Geochemistry of low-temperature water–rock interaction: evidence from natural waters, andesite, and iron-oxyhydroxide precipitates at Nishiki-numa iron-spring, Hokkaido, Japan
Geochemistry of low-temperature water–rock interaction: evidence from natural waters, andesite, and iron-oxyhydroxide precipitates at Nishiki-numa iron-spring, Hokkaido, Japan
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DOI：
10.1016/s0009-2541(98)00086-2
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发表时间：
1998-10
期刊：
影响因子：
3.9
通讯作者：
M. Bau;A. Usui;B. Pracejus;N. Mita;Y. Kanai;W. Irber;P. Dulski
中科院分区：
文献类型：
--
作者：
M. Bau;A. Usui;B. Pracejus;N. Mita;Y. Kanai;W. Irber;P. Dulski
从日本北海道的西ki -numa铁泉中连续两年取样，并对阴离子和30种阳离子进行了分析。酸性硫酸盐水的化学成分与过滤无关（0.2 μm - 0.8 μm），且时间变化较小。富铁水最显著的特征是高丰度的溶解稀土元素（ΣREE: 385 nM）和Y （281 nM）。球粒正态稀土和Y （REYCN， Y插入到Dy和Ho之间）模式表现出强烈的负欧几纳异常，从La到Pr略有增加，从Pr到Lu有系统地减少。泉水中的REY形态以硫酸盐络合物为主，阻止了REY系列溶液络合的显著变化。在Nishiki-numa的安山岩岩石上进行的浸出实验使我们能够表征其总元素含量的易于获取的部分。碱和碱土元素明显比U和REY更难接近，后者是所有元素中最容易接近的。这表明，在蚀变过程中经常观察到的REY的微小或可忽略的流动性几乎完全是由于含REY的次生矿物的形成。在REY系列中，从La到Nd的可达性是恒定的，从Nd到Lu的可达性是降低的，但Eu的可达性明显低于其REY相邻的可达性。这表明容易接近的元素组分不是来自造岩矿物，而是来自细粒基质中的边界膜和/或玻璃。Nishiki-numa泉水的负eucnanomy反映了这种异常低的Eu可达性。进一步比较水的组成与浸出实验的结果显示出惊人的相似性，表明在西木沼，二次相去除对大多数所研究的元素来说是次要的。例外的是Ba和U，分别因为形成重晶石和较难溶的U（IV）种。一旦泉水从表面排出，由于水合铁沉淀物的清除作用，部分元素从溶液中除去。在水合铁和弱酸性泉水（appKREYD）之间，REY的表观体积系数呈s型分布，与Y的总体趋势有很强的负偏离，表明Y从其地球化学孪生体Ho中分馏出很强。考虑到所有REY的形态形成（溶液络合）都是相似的，单个应用kreydvalue之间的差异一定与铁水合体表面官能团的络合有关。我们的数据表明，Y-Ho分馏并不局限于轻度碱性的海洋环境，而是溶解的REY与铁氧氢氧化物相互作用的典型结果。
Cold, mildly acidic, and slightly oxidizing spring water from Nishiki-numa iron-spring, Hokkaido, Japan, has been sampled in two consecutive years, and analyzed for anions and thirty cations. The chemical composition of the acid–sulphate water is independent of filtration (0.2 μm–0.8 μm), and shows only minor temporal variation. The most striking feature of the Fe-rich water is the high abundance of dissolved rare-earth elements (ΣREE: 385 nM) and Y (281 nM). Chondrite-normalized Rare-Earths and Y (REYCN; Y inserted between Dy and Ho) patterns show a strong negative EuCNanomaly, increase slightly from La to Pr, and decrease systematically from Pr to Lu. REY speciation in the spring water is dominated by sulphate complexes, preventing any significant change of the solution complexation along the REY series. Leaching experiments performed on the andesitic country-rock at Nishiki-numa allowed us to characterize the easily accessible fraction of its total element content. Alkali and alkali–earth elements are significantly less easily accessible than U and REY, the latter being the most easily accessible of all elements considered. This suggests that the often observed minor to negligible mobility of REY during alteration is almost entirely due to the formation of REY-bearing secondary minerals. Within the REY series accessibilities are constant from La to Nd and decrease from Nd to Lu, except for Eu which is considerably less easily accessible than its REY neighbours. This indicates that the easily accessible element fraction is not derived from the rock-forming minerals, but from boundary films and/or glass in the fine-grained matrix. The negative EuCNanomaly of Nishiki-numa spring water is a reflection of this anomalously low accessibility of Eu. Further comparison of water composition to results from leaching experiments shows striking similarities, suggesting that at Nishiki-numa removal by secondary phases is of minor importance for most of the elements studied. Exceptions are Ba and U, because of the formation of barite and less soluble U(IV) species, respectively. Once the spring water is expelled at the surface, elements are partially removed from solution due to scavenging by ferrihydrite precipitates. Apparent bulk coefficients for `partitioning' of REY between the ferrihydrite and the mildly acidic spring water,appKREYD, give a sigmoidal pattern with a strong negative deviation from the general trend for Y, indicating strong fractionation of Y from its geochemical twin Ho. Considering that speciation (solution complexation) is similar for all REY, the differences between the individualappKREYDvalues must be related to complexation with functional groups on the ferrihydrite surface. Our data show that Y–Ho fractionation is not confined to the mildly alkaline marine environment, but the typical result of interaction of dissolved REY with iron-oxyhydroxides.