Canadian Shield groundwater characterization studies have been conducted over the last four decades through operating mines, underground research areas, and wells installed for a variety of purposes. A newly available database containing chemical and isotopic analytical results of groundwaters includes data from all of these sources and spans the Canadian Shield. The Precambrian Canadian Shield Groundwater and Gas Geochemistry (PCSG) database provides the most comprehensive data of groundwater chemistry in the Canadian Shield region to date. In this initial review of the PCSG database, major ion, Br, water type, δO, δH and H trends with depth and salinity are described. In future reviews, other aspects of the database will be examined, including minor and trace elements, other isotopes, and gases. The PCSG database is comprised of 69 % freshwaters, mostly found at depths <1000 m, and dominated by Ca-HCO and Na-HCO water types; 17 % brackish waters, at depths <2000 m, and dominated by NaCl, CaCl, Ca-HCO, and Ca-SO water types; 9 % saline waters, mostly at depths >1000 m, and dominated by CaCl, NaCl, Ca-HCO, and Na-HCO water types; and 4 % brine samples, identified at depths up to 1800 m, composed entirely of CaCl water types. An increase in all major ion and Br concentrations with depth is observed, except for HCO, with groundwaters typically becoming more saline with depth. Variability in salinities at specific depths and at individual sites across the Canadian Shield reflect the effect of (primarily) anthropogenically induced mixing, although heterogeneous geology and hydrogeologic flow paths are also important. When eliminating data that are likely affected by anthropogenically-induced mixing, saline waters are the most affected, with median depths of NaCl and CaCl type waters shifting downward, and median concentrations of NaCl type waters increasing. The isotopic data indicate that groundwaters from across the Canadian Shield reflect a variety of water recharge sources, with many samples plotting along the Global Meteoric Water Line (GMWL). Deviations to the right of the GMWL are indicative of freezing and mixing with drill fluid, while deviations to the left are indicative of isotopic exchange between water and rock and/or silicate hydration over long time scales. Rock/silicate-water interactions over hundreds of million of years resulted in development and isolation of CaCl brines at multiple locations. Cold climate processes, including glacial meltwater recharge and/or ionic concentration during permafrost formation, yielded a third end-member. A conceptual model of the expected groundwater chemistry variation with depth across the Canadian Shield is presented based on an evaluation of the variation of water type and salinity with depth. This model shows that groundwater chemistry changes from shallow groundwater dominated by Ca,Na-HCO to deep groundwater dominated by CaCl, and details intermediate water type and TDS variations with depth.

中文翻译：

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加拿大地盾结晶岩地下水主要化学和同位素特征综述


过去四十年来，加拿大地盾公司通过运营矿山​​、地下研究区和为各种目的安装的井进行了地下水特征研究。新推出的数据库包含地下水的化学和同位素分析结果，其中包括来自所有这些来源并跨越加拿大地盾的数据。前寒武纪加拿大地盾地下水和气体地球化学 (PCSG) 数据库提供了迄今为止加拿大地盾地区最全面的地下水化学数据。在 PCSG 数据库的初步审查中，描述了主要离子、Br、水类型、δO、δH 和 H 随深度和盐度的变化趋势。在未来的审查中，将检查数据库的其他方面，包括微量元素和痕量元素、其他同位素和气体。 PCSG数据库由69％的淡水组成，主要发现于深度％3C1000米，并且以Ca-HCO和Na-HCO水类型为主； 17% 的咸水，深度为 <2000 米，以 NaCl、CaCl、Ca-HCO 和 Ca-SO 水类型为主； 9%咸水，主要位于>1000米深度，以CaCl、NaCl、Ca-HCO和Na-HCO水类型为主； 4% 的盐水样本，在深度达 1800 m 处鉴定，完全由 CaCl 水类型组成。除 HCO 外，所有主要离子和 Br 浓度均随深度增加而增加，地下水通常随着深度的增加而变得更加含盐。尽管异质地质和水文地质流动路径也很重要，但加拿大地盾特定深度和各个地点的盐度变化反映了（主要）人为引起的混合的影响。 当消除可能受到人为引起的混合影响的数据时，咸水体受到的影响最大，其中 NaCl 和 CaCl 类水域的中位深度向下移动，并且 NaCl 类水域的中位浓度增加。同位素数据表明，加拿大地盾两端的地下水反映了多种水补给来源，许多样本沿着全球大气水线（GMWL）绘制。 GMWL 右侧的偏差表示冻结并与钻井液混合，而左侧的偏差表示水与岩石和/或硅酸盐水合之间在长时间尺度上的同位素交换。数亿年的岩石/硅酸盐-水相互作用导致了多个地点氯化钙卤水的形成和分离。寒冷的气候过程，包括冰川融水补给和/或永久冻土形成过程中的离子浓缩，产生了第三个端元。基于对水类型和盐度随深度变化的评估，提出了加拿大地盾预期地下水化学随深度变化的概念模型。该模型显示地下水化学变化，从以 Ca,Na-HCO 为主的浅层地下水到以 CaCl 为主的深层地下水，并详细说明了中间水类型和 TDS 随深度的变化。