Abstract:The Na'a deposit in Chayu County, Xizang, Southwest China, is located in the most eastern section of the Gangdis metallogenic belt, which is a typical skarn tungsten ore deposit, contains multiple generations of garnet in skarn and sulfide-carbonate altered rocks. Garnet is a representative mineral in skarn deposit. The systematic research on garnet fills the gap of previous research and provides new data. The composition characteristics and ring band changes of garnet are often used to indicate the physical and chemical properties, migration and evolution, and the metallogenic process of the fluid. According to the alteration mineral combination and interpenetration relationship in field observation and indoor identification, garnet can be divided into three types from early to late: BR type (brown red), DB type (dark brown), and B type (brown) garnet. The garnet is mainly composed of grossularite, followed by andradite. Its formation is characterized by brown-red to dark brown to brown, which is accompanied by the decrease of grossularite component and the increase of andradite and spessarite components. All three types of garnet developed typical octagon and ring band characteristics under the microscope, with the characteristics of high calcium, low manganese and low magnesium components, showing the typical hydrothermal erosion into the cause. The high grossularite content of BR and DB indicates the relative reduction of the forming environment, whereas the increasing andradite content of type B indicates the trend of fluid evolution to oxidation environment. The REE content and Fe³⁺ / (Fe³⁺ + Al³⁺) ratio are indicating the relative reduction of the overall crystallization conditions. The garnet all showed the characteristics of depleted light rare earth, enriched heavy rare earth content, negative Eu content and gradually increasing content, indicating that the metallogenic hydrothermal fluid in the skarn stage is in relatively neutral conditions. The mass-like substitution mechanism of rare earth elements is mainly ^Ⅷ+^Ⅳ→^Ⅷ+^Ⅳ及^Ⅷ+^Ⅵ→^Ⅷ+^Ⅵ. By comparing the contents of garnet W and Sn in different types of polymetallic skarn deposits, the results showed that the content of garnet W and Sn in W mineralized deposits was significantly higher than that of non-W mineralized deposits, indicating that the W and Sn content of garnet had certain indicator significance for mineralization. Furthermore, elements U and Eu can dynamically reflect the redox conditions for mineral growth, the W-U and W- δEu relationship characteristics of garnet can be used as an indicator of different types of skarn W deposits.

Abstract:The newly discovered Dana ancient volcanic edifice in the Nanmulin area of Xizang provides a window for exploring the lithofacies composition of continental volcanic edifice and its tectonic significance. This study conducts geological profile measurements and petrographic studies on the Dana ancient volcanic edifice, and conducts zircon LA-ICP-MS U-Pb dating and the whole-rock geochemical analysis for the porphyric monzonitic granite which intrusived into volcanic channel laterly. The results show that the zircon U-Pb age of the porphyric monzonitic granite is 54.0±1.4 Ma, with high silicon (SiO₂=71.03%~75.88%), high potassium and low sodium (K₂O/Na₂O=1.45~1.79), rich alkali (ALK=8.97%~9.67%), and low titanium (TiO₂=0.17%~0.37%) characteristics. The A/CNK value ranges from 0.95 to 1.00, and the Rittman index (σ) ranges from 2.45 to 3.38, belonging to the quasi-aluminous and calc-alkaline rock series. Enrichment of light rare earth elements and relative depletion of heavy rare earth elements (LREE/HREE=7.60~9.78), with obvious differentiation characteristics, (La/Sm) _N=2.85~4.21; Large ion lithophilic elements such as Rb, Th, U (LILE) and incompatible elements are relatively enriched, while high field strength elements such as Nb, Ta, P, Ti (HFSE) are relatively depleted, exhibiting typical geochemical properties of subduction arc or crustal magmatic rocks. Based on the above geological information, it is indicated that the Dana ancient volcanic edifice was formed before 54 Ma, and the porphyric monzonitic granite was formed in the tectonic background of the active continental margin during the India-Eurasia collision. Under the action of mantle-derived magma intrusion, the middle and lower crust melted, and then the magma differentiated and ascended to infiltrate and crystallize in the volcanic channel.

Abstract:Laoshan granites are widely distributed in Jiaodong area. Their typology, magma source and petrogenesis are still controversial, and the magmatic evolution and petrogenesis of highly fractionated I-type granite have not been well constrained. In this study, the Laoshan Early Cretaceous granites are selected as the research theme. The granites are analyzed by petrology and petrography, whole rock major and trace elements, zircon U-Pb dating and Lu-Hf isotopes, plagioclase electron probe analysis. LA-MC-ICP-MS zircon U-Pb dating results show that the diagenetic ages of quartz monzonite, monzogranite, syenogranite and granitic porphyry in Laoshan are 128.6±2.7 Ma, 122.8±2.5 Ma~118.6±1.2 Ma, 121.5±2.7 Ma~121.3±1.2 Ma and 114.5±1.2 Ma, respectively, indicating that they were all emplaced during the Early Cretaceous. The geochemical composition of Laoshan granites show high contents of silicon and alkali, low abundances of aluminum, magnesium and iron. They are also depleted in Rb, Th, U,Ba and Sr, with significant negative Eu anomaly. The zircons εHf(t) values of Laoshan granites range from -21.0 to -15.1 , and Hf isotope second-stage model ages (t_DM2) range from 2 482 to 2 149 Ma. Based on mineralogical, petrological and geochemical evidence, the quartz monzonite and monzogranite are I-type granites, and the syenogranite and granitic porphyry are classified are high fractionated I-type granites. Combined with the previous researches results in Jiaodong area, in the extensional tectonic setting generated by the subduction of the Paleo-pacific plate, magmas from the asthenosphere underplated into the lower crust, inducing partial melting of the lower crust material to form felsic magmas. After different degrees of fractional crystallization and evolution of felsic magmas, granites with varying degrees of differentiation in Laoshan area are formed ultimately.

Abstract:Muscovite is a common mineral in peraluminous granites, it could be a mineral barometer to constrain the emplacement depth of peraluminous granites. Chemical compositions of muscovite from the Jintan two-mica granite are determined using electron microprobe. According to the calculation for the crystallization pressure of the muscovite, the pressure of emplacement of the Jintan pluton is 4.9×10⁸~6.1×10⁸ Pa with average 5.4×10⁸ Pa, corresponding to 16~20 km with average 18 km in depth. Combing with previous studies, we suggest that the emplace depth is 17~19 km, and we can presume that crustal thickness of South China in the Indosinian period was likely ≥50 km, but it may be denudated because of extensive weathering in the Yanshanian period, which can be a new explanation for the lacking Indosinian volcanic rocks in South China.

Abstract:This article conducts carbon and oxygen isotopes, rare earth, and trace element geochemical analyses of carbonate samples from the Triassic Sanhedong Formation in the Hexi Area of the northwest Yunnan Province. The analyzed results demonstrate that their carbon and oxygen isotope values are consistent with the normal marine carbonate rocks. Samples from the Sanhedong Formation have a high Sr and Ba content, low Co, Cu, Th, U, Ho and total rare earth element content, and a negative anomaly of Eu, but they are slightly enriched in light rare earth elements. Paleosalinity parameter Z value, and Sr/Ba, Sr/Cu and Rb/Sr ratios indicate that they deposited in a marine saline water environment with dry-hot climate. The ratios of Cu/Zn, V/Cr, Ni/Co and U/Th indicate an anoxic environment. Y/Ho, δCe and δEu values indicate that the limestone of the Sanhedong Formation is less affected by diagenesis during sedimentation. These characters are similar to that of the Xujiahe Formation in the northern part of the Sichuan Basin, indicating that the Lanping Basin and the Sichuan Basin in the Upper Yangtze Plate probably have a similar tectonic and sedimentary environment during Late Triassic, which can help to study the paleoenvironment and tectonic attributes of the Lanping-Simao Block.

Abstract:The environmental changes in the Ediacaran epigenetic system of the Earth are closely linked to the evolution of organisms. However, there is still ongoing debate surrounding their interaction. This study focuses on the carbonate sedimentary sequences of the Ediacaran Doushantuo Formation in the Jiulongwan section of the Three Gorges Region, South China. The rare earth elements information was extracted from the carbonate phase using dilute acetic acid distribution leaching. The obtained data was then utilized to construct the evolution curve of Ce anomalies, which underwent a process involving of reduction/manganization-strong oxidation-suboxidation-strong oxidation-weak oxidation/reduction. Two significant negative Ce anomalies were observed, indicating the occurrence of two significant oxygenation stages during the prolonged oxidation process of the Ediacaran Doushantuo shallow water. These two oxygenation events align with the periodic oxidation of deep water at 632 Ma and 580 Ma, respectively. Moreover, Ce negative anomalies were also found in contemporaneous sedimentary sequences in Australia, suggesting that global oxygenation events occurred in the Ediacaran Doushantuo ocean. The fossil record of the Doushantuo Formation in the Yangtze Plateform reveals that the duration of Doushantuo ocean oxidation corresponds to the production strata of major fossil groups. This finding supports the understanding that marine oxidation facilitated the origin and evolution of Ediacaran Doushantuo metazoans.

Abstract:Recently, the bauxite gas reservoir of Taiyuan Formation has become a hot spot of exploration in Longdong area of Ordos Basin. In order to systematically explore the distribution of bauxite rock and the main controlling factors of reservoir formation, based on the latest drilling cores, rock slices, three-dimensional seismic, logging, scanning electron microscopy, model forward modeling and other methods, the distribution characteristics of bauxite rock in Taiyuan Formation were studied in detail, and then the main controlling factors of bauxite rock reservoir formation were expounded. The results show that the aluminiferous rock series has a typical five-stage type in the longitudinal direction, in which the C section is the main reservoir section of the bauxite rock, and the content of diaspore is more than 80%. The longitudinal lithologic association of the aluminiferous rock series is mainly controlled by the karst paleogeomorphology unit. The distribution characteristics of bauxite in karst highland, karst slope and karst depression are punctate, banded and flaky, respectively. The bauxite reservoir in the karst slope area is the most developed. The enrichment of natural gas in bauxite rock is mainly controlled by high-quality reservoirs, faults, fractures and structural positions. Reservoirs are the premise of natural gas enrichment and high yield. Early faults show construction effect, and late faults show destruction effect. Fractures can improve reservoir physical properties. Low-amplitude structures or nose-like traps in high structural parts are more likely to accumulate. Karst slope area is the most favorable paleogeomorphologic unit for natural gas accumulation in bauxite rock.

Abstract:The potassium and lithium-rich brine is found in the central and northern part of Jiangling depression, while the southwest area is dominated by solid evaporites without potassium and lithium. This study aims to investigate the evolution of the paleo-saline lake brine in the southwestern Jiangling depression and sources of K and Li by the chemical composition of halite fluid inclusions of well ZK0303. Microscopic observations revealed the presence of primary fluid inclusions with chevron and cumulate structures in three groups of halite layers. The concentrations of Li, K, Mg, Ca, Br from the individual primary fluid inclusions were analyzed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). According to the analysis of experimental data, the brine of Eocene halite fluid inclusion in the southwestern of the Jiangling depression is Na-K-Mg-Ca-Cl type, in which the highest concentration of K is 3 362.15 mg/L, and the highest concentration of Li is 15.10 mg/L. The relationship between Mg-Ca-2K of three halite layers in well ZK0303 shows that the brine of Eocene saline lake in the southwestern depression reached the stage of sylvite precipitation. The changes of each ion concentration of the three halite layers show that the degree of evaporation of Eocene saline lake had changed from low to high and then decreased. According to previous studies, the sources of Li and K in the brine are closely related to the basalt in the depression. However, the southwest area of the depression is far from the basalt distribution area, and it is difficult to obtain sufficient material supply. Lithium and K of the Eocene saline lake brine in this area may come from the dissolution of early halite in addition to evaporation.

Abstract:The Mengyejing potash deposit, which is located in the Simao Basin, Yunnan, contains different clastic rocks, namely greyish-green breccias coexisting with potash veins ("green potash"), brownish-red breccias coexisting with potash veins ("red potash") and yellowish-brown mudstones. XRD, SEM and TEM analyses were performed on those fine-grained clays extracted from clastic components. SEM and TEM observation suggests that those clay minerals are mainly composed of hexagonal, euhedral illites. It is very likely those illites are authigenic origin. The XRD results show that the "red potash" are composed of chlorite and illite, whereas both "green potash" and yellowish-brown mudstone contain "pararectorite" type clays, in addition to chlorite and illite. The Kübler values (indication of illite crystallinity) of the "red potash" range from 0.327 to 0.452°Δ2θ, which are much higher than those of the "green potash" and yellowish-brown mudstone (0.221 to 0.283°Δ2θ), indicating illites from the "green potash" and yellowish-brown mudstones have higher crystallinities than those from the "red potash". The "green potash" and "red potash" derived from the same provenance, and have undergone similar geologic processes. Thus the discrepancies with respect to clay assemblages and crystallinities among different clastic sediments were not merely caused by temperature and pressure. Previous studies have shown that the "green potash" were more reductive, imposed by more bacterial activities and had lower pH values, which are favourable to facilitate the crystallization of illite.

Abstract:The crystal chemical mechanism of mineral cleavage/fracture and its relationship with interplanar spacing were quantitatively studied using density functional theory, broken bond theory, and crystal chemistry properties. It was found that the common cleavage/fracture planes of minerals do not always correspond to the crystal planes with the maximum interplanar spacing, showing a weak correlation. The theoretical calculations suggested that the common cleavage/fracture planes of minerals correspond to the crystal planes with the lowest surface energy, and the surface energy is positively correlated with the reticular density and the average broken bond number τ of the crystal plane atoms. The interplanar spacing is positively correlated with the reticular density, implying that when crystal planes with large interplanar spacing become common cleavage/fracture planes, the surface energy needs to be reduced by decreasing the average fracture bond number τ of the crystal plane atoms. However, the analysis revealed a poor correlation between the interplanar spacing and τ, which indicates that the interplanar spacing is not directly related to the cleavage/fracture patterns of minerals. The results of this study can provide theoretical insights for research on the cleavage/fracture patterns of minerals and surface properties.

Abstract:In recent years, the Tanshan-Shangfu Nb-Ta-Li-Be metallogenic prospective area has been predicted in the southern of Jiuling area, northwest Jiangxi Province. Mineralization types include granite-type and aplite-type. Study on the formation age and genetic mechanism of rare metal deposits, is the key points of the enrichment and mineralization of rare metals in Jiuling area. Based on the study of the columbite-group minerals U-Pb geochronology, petrography and petrogeochemistry, to determine the diagenetic age and mineralization age, rock formation and magma source characters of the Nb-Ta-bearing aplite, and make analysis on its metallogenic potential. The LA-ICP-MS niobite-tantalite U-Pb dating yields an age of 142±1 Ma, suggesting that the Nb-Ta-bearing aplite was formed in the Early Yanshanian period. The aplite is characterized by rich silica, alkali and aluminum, poor titanium and ∑REE, the wide range of Rb/Sr, and there exists obvious enrichment of niobium-tantalum-lithium-rubidium, and CaO/(K₂O+Na₂O)≤0.10, Al₂O₃/TiO₂＞160, high differentiation index. The REE diagram shows rightward incline and obvious negative Eu abnormity. The spider diagram of trace elements shows left side is uplifted and right side is gentle. All of these indicate that the aplite show features of highly differentiated S-type granitoids. It may be that the metamorphic argillaceous rocks of the Neoproterozoic Shuangqiaoshan Group in the Jiuling area were partially melted to form granitic magma, which during the transition stage from syn-collision to post-collision, and then to form highly fractionated aplite. In the late stage of magmatic differentiation and evolution, the interaction between fluid and melt leads to the enrichment of metal ore-forming elements like Nb-Ta-Li in the highly fractionated aplite. The Dongcao Nb-Ta-bearing aplite and the Nanling Nb-Ta-bearing granite, the Dahutang Nb-Ta-bearing granite porphyry have similar geochemical characteristics. Which is regarded as the main metallogenic geological body in the Tanshan-Shangfu Nb-Ta-Li-Be metallogenic prospective area.

Abstract:The north Wuyi area in Jiangxi Province is located on the southern side of the Pingxiang-Guangfeng junction zone on the Qinhang mineralization belt. Multiple tectonic events and magmatic activities formed a complex geological structure pattern in this area, and metallogenic potential of copper and lead-zinc polymetallic deposits is enormous. However, due to the generally small scale and insufficient research of lead-zinc deposits in the northern Wuyi area of Jiangxi Province, there is a lack of in-depth understanding of material sources, metallogenic conditions, and deposit genesis. This paper takes Laohudong Pb-Zn deposit in the northern Wuyi area of Jiangxi Prov-ince as the research object. EPMA, LA-ICP-MS and LA-MC-ICP-MS were used to reveal the major and trace element and sulfur isotope composition of sulfides, then many important information concerning the mineralization temperature, the source of metallogenic materials and the genesis of the deposit were investigated. EPMA testing shows that the Fe content in sphalerite ranges from 7.58% to 8.27%. Combined with LA-ICP-MS trace element testing, sphalerite is rich in Fe, Mn, Cu, Cd elements, followed by Co, Ni, Ag, In and Pb elements, the contents of Ga, Ge, As, Se, Sn and Bi elements are low. In sphalerite, Mn, Fe, Cd, In and Co exist in the form of isomorphism,while Cu, Ag, Pb exist in the form of isomorphism and microscopic inclusions. The content of Fe, the values of Ga/In (0.001~0.129), Zn/Cd (262~312) and calculation results of relevant formulas of sphalerite all indicated that sphalerite was formed under medium to high temperature mineralization conditions (about 327~337℃). The δ³⁴S of sphalerite and pyrite respectively concentrated between 2.07‰~4.16‰ and 0.82‰~3.19‰,they all indicated magmatic sulfur. Compared with multiple Pb-Zn deposits in China, the trace element composition of sphalerite in Laohudong Pb-Zn deposit is consistent with typical skarn deposits. The Laohudong Pb-Zn deposit has a close genetic relationship with the Gexianshan granite complex, and the age of Gexianshan granite complex (153.9±2.7 Ma and 162.8 ± 1.2 Ma) can represent the lower limit of the mineralization time, which is consistent with the range of the main polymetallic Pb-Zn deposits in the north Wuyi area.

Abstract:In the process of ore prospecting prediction, basic geological big data has a significant impact, resulting in poor accuracy of screening results when applied to complex geological areas. Therefore, a remote sensing prospecting prediction method for Pengshan ore field in De'an County, Jiangxi Province was studied. As a typical ore field in the Pengshan area, the Xiabianshan tin ore area is analyzed for its geological characteristics and mineralization rules. Based on the analysis results and remote sensing technology, remote sensing prospecting elements and remote sensing alteration information are obtained. A remote sensing comprehensive information prospecting target area prediction model is established, and the quantitative prediction results of the prospecting target area in the Pengshan area are obtained. The prediction results show that three typical prospecting target areas have been quantitatively predicted in the study area, located on the northwest, west, and east sides of the area, mainly consisting of annular and banded structures, and the structural development directions are mainly northeast, northwest, and nearly south-north. The remote sensing alteration information extracted mainly includes carbonation, epidotization, chloritization, sericitization, kaolinization, and iron staining. All three target areas have good mineralization conditions. The field investigations have confirmed the existence of kaolinization, iron staining and carbonation in the three target areas, and the contents of Cu and Au in the altered rock blocks are high. The predicted results have been confirmed, providing reliable reference for ore prospecting in this area.

Abstract:Ferrihydrite is a common iron oxide mineral in soil and also the main arsenic carrying mineral. Releasing arsenic from ferrihydrite is a way to alleviate arsenic pollution in soil. In this paper, it is intended to promote the release of arsenic by biological reduction of arsenic-containing ferrihydrite (As-Fh) by sulfate reducing bacteria (SRB) and acidiphilium cryptum JF-5 (JF-5), so as to achieve the purpose of soil remediation.To this end, two kinds of microbial shaker experiment and biological injection experiment were carried out by collecting typical arsenic-containing ferrihydrite from Shimen mining area in Hunan Province, to explore the arsenic release and form of ferrihydrite, the change of suspended particulate matter in the process of biological dissolution, and the permeability of the system. The results showed that: ① In two cycles, according to the total amount of arsenic released, JF-5+SRB operations> JF-5+JF-5 operations>SRB+JF-5 operations>SRB+SRB operations, corresponding to these operations were able to release 16.4,16.2,7.3 and 3.3 mg per gram of ferrihydrite, respectively; ② Hydrochemical analysis also showed that SRB could provide stronger reducibility than JF-5 under the same operation; ③ The biological column experiment showed that compared with SRB, JF-5 injection could produce iron suspended particulate matter with an average concentration of 1 419 mg/L, 7.25 times that of SRB; At the same time, the permeability of SRB column system (mean water pressure difference of 0.51 psi) was significantly better than that of JF-5 (mean water pressure difference of 2.22 psi), and the dispersion of highly suspended particles was the main reason for the permeability change.These results demonstrate that continuous injection of SRB into the ferrihydrite system is an effective technique for reducing arsenic concentration in soil.

Abstract:Muscovite is the important component of mineral aerosols in the atmosphere. The researches for heterogeneous reactions of common gases in the atmosphere on the surface of muscovite will reveal the chemical reaction process in the atmosphere to a certain extent. In this study, the heterogeneous reaction of SO₂ and NO₂ on the surface of muscovite particles was investigated by a self-made quartz glass microreactor, and the effects of relative humidity (RH) and light on the reaction were also discussed. The results showed that muscovite has certain adsorption activity for both SO₂ and NO₂. The products in SO₂ reaction with and without ultraviolet irradiation were mainly salt compounds containing SO^2-₄ and SO^2-₃, respectively, while the products in NO₂ reaction were always mainly salt compounds containing NO^-₃. The increase of RH or ultraviolet light had a promoting effect on the reaction, and they had a synergistic effect on the formation of sulfate and nitrate. When SO₂ and NO₂ coexist on the surface of muscovite, there were both synergistic effect and competitive effect, and the generation amount of SO^2-₄ and NO^-₃ was 2.09 times and 77% of that in the presence of a single gas, respectively. Therefore, NO₂ promoted the formation of sulfate, but SO₂ had a significant inhibitory effect on the formation of nitrate.

Abstract:0.015%, 0.025%, 0.05% and 0.1% δ-MnO₂ were added to yellow soil of Guizhou Qinglong antimony mine by in-situ processing. After 20 days of flooding, the content of Mn and Sb in suspension and the content of each speciation of Mn and Sb in soil were determined, and the correlation analysis of each parameter were performed to clarify the effect of Mn oxides on the speciations of Sb. The results showed that the contents of Mn in suspension and three speciations of Mn in soil gradually increased with the increase of δ-MnO₂, and the order of Mn content of all speciations in soil was consistent with that in control soil. With the increase of δ-MnO₂, the contents of non-specific adsorption, specific adsorption and residual Sb decreased, while the content of Fe/Mn/Al oxide bound Sb increased. The Mn loading was significant positive correlation with all speciations of Mn and Fe/Mn/Al oxide bound Sb (P<0.05), and significant negative correlation (P<0.1) with residual Sb. Fe/Mn/Al oxide bound Sb and residual Sb were significant positive correlation (P<0.05) and negative correlation (P<0.1) with all speciations of Mn, respectively. δ-MnO₂ existed in various speciations in yellow soil. After flooding, the speciations of Mn transformed to different degrees, and various speciations of Mn were oxidized, adsorbed and complexed with Sb, which made the non-specific adsorption Sb, specific adsorption Sb and residual Sb transform to Fe/Mn/Al oxide bound Sb in soil.

Abstract:Mississippi Valley-type (MVT) lead-zinc deposits are closely related to evaporite rocks, however, the fact that evaporite minerals dissolve or transform into other minerals and "disappear" is often overlooked. Drawing on previous research results, we summarized the transformation and identification characteristics of evaporite, and its relationship with MVT Zn-Pb mineralization that is reflected in the source of mineralizing fluids, the source of sulfur, and the ore-bearing structures. The formation of MVT deposits involves basin brines, primarily derived from evaporated seawater, with a small portion originating from the dissolution of evaporite rocks. Meanwhile, the deve-lopment of regional evaporite rocks indicates the formation conditions for mineralizing fluids. The sulfur in lead-zinc metal sulfides totally comes from the reduction of sulfates, and evaporite minerals, such as gypsum, anhydrite, etc., are important suppliers of sulfates. Moreover, dissolution-collapse evaporites form breccias and collapse spaces, and lead-zinc mineralization can occur within the breccias and/or adjacent strata. Salt diapiric structures create favorable structural/chemical traps for fluid accumulation and mineral precipitation, and lead-zinc mineralization can be found in the caprock, transition zones and peridiapiric rocks of salt diapirs, vertically oriented salt diapiric breccia pipes, or top of domes formed by lateral salt diapirism. Pseudomorphs after evaporite minerals and residual evaporite minerals are direct evidence of the existence of "disappeared" evaporites, while minerals such as albite and scapolite, length-slow chalcedony/quartz, alkali-enriched double-terminated quartz, etc., may indicate the past existence of evaporites. The evaporite dissolution-collapse structures exhibit the characteristics of lateral extension along with the stratigraphic strike, and salt diapiric structures have features such as cross-cutting and breccias derived from lower strata, both of which can help identify evaporite-related structures. In exploration for MVT deposits, the regional stratigraphic record of evaporative sedimentary environments is necessary for MVT mineralization, and evaporite dissolution-collapse structures as well as salt diapiric structures are important prospecting targets.

Abstract:The mafic-ultramafic intrusions contain a large amount of information from the deep earth, and the magmatic deposits they contain are of great economic value. Fe is an element directly involved in mineralization, and Fe isotope method has a natural advantage in tracing the source of metallogenic material and metallogenic process. In recent years, with the appearance and development of MC-ICP-MS, many scholars have carried out a series of Fe isotope studies on mafic-ultramafic intrusions and made important progress. In this paper, the fractionation mechanism of Fe isotopes in mafic-ultramafic intrusions is discussed by summarizing the composition characteristics of Fe isotopes in magmatism and metallogenesis. The results show that the composition of Fe isotope in different geological bodies is different. The chondrite represents the initial Fe isotope composition of the earth, and the other geological bodies are subjected to different degrees of later geological processes and produce fractionation of Fe isotope. The framework of Fe isotope fractionation mechanism in mafic-ultramafic intrusions is constructed: Fe isotope fractionation mechanism includes thermodynamic equilibrium fractionation and kinetic fractionation. In natural minerals, Fe³⁺ forms stronger chemical bonds than Fe²⁺, so mineral rich in Fe³⁺ (such as magnetite) are more enriched in heavy isotopes than mineral rich in Fe²⁺ (such as pyrrhotite and pentlandite). Many kinetic processes such as redox process, fractional crystallization, partial melting and diffusion are the factors leading to kinetic fractionation. Due to its unique geochemical properties, Fe isotopes have a wide application and prospect in the fields of Cu-Ni-PGE sulfide deposits, V-Ti magnetite deposits and chromite deposits related to mafic-ultramafic intrusions. Combined with other stable isotopes, such as Li-S-Mg-Ni isotopes, they can be used to trace the assimilation of sediment, invert the crystallization process of sulfide melt and reveal the genesis of deposit.

Abstract:Zircon is a robust dating accessory mineral, and often develop thin ring (generally less than 5 μm), which poses challenges to obtaining accurate ages of this ring. This article conducted a series of comparative and experimental studies from three aspects: ① sample preparation methods; ② experimental conditions, and ③ data algorithms to evaluate the reliability of multi-pulse short time ablation method for LA-ICP-MS U-Pb dating of ultra-thin ring (~1 μm) in natural zircons. The results showed that although the double-sided adhesive sample preparation method is fast, the sample observation under microscopic and laser system are poor. The resin-fixed preparation method has high efficiency, is easy to observe with transmitted light and reflected light, and is conducive to sample surface focusing. For laser setting parameters, data results in 5 Hz/2 s ablation are more stable than those in 10 Hz/1s ablation. The peak integration method is superior to linear regression and mean value methods for data reduction. Our results show that by using rapid erosion method for Pleovice and Qinghu zircon dating are consistent with the recommended values within the error range, but the data error is relatively large (~5%, 1σ). The zircon standards Pleovice and Qinghu are improved by 3% and 2% respectively when the 50%~60% of each signal peak value peak integration method was used. The combination of resin-fixed sample preparation, peak integration data processing method and multi-pulse short time ablation method can get an acceptable age of ultra-thin zircon ring. This method can provide more age constraints for multi-age geological processes.

Abstract:The determination of Ca isotope ratios by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) is sensitive to the matrix effect, especially that is generated by Cr elements, which leads to a deviation in Ca isotope compositions. Traditional methods using dilute HCl medium and strong acid cation exchange resin can achieve high-efficiency separation of most matrix elements and Ca, except Cr, where nearly 10% of Cr cannot be removed from Ca elution. For geological samples with high Cr, such as ultramafic rocks, the Cr/Ca ratio can be as high as 10. To achieve Ca isotope analysis of these special geological samples, here we studied the elution of Cr-Ca in concentrated HCl medium based on AG50W-X12 (200-400 mesh) strong acid cation exchange resin. The results showed that efficient and rapid separation of Cr-Ca can be achieved when using 10 mol/L HCl, with a Cr separation rate >99.9%. Moreover, this method can achieve efficient and rapid separation of elements such as K, Mg and Al from Ca. To test the validation of this method for Ca isotope analysis, δ⁴⁴/⁴²Ca of the Ca single-element solution after column separation was determined using MC-ICPMS, with the results consistent with the theoretical value within the analytical error. This indicates that this method is efficient for Ca element purification and valid for Ca isotope analysis for those high Cr samples.