Zeolites--A Potential New Tool for Environmental Studies? Isotope and Elemental Studies of Zeolites

该提案描述了一个为期三年的项目，研究天然沸石及其与环境变化的关系。由于沸石与环境之间的交换速率受到许多因素的影响，我们的方法包括从许多不同的环境中收集样品，并使用化学和同位素示踪剂，这些示踪剂对各种环境因素的响应具有不同的灵敏度。这些示踪剂是氧、氢和氮的同位素组成，K/Ar测年，以及主要和微量元素。由于两个原因，我们最初的努力将集中在Yucca山钻探岩心样本上。首先，沸石、黏土矿物氧同位素组成和K/Ar测年的初步结果为项目的可行性提供了非常肯定的指示。氧同位素组成表明，尤卡山斜沸石与当前温度和流体条件不平衡。结果也暗示了确定自沸石形成以来地下水位变化的可能性。第二个也是一个明显的原因是，由于对该国第一个高水平核废料处置库的场址进行了定性工作，因此对该场址进行了大量的跨学科研究。还将取样若干其他含沸石的单位进行比较研究。这些单元将包括俄勒冈州的John Day组，加利福尼亚州Inyo县的Barstow组，Mud Hills和Lake Tecopa，以及中国东北的一些沸石矿床。这些遗址在年龄、成岩历史和水文环境方面各不相同，可以与尤卡山遗址进行比较。对于每种示踪剂，我们将研究沸石和其他自生矿物的矿物分离，这些矿物的交换性要小得多，如长石和粘土矿物。这些可交换性较低的矿物可被认为保存了地层信息，并可用于推导沸石形成时的条件和环境（温度、流体的化学和同位素组成）。如果我们假设所有自生矿物都是在同一时间、同一流体中形成的，那么沸石目前的组成可能与其形成后发生的环境变化有关。对于沸石，如果可能的话，我们还将研究不同大小馏分的化学和同位素组成。这将有助于我们了解沸石与流体之间的交换机制（扩散与再结晶），并确定沸石是否与当前孔隙流体在当前温度下达到平衡。将进行实验研究，了解沸石与环境流体之间的化学和同位素交换机制，并确定从天然沸石的分析数据中量化交换速率所需的物理常数（如扩散系数和速率常数）。

Feng 9628402 This proposal describes a three year project that studies natural zeolites and their relationship to environmental change. Since the exchange rate between zeolite and the environment is affected by many factors, our approach includes collecting samples from a number of different environments and using chemical and isotope tracers that respond to various environmental factors with different sensitivity. These tracers are oxygen, hydrogen and nitrogen isotopic compositions, K/Ar dating, and major and trace elements. Our initial efforts will be focused on Yucca Mountain drill core samples for two reasons. First, preliminary results on oxygen isotopic compositions of zeolites and clay minerals and the K/Ar dates have provided very affirmed indication for the feasibility of the project. Oxygen isotope compositions show that clinoptilolite from Yucca Mountains is out of equilibrium with the current temperature and fluid conditions. The results also imply a possibility to determine groundwater level variations since zeolite formation. The second and an obvious reason is that there has been a great amount of interdisciplinary research done for the site as a result of the site characterization efforts of the nation's first high-level nuclear wastes repository. A number of other zeolite-containing units will also be sampled to do a comparative study. These units will include the John Day Formation of Oregon, The Barstow Formation, Mud Hills and Lake Tecopa of Inyo County, California, and few zeolite ore deposits in Northeast China. These sites vary in age, diagenetic history and hydrological environments, and can be compared to the Yucca Mountain site. For each tracer, we will study mineral separates of zeolites and other authigenic minerals that are much less exchangeable, such as feldspars and clay minerals. These less exchangeable minerals can be considered to have preserved the formational information, and can be used to derive the conditions and environments (temperat ure and chemical and isotopic compositions of fluid) at the time of zeolite formation. If we assume that all the authigenic minerals formed at the same time and from the same fluid, the current compositions of zeolites may be related to the environmental changes occurred after their formation. For zeolites, we will also study, if possible, the chemical and isotopic compositions of different size fractions. This would help us understand the mechanisms (diffusion versus recrystallization) of exchange between zeolite and fluid, and determine whether zeolite has reached equilibrium with the current pore fluid and at the current temperature. Experimental studies will be conducted to understand the mechanism for chemical and isotopic exchange between zeolites and the environmental fluid, and to determine the physical constants (such as diffusivity and rate constants) necessary for quantifying the rate of exchange from the analytical data of natural zeoliltes.