Genesis of Re-rich Molybdenite in the Baishan Mo deposit,Eastern Tianshan,Xinjiang, Northwest China     

Longxiang Ye  Dayu Zhang  Shiwei Wang  Taofa Zhou  Feng Yuan  Noel C. White  Wenjiao Xiao 《Resource Geology》2022,72(1):e12269

The Baishan molybdenum deposit is located in the central part of the Eastern Tianshan-Beishan tectonic belt, NW China. The deposit is hosted in early Carboniferous Gandun Formation biotite-rich hornfels and is genetically related to unexposed granodiorite porphyry beneath the orebodies. The molybdenite occurs in three different types from early to late stage: Molybdenite - Fe-Cu-sulfides - K-feldspar - quartz veins (Group 1); Molybdenite - Fe-Cu-sulfides - quartz veins (Group 2); and disseminated molybdenite in the wall rock (Group 3). Rhenium concentrations in the molybdenite grains range from 108 to 277 ppm in Group 1, 69–121 ppm in Group 2 and 46–135 ppm in Group 3. The Re concentrations of molybdenite in the Baishan Mo deposit decrease from early to late and from the center to periphery, and molybdenite types vary from the 2H₁ poly-type in Groups 1 and 2 to the 2H₁ + 3R2H₁ poly-type in Group 3, based on X-ray diffraction results. The Re-enriched molybdenite probably formed from an oxidized magmatic fluid that separated from a highly oxidized and H₂O- and volatile-enriched adakitic intrusion generated in the lower crust.  相似文献   

Time evolution and temperatures of hypervelocity impact‐generated tracks in aerogel     

Gerardo Dominguez 《Meteoritics & planetary science》2009,44(10):1431-1443

Abstract— Aerogel collectors have been used to capture cometary, interplanetary, and interstellar dust grains by NASA's Stardust mission, highlighting their importance as a scientific instrument. Due to the fragile and heterogeneous nature of cometary dust grains, their fragments are found along the walls of tracks that are formed during the capture process. These fragments appear to experience a wide range of thermal alteration and the causes of this variation are not well understood at a theoretical level as physical models of track formation are not well developed. Here, a general model of track formation that allows for the existence of partially and completely vaporized aerogel material in tracks is developed. It is shown that under certain conditions, this general track model reduces to the kinetic “snowplow” model that has previously been proposed. It is also shown, based on energetic considerations, that track formation is dominated by an expansion that is snowplow‐like in the later stages of track formation. The equation of motion for this snowplow‐like stage can be solved analytically, thus placing constraints on the amount of heating experienced by cometary dust fragments embedded in track walls. It is found that the heating of these fragments, for a given impact velocity, is expected to be greater for those embedded in larger tracks. Given the expected future use of aerogels for sample return missions, the results presented here imply that the choice of aerogel compositions can have a significant effect on the modification of samples captured and retrieved by these collectors.  相似文献   

Mineralogical, fluid inclusion, and stable isotope constraints on mechanisms of ore deposition at the Samgwang mine (Republic of Korea)—a mesothermal, vein-hosted gold–silver deposit     

Bong Chul Yoo  Hyun Koo Lee  Noel C. White 《Mineralium Deposita》2010,45(2):161-187

The Samgwang mine is located in the Cheongyang gold district (Cheonan Metallogenic Province) of the Republic of Korea. It consists of eight massive, gold-bearing quartz veins that filled NE- and NW-striking fractures along fault zones in Precambrian granitic gneiss of the Gyeonggi massif. Their mineralogy and paragenesis allow two separate vein-forming episodes to be recognized, temporally separated by a major faulting event. The ore minerals occur in quartz and calcite of stage I, associated with fracturing and healing of veins. Hydrothermal wall-rock alteration minerals of stage I include Fe-rich chlorite (Fe/(Fe+Mg) ratios 0.74-0.81), muscovite, illite, K-feldspar, and minor arsenopyrite, pyrite, and carbonates. Sulfide minerals deposited along with electrum during this stage include arsenopyrite, pyrite, pyrrhotite, sphalerite, marcasite, chalcopyrite, galena, argentite, pyrargyrite, and argentian tetrahedrite. Only calcite was deposited during stage II. Fluid inclusions in quartz contain three main types of C–O–H fluids: CO₂-rich, CO₂–H₂O, and aqueous inclusions. Quartz veins related to early sulfides in stage I were deposited from H₂O–NaCl–CO₂ fluids (1,500–5,000 bar, average 3,200) with T _htotal values of 200°C to 383°C and salinities less than about 7 wt.% NaCl equiv. Late sulfide deposition was related to H₂O–NaCl fluids (140–1,300 bar, average 700) with T _htotal values of 110°C to 385°C and salinities less than about 11 wt.% NaCl equiv. These fluids either evolved through immiscibility of H₂O–NaCl–CO₂ fluids as a result of a decrease in fluid pressure, or through mixing with deeply circulated meteoric waters as a result of uplift or unloading during mineralization, or both. Measured and calculated sulfur isotope compositions (δ³⁴S_H2S = 1.5 to 4.8‰) of hydrothermal fluids from the stage I quartz veins indicate that ore sulfur was derived mainly from a magmatic source. The calculated and measured oxygen and hydrogen isotope compositions (δ¹⁸O_H2O = −5.9‰ to 10.9‰, δD = −102‰ to −87‰) of the ore-forming fluids indicate that the fluids were derived from magmatic sources and evolved by mixing with local meteoric water by limited water–rock exchange and by partly degassing in uplift zones during mineralization. While most features of the Samgwang mine are consistent with classification as an orogenic gold deposit, isotopic and fluid chemistry indicate that the veins were genetically related to intrusions emplaced during the Jurassic to Cretaceous Daebo orogeny.  相似文献   

Climate impacts of recent multidecadal changes in Atlantic Ocean Sea Surface Temperature: a multimodel comparison   总被引：4，自引：4，他引：0  

Daniel L. R. Hodson  Rowan T. Sutton  Christophe Cassou  Noel Keenlyside  Yuko Okumura  Tianjun Zhou 《Climate Dynamics》2010,34(7-8):1041-1058

During the twentieth century sea surface temperatures in the Atlantic Ocean exhibited prominent multidecadal variations. The source of such variations has yet to be rigorously established—but the question of their impact on climate can be investigated. Here we report on a set of multimodel experiments to examine the impact of patterns of warming in the North Atlantic, and cooling in the South Atlantic, derived from observations, that is characteristic of the positive phase of the Atlantic Multidecadal Oscillation (AMO). The experiments were carried out with six atmospheric General Circulation Models (including two versions of one model), and a major goal was to assess the extent to which key climate impacts are consistent between the different models. The major climate impacts are found over North and South America, with the strongest impacts over land found over the United States and northern parts of South America. These responses appear to be driven by a combination of an off-equatorial Gill response to diabatic heating over the Caribbean due to increased rainfall within the region and a Northward shift in the Inter Tropical Convergence Zone (ITCZ) due to the anomalous cross-equatorial SST gradient. The majority of the models show warmer US land temperatures and reduced Mean Sea Level Pressure during summer (JJA) in response to a warmer North Atlantic and a cooler South Atlantic, in line with observations. However the majority of models show no significant impact on US rainfall during summer. Over northern South America, all models show reduced rainfall in southern hemisphere winter (JJA), whilst in Summer (DJF) there is a generally an increase in rainfall. However, there is a large spread amongst the models in the magnitude of the rainfall anomalies over land. Away from the Americas, there are no consistent significant modelled responses. In particular there are no significant changes in the North Atlantic Oscillation (NAO) over the North Atlantic and Europe in Winter (DJF). Additionally, the observed Sahel drying signal in African rainfall is not seen in the modelled responses. Suggesting that, in contrast to some studies, the Atlantic Multidecadal Oscillation was not the primary driver of recent reductions in Sahel rainfall.  相似文献   

Delineation of a Saline Ground-Water Boundary from Borehole Geophysical Data     

Douglas J. Schnoebelen  Edward F. Bugliosi  Noel C. Krothe 《Ground water》1995,33(6):965-976

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Hydrochemical Facies in a Tertiary Basin in the Milligan Canyon Area, Southwest Montana     

Noel C. Krothe  Marcel P. Bergeron 《Ground water》1981,19(4):392-399

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Robust estimation of the variogram: I   总被引：9，自引：0，他引：9  

Noel Cressie  Douglas M. Hawkins 《Mathematical Geology》1980,12(2):115-125

It is a matter of common experience that ore values often do not follow the normal (or lognormal) distributions assumed for them, but, instead, follow some other heavier-tailed distribution. In this paper we discuss the robust estimation of the variogram when the distribution is normal-like in the central region but heavier than normal in the tails. It is shown that the use of a fourth-root transformation with or without the use of M-estimation yields stable robust estimates of the variogram.Visiting Scientist, NRIMS, during the period in which this work was carried out.  相似文献   

The geomorphic and climatic significance of rock glaciers     

Eric J. Steig  Douglas H. Clark  Noel Potter  Jr.  Alan R. Gillespie 《Geografiska Annaler: Series A, Physical Geography》1998,80(3-4):173-174

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Transport of Bromide and Other Inorganic Ions by Infiltrating Storm Water Beneath a Farmland Plot     

Mohammad Z. Iqbal  Noel C. Krothe 《Ground water》1996,34(6):972-978

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Dynamic response of axisymmetric embedded foundations     

J. M. Emperador  J. Dominguez 《地震工程与结构动力学》1989,18(8):1105-1117

The boundary element method is used to obtain dynamic stiffness functions of rigid cylindrical foundations embedded in a uniform or layered viscoelastic half-space. Dynamic stiffness functions of hemispherical foundations embedded in a uniform half-space are also computed. The direct integral equation formulation is used in combination with the complete space point load fundamental solution that is integrated numerically along the azimuthal coordinate. The approach is easy to implement because of the simplicity of the fundamental solution. The numerical results obtained by this method for cylindrical and hemispherical foundations are very close to corresponding published results obtained by different procedures. A parametric study shows the important effects of the Poisson's ratio on the dynamic stiffness functions of cylindrical foundations embedded in a uniform viscoelastic half-space. The effect of the bedrock compliance on the stiffness functions is also shown in the case of cylindrical foundations embedded in a soil layer that rests on a bedrock.  相似文献