大别杂岩中混合岩的矿物空间分布研究

介绍了矿物空间分布研究的基本原理及两种统计方法(接触频数法和线切法)。作者对混合岩矿物空间分布的研究表明:(1)前人提出的统计方法存在方法上的缺陷和应用上的局限性,作者推导出矿物接触类型的概率公式;(2)部分浅色体中矿物显示聚集分布的特征,而绝大部分的浅色体中矿物具有分散分布的特点。结合质量平衡和地球化学研究认为:大别杂岩中主体混合岩成因机制是重熔和交代作用。     

The history and impact of air pollution at Čertovo Lake,southwestern Czech Republic

This multi-disciplinary investigation documents the longterm effects of atmospheric pollution of metals and acids on a geologically sensitive catchment in the umava Mountains, southwestern Czech Republic, a region with a long history of human disturbance. A 30 cm long sediment core (I) from ertovo Lake was analyzed for natural and artifical radionuclides, metals, diatoms, chrysophytes, and pollen in sediments accumulated during the last 200 years. A second core (II), extending to 95 cm, included sediment judged to be free of atmospheric deposition of pollutants associated with the Industrial Revolution. Chronostratigraphic markers include several changes in the pollen assemblages corresponding to well-documented changes in land-use, and distinct distributions of ¹³⁷Cs, ¹³⁴Cs and ²⁴¹Am from weapons testing and the 1986 nuclear accident at Chernobyl, Russia. These markers corroborate the ²¹⁰Pb dating and, together, produce a reliable chronology extending back nearly to 1800 A.D.Stratigraphic profiles of Cu, Pb, and Zn in Core I are unlike any previously reported in the literature. Concentrations of Cu, Pb, and Zn remain generally above 100, 400, and 200 g g^-1, respectively, for the 200 years represented by Core I. These values are unusually high for sediments from a watershed with no known heavy-metal ore bodies. Accumulation rates for Cu, Pb, and Zn, which include both atmospheric and watershed contributions, are also high (ca 1, > 1 and > 1 g cm^-2 yr^-1, respectively) for the same period, although the anthropogenic contribution of Zn rose from nearly zero at 1800 A.D. The Cu and Pb accumulation rates rose dramatically about 1640 A.D.Accumulation rates of anthropogenically-derived Be, a relatively abundant element in the soft coals of the region, are also elevated by about 0.01 g cm^-2 yr^-1 in sediments of this period. Vanadium accumulation rates increased only since 1980 A.D., presumably along with increased consumption of oil.Diatom assemblages illustrate that the lake was acidic (pH between 4.5 and 5) through at least the past 200 years. The pH declined significantly (from ca 5 to 4) between 1960 and 1985 with a slight increase to 4.5 in the last few years. Recent diatom and chrysophyte assemblages suggest high trace metal concentrations, consistent with the present lake-water chemistry.     

流体在岩浆型铬铁矿和铂族元素成矿过程中的作用及意义

镁铁- 超镁铁岩是揭示地幔物质组成和壳幔相互作用的重要窗口，也是Ni- Cu- PGE- Cr等金属矿产资源的重要载体。不同的镁铁- 超镁铁岩体赋矿特征明显不同：蛇绿岩以产出铬铁矿床为特征，阿拉斯加型岩体主要赋含铂族元素(PGE)矿床，大型层状岩体则可同时产出铬铁矿床、PGE矿床和Cu- Ni硫化物矿床。这种成矿差异显然与赋矿岩体形成的构造背景、母岩浆经历的岩浆演化过程有关，但缺少关键控制因素的研究。前人对上述不同种类矿床的研究工作主要集中于地幔源区的部分熔融、上升过程中或岩浆房内的围岩混染和结晶分异等岩浆过程，而极少关注流体作用。近年来，实验岩石学和岩石地球化学的研究均表明幔源岩浆演化过程中的流体活动可能对成矿元素的富集迁移起到至关重要的作用，同时这些成矿元素的赋存状态和分配系数也在不断更新。厘清Cr和PGE在熔体演化——尤其是流体出溶过程中的地球化学行为，刻画并揭示其迁移富集、分离和再富集的成矿过程及控制因素，已成为当前岩浆矿床研究的热点。本文围绕富水流体与铬铁矿和PGE成矿关系的科学问题，总结了不同镁铁- 超镁铁岩体的成矿差异以及铬铁矿和PGE矿床成矿过程中的流体活动记录，提出流体性质和组分对铬铁矿和PGE迁移富集的控制作用，强调有必要开展蛇绿岩、大型层状镁铁- 超镁铁岩体和阿拉斯加型岩体的对比研究。     

浙东晚白垩世小雄破火山中火山-侵入杂岩的岩石成因

破火山内出露的火山岩与浅成侵入岩为硅质岩浆演化研究提供了一个重要窗口，从而备受关注。小雄破火山内的火山-侵入杂岩是中国东南沿海晚白垩世岩浆活动的典型代表，包括小雄组火山岩（K₂x）与两类侵入岩（花岗斑岩、正长斑岩）。本文以小雄火山-侵入杂岩为研究对象，开展了系统的锆石U-Pb年代学、岩石学和地球化学研究，旨在深入探讨破火山内火山岩与侵入岩之间的成因联系和岩浆演化过程。系统的LA-ICP-MS 锆石U-Pb年代学研究表明，小雄组火山岩形成于98~88Ma，并具有多期次喷发的特点，可分为下段、中段和上段，年龄分别为98~96Ma（K₂x¹）、95~92Ma（K₂x²）、~ 88Ma（K₂x³）。小雄花岗斑岩形成年龄为90Ma；正长斑岩形成稍晚，约88Ma。与下段流纹质玻屑凝灰岩的Nd-Hf同位素组成[ε_Nd（t）=-8.3~-7.2， ε_Hf（t）=-11.8~-7.2]相比，中段流纹岩要更为亏损[ε_Nd（t）=-5.84~-5.32， ε_Hf（t）=-10.1~-0.5]。研究表明，小雄组流纹质火山岩的母岩浆可能起源于发生在深部岩浆房中渐进的壳幔相互作用，中段流纹岩的源区混入了更多的亏损幔源组分。中段流纹岩与花岗斑岩具有相似的Nd-Hf同位素组成，以及 "互补"的微量元素地球化学特征，由发生在浅部岩浆房的分离结晶作用和堆晶作用所制约。值得注意的是，正长斑岩与花岗斑岩并不存在直接的成因演化关系，两者应是不同的起源。不同的正长斑岩岩株具有高度一致的结晶年龄、微量元素特征以及Nd-Hf同位素组成，以上特征均表明小雄破火山内的正长斑岩具有相同的起源。正长斑岩母岩浆起源于富集岩石圈地幔的部分熔融，岩浆源区混入了来自亏损的软流圈地幔组分，其地球化学成分变化主要受"普通辉石+磷灰石+钛铁矿"的分离结晶所控制。     

Chemical aspects of iron oxide coagulation in water: Laboratory studies and implications for natural systems

Initial coagulation rates of colloidal hematite (-Fe₂O₃) particles (diameter less than 0.1 µm) were measured experimentally in well-defined laboratory systems at constant temperature. The relative stability ratio,W, was obtained at various ionic strengths in NaCl medium and at pH values in the range from 3 to 12. ExperimentalW values ranged from 1 to 10⁴ in various systems. The results delineate the roles ofspecific andgeneralized coagulation mechanisms for iron oxides. Among the specifically-interacting species (G _ads ⁰ >G _coul ⁰ ) studied were phosphate, monomeric organic acids of various structures, and polymeric organic acids. The critical coagulation-restabilization concentrations of specifically-interacting anions (from 10^–7 to 10^–4 molar) can be compared with the general effects of non-specific electrolyte coagulants (10^–3 to 10^–1 molar). The laboratory results are interpreted with the help of a Surface Complex Formation/Diffuse Layer Model (SCF/DLM) which describes variations of interfacial charge and potential resulting from variations of coagulating species in solution. Comparison of these laboratory experiments with observations on iron behavior in estuarine and lake waters aids in understanding iron removal mechanisms and coagulation time scales in natural systems.     

Environmental aspects of selected trace metals in soils and waters surrounding Singaran Nala, Raniganj Coalfield

The Raniganj Coalfield is the oldest coalfield in India that has been continuously and extensively mined since the late eighteenth century. The present study reports a geochemical investigation and environmental quality assessment using soil and water in the area surrounding a stream, locally known as Singaran Nala （Nala means storm water drains in Bengali）, in the Raniganj Coalfield. Soil （top soil, mud, silty clay and laterite） and rock samples （sandstone and shale） were collected from the study area and were analyzed for trace metals （Cr, Cu, Fe, Mn, Ni and Zn）. Surface waters from the stream and the Damodar River as well as ground waters from hand pumps and underground mine pits were collected. Water samples were analyzed for major ions （Na^＋, Ca^2＋, Mg^2＋, Cl^-, HNO3^- and SO4^2-） and trace metals （Cu, Fe, Mn, Ni, and Zn）. Trace metal concentrations in soil samples are found higher than the average world soil composition. Nevertheless, trace metal （Cr, Cu, Ni and Zn） concentrations in soils exceed or reach the maximum allowable concentrations （MAC） proposed by the European Commission for agricultural soils. In particular, Ni concentrations exceed the typical value for cultivated soils. Chromium, Cu and Ni concentrations in laterite and Cr concentration in topsoil exceed the ecotoxicological limit.     

Geochemistry and Origin of Ananai Stratiform Manganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan

Abstract. Major and trace element contents are reported for Permian manganese ore and associated greenstone from the Ananai manganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The manganese deposit occurs between greenstone and red chert, or among red chert beds. Chemical compositions of manganese ore are characterized by enrichments in Mn, Ca, P, Co, Ni, Zn, Sr and Ba, and negative Ce and positive Eu anomalies relative to post-Archean average Australian Shale (PAAS). Geochemical features of the manganese ore are similar to those of modern submarine hydrother-mal manganese deposits from volcanic arc or hotspot setting. In addition, geochemical characteristics of the greenstone closely associated with the Ananai manganese deposit are analogous to those of with-in plate alkaline basalt (WPA). Consequently, the Ananai manganese deposit was most likely formed by hydrothermal activity related to hotspot volcanism in the Panthalassa Ocean during the Middle Permian. This is the first report documenting the terrestrially-exposed manganese deposit that was a submarine precipitate at hotspot.