Fluid sources for the La Guitarra epithermal deposit (Temascaltepec district, Mexico): Volatile and helium isotope analyses in fluid inclusions

The La Guitarra deposit (Temascaltepec district, South-Central Mexico), belongs to the low/intermediate sulfidation epithermal type, has a polymetallic character although it is currently being mined for Ag and Au. The mineralization shows a polyphasic character and formed through several stages and sub-stages (named I, IIA, IIB, IIC, IID, and III). The previous structural, mineralogical, fluid inclusion and stable isotope studies were used to constrain the selection of samples for volatile and helium isotope analyses portrayed in this study. The N₂/Ar overall range obtained from analytical runs on fluid inclusion volatiles, by means of Quadrupole Mass Spectrometry (QMS), is 0 to 2526, and it ranges 0 to 2526 for stage I, 0 to 1264 for stage IIA, 0 to 1369 for stage IIB, 11 to 2401 for stage IIC, 19 to 324 for stage IID, and 0 to 2526 for stage III. These values, combined with the CO₂/CH₄ ratios, and N₂-He-Ar and N₂-CH₄-Ar relationships, suggest the occurrence of fluids from magmatic, crustal, and shallow meteoric sources in the forming epithermal vein deposit. The helium isotope analyses, obtained by means of Noble Gas Mass Spectrometry, display R/Ra average values between 0.5 and 2, pointing to the occurrence of mantle-derived helium that was relatively diluted or “contaminated” by crustal helium. These volatile analyses, when correlated with the stable isotope data from previous works and He isotope data, show the same distribution of data concerning sources for mineralizing fluids, especially those corresponding to magmatic and crustal sources. Thus, the overall geochemical data from mineralizing fluids are revealed as intrinsically consistent when compared to each other.The three main sources for mineralizing fluids (magmatic, and both deep and shallow meteoric fluids) are accountable at any scale, from stages of mineralization down to specific mineral associations. The volatile and helium isotope data obtained in this paper suggest that the precious metal-bearing mineral associations formed after hydrothermal pulses of predominantly oxidized magmatic fluids, and thus it is likely that precious metals were carried by fluids with such origin. Minerals from base-metal sulfide associations record both crustal and magmatic sources for mineralizing fluids, thus suggesting that base metals could be derived from deep leaching of crustal rocks. At the La Guitarra epithermal deposit there is no evidence for an evolution of mineralizing fluids towards any dominant source. Rather than that, volatile analyses in fluid inclusions suggest that this deposit formed as a pulsing hydrothermal system where each pulse or set of pulses accounts for different compositions of mineralizing fluids.The positive correlation between the relative content of magmatic fluids (high N₂/Ar ratios) and H₂S suggests that the necessary sulfur to carry mostly gold as bisulfide complexes came essentially from magmatic sources. Chlorine necessary to carry silver and base metals was found to be abundant in inclusion fluids and although there is no evidence about its source, it is plausible that it may come from magmatic sources as well.     

快速城市化过程中城市土地覆被的时空动态特征

1990~2005年间,是广州市经济快速发展和城市景观变化最大的时期,以同时段TM影像解译得到广州市的土地覆被类型图,从数量结构、空间信息及位置转移和景观等方面,分析了广州市土地覆被的动态特征.数量结构的研究结果显示:在快速城市化过程中广州市的耕地、林地等自然资源的利用程度在加大,自1995年起,这种变化的趋势开始减缓;土地覆被类型之间的信息与位置的转移变化频繁,并且表现出空间位置分异的特征.景观特征指数分析结果表明:广州市城市土地覆被向破碎化方向发展,城市建设用地呈扩展之势.     

Modelling net erosion responses to enviroclimatic changes recorded upon multisecular timescales

Land use change has been recognized throughout the Earth as one of the most important factors influencing the occurrence of rainfall-driven geomorphological processes. However, relating the occurrence of historical soil erosion rates is difficult because of the lack of long-term research projects in river basins. Also, complex models are not adequate to reconstruct erosion rate changes because they require significant input data not always available on long timescales. Given the problems with assessing sediment yield using complex erosion models, the objective of this study is to explore a parsimonious scale-adapted erosion model (ADT) from the original Thornes and Douglas algorithms, which aims at reconstruction of annual net erosion (ANE) upon multisecular timescales. As a test site, the Calore River basin (3015 km² in southern Italy) provides a peculiar and unique opportunity for modelling erosion responses to climate and land cover changes, where input-data generation and interpretation results were also supported by documented hydrogeomorphological events that occurred before and after land deforestation. In this way, ANE_ADT-values were reconstructed for the period 1675–2004 by using precipitation indexes, complemented by recent instrumental records, and by using land cover statistics from documented agrarian sources. Pulses of natural sedimentation in the predeforestation period have been related to Vesuvius volcanic activity and changes in rainstorm frequency. After deforestation, the basin system became unstable with sudden fluctuations in the hydrogeomorphological regime contributing significantly to increased erosion and, in turn, sediment transport sequences via river drainage towards the Tyrrhenian coast.     

Design of Inclined Covers with Capillary Barrier Effect

A design procedure is proposed to minimize water infiltration into landfills by optimizing the water diversion length of inclined covers with capillary barrier effect (CCBE). This design procedure is based on a conceptual, mathematical and numerical approach and aims at selecting materials and optimizing layer thickness. Selection among candidate materials is made based on their hydraulic conductivity functions and on a threshold infiltration rate imposed on the designer. The capillary break layer (CBL; bottom layer) is characterized by a weak capillarity, while the moisture retention layer (MRL; upper layer) is characterized by a compromise between strong capillarity and high hydraulic conductivity. The thickness of the CBL corresponds to the height where suction reaches its maximum value for a given infiltration rate. This height can be calculated using the Kisch [Géotechnique 9 (1959)] model. The optimal thickness of the MRL is determined by applying an adaptation of the Ross [Water Resources Research 26 (1990)] model. The results obtained using the proposed design procedure were compared to those obtained from numerical simulations performed using a finite element unsaturated seepage software. The procedure was applied for two cover systems; one where deinking by-products (DBP) were used as MRL and sand as CBL and another where sand was used as MRL and gravel as CBL. Using this procedure, it has been shown that an infiltration control system composed of thin layers of sand over gravel is highly efficient in terms of diversion length and that its efficiency can be enhanced by placing a hydraulic barrier – such as a layer of DBP – above the MRL.     

中国MODIS卫星影像彩色镶嵌图制作

本文介绍了大范围卫星影像彩色镶嵌图的制作流程．对于大范围卫星影像彩色镶嵌图制作的技术难点（去云、拼接、调色），文章进行了重点介绍并提出技术解决办法．利用MODIS卫星数据制作了两幅全国彩色影像镶嵌图：一幅为红波段（B1）、绿波段（B4）和蓝波段（B3）构成的真彩色合成影像：一幅为红波段（B1）．近红外波段（B2）和蓝波段（B3）构成的假彩色合成影像．两幅影像色彩精美，信息量丰富．     

Spectral Filtering and Classification of Terrestrial Laser Scanner Point Clouds

A method is presented for filtering and classification of terrestrial laser scanner point clouds. The algorithm exploits the four-channel (blue, green, red and near infrared) multispectral imaging capability of some terrestrial scanners using supervised, parametric classification to assign thematic class labels to all scan cloud points. Its principal advantage is that it is a completely data-driven algorithm and is independent of spatial sampling resolution since the processing is performed in four-dimensional spectral feature space. Its application to two data-sets of different spatial extent and spatial and spectral complexity is reported, for which respective overall classification accuracies of 87·0% and 82·0% were achieved. Analysis of the input data with emphasis on the characteristics pertinent to the anticipated outcomes precedes detailed analysis of the classification results and error sources and their causes. Erroneously classified points are attributed to radiometric errors stemming from both detector hardware and physical effects.     

佳木斯地区冬、春季大-暴雪成因分析

冬、春季的天气影响系统既有共同点，又有不同之处。通过近20a大-暴雪个例的物理成因及卫星云图等特征的分析，总结出有预报意义的指标。     

用SSM/I微波遥感图像分析海上台风的螺旋云带

文中介绍了美国国防气象卫星专用微波成像仪 (SSM /I)上各通道的特性 ,分析了大气中各种粒子 (尤其是云滴和降水滴 )对各通道辐射的吸收和散射效应。通过对SSM /I图像上台风单通道剖面、双通道散点图的分析 ,揭示了台风在微波图像上表现形式的内在物理原因。在此基础上 ,设计了一个降水指数 ,方法是 :将 85 .5GHz的吸收段对称拉伸到散射段的延长线上 ,然后求归一化后的 19.35 ,37.0GHz和经拉伸处理的 85 .5GHz图像 3者的平均值。 3个通道合成降水指数克服了 37.0GHz对大雨滴不敏感 ,和 85 .5GHz对中等大小雨滴不敏感的缺点 ,比原始单通道微波图像更清楚地显示了台风的螺旋云带结构     

乌鲁木齐雷暴天气的云图分析

通过对1997－1999年乌鲁木齐发生的11次雷暴天气的分析表明，雷暴天气发生于850hPa上反气旋环流的东南边缘的高能量区，雷暴云图由孤立的对流云图和锋面及涡旋云系中的对流云图发展而成，其形状不规则，生命史4－8h，当雷暴云图成熟时产生雷暴天气现象。     

北疆夏季两次冰雹天气过程的对比分析

北疆夏季两次冰雹天气过程的对比分析发现，充足的水汽、足够大的上升运动和不稳定的层结果冰雹天气出现的必备条件，而降雹的强弱则与对流云图的发展和强度有关。