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Lithium is one of the important strategic energy metals, which is in short supply in China. There are three major types of lithium deposits: brine and salt lake type, highly differentiated granite or pegmatite type, and carbonate-clay type. In recent years, some new types of lithium deposits have also begun to receive great attention and subject recent research. There are many crypto-explosive breccia pipe type deposits in the world, including copper, gold, lead, zinc, tungsten and tin deposits, but little is known about this type of lithium deposit. This paper introduces the latest research results of the Weilasituo Sn−Li−Rb polymetallic deposit in Inner Mongolia (NE China), which occurs in the middle-southern section of the Great Xing’an Range metallogenic belt. A remarkable feature of this deposit is the coexistence of various mineralization types, including granite type Rb and Sn−Zn, hydrothermal crypto-explosive breccia pipe type Li−Rb, quartz vein type Sn−Zn and sulfide vein type Pb−Zn−Ag mineralization. Among them, hydrothermal crypto-explosive breccia pipe type Li-Rb deposit is currently very rare at home and abroad, which is likely a new type of rare metal deposit that worthy of our attention. This paper systematically summarizes the geology, alteration and mineralization, geochemistry, isotopes and geochronology of the Weilasituo deposit, and establishes a new petrogenic and metallogenic model.

Two suites of granitoids, the Late Jurassic (158 ± 3 Ma) Linglong suite and the Early Cretaceous (130–126 Ma) Guojialing suite, crop out in the northwestern Jiaodong Peninsula, eastern China. The Linglong suite is a monzogranite, comprising alkali feldspar, plagioclase, quartz and Fe-rich biotite. The Guojialing suite includes at least five plutonic bodies of both granodiorite and monzo-granite. The rocks are composed of plagioclase, alkali feldspar, quartz, Mg-rich amphibole and Mg-rich biotite. Both the Linglong and Guojialing suites have adakitic affinity. They are enriched in LREE with high La/Yb ratios and show positive Eu anomalies. The rocks are also enriched in LILE and depleted in HFSE with high Sr/Y ratios. The Linglong granite shows very uniform Sr–Nd isotopic compositions with initial 87Sr/86Sr ratios of 0.7119–0.7126 and εNd (T) values of −21.3 to −21.6, which are similar to those of the local Neoarchaean basement. The Guojialing suite has variable initial 87Sr/86Sr ratios (0.7108–0.7120) and εNd (T) values (−10.8 to −17.2), which are distinct both from those of the Neoarchaean basement and from those of the local enriched lithospheric mantle inferred from the coeval mafic dykes in the studied area. Detailed petrological and geochemical data indicate that the Linglong suite was derived by partial melting of Neoarchaean metamorphic lower-crustal rocks at depth of > 50 km with a eclogite residue, whereas the Guojialing suite was formed by the reaction of delaminated eclogitic crust-derived melt with the upwelling asthenospheric mantle. The petrogenesis of these two contrasting adakitic granitoids suggests intensive lower-crustal delamination during Early Cretaceous times, following a crustal thickening process from the late stage of the Early Jurassic to early stage of the Late Jurassic with crustal thickness of < 32 km to > 50 km, respectively.

Early Cretaceous mafic rocks are first reported in the northern Guangxi region from the western Qin-Hang belt in the interior South China Block. A systematic investigation of zircon U–Pb dating, whole-rock geochemistry, Sm–Nd isotopes and zircon Hf–O isotopes for these mafic rocks reveals their petrogenesis and the mantle composition as well as a new window to reconstruct lithospheric evolution in interior South China Block during Late Mesozoic. Zircon U–Pb dating yielded ages of 131 ± 2 Ma to 136 ± 2 Ma for diabase and gabbro from Baotan area, indicating the first data for Early Cretaceous mafic magmatism in the western Qing-Hang belt. These mafic rocks show calc-alkaline compositions, arc-like trace element distribution patterns, low zircon ε Hf ( t ) of − 9.45 to − 6.17 and high δ 18 O values of + 5.72 to + 8.09‰, as well as low whole-rock ε Nd ( t ) values of − 14.27 to − 9.53. These data suggest that the studied mafic rocks are derived from an ancient lithospheric mantle source that was metasomatized during Neoproterozoic subduction. Thus, the occurrence of these mafic rocks indicates a reactivation of Neoproterozoic subducted materials during an extension setting at Late Mesozoic in the western Qin-Hang belt, an old suture zone that amalgamates the Yangtze and Cathaysia blocks.

The genesis of Earth’s largest rare earth element (REE) deposit, Bayan Obo (China), has been intensely debated, in particular whether the host dolomite marble is of sedimentary or igneous origin. The protracted (Mesoproterozoic to Paleozoic) and intricate (magmatic to metasomatic) geological processes complicate geochemical interpretations. In this study, we present a comprehensive petrographic and in situ, high-spatial resolution Sr-Pb isotopic and geochemical investigation of the host dolomite from the Bayan Obo marble. Based on petrographic evidence, the dolomite marble is divided into three facies including coarse-grained (CM), fine-grained (FM), and heterogeneous marble (HM). All carbonates are ferroan dolomite with high SrO and MnO contents (> 0.15 wt.%), consistent with an igneous origin. Trace element compositions of these dolomites are highly variable both among and within individual samples, with CM dolomite displaying the strongest LREE enrichment. In situ 206Pb/204Pb and 207Pb/204Pb ratios of the dolomite are generally consistent with mantle values. However, initial 208Pb/204Pb ratios define a large range from 35.45 to 39.75, which may result from the incorporation of radiogenic Pb released from decomposition of monazite and/or bastnäsite during Early Paleozoic metasomatism. Moreover, in situ Sr isotope compositions of dolomite indicate a large range (87Sr/86Sr = 0.70292–0.71363). CM dolomite is characterized by a relatively consistent, unradiogenic Sr isotope composition (87Sr/86Sr = 0.70295–0.70314), which is typical for Mesoproterozoic mantle. The variation of 87Sr/86Sr ratios together with radiogenic 206Pb/204Pb signatures for dolomite within FM and HM possibly represents recrystallization during Early Paleozoic metasomatism with the contribution of radiogenic Sr and Pb from surrounding host rocks. Therefore, our in situ geochemical data support a Mesoproterozoic igneous origin for the ore-bearing dolomite marble in the Bayan Obo deposit, which subsequently underwent intensive metasomatism during the Early Paleozoic.

The fundamental advances in silicon isotope geochemistry have been systematically demonstrated in this work. Firstly, the continuous modifications in analytical approaches and the silicon isotope variations in major reservoirs and geological processes have been briefly introduced. Secondly, the silicon isotope fractionation linked to silicon complexation/coordination and thermodynamic conditions have been extensively stressed, including silicate minerals with variable structures and chemical compositions, silica precipitation and diagenesis, chemical weathering of crustal surface silicate rocks, biological uptake, global oceanic Si cycle, etc. Finally, the relevant geological implications for meteorites and planetary core formation, ore deposits formation, hydrothermal fluids activities, and silicon cycling in hydrosphere have been summarized. Compared to the thermodynamic isotope fractionation of silicon associated with high-temperature processes, that in low-temperature geological processes is much more significant (e.g., chemical weathering, biogenic/non-biogenic precipitation, biological uptake, adsorption, etc.). The equilibrium silicon isotope fractionation during the mantle-core differentiation resulted in the observed heavy isotope composition of the bulk silicate Earth (BSE). The equilibrium fractionation of silicon isotopes among silicate minerals are sensitive to the Si–O bond length, Si coordination numbers (CN), the polymerization degrees of silicate unites, and the electronegativity of cations in minerals. The preferential enrichment of different speciation of dissoluble Si (DSi) (e.g., silicic acid H4SiO40 (H4) and H3SiO4− (H3)) in silica precipitation and diagenesis, and chemical weathering, lead to predominately positive Si isotope signatures in continental surface waters, in which the dynamic fractionation of silicon isotope could be well described by the Rayleigh fractionation model. The role of complexation in biological fractionations of silicon isotopes is more complicated, likely involving several enzymatic processes and active transport proteins. The integrated understanding greatly strengthens the potential of δ30Si proxy for reconstructing the paleo terrestrial and oceanic environments, and exploring the meteorites and planetary core formation, as well as constraining ore deposits and hydrothermal fluid activity.

There is growing agreement that subducted sediments recycled into the deep mantle could make a significant contribution to the generation of various mantle-derived rocks. However, solid evidence and examples to support this view are few, and whether or not the subducted sediments can act as the dominating material source for the magma is unclear. Here, we report a comprehensive geochemical study that demonstrates that the newly identified Early Mesozoic calc-alkaline lamprophyres in the northern Guangxi Province, southeastern Yangtze Block in South China were likely derived in large part from the partial melting of the subducted terrigenous sediments in the deep mantle. The investigated lamprophyres are SiO 2 -rich minettes, characterized by moderate TFeO and MgO and high Mg # (>70). The multi-element pattern shows a typical crustal-like signature, such as enrichments in large-ion lithophile elements (LILE) and light rare earth elements (LREE) with troughs in Nb-Ta, Ti and Eu and peaks in Th-U and Pb. These rocks also show sediment-like ratios of Nb/U, Nb/Th and Ce/Pb, together with extremely radiogenic 87 Sr/ 86 Sr (0.71499–0.71919), unradiogenic 143 Nd/ 144 Nd (0.51188–0.51195) and radiogenic 207 Pb/ 204 Pb (15.701–15.718) isotopic compositions.

Qinzhou-Hangzhou metallogenic belt is an important polymetallic (Cu, Mo, W, Sn, Pb, Zn, Au, and Ag) belt in South China. The Xinmin polymetallic deposit is located in the southwestern segment of this belt, which ore bodies hosted in the contact zone of granite and Lower Devonian sedimentary strata and in the structure fractured zone within the strata. Three hydrothermal stages can be distinguished: quartz+tourmaline+pyrite (early stage), tourmaline+pyrite+galena+bismuthinite+sphalerite+chalcopyrite+pyrrhotite (main stage), and quartz+calcite+dolomite (late stage). The mineralizing fluid system can be described as aqueous with medium-high salinity (2.7-50.7 wt.‰ NaCl equiv. in the main stage and 0.18-8.81 wt.‰ NaCl equiv. in the late stage) and medium-high temperature of 485°C to 205°C (main stage) and 300°C to 116°C (late stage). The trapping pressures varied from 2 MPa to 30 MPa (main stage) and 0.4 MPa to 9 MPa (late stage). The δ18O values of quartz range from 6.7‰ to 8.5‰, and the δD values for fluid inclusions in quartz range from -45‰ to -52‰. The calcite has C-isotopes ranging from -5.8‰ to +0.7‰ and O-isotopes from +12.7‰ to 21.4‰. H-O-C isotope data are consistent with a hydrothermal fluid derived from the Cretaceous granitoid magma. The δ34S values of sulfides are -3.3‰ to +1.9‰. Sulfides have 206Pb/204Pb ratios of 18.377 to 18.473, 207Pb/204Pb ratios of 15.606 to 16.684, and 208Pb/204Pb ratios of 38.613 to 38.902. The S-Pb isotope data suggest derivation of S and Pb mainly from the Cretaceous granitic magma. It is concluded that the Xinmin deposit is a medium-high temperature, medium-high salinity hydrothermal polymetallic deposit, related to the granitic magmatism and strictly controlled by the fault and shattered zones.

Unlike classic skarn-type scheelite deposits directly acquiring sufficient Ca2+ from surrounding limestones, all of the scheelite orebodies of the Shangfang tungsten (W) deposit occur mainly in amphibolite, and this provides a new perspective on the mineralization mechanism of W deposits. The ability of hydrothermal scheelite (CaWO4) to bind REE3+ in their Ca2+ crystal lattices makes it a useful mineral for tracing fluid-rock interactions in hydrothermal mineralization systems. In this study, the REE compositions of scheelite and some silicate minerals were measured systematically in-situ by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to assess the extent of fluid-rock interactions for the Late Mesozoic quartz-vein-type Shangfang W deposits. According to the variations in CaO and REE among scheelite and silicate minerals, the amphibole and actinolite in amphibolite may be able to release large amounts of Ca2+ and REE3+ into the ore-forming fluids during chlorite alteration, which is critical for scheelite precipitation. Furthermore, an improved batch crystallization model was adopted for simulating the process of scheelite precipitation and fluid evolution. The results of both the in-situ measurements and model calculations demonstrate that the precipitation of early-stage scheelite with medium rare-earth elements (MREE)-rich and [Eu/Eu*]N<1. The early-stage scheelite would consume more MREE than LREE and HREE of fluid, which will gradually produce residual fluids with strong MREE-depletion and [Eu/Eu*]N>1. Even though the partition coefficient of REE is constant, the later-stage scheelite will also inherit a certain degree of MREE-depletion and [Eu/Eu*]N future from the residual fluids. As a common mineral, sheelite forms in various types of hydrothermal ore deposits (e.g., tungsten and gold deposits). Hence, the improved batch crystallization model is also possible for obtaining detailed information regarding fluid evolution for other types of hydrothermal deposits. The results from model calculations also illustrate that the Eu anomalies of scheelite are not an effective index correlated to oxygen fugacity of fluids but rather are dominantly controlled by the continuous precipitation of scheelite.

The Hermyingyi W-Sn deposit, situated in southern Myanmar, SE Asia, is a typical quartz-vein type W-Sn deposit. The ore-bearing quartz veins are mainly hosted by the Hermyingyi monzogranite which intruded into the Carboniferous metasedimentary rocks of Mergui Series. According to mineral assemblages and crosscutting relationships, four ore-forming stages are recognized: (1) silicate-oxide stage; (2) quartz-sulfide stage; (3) barren quartz vein stage; (4) supergene stage. Five molybdenite samples from the deposit yield Re-Os model ages ranging from 67.8±1.6 to 69.2±1.6 Ma (weighted mean age of 68.7±1.2 Ma), and a well-defined isochron age of 68.4±2.5 Ma (MSWD=0.18, 2 σ ). This Re-Os age is consistent with the previously published zircon U-Pb age of the Hermyingyi monzogranite (70.0±0.4 Ma) (MSWD=0.9, 2 σ ) within errors, which indicates a genetic link between the monzogranitic magmatism and W-Sn mineralization. The new high-precision geochronological data reveal that the granitic magmatism and associated W-Sn mineralization in southern Myanmar took place during the Late Cretaceous (70-68 Ma). The extremely low Re contents (22.9 ppb to 299 ppb) in molybdenite, coupled with sulfide δ 34 S values in the range of +1.9‰ to +5.6‰ suggest that ore-forming metals were predominately sourced from the crustal-derived granitic magma.