The tectonic inversion of the Songliao Basin during the Cenozoic may have played an important role in controlling the development of sandstone-type uranium deposits. The widely distributed mafic intrusions in the host sandstones of the Qianjiadian U ore deposits provided new insights to constrain the regional tectonic evolution and the genesis of the U mineralization. In this study, zircon U-Pb dating, whole-rock geochemistry, Sr-Nd-Pb isotope analysis, and mineral chemical compositions were presented for the mafic rocks from the Qianjiadian area. The mafic rocks display low SiO2 (44.91–52.05 wt.%), high TFe2O3 contents (9.97–16.46 wt.%), variable MgO (4.59–15.87 wt.%), and moderate K2O + Na2O (3.19–6.52 wt.%), and can be subdivided into AB group (including basanites and alkali olivine basaltic rocks) and TB group (mainly tholeiitic basaltic rocks). They are characterized by homogenous isotopic compositions (εNd (t) = 3.47–5.89 and 87Sr/86Sr = 0.7032–0.7042) and relatively high radiogenic 206Pb/204Pb (18.13–18.34) and Nb/U ratios (23.0–45.6), similar to the nearby Shuangliao basalts, suggesting a common asthenospheric origin enriched with slab-derived components prior to melting. Zircon U-Pb and previous Ar-Ar dating show that the AB group formed earlier (51–47 Ma) than the TB group (42–40 Ma). Compared to the TB group, the AB group has higher TiO2, Na2O, K2O, P2O5, Ce, and HREE contents and Ta/Yb and Sr/Yb ratios, which may have resulted from variable depth of partial melting in association with lithospheric thinning. Combined with previous research, the Songliao Basin experienced: (1) Eocene (~50–40 Ma) lithospheric thinning and crustal extension during which mafic rocks intruded into the host sandstones of the Qianjiadian deposit, (2) a tectonic inversion from extension to tectonic uplift attributed to the subduction of the Pacific Plate occurring at ~40 Ma, and (3) Oligo–Miocene (~40–10 Ma) tectonic uplift, which is temporally associated with U mineralization. Finally, the close spatial relation between mafic intrusions and the U mineralization, dike-related secondary reduction, and secondary oxidation of the mafic rocks in the Qianjiadian area suggest that Eocene mafic rocks and their alteration halo in the Songliao Basin may have played a role as a reducing barrier for the U mineralization.
The Qianjiadian-Baixingtu uranium deposit (QBUD) is in the post-Jurassic extensional Kailu basin of northeast China. There is a well-developed fault system in and adjacent to the deposit, and uranium mineralisation appears controlled by faults F 1, F 2, and F 3. Lots of diabase (dolerite) intrusions related to regional faults are extensive throughout the QBUD. The ellipsoidal and lenticular mineralised bodies in the QBUD conflict with the interlayered oxidation genesis. Furthermore, heat from the diabase intrusions not only makes the wall rocks hard, but plenty of new cement minerals are precipitated from hot fluid flow (HFF). The clastic grains in the host sandstone are strongly altered by HFF. Carbonate cements involves calcite, ankerite, and Fe-rich dolomite. There are three inclusion temperature peaks: ∼90°C, 110-120°C, and 140-150°C, and three ranges of inclusion salinity: 5.0-10.0 wt-% NaCl equivalent, 10.1-15.0 wt-% NaCl equivalent, and 15.1-20.07 wt-% NaCl equivalent.
Abstract: The Dongping deposit, located near the center of the northern margin of the north China craton, is one of the largest gold deposits in China. It is spatially, temporally, and genetically associated with the shallowly‐emplaced Hercynian Shuiquan‐gou alkaline intrusive complex. The complex intrudes high‐grade metamorphic rocks of the Archean Sanggan Group along a deep‐seated fault zone within the north China craton. Four major ore bodies (Nos. 1, 2, 22, and 70), consisting mainly of a set of en echelon lenses and veins, have been delineated at the Dongping deposit. Hypogene hydrothermal activities can be divided into four periods from early to late including: (1) gold‐bearing K–feldspar–quartz stockworks and veins; (2) disseminated sulfide and gold zones; (3) gold‐bearing quartz veins, and (4) barren calcite‐quartz veins. Individual veins and stockwork systems can be traced along strike for 125 to 600 m and downdip for 100 to 600 m; they range from 0. 5 to 3 m in thickness. The mineralogical composition of the ore in the first three hypogene periods is relatively simple. It is composed of pyrite, galena, sphalerite, magnetite, specularite, chalcopyrite, native gold, electrum, calaverite, and altaite. Gangue minerals include K–feldspar, quartz, sericite, chlorite, epidote, albite, and calcite. Ore grade averages 6 g/t Au, but varies between 4. 14 and 22. 66 g/t Au. Gold is generally fine‐grained and not visible in hand specimen. Fluid inclusions in ore‐bearing quartz of periods 1, 2, and 3 are CO 2 –rich, variable salinity (2. 5–21 wt% equiv. NaCl), and have variable homogenization temperatures of 195° to 340°C. Quartz in the gold‐bearing K–feldspar–quartz stockworks (period 1), disseminated sulfide and gold zones (period 2), and the gold‐bearing quartz veins (period 3) has calculated δ 18 O H2O values between –1. 7 and 6. 9%, and δ values of fluid inclusion waters between –101 and –66%. All these isotope data of the ore‐forming fluids plot between the magmatic fluid field and the meteoric water line. Sulfide minerals disseminated in host rocks show positive δ 34 S values of 1. 9 to 3. 5%. Pyrite separates from he gold‐bearing K–feldspar–quartz stockworks and veins (period 1) have a δ 34 S range of –4. 3 to 0. 5%, whereas δ 34 S values of pyrite, chalcopyrite, galena, and sphalerite from the disseminated sul‐fide and gold zones (period 2) and the gold‐bearing quartz veins (period 3) vary from –5. 3 to –13. 4%. Gold ores are also characterized by relatively radiogenic lead isotope compositions compared to those of the alkaline syenite host rock. The data are interpreted as indicative of a mixing of lead from the alkaline intrusive complex with lead from Archean metamorphic rocks. The combined fluid inclusion measurements, sulfur, oxygen, hydrogen, and lead isotope data, and petrological observations indicate that the Dongping deposit was formed from the mixing of these magmatic fluids with meteoric waters. The deposit is, therefore, believed to be a product of Hercynian alkaline igneous processes within the north China craton.
Abstract The Hashitu molybdenum deposit is located in the southern part of the Great Hinggan Range, NE China. Molybdenum mineralization is hosted by and genetically associated with monzogranite and porphyritic syenogranite. Sr‐Nd‐Pb isotopes of the intrusions show that the porphyritic syenogranite has initial 87 Sr/ 86 Sr ratios of 0.70418–0.70952, ε Nd ( t ) values of 1.3 to 2.1 ( t =143 Ma), 206 Pb/ 204 Pb ratios of 19.191–19.573, 207 Pb/ 204 Pb ratios of 15.551–15.572, and 208 Pb/ 204 Pb ratios of 38.826–39.143. The monzogranite has initial 87 Sr/ 86 Sr ratios of 0.70293–0.71305, ε Nd ( t ) values of 1.1 to 2.0 ( t =147 Ma), 206 Pb/ 204 Pb ratios of 19.507–20.075, 207 Pb/ 204 Pb ratios of 15.564–15.596, and 208 Pb/ 204 Pb ratios of 39.012–39.599. The calculated Nd model ages ( T DM ) for monzogranite and porphyritic syenogranite range from 866 to 1121 Ma and 795 to 1020 Ma, respectively. The granitic rocks in the Hashitu area have the same isotope range as granites in the southern parts of the Great Hinggan Range. The isotope composition indicates that these granites are derived from the partial melting of a juvenile lower crust originating from a depleted mantle with minor contamination by ancient continental crust. The integrating our results with published data and the Late Mesozoic regional tectonic setting of the region suggest that the granites in the Hashitu area formed in an intra‐continent extensional setting, and they are related to the thinning of the thickened lithosphere and upwelling of the asthenosphere.
The Mesozoic to Cenozoic intraplate deformation of the North China Craton (NCC) is an intriguing phenomenon that led to different evolutions of the Ordos Basin and the eastern part of the NCC. Located in the central part of the NCC, the Lüliangshan is regarded as a boundary between the Ordos Basin and the eastern NCC, but the exact location of this boundary is still debated. Our field investigations suggest that the Lüliangshan anticline is a classical Mesozoic basement-involved anticline. The Lishi fault on the west of the southern part of the Lüliangshan anticline is argued to be a large fault and the east boundary of the Ordos Basin. However, our investigations show that it is not a continuous single fault but a deformation zone composed of several segments without connection along the strike. In front of the western Lüliangshan, this tectonic zone is a top-to-the-west breakthrough thrust placing the western Lüliangshan basement-involved anticline in the hanging wall with limited displacement. Field investigations show that the traditional view of the northern segment of the Lishi fault as a boundary between blocks is not clear. With a similar deformation style, the southern Lishi fault passes Lishi City, extends northeastward, connects to the Ximafang fault, and then extends to link with the Kouquan fault as the west boundary of the Datong Basin. All these faults show a map pattern of relay array. The eastern margin of the Ordos Basin was deformed by a series of thrusts that controlled the basement-involved folds. The Lüliangshan anticline and its boundary faults were formed in the Late Jurassic, and the driving force of the intraplate deformation is inferred to the westward low-angle subduction of the Paleo-Pacific plate from the east.
Abstract Twenty‐one Mo–W–Cu deposits and prospects have been discovered in the Honggor–Shamai district, Inner Mongolia, north China during past 5 years. This district is located in the central and western parts of the Chagan Obo–Aoyoute–Chaobulen tectono‐magmatic belt, which is part of the Central Asian Orogenic Belt. The Mo–W–Cu deposits in the district are associated with Mesozoic granitoid intrusions and occur as veins, stockwork, and dissemination. The geological features of these newly discovered deposits are similar to porphyry‐type deposits worldwide. Two mineralization events have been identified: Indosinian (235–224 Ma) and Yanshanian (137–131 Ma). It is proposed that these deposits and prospects in the Honggor–Shamai district were related to the post‐collisional extension linked to the Indosinian orogeny during the Middle–Late Triassic period, but some of those deposits were overprinted by mineralization associated with the Cretaceous magmatic‐hydrothermal (Yanshanian) event.
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