Clay minerals are the signature of hydrothermal alterations related to fluid circulation in volcanic and crystalline rocks. In the French part of the Upper Rhine Graben, in the deep-seated granites, illitic minerals (illite and I/S mixed layers (ml)) are typical products of the structurally-controlled argillic alteration in the Paleozoic granitic basement. In the new Illkirch geothermal well, GIL-1, drill-cuttings were studied with various petrographic methods to determine the characteristics of illite in paleo- and present-permeable zones, and to compare the alteration mineralogy with that of geothermal Soultz-sous-Forêts and Rittershoffen sites. Alteration petrography, crystal structure as well as the chemical composition of the illitic minerals and the altered bulk rocks were performed all along the well. This complete characterization, combined with geophysical logs and structural results, highlighted that the illitic minerals at Illkirch, Soultz-sous-Forêts, and Rittershoffen are composed of illite and illite-rich illite-smectite mixed layers (I/S ml) (<10% smectite). Two mineralogical assemblages were distinguished: chlorite + illite resulting from the propylitic alteration after the emplacement of the granitic basement under temperatures higher than 350 °C, and illite + I/S ml + carbonates + quartz resulting from the argillic alteration due to fluid circulation in the fractures at temperatures between 130 and 160 °C. Fracture zones are characterized by the occurrence of illitic minerals (illite and I/S ml), and specifically, by higher quantities of I/S ml in present-day permeable zones than in paleo-permeable zones. A conceptual model of the fracture zones at the interface between the overlying sedimentary rocks and the granitic basement is proposed. The present-day permeability distribution is controlled by the fault and fracture network, which consists of sealed zones and unsealed zones. Fluid convection in the URG implies paleo and present fluids circulating in both fractured sedimentary and crystalline reservoirs. Such circulations develop illitic minerals that could be considered as exploration guides for future geothermal sites in the URG. At Illkirch, the repartition of the present-permeable fracture zones (KFZs) in the GIL-1 well indicates that the moderately argillically altered granite distally situated from the Eschau fault is more permeable than the intensely argillically altered granite close to the Eschau fault.

中文翻译：

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粘土矿物学：莱茵河上中部Graben花岗岩地热储层的标志

粘土矿物是与火山岩和结晶岩中流体循环有关的热液蚀变的标志。在上莱茵河格拉本的法国部分，深层花岗岩中，非法矿物（伊利石和I / S混合层（ml））是古生代花岗岩基底中结构受控的泥质蚀变的典型产物。在新的伊尔基希（Illkirch）地热井GIL-1中，采用各种岩相学方法研究了钻屑，以确定古渗透层和当前渗透区的伊利石特征，并比较了地热苏尔兹-苏-福提斯的蚀变矿物学。和Rittershoffen网站。沿井一直进行蚀变岩相学，晶体结构以及硅质矿物和蚀变块状岩石的化学成分。这个完整的特征，结合地球物理测井和结构结果，强调了Illkirch，Soultz-sous-Forêts和Rittershoffen的非法矿物由伊利石和富含伊利石的伊利石-蒙脱石混合层（I / S ml）（<10％蒙脱石）组成。区分了两种矿物学组合：在高于350°C的温度下将花岗岩基底放置后，由亚丙基改变引起的绿泥石+伊利石，以及由于流体循环引起的泥质改变而引起的伊利石+ I / S ml +碳酸盐+石英。在130至160°C的温度下产生裂缝。断裂带的特征是存在非法矿物（伊利石和I / S ml），特别是，当今的可渗透带比古可渗透带的I / S ml含量更高。提出了上覆沉积岩与花岗岩基底之间界面断裂带的概念模型。目前的渗透率分布是由断层和断裂网络控制的，断层和断裂网络由密封区和非密封区组成。URG中的流体对流意味着古今的流体在破裂的沉积储层和晶体储层中都在循环。这种循环会发展出非法矿物，这些矿物可被视为URG未来地热站点的勘探指南。在伊尔基希（Illkirch），GIL-1井中当前可渗透裂缝区（KFZs）的重新划分表明，位于埃绍断层远侧的中度经阿尔吉斯蚀变的花岗岩比靠近埃绍断层的经深隆起而蚀变的花岗岩具有更高的渗透性。