Xinbiao Lü’s research while affiliated with China University of Geosciences and other places

The Anwangshan gold deposit is located in the northwestern part of the Fengtai Basin, Western Qinling Orogen (WQO). The gold ore is hosted within quartz syenite and its contact zone. The U–Pb weighted mean age of the quartz syenite is 231 ± 1.8 Ma. It is characterized by high potassium (K2O = 10.13%, K2O/Na2O > 1) and high magnesium (Mg# = 55.31 to 72.78) content, enriched in large ion lithophile elements (Th, U, and Ba) and light rare earth elements (LREE), with a typical “TNT” (Ti, Nb, and Ta) deficiency. The geochemical features and Hf isotope compositions (εHf(t) = −6.68 to +2.25) suggest that the quartz syenite would form from partial melting of an enriched lithospheric mantle under an extensional setting. Three generations of gold mineralization have been identified, including the quartz–sericite–pyrite (Py1) stage I, the quartz–pyrite (Py2)–polymetallic sulfide–early calcite stage II, and the epidote–late calcite stage III. In situ sulfur isotope analysis of pyrite shows that Py1 (δ34S = −1.1 to +3.8‰) possesses mantle sulfur characteristics. However, Py2 has totally different δ34S (+5.1 to +6.7‰), which lies between the typical orogenic gold deposits in the WQO (δ34S = +8 to +12‰) and mantle sulfur. This suggests a mixed source of metamorphosed sediments and magmatic sulfur during stage II gold mineralization. The fluid inclusions in auriferous quartz have three different types, including the liquid-rich phase type, pure (gas or liquid)-phase type, and daughter-minerals-bearing phase type. Multiple-stage fluid inclusions indicate that the ore fluids are medium-temperature (concentrated at 220 to 270 °C), medium-salinity (7.85 to 13.80% NaCleq) CO2–H2O–NaCl systems. The salinity is quite different from typical orogenic gold deposits in WQO and worldwide, and this is more likely to be a mixture of magmatic and metamorphic fluids as well. In summary, the quartz syenite should have not only a spatio-temporal but also a genetical relationship with the Anwangshan gold deposit. It could provide most of the gold and ore fluids at the first stage, with metamorphic fluids and/or gold joining in during the later stages.

The Qieganbulake deposit associated with a mafic–ultramafic–carbonatite complex in the Kuluketage block is not only the world’s second-largest vermiculite deposit, but also a medium-size carbonatite-related phosphate deposit. Field observations, radiometric dating results and Sr–Nd–Hf isotopes reveal that the parental magmas of the carbonatite and mafic–ultramafic rocks are cogenetic and formed synchronously at c . 810 Ma. Geochemical characteristics and Sr–Nd–Hf–S isotopes (( ⁸⁷ Sr/ ⁸⁶ Sr) i = 0.70581–0.70710; ϵ Nd (t) = −0.20 to −11.80; ϵ Hf (t) = −7.5 to −10.3; δ ³⁴ S = +0.7 ‰ to +3.0 ‰ (some sulfides with high δ ³⁴ S values (+3.2 to +6.6) were formed by late hydrothermal sulfur)), in combination with mineral compositions and previous research, strongly indicate that the Qieganbulake mafic–ultramafic–carbonatite complex formed via extensive crystal fractionation/cumulation and liquid immiscibility of a carbonated tholeiitic magma, possibly derived from partial melting of an enriched subcontinental lithospheric mantle previously modified by slab-released fluids and sediment input in a continental rift setting. The coupled enriched Sr–Nd isotopic signatures, in combination with previous research, suggest that the enriched subcontinental lithospheric mantle could have been metasomatized by asthenospheric mantle melts to different degrees. The Qieganbulake carbonatite-related phosphate ores were the products of normal fractional crystallization/cumulation of P–Fe ³⁺ complex enriched carbonatite magma in high oxygen fugacity conditions, which was generated by liquid immiscibility of CO 2 –Fe–Ti–P-rich residual magma undergoing high differentiation.

The Kawuliuke Fe-P-Ti oxide-rich intrusive complex is one of the largest layered mafic–ultramafic complexes associated with Fe-P-(Ti) oxide deposits in the Kuluketage Block, northeastern Tarim Craton, NW China. Here, based on new field observations, whole-rock trace element, radiometric dating analyses as well as Sr-Nd-Hf isotopes we propose a non-cogenetic origin of the parental magmas of the mafic–ultramafic rocks and syenite in the Kawuliuke intrusive complex (KIC), both of which formed synchronously at circa 808 Ma. Geochemical characteristics and Sr-Nd-Hf-S isotopes ((⁸⁷Sr/⁸⁶Sr)i = 0.70437–0.70560; εNd(t) = -2.60 to −7.15; εHf(t) = -1.3 to −10.0; δ³⁴S = -2.98 ‰ to + 2.36 ‰), in combination with minerals composition and previous research, strongly indicate that the mafic–ultramafic rocks of the KIC formed via extensive crystal fractionation/cumulation of a tholeiitic magma, possibly derived from partial melting of an enriched subcontinental lithospheric mantle previously modified by slab-released fluids in a continental rift setting. The Kawuliuke syenite, meanwhile, is interpreted as generated by the emplacement of syenitic melts from the differentiation of newly coeval underplating basaltic magmas at depth based on lines of evidence from petrography, geochemical signatures and Sr-Nd-Hf isotopes. Our newly presented enriched Sr-Nd-Hf isotopic signatures, together with previous research, suggest that the enriched subcontinental lithospheric mantle could be metasomatized by asthenosphere mantle melts in different degrees. We further show the Kawuliuke clinopyroxenite-related apatite-rich oxide ores were the products of normal fractional crystallization/cumulation of H2O-Fe-P-Ti enriched residual magma in high oxygen fugacity condition, which experienced high differentiation. The tempo-spatial relationships of the KIC and other regional coeval mafic rocks jointly suggest that the KIC was most likely formed in response to the proposed mid-Neoproterozoic mantle plume in Tarim Craton, which likely induced partial malting of, and likely mixed with, the metasomatized subcontinental lithospheric mantle, to form the KIC with clinopyroxenite-related Fe-P-Ti oxide mineralization.

The Pangjiahe deposit is an orogenic gold deposit located on the northwestern margin of the Fengtai Basin and has proven reserves of 38 t Au at an average grade of 6.3 g/t. Phyllite is widely distributed in the mining area with Triassic granite porphyry and diabase dykes intruded in faults crosscutting it. Gold mineralization is mainly hosted in phyllite rocks. The granite porphyry present in the deposit is locally mineralized when it shares the same space with ore-controlling faults. Pyrite always displays zoning textures: Py0 and Py1 are present in the core; rim Py2 replaces and/or overgrows Py0 and Py1; and Py3 comprises the outermost rim. Previously determined in situ δ³⁴S values indicate that Py0, Py1, and Py2 and Py3 are diagenetic, magmatic hydrothermal, and hydrothermal ore stage in origin, respectively. Electron microprobe analysis (EMPA) mapping of the zoned pyrite (especially Py2) shows a negative correlation between sulfur and arsenic, indicating the substitution of sulfur by As¹⁻. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) mapping and spot analysis of Py2 and Py3 reveal two Au and As relationships. In the mineralized phyllite and granite porphyry, Au has strong positive correlations with As, Sb, Cu, and Ag, similar to other arsenian pyrites in hydrothermal ore deposits. However, in altered samples, Au and As display decoupled geochemical behavior, especially in Py2, which has the same levels of As, Sb, Cu, and Ag but 2–5 orders of magnitude lower Au. We think that the ore fluid reacted with altered samples located distal to the ore-controlled fault (distal to the ore fluid center), and the fluid may not have been sufficiently charged with those elements, especially Au. Because As, Sb, Cu, and Ag could maintain at the same level in the ore fluid after precipitation of pyrite enriched in those elements, but Au was sharply depleted. This was also noted in a published fluid inclusion study in Carlin-type gold deposits in Guizhou Province, which has similar zoned pyrite texture. Based on the similar δ³⁴S values (8 ‰ and 10 ‰) and trace element enrichments (Au, As, Sb, Cu, and Ag) between hydrothermal ore-stage pyrite and the Devonian seafloor exhalation sequence in the Fengtai Basin, the source of the gold in the Pangjiahe deposit should be attributed to metamorphism of the Devonian seafloor exhalation sequence during the Triassic orogeny.

Massif-type anorthosites, mainly Proterozoic in age, have long been recognized as a signature rock type of crust-mantle interactions in the Proterozoic Eon. The Daxigou Anorthosite Complex (DAC) is one such massif situated in the Kuluketage block, a tectonically important domain between the Tarim Craton and the Central Asian Orogenic Belt. In this contribution, a combination of geochronological and geochemical analyses of fine-grained DAC diabase are used to constrain the characteristics of the parental magma and the initiation time of DAC magmatism. We then pinpoint the DAC’s closure time by in-situ petrographic thin section U–Pb dating of zircon coronas around Fe-Ti oxides identified in a gabbroic anorthosite. Within data uncertainty, we find that the closing age of 1813 ± 9 Ma, is indistinguishable from the 1804 ± 7 Ma crystallization age of its last episode of parental magma. MELTS simulations of the parental diabase magma suggest a pressure of 8 kbar at a fayalite-magnetite-quartz oxygen fugacity leads to broadly observed mineral compositions and mineral phases. The bulk rock major and trace elements, integrated with the Sr–Nd and Hf isotopes in zircon, indicate that the DAC was formed by partially melting of a metasomatized sub-continental lithospheric mantle, which was likely induced by a post-collisional slab break-off with minor crustal assimilation. Finally, we propose that DAC magmatism can be ascribed to a series of Paleoproterozoic tectono-thermal events along the northern and southern margins of the Tarim Craton, which could have provided important implications for the Tarim Craton and the North China Craton associated with the assembly of Columbia supercontinent.

The Matigou gold deposit, located in the Fengtai Basin, is newly discovered and contains more than 30 t Au. The gold ore bodies are mainly hosted in shear structures as auriferous quartz veins and in the upper Devonian Luohansi Formation as disseminated ores. Granite porphyry and dacite porphyry dykes have been recognized in the ore zone. The granite porphyry dykes normally share the same structure as gold ore bodies and are locally mineralized. Dacite porphyry dykes likely intruded later, as they occasionally cut gold ore bodies. Pyrite is common in all kinds of rocks in the deposit. Multiple isotope (H-O-S) analyses of different minerals (quartz and pyrite), together with the geological characteristics, suggest that the Matigou deposit should be classified as an orogenic gold deposit like others in the Fengtai Basin. Zircon U-Pb dating of magmatic dykes and ⁴⁰Ar/³⁹Ar dating of hydrothermal ore-stage sericite both indicate that the Matigou deposit formed at ∼234 Ma. It is coeval with the Pangjiahe deposit (231.2 Ma) 20 km to the west but much older than previously published orogenic gold ages (216 to 200 Ma). The ca. 230 Ma gold mineralization occurred between two episodes of magmatism (245-235 Ma and 227-205 Ma) in the Qinling orogen. The later orogenic gold mineralization is consistent with the later episode of magmatism, which is widely believed to have formed in a postcollisional extensional regime. The early episode of magmatism is still debated as related to either subduction or an early postcollisional stage. Because the ca. 230 Ma gold mineralization displays no strong deformation or metamorphism after formation, and the orogenic gold deposits imply a relatively extensional background. Hence, the early episode of magmatism may have intruded in a compressional regime after continental collision. The ca. 230 Ma gold mineralization occurred at the beginning of the transition in a tectonic setting from compression to transpression. Otherwise, the gold ore bodies would have been destroyed to some extent during the late collision. Due to the continuous extension background, more orogenic gold deposits with ages of 216 to 230 Ma are expected to be discovered in the Qinling orogen.

The Wunuer Pb–Zn–Ag–Mo deposit is a newly explored polymetallic ore deposit located in the middle segment of the Great Xing'an Range, Inner Mongolia, NE China. Three stages of mineralization, composed of an early porphyry stage, an intermediate hydrothermal (cryptoexplosive breccia) stage, and a later epithermal stage, have been identified in the Wunuer deposit. Sphalerite is one of the principal metal sulphides in both hydrothermal and epithermal stages, and thus two generations of sphalerite, with the first‐generation sphalerite (Sp1) precipitated in hydrothermal stage and the second‐generation sphalerite (Sp2) precipitated in epithermal stage, were discriminated. The Sp1 is generally euhedral, transparent and colour‐zoned, and is usually replaced by Sp2, galena and chalcopyrite. The Sp2 is generally anhedral, opaque and black in colour. Chalcopyrite inclusions in Sp1 and Sp2 have different genetic mechanisms: chalcopyrite inclusions in Sp1 were produced by replacement as the result of interaction of sphalerite with Cu‐rich fluids, while chalcopyrite inclusions in Sp2 were produced by coprecipitation of sphalerite and chalcopyrite during crystal growth. Electron probe microscope analyser and laser ablation inductively coupled plasma mass spectrometry in‐situ analysis techniques have been used to obtain chemical compositions of sphalerite. The Sp1 is enriched in Cd and In, and depleted in Mn, Fe, Cu, Ag, Sb and Pb. In contrast, the Sp2 is enriched in Mn, Fe, Cu, Ag, Sb and Pb, and depleted in Cd and In. Elements of Pb, Ag, Bi and some of Fe, Cu concentrated in Sp2 are greatly attributed to micro‐mineral inclusions like chalcopyrite and galena, while most elements concentrated into Sp1 are generally incorporated into crystal structure in mechanisms of direct substitution (e.g. Fe2+ → Zn2+) or coupled substitution ((Cu+ + In3+) → 2Zn2+). In‐situ sulphur isotope results reveal similar slightly positive sulphur isotope compositions (+1.55‰ to +3.33‰ δ34SV‐CDT for Sp1, and +1.71‰ to +2.34‰ δ34SV‐CDT for Sp2) of the two generations of sphalerite, implying a magmatic material for both Sp1 and Sp2. Fluid inclusions in molybdenite‐bearing quartz vein, Sp1 and Sp2‐coexisting quartz have been studied to reveal fluid temperature and salinity evolution from porphyry to hydrothermal and to epithermal stage mineralization. Primary fluid inclusions in porphyry stage quartz homogenized to a liquid phase by high homogenization temperatures (range from 385 to 416°C, with an average of 399°C), with salinities ranging from 12.4 to 25.3 wt% (average of 19.4 wt%). The Sp1 was precipitated from fluids with medium temperature (302–317°C) and medium salinity (5.1–7.3 wt% NaCl) in the hydrothermal stage, and later been altered by metasomatic fluids with low temperature (142–186°C) and low salinity (0.7–5.3 wt% NaCl). The Sp2 was precipitated from fluids with low temperature (150–234°C) and low salinity (0.4–6 wt% NaCl) in the epithermal stage.

Abundant granitoids are exposed along the East Kunlun orogenic belt (EKOB), and many skarn deposits occur at the contacts between intrusions and strata. One such is the Xiaowolong deposit, a skarn-type tin polymetallic deposit that is temporally and spatially associated with porphyry monzogranite. Tin mineralization is mainly hosted by the skarn. In this study, we reported zircon and cassiterite U–Pb ages, whole-rock geochemistry, and Sr–Nd–Hf isotopic data, and used these to constrain the timing of intrusion and mineralization in the Xiaowolong deposit and identify the origin of the ore-related granites and the link between Sn mineralization and granitic magmatism. Age determinations by LA-ICP-MS U–Pb zircon dating indicated that the porphyry monzogranite formed at 260.0 ± 0.7 Ma. Cassiterite from the ore-bearing skarn yielded a Tera-Wasserburg U–Pb lower intercept age of 258.0 ± 3.7 Ma. These ages suggested that both granitic intrusion and related Sn mineralization in the Xiaowolong deposit were initiated during the Permian (ca. 260 Ma). The porphyry monzogranites had high SiO2 (71.26–73.13 wt%) and Al2O3 (13.84–14.46 wt%) contents, were alkali-enriched (K2O + Na2O = 7.08–7.69 wt%), had A/CNK values that ranged from 1.01 to 1.05, were enriched in light REEs and large ion lithophile elements such as Rb, Th, U and K, were depleted in high field strength elements, and had relatively low Zr, Nb, Y and Ce contents. They thus exhibited the geochemical characteristics of I-type granite. The porphyry monzogranite had consistent negative whole rock ɛNd(t) (−6.8 to −7.1) and magmatic zircon ɛHf(t) values ranging from −7.4 to −1.6, and two-stage Hf model ages ranging from 1393 Ma to 1758 Ma. Detailed elemental and isotopic data demonstrated that the porphyry monzogranite were derived from partial melting of ancient crustal source, and emplacement in a subduction tectonic setting. The Xiaowolong tin mineralization event indicated that the EKOB has great potential for exploration focusing on Permian-Triassic Sn skarn deposits.

The Reshui porphyry Mo deposit is located in the East Kunlun orogenic belt (EKOB). Molybdenum mineralization is distributed in monzogranite and porphyritic monzogranite rocks, mainly presenting as various types of hydrothermal veinlets in altered wall rocks, and the orebodies are controlled by three groups of fractures. In this paper, we present the results of fluid-inclusion and isotopic (S and Pb) investigations of the Reshui Mo deposit. The ore-forming process of the deposit can be divided into three stages: an early disseminated molybdenite stage (stage 1), a middle quartz–molybdenite stage (stage 2) and a late quartz–polymetallic sulfide stage (stage 3). The alteration was mainly potassic and silicic in stage 1, silicic in stage 2, and sericitic and silicic in stage 3. Five types of fluid inclusions (FIs) can be distinguished in quartz phenocrysts and quartz veins, namely W, PL (pure liquid inclusions), PV (pure gas inclusions), C (CO2 three-phase inclusions), and S (daughter mineral-bearing inclusions). The homogenization temperatures of fluid inclusions belonging to stages 1 to 3 are 282.3–378 °C, 238.7–312.6 °C and 198.3–228 °C, respectively. The fluid salinities at stages 1 to 3 are 4.65–8.14% NaCl eq., 4.34–42.64% NaCl eq., and 3.55–4.65% NaCl eq., respectively. The fluids of this deposit were generally moderate–high temperature and moderate–low salinity and belong to the H2O–NaCl–CO2 ± CH4 system. The temperature and pressure changed considerably between stage 2 (high–medium-temperature) and stage 3 (low-temperature). The evidence for ore-forming fluids containing different types of coexisting inclusions in stage 2 and a decrease in the fluid temperature from stage 2 to stage 3 indicate that fluid boiling and fluid mixing were the main mechanisms of ore precipitation. The sulfide 34SV-CDT values range from 4.90‰ to 5.80‰, which is characteristic of magmatic sulfur. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the ore minerals are 18.210–18.786, 15.589–15.723, and 38.298–39.126, respectively. These lead isotopic compositions suggest that the ores were mainly sourced from crustally derived magmas, with minor input from the mantle. The fluid inclusions and S–Pb isotopes provide important information on the genesis of the Reshui porphyry Mo deposit and indicate that the Triassic has high metallogenic porphyry potential in the EKOB.

In the past ten years, a great deal of geological study has been reported on the magmatic rocks exposed in the central and western region of the Kuluketage Block, while similar research in the eastern region has rarely been reported. In this paper, we report zircon U–Pb geochronological, zircon Lu–Hf isotopic, whole-rock elemental and Sr–Nd–Pb isotopic data for the Dapingliang intermediate-acid intrusive rocks in the eastern Kuluketage Block, in order to evaluate its petrogenesis and tectonic significance. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating provided a weighted mean ²⁰⁶ Pb/ ²³⁸ U age of 735 ± 3 Ma for the albitophyre (D1), 717 ± 2 Ma for the granite porphyry (D2) and 721 ± 1 Ma for the diorite porphyrite (D3). Geochemical analyses reveal that D1 and D2 belong to Na-rich alkaline A-type granites, and D3 shows the features of high-K calc-alkaline I-type granite. D1 and D2 are characterized by light rare earth element (LREE) enrichment and relative depletion of high field strength element (HFSE), with relatively flat heavy rare earth element (HREE) patterns and obviously negative Eu anomalies. D3 is characterized by the enrichment of LREE and depletion of HFSE, with negative slope HREE patterns and slightly negative Eu anomalies. In tectonic discrimination diagrams, D1 and D2 fall in the within-plate granite (WPG) field, indicating a rift setting. Although D3 falls within the volcanic arc granite (VAG) field, it most likely formed in a rift setting, as inferred from its petrology, Sr–Nd–Hf isotopes and regional tectonic evolution. Based on pronounced εNd ( t ), εHf ( t ), Pb isotopic data, TDM2 and high ( ⁸⁷ Sr/ ⁸⁶ Sr) i and elemental compositions, D1 was derived from the partial melting of basement amphibolites of the old lower crust. D2 originated from a mixture of the old lower crust and depleted mantle-derived magmas and was dominated by partial melting of the basement amphibolites of the lower crust. D3 could have been formed by partial melting of K-rich hornblende in the lower crust. Combining previous studies, we think that the c . 745–710 Ma magmatic rocks were formed in a continental rift setting. A partial melting scheme, triggered by underplating of mantle plume-derived magmas, is proposed to interpret the formation of c . 745–710 Ma A-type and I-type granitoids, mantle-derived mafic dykes, bimodal intrusive rocks, adakitic granites and volcanic rocks. These magmatic activities were probably a reflection of the break-up of the Rodinia supercontinent. Highlights (1) Circa 720 Ma magmatism in the eastern Kuluketage Block. (2) Na-rich granite was derived from partial melting of basement amphibolites. (3) The c . 745–710 Ma magmatic rocks were formed in a continental rift setting. (4) The underplating of mantle plume-derived magmas is proposed.