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

The Poyi Cu-Ni deposit is hosted by the Early Permian Pobei mafic-ultramafic complex along the northern margin of the Tarim Plate. This series of multiple intrusions in the Poyi deposit can be divided into four lithologies: gabbro, dunite, hornblende peridotite, and wehrlite. The ore body consists mainly of disseminated sulfides hosted by hornblende peridotite. All the Poyi deposit sulfides show positive Δ³³S values from 0.004 to 0.221‰ and negative δ³⁴S values from −0.8 to −3.5‰. High Ni contents occur in the hornblende peridotites, which exhibit the highest Δ³³S value of 0.221‰ and the lowest δ³⁴S value of −3.5‰, indicating contamination by sulfides from Archean sedimentary rocks. This contamination was important during sulfide saturation in the Poyi intrusions and likely occurred at depth before the emplacement of the Poyi intrusions. The intrusions incorporated country rocks during their emplacement and consolidation, and the degree of assimilation increases from the central lithofacies (i.e., the hornblende peridotite) to the marginal lithofacies (i.e., the wehrlite, dunite, olivine gabbro, and gabbro). Higher Ni contents are correlated with lower degrees of contamination; thus, we infer that the contamination by the country Paleoproterozoic rocks, which contain significant amounts of gneiss and marble, hindered sulfide saturation. The whole-rock Ni content is negatively correlated with the MgO and Fo contents in the olivine and positively correlated with the FeO and MnO contents in the olivine. During crystallization, olivine becomes gradually richer in FeO but poorer in MgO, and Mn tends to be enriched in the late stages of the melt. We infer that the fractional crystallization of olivine was an important factor during sulfide saturation.

The Huanggang iron–tin polymetallic skarn deposit is located in the southern Great Xing'an Range. According to the ore types and mineral assemblages, the paragenetic sequence of the Huanggang deposit can be divided into three stages, and these magnetite grains were mainly formed at the retrograde and sulphide skarn stages. The magnetite (sample HG12-13) from the early retrograde stage is represented by fine-grained magnetite cutting across coarse-grained magnetite surrounded by quartz and calcite. The magnetite (sample HG12-73) from the late retrograde stage is locally replaced by haematite along the margin or interior and is surrounded by calcite. The magnetite (sample HG12-88) from the early sulphide stage is characterized by obvious core–rim textural features. The magnetite (sample HG-62) from the late sulphide stage is featured by zone-like magnetite occurring along the margin and interior of the primary magnetite.

The Zhengguang gold deposit in the Duobaoshan ore field, hosted in volcanic rocks of the Middle Ordovician Duobaoshan Formation, is one of the largest gold deposits in the Northeastern Great Xing’an Range of the Central Asian Orogenic Belt (CAOB). The deposit comprises the No. I, II and III ore zones with a total resource exceeding 35 tonnes of Au, 100,000 tonnes of Zn and 100 tonnes of Ag. A genetic relationship between gold mineralization and concealed tonalite porphyry is inferred based on the characteristics of cryptoexplosive breccia and hydrothermal alteration indicative of porphyry-type and epithermal mineralization. Zircon LA-ICPMS U-Pb dating reveals that the tonalite porphyry was emplaced at 462.1±1.8 Ma (Middle Ordovician). The δ³⁴SV-CDT values of sulfide minerals range from -3.0‰ to -1.7‰ with an average of -2.33‰, indicating that sulfur was mainly derived from a magmatic source. The Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb ranging from 17.572 to 17.629, ²⁰⁷Pb/²⁰⁴Pb from 15.424 to 15.486, and ²⁰⁸Pb/²⁰⁴Pb from 37.206 to 37.418) suggest a major mantle component for Pb and, by inference, for other ore metals. Therefore, we suggest that the ore-forming elements in the Zhengguang gold deposit may be related to the mantle-sourced tonalite porphyry. On the basis of the geological characteristics and geochemical signatures documented in this study, we conclude that the Zhengguang gold deposit was formed in a porphyry to epithermal transitional environment associated with the concealed tonalite porphyry, as part of the Duobaoshan porphyry-epithermal ore system that is related to the subduction of the Paleo-Asian Ocean during the Ordovician.

The Dongping gold deposit, located in Chongli County (Hebei Province) about 200 km northwest of Beijing, is one of the largest gold-producing areas along the northern margin of the North China Craton. It is located in the of Shuiquangou alkaline igneous complex of Middle Devonian age (394.3 ± 3.2 Ma), composed chiefly of highly alkaline syentite and quartz_ syenites. This study reveals the age of the Carboniferous in the deposit at 351.7 ± 2.8 Ma (MSWD = 1.9). The Dongping deposit is locally hosted in Cretaceous (~ 143 ± 1 Ma) alkali granites that intruded the older and the gold min-eralization is closely associated genetically with this event. Hydrothermal zircons in the alkali granites have Th/U ratios mostly ranging between 0.01 and 0.7 indicating oscillatory zoning. A few grains with high Th/U ratios (1.31–2.07) may be from metamorphic domains. Negative εHf(t) values of the zircon mainly range between − 19.75 and − 16.93, suggesting that they originated principally by the melting of recycled continental crust. Less abundant zircons with εHf(t) ranging from − 25.76 to − 23.46, with Hf model ages (T DM2) of 2.54 to 2.67 Ga, (mainly 2.2 to 2.3 Ga) suggest that recycled Neoarchean basement was also present in the source region. The Devonian syenites and quartz syenites have T DM1 ages ranging from 1.96 to 2.08 Ga. Zircons from these rocks have εHf(t) values of − 11.9 to − 18.9. Certain zircons from the gold-bearing granite of Paleozoic age have an initial 176 Hf/ 177 Hf ratio of 0.281816 to 0.282058 and 0.282147 to 0.282348, reflecting a homogenous distribution of hafnium isotopes typical of magmatic sources. The T DM1 and T DM2 of the latest intrusion varying 1.33 to 1.59 Ga and 1.72 to 2.11 Ga respectively, indicating that the Neoproterozoic to Mesoprotero-zoic rocks of this area are an important source for the younger magma which are important to forming ore deposits. The TDM 2 indicate that the magma may be derived from a very old crustal basement (~ 2.67 Ga) in the northern margin of North China Craton by partial melting.

It is well known that a genetic link exists between the formation of ultramafic-rocks-hosted PGE-Cu–Ni sulfide deposits and the eruption of associated continental flood basalts. We here present a new model for the relationship between the Cu–Ni deposits located along the northeastern margin of Tarim and the internal Tarim basalt. Sr–Nd isotope and Hf isotope two-stage crust model ages TDMc indicate that whereas the Cu–Ni deposits along the northeastern margin of Tarim have Neoproterozoic and Mesoproterozoic lithology contamination, the surrounding rocks of Cu–Ni deposits in Beishan (Pobei) and Central Tianshan do not have Neoproterozoic lithologies. We propose that this is the result of mixing with the Neoproterozoic rocks in the interior of Tarim block. There is also an east–west trending positive magnetic anomaly belt in the central Tarim Basin, while Early Permian mafic–ultramafic rocks found along the northeastern margin of Tarim probably have a relationship with the Tarim Basin basalt. According to the Bouguer gravity map, the Bachu area near the center of Early Permian plume has high gravity values, with the northeastern high gravity belt in the central Tarim Basin possibly the result of a tilt of the mantle plume to the southwest below the Tarim block, which could be consistent with the earlier uplift and denudation in northeastern Tarim and later in southwestern Tarim from the Early Carboniferous to the Late Permian, as well as with observed uplift in the Bachu area in the Permian. We infer that the tilt of a mantle plume to the southwest below the Tarim block led to the inclined attitude of overlying rocks, with Early Permian magma flowing toward the northeast margin of Tarim. Based on this model, new PGE-Cu–Ni magmatic sulfide deposits related to Early Permian mafic–ultramafic intrusions may be found in the southwest area of Beishan, although this area is covered by Mesozoic and Cenozoic sediments.

A new method is being developed as part of this study to measure the Pressure-Volume-Temperature-composition (P-V-T-x) properties of the CO2-H2O system at temperatures from 273.15 to 513.15 K and pressures from 30 to 120 MPa. The density of a CO2-H2O solution is determined by measuring the volumetric change of the solution sealed in a capillary High-Pressure Optical Cell (HPOC), through a systematic correction. This study partially fills the current density/M volume data gap for dilute CO2-H2O systems. Data show that the density of CO2-H2O mixture (ρCO2-H2O) changes little below 298.15 K, then decreases more rapidly than ρH2O with increasing temperature at constant pressure, and eventually becomes lower than ρH2O in high temperature range (for example, above 489 K at 30 MPa). This pivoting temperature (Tp, above which ρCO2-H2O becomes lower than ρH2O) monotonously increases with increasing pressure (to 575 K as the pressure reaches 120 MPa). The calculated apparent molar volume of CO2 in water (VΦ,CO2) is independent of CO2 concentration, but is negatively correlated to pressure when the temperature is above 298.15 K. A revised VΦ,CO2 model for dilute CO2-H2O systems is proposed based on this study. This revised model can reproduce both the current and previous density data with an acceptable error range at temperatures up to 573.15 K and pressures up to 120 MPa. It can be used reliably to simulate geological sequestration of CO2 into water aquifers, and in the study of P-V-T-x evolution of geo-fluids (e.g., CO2-bearing aqueous ore forming fluids).

The Posan ultramafic intrusion is one of the ~280 Ma Pobei mafic–ultramafic complexes located in the Beishan rift, on the northeastern margin of the Tarim Craton. Given that three finished drill holes reveal less economic mineralization, it is necessary to understand the ore potential of this little ultramafic intrusion. Detailed fieldwork shows that it is comprised of five stages of magma events. Among them, stages I, II and III are the mafic bodies dominated by gabbro, gabbronorite and olivine gabbro, and stages IV and V are the ultramafic bodies characterized by layered intrusions. Theoretically, the Posan ultramafic intrusion meets the first requirement of ore mineralization because of its high MgO contents (14.76%) of the parental magma. Moreover, the low Ni content (less than 1900 ppm) in olivine and the paragenesis of sulfides and spinel demonstrate that the Posan intrusion experienced early sulfur saturation before or during the fractional crystallization of spinel and olivine. This part of the sulfide, which may contain Ni–Cu or PGE mineralization, deserves to be the focus of future work. In stage IV, the continuous decrease of Ni contents in olivine with the fractional crystallization, the calc-crustal contamination (irregular distributed plagioclase, high Th/Yb ratios, Nb and Zr depletion and K, Rb, Ba, U, Th and Pb enrichment) instead of sulfur-rich crustal contamination, and the high level of oxygen fugacity (+2.1 < fO2QFM < +3.0) result in no obvious disseminated sulfides created in this stage. A clinopyroxene TiO2-Alz diagram confirms that the Beishan mafic–ultramafic complexes were formed in a rift-related circumstance rather than the arc-related cumulus. Low TiO2/Yb and Nb/Yb ratios reflect that the Beishan complexes were derived from the shallow depleted mantle without garnet. Considering the temporal and spatial relationship of the Tarim large igneous province and the large numbers of mafic–ultramafic intrusions in the Beishan region, it is reasonable to speculate that the Beishan mafic–ultramafic complexes, including the Posan intrusion (275.8 ± 2.7 Ma), have a genetic affiliation with, but were not directly formed by, the early Permian Tarim Plume.

The Kuluketage block is the best area for Precambrian geology in north western China, because it contains the most complete Precambrian lithology units. Thus, the study of this ancient basement can improve the understanding of the Precambrian evolution of the Tarim Craton. In this study, we report LA-ICPMS zircon U-Pb ages and Hf isotopes of detrital zircons from a magnetite quartzite from the Shayiti Formation of the Xingditage Group. The 65 zircon ages and Hf isotopes obtained are used not only to constrain the maximum depositional ages of the Shayiti Formation but also to obtain the information about the evolution of regional tectonic-magmatic activities in the Paleoproterozoic of the Kuluketage block. According to the youngest concord Pb-207/Pb-206 zircon age of 1851 +/- 36 Ma in magnetite quartzites and the 1.47 Ga of the diabase sills which intrude into the Shayiti Formation, the most probable depositional age of the Shayiti Formation is between 1.47 Ga and 1.85 Ga. The detrital zircon dates are mainly clustered at 1806 Ma to 1889 Ma, 1898 Ma to 1981 Ma, and 1988 Ma to 2054 Ma, with the most prominent age peak appearing at around 1900 Ma and the subordinate peak age at around 1960 Ma. The magmatic features of Cathodoluminescence (CL) images indicate that two large magmatic tectonic-magmatic activities occurred in this district. The metamorphic rims of magmatic zircons and some baddeleyites also show regional metamorphism in the Paleoproterozoic, which may be related to the amalgamation of the Columbia supercontinent. We obtained two sets of concordant U-Pb ages older than 2.5 Ga, and several sets of two-stage Hf model ages older than 3.0 Ga. Combined with previous data in the literature, we suggest that Meso- to Neo-Archean basement rocks existed in the Kuluketage block, but were strongly reformed by tectonics, magmatism, and metamorphism in the Paleoproterozoic.

The southern Great Xing'an Range is one of the most important metallogenic belts in northern China, and contains numerous Pb–Zn–Ag–Cu–Sn–Fe–Mo deposits. The Huanggang iron–tin polymetallic skarn deposit is located in the Sn-polymetallic metallogenic sub-belt. Skarns and iron orebodies occur as lenses along the contact between granite plutons and the Lower Permian Huanggangliang Formation marble or Dashizhai Formation andesite. Field evidence and petrographic observations indicate that the three stages of hydrothermal activity, i.e., skarn, oxide and sulfide stages, all contributed to the formation of the Huanggang deposit. The skarn stage is characterized by the formation of garnet and pyroxene, and high-temperature, hypersaline hydrothermal fluids with isotopic compositions that are similar to those of typical magmatic fluids. These fluids most likely were generated by the separation of brine from a silicate melt instead of being a product of aqueous fluid immiscibility. The iron oxide stage coincides with the replacement of garnet and pyroxene by amphibole, chlorite, quartz and magnetite. The hydrothermal fluids of this stage are represented by L-type fluid inclusions that coexist with V-type inclusions with anomalously low δD values (approximately − 100 to − 116‰). The decrease in ore fluid δ¹⁸OH2O values with time coincides with marked decreases in the fluid salinity and temperature. Based on the fluid inclusion and stable isotopic data, the ore fluid evolved by boiling of the magmatic brine. The sulfide stage is characterized by the development of sphalerite, chalcopyrite, fluorite, and calcite veins, and these veins cut across the skarns and orebodies. The fluids during this stage are represented by inclusions with a variable but continuous sequence of salinities, mainly low-salinity inclusions. These fluids yield the lowest δ¹⁸OH2O values and moderate δD values ( − 1.6 to − 2.8‰ and − 101 to − 104‰, respectively). The data indicate that the sulfide stage fluids originated from the mixing of residual oxide-stage fluids with various amounts of meteoric water. Boiling occurred during this stage at low temperatures. The sulfur isotope (δ³⁴S) values of the sulfides are in a narrow range of − 6.70 to 4.50‰ (mean = − 1.01‰), and the oxygen isotope (δ¹⁸O) values of the magnetite are in a narrow range of 0.1 to 3.4‰. Both of these sets of values suggest that the ore-forming fluid is of magmatic origin. The lead isotope compositions of the ore (²⁰⁶Pb/²⁰⁴Pb = 18.252–18.345, ²⁰⁷Pb/²⁰⁴Pb = 15.511–15.607, and ²⁰⁸Pb/²⁰⁴Pb = 38.071–38.388) are consistent with those of K-feldspar granites (²⁰⁶Pb/²⁰⁴Pb = 18.183–18.495, ²⁰⁷Pb/²⁰⁴Pb = 15.448–15.602, ²⁰⁸Pb/²⁰⁴Pb = 37.877–38.325), but significantly differ from those of Permian marble (²⁰⁶Pb/²⁰⁴Pb = 18.367–18.449, ²⁰⁷Pb/²⁰⁴Pb = 15.676–15.695, ²⁰⁸Pb/²⁰⁴Pb = 38.469–38.465), which also suggests that the ore-forming fluid is of magmatic origin.

Neoproterozoic igneous rocks are widely distributed in the Kuluketage block along the northern margin of the Tarim Craton. However, the published literature mainly focuses on the ca. 800 Ma adakitic granitoids in the area, with the granites that intrude the 735–760 Ma mafic–ultramafic rocks poorly studied. Here we report the ages, petrography and geochemistry of two granites in the Xingdi mafic–ultramafic rocks, in order to construct a new view of the non-adakitic younger granites. LA-ICP-MS zircon U–Pb dating provided weighted mean 206Pb/238U ages of 743.0 ± 2.5 Ma for the No.I granite (G1) and 739.0 ± 3.5 Ma for the No.II granite (G2). A clear core-rim texture of similar age and a high zircon saturation temperature of ca. 849 ± 14 °C were observed for the No.I granite; in contrast, G2 has no apparent core-rim texture but rather inherited older zircons and a lower zircon saturation temperature of ca. 763 ± 17 °C. Geochemical analysis revealed that G1 is an alkaline A-type granite and G2 is a high-K calc-alkaline I-type granite. Both granites share similar geochemical characteristics of arc-related magmatic rocks and enriched Sr–Nd–Hf isotopes, likely due to their enriched sources or mixing with enriched magma. Whereas G1 and its host mafic rocks form typical bimodal intrusions of the same age and similar Sr–Nd–Hf isotope compositions, G2 is younger than its host mafic rocks and its Sr–Nd–Hf isotope composition indicates a lower crust origin. Although they exhibit arc-related geochemical features, the two granites likely formed in a rift setting, as inferred from thier petrology, Sr–Nd–Hf isotopes and regional tectonic evolution.