Abstract:The Himalayan orogenic belt is a natural laboratory for studying plate tectonics. Located at the core of the Himalayan orogen, the Greater Himalayan Sequence (GHS) is the key to revealing the collisional orogenesis and orogenic evolution. This paper presents the petrography, zircon and monazite U-Th-Pb chronology and geochemistry of the GHS granitic gneisses from the Yadong area. The field survey and microstructure show that these rocks have the mineral assemblage of plagioclase + K-feldspar + quartz + biotite + garnet, and have experienced a metamorphism of the upper-amphibolite to granulite facies with partial melting. Chronology and geochemistry indicate that the protoliths of granitic gneisses include the Neoproterozoic (~800 Ma) granodiorite and the Silurian (~440 Ma) granite, both of which experienced metamorphism in Miocene (~16 Ma). The Neoproterozoic granodiorite has negative εHf(t) values of -16.4~-12.2, and crust model ages t_DM^C of 3.11~2.79 Ga, suggesting that the rock was derived from partial melting of the ancient lower crust. The Neoproterozoic granodiorite and Silurian granite have similar geochemical characteristics to arc granitic rocks, with negative anomalies of high field strength elements Nb, Ta, P and Ti. The present study reveals that the Greater Himalayan Sequence has experienced multistage tectono-thermal events, including not only the Cenozoic collisional orogeny but also the Neoproterozoic magmatism associated with the evolution of the supercontinent Rodinia as well as the surrounding Andean orogeny after the Paleozoic formation of Gondwana.

Abstract:Through the study of lithology and LA-ICP-MS zircon U-Pb dating, the main invasion period of Hongshanzi rock and the age of intrusive rock formation were determined. It is clear that Hongshanzi rock is a complex rock. The authors discussed its geological significance. The study of petrography indicates that Hongshanzi complex rock is composed of middle coarse grained alkali feldspar granite, porphyritic biotite granite, finebiotite granite and granite porphyry. The LA-ICP-MS zircon U-Pb dating results show that the age is 153.6±1.2 Ma for middle coarse grained alkali feldspar granite, and 151.4±1.1 Ma for porphyritic biotite granite, which are in accordance with the data obtained around the ore-bearing volcanic basin, and belong to the early period of Late Jurassic. The age of finebiotite granite is 131.5±1.8 Ma and that of granite porphyry is 133.3±1.4 Ma, consistent with the age of the granite porphyry which invaded Hongshanzi Basin and belonging to the early period of Early Cretaceous. Therefore, Hongshanzi Yanshanian complex rock is composed of two different periods in Yanshanian epoch, whose time span is 20 Ma. Studies show that the Hongshanzi uranium ore deposit occurs along the contact zone of granite porphyry of early Early Cretaceous and volcanic rocks of Late Jurassic, which indicates that the contact zone between complex rock of middle coarse grained alkali feldspar granite, porphyritic biotite granite and fine biotite granite and granite porphyry is the best place for mineral exploration, and this conclusion was verified by the uranium ore exploration.

Abstract:The Shexian Group and the Yulingguan Group are important Precambrian stratigraphic units in the northeastern part of the Jiangnan orogenic belt. Zircon dating ages of tuff bedding from the Changqian Formation (852±6 Ma, 840±11 Ma) and the Jingtan Formation (809±10 Ma) in south Anhui Province are reported in this paper, which constrain the ages of the Shexian and Yulingguan Groups, adding some reliable age basis to the correlation of the Neoproterozoic strata in southern Anhui Province. Integrating a large number of high precision dating data obtained from the Jiangnan orogenic belt in recent years, the authors have reached the conclusion that the Shexian Group is equivalent to the Fanjingshan Group, the Sibao Group, the Lengjiaxi Group, the Shuangqiaoshan Group, and the Xikou Group. And the Yulingguan Group, overlying the Shexian Group, is equivalent to the Xiajiang Group, the Danzhou Group, the Banxi Group, the Majianqiao Formation, the Dengshan Group, and the Shangshu Formation.

Abstract:The Etouchang Fe-Cu deposit is one of the well-known Proterozoic copper-bearing iron deposits in central Yunnan Province. Besides Fe and Cu, rare earth elements (REEs) coexist in the deposit. In this study, the authors used the automated mineral identification and characterization system (AMICS), which is the most up-to-date mineral automatic analysis system in mineralogy and geology in the world, in combination with scanning electron microscope and X-ray energy dispersive spectrometer (SEM-EDS) microstructure in-situ analysis technique, to perform quantitative mineral identification in the Etouchang Fe-Cu deposit, and obtained the undertaking unattainable by conventional means of rock-mineral identification. The authors found for the first time independent rare earth minerals (e.g., parisite, bastnaesite and fergusonite) in the ores from the Etouchang Fe-Cu deposit. Parisites are mainly concentrated in the banded magnetite ores, mainly exist as hypidiomorphic or allotriomorphic granular texture, irregular micro fine-grained granular aggregates, and are closely associated with gangue minerals such as calcite and chlorite, which are located in the marginal fissures of magnetites. And in the parisites, there exist widely distributed bastnaesite precipitates, which are mainly tabular or columnar, lamellar and acicular in form. Fergusonites are also mainly concentrated in the banded ores coexisting mainly with chlorites, and mainly exist as small fine-grained hypidiomorphic or allotriomorphic granular particles. Energy dispersive analysis of X-rays show that parisites and bastnaesites are rich in light rare earth elements (LREEs), dominated by Ce, Nd and La, with the order of Ce > La > Nd generally. In addition, they contain a small amount of Pr and Y. Fergusonites contain many kinds of metallic elements such as Nb, Fe, Y, Ce, Nd, Ti, Mg, Ca and U, and the content of Nb in the mineral is relatively high (Nb=39.15%~45.03%), rare earth elements are mainly Y, with a small amount of Ce and Nd. The discovery of rare earth minerals in the ore has important implications for the study of the genesis of this deposit and Precambrian (Mesoproterozoic) Fe-Cu (-REE) deposits in central Yunnan Province. According to the generation characteristics of rare earth-iron oxides in the deposit and regional metallogenic geological background, combined with previous research results, the authors consider that the formation of rare earth-iron oxides of this deposit was related to the deep (mantle) magmatic activity during the breakup of the Columbia supercontinent and was reformed and superimposed by the late hydrothermal event during the Grenville orogeny and breakup of the Rodinia supercontinent.

Abstract:Located in the southwest of the Hatu gold deposit in Tuoli County of Xinjiang, the Haxi gold deposit is a relatively large metallogenic potential deposit discovered in recent years. The orebody is controlled by the NE-trending Anqi fault and its thickness is 0.10~3.42 m, with gold grade being 0.17~64.60 g/t. It mainly occurs in the strata of Carboniferous Telegula Formation and is closely related to basalt. The primary ore of the Haxi gold deposit is divided into two types:altered rock type and quartz vein type. The main ore minerals include pyrite, arsenopyrite, chalcopyrite, gersdorffite, pyrrhotite and native gold. According to the mineral assemblage, the metallogenic process can be divided into two periods, i.e., hydrothermal period and supergene period, and four stages, namely, quartz-sulfide stage, quartz-sulfide-native gold stage, carbonate stage, and oxidation stage. The modes of occurrence of native gold are mainly fissure gold, inclusion gold and intergranular gold with an average gold content of 954.19‰. The particle sizes of native gold are mainly concentrated in 20~50 μm, thus belonging to the microscopic gold.

Abstract:The compositional evolution of ore and gangue minerals has recorded detailed information concerning the hydrothermal mineralization process. Based on petrographic observation, the authors used the combined EMP and LA-ICP-MS analytical techniques for mica and wolframite to constrain the shallow hydrothermal mineralization process of the Songshugang Ta-Nb-W-Sn deposit in northeastern Jiangxi Province. The W-Sn orebody in the shallow part of the Songshugang deposit contains four different types of quartz veins from early stage to late stage and from deep to shallow:wolframite-quartz vein, cassiterite-quartz vein, sulfide-quartz vein and barren vein, respectively. The four types of quartz veins all contain early crystallized zinnwaldite and late formed muscovite-iron oxides. The mica in the early veins is mainly zinnwaldite, while the mica in the late-stage veins is dominated by muscovite. Compared with the chemical compositions of zinnwaldite, the muscovite contains less Ti, Na, Rb, Cs, W, Nb, Zn, Li₂O but significantly higher Pb, Cu and B. From the early veins to the late veins, the mica compositions have following variable trends:Ti, Na, W, Nb concentrations decrease, and Pb, Zn, Cu, Li₂O, B concentrations increase. Wolframite-quartz veins of different depths contain two different compositions of wolframite, but they belong to the same period of evolution. Compared with wolframite deposited early in the hydrothermal fluid, the late wolframite has a significantly lower Nb, Ta, Zr, Hf, Ti, Sn, U, In, and Sc but higher Mo and FeO/MnO ratio. The evolution of trace elements in mica and wolframite implies two different fluids involved in the hydrothermal mineralization process. One was granite-related hydrothermal fluid and the other originated from water-rock reactions. In the early stage of mineralization, magmatic hydrothermal crystallization was dominant, and in the late stage, due to the intensification of water-rock reaction, surrounding rock materials made more contribution.

Abstract:NWA 12279 is a piece of anorthosite lunar meteorite newly discovered in 2016, consisting of 86% anorthite and 14% impact melt breccia. The anorthosite, has a poikilitic texture and is composed of plagioclase (70.6%), olivine (11.3%), pyroxene (10.0%) and magnesium-aluminum spinel (7.0%), with a small amount of quartz, chromite and ilmenite. The impact melt breccia is mainly composed of lithic clasts such as anorthosite, gabbro-troctolite-anorthosite, microporphyritic crystalline impact melt breccias and gabbro, and such mineral fragments as olivine, pyroxene, plagioclase and spinel, and glass as well as matrix. The anorthosite has the same mineral composition as the breccia:plagioclase (An_92.9~98.4), hypersthenes (Fs_15.5~32.2Wo_2.98~4.22), pigeonite (Fs_27.9~53.1Wo_7.19~14.7), augite (Fs_8.42~38.9Wo_17.0~44.1), olivine (Fo_53.7~89.4), and magnesium aluminum spinel (Mg_4.97Fe_0.86)_5.83 (Al_11.4Cr_0.61)_12.0O₂₄. Based on mineral composition, clastic composition, mineral components, total rock composition and shock-metamosphism features of the meteorite, as well as a comparison with the discovered lunar anorthosite, the authors hold that the meteorite may originate from a new spinel-rich gabbro-troctolite-anorthosite highland. Anorthite and breccia of this meteorite have different shock metamorphic features. Planar fractures in olivine, maskelynite of plagioclase and impact melt veins containing unmelted pyroxene and olivine fragments were produced in the anorthite, and vitreous veins, impact melt-pockets and rock brecciation were developed in the breccia. The peak shock pressures in anorthosite and breccias are estimated to be~45 GPa and~78 GPa respectively, and the shock temperature peaks to be~1 100℃ and~1 890℃ respectively. The shock stage is S₅~S₆.

Abstract:Nyböite has been found in several sites of ultra-high pressure (UHP) eclogite in the world, but the p-T range of its stability is still controversial. In this study, the authors conducted a set of thermodynamic modelling in the system of Na₂O-CaO-K₂O-FeO-MgO-Al₂O₃-SiO₂-H₂O-TiO₂-Fe₂O₃ (NCKFMASHTO) to constrain the stability of nyböite, on the basis of the Jianchang eclogite (Sulu UHP metamorphic belt, northern Jiangsu Province). Modelling results reproduce the observed mineral assemblage and show that nyböite is only stable at t<500℃, p<1.20 GPa, and geothermal gradient of 12~17℃/km. The modeled composition of nyböite is broadly consistent with measured data. The formation of nyböite in eclogite is mainly controlled by X_Na and X_Al of the bulk composition, the condition of X_Na=0.58~0.65 and X_Al<0.15 is necessary for the formation of nyböite. The nyböite investigated here is characterized by enrichment of F (1.88%~2.54%), while F was not taken into account in the modelling for the lack of F-bearing amphibole thermodynamic model hitherto. However, the substitution F for OH seems to significantly affect the stability of nyböite. The occurrence of nyböite in eclogite indicates that the bulk composition is rich in Na and Al, possibly corresponding to an alkali basalt protolith, and the host rock underwent low temperature and intermediate to high pressure metamorphism.

Abstract:The Beiya Fe-Au-polymetallic deposit lies in the alkali-rich porphyry polymetallic metallogenic belt of northwest Yunnan Province. There exist the contact metasomatic-hydrothermal alteration, ore types of metasomatite and filling veins in the host rocks, which have formed a mineralization system of porphyry. Within cracks and fracture zones of the host rocks or Fe orebody, there are lots of associated sulfide minerals such as siderites, gelenites, pyrites and chalcopyrites. The siderites at Ⅱ stage is obviously later than magnetites at Ⅰ stage, and they are the ideal minerals. A study of chalcography shows that the siderites can be classified into three types, i.e., magnetite-siderite (Sd1), pyrite-chalcopyrite-magnetite-siderite (Sd2) and gelenite-siderite (Sd3). EPMA and ICP-MS analysis of siderites show that, during the transition from Ⅰ-stage to Ⅱ-stage, the intermediate or weakly alkaline, high temperature and oxidation mineralization was converted to weak acid, low temperature and weak reduction, as marked by the generation of mushketovite. Meanwhile, there were a lot of polymetallic sulfides, with pyrites as the main Au-bearing minerals, and Au deposits were simultaneously developed. With the further decreasing temperature, the ore-forming process completely changed into acidity and strong reduction, with the deposition of gelenites and siderites. So all types of siderites and earlier magnetites had the same trace ore-metal source and ore-forming process, resulting from the evolution of ore-forming fluids at different stages and periods, and mineralization occurred at proper location with different ore-forming processes and decreasing temperature.

Abstract:In conventional geophysical exploration method for pegmatite lithium mineral exploration, there exist the problems that the difference between the orebody and the surrounding rock is not significant, the application effect is poor, and the geochemical exploration method has no obvious effect on the concealed lithium deposit. In view of such a situation, the authors investigated the technical problems related to the application of geogas method in the exploration of pegmatite lithium deposits. With Kalu'an in Xinjiang as the study area, the authors deployed two geogas research sections with a total length of 6 605 m, and completed the case study of pegmatite lithium deposits with 191 measuring points, which was performed for the first time both in China and abroad. The values of 39 elements such as Li, Rb, Be, Cs, Nb, and Y were determined. On such a basis, the characteristics of geogas anomalies in the Kaluan pegmatite lithium deposit were studied. The results show that significant gas anomalies containing Li, Rb, Be, Cs, Nb, Y, and other elements can be captured on the tilted side of the pegmatite lithium veins, that, above the barren pegmatite, the abnormal amplitude of geogas in Rb element will increase, and the anomaly amplitude of other elements will obviously decrease, with no gas anomaly, and that, in other lithologies, there is no abnormal geogas. It is confirmed that the geogas method is accurate and effective in the search for pegmatite lithium deposits.

Abstract:Taking the ore in the periphery of the Taiping bauxite mining area in Pingguo County of Guangxi as the research object, the authors systematically studied the chemical composition, mineral composition and mineral distribution characteristics of the ore by means of chemical analysis, X-ray powder diffraction, optical microscopic identification and X-ray energy spectrum analysis. The results show that the bauxite in the periphery of the Taiping mining area belongs to diaspore type bauxite with high iron content, with Al₂O₃ 53.06% and A/S ratio 10.74, which is suitable for Bayer process recovery; Fe₂O₃, TiO₂, Ga and Nb in the associated components have achieved comprehensive recycling indices. The target element Al for ore smelting and recovery is mainly in the form of diaspore and gibbsite, whose phase proportions are 85.9% and 6.73%, respectively. The complex structure of the ore, the size of the mineral dissemination, the uneven distribution of Fe, Si and other elements in the ore have certain effects on the selection and recovery of Al element.