The porphyries have a calculated water content of 4.47–4.94 wt % and a relatively high magmatic oxygen fugacity. These porphyries were emplaced mainly at 230–203 Ma with a peak at 218–215 Ma. The Sr–Nd–Pb–Hf isotope data suggest that the porphyries in the Zhongdian arc were derived from a mixed melt of 50–65 % asthenospheric mantle and 35–50 % eclogite from the western Yangtze lower crust that experienced low-degree partial melting of 2–10 %. Subsequent fractional crystallization resulted in the decreasing trends of the major- and trace-element contents. The high Sr/Y and La/Yb values are the result of the low degree of partial melting of the western Yangtze lower crust rather than fractional crystallization, because no linear relationship was noted between Sr/Y or La/Yb and SiO2. The mixed melts from the lower crust and asthenospheric mantle provided a fertile magma source, and subsequent fractional crystallization under the favourable magmatic conditions of high water content and high oxidation state resulted in the formation of the porphyry Cu–Au deposits.

Sign in / Sign up

Export Citation Format

Share Document