Abstract The evolution of the petrophysical properties of rocks induced by hydrothermal alteration is often considered qualitatively by sorting the hydrothermal alterations encountered from low to high intensity, depending on the identified mineral paragenesis. In this paper, we studied the evolution of three different petrophysical properties (connected porosity, permeability and electrical conductivity) as a function of the argillization degree of andesites affected by argillic alteration identified in the caprock formation of the Petite Anse-Diamant hydrothermal system in Martinique. These petrophysical measurements were supplemented by quantitative mineral evaluation via scanning electron microscopy (i.e., the Quantitative Evaluation of Minerals by Scanning electron microscopy or the QEMSCAN® method), connected porosity mapping using 14C-PMMA method and measurements of methylene blue (MB) values and structural water proportions (H2O+). In the series of rocks investigated, an increasing trend of clay mineral abundances (montmorillonite and kaolinite) from 5.68 to 37.56% was revealed by the QEMSCAN® method. Based on the quantitative results, the structural water proportions were used as a proxy of argillic alteration progression. Comparison between the mineral maps provided by the QEMSCAN® system and connected porosity mapping observed in autoradiographs using 14C-PMMA method revealed a good correlation with clay mineral phases, dissolution vugs and fractures. The connected porosities evaluated with the triple weight method range from 3.74 to 35.35% and show a good correlation (R2 = 0.8835) with the H2O+ values, revealing that porosity development is mainly due to the replacement of primary phases by clay minerals. In contrast, the crystallization of silica, carbonates and, to a lesser extent, iron oxides tends to clog connected pores, inducing a local decrease in connected porosity, as revealed in autoradiographs. The Darcian permeability ranges from 7.66∙10−20 to 5.36∙10−17 m2 and shows a moderate correlation with the connected porosity. The bulk electrical conductivity measured as a function of the conductivity of the saturating solution reveals the significant contribution of surface conduction arising from montmorillonite. At a pore fluid salinity of 2 wt% (the salinity of the Eaux Ferrees thermal spring), the bulk electrical conductivity shows a relatively good correlation with the H2O+ values (R2 = 0.8591) and an even better correlation with the MB values (R2 = 0.9579). The contribution of montmorillonite to the bulk electrical conductivity was estimated with the use of the isoconductivity point, showing an increase in the BM values and a strong correlation (R2 = 0.9806).

中文翻译：

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马提尼克岛 Petite Anse-Diamant 热液系统中受泥质蚀变影响的安山岩岩石物理性质的定量演化

摘要 由热液蚀变引起的岩石岩石物理性质的演化通常通过将遇到的热液蚀变从​​低强度到高强度分类来定性地考虑，这取决于已识别的矿物共生作用。在本文中，我们研究了三种不同的岩石物理性质（连通孔隙度、渗透率和电导率）随马提尼克岛 Petite Anse-Diamant 热液系统盖层岩层中受泥质蚀变影响的安山岩泥化程度的变化。 . 这些岩石物理测量由通过扫描电子显微镜进行的定量矿物评估（即通过扫描电子显微镜或 QEMSCAN® 方法对矿物进行定量评估）进行补充，使用 14C-PMMA 方法连接孔隙度映射，并测量亚甲蓝 (MB) 值和结构水比例 (H2O+)。在所研究的岩石系列中，通过 QEMSCAN® 方法揭示了粘土矿物丰度（蒙脱石和高岭石）从 5.68% 增加到 37.56% 的增加趋势。根据定量结果，结构水比例被用作泥质蚀变进程的代表。QEMSCAN® 系统提供的矿物图与使用 14C-PMMA 方法在放射自显影中观察到的连接孔隙度图之间的比较揭示了与粘土矿物相、溶蚀孔洞和裂缝的良好相关性。使用三重权重法评估的连通孔隙率范围为 3.74% 至 35.35%，并显示出与 H2O+ 值的良好相关性 (R2 = 0.8835)，揭示孔隙度的发展主要是由于粘土矿物取代了初级相。相比之下，如放射自显影照片所示，二氧化硅、碳酸盐以及较小程度的氧化铁的结晶往往会堵塞连接的孔隙，导致连接孔隙率的局部降低。达西渗透率范围为 7.66∙10−20 至 5.36∙10−17 m2，与连通孔隙度呈中等相关性。作为饱和溶液电导率的函数测量的体电导率揭示了蒙脱石产生的表面传导的显着贡献。在 2 wt% 的孔隙流体盐度（Eaux Ferrees 温泉的盐度）下，体电导率与 H2O+ 值（R2 = 0. 8591) 以及与 MB 值的更好相关性 (R2 = 0.9579)。使用等导点估计蒙脱石对体电导率的贡献，显示 BM 值增加和强相关性 (R2 = 0.9806)。