山东省兰陵县草主山矿区铁矿床地质特征和找矿远景分析

兰陵县草主山矿区属苍峄铁矿带一部分,区内赋存有全隐伏的"鞍山式"铁矿床,经勘查共圈定了南北2个主矿带,5个矿体。矿体赋存于泰山岩群山草峪组中,其形态受基底褶皱控制,具有平行延伸的特点,经过以往地质勘查工作,基本查明了-800m以浅矿体的产出位置、形态、产状、规模、分布、厚度、矿石质量等。矿体沿走向倾向尚未封闭,有继续延伸的趋势,并且矿石品位和矿体厚度未有减弱趋势,由此可得结论其-800m以深仍有很大的找矿前景,满足深部找矿的要求,总结其成矿规律、找矿标志,建立找矿模式,可为进一步勘查提供可靠的地质参考依据。     

太湖水体中胶体磷含量初探

室内静态模拟不同温度下太湖15个湖区柱状沉积物磷酸根释放,分析了相应表层沉积物形态磷,以及梅梁湾间隙水中相关离子Al(Ⅲ)、Fe(Ⅱ)、Ca(Ⅱ)和PO43-含量的季节变化．研究表明,受陆源影响较大的泥区通常是太湖内源磷的稳定源;而在开敞度较大的湖区,由于表层沉积物胶体的物化吸附,使得温度对底泥磷释放的影响作用减弱,并易产生磷的“内汇”现象;在梅梁湾区成汇区,还加上春夏季藻类的局部超负荷需磷这一控制因素,从而使得太湖大部分泥区在一年中至少发生一次源-汇转换过程．化学热力学分析揭示,Al-P较之Fe-P和Ca-P更易在界面发生溶解可能是太湖表层沉积物Al-P与PO43-P释放速率呈显著相关(r=0．3858>r1-0．01,n=45)的内在原因．虽然沉积物中Fe-P有较高的释磷潜力,但浅水湖所营造的沉积物表层氧化层和广泛覆盖的无机胶体及粘土矿物的强吸附介质,可能是抑制沉积物中Fe-P释放成为优势的主要因素．估算太湖沉积物-水界面磷的净通量为899．4±573．6 t／a,约占太湖磷入湖量的1／4-1／2,其中成汇通量约为-91．2±42．4 t/a．     

Ni isotope fractionation during coprecipitation of Fe(III)(oxyhydr)oxides in Si solutions

The dramatic decline in aqueous Ni concentrations in the Archean oceans during the Great Oxygenation Event is evident in declining solid phase Ni concentrations in Banded Iron Formations (BIFs) at the time. Several experiments have been performed to identify the main removal mechanisms of Ni from seawater into BIFs, whereby adsorption of Ni onto ferrihydrites has shown to be an efficient process. Ni isotopic measurements have shown limited isotopic fraction during this process, however, most experiments have been conducted in simple solutions containing varying proportions of dissolved Fe and Ni as NO₃ salts, as opposed to Cl salts which are dominant in seawater. Further, Archean oceans were, before the advent of siliceous eukaryotes, likely saturated with amorphous Si as seen in the interlayered chert layers within BIFs. Despite Si being shown to greatly affect the Ni elemental partitioning onto ferrihydrite solids, no studies have been made on the effects of Si on the Ni isotope fractionation. Here we report results of multiple coprecipitation experiments where ferrihydrite precipitated in mixed solutions with Ni and Si. Ni concentrations in the experiments ranged between 200 and 4000 nM for fixed concentrations of Si at either 0, 0.67 or 2.2 mM. The results show that Si at these concentrations has a limited effect on the Ni isotope fractionation during coprecipitation of ferrihydrite. At 0.67 mM, the saturation concentration of cristobalite, the isotopic fractionation factors between the precipitating solid and experimental fluid are identical to experiments not containing Si (0.34 ± 0.17‰). At 2.2 mM Si, and the saturation concentration of amorphous silica, however, the Ni isotopic composition of the ferrihydrite solids deviate to more negative values and show a larger variation than at low or no Si, and some samples show fractionation of up to 0.5‰. Despite this seemingly more unstable fractionation behaviour, the combined results indicate that even at as high concentrations of Si as 2.2 mM, the δ⁶⁰Ni values of the forming ferrihydrites does not change much. The results of our study implicate that Si may not be a major factor in fractionating stable Ni isotopes, which would make it easier to interpret future BIF record and reconstruct Archean ocean chemistry.     

Fractal properties of multi-order folding as a tool for exploration of low-grade banded iron ores in the Krivoy Rog basin (Ukraine)

The low-grade Palaeoproterozoic stratabound banded iron ores of the Krivoy Rog basin (Ukraine) underwent strong tectonometamorphic deformation into superimposed folds of several orders, with amplitudes from centimetres to hundreds of metres. The across-strike sections of bed surfaces defining the low-grade ore bodies resemble self-similar fractal curves; hence, a fractal geometrical model was developed in order to quantify the complexity and sinuosity of bed contours. Two different methods of measurement (polygonal approximation and two-dimensional grid cell counting) were used for 5–8 different scales. Factual similarity dimension D and other model parameters have been estimated by means of linear regression and compared for both measurement methods. From the fractal model a sinuosity coefficient of contours of the folded bed surfaces K _s and a coefficient of degree of exploration of iron ore bodies K _e were constructed. It is pointed out that parameters of the model can be used for determination of the optimal exploration length scales.     

论合理开发利用舞阳铁矿的几个问题

舞阳铁矿系指位于河南省平顶山市所辖舞钢市区内含铁矿大小共计１２处的一群铁矿区,总储量占河南省铁矿探明储量的５３％,主要有铁山（含铁古坑、铁山庙）、八台（含赵案庄、王道行）及经山寺等大、中型铁矿区。矿床类型主要为沉积变质型,次为岩浆型;区内铁矿品位不高,主要矿物为磁铁矿及部分赤铁矿。在阐述资源概况及建矿历程的基础上,对如何合理开发利用舞阳铁矿,重点就矿区的规划,红矿的利用,磷、铀的综合利用,矿产开发对环境的影响,以及矿山开发管理等问题进行了较为详细的论述,提出了相应的对策建议     

南极大陆沿岸地面臭氧损耗事件的研究

利用南极大陆沿岸中山站2008-2013年的地面臭氧连续观测数据和相关资料,对地面臭氧损耗事件（ODE）进行研究。结果显示,春季南极中山站常发生臭氧损耗事件。在该事件发生期间,气象要素有明显的突变过程,包括气温明显下降,风向由偏东风转变为偏北风,风速随之下降。来自海冰区的偏北风增多,风速很小,使臭氧浓度维持在较低水平。地面臭氧损耗事件主要与南极沿岸海冰区的活性溴（BrO）浓度有关。春季南极大陆沿岸海冰冻融过程中形成的冰间水道和冰间湖,在低温的作用下会再次冻结,形成薄冰和霜花。卫星资料能够观测到薄冰区释放的活化海盐溴高浓度区,活性溴与臭氧发生化学反应形成地面臭氧损耗事件。臭氧损耗现象是在未受到人为影响的自然状态下发生的,与中高纬度地区光化学反应导致臭氧消耗有所不同。      

白云鄂博铌、稀土铁矿的成矿地质条件及矿床成因

白云鄂博矿区的铁矿和铌、稀土矿分属两个成矿期和两种不同的成因。铁矿是中元古界蓟县系哈拉霍疙特组内的层控受变质铁矿，赋存在宽沟南侧的层状白云岩中，该白云岩及铁矿层是在两条同生断裂所控槽状泻湖中沉积的。除白云岩外，宽沟南北两侧地层均可对比，同属白云鄂博群。铁矿层的原生矿物为以菱铁矿为主的FeCO3－MgCO3系列矿物，受后期侵入岩的热变质作用转变为磁铁矿及赤铁矿。铌、稀土成矿作用与脉状、瘤状碳酸岩有关。矿区已发现该类脉岩40余条，可分为白云石质及方解石质两类，以前者为主。两类碳酸岩的稀土元素特征均为轻稀土高度富集型，铕弱亏损到富集，其来源较深碳酸岩体沿断裂侵入造成强烈而广阔的碱交代蚀变带，以霓长石化为主，其强度与稀土矿化强度呈正相关关系。推测矿区在不大的深度内赋存有较大的隐伏碳酸岩侵入体。     

秘鲁邦沟铁多金属矿地质特征及成矿阶段划分

秘鲁首都利马至查拉400km沿海成矿带赋存多处铁、铜、金矿床,铜金矿床具有IOCG(铁氧化物)型,铁矿多为矽卡岩型。邦沟铁多金属矿规模巨大,矿床位于西科迪勒拉山西部边缘的伊卡-纳斯卡拗陷附近。矿床类型既有矽卡岩特征,也具有IOCG特点。总结矿床地质特征认为,邦沟铁和多金属矿矿化存在同期不同阶段的特点,铁矿化发生在第一期,铜金硫化物矿化发生在第二期;铜金硫化物在空间上与主铁矿体异位,铜金矿有较大找矿潜力。     

条带状铁建造（BIF）的形成时代及其研究方法

对条带状铁建造（BIF）进行精确的年代学约束,具有非常重要的科学意义,可以获得BIF的时间分布趋势,反映对应时代的大气和海洋环境,准确建立与重大地质事件的对应关系,为铁建造的成因提供依据。本文在综合前人资料的基础上,重新绘制了全球BIF形成时代的分布图,结果表明BIF在3.6～1.6 Ga连续分布,在2.8～2.7 Ga、 2.5～2.4 Ga、 1.9～1.8 Ga的3个区间范围内形成高峰;Algoma型BIF主要集中于中-晚太古代,而Superior型BIF主要出现在古元古代。本文重点对前人关于BIF年代学的测试方法及其应用进行了介绍和评述,结果表明目前锆石U-Pb测年法依然为主要手段,而Sm-Nd等时线法和Re-Os等时线法尽管有效,但直接测定BIF条带的Sm-Nd等时线和磁铁矿的Re-Os等时线年龄仍存在较大问题,但可用来反映物质的来源以及后期构造热事件的改造等问题,而采取BIF相关单元的年龄来间接代表BIF的形成年龄是目前较为成熟的方法,其中测定铁建造火山岩夹层锆石U-Pb年龄是国际上测定BIF时代常用的手段。     

矿浆型铁矿的氧同位素判别标志:以宁芜玢岩铁矿为例

自然界是否存在矿浆型铁矿以及如何判别矿浆型铁矿是地质学家争论探索了几十年的问题。大量地质现象和实验研究证实,中酸性岩浆在高氧逸度、富磷等挥发分和助熔剂的条件下,硅酸盐熔体与铁氧化物熔体之间可以发生液态不混熔,熔离出富铁氧化物熔体或富铁岩浆。但有些学者认为实验无法直接一次性熔离出高品位铁矿浆,因此不存在矿浆型铁矿。实际上,高品位富铁矿浆可能是经过多次熔离富集形成的,而非一次简单熔离完成;磁铁矿中钛含量偏低,可能与矿浆型铁矿遭受后期热液改造、钛大量丢失有关,最典型的例子莫过于智利拉科铁矿。长江中下游玢岩铁矿是我国重要铁矿资源类型,其中是否发育矿浆型铁矿也一直存在激烈争论。为了避免不必要的争议,本文将铁矿浆限定为由岩浆熔离形成的铁氧化物浓度30%的富铁熔体,由铁矿浆演化形成的铁矿床称为矿浆型铁矿。根据宁芜成矿岩体中锆石的钛温度计确定了岩浆的温度,根据锆石的氧同位素组成及磁铁矿与锆石之间的氧同位素分馏方程,计算出岩浆温度下直接从熔体中熔离出来的磁铁矿的δ~(18)O_(Mt)值为4.2‰。据此建立了宁芜玢岩铁矿中矿浆型铁矿的氧同位素判别标志,如果矿体中磁铁矿的δ~(18)O_(Mt)≥4.0‰,则为矿浆型铁矿,否则为热液型或浆-液过渡型铁矿。判别结果表明,钟姑山矿田矿浆型和热液型矿体同时存在,梅山铁矿介于矿浆型-热液型之间,而凹山矿田铁矿则为热液型,与野外观测及前人研究结果一致。