Deformation Mechanism and Stability of a Rocky Slope

A high slope is located on the side of the spillway at a hydropower station in Southwest China, which has some weak inter-layers inclining outwards. Parts of the slope show heavy weathering and unloading. There appeared deformation and tensile crack either on the surface or on the afteredge of the slope during excavation, and under a platform （elev. 488 m）, two levels of slopes collapsed on the downriver side. Based on the investigation in situ and the analysis of the geological structure, the conceptual model of deformation and failure mechanism was erected for this slope. Furthermore, the deformation characteristics were studied with FLAC^3D numerical simulation. Comprehensive analysis shows that the whole deformation of the slope is unloading rebound in certain depth scope and the whole body does not slide along any weak interlayer. In addition, two parts with prominent local deformation in the shallow layer of the slope show the models of ＂creep sfiding-tensile cracking＂ and ＂slidlng-tensile cracking＂, respectively. Based on the above analysis, the corresponding project of support and reinforcement is proposed to make the slope more stable.     

Animals and Mineralization of Phosphorus: Ore-Forming Mechanism of Insular Phosphorites

Phosphorite, or guano, or insular phosphorite, commonly containing 10-35% P_2O_5, is one of the sources of phosphatic fertilizer. Taking the modern insular phosphorite on the Xisha Islands as an example. this paper discusses the ore-forming mechanism of phosphate and the important contribution made by animals to this process.The phosphorite occurs in the middle part of carbonate sand cays of coral reef surrounded by longshore sandbanks, which assumes a dish-shape. The surface of the cays is covered by unconsolidated guano. The phosphorite, yellowish brown to dark brown, is made up of thick-bedded sand and gravel cemented by collophanite, and partly replaced by carbonate apatite.The mechanism of mineralization is as follows:The average content of phosphorus in the sea water is only 0.07 ppm, but through the sea food chain concentration, phosphorus content may become higher. The phytoplanktons, as producers, suck up phosphorus out of sea water. The primary consumers, zooplanktons, obtain phosphorus by eating phytoplanktons, then they are followed by the second and third consumers. Sea birds living on fish, as the third consumers, concentrate and transport the phosphorus to the carbonate sand cays. Finally layers of guano are deposited under the arbores.Under the tropical climatic conditions with high temperature and plentiful rainfall soluble matters are leached out of the guano and infiltrated into deeper horizon. In alkaline groundwater with pH greater than 7.0. the phosphoritization takes place, bioclastics are cemented and replaced by collophanite or carbonate apatite. Finally, the phosphorus is fixed and phosphate formed.     

Origin, Evolution and Mechanism of the Jehol Fauna

This paper deals with the geographic distribution and geological setting of the Jehol (northeastHebei-southwest Liaoning-southeast Inner Mongolia) fauna, and discusses the origination and the evolution ofits major biological groups. It is demonstrated that the Yan-Liao (northern Hebei-western Liaoning) area is theprovenance for the fauna. Why the fauna originated and developed in the area was intimately related to suchfactors as the palaeoclimate, palaeogeography, crustal movement, volcanism and frequent reversals of magnet-ic polarity at that time, in addition to the internal factors of the organisms themselves.     

Main Mineralization Mechanism of Magmatic Sulphide Deposits in China

Before intruding, primary magmas have undergone liquation and partial crystallization atdepth; as a result the magmas are partitioned into barren magma, ore-bearing magma, ore-richmagma and ore magma, which then ascend and are injected into the present locations once ormultiple times, thus forming ore deposits. The above-mentioned mineralizing process is knownas deep-seated magmatic liquation-injection mineralization. The volume of the barren magma isgenerally much larger than those of the ore-bearing magma, ore-rich magma and ore magma. Inthe ascending process, most of the barren magma intrudes into different locations or outpoursonto the ground surface, forming intrusions or lava flows. The rest barren magma, ore-bearingmagma, ore-rich magma and ore magma may either multiple times inject into the same space inwhich rocks and ores are formed or separately inject into different spaces in which rocks and oresare formed. The intrusions containing such deep-seated magmatic liquation-injection depositshave a much smaller volume, greater ore potential and higher ore grade than that of in-situmagmatic liquation deposits. Consequently this mineralizing process results in the formation oflarge deposits in small intrusions.     

Mechanism of Seasonal Deterioration of Water Quality in Lake Baihua,China

Water quality of Lake Baihua was found worsening in the autumn of 1994.Studies have shown that the decomposition of organic matter in the upper-level sediments resulted in seasonal anoxia with the release of P,Mn,and S^2- from the sediments to the overlying water column,and the increase of NO2^- concentration led to blackening of the water column,deat of fishes and secondary Mn pollution.     

Mechanism of formation of superdeep sedimentary basins: lithospheric stretching or eclogitization?

The superdeep North Caspian, South Caspian, and Barents basins have their sedimentary fill much thicker and the Moho, correspondingly, much deeper than it is required for crustal subsidence by lithospheric stretching. In the absence of large gravity anomalies, this crustal structure indicates the presence under the Moho of a thick layer of eclogite which is denser than mantle peridotite. Crustal subsidence in the basins can be explained by high-grade metamorphism of mafic lower crust. The basins produced by lithospheric stretching normally subside for the first ～100 myr of their history, while at least half of the subsidence in the three basins occurred after that period, which is another evidence against the stretching formation mechanism. According to the seismic reflection profiling data, stretching can be responsible for only a minor part of the subsidence in the Caspian and Barents basins. As for the South Caspian basin, there has been a large recent subsidence event in a setting of compression. Therefore, eclogitization appears to be a realistic mechanism of crustal subsidence in superdeep basins.     

Thermodynamic Modelling of Ore-Forming Mechanism of the Changkeng Gold-Silver Deposits in Guangdong Province

The Changkeng gold-silver deposits consist of a sediment-hosted, disseminated gold deposit and a replacement-type silver deposit. The mineralizations of gold and silver are zoned and closely related to the silicification of carbonate and clastic rocks, so that siliceous ores dominate in the deposit. The mineralizing temperature ranges mainly from 300 to 170℃, and K+, Na+, Ca2+, Mg2+, and Cl- are the major ions in the ore-forming fluid. Calculations of distribution of metal complexes show that gold is mainly transported by hydrosulphide complexes, but chloride complexes of silver, iron, lead, and zinc, which are transformed into hydroxyl and hydrosulphide complexes under neutral to weak-alkaline circumstances in the late stage, predominate in the ore-forming solutions. Water-rock interaction is confirmed to be the effective mechanism for the formation of silver ores by computer modelling of reaction of hydrothermal solution with carbonate rocks. The solubility analyses demonstrate that the precipitation     

Primordial Black Holes and Modification of Zeldovich–Novikov Mechanism

Astronomy Reports - Bulk of various astronomical observations of black holes suggest that virtually all observed black holes can be of primordial origin. A modified mechanism of the primordial...     

Crust-Mantle Structures and Gold Enrichment Mechanism of Mantle Fluid System

Gold enrichment mechanism of ore-forming fluid is the essence of gold metallization.This paper summarizes the distinguishing symbols of mantle fluid and effect of crust-mantle structure on fluid movement. Fluid moving processes include osmosis, surge, gas-liquid alterna-tion and mutation of fluid speed. During fluid movement, gold will be enriched gradually. Final-ly, a layered circulatory system is illustrated in this paper.     

Analysis of the Geodynamic Mechanism of the Large-Scale Gold Mineralization in Northeastern Hunan Province

Please refer to the attachment(s) for more details.     

The Characteristics and Genetic Mechanism of Igneous Topazites in South China

Igneous topazites found recently in South China are closely associated with F-rich granites in time and space. They have a typical igneous porphyritic texture. The phenocrysts are topaz and quartz, while the groundmass consists mainly of prismatic or acicular topaz microlites and anhedral quartz. Compared with granites, topazites are rich in SiO2 (65.06%-81.12% ) and Al2O3 (13.01%-18.09%) but poor in MgO and Na2O and strongly peraluminous with A/NKC = 3.204-37.313. Geochemically, the rocks are evidently depleted in Sr and Ba, but enriched in Sn, W, Nb and F. The concentrations of Sn and partial W in the topazites are 1-2 orders of magnitude higher than the average of acid rocks. The F-riched granites related to the topazites in the area usually have much higher ISr (0.7103-0.7460) and δ18OQ‰ (9.5-14.24), but lower INdCT) (-4.8- 9.4). It suggests that the topazite is similar to S-type granites in genesis. Hydroxylated silicate melt inclusions, consisting of several grains of quartz and aqueous fluids,     

Early Mesozoic Basin-Mountain Coupling Mechanism and Basin Geodynamics of East China

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Failure Mechanism of Soil Nail—Prestressed Anchor Composite Retaining Structure

Enhancing the strength of retaining structure with soil nails and prestressed anchors is a new technique that can be used in the excavation of deep foundation pit. Finite element analysis (FEA) based on ABAQUS is presented in this paper to investigate the failure mechanism of such retaining structure. The model used in the FEA is firstly validated by comparing the modelled results with field measurements for a specific case. The model is then extended to investigate the influence of the prestressed anchor on the (1) horizontal deformation of foundation pit and (2) the distribution of axial forces along the soil nails. It is found that the magnitude of anchor force is the key factor governing the performance of the entire retaining system. However, the influence of the prestressed anchor is sensitive to the rigidity of the concrete surface layer of the retaining structure. Based on the results of the modelling, the failure mechanism of soil nail—prestressed anchor composite retaining structure is discussed.     

Metallogenic Mechanism of the Tianbaoshan Pb—Zn Deposit,Sichuan

The Tianbaoshan Pb-Zn deposit in Sichuan Province,exhibiting open-space-filling and /or replacement textures,occurs as being of vine style in the Sinian(Late Proterozoic) carbonate rocks,and is simple in ore composition.A systematic study of lead isotope and rareearth elements reveals that the ore-forming materials were derived from multiple sources.The ultimate source of the sulfur in all stages in seawater sulfate but the reducing mechanisms are different,The carbon was derved from marine carbonate and organic matter,The ore-forming fluid,meteoric in origin,belongs to a Ca^2 -Mg^2 -Cl^--Hco3^- type of weak acidic to alkalic solutions with a salinity of about 5wt% NaCl.The ore was formed at the depth of about 1 km from 150 to 250℃ during the main stage of ore deposition.The heated meteoric water,after extracting ore materials from wall rocks,evolved into ore-forming solution with a low salinity, in which metals were trasported as chloride complexes such as PbCl,ZnCl and ZnCl.The metal-bearing solution moved upward along deep faults to low-pressure zones,where the metal ions reacted with reduced sulfur and were precipitated as sulfied minerals.The textures of the minerals were controlled by the rate at which the reduced sulfur was supplied.     

A New Mechanism of Formation of the Silver—Rim Structure on Primary Gold Grains

Gold minerals in the Baochun skarn-type gold deposit are Au-Ag allogy with Ag contents within the range of 15-35.5wt% and the inerals vary from 5μm to 50μm in size.As viewed from the electron microprobe images,most gold grains show silver rims with a high Ag content as compared with the core,ranging generally from 2 to 3μm in width.From dynamic calculations based on the mass action and mass balance constratints on the crystallization of native gold,it is considered that the enrichment of silver in the rim of gold minerals in due to gradual enrichment of silver in the ore-forming solutions with its evolution from the early to the late metallogenic stage.     

Concentration Mechanism of Ore-Forming Fluid in Huize Lead-Zinc Deposits, Yunnan Province

The Huize Pb-Zn deposits of Yunnan Province, located in the south-central part of the Sichuan-Yunnan-Guizhou (SYG) Pb-Zn multimetal mineralization district (MMD), are strictly controlled by fault zones. The sources of ore-forming fluid in the deposits have been debated for a long time. Calcite, a gangue mineral, has uniform C and O isotopes. The δ13CPDB and δ18OSMOW values vary respectively from -2.1×10-3 to -3.5×10-3 (mean -2.8×10-3) and 16.7×10-3-18.6×10-3 (mean 17.7×10-3). No obvious difference can be found in C and O isotopes among occurrences and elevations and even ore-bodies. Types of inclusions include those of pure liquid (L), liquid-rich gas-liquid (L V), and three-phase ones containing a daughter mineral (S L V) and immiscible CO2 with three-phases (VCO2 LCO2 LH2O). Their homogenization temperatures vary from 110 to 400 ℃, and two peaks are shown. (87Sr/86Sr)0 ratios of calcite in the deposits are higher than those in the mantle and Emeishan basalts, and slightly higher than those in the Baizuo Formation, which the Huize lead-zinc deposits are found in. All of the (87Sr/86Sr)0 are low relative to those in the basement rocks. Fractionation of Sr isotope did not occur in the ore-forming fluid during the precipitation of minerals. The results indicate that the ore-forming fluid is homogeneous and derived from the mixing of different fluids. Gas-liquid inclusions can be separated into two groups in 300-400 ℃ with a salinity of 5 %-6 % and 12 %-16 % NaCl respectively. However, the salinities of inclusions vary from 7 % to 23 % NaCl in 100-300 ℃, especially in 150-250 ℃. The formation pressures of faulted zones are (50-320)×105 Pa. The estimated pressures of the overlying rocks on the ore bodies are 574×105-640×105 Pa. The pressures of ore-forming processes would be 145×105 to 754×105 Pa. Therefore, pressure sharply reduced and boiling occurred when the ore-forming fluid flew into the fault zones. As a result, the ore-forming fluid was highly concentrated, and metallic minerals began to precipitate from the fluid on a great scale. The high-grade lead-zinc deposits were formed when the fluid was under saturation or over-saturation conditions.     

Differentiation Mechanism and Evolution of High-level Magma Chamber at Xiangshan,China

The calc-alkaline volcanic magmas,which formed the Mesozoic uraniferous volcanic complex of Xiangshan,resulted from partial melting of the mixture of lower crust and enriched mantle with a high mixing proportion in a specific tectonic setting such as active continental margin or ocean-continent collision zone.The preliminary concentrations of Uand Th occur in low-degree par-tial melts.Only small part of these melts was rapidly extracted and erupted and most intruded into the high-level magma chamber(depth:12-13 km) of the compressed upper lithosphere ,in which occurred a strong differentiation which would resulted in strong preconcentrations of the high-hygromagmaphile elements U and Th associated with strong depletion of the 3-d transition ele-ments Ti,Sc,Co,Zr,etc.At the final stage of subduction of the West-Pacific-Kula plate towards the Asian continental plate,the regional tectonic environment was transformed from a compressive in-to a tensional setting.The strongly differentiated,U(and Th) enriched silicic alkalic magmas in high level magma chamber extensively erupted,extruded and intruded.The hydrothermal fluids released as a result of late volcano-degassing and dewatering during crystallization-solidification of magmas,re-sulted in the remobilization,leaching,migration and reconcentration of uranium ,which had been preconcentrated in volcanic rocks.Therefore,specific regional petrogeochemical criteria are expected for the uraniferous volcanic series.     

Formation Mechanism and Stability Assessment of the Colluvial Deposit Slope in Zuoyituo

The basic features of the colluvial deposit slope in Zuoyituo such as geological conditions, dimensions, slip surfaces and groundwater conditions are described concisely in this paper. The formation mechanism of the slope is discussed. It is considered that the formation of the colluvial deposit slope in Zuoyituo has undergone accumulation, slip, load, deformation and failure. The effects of rainfall on slope stability are categorized systematically based on existing methodology, and ways to determine the effects quantitatively are presented. The remained slip force method is improved by the addition of quantitative relations to the existing formulae and programs. The parameters of the colluvial deposit slope are determined through experimentation and the method of back-analysis. The safety factors of the slope are calculated with the improved remained slip force method and the Sarma method. The results show that rainfall and water level in the Yangtze River have a significant effect on the stability of the colluvial deposit slope in Zuoyituo. The hazards caused by the instability of the slope are assessed, and prevention methods are put forward.