Rare-Earth Element Mobility During Ore-Forming Hydrothermal Alteration: A Case Study of Dongping Gold Deposit, Hebei Province, China

REE mobility during hydrothermal ore-forming processes has been extensively investigated in recent years and the potential of REE to provide information about ore forming processes has commonly been recognized. The Dongping gold deposit, which is located in northwestern Hebei Province, China, occurring in the inner contact zone of the Shuiquangou syenite complex, is spatially, and probably genetically, related to the syenite. The deposit was formed under the moderate to high temperature (220℃ to 320℃), weakly acidic to weakly alkaline, rather high f O 2 (lgf O 2=-30 ～- 34) environment. The REE study of the host rocks, altered wall rocks, ores and gangue minerals from the deposit suggests that the REEs have been mobilized and differentiated during K-feldspathization and silicification. The extremely altered syenite enveloping auriferous quartz vein shows positive Ce anomaly and larger LREE/HREE ratio than that of the unaltered syenite. The REE concentrations and patterns of the ores are determined by the ore types and mineral assemblages. LREE/HREE ratios in the gangue quartz and hydrothermal K-feldspars are relatively low. The most significant observation is that the gangue quartz shows significant positive Eu anomaly, whereas the hydrothermal K-feldspars show less significant or no positive Eu anomaly at all relative to the primary feldspar in the unaltered syenite. It is evident that the REEs are mobile during K-feldspathization and silicification in the ore forming process. Weak to moderate K-feldspathization caused REE mobility without apparent differentiation with the exception of extreme K-feldspathization and silicification which resulted in significant depletion of HREE and Eu and relative enrichment of Ce. The REE, Y, U, Th and Au contents of the syenite decrease as the degrees of K-feldspathization and silicification of the rocks increase towards the auriferous quartz veins. As the ores were deposited under a rather oxidized environment, Ce 4+ predominated over Ce 3+. The precipitation of the former in the form of CeO 2 or absorpted onto the secondary mineral assemblage resulted in the inconsistent removal of the REE and the relative Ce enrichment in the strongly altered rocks. In contrast, Eu was present mainly in a low valence state (Eu 2+). The geochemical differences from the other REE 3+ and much less sites in the secondary minerals to accommodate the Eu released from the original minerals resulted in the enrichment of Eu in the fluids. The mobility and differentiation of REE and the coherent mobilities of Y, U, Th and Au also support the argument that the syenite is one of the source rocks for gold mineralization. The REE contents and patterns of the altered rocks enveloping the auriferous quartz vein could be used as a guide for locating ore veins in mineral exploration.

On the analysis of the high-resolution sequence stratigraphy and coal accumulating law of jurassic in Ordos Basin

The strata of Jurassic was divided into three tectonic sequences and eight se- quences of third rank,according to the developing feature of the tectonic inconformity and the transforming feature of the depositional system tracts.Also the identification and the division of the base-level cycle of different period were carried through.Therefore three cycles of super period,eight cycles of long period,twenty-four cycles of middle period and some cycles of short period were identified.From the overall character of the coal-accu- mulation in the Mesozoic,we can see that the Yan'an formation is of the best nature of coal bearing.When the coal bearing systems of Jurassic were depositing,the Ordos area is the coal accumulating basin of terrene of large scale and located in the same tectonic unit.But the local structure of different part and the paleolandform are different in the basin which resulted in the difference of the depositional environment.So the layer number and the distribution of the thickness of the coal beds are different in the different part of the ba- sin.The coal-accumulating action migrated regularly along with the development,evolve- ment and migration of the depositional systems.The layer numbers of the coal beds, which can be mined,are more in the north and west fringe of the basin,whose distributing area is extensive,and they are more steady in the landscape orientation,also the total thickness is great.Therefore the nature of coal bearing and the coal-accumulating action of different part changed obviously in the space in Ordos area.

Identifications of products of geographical origin based on geochemical zoning

The protection system of products of geographical origin has become one hot subject with which various countries throughout the world are concerned. Results of element-Pb isotope geochemical mapping indicate that there emerge a number of famous-brand high-quality product groups of geographical origin in China. The environment of production of China’s famous-brand white spirits of geographical origin at the Sichuan-Guizhou border is still a mystery to be solved. China has two main communities of white spirits of geographical origin, i.e., the most famous are Moutai and Wuliangye spirits. By element-Pb isotope geochemical tracing, we can establish the natural background geological, geographical and geochemical scientific data mark ers in close relation with source areas. Research on the product of geographical origin, named Kaempferia galangal L. in the Shuangjiao district, Yangchun, Guangdong Province, showed that the trace elements have an excellent heritance between Kaempferia galangal L. and soil in this area, and the trace elements are highly effective for tracing the origin.

The Structure of Montmorillonites Modified with Zwitterionic Surfactants and Their Sorption Ability

In the past four decades, there is a growing use of surfactant modified clay complexes in wide range of applications. The mostly used surfactants to modify the swelling clay minerals are cationic surfactants, such as quaternary ammonium, which consists of two distinct moieties, a hydrophilic head, where the positive charge is concentrated, and a hydrophobic hydrocarbon chain tail. During the surface modification, this kind of surfactant molecules attach on the inner and outer surface of clay minerals, the hydrophilic surface of raw clay minerals may changed into hydrophobic surface. The changes of organophilicity and hydrophobicity of clay minerals enable them used in more wide fields, such as adsorbents for organic contaminant, geotechnical barriers, filling of nanocomposite, etc.

Isotopic dating of the Chengjiang Fauna-bearing horizon in Central Yunnan Province, China

Twenty black shale samples, which are free from the influence of weathering, were collected from the Chengjiang Fauna-bearing horizon, central Yunnan Province, yielding a Pb-Pb isochron age of 534±60 Ma. Although this age is younger than both the Rb-Sr isochron age and 40Ar-39Ar age, it should represent the lower isotopic age limit of the Chengjiang Fauna.

Variation Law of Organic Contaminant in Lijiang River

Water environmental capacity of Lijiang River within Guilin city is researched. The relationship among concentration of pollutants and flow rate as well as water environmental capacity of Lijiang River is discussed. The changes of pollutant concentration in past years is analyzed. The results show that there exists a certain value of flow rate corresponding to a certain average concentration of pollutants on the upper and lower sections of the research area. If flow rate is greater than that value, the concentration of pollutants will decrease with the increase of flow. While the result will be the contrary when river flow is smaller than that value, that is to say, the concentration will increase with the increase of flow. To be aware of this regularity is of vital significance in water resource protection and comprehensive utilization[1].

Geological Implications for the Deep-Derived Mafic Enclaves from Cenozoic Shoshonitic Rocks in Jianchuan-Dali Area, West Yunnan

There exist intermediate to intermediate-acid shoshonitic rocks dated at 26.3- 36.7Ma in the Early Tertiary extensional basins along the NE flank of the Dali-Jianchuan section of the Honghe-Ailaoshan left-lateral strike-slip ductile shear zone, where some high- and medium-high grade metamorphosed mafic enclaves have been found. According to the P-T conditions and mineral assemblage characteristics, the enclaves are grouped into three types: type-Ⅰ, garnet diopsidite, formed at lower crust or in the transitional section between the mantle and the crust with the metamorphic condition P=(10.47-11.51)×108 Pa and T=771-932℃; type-Ⅱ, garnet- and diopside-bearing amphibolite, formed at the depth of middle to lower crust with the metamorphic condition: P=(6-10) ×108 Pa and T=780-830℃; type-Ⅲ, metamorphosed gabbro, formed at relatively higher levels than the above 2 types with lower metamorphic condition. Type-Ⅰand type-Ⅱenclaves had experienced a decompressional retrograde metamorphism caused by tectonic elevation associated with the metasomatism of SiO 2, Na 2O-rich fluid phase with the new equilibrated temperature at T=761-778℃. Geochemical evidence indicates that both deep-derived mafic enclaves and host rocks have similar EM Ⅱ properties, which are related to the involvement of subducted materials. The sustaining subduction, compression and strike-slip ductile shearing between the India plate and the Yangtze craton are the main constraints on the subcontinental mantle properties, interaction between crust and mantle, and the formation and evolution of alkali-rich magma.

Humidity and PM_(2.5) composition determine atmospheric light extinction in the arid region of northwest China

Atmospheric visibility can directly reflect the air quality.In this study,we measured watersoluble ions(WSIs),organic and element carbon(OC and EC)in PM 2.5 from September 2017 to August 2018 in Urumqi,NW China.The results show that SO4^2-,NO 3^(-)and NH4^(+)were the major WSIs,together accounting for 7.32%-84.12%of PM 2.5 mass.Total carbon(TC=OC+EC)accounted for 12.12%of PM 2.5 mass on average.And OC/EC>2 indicated the formation of secondary organic carbon(SOC).The levels of SO4^2-,NO3^(-)and NH4^(+)in low visibility days were much higher than those in high visibility days.Relative humidity(RH)played a key role in affecting visibility.The extinction coefficient(b ext)that estimated via Koschmieder formula with visibility was the highest in winter(1441.05±739.95 Mm-1),and the lowest in summer(128.58±58.00 Mm^(-)1).The b ext that estimated via IMPROVE formula with PM 2.5 chemical component was mainly contributed by(NH 4)2 SO4 and NH4 NO3.The b ext values calculated by both approaches presented a good correlation with each other(R^2=0.87).Multiple linear regression(MLR)method was further employed to reconstruct the empirical regression model of visibility as a function of PM 2.5 chemical components,NO_(2) and RH.The results of source apportionment by Positive Matrix Factorization(PMF)model showed that residential coal combustion and vehicle emissions were the major sources of b ext.

Haze insights and mitigation in China: An overview

The present article provides an overview of the chemical and physical features of haze in China, focusing on the relationship between haze and atmospheric fine particles, and the formation mechanism of haze. It also summarizes several of control technologies and strategies to mitigate the occurrence of haze. The development of instruments and the analysis of measurements of ambient particles and precursor concentrations have provided important information about haze formation. Indeed, the use of new instruments has greatly facilitated current haze research in China. Examples of insightful results include the relationship between fine particles and haze, the chemical compositions and sources of particles, the impacts of the aging process on haze formation, and the application of technologies that control the formation of haze. Based on these results, two relevant issues need to be addressed： understanding the relationship between haze and fine particles and understanding how to control PM2.5.