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    Volume 40,2021 Issue 1
      非金属矿产专题
    • WANG Chun-lian, MENG Ling-yang, LIU Cheng-lin, YU Xiao-can, YAN Kai, LIU Si-han, YOU Chao, LI Ke-kun, TENG XIAO-hua

      2021,40(1):1-13, DOI:

      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.

    • AN Fu-yuan, ZHANG Xi-ying, CHENG Xia-li, MA Zhen-ying, GENG Jun, LI Jiang-yao

      2021,40(1):14-26, DOI:

      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.

    • DAI Xiao-guang, SHANG Peng-qiang, ZHANG Cheng-xin, LIANG Zhong-peng, WANG Jin-peng, LI Jian, YANG Hai-bo, NIE Xin-ming

      2021,40(1):27-38, DOI:

      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% NaCleq, 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.

    • ZHU Zheng-jie, YANG Zheng-zhou, ZHANG Xiong, LIU Cheng-lin, ZHAO Yan-jun, CUI Zhi-wei

      2021,40(1):39-48, DOI:

      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.

    • LAN Ye-fang, REN Chuan-jian, HUANG Yu, CHEN Hao, REN Shu-ming

      2021,40(1):49-64, DOI:

      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 (Ro=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.

    • LIU Dian-he, ZHANG Xue-hua, WANG Chun-lian, ZHANG Hua

      2021,40(1):65-75, DOI:

      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.

    • LI Rui-qin, LIU Cheng-lin, ZHAO Yan-jun, LIU Wan-ping, WANG Shi-jun, JIANG Yu-tong

      2021,40(1):76-88, DOI:

      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.

    • LI Chang-zhong, CHENG Huai-de, ZHANG Xi-ying, SONG Jian-guo, MA Xue-hai, JIANG Tian-ming, LI Jun, HAI Qing-yu

      2021,40(1):89-98, DOI:

      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-, SO42- 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.

    • SHEN Li-jian, LIU Cheng-lin, JIAO Peng-cheng, WANG Chun-lian, CAO Yang-tong

      2021,40(1):99-108, DOI:

      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.

    • LIU Li-hong, GAO Yong-jin, WANG Dan-dan, BAI Zhong-kai, ZHANG Yuan-yin, HAN Miao

      2021,40(1):109-120, DOI:

      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 SO42- 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.

    • GENG Jun, ZHANG Xi-ying, LI Wen-xia, GUO Xiao-ning, ZHANG Hai-xiao, TANG Qi-liang, CHEN-Liang

      2021,40(1):121-130, DOI:

      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.

    • WANG Jiu-yi

      2021,40(1):131-141, DOI:

      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.

    • 非主题来稿
    • YANG Hua, LIU Qiong

      2021,40(1):142-152, DOI:

      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 Tc=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.

    • ZHANG Ming-hong, YAO Yong, CHENG Zhi-guo, ZHANG Zhao-chong

      2021,40(1):153-168, DOI:

      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.

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    Volume 40,2021 Issue 1
      专题研究
    • ZHANG Li-cheng, WANG Yi-tian, CHEN Xue-feng, MA Shi-qing, WANG Zhi-hua, YU Chang-fa

      2013,32(4):431-449, DOI:

      Abstract:

      The Hongyuntan iron deposit is hosted in pyroclastic rocks of the Lower Carboniferous Yamansu Formation. The ore bodies occur as layers, stratoid bodies or lenses. The principal ore mineral is magnetite, together with minor maghemite, specularite, pyrite and trace chalcopyrite. The gangue minerals include garnet, diopside, actinolite, chlorite, tremolite, epidote, biotite, albite and quartz. The ore structures are mainly of massive and disseminated forms, with occasional banded or veined forms. The ore textures are of subhedral-anhedral granular and metasomatic types. The wall rock alteration shows symmetrical zoning, and the alteration colors change from dark to light from ore bodies outwards. On the basis of observed mineral assemblages and ore fabrics, two periods of ore deposition were recognized, i.e., skarn period and hydrothermal ore-forming period, which could be further subdivided into four metallogenic stages, namely skarn stage, retrograde alteration stage (main ore-forming stage), early hydrothermal stage and quartz-sulfide stage. Electron microprobe analyses show that the end member of garnet is mainly andradite-grossularite. The composition of pyroxene is mainly diopside-asteroite. The amphiboles is composed mainly of actinolite and tremolite with minor magnesiohornblende. The composition of these skarn minerals suggests that skarn in the Hongyuntan iron deposit is calcic skarn, belonging to metasomatic skarn. The characteristics of main and trace elements suggest that the formation of magnetite was closely related to the skarn. In combination with geological characteristics, the authors suggest that the skarn might have resulted from interaction between Ca-rich pyroclastic and Fe-rich magmatic hydrothermal fluid which was transported along the fault system. The formation of magnetite was hence related to the regressive metamorphism of the skarn.

    • Gan Guoliang Yichang Institute of Geology, Mineral Resources, Chinese Academy of Geological Sciences Department of Grologicol, Atmospheric Sciences, lows State Univeraity, Ames, IAS0011, U.S.A

      1993,12(2):144-181, DOI:

      Abstract:

      This paper presents partition coefficients of 69 chemical elements (Li, Rb,Cs, K, Na, Ca, Ba, Sr, Mn, Fe, Mg, Cu, Pb, Zn, Co, Ni, Be, La, Ce, Nd,Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc, Cr, In, Ga, Al, B,Cd, Sb, Bi, U, Th, Zr, Hf, Si, Ti, Ge, Sn, Mo, Nb, Ta, W, V, P, F, Cl,S, N, O, C, As, Pu, Re, Os, He, Ne, Ar, Kr and Xe) and the univalent radical (OH) in 28 minerals (olivine, clinopyroxene, orthopyroxene, amphibole,biotite, Phlogopite, plagiocla-se, K--feldspar, quartz, magnetite, ilmenite, garnet,zircon, apatite, allanite, topaz, sphene, cordierite, hauyne, leucite, nepheline,whit-lockite, brookite, petovskite, melilite, armalcolite, spinel and rutile) from 8 types of rocks, namely metaluminous (ultra) basic rock, peralkaline (ultra) basic rock, metaluminous intermediate rock, peralkaline intermediate rock,metaluminous acid rock, peralkaline acid rock, peraluminous acid rock and ultra-acid rock. It is found through an integrated ahalysis and comparison that the composition and structure of minnerals and melts seem to be the most important factors controlling mineral-melt element partitioning. Importanceshould be attached to minral structure and Al-supersaturation of melt which have, not been discussed by research workers. Finally, the present state and theproblems to be solved in the study of mineral--melt element partition coefficients are analysed, and the future trends of this research field are predibted.

    • 专题研究
    • HE Shi-ping, WANG Hong-liang, XU Xue-yi, ZHANG Hong-fei, REN Guang-ming

      2007,26(4):295-309, DOI:

      Abstract:

      Early Paleozoic volcanic rocks in Tianshui and Baoji areas along the eastern segment of North Qilian orogenic belt consists of Hongtubu basaltic lavas and Chenjiahe intermediate-acid volcanic rocks. Geochemical analyses show that Hongtubu basaltic lavas are similar to the intercalated basalts in Chenjiahe intermediate-acid volcanic rocks in characteristics, both fallen in the tholeiite series with high TiO2 (1.50%~2.73%). Their∑REE are 65.97×10-6~133.46×10-6 and 78.04×10-6~175.55×10-6 respectively, both are slightly enriched in LREE [(La/YbN being 2.00~4.40 and 2.71~4.40 respectively],and both have no obvious Eu anomaly or weak Eu negative anomaly(δEu being 0.85~1.10 and 0.85~0.99 respectively). Basalts from two groups are typically characterized by selected enrichment of LILEs, low abundances of HFSEs relative to NMORB, and prominent troughs of Nb and Ta, with low Nb/La ratio(0.28~0.43), which indicates the affinity of these volcanic rocks to island arc tholeiite(IAT). In addition, εNd(t)(+2.22~+4.08)values of basalts suggest that their mantle sources are similar to the depleted mantle source. Zr/Nb=17.21~36.33 and Ce/Nb=5.73~8.17, implying geochemical characteristics of N-MORB. Sr, Nd and Pb isotopes from Hongtubu basalts are similar to those in Chenjiahe basalts in composition. In the diagrams of εNd(t)-(87Sr/86Sr)t, (207Pb/204Pb)t-(206Pb/204Pb)t,(87Sr/86Sr)t-(206Pb/204Pb)t and εNd(t)-(206Pb/204Pb)t for basalts, the data are fallen in the DM, EMⅠand EMⅡ areas, probably with a little crustalontamination, indicating that the magma of basalts might have had a mixed gin.Thentermediate-acid volcanic rocks from Chenjiahe belong to the calc-alkaline series,they have relatively high abundances of REE∑REE=127.51×10-6~276.01×10-6), and are significantly enriched in LREE[(La/YbN= 4.79~13.51]. Most intermediate-acid volcanic rocks show weak Eu negative anomaly (δEu=0.53~1.20). The trace element patterns of Chenjiahe acid volcanic rocks are similar to those of the ocean ridge granite (ORG), with marked troughs of Nb, Ta, Zr and Hf. A synthetic study shows that the Chenjiahe intermediate-acid volcanic rocks in the eastern segment of North Qilian orogenic belt were formed in an island-arc setting, whereas the Hongtubu basalts were formed in an intra-arc rift setting (or an initial back-arc basin setting), probably being products of the early spreading evolution of the island_arc system towards the back-arc basin in the eastern segment of North Qilian during late Early Paleozoic. The results obtained provide evidence for the existence of the trench-arc-basin system at the juncture of Qilian and North Qinling orogenic belts.

    • 宝玉石矿物学
    • YAN Ruogu, QIU Zhili, DONG Chuanwan, LI Liufen

      2009,28(3):292-298, DOI:

      Abstract:

      High grade black jadeite is a kind of upscale and fashionable jade material that has become one of the jadeites characterized by fastest growing values in the past 20 years. Based on a comparison of mineralogical and geochemical characteristics between black jadeites (inky black jades)from different producing areas of the world, the authors hold that the black jadeites currently on the market can be mainly classified into jadeite jade, omphacitic jadeite jade and hornblende jade whose main components are jadeite, omphacite and dark green hornblende respectively. They include black chicken jade, ink jadeite and black kosmochlor from Myanmar and jade negro and galactic gold from Guatemala, with black chicken jades similar to those from Myanmar also seen in Japan and Kazakhstan. The research results suggest that the main mineral composition, jade structure and inclusion characteristic combinations of black jadeite jades from different producing areas have their respective typomorphic natures, which can be used as the distinctive characteristics for their sources.

    • 综合资料
    • SHEN Qi-han

      2009,28(5):495-500, DOI:

      Abstract:

      This paper has mainly recommended a mineral abbreviation list (see Table 2 and Table 3). Table 2, which contains 243 minerals, was compiled by IUGS Subcommittee on the Systematic of Metamorphic Rocks (SCMR) in 2007. The author selected other 29 minerals and, on such a basis, formulated Table 3. Thus, the total mineral abbreviations come to 272. It is hoped that they can be popularized in future and become more and more perfect through utilization, so as to provide a basis for ultimate standardization and unification.

    • 综述与进展
    • ZHANG Wei

      2014,33(4):747-762, DOI:

      Abstract:

      Cordierite is a mineral material characterized by low thermal expansion coefficient and good thermal shock resistance. Cordierite mineral material is relatively rare in nature, so cordierite is synthesized usually by the method of artificial synthesis. Based on the newest investigation results of synthetic cordierite, this paper deals with the progress of researches on such synthesis methods of cordierite as high purity oxide solid reaction at high temperature, natural mineral solid reaction at high temperature, the utilization of industrial wasted materials, the employment of agricultural wasted materials, the sol-gel and the low-temperature combustion synthesis. At present, the method of natural mineral solid reaction at high temperature is used for the preparation of cordierite in industry. In spite of a lot of advantages, this method also has many disadvantages. Therefore, the development trend of cordierite synthesis seems to solve the problem as to how to apply other synthesis methods to industrial preparation.

    • 专题研究
    • CAO Guang-yue, XUE Huai-min, WANG Jin-guang

      2014,33(6):1019-1038, DOI:

      Abstract:

      In this paper,LA-ICP-MS zircon U-Pb dating was carried out for four samples of volcanic rocks from Qingshan Group in Jiaodong area and, as a result, their concordant ages were obtained, which are 119.4±0.9 Ma, 118.2±1.0 Ma,120.2±0.9 Ma and 120.0±0.8 Ma, respectively. The results show that all the volcanic rocks in Jiaodong area were formed from about 120 Ma to 118 Ma in the Early Cretaceous period. The ages of Qingshan Group volcanic rocks from Shandong Province controlled by Tan-Lu fault are similar to those from the Su-Wan segment of the Tan-Lu fault zone,but younger than those around the Tan-Lu fault zone,which indicates that the duration of volcanic eruption along Tan-Lu fault is probably longer than the duration in other areas under the background of lithospheric thinning in eastern China. Geochemically, all the intermediate and acidic volcanic rocks have high K2O, ALK, LREE values and low MgO, TiO2, Ni, Cr, HREE values. According to the geochemical features, the volcanic rocks can be subdivided into trachyte-trachydacite and rhyolite. The trachyte-trachydacite is characterized by LILE enrichment(Rb,Ba,K)and HFSE depletion(Nb,Ta,Ti,P), but the rhyolite exhibits stronger depletion of Ba,Sr and HFSE (Ti,P). Compared with the rhyolite,the trachyte-trachydacite possesses higher Sr and Ba values as well as La/Nb and Ba/Nb ratios,but lower Rb/Ba ratios and δEu values. All these data indicate that they might have been derived from different magma sources. It is inferred that the trachyte-trachydacite rocks were derived from the mixture of the partial melting of the lower crust(Yangtze Craton or North China Craton)and enriched lithospheric mantle. In addition, the rhyolites were related to the partial melting of the lower crust in the regional extension environment and high geothermal anomaly background with crystallization differentiation during the magma evolution.

    • 宝玉石矿物学
    • GUO Li-he, HAN Jing-yi, LUO Hong-yu

      2006,25(4):349-356, DOI:

      Abstract:

      At present, the infrared transmission spectroscopy is the best technique for determining whether jadeite is polymer-impregnated or not, and the infrared reflectance spectroscopy is a nondestructive and rapid determination method that provides mainly the fundamental frequency vibration spectra data of minerals and shows new application potentials in gemological research, especially in the identification of gem species. The gemological application of IR reflectance spectroscopy and the identification system of IR spectra of gems, including a database of 318 spectra and a searching and identifying program, are described in this paper.

    • 专题研究
    • LIN Guang-chun

      2013,32(4):485-495, DOI:

      Abstract:

      Petrology, geochemical and Nd isotopic data are reported for the Neoproterozoic Danba metabasalt in the Kangdian Rift on the western margin of the Yangtze block. Samples were collected from alkaline basalts, which are enriched in MgO, TiO2, with Mg# being 0.51~0.59. They have high total rare earth elements and show high fractionation between LREE and HREE. The trace elements are characterized obviously by enrichment of Th, Nb, Ta, Zr, Hf and LREE but depletion of Y and HREE. Their geochemical and Nd isotopic characteristics suggest that they are similar to OIB. The basaltic magma was generated in an intraplate setting, and was generated by partial melting of OIB mantle source region, with variable degrees of contamination of SCLM during magma ascending; in addition, some samples might have experienced contamination of the lower crust. These samples reveal some plume magmatism characteristics in petrochemistry, and imply that magmatism was probably related to the Neoproterozoic plume event, which resulted in the breakup of Rodinia supercontinent.

    • ZHANG Kan, ZHU Xiang-kun

      2013,32(4):529-537, DOI:

      Abstract:

      The newly-exposed lower strata of the Xiamaling Formation near Tielingzi Village in Jixian County contain rich siderites. This paper reports the basic geological characteristics of these siderite-rich strata in terms of the field outcrop, petrology and major elements. Studies show that the profile is characterized by black shale interbedded with silty iron-rich layers/siderite concrete layers, and also has minor siltstone. Some iron-rich strata have turned into limonite layers in the outcrop because of intense weathering. Siderite is the main iron mineral phase in the strata. Siderites can form iron concretes, showing micritic or microcrystalline granulitic textures under the microscope, or form silty ferruginous layers with almost a comparable amount of silty quartz; it can also distributed sporadically in siltstone and black shale with relatively coarse particles. There also exists very little siderite residue in weathered limonite layers. The overall features of major elements show that the strata are rich in SiO2, TFe and TOC, but poor in MnO, CaO, MgO, P2O5 and S. Except for ferriciron in weathered layers, there is mainly ferrous iron in the strata. The TOC content decreases in order of siderite concrete, silty iron-rich layer, black shale and siltstone. The correlation diagram between TFe and Al2O3 content shows a negative correlation in iron-rich layers, while a positive correlation between them exists in normal black shale and siltstone, which suggests that iron in the former form originated from the ocean itself, while iron in the latter form originated mainly from terrigenous detritus. In addition, FeO content has a positive correlation with TOC content in fresh samples, which implies that the genesis of siderites may have some relationship with organic matter.

    • Zhou Zheng

      1997,16(1):81-90, DOI:

      Abstract:

      From the discovery of the first new mineral hsianghualite in 1958 to the end of 1995,74 new minerals found in China had been approved by IMA CNMMN. Among them, 2/3 were discovered after 1981. The discovery of new minerals in China has the following features:(1) With the development of analytical methods, the number of new minerals discovered per year increases gradually: from the end of 1950s to 1960s, only one new mineral was discovered every year on the average, whereas from 1980s till now, three new minerals were discovered averagely every year. (2) The structures of many new minerals have been determined. (3) Most of the new minerals are in the lower category, mainly in the monoclinic system, and perfect crystals are rare; hsianghualite has the most abundant crystal faces, whose ideal faces can reach 146. (4) Among those new minerals, silicates take the first place in number, followed by native elements, alloys, and then oxides. (5) The modes of occurrence of new minerals are varied, most of them occurring in oxidized zones of various deposits and deposits related to ma fic or ultramafic rock masses. There are a few new minerals occurring in skarn and placer deposits or even in cosmic dusts and meteorite.(6) The new minerals are characterized by wide but uneven distribution. Till now, new minerals have been discovered in 20 provinces or autonomous regions, especially in Hebei, Qinghai, Inner Mongolia and Henan. The number of new minerals found in North China is larger than that found in South Chine. (7) The number of discoverers of new minerals is in tens. The first discoverer of new mineral is Prof. Huang Yunhui, whereas Prof. Yu Zuxiang is the one who discovered the most numerous new minerals in China, totally disclosing 11 new minerals by himself or together with other experts. Most of the discoverers are members of the Chinese Academy of Geological Sciences, China University of Geosciences, and Institute of Geochemistry, Academia Sinica as well as other educational and scientific research institutions. The discovery of new minerals has promoted the development of mineralogy in China. Tens of discoverers were awardees of the National Natural Sciences Prize or the Science and Technology Progress Prize of the Ministry of Geology and Mineral Resources for the discovery and research results of new minerals in 1980s. More than 60 new mineals discovered in China were collected by the Geological Museum of China, with some of them exhibited in the Minerals and Rocks Exhibiting Room.

    • 其他
    • LUO Yue-ping, DENG Wang-hui, DUAN Ti-yu, WANG Chun-sheng

      2011,30(Z1):181-186, DOI:

      Abstract:

      As more and more treated turquoises appear on Chinese gem market, the authors collected lots of turquoises from different deposits on Chinese gem market in order to sum up the characteristics of the natural turquoises on Chinese gem market. At the same time, different types of treated turquoises were studied to find general difference between them and natural turquoises. The results show that natural turquoise and treated turquoise have different shades of color, inclusions and appearances. IR spectra of both natural and treated turquoises were studied, indicating that there are absorption peaks at 1 735, 1 600 and 1?500 cm-1 in treated turquoises, which are caused by the man-made polymer. If the turquoise is treated by polymer, there are absorption peaks at 1 735, 1 600 and1 500 cm-1 in a turquoise, and this can serve as convincing evidence in this aspect.

    • 专题研究
    • ZHU Xin-you, WANG Yan-li, CHENG Xi-yin, TIAN Ye

      2016,35(1):16-32, DOI:

      Abstract:

      There are several types of xenoliths, such as monzonite, quartz diorite porphyry, black rock and greisen schlieren, in the alkali feldspar granite of the Yaogangxian tungsten deposit, Hunan Province. The xenoliths are different in geological and geochemical characteristics, sources and evolution paths, which implies the genesis and magma evolution history of the Yaogangxian granite. In this paper, the authors studied the petrology, geochemistry of the xenoliths, alkali feldspar granite, and monzonite batholiths formed in late Jurassic period. It is detected that the monzonite inclusion (Ⅰb) came from early crystallization of deep magma chamber similar to the monzonite batholith. The quartz diorite porphyry and black rock xenoliths seem to have been the residue of Precambrian metamorphic rocks in the melting. The greisen schlieren resulted from the transition from the alkali feldspar granite stage to the magma-hydrothermal stage. The fine biotite granite xenolith (Ⅲb) in the quartz porphyry was captured from the supplementary granite which was differentiated from the main magma, or from the granite pluton formed from the supplementary rocks. The granite (Ⅰ) was rich in volatiles, which resulted in strong contamination of the xenoliths, and a certain amount of fluorite, mica, tourmaline and sulfide minerals formed in the xenoliths. The Yaogangxian granite is a product of the intrusion of highly fractionated magma derived from the magma chamber equivalent to monzonite batholith. The quartz porphyry magma directly resulted from the residue of segregation from fractional crystallization of magma chamber, rather than from the alkali feldspar granite of Yaogangxian. It is suggested that the magma evolved in order of magma chamber (main) (coarse monzonite) → fine biotite granite (supplementary) → alkali feldspar granite → magma-hydrothermal transition fluid (tungsten mineralization) → quartz porphyry veins.

    • LI Yu-long, YANG Zhu-sen, TIAN Shi-hong, ZHAO Zhi-yi, LU Shi-yin, ZHANG Yao, LIU Ying-chao

      2015,34(5):648-664, DOI:

      Abstract:

      Two kinds of carbonate hosted Pb-Zn deposits, namely carbonate-rich Pb-Zn deposits and fluorite-rich Pb-Zn deposits, extensively exist in the same Pb-Zn metallogenic belt in the world according to the classification based on gangue mineral assemblages. The relationship between the two kinds of deposits remains unclear. In the middle part of the 'Sanjiang' metallogenic belt in the Tibetan Plateau, the Dongmozhazhua carbonate-rich Pb-Zn deposit and the Mohailaheng fluorite-rich Pb-Zn deposit occur in the same carbonate-hosted Pb-Zn ore concentration area. In the two deposits, the carbonate strata are host rocks, the thrust faults are the main ore-controlling structures, the main orebody attitudes are of stratabound type, and sphalerite and galena are the main ore minerals. However, calcite and dolomite are the main gangue minerals in the Dongmozhazhua deposit while calcite and fluorite are the main gangue minerals in the Mohailaheng deposit. The geochemical features of rare earth elements (REE) in calcium-bearing minerals are different in the two deposits. The REE values of calcite in the Dongmozhazhua deposit are mainly characterized by obvious fractionation of LREE and HREE, enrichment of LREE, negative Eu anomalies and 'V'_shaped curves of chondrite-normalized REE patterns with right deviation. In contrast, the REE values of calcite and fluorite in the Mohailaheng deposit are chiefly characterized by no obvious fractionation between LREE and HREE, negative Eu anomalies and 'M'_shaped curves of chondrite-normalized REE patterns with right deviation. The total concentrations of REE (∑REE) of calcite (0.46×10-6~10.79×10-6) in the Dongmozhazhua deposit are higher than those in the Mohailaheng deposit (0.25×10-6~5.88×10-6). The geochemistry of the REE indicates that calcium-bearing minerals in the two deposits were all precipitated from a kind of hydrothermal fluids which had nothing to do with igneous activities. The salinity and reducibility of the fluids decreased with the sulfide precipitation. The two kinds of deposits had similar hydrothermal fluids; nevertheless, there existed another kind of fluid for the Mohailaheng deposit, which was a kind of fluorine-rich fluid from deep metamorphic basement. This fluorine-rich fluid controlled the location of the fluorite-rich carbonate hosted Pb-Zn deposits and could be used to explain the phenomenon why this kind of Pb-Zn deposits were more easily precipitated near the main thrust faults and the lowest carbonate strata in the region. The result achieved by the authors could answer the question why the carbonate-rich Pb-Zn deposit and the fluorite-rich Pb-Zn deposit can occur in the same region and same time in the world.

    • ZHANG Wen, WU Tai_ran, HE Yuan_kai, FENG Ji_cheng, ZHENG Rong_guo

      2010,29(6):719-731, DOI:

      Abstract:

      Beishan area is located in the west of Inner Mongolia and Gansu Province, which is the conjunction zone of Tarim plate, Sino-Korea plate and Kazakhstan plate and plays an important role in the study of the Central Asia Orogenic Belt (CAOB). The relationship of the three plates is so complicated that there exists much controversy concerning Paleozoic tectonic evolution in this area. Granitoids, especially Late Paleozoic granitoids, are widely distributed in Beishan area, which are of great importance in the study of Paleozoic magmatic evolution. Through analyzing the spatial and temporal distribution of the Late Paleozoic granitoids, we can find the relationships between these granitoids and explore the crust-mantle interaction in Beishan area during Late Paleozoic, which is important for determining the geotectonic evolution of this area. In the southern belt of Beishan, the most important tectonic event in Permian is the formation of Yin'aoxia rift zone, which makes the study of Late Paleozoic evolution more complex. The results of studying Xijianquanzi granite lying in the southern belt of Beishan in such aspects as major elements, trace elements, REE and LA-ICP-MS zircon U-Pb geochronology have provided new evidence for regional tectonics. The LA-ICP-MS zircon U-Pb age of Xijianquanzi granite is 266.1±2.2 Ma, and the Hf modal ages are 746~871 Ma. εHf(t) values are +1.3~+4.7 with an averageof +2.7, which implies the mixture of crustal and mantle.derived magmas. This feature coincides with that of other areas in the Central Asia Orogenic Belt (CAOB). Therefore, the granites in the belt may have similar magma sources. The granitic body mainly consists of monzonitic granites which belong to alkaline series with high content of SiO2 (74.33%~76.67%), Na2O+K2O (9.26%~9.57%, NK/A=0.9~1.08) and K2O (Na2O/K2O<1) . In addition, chondrite-normalized REE patterns and primitive mantle normalized geochemical patterns of all samples are approximately parallel to each other, which shows that they evolved from the same magma source. Chondrite-normalized REE patterns of the intrusive body are of “V" types and show enrichment of light rare earth elements (LREE) with low ratio of (La/Yb) N (3.18~5.29) and negative Eu anomalies (δEu =0.10~0.16). Except for Eu, the abundance of rare earth elements are demonstrably over 10 times that of chondrite. Depletion of Nb, Ba, Sr, Ti, P and enrichment of Rb, Th, K can be seen in the spidergram. Based on regional geological and geochemical characteristics, the authors have reached the conclusion that the Xijianquanzi intrusive body is an alkali-rich potassium-high granite which is a mixed product of crustal and mantle-derived magmas and was formed at the stage of rifting in the post-collisional extensional period, affected greatly by Yin'aoxia rift zone. This implies that the area entered into the stage of rifting in Middle Permian.

    • 中国大陆环境典型斑岩型矿床成矿规律和找矿模型:研究进展(Ⅱ)专辑
    • ZHOU Jin-sheng, JI Xian-hua, YANG Zhu-sen, HOU Zeng-qian, ZHUANG Liang-liang

      2015,34(4):557-567, DOI:

      Abstract:

      In the magma-related deposits, the ore-forming plutons generally experienced high-degree evolution and differentiation, so its petrologic and geochemical characteristics can only reflect the final state of magma evolution. The evolution of ore-hosted magma and the geochemical behavior of main metallogenic elements in the evolution remain unclear. However, the study of contemporaneous and sympatric magmatic rocks provides a potential solution for this question. Here the authors made a case study of the northern Gangdise Pb-Zn ore belt in Tibet formed in the early period of continental collision. Based on the statistical study of lots of published geochemical analyses of magmatic rocks from the Gangdise belt, this paper presents the evolution of magma and its control of metallogenesis. The results suggest that, besides the crystallization differentiation of magma itself, crustal contamination was another factor controlling the evolution from basic magma to acid magma during differentiation. It is also found that most of the magmatic rocks formed in the early period of continental collision are less oxidized and less hydrous; nevertheless, when magma evolved to the middle and late period, the oxidation of magma increased with progressive evolution. Mantle-derived magmas are enriched in S and H2O, which experienced underplating at the base of Zn-enriched crust materials and induced partial melting. Crust-derived magmas experienced high-degree evolution, and finally resulted in the formation of the northern Gangdise Pb-Zn ore belt.

    • 综合资料
    • AI Yu-jie, FAN Guang

      2015,34(1):117-128, DOI:

      Abstract:

      This paper presents a collection of 31 new uranium minerals approved by the Commission on New Minerals, Nomenclature and Classification (CNMMN) of the International Mineralogical Association (IMA) between January 2003 and December 2013. It lists the mineral names both in English and Chinese together with their structural formulae, crystal structure data, physical and optical properties, localities and modes of occurrence. The crystallochemical classification and characteristics of these new minerals are discussed. Some suggestions are put forward concerning China's uranium minerals research work in the hope of providing valuable reference for China's uranium researchers.

    • ZHANG Xi-huan, REN Yu-feng

      2008,27(2):135-151, DOI:

      Abstract:

      本文以表格的形式列举了经国际矿物学协会(IMA)新矿物与矿物命名委员会(CNMMN)批准、并于2003年度正式发表的新矿物共55种,其中硅酸盐31种,磷酸盐5种,砷酸盐2种,硫酸盐4种,硫化物3种,碳酸盐2种,钒酸盐2种,硼酸盐1种,硒化物1种,硫盐1种,氧化物1种,氢氧化物1种,复杂卤化物1种.文中表格依次列出了矿物的中外文名称及化学式、晶系及晶胞参数、主要粉晶数据、物理性质、光学性质、产状及共生(伴生)组合等.

    • 专题研究
    • SHI Jian-rong, LIU Fu-lai, LIU Ping-hua, MENG En, LIU Chao-hui, YANG Hong, WANG Fang, CAI Jia

      2014,33(1):29-50, DOI:

      Abstract:

      Eclogites and blueschists are exposed mainly as slices or variable tectonic lenses within garnet phengite schists in Habutengsu area, southwestern Tianshan Mountains, Xinjiang. In this paper, petrography, mineralogical chemistry and p-T conditions of the eclogites and blueschists were studied in detail. The eclogites could be divided into four groups, i.e., glaucophane eclogites, paragonite eclogites, epidote eclogites, and glaucophane-garnet amphibolites (retrograde eclogites), whereas blueschists could be divided into three groups, namely glaucophane-bearing garnet-muscovite-albite schists, garnet-muscovite-glaucophane schists and garnet-muscovite-glaucophane-quartz schists. Major mineral assemblages are Grt+Omp+Pg+Ep for the fresh eclogites, Grt+Gln+Amp for the retrograde eclogites, and Grt+Gln+Phe+Pg+Ab+Qtz for the blueschists. Porphyroblastic garnets show perfect prograde zoning, with XMn and XFe deceasing and XMg and XCa increasing from the core to the rim, which indicates a process of increasing temperature and prograde metamorphism. According to the paragenetic assemblages of inclusions within garnet as well as in matrix, four stages of metamorphism were recognized, viz., pre-peak lawsonite-blueschist facies metamorphic stage, peak eclogite facies stage (t=543~579℃, p=1.5~1.6 GPa), retrograde epidote-blueschist facies stage (t=~450℃, p<1.0 GPa), and post-peak retrograde blueschist-greenschist facies stage (t<400℃, p<0.5 GPa). The p-T pseudosection calculation shows that the peak metamorphic conditions were 520~550℃ and 1.7~1.9 GPa for the eclogites, and 520~620℃ and 1.7~2.3 GPa for the blueschists, similar to the results of traditional geothermobarometer. Previous researchers reported coesites preserved in some eclogites and country rocks, which suggested that partial eclogites and partial country rocks within the southwestern Tianshan metamorphic belt underwent UHP metamorphism, but this conclusion is inconsistent with the results constrained by the eclogites in this study. The possible reasons might be as follows: ① the eclogites were affected by later thermal events, which led to the partial variation of both minerals and whole rock compositions. On the basis of the changed whole-rock compositions, the traditional thermobarometer Grt-Cpx-Phe and phase equilibrium simulations certainly show relatively low pressure results, and ② not all eclogites from the southwestern Tianshan underwent UHP metamorphism, and HP-UHP eclogites may represent the metabasites subducted to different depths.

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    Editor:Zengqian Hou

    Started in:1982

    ISSN 1000-6524

    CN 11-1966/P