Abstract:Tuomoerrite ophiolitic mélange is located in the eastern segment of the northern margin of Qaidam terrane. This paper presents a systematic geochronological and petrogeochemical study of the meta-basaltic rocks in the ophiolite mélange. The metabasalts have whole-rock SiO₂ contents of 47.78%~50.01%,MgO contents of 4.52%~9.36%, ^TFeO contents of 8.00%~14.94%,K₂O contents of 0.04%~0.80%,and Na₂O contents of 1.02%~4.20%, resembling those features of tholeiitic magma. They show slightly depletion in LREE, enrichment in LILE and LREE,and depletion in HFSE,similar to the patterns of arc-related volcanic rocks. These features collectively suggest a back-arc setting for the meta-basalts. The zircon U-Pb age of these metabasalts determined by LA-ICP-MS is 480.1±1.8 Ma,suggesting that the expansion time of the back-arc basin in this area should be around 480 Ma,and the oceanic slab subduction occurred in Early Ordovician.

Abstract:The Chaiwa area of Tibet was located in the middle eastern part of the Tethys Himalayan structural belt, and a large number of nearly East-West trending mafic dykes were widely developed. These mafic dykes were of great significance for studying the geological structural evolution in this area. This paper has carried out systematic petrology, chronology, and geochemistry studies on the mafic dyke rocks in the Chaiwa area. The rock types of mafic dykes in Chaiwa area were mainly diabase and gabbro porphyrite. Zircon U-Pb geochronology revealed that the crystallization ages of mafic dykes are 146~145 Ma. The basic dykes in Chaiwa were enriched in Ti, Fe, and P elements, belonged to alkaline series and enriched in LREE, showing the feather of low SiO₂(47.20%~50.54%) and high Mg^# (39.78~53.79), which were relatively enriched in high field strength elements(Nb, Ta, Zr, HF, Th) and were similar to the geochemical characteristics of the OIB. These geochemical characteristics indicated that the Chaiwa mafic dykes were originated from the partial melting of the asthenosphere mantle and were formed in continental margin rift setting. Combined with the development of mafic rocks in regional volcanic province, it is considered that the mafic dykes in the Chaiwa area were the products of the Kerguelen mantle plume under the back ground of continental margin rift. Although the crystallization age of the Chaiwa dyke was earlier than the peak period of Kerguelen mantle plume activity(132 Ma), it might belong to the small-scale magmatic activity before the peak period of mantle plume.

Abstract:Quantitatively determining the timescale during mantle-derived magma ascent from the source to eruption or emplacement is essential for the understanding of magmatism, however, the timescales of eruption/emplacement are still poorly constrained. Shanxi Datong Cenozoic volcanic field, north of the North China Craton, is an ideal area for the investigation. In this study, we focused on the mantle olivine xenocrysts entrained in ca. 0.2 Ma Shenquansi alkali basalt, and its timescale of residence in the host magma prior to eruption. According to mineral chemistry, cores of these mantle olivine xenocrysts have Fo values up to 97.7, which can be defined as extremely magnesian olivine. They are also characterized by the extremely low contents in Ca, Mn and Ni, suggesting they were captured from metasomatized mantle peridotite. Moreover, both of the mantle olivine xenocrysts display complex CaO profiles, attributed to complex magmatic processes in the magma plumbing system. The reaction rim widths of one olivine xenocryst vary significantly, implying it has experienced multiple crack processes when captured or dur- ing transport. The Fo values of the mantle olivine xenocrysts rims are about 70, indicating they are in diffusion equilibrium with the host magma (alkali basalt) at rims. Timescales obtained by Fe-Mg diffusion chronometry of olivine mantle xenocrysts show that they have only resided in the magma for months. For a lithospheric mantle thickness of 40~70 km, the fastest average ascent rate may exceed 500 m/d.

Abstract:A large number of magmatic rocks were formed in the Gangdese belt of the Qinghai-Tibet Plateau. To better understand the petrogenesis, magma source region and evolution, we have studied the petrography, geochemistry, zircon trace elements and Hf isotope analysis of the granite porphyry and rhyolitic crystal tuff in Mamu, Gakyi, western of the Central Lhasa Terrane. The granite porphyry and rhyolitic crystal tuff in Mamu were both formed at Early Cretaceous period. They are both shoshonitic rocks, enriched in large ion lithophile elements, and light rare earth elements, and depleted in high field-strength elements(HFSE) and Eu. They have high negative εHf(t) values of -9.57~-3.43 and -8.79~-4.80, and the older Hf isotopic crustal model age t_DM2 of 1 774~1 388 Ma and 1 727~1 477 Ma, respectively. The Early Cretaceous magmatic rocks originated from the remelting of ancient lower crustal materials, with the mixing of mantle material. After the magma mixing, the amphibole, feldspar and biotite were first separated and crystallized, finally formed the granite porphyry and rhyolitic crystal tuff. Combined with previous studies and this paper, we infer that the Early Cretaceous magmatism in Mamu is probably due to the southward subduction of the southward subduction of Bangong-Nujiang suture zone.

Abstract:Lying along the Solonker-Linxi collisional orogenic suture zone in Sonid Youqi of Inner Mongolia, the Chaganchulu A-type monzogranite intruded into the Early Permian Halengling SSZ type ophiolitic tectonic melange belt. Based on the systematic field geological characteristics, petrology, geochemistry, zircon U-Pb chronology, the purpose of this study is to determine the genetic type of pluton, tectonic setting, and provide evidence for the closing time of the ocean basin in the eastern part of the Paleo-Asian Ocean. LA-ICP-MS zircon U-Pb dating shows that the age of the granite is 245.9±1.3 Ma, indicating that the formation age is Middle Triassic. The granite contains more alkaline feldspars, and the dark mineral is mainly biotite, with cave structure. The granite is geochemically characterized by high SiO₂ (76.75%~77.18%) and alkali (Na₂O+K₂O=8.19%~8.62%), but low CaO (0.40%~0.44%) and MgO (0.03%~0.05%). The granite has obvious negative Eu anomaly (Eu=0.03~0.09), relative enrichment of Rb, Th, U, K and Ga, depletion of Ba, Sr, P and Ti, as well as high 10 000 Ga/Al (2.72~3.52), ^TFeO/MgO (29.16~57.82), (Na₂O+K₂O)/CaO (15.08~21.39). The petrological, mineralogical and geochemical characteristics of the granite show the characteristics of A-type granite. According to the regional, Mesozoic A-type granites have positive correlation εNd(t) value and young Nd age suggest that the granite may be caused by partial melting of intermediate basic crust in neoaccretion under low pressure and high temperature. The zircon U-Pb age of the newly obtained Chaganchulu A-type monzogranite restricts the closing time of the eastern part of the Paleo-Asian Ocean before the Middle Triassic.

Abstract:The Zongwulong tectonic belt is located between the northern Qaidam tectonic belt and the South Qilian tectonic belt, which is generally distributed in a NWW direction. The voluminous magmatic activity in the eastern part of the tectonic belt records the process of breakup and closure of the tectonic belt during the late Paleozoic Mesozoic, while the magmatic activity in the western part is relatively rare, so it is unclear whether the eastern and western parts of the belt have the same tectonic evolution. Based on the analysis of geochemical characteristics, detrital zircon U-Pb ages and Hf isotopic compositions of the clastic rocks of the Triassic Longwuhe Formation in the western part of the tectonic belt, it is considered that the provenance of the detrital sediments in the Longwuhe Formation was slightly weathered without sedimentary recycling characteristics, and their original rocks are mainly felsic rocks. The main provenance of clastic rocks in the Longwuhe Formation is the southern Qilian Neoproterozoic granitic gneiss and early Paleozoic continental arc granite rocks, and the clastic rocks may have been deposited in Early-Middle Triassic flexural basins. Zircon U-Pb age analysis shows that the tectonic evolution of the eastern and western segments of Zongwulong tectonic belt has different processes. Limited ocean basins developed in the eastern segment but not in the western segment, the transition zone may be located between Shengge and Luogenguole area.

Abstract:Lamei iron deposit in Central Yunnan is located in the middle section of the Jinshajiang-Ailaoshan- Honghe alkali-rich porphyry belt in the "Sanjiang" area of Southwest China. Its mineralization type is unknown and its metallogenic mechanism and resource potential are unclear, which restricts the in-depth study of prospecting and exploration in this area. On the basis of detailed geological survey, and according to the output characteristics of the ore bodies, magnetite is divided into three types: bean-star point magnetite in syenite porphyry(Ⅰ-Mag), disseminated-agglomerate magnetite in diopside hornstone(Ⅱ-Mag) and vein-shaped and sac-like filling magnetite in interlayer fracture zone(Ⅲ-Mag). Through LA-ICP-MS in-situ micro-area composition comparison, it is found that the three types of magnetites are generally enriched in Ti, Mn, V, Mg, Zn and Ni, poor in Sn, Ga and Sc and other elements. Ⅰ-Mag→Ⅱ-Mag→Ⅲ-Mag, the content of Mg, V, Zn and the ratio of Ni/Cr gradually increase, and the content of Cr, Sn and REE gradually decrease, reflecting the evolution characteristics of the three types of magmatite from magmatic origin to hydrothermal origin. Combined with Ni/(Cr+Mn) -(Ti+V), (Al+Mn)-(Ti+V) diagrams and the ore facies characteristics of magnetite, the deposit is considered to be a contact metasomatic hydrothermal iron deposit, and its mineralization material source is closely related to alkali-rich porphyry. The formation temperature of three types of magnetite is about 300~500℃, and the oxygen fugacity of Ⅰ-Mag→Ⅱ-Mag→Ⅲ-Mag tends to decrease gradually. Geochemical characteristics, mineralization temperature, oxygen fugacity and other information indicate that the deep part of Lamei iron deposit has the metallogenic potential of a porphyry copper polymetallic deposit.

Abstract:Anhui Province is located in the southeastern China, where magmatism is frequent, and the Yanshanian magmatism is the most developed. The exposed area of magmatic rocks is more than 13 000 km², and rocks of different types and origins are all developed, and they are concentrated in the Dabie Mountains, the middle and lower reaches of the Yangtze River, and southern Anhui. In this study, we collected 159 samples from different magmatic rock belts in Anhui Province and carried out rock density and radioactive heat-generating element content determinations. Combined with the previous test results of radioactive heat-generating elements of magmatic rocks in Anhui Province, we have carried out a systematic study on radioactive heat-generating elements of magmatic rocks in Anhui Province for the first time. The results suggest that the average contents of U, Th, and K of magmatic rocks in Anhui Province is quite different. Granitic rocks and intermediate-acid volcanic rocks have higher U, Th, and K contents, and basic magmatic rocks have relatively lower U, Th, and K contents. The radioactive heat generation rate of different types of magmatic rocks is quite different. The heat generation rates of granitic rocks and intermediate-acid volcanic rocks are relatively higher and the variation range is wide, while basic magmatic rocks are relatively lower and the variation range is narrow. The heat generation rates of some granites in Jinzhai and the middle and lower reaches of the Yangtze River exceed 5 μW/m³, which are high heat production granites. The main thermal contribution of magmatic rocks comes from the radioactive decay heat of U and Th, while that of K is relatively lower, generally no more than 10%. Through this study, combined with previous research results on geology and geothermal in Anhui Province, it is found that the radioactive heat generation of magmatic rocks is of great significance to the distribution of hot springs, dry hot rock exploration and U deposits exploration in Anhui Province, which can provide further support for the subsequent exploration and development of geothermal resources in Anhui Province.

Abstract:The Southern Da Hinggan Mountains is one of the most important metallogenic belt, where varied types of mineral deposits have been reported over the past few decades. The Hongling(Haobugao) Pb-Zn polymetallic ore deposit is situated in the northeast of Huanggang-Ganzhuermiao polymetallic metallogenic belt, which is located in the southern segment of the Da Hinggan Mountains, Inner Mongolia. The ore genesis and ore controls of the deposit has been widely reported, but the detailed geological work, especially the lithology of the wall rock, and the spatial distribution of mineralization and alteration in the mining area is still weak. Based on the field observation, petrographic and SEM/EDS results of the ore and altered wall rocks, this paper proposed that the Permian of the area comprise of marble and meta-volcanic or volcaniclastic rocks which has been referred to as meta-sedimentary clastic rocks. The discovery of pressure shadow with chalcopyrite and sphalerite aggregate as the core mineral imply a primary copper and zinc mineralization of Permian. Except the dominant skarn mineralization, we also confirmed some other mineralization types in the mining area, including breccia type, hydrothermal veins and carbonate replacement type. Varied types of mineralization provide new idea for the ore prospecting in the area.

Abstract:Stromatolites of Tungussia cf. nodosa Semikhatov and Baikalia lacera semikhatov were discovered for the first time in the Langyashan Formation of the original Jixian System near Shuiquanzigou, Qimantag area, Ruoqiang County, Xinjiang. The stromatolites are mostly nodular and columnar, and their overall morphological characteristics can be compared with the characteristics of Tungussia cf. and Baicalia stromatolites distributed in Neoproterozoic strata in Huaishan, Anhui and Eastern Liaoning, and some stromatolites in Jiawengmen area of East Kunlun, which is equivalent to stromatolite assemblage IV in North China. Through our work, Sm-Nd whole-rock isotopic isochron age of 815±26 Ma from the host rock of stromatolites is obtained. According to the Sm-Nd isochron age, the main characteristics of stromatolites in study area and other areas, the geological time of Langyashan Formation in Qimantag area should belong to the Neoproterozoic Qingbaikouan Period. Their host rock should expose in passive margin of a Precambrian micro-continent block disintegrated from Tarim Craton(?), which was probably assigned to Rodinian Super-Continent. The discovery of the stromatolites and dating results of the host rock provide new evidence for the tectonic evolution and diagenetic environment in western segment of the East Kunlun Mountains.

Abstract:Nephrite has a long history of mining and use in China, and occupies an important position in China's jade culture. According to the occurrence, the genetic types of marble-related nephrite can be divided into contact metasomatism type (skarn-type/magmatic hydrothermal type), regional metamorphism and metamorphic hydrothermal type, in which contact metasomatidm type is the most important and the main genetic type of high-quality nephrite. According to the age of the surrounding rock, the age of the ore belt formed by zircon or mica dating in nephrite and the regional geographical location, Chinese marble-related nephrite can be divided into six ore belts: Xinjiang (the upper limit of the formation age is 450~350 Ma) of the West Kunlun ore belt, Golmud of Qinghai Pro- vince (the formation age is 300~240 Ma) of the East Kunlun ore belt, Northeast China (hematite about 250~150 Ma, Laoyu about 1 700 Ma), Southwest China, Central South(volcanic rock about 682 ±62 Ma, diabase about 260 Ma) and East China. This paper mainly summarizes the geological occurrence, mineral composition, main and trace element characteristics of the whole rock, ore-forming fluid composition, zircon/mica age, spatial distribution and metallogenic regularity of nephrite deposit from the six ore belts in China. The main mineral composition of nephrite is tremolite. The ore-forming fluid composition of contact metasomatism type nephrite deposit is mainly composed of magmatic water, meteoric water and CO₂ derived from decarbonation of the surrounding dolomite marble in different proportions. The ore-forming materials of Mg and Ca come from dolomite marble, while Si and H₂O come from magmatic hydrothermal fluids (such as Hetan ore belt in Xinjiang). The formation of nephrite mainly experienced contact metamorphism and metamorphic metasomatism stage, prograde metamorphism stage and retrograde metamorphism stage. The metasomatism process was dolomite marble→diopside skarn or epidote skarn→tremolite skarn (coarse-grained tremolite) and coarse-grained tremolite → fine-grained tremolite. Tremolite was mainly formed in prograde metamorphism stage. The mineralization of regional metamorphic nephrite is closely related to regional metamorphism rather than magmatic activity, the ore-forming fluid is mainly meteoric water (such as Chunchuan, South Korea). The ore forming fluid of metamorphic hydrothermal nephrite is mainly metamorphic water, and the ore-forming materials Mg and Ca come from marble, Si and H₂O may come from the siliceous hydrothermal solution formed by regional metamorphism and mixed magmatism(such as Xiuyan in Liaoning Province). Nephrite mainly occurs in the areas with strong tectonic activity and sections with strong contact alteration zone between intrusive rocks and carbonate rocks. The primary marble-related nephrite deposit can be explored according to mineralization mark, tectonic mark, wall rock alteration mark, secondary deposit mark, ancient mines mark, etc.

Abstract:The content of nickel oxide in neodymium oxide was determined by ICP-OES method. The content of nickel oxide was 0.002 7%. Various influencing factors in the detection process were analyzed. The reliability of the measurement results was expressed by relative expansion uncertainty (U_rel=12%, k=2). The calculation of re-lative uncertainty component shows that the relative uncertainty component introduced by standard curve fitting is the largest, u_rel(c₂)=5.639%, followed by the relative uncertainty component introduced by the preparation of standard solution, u_rel(c₁)=0.879%. This paper can provide a reference of the result uncertainty analysis for relevant testing personnel.

Abstract:Natural pyrite has strong treatment capacity for Cr(Ⅵ). In this study, a natural lead-bearing pyrite sample from Shiyan, Hubei Province was selected to treat the Cr(Ⅵ)-containing wastewater. The structure and composition of the sample were analyzed by X-ray diffraction and X-ray fluorescence spectroscopy, and the influencing factors of Cr(Ⅵ) removal reaction were investigated. The results show that the natural lead-bearing pyrite sample has a good ability to remove Cr(Ⅵ), and the removal rate of Cr(Ⅵ) wastewater with a concentration of 50 mg/L is 95%~99%. The effects of pyrite particle size, reaction time and pH value on the treatment of Cr(Ⅵ)-containing wastewater were systematically studied. It was found that Cr(Ⅵ) was mainly adsorbed on the surface of pyrite particles to form flocculent substances. The results of SEM and XRD analysis of the products after the reaction showed that the flocculent substances was needle crocoite containing chromium and lead elements, which had further research significance for the use of secondary mineral precipitation as a new method for chromium removal.