Abstract:The proved boron resources in China are mainly distributed in Northeast China, Qinghai, Tibet and some other regions. These deposits have low grade, many associated minerals, high development cost and low development and utilization degree, and hence it is difficult for them to meet the needs of industrial development. At present, exploration in Jiangling Depression of Jianghan Basin shows that the B₂O₃ concentration in the brine reaches 3 g/L, and the content of lithium, potassium, bromoiodide, rubidium and cesium exceeds the industrial grade, with high comprehensive utilization value. On the basis of previous studies, the authors studied hydrochemistry, isotopic geochemistry and experimental geochemistry of Cenozoic brine boron deposits in Jiangling Depression in this paper, with the emphasis placed on the influence of paleoclimate, structure and provenance on brine mineralization as well as the genetic mechanism. It is preliminarily concluded that different halogen lithologies have different geochemical and isotopic characteristics, and basalt has experienced strong alteration, indicating that underground fluid metasomatism of igneous rocks exists, and the water-rock reaction of basalt is an important material source of boron-rich brine deposits. The fluid with a certain salinity is more conducive to the activation of boron ions. The fluid with a high salinity is the main transport carrier of boron ore-forming elements. The evaporation and concentration of ore-bearing water in the dry and hot paleoclimate under the supergenic environment constitute an important process for the enrichment and mineralization of boron-rich brine.

Abstract:Located in the middle part of the east Kunlun Mountains, the Golmud River catchment is covered with a large area of granite, especially the potassium-rich granite in local areas. In order to understand the evolution of distal Qarhan Salt Lake, it is important to study the distribution of these granites, the variation of the K, B, and Li elements, and their temporal and spatial migration. In this study, the authors collected samples from granites and their weathered detrital materials along Kunlun River section, Xidatan River section, and Xiaogangou section of Golumd River catchment. Based on major and trace element analysis, rock slice identification, chemical weathering index, and optical stimulated luminescence dating (OSL), the authors investigated the salt-forming elements in the granites and their weathered products. The results are as follows:① In the Xidatan and Kunlun River catchment, gray-white, medium-fine grained late Variscan granulites are predominant, with intermediate level potassium content; In the Xiaogangou River section, there are mainly gray-white and flesh red late Yanshanian porphyritic adamellites, which are potassium-rich granites, and thus these areas are advantageous metallogenic targets of potassium; ② K content gradually decreases and B, Li element content gradually increases with the increasing weathering degree in the granite. The Xiaogangou River section has high K, B content, but the Kunlun River section shows high Li content; ③ The chemical weathering indexes, such as WPI, LOI, are well coupled with the element content variations of different weathering degree samples, indicating that these two chemical weathering indexes are sensitive to the variation of weathering degree; ④ The alluvial sediments section of Xiaogangou River catchment has OSL ages from 95.9±10.5 ka in the bottom layer to 17.7±1.0 ka in the upper layer, and the WPI index, K, B and Li content variation curves in the sections indicate that the salt-forming elements migrations in the granites in the Golmud River catchment seem to have been related to the chemical weathered degree change associated with the glacial-interglacial cycles since late Pleistocene, and these elements have provided abundant saline minerals for the Qarhan Salt Lake.

Abstract:The Zhaosugou fluorite deposit is a typical fluorite deposit in Longhua area. The deposit is located in the fault structure of volcanic rocks of Zhangjiakou Formation and early Cretaceous syenite porphyry. The occurrence of its orebody is strictly controlled by faults. Trace elements and rare earth elements in fluorite ores and surrounding rocks were systematically analyzed. Trace elements show that all samples have relatively high Co, Cr, Cu and Ni content, and the changes are stable, especially the Ni content is obviously higher. The values of U, Be and Mo are low and vary greatly. The distribution pattern of rare earth elements in fluorite ore shows a rightward light rare earth enrichment type, with both positive and negative Eu anomalies, and Ce shows a slight negative anomaly. The ore-forming inclusions are mainly liquid-rich inclusions and pure liquid inclusions. The temperature measurement of the inclusions shows that the complete homogenization temperatures are 137~238℃, and the homogenization temperatures are relatively concentrated, with an average of 189℃, the salinities are 0.88%~2.07% NaCl_eq, with an average of 1.61%, and densities are 0.63~0.89 g/cm³. Overall, the ore-forming fluid of the Zhaosugou fluorite deposit was a relatively uniform low temperature, low salinity and low density fluid. According to the metallogenic pressure, the metallogenic depth is estimated to be 0.289~0.538 km, with an average of 0.428 km. The geochemical characteristics of ore and surrounding rocks and the characteristics of ore-forming fluid inclusions show that the fluorite ore system was of low-temperature hydrothermal origin.

Abstract:The Sichuan Basin is one of the most important salt basins in China; nevertheless, whether it can produce industrial marine potash deposit or not remains a problem of much controversy. In this study, with the source of polyhalite, the forming condition, the sub-depression and the prediction of targets of potash deposits as main lines, and on the basis of microscopic identification, scanning electron microscope, strontium isotopic composition, seismic interpretation and magnetotelluric sounding, the authors systematically analyzed the potential of marine potash resources in the Lower-Triassic Formation, and made a prospecting breakthrough of marine potash exploration in eastern Sichuan Basin. The authors hold that the polyhalite existent in halite in eastern Sichuan Basin is authgenic, and the seawater was highly concentrated and had reached the critical point of the potassium and magnesium salts precipitation in the early Triassic period. Two sub-depressions exist in the Diangjiang salt basin, i.e. the Hexing and Dongjiachang, and the potash salt in the sub-depression was well preserved and subjected to be less reconstructed by later tectonic movements. The results of the seismic interpretation and magnetotelluric sounding were used to delineate the exploration target area of Shuanglong-Baohe Village, and resources of potash salt were predicted, which should be useful for drilling verification.

Abstract:The Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation is one of the main targets for shale gas exploration in southern China. In this paper, the authors studied the thickness and burial depth of the black shale in Yanzikou area of northwestern Guizhou and its key features of shale gas accumulation such as lithofacies characteristics, mineral composition, total organic carbon content, thermal maturity, storage space and physical properties.The results are as follows:① The thickness of the Wufeng Formation can reach 20 m in western Yile area, while that of the Longmaxi Formation gradually increases from Qianzhong uplift northward, and its maximum thickness is over 250 m in Dingmu'ao-Daping area; ② Effective source rocks are mainly distributed in the lower part of Wufeng Formation and Longmaxi Formation, consisting of clay shale, silty shale and calcareous shale. They are mainly composed of clay minerals, quartz and carbonate minerals with high rock brittleness index (47.3%~76.8%), showing good fracturing ability; ③ Fractures, dissolved pores, intergranular pores, and intercrystalline pores can be identified by SEM, among which dissolved pores and fractures are the main reservoir space. The reservoir has high porosity and shows a good correlation between the BET(13.4~24.9 m²/g) and the total organic carbon content; ④ Geochemical analysis shows that the organic-rich shale section has good types of organic matter, with high organic carbon content (2.56% on average) and organic matter maturity (R_o=2.5%). According to comprehensive research, the north of Yanzikou area and the Gulin-Xuyong border area in southeastern Sichuan is a fairly favorable exploration potential area for Wufeng-Longmaxi shale gas.

Abstract:Systematic sampling and processing of such bentonite deposits as Erdaohe, Hartao, Beiwopeng and Xiazhalanboluo deposits in Zidutai-Yusi Basin were carried out, and petrological and mineralogical characteristics of ore-bearing rock series related to the deposit were investigated. The samples were analyzed and tested by means of basic analysis, XRD, chemical analysis and cation exchange capacity. The results show that rocks rich in volcanic glass, such as sedimentary tuff, rhyolitic ignimbrite and sandy tuff, are easier to hydrolyze to form bentonite ore. Bentonite is generally alkaline, and its mineral composition is mainly montmorillonite, followed by associated minerals such as quartz and plagioclase. XRD and cation exchange capacity show that calcium-based bentonite and sodium-based bentonite are developed in Erdaohe and Hartao bentonite deposits on the north side, showing layered characteristics of upper calcium-based bentonite and lower sodium-based bentonite. The results obtained by the authors are of guiding significance in search for sodium bentonite deposits in the deep part of Xiazhalanboluo and Beiwopeng bentonite deposits in the south of the basin.

Abstract:Potassium resources are one of the seven major scarce mineral resources in China. For a long time, China depends on imports for potassium resources. It is not easy to find potassium deposits in China. After more than 50 years' exploration, it is difficult to get a new breakthrough for potassium in the saline lake. There are hundreds of millions of tons of low-grade potassium in Qarhan Salt Lake, Mahai, and Lop Nur, equivalent to a large potash deposit. The development and exploitation of low-grade potassium is an important and feasible direction to solve the shortage of potash in China. In this paper, the authors carried out field experiments on liquefaction and exploitation of low-grade solid potassium in Bieletan, Qinghai Province, mainly studying the hydrodynamic and hydrochemical change. In the process of converting low-grade solid potassium into liquid, there exists big difference of water level change in different units of the experimental area in different periods, showing that there are significant differences in geological structure, tectonics, and especially porosity in Bieletan. In the process, the content change of KCl in the brine is different. In the initial stage of the process, the change of KCl content of brine in the detective pit is opposite to that of water level, and where the water level rises obviously, the quality of the brine is poor. However, with the constant replenishing of the solvent and the increasing of reaction time between solid potassium and solvent, the KCl content of the brine in the experimental area tends to become average, but the overall content is low. After months of liquefaction of low-grade solid potassium, the KCl content of the brine is still low and doesn't rise obviously. These phenomena may be attributed to the fact that many years mining of low-grade potassium has led to the reduction of potassium minerals in this area.

Abstract:Representative nitrate type salt lakes are distributed in the Kumishi Basin in Xinjiang. The concentration of Sr²⁺ in the basin salt lakes is higher than that of other salt lakes in Xinjiang, but the migration and enrichment regularity of strontium ions in the salt lakes in the study area requires further investigation. In this paper, the research object is the content of strontium ions in nitrate salt lakes. The migration and enrichment regularity of strontium ions in nitrate typical salt lakes in the study area is discussed. The results are as follows:① Concentrations of Sr²⁺ tend to be enriched from northwest to southeast in the water bodies and sediments of the Kumishi Basin, consistent with the converging direction of the river. It is shown that Sr²⁺ of the salt lakes is mainly concentrated in the salt formation depression along with the river water (including groundwater); ② Regardless of water bodies or sediments, the variation trend of Sr²⁺ is consistent with that of K⁺ and Ca²⁺, NO₃^-, SO₄^2- in chemical composition nitrate-type salt lakes. It is greatly affected by the material supply source of chemical components. Under the action of evaporation and concentration, the salinity of salt lake water bodies gradually increases, and the content of Sr²⁺ also increases. It is shown that the enrichment of Sr²⁺ is related to evaporation and concentration processes; ③ Main replenishment source of Sr²⁺ is the celestite deposit in the northwest and carbonate rocks (mainly Devonian limestone) and strontium-rich intrusive rocks in the northeast and northwest of nitrate-type salt lakes in the Kumishi Basin. Comprehensive analysis shows that migration and enrichment of strontium ions have the characteristics of multi-source and multi-directional replenishment.

Abstract:The formation age of potash deposits in Central Asia Basin was constrained roughly from Late Jurassic to Early Cretaceous. The formation age of salt minerals could be determined if they have not been altered since deposition. Otherwise, the isotopic dating results could only indicate their postdepositional process. To obtain the formation age of the Central Asia Basin potash deposits and/or understand the post-depositional alterations of salt minerals, the authors performed rubidium-strontium (Rb-Sr) isotopic dating on these salt minerals. The result shows that there is no reliable Rb-Sr isochron, indicating that these salt minerals have not kept closed after their formation. The Rb-Sr model ages of the potash minerals and rock salts range from approximately 9 to 4 Ma and 190 to 170 Ma, respectively. This result seems to have been caused by dissolution and recrystallization by extraneous or decomposition of carnallite fluids. The potash salts accumulated more radiogenic ⁸⁷Sr than the rock salts, because the potash salts contained more Rb than the rock salts. The dissolution and recrystallization of the potash and rock salts resulted in decreasing of ⁸⁷Sr/⁸⁶Sr ratios in the potash salts, but increasing of ⁸⁷Sr/⁸⁶Sr ratios in the rock salts. Although dating of salt minerals in other potash deposits of the world indicates that salt minerals are not suitable for dating the formation age of potash deposits, radiogenic isotopes of salt minerals can be used to constrain the metamorphic and hydrologic history of potash basins.

Abstract:The Cambrian dolomite in Tarim Basin has become focus in recent years as the significant strategic area. Previous studies have mainly focused on the dolomitization mechanism and the capping effect of salt rock. However, studies of the impact of salt rock on the dolomitization and reservoir formation are very rare. In this study, the authors summarized the dolomite reservoir characteristics of Cambrian Tarim basin and discussed the impact of salt rock on the subsalt dolomite. The Cambrian dolomite in Tarim basin can be classified into two major types, i.e. crystalline dolomite and microbial dolomite. The crystalline dolomite can further be divided into dolomicrite, crystal dolomite and granular dolomite. The microbial dolomite can be divided into thrombolites dolomite, stromatolite dolomite and foamite dolomite. Influenced by salt rock, the dolomite reservoir can be classified into anhydrite dissolved pores type reservoir, intercrystalline pores type reservoir and intercrystalline dissolved pores type reservoir. The salt rock mainly exerted impact on the dolomitization process and the formation of reservoir pores. The precipitation of gypsum and anhydrite in evaporated flat settings increased the Mg²⁺/Ca²⁺ ratio in the formation fluid, which was favorable for the dolomitization. Besides, the reduction of SO₄^2- influenced by microbial action promoted the precipitation of dolomite. In the aspect of impact on reservoir, the anhydrite dissolved pores were normally good reservoir space, the relative high thermal conductivity was favorable for the retrograde solution of dolomite, the dissolution of sulfate in near-surface condition was favorable for the precipitation of dolomite, and thermochemical sulfate reduction produced sour gas to form dissolved pores.

Abstract:There are many salt lakes in the Qaidam Basin, and topsoil salinization and salinization are well developed. A large amount of salt dust produced by wind erosion of these saline topsoil will harm the ecological environment and human health of the basin. Therefore, the authors systematically collected 129 different types of topsoil samples in the middle east of Qaidam Basin, and analyzed the composition and distribution characteristics of salt minerals. The result shows that the main salt minerals in the topsoil include halite, gypsum and a small amount of thenardite; In the middle east of the basin, the high-value area of salt content is concentrated in the vicinity of Yiliping Salt Lake, East-West Ginair Lake in the east of Gas Hure Lake and the area of the oasis front in central Golmud-Nuomuhong area; the salt content of different topsoil in the basin is in order of playa, Yardang, saline meadow, Gobi desert and desert. The comprehensive analysis shows that Yardang and playa are probably the main source areas of salt dust storm, and other types of topsoil contribute less; the characteristics and distribution of salt in topsoil may be influenced by many factors, such as structure, salt lake evolution, climate and hydrology. The results of this study can provide important scientific basis for the formation mechanism of salt dust storm and disaster prevention in Qaidam Basin.

Abstract:High purity quartz, a strategical material that is indispensable for producing integrated circuit, semiconductor, photovoltaics, optical fiber and novel glass, has seen growing demand worldwide. Ore deposits from which high purity quartz is extracted, however, are extremely rare throughout the world. Present ore deposits, including active and inactive, are located in the USA, Australia, Norway, Russia, China, Mauritania, and Canada, with resources in the USA and Australia possessing top reserves. Apart from China, there are 14 ore deposits, and their types include alaskite, pegmatite, hydrothermal quartz vein, tailings, and weathered granitoid. Ore fluids yielding the purest quartz were more likely differentiated from Paleozoic-Mesozoic magmas, and intruded ambient Archaean-Proterozoic metamorphic rocks, such as biotite gneiss, granite gneiss and schist, controlled by long-term multi-stage metamorphism. China is faced with a much more severe difficulty as it barely preserves any high purity quartz deposits, leading to massive import annually for high purity quartz sands, especially from the USA. Under current fluctuating global economic and political environments, China's premier task undoubtedly is to put more effort on geological survey on domestic Archaean-Proterozoic metamorphic rocks, and meanwhile intensify quality assessment, aiming toidentify hydrothermal veins, pegmatite, and alaskite that possess potential for extracting high purity quartz. Attentions should be paid to quartz in tailings from granodiorite, pegmatite, kaolin ores, and beneficiation trails should be implemented to evaluate their resource potentiality. In addition, China should build diversified pipelines for importing high purity quartz sands and products, and shift from sole reliance on the USA to other countries, such as Norway, Russia and Mauritania, thus providing safe and stable resource supply for national security.

Abstract:The phase evolution of high purity natural aragonite from room temperature to 1 073 K and the thermal expansivity of both aragonite and calcite were studied by using high-temperature powder X-ray diffraction, and the difference and influencing factors of geological and biogenic aragonite were analyzed. The results show that orthorhombic aragonite transforms to trigonal calcite at 693~733 K with the critical temperature T_c=723 K and an increase in molar volume by 5.97%. The variation of volume thermal expansion coefficient of aragonite with the absolute temperature T(K) at 300~663 K is α(V) (10^-5/K)=3.59(79)+7.17(170)×10^-3 T. The expansion of aragonite is strongly anisotropic, with the axial expansion decreasing in order of α(c) > α(b) > α(a). The thermal expansion coefficients α (10^-5/K) of calcite at 733~973 K are α(V)=3.78(25), α(a)=-0.27(2), and α(c)=4.31(29), with negative thermal expansion for the a axis. The phase transition temperature of biogenic aragonite is 60~140 K lower than that of synthetic and geological aragonite, and that of pulverized aragonite is lower than that of single crystal and undisturbed aragonite. Pulverized biogenic aragonite and calcite have similar thermal expansion coefficients to non-biogenic aragonite and calcite; however, the uncrashed biogenic aragonite has a smaller thermal expansion coefficient.

Abstract:The Qiongheba area in the East Junggar terrain is located in the middle section of the Central Asian metallogenic domain. Although many Paleozoic porphyry copper (molybdenum) deposits have been discovered in this area in recent years, these deposits are all small in scale and the metallogenic potential requires further evaluation. The Baxi copper deposit is one of the typical and representative porphyry copper deposits. The quartz diorite and quartz monzodiorite are closely related to porphyry copper mineralization. The zircon mean U-Pb weighted average age of quartz diorite is 345.7±3.0 Ma, indicating that it was formed in the Early Carboniferous. The plagioclase in quartz diorite and quartz monzonite is not andesine that is common in intermediate rocks, but calcium-richer labradorite. The bulk-rock geochemical characteristics show that they have meta-aluminum-weak peraluminum calc-alkaline I-type geochemical signatures. The primitive mantle normalized incompatible element patterns show the enrich-ment of large ion lithophile elements relative to high field strength elements as well as significantly negative Nb, Ta and Ti anomalies, suggesting a typical island arc-like geochemical feature. The mafic microgranular enclaves (MMEs), positive εHf(t) values (+13.66~+15.56) and the calcium-rich plagioclase in the rocks suggest that the magma originated from the mantle-derived basic magma mixed with felsic magma derived from juvenile crust. Based on the amphibole compositions, the authors calculated the pressure (28.6~166.9 MPa, equivalent to 0.6~3.1 km), temperature (673~908℃), water content (3.18%~4.64%), and oxygen fugacity (ΔNNO-0.22~ΔNNO+3.27). Combined with the tectonic setting and geophysical anomaly of the mining area, the high water content and oxygen fugacity of magmas indicate that the area has good prospecting potential for porphyry copper deposits.