Grain-Size Distribution of Detrital Sediment in the Amami Sankaku Basin Since Late Pleistocene and Its Provenance and Palaeoclimate Implications

The grain size composition of detrital sediments in Hole U1438A from the Amami Sankaku Basin(ASB) in the northwest of the Philippine Sea since the last 350 ka was analyzed. The result shows that the mean grain size of the detrital sediment is about 13.1 μm, ranging from 0.04 to 160 μm. The grain size distribution displays a four-peak pattern and positive skewness. Four independent grain size components were separated by using Weibull distribution function. The ultra-fine component varies from 0.04 to 0.9 μm, with a size mode at about 0.3 μm, which may be genetically related to marine authigenetic clay. The fine-grained fraction ranges from 0.2 to 32 μm, with a size mode at about 3.5 μm, and slightly coarser than the eolian dust of the North Pacific. We argued that this fraction was mainly derived from Asian dust. The coarse-grained and ultra-coarse-grained fractions show distinct size mode at about 10 μm and 40 μm, and range from 0.3 to 90 μm, and from 3 to 160 μm respectively. Both the coarse and ultra-coarse components represent volcanic materials which were mainly derived from the ridges and islands around ASB. The variation of the ratio of environmentally sensitive size population 1.3~2.2 μm/28~40 μm was similar with the ratio of fine-sized component (Asian dust) and coarse-sized component (volcanic material) (0.9~3 μm/>10 μm), showing higher value during glacial period than that during interglacial, which is also identical with the variation of the mass accumulation of eolian dust in the North Pacific and Chinese Loess Plateau, and grain size in Chinese Loess Plateau. The increased ratio responded to the enhanced aridity of Asian continent and strengthened East Asia Winter Monsoon (EAWM)/westerly during glacial period. We argued that the increase of eolian fraction was driven by the enhanced aridity of Asian continent and strengthened East Asia Winter Monsoon (EAWM)/westerly during glacial period. Therefore, the ratio of 0.9~3 μm/>10 μm can be used as a proxy of the increased aridity and enhanced atmospheric circulation of Asian continent. These results suggest that the grain size composition of the detrial sediment in the ASB can be used to reconstruct the history of Asian aridity and atmospheric circulation.     

云南金顶异极矿晶体化学特征与颜色成因探讨

为研究云南金顶铅锌矿床中异极矿谱学特征和颜色成因,利用湿法化学全分析、振动光谱仪、X光粉晶衍射仪和电子探针对5组异极矿样品谱学特征和化学成份进行研究。湿法化学全分析得出了异极矿的化学成份,成份中出现了可能致色的铜、铁和镍元素;X光粉晶衍射和振动光谱分析得出异极矿晶胞参数和特征谱线表明样品蓝色和白色环带均为异极矿,5组样品的平均晶胞参数为：a=0．8372nm,b=1．0702nm,c=0．5116nm;红外光谱测试中获得了未见报道的452cm。以下异极矿晶体结构吸收峰,同时分析了异极矿中的结构水、结晶水吸收谱带;对红外光谱和拉曼光谱中的各吸收谱带和特征峰进行了归属。通过电子探针、红外光谱、拉曼光谱测试和分析认为异极矿的蓝色与Cu^2＋的类质同像替代有关,白色异极矿不含铜元素,白色和蓝色异极矿结构相似,异极矿玻璃光泽和土状光泽与其含有较多的结晶水有关。     

具磷灰石假象绿松石的热性能

绿松石的热性能分析在对其水的结构特征、呈色机理等的研究中具有重要指示作用.采用热重-差热分析(TG-DSC)、红外光谱(IR)和X-射线粉晶衍射(XRD) 分析方法, 对安徽马鞍山具磷灰石假象绿松石的热性能特征进行了研究.研究结果显示从室温到1100℃, 假象绿松石的热相变可划分为6个变化阶段: 100~200℃时, 为吸附水脱水阶段; 250~330℃, 假象绿松石中羟基和晶格水分子脱失; 330~750℃为非晶态物相阶段; 约750℃时为新物相形成阶段; 750~1100℃为具磷石英结构磷酸铝的形成阶段; 1100℃时磷酸铝的结晶有序度增加.假象绿松石结构及水的存在形式、总量和结合方式制约和影响着颜色的变化.      

方解石-白云石-菱镁矿的中远红外光谱学特征研究

利用拉曼光谱和红外光谱研究了方解石、白云石和菱镁矿的光谱学特征,探究了影响三种矿物红外辐射性能的因素。三种矿物的拉曼光谱(Raman)、中红外吸收光谱(MIR)、远红外吸收光谱(FIR)显示随着矿物中镁含量的增大将会影响CO₃^2-的面外弯曲振动(ν₂)、反对称伸缩振动(ν₃)和平面内弯曲振动(ν₄),使各光谱特征峰均向高频端迁移。基于黑体辐射定律以及在80 ℃、400~2 000 cm^-1矿物的辐射能量谱,结果显示方解石、白云石、菱镁矿的发射率依次减少(0.951,0.938,0.895)。三种矿物的红外吸收光谱和发射光谱中的振动位置均受CO₃^2-基频的显著影响,在1 300~1 650 cm^-1均产生宽的低吸收带,该吸收带与CO₃^2-的反对称伸缩振动相关,且吸收带范围(202,236,272 cm^-1)与发射率之间呈负相关关系。因此,当最强化学键的振动出现在发射光谱窄的吸收带范围内会产生相对较高的辐射能和发射率。此外,矿物的晶体结构也会影响发射率,大的离子半径、键长和晶胞体积将降低辐射过程中能量的吸收,增强辐射特性。综上研究结果,方解石、白云石和菱镁矿的拉曼光谱和红外光谱揭示了金属原子的相对质量对光谱学特征的显著影响,其发射率可能受到C—O键的反伸缩振动范围、最强吸收带控制的最低发射率以及矿物晶体结构的共同影响。这项研究呈现了必要的光谱信息和热发射率数据以识别特定的碳酸盐矿物,为类似矿物的光谱特征研究奠定了基础;同时为进一步认识地壳中大量的碳酸盐矿物提供了研究方法,也为地外勘探的深入研究给予相关的理论基础。     

Stream-scanning laser system, electric sensing counter and settling grain size analysis: a comparison using reference materials and marine sediments

Surface and deep-sea core sediments and two sets of standards were measured by three different techniques — Galai Cis-1 laser system, Coulter Counter TA II, and Micromeritics SediGraph 5000D — in order to compare the Galai results with the other two. The differences between the three types of measuring device turned out to be greater in sediments than in standards, and were attributed to the physical properties, shape, density and composition of the particles (complexity of the matrix). Comparison of moment statistics showed that the Galai determines coarser grain sizes than the Coulter and finer than the SediGraph, particularly as regards analysis of surface sediments. The relationships between Galai and SediGraph were estimated using analysis of variation/residuals within individual intervals. The analysis showed a higher variability of residuals for the coarser fractions (8–16 μm and 16–32 μm) with respect to the finer (2–4 μm and 4–8 μm) fractions. The <2 μm SediGraph fraction, with a cut-off at 0.49 μm, showed good correspondence with the <2.5 μm Galai analysis.     

黔中息烽磷矿床成矿环境、成矿作用及成矿模式探讨*

息烽磷矿是贵州地区震旦纪陡山沱期磷矿的重要组成部分,以矿层厚、品位高、断裂构造发育、叠层石丰富而独具特色。通过对矿床地质特征及矿床地球化学特征综合研究认为,从陡山沱组底到顶气候经历温湿—干热—湿热变化,海平面对应经历了海进—海退—海进,其内的磷块岩和磷质岩是在热水沉积作用、生物作用和正常海水沉积作用等共同作用下形成于前滨—临滨环境。综合以上,反演息烽陡山沱期成矿过程,发现矿床经历了“海进—海退—海进”三阶段成矿,在陡山沱早期海进阶段形成下矿层,随后的海退阶段和海进阶段形成上矿层。空间上,2矿层之间夹白云岩,且交于靠黔中古陆一侧,当第2次海进越过第1次海进的前滨—临滨位置后,只形成上矿层,是开阳、息烽磷矿床1层矿体形成的对应部位。瓮福磷矿床有2层矿体,对应处于经历了“三阶段成矿”的前滨—临滨部位,且瓮福磷矿成矿时的位置高程明显低于息烽磷矿、息烽磷矿略低于开阳磷矿,通过岩性特征对比,与实际基本吻合。因此,在对陡山沱期的磷矿进行成矿预测和找矿勘查中,与息烽磷矿床相似的黔中及附近区域的动态前滨—临滨环境,均为磷矿床的找矿靶区,利用“三阶段成矿”形成相交的2矿层特点,可高效对已知矿床、矿化点和前滨—临滨带周围进行成矿预测。     

塔河油田奥陶系生物扰动碳酸盐岩储集层微观孔隙结构的数字化表征与连通性分析*

塔河油田奥陶系鹰山组和一间房组发育大规模生物扰动碳酸盐岩储集层。在岩心观测和详细描述的基础上,通过岩石薄片的偏光显微镜、阴极发光显微镜观测和柱塞样品的X射线显微镜扫描与分析,实现了塔河油田奥陶系生物扰动碳酸盐岩储集层孔隙结构的数字化表征与连通性分析。结果表明: (1)由于生物扰动区潜穴充填物和围岩基质的岩石组构差异大,使这类储集层呈现极强的非均质性。(2)生物潜穴充填物主要由白云石晶体组成,白云石晶体以自形、半自形晶体为主;白云石晶间孔隙发育,孔隙体积集中于10~100μm³,喉道半径一般小于10μm,喉道长度一般小于40μm,白云石晶间孔为这类储集层的主要储集空间,围岩基质孔隙不发育。(3)生物潜穴充填物孔隙度介于7%~10%,孤立孔隙虽然数量多,但连通孔隙体积占比大,且连通孔隙拓扑结构复杂,孔隙连通性很好;通过表征单元体的尺度粗化升级分析发现,这类储集层的孔隙局部连通较好,而整体连通性相对较差。该研究真实、直观、准确刻画了生物扰动碳酸盐岩储集层微观孔隙结构特征,可为后续这类生物扰动碳酸盐岩储集层的微观渗流模拟研究提供所需的特征参数;未来将这类生物扰动碳酸盐岩储集层微观尺度上的孔隙结构数字化表征和渗流模拟结果与宏观分布规律相结合并应用到实际储集层评价中,可为这类储集层的油气资源量估算、开发方案优选、产能预测和提高采收率提供指导。     

碳氟磷灰石的红外吸收光谱

众所周知,磷灰石族矿物是很复杂的一族矿物,在磷灰石结构内可以有多种类质同象置换,而其基本结构并无重大改变,因而它的结晶学的研究是一项复杂的任务。至今,对磷灰石的结晶学问题了解得还不很清楚,在沉积岩中分布最广、颗粒细小而又具经济价值的碳氟磷灰石所引起的争论最为激烈,关于磷灰石中(CO₃)^2-离子的存在形式,是长期以来进行争论的问题。本文主要就作者所做磷灰石的红外吸收光谱工作,并引用晶胞常数和化学分析数据,对此问题进行讨论。     

Overcoming problems of density and thickness measurements in FTIR volatile determinations: a spectroscopic approach

The Beer–Lambert law is traditionally used to determine water and carbon concentrations in glasses from their infrared (IR) spectra. In practice, this method requires estimation of the thickness and density of the glass as well as the calibration of the molecular absorptivities of the species concerned. All of these parameters can be sources of practical difficulties and analytical uncertainty. These weaknesses in the application of the Beer–Lambert law have been overcome by an empirical analysis of the infrared spectra. Using a set of 292 spectra obtained on 113 natural and experimental tholeiitic glasses (SiO₂ 48.5–51 wt%; water contents 0–4000 ppm H₂O), it can be shown that the thickness–density (ρ d) product of a glass sample can be directly and reliably inferred from its IR spectrum. This allows the Beer–Lambert law to be rewritten. The new form no longer requires thickness or density estimations to determine volatile contents. Moreover, if needed, the thickness of the glass slab can also be accurately determined from the IR spectra. This new method is developed for quantitative determination of water concentrations in MORB glasses but can also be applied to any minor species (carbon, sulfur, etc.) provided it is active in the IR domain and that a suitable independent frequency of IR absorption can be identified. Precision is about 60 ppm H₂O on O–H⁻ contents. This method, tested on natural and experimental MORB-type glasses, can be applied to any chemical composition provided a set of reference spectra is available. Received: 16 September 1999 / Accepted: 18 February 2000     

基于岩性相单元和孔隙结构的低孔低渗储层有效性测井识别方法:以西湖凹陷NB1构造为例

东海西湖凹陷是近海最大的盆地之一,近些年在中深层花港组储层中获得重大发现.然而,由于储层具有厚度大、非均质性强、低孔低渗、孔隙结构复杂等特征,给精细评价和甜点储层的预测带来极大困难.利用高分辨率电成像资料,在岩性和层理构造识别的基础上,将研究区储层划分成槽状交错层理细中砂岩、板状交错层理细中砂岩、槽状交错层理细砂岩、板...     

Relationship between sediments and their igneous source rocks using clay mineral multi-element chemistry: the Cenozoic lacustrine Anloua basin (Adamaoua, Cameroon)

The Cenozoic lacustrine basin of Anloua (Adamaoua, Cameroon), is filled with the weathering products of the surrounding rocks. In order to determine the origin of these sediments, multi-element, especially trace element, analysis of their < 2 μm fraction was undertaken. The chemical compositions of these fractions were compared with those of the rocks surrounding the basin by multivariate statistical analysis and also graphically. A principal component analysis allowed the most discriminant elements to be selected, and a hierarchical ascending classification (HAC) made with these elements divided the samples into groups. Some of these groups contain < 2 μm fractions of both the lake sediments and surrounding rocks. These sediments are determined as deriving by weathering from the surrounding rocks. Some of the other groups contain no samples from the surrounding rocks and their petrographic origin cannot be given. A graphic comparison of the relative amounts of the elements (determined by HAC) from the < 2 μm fractions of the various groups and the rocks surrounding the basin allowed attribution of a petrographic origin for the various sediments analysed by using the fit between the curves.

The clay mineralogy, the amounts of Ti, Zr, and heavy minerals in the < 2 μm fractions and their distribution in the area studied, as well as the presence of angular quartzite pebbles in some sediments gives an indication of the paleogeography of the Anloua basin. There was deltaic input towards the north and a high energy input, possibly torrential, to the west.     

电气石红外光谱和红外辐射特性的研究

精确测试和研究了不同种属电气石的红外光谱特征及不同种属、不同温度条件下热处理电气石的红外辐射特性。结果表明：电气石具有高红外发射率的本质在于其晶体结构中的分子振动具红外活性;铁、镁电气石红外发射率相近,且都大于锂电气石的红外发射率;电气石热处理的温度与红外发射率之间存在一定的对应关系,随着热处理的温度的增加,红外发射率减小,当温度增大到800℃红外发射率达到最大值,超过900℃,电气石开始分解,红外发射率开始下降;电气石在室温下最大单色辐出度相应的波长为9~10μm 与绝对黑体9.72 μm 吻合较好,为良好的红外吸收与发射材料。     

南极半岛西摩岛始新世拉揭塞塔组Teredolites遗迹化石研究

Teredolites遗迹化石是一类赋存于海相地层中的以木质基底为特征的钻孔遗迹组合,是由海相钻木类双壳动物(如船蛆、海笋等)寄生于漂浮或沉入海洋的树干中形成。Teredolites遗迹化石可指示浅海沉积环境,提供寄生木材的分类信息、古地理信息以及埋藏过程中的环境信息。本文研究了南极半岛西摩岛拉揭塞塔组顶部首次发现的一例Teredolites longissimus(Apectoichnus longissimus)遗迹化石,层位时代为晚始新世,根据木基底内保存的船蛆化石的发育特征和分布特征,确定本例为船蛆幼年群体对木基底的初期感染形成的钻孔遗迹。利用场发射扫描电镜(FESEM)和X射线能谱仪(EDS)对基底木化石和船蛆化石进行深入研究分析,将本例Teredolites遗迹化石的基底木化石定为裸子植物罗汉松科(Podocarpaceae)叶枝杉型木属未定种(Phyllocladoxylon sp.),证实了叶枝杉型木属在西摩岛上的分布延续至始新世晚期;船蛆化石内部赋存大量草莓状黄铁矿,其中粒径超过10 μm的草莓状黄铁矿占比达39.2%,最大粒径达到44 μm,粒径的统计和分析显示其形成于氧化水体沉积环境,证明始新世晚期南极半岛地区古海洋处于氧化海状态。     

Crystal chemistry of suspended matter in a tropical hydrosystem, Nyong basin (Cameroon, Africa)

Suspended matter (SM) from the Nyong basin (Cameroon, Africa), a tropical watershed, was collected by tangential flow ultrafiltration to separate particulate (>0.45 μm) and colloidal (<0.45 μm; >20 kDa) fractions. In this basin, two distinctive systems in a selected small catchment (Nsimi–Zoétélé) of the Nyong river basin have been considered: (i) colourless water (groundwater and spring) with a low suspended load (<3 mg/l) and a low total organic carbon content (TOC<1 mg/l) and (ii) coloured water (Mengong brook and Nyong river), which is organic rich (TOC>10 mg/l) and contains higher amounts of SM (10–20 mg/l) than the colourless water. Freeze-dried samples of SM have been analysed by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), electron paramagnetic resonance spectroscopy (EPR), and visible diffuse reflectance spectroscopy (DRS).

Colourless water mainly contains mineral phases, such as poorly ordered kaolinite, plus quartz and goethite in the particulate fraction, and euhedral kaolinite plus amorphous iron oxyhydroxides in the colloidal fraction. In contrast, the SM in coloured water is mainly organic in nature. The mineral phases in the particulate fraction are similar to those from clear water, but with additional phytoliths and diatom frustules composed of biogenic opal. In the colloidal fraction, complexation of Fe³⁺ and Mn²⁺ with organic matter is evidenced by EPR, together with significant occurrence of Fe oxyhydroxides associated with organic matter.

The sites of Al, Si, Fe, Mn in colloidal fractions derived from spectroscopic analyses are discussed with reference to chemical analyses performed by inductively coupled plasma mass spectrometry. Most of the observed solid phases or species correspond to those expected from published thermodynamic calculations for the same hydrosystem, except the colloidal iron oxyhydroxides in the coloured water. The presence of such iron phases is emphasised since they are expected to have large sorption capacities for numerous trace elements.

The crystal chemistry of SM is used to discuss the origin of the mineral particles transported from the soil to the main rivers in terms of mechanical and chemical erosion processes.     

沉积磷灰石形成中的生物有机质因素

本文研究了黔中磷块岩中磷灰石的化学成分、红外光谱、碳和硫同位素组成以及伴生微量元素和稀土元素地球化学特征,获得了若干生物有机质成因的证据.磷灰石红外光谱特征表明CO₃^2-和SO₄^2-以类质同象部分替代PO₄^2-而进入磷灰石晶格,而碳、硫同位素特征表明,这CO₃^2-及SO₄^2-的相当部分是由生物有机质分解演化而来;叠层石磷灰石的P₂O₅含量与亲生物微量元素关系非常密切,而非叠层石者关系不甚密切;稀土元素地球化学特征表明,磷灰石的形成具有两种既有联系又各不相同的作用机制,即直接的生物作用和间接的有机质作用.     

构建红外光谱显微系统实验平台——原位模拟物质反应动力学过程

本项目通过对商用布鲁克Vertex 70v真空型红外光谱仪进行拓展,来构建一套水平红外光路的系统,并与红宝石测压系统、外加温温控系统联用,适用于高压、高/低温测量的傅立叶变换红外显微系统,从而真正实现在原位条件下观察与研究地球内部物质的性质和结构特征的实验平台。在此平台上,模拟并观察在俯冲带中不同深度(温压)环境下的绿帘石红外光谱特征,同时结合拉曼光谱特征,了解晶体结构和晶体化学的稳定性、水溶解度、高压化学和高压物理学现象,从而窥视洋壳/陆壳俯冲全过程中矿物物理化学性质及其水循环的动力学演化。     

青藏高原东缘湖相沉积和黄土高原黄土沉积磁化率与粒度相关性对比*

为探讨构造稳定地区(如黄土高原)和构造活跃地区(如青藏高原东缘)粉尘沉积物中磁化率(SUS)与粒度的相关性及其对环境事件的指示意义,本次研究分析了黄土高原蓝田剖面黄土—古土壤样品和青藏高原东缘湖相沉积样品的粒度和磁化率记录。黄土高原黄土—古土壤沉积SUS与2~10 μm粒度组分最强正相关,青藏高原东缘湖相沉积的SUS与2~10 μm粒度组分最强负相关,反映2~10 μm粒度组分为黄土高原和青藏高原乃至亚洲干旱—半干旱地区连续稳定敏感的背景沉积组分。黄土高原黄土—古土壤沉积的SUS与32~63 μm粒度组分最强负相关,青藏高原东缘湖相沉积的SUS与32~63 μm粒度组分最强正相关,反映32~63 μm粒度组分不仅是黄土高原尘暴事件沉积的敏感指标,也是青藏高原东缘湖相沉积记录的地震事件敏感指标。SUS与粒度组分的相关性在青藏高原东缘地区地震事件层开始部分高于结束部分,也较好地反映地震事件为研究区添加新鲜沉积物后随地形地貌恢复逐步减少的过程。SUS与粒度组分相关性也受当地物源的影响。     

青藏高原东缘湖相沉积和黄土高原黄土沉积磁化率与粒度相关性对比*

为探讨构造稳定地区(如黄土高原)和构造活跃地区(如青藏高原东缘)粉尘沉积物中磁化率(SUS)与粒度的相关性及其对环境事件的指示意义,本次研究分析了黄土高原蓝田剖面黄土—古土壤样品和青藏高原东缘湖相沉积样品的粒度和磁化率记录。黄土高原黄土—古土壤沉积SUS与2~10 μm粒度组分最强正相关,青藏高原东缘湖相沉积的SUS与2~10 μm粒度组分最强负相关,反映2~10 μm粒度组分为黄土高原和青藏高原乃至亚洲干旱—半干旱地区连续稳定敏感的背景沉积组分。黄土高原黄土—古土壤沉积的SUS与32~63 μm粒度组分最强负相关,青藏高原东缘湖相沉积的SUS与32~63 μm粒度组分最强正相关,反映32~63 μm粒度组分不仅是黄土高原尘暴事件沉积的敏感指标,也是青藏高原东缘湖相沉积记录的地震事件敏感指标。SUS与粒度组分的相关性在青藏高原东缘地区地震事件层开始部分高于结束部分,也较好地反映地震事件为研究区添加新鲜沉积物后随地形地貌恢复逐步减少的过程。SUS与粒度组分相关性也受当地物源的影响。     

景德镇地区高岭石红外光谱分析

采用红外光谱实验结合氢氟酸化学处理方法深入研究景德镇地区高岭石结构特征。通过解析红外光谱图确定该区高岭石为无序高岭石范畴,其结构中含有似地开石结构BCBCBC的八面体空位取代。通过对比氢氟酸处理前后的红外图谱,分析出该地区高岭土不含有地开石和珍珠石这两种多型。实验表明红外光谱分析对高岭土中存在的次要矿物伊利石不灵敏,而利用氢氟酸处理可以有效地鉴别,因而提出了一种利用红外光谱鉴定高岭石-伊利石混合物相的新方法。     

Variation in element release rate from different mineral size fractions from the B horizon of a granitic podzol

Far-from-equilibrium batch dissolution experiments were carried out on the 2000–500, 500–250, 250–53 and 53–2 μm size fractions of the mineral component of the B horizon of a granitic iron humus podzol after removal of organic matter and secondary precipitates. The different size fractions were mineralogically and chemically similar, the main minerals present being quartz, alkali and plagioclase feldspar, biotite and chlorite. Specific surface area increased with decreasing grain size. The measured element release rates decreased in the order 53–2>>>2000–500>500–250>250–53 μm. Surface area normalised element release rates from the 2000–500, 500–250 and 250–53 μm size fractions (0.6–77×10⁻¹⁴ mol/m²/s) were intermediate between literature reported surface area normalised dissolution rates for monomineralic powders of feldspar (0.1–0.01×10⁻¹⁴ mol/m²/s) and sheet silicates (100×10⁻¹⁴ mol/m²/s) dissolving under similar conditions. Element release rates from the 53–2 μm fraction (400–3000×10⁻¹⁴ mol/m²/s) were a factor of 4–30 larger than literature reported values for sheet silicates. The large element release rate of the 53–2 μm fraction means that, despite the small mass fraction of 53–2 μm sized particles present in the soil, dissolution of this fraction is the most important for element release into the soil. A theoretical model predicted similar (within a factor of <2) bulk element release rates for all the mineral powders if observed thicknesses of sheet silicate grains were used as input parameters. Decreasing element release rates with decreasing grain size were only predicted if the thickness of sheet silicates in the powders was held constant. A significantly larger release rate for the 53–2 μm fraction relative to the other size fractions was only predicted if either surface roughness was set several orders of magnitude higher for sheet silicates and several orders of magnitude lower for quartz and feldspars in the 53–2 μm fraction compared to the other size fractions or if the sheet silicate thickness input in the 53–2 μm fraction was set unrealistically low. It is therefore hypothesised that the reason for the unpredicted large release rate from the 52–3 μm size fraction is due to one or more of the following reasons: (1) the greater reactivity of the smaller particles due to surface free energy effects, (2) the lack of proportionality between the BET surface area used to normalise the release rates and the actual reactive surface area of the grains and, (3) the presence of traces quantities of reactive minerals which were undetected in the 53–2 μm fraction but were entirely absent in the coarser fractions.