Organic Gases in Fluid Inclusions of Ore Minerals and Their Constraints on Ore Genesis: A Case Study of the Changkeng Au-Ag Deposit, Guangdong, China

The newly discovered Changkeng Au-Ag deposit is a new type of sediment-hosted precious metal deposit. Most of the previous researchers believed that the deposit was formed by meteoric water convection. By using a high vacuum quadrupole gas mass spectrometric system, nine light hydrocarbons have been recognized in the fluid inclusions in ore minerals collected from the Changkeng deposit. The hydrocarbons are composed mainly of saturated alkanes C1-4 and unsaturated alkenes C2-4 and aromatic hydrocarbons, in which the alkanes are predominant, while the contents of alkenes and aromatic hydrocarbons are very low. The Σalka/Σalke ratio of most samples is higher than 100, suggesting that those hydrocarbons are mainly generated by pyrolysis of kerogens in sedimentary rocks caused by water-rock interactions at medium-low temperatures, and the metallogenic processes might have not been affected by magmatic activity. A thermodynamic calculation shows that the light hydrocarbons have reached chemical equilibrium     

Discovery and Significance of Diamonds and Moissanites in Chromitite within the Skenderbeu Massif of the Mirdita Zone Ophiolite, West Albania

In recent years diamonds and other unusual minerals(carbides,nitrides,metal alloys and native elements) have been recovered from mantle peridotites and chromitites(both high-Cr chromitites and high-Al chromitites) from a number of ophiolites of different ages and tectonic settings.Here we report a similar assemblage of minerals from the Skenderbeu massif of the Mirdita zone ophiolite,west Albania.So far,more than 20 grains of microdiamonds and 30 grains of moissanites(SiC) have been separated from the podiform chromitite.The diamonds are mostly light yellow,transparent,euhedral crystals,200~300 μm across,with a range of morphologies;some are octahedral and cuboctahedron and others are elongate and irregular.Secondary electron images show that some grains have well-developed striatums.All the diamond grains have been analyzed and yielded typical Raman spectra with a shift at ~1325 cm~(-1).The moissanite grains recovered from the Skenderbeu chromitites are mainly light blue to dark blue,but some are yellow to light yeUow.All the analyzed grains have typical Raman spectra with shifts at 766 cm~(-1),787 cm~(-1),and 967 cm~(-1).The energy spectrums of the moissanites confirm that the grains are composed entirely of silicon and carbon.This investigation expands the occurrence of diamonds and moissanites to Mesozoic ophiolites in the Neo-Tethys.Our new findings suggest that diamonds and moissanites are present,and probably ubiquitous in the oceanic mantle and can provide new perspectives and avenues for research on the origin of ophiolites and podiform chromitites.     

The Development Characteristics and Distribution Predictions of the Paleogene Coal‐measure Source Rock in the Qiongdongnan Basin,Northern South China Sea

There are known to be enormous Cenozoic coal-type oil and gas resources located in the basins of the South China Sea,among which the Paleogene coal-measure source rock are one of the main source rock.In order to more effectively analyze the distribution laws of coal-measure source rock in marginal sea basins and guide coal-type oil and gas explorations,the Oligocene coal-measure source rock in the Qiongdongnan Basin were selected as examples in order to systematically analyze the types,development characteristics,control factors,and distribution prediction methods of coalmeasure source rock in marginal sea basins.The Qiongdongnan Basin is located in the northern region of the South China Sea.Previous explorations of the area have determined that the Oligocene coal-measure source rock in the Qiongdongnan Basin have typical"binary structures",which include coal seams and terrigenous marine mudstone.Among those,the terrigenous marine mudstone has been found to greatly expand the scope of the coal-measure source rock.In addition,the coal seams which have been exposed by drilling have been observed to have the characteristics of thin single layer thickness,many layers,and poor stability.Meanwhile,the terrigenous marine mudstone has the characteristics of large thickness and wide distribution.The development of coal-measure source rock is known to be controlled by many factors,such as paleoclimate and paleobotany condition,paleo-structure and topography,paleo-geography,rise and fall of base level,and so on.In accordance with the comprehensive analyses of various control factors of coal-measure source rock,and the changes in water body energy in sedimentary environments,a genetic model of the"energy belt"for the development and distribution of coal-measure source rock was proposed.Also,the development and distribution characteristics of coalmeasure source rock in different types of energy belts were clarified.Then,based on the development and distribution characteristics of coal-measure source rock and their controlling factors,prediction methods of the distribution ranges of coal-measure source rock were proposed from both qualitative and(semi-)quantitative aspects.That is to say,a method for(semi-)quantitative predictions of the distribution ranges of coal-bearing intervals based on model wave impedance inversion and neural network wave impedance inversion,along with a method for(semi-)quantitative predictions of the distribution ranges of terrigenous marine mudstone based on topographical slopes,were introduced in this study.     

Geochemical characteristics of Lower Permian coal-measure source rocks in Northeast Ordos Basin

General characteristics and biomarker distributions of Lower Permian coal-measure source rocks in northeastern Ordos Bsain have been analyzed in this paper. The results show that the source rocks are type III kerogen, thermally mature, with high content of total organic carbon. The extracts of the source rock samples with different lithologies from Well Su 27 feature high Pr/Ph ratios, high C19TT and C24Te, high rearranged hopanes, a predominance of C29 sterane in regular steranes, and the absence of C30 4-methylsteranes. These data suggest that the source rocks were deposited in suboxic to oxic conditions with dominantly terrigenous higher plant input. In contrast, the source rocks from wells Shuang 1 and Yu 20, are characterized by low Pr/Ph ratios, low C19TT and C24Te, high C23TT, similar content of C27 sterane and C29 sterane, and the presence of C30 4-methylsteranes, showing that the source rocks were deposited in reducing environment with algae and/or microorganisms and terrigenous higher plant input.     

Jurassic Brachiopods and Paleogeography of North Qinghai-Tibetan Plateau

This paper deals with Jurassic brachiopods from North Tibet and SouthQinghai and the stratigraphical subdivision there.Based on faunas andstrata,a general outline of the palaeogeographical evolution has been traced outalong the line of plate-tectonic movements.In this paper,10 species of 8 gen-era are described,among which the species Lacunosella rhombica,Pentithyrisvulgaris,Tanyothyris appositus,Apatecosia navicularis and Flabellothyris sp.nov.have been recognized as new.     

广西某矿田磁黄铁矿的研究及其区别特征

Naturally occurring hexagonal and monoclinie pyrrhotites have been recognized by X-ray diffraction analysis and DTA from an ore deposit in Guangxi. They are distinguishable from each other in magnetism, reflectivity, hardness and some other properties. A correct distinction between hexagonal and monoclinie pyrrhotites is of practical importance in prospecting and theoretical study.     

GEOLOGICAL CONTEMPORANEITY AS VIEWED FROM THE THEORY OF RELATIVITY

Since the importance of tho iron ore resources of the contact metamorphic type in China has been well recognized by many geologists and their geological occurrence and economic prospects have been described and published in detail 1, it seems desirable to have a review of those rocks known     

Geochronological, Geochemical and Paleomagnetic Clues for Existence of a ~2.1Ga Dyke Generation in the Mashishing Area, South Africa

正Dyke swarms are widespread throughout the Kaapvaal Craton(KC)in South Africa and have been documented in some detail.Up to date,only the~2.9 Ga SE-trending and the~2.7 to~2.66 Ga radiating dyke arrays are recognized     

Speleogenesis of Selected Caves beneath the Lunan Shilin and Caves of Fenglin Karst in Qiubei, Yunnan

Yunnan is famous for its attractive karst landscapes especially shilins, fengcong and fenglin. The development of caves beneath the shilins in the vicinity of Lunan is closely connected with the formation of shilins. Most of the waters percolating through shilins run through the caves beneath them and are responsible for their formation. The study of cave speleogenesis deepens knowledge about both the development of shilins and karst structure. In the vicinity of the Lunan Shilin, speleological, morphological and structural geological studies of four karst caves have been accomplished. At Puzhehei, Qiubei, which is characterised by numerous fenglin, fengcong and caves, speleological and morphological studies have been performed. Cave sediments for paleomagnetic analyses have been taken from all studied areas (samples CH 1-9). Karst caves in SE Yunnan are probably much older than the age of the cave sediments (<780,000 years B.P.). The studied areas are located in the vicinity of the Xiaojiang fault (N-S     

A Sedimentological Study of Carboniferous Bauxitic Formations in North China

The authors have found in their studies many new genetic types of microtextures of bauxite. A sedimentological genetic classification of bauxites based on these features and a division of the microfacies types of bauxites formed in major microenvironments are proposed. Four kinds of sedimentary sequence of bauxitic sediments have also been recognized. On these bases, a generalized sedimentary model of Carboniferous bauxites in North China is presented, in which storm-turbidite currents play an important role in the formation and enrichment of bauxite deposits.     

Biostratigraphy of Triassic Marine Reptiles in Southwest Guizhou and Its Adjacent Area

This paper briefly reviews the Triassic marine reptile fossils in Guizhou Province, especially the fossils that have been recently found in the Guanling area. Based on three sections at Guanling and Xingyi, Guizhou Province and Luoping, Yunnan Province, four horizons with vertebrate fossils are recognized in the Middle and Upper Triassic of this area; They are from bottom to top: Member I and Member II of the Guanling Formation, and the Zhuganpo Member and the Wayao Member of the Falang Formation.     

Mesoarchean Gridino Mafic Dykes Swarm of the Belomorian Eclogite Province of the Fennoscandian Shield(Russia)

正Two eclogite associations have been recognized within Belomorian TTG gneisses:(1)the subduction-type Salma association and(2)Gridino eclogitized mafic dykes.Protoliths of the Salma eclogites represent a sequence     

Reconstruction of the Yangtze Ramp during Floian to Darriwilian (Ordovician) in South China: Its Morphology, Controlling Factors and Significances

A robust stratigraphic framework and a coherent depositional ramp model for the Zitai, Dawan, Meitan and Ningkuo formations of Floian–Darriwilian age (Early–Middle Ordovician) in the Yangtze (Daoba, Xiangshuidong, Daling, Gudongkou and Honghuayuan sections) and Jiangnan regions (Nanba section) was created based on lithofacies and major element analysis. Three siliciclastic (LF1–3) and six carbonate (LF4–9) lithofacies are recognized representing sediments that were deposited in mixed siliciclastic and carbonate ramp environment. The intensity of mixed sedimentation and terrigenous input were evaluated using the elemental proxies Intensity of Mixed sedimentation (IM) and Aluminum Accumulation Rate (AlAR), as well as their mean values during certain time intervals. Mixed sediments are most well-developed along the marginal Yangtze region, strongly impacted by recurrent influx of westerly derived terrigenous materials in response to global eustatic changes and regional tectonic movements, shaping the gently southeast-dipping morphology. Regular terrigenous influx resulted in periods of enhanced primary productivity on the Yangtze Ramp as evidenced by matching biodiversity peaks in planktonic organisms, i.e., chitinozoans and acritarchs. Brachiopods and other shelly fauna were also able to proliferate as new niches developed along the gently dipping ramp floor with substrate changes. The biodiversification patterns suggest that terrigenous influx controlled in part by regional tectonics played a more important role than previously thought in the development of Great Ordovician Biodiversification Event in South China.     

Late Permian- Early Triassic Conodont Biofacies and Bioprovinces in South China and Himalaya

On the basis of existing conodont data, the authors have studied the Late Permian-Early Triassic conodonts of different forms and biofacies in detail. Five conodont biofacies are recognized, from shallow to deep waters 1. Hindeodus conodont biofacies, 2. Pachycladina-Parachi rognathus conodont biofacies, 3. Gondolella -Hindeodus conodont biofacies, 4. Gondolella-Neospathodus conodont biofacies, and 5. Xaniognathus conodont biofacies. Considering the temporal and spatial changes of these conodont biofacies, 3 conodont bloprovinces have been divided. In light of the biofacies changes of each bioprovince, the authors also discuss, in this paper, the regularity of transgression-regression cycles of eastern Tethys and their possible relation to the mass biotic alternation.     

吉林陨石中包裹体特征，形成温度及其意义的探讨

Glass and gas inclusions have been observed in olivine and other minerals in 30 doubly polished tin sections of Jilin meteorites, indicating that there must have been melting And condensation stages during the process of meteorite formation. Temperatures of formation have been determined by homogenization and quenching runs,giving 1050-200℃ and 502℃ for glass and gas inclusions respectively, Meanwhile,the fibrous radial crystals of pyroxene have been notieed to grow when heated over 800℃. These observations are in general agreement with the available experimental data and theoretical calculations regarding meteorite.     

Fluid Inclusions of Orogenic Gold Deposits in the Zhongchuan Area,Western Qinling and Their Geological Significance

Orogenically-derived gold deposits of the Zhongchuan area in the western Qinling are distributed in the exo-contact thermal metamorphic zone. The country rocks hosting the deposits are predominantly of Devonian age with low-grade metamorphism and strong deformation with the ore deposits directly controlled by multi-level tectonic systems. Three types of inclusions from these deposits have been recognized: CO2-H2O, CO2-rich, and aqueous. The ore-forming fluids were mainly CO2-NaCl-H2O type characterized by rich CO2, low salinity, high temperature and immiscibility. Incorporated with earlier isotopic data, the regional geological setting and features of diagenesis and metallogeny, it can be concluded that the ore-forming fluids were derived from deep magma and mixed with meteoric and metamorphic water. The deposits formed during an intra-continent collisional orogeny, and some of the materials derived from the deep might have been involved in the ore-forming process.     

Cambrian- Ordovician Deep - Water Deposits in Southwest Jiangxi, China

The Cambrian-Ordovician rocks in southwestern Jiangxi are mainly composed of deep-water deposits, in which 5 facies have been recognized: sandstone facies, sandstone-mudstone facies, siltstone-mudstone facies, mudstone (slate)facies, and chert facies. They are of turbidity current origin and are related to pelagic and hemipelagic deposits. In the light of facies distribution, the Cambrian-Ordovician deposits can be classified into 3 facies associations formed in middle fan, outer fan and deep-sea plain environments respectively. The 3 different orders of vertical cycles in the stratigraphic sequence are considered to be controlled by factors such as sea-level fluctuation, basin subsidence and submarine fan progradation. The tectonic setting of the sedimentary basin is interpreted as passive continental margin based on the chemical composition analysis of the sandstone.     

Geochemical Characteristics of the Cenozoic Volcanic Rocks in Central Qiangtang, Tibet: Relation with the Uplift of the Qinghai Tibet Plateau

1. Introduction The uplift and evolution of the Qinghai Tibet Plateau has been the most important projects for studying the dynamic process of the plateau, and the uplift mechanism and history are the essential problems. Researches have been done extensively in terms of tectonics, sedimentology, geophysics, paleontology, paleoclimate and paleomagnetism for several tens of years. Many evolution models have been suggested but so far none of them have been explained perfectly. In recent years,…     

Light Hydrocarbons in Fluid Inclusions and Their Constraints on Ore Genesis: A Case Study of the Songxi Ag (Sb) Deposit, Eastern Guangdong, China

The Songxi deposit is a newly discovered large Ag (Sb) deposit. By using a suite of high-vacuum quadrupole gas mass spectrometer systems, the authors have recognized many kinds of light hydrocarbons in fluid inclusions of minerals. These hydrocarbons are mainly composed of C1-C4 saturated alkanes, while the contents of C2-C4 unsaturated alkenes and aromatic hydrocarbons are quite low, suggesting that the metallogenic processes have not been affected by magmatic activities. Chemical equilibrium studies show that these hydrocarbons may be a mixture of organic gases generated by microorganism activity and those by thermal cracking of type-n kerogens (kukersite) in sedimentary host rocks, and the former may constitute more than two-thirds, implying that microorganism might have played an important role in the metallogenesis. The equilibrium temperature of the latter is about 300℃, which is much higher than the geothermal temperature at the estimated depth of metallogenesis. Thus, the light hydrocarbons gen     

Transition-Zone Mineral Assemblages in Peridotite Massifs, Tibet: Implications for Collision-zone Dynamics and Orogenic Peridotites

<正>Diamonds have been reported from Tibetan"ophiolites"for≥30 years,but have been widely dismissed as contaminants,because their unusual morphology and light C(δ~(13)C=-18 to–27)are unlike those of kimberlitic diamonds.However,the diamonds have now been found in situ in both the chromitites and the peridotites of