Effects of Reactive Flow & Faults in Carbonate-Hosted Lead- Zinc Ore Formations

该提案旨在增加我们对大规模地下水流动在碳酸盐岩层控矿床形成等地质过程中的作用的基本认识。北美古老的灰岩-白云岩含水层含有大量的铅、锌、重晶石和萤石矿床，这些矿床的起源似乎与10公里至100公里的深层地下水迁移有关。在过去的二十年里，一个大型矿区一直是勘探和密集地质研究的重点：密苏里州东南部的Ozark Dome。虽然对该区的地质特征和成矿条件已经有了很多了解，但围绕成矿作用的地球化学反应、卤水运移的实际途径（含水层或断层）、成矿流体运移的机制等问题仍存在很多争议。该碳酸盐岩含矿区地质地球化学资料丰富。最近旨在了解盆地尺度的水文地质过程的工作表明，密苏里州的矿石可能是由深部地下水通过前陆盆地和靠近Ozark Dome的裂谷向上移动形成的（Garven等人，1993年），但实际的流动模式尚未在较小的尺度（l10公里）上绘制。许多地球化学模型已经被推测为在东南密苏里地区的矿石沉积，但还没有机制在一个包括流体流动和热传输影响的框架内进行测试。本提案的主要目标是使用最近开发的水文地质-地球化学建模工具来探索和比较密苏里州东南部成矿的古水文地质。此前，美国国家科学基金会支持约翰霍普金斯大学的水文地质项目，开发了一种新的三维有限元程序，用于模拟沉积系统中耦合的地下水和热输运。JHU的进一步研究开发了一种新的二维反应流计算机代码，可用于模拟地下水化学、岩石蚀变模式和地质时期的矿石成矿作用。该提案项目将应用这些工具来测试密苏里州东南部矿石形成的概念模型。

Garven 9418011 This proposal seeks to increase our basic understanding of the role of large-scale groundwater flow in geologic processes such as stratabound ore formation in carbonate rocks. Ancient limestone-dolostone aquifers in North America contain significant ore deposits of lead, zinc, barite, and fluorite that appear to have origins related to the migration of deep groundwater over 10's and 100's of kilometers. A large ore district has been the focus of exploration and intensive geologic research over the past two decades: The Ozark Dome in southeast Missouri. Although much has been revealed about the geologic characteristics and conditions of ore formation in this setting, much controversy still surrounds issues such as the geochemical reactions causing ore mineralization, the actual pathways for brine migration (aquifers or faults), and the mechanisms causing migration of the ore-forming fluids. Geological and geochemical data are now abundant for this carbonate-hosted ore district. Recent work aimed at understanding hydrogeologic processes at the basin-scale has shown that the ores in Missouri were probably formed by deep groundwater moving updip through foreland basins and rifts adjacent to the Ozark Dome (Garven et al., 1993), but the actual flow patterns have yet to be mapped at smaller scales (L10km). Many geochemical models have been conjectured for ore deposition in the Southeast Missouri district, yet no mechanisms have been tested in a framework that includes the effects of fluid flow and heat transport. A primary objective of this proposal is to use recently developed hydrogeologic-geochemical modeling tools to explore and compare the paleohydrogeology of ore formation in the Southeast Missouri. Prior NSF support of the Hydrogeology Program at Johns Hopkins University has resulted in the development of a new three-dimensional finite element code for modeling coupled groundwater and heat transport in sedimentary systems. Additional research at JHU has resulted i n the development of a new two-dimensional, reactive flow computer code that can be used to simulate groundwater chemistry, patterns of rock alteration, and ore mineralization over geologic time. The proposal project will apply theses tools to test conceptual models of ore formation in Southeast Missouri.