墨西哥国立自治大学Pandarinath, Kailasa小组使用多参数方法，探究了墨西哥Acoculco地热场火山岩表面的热液蚀变。相关论文于2024年4月8日发表于国际顶尖学术期刊《地球化学学报》杂志上。

研究人员称，墨西哥Acoculco地热场(AGF)具有高温、极低渗透率的特点，被认为是一个有前景的增强型地热系统。由于热液蚀变的增加，岩石中出现了以下变化：(1)CIA、LOI和S值增加，WIP降低；(2)石英和石英多晶矿物(硅化)和粘土矿物(泥化)增加；(3) χlf值减小。在AGF，蚀变最多的表面酸性岩以石英及其多晶型和粘土矿物为特征。

本研究还表明了主要元素(长英质与镁铁质成分)二元图和岩石磁性参数(χlf与χfd%)的适用性。χfd%值为2-10，χlf值小于0.5×10^-6m³kg^-1，表明存在单畴和稳定的单畴颗粒，反过来表明其为蚀变岩。研究结果强调，这些方法应用简单、快速、可靠，有望成为地热勘探初期热液蚀变岩识别的有效工具。

据悉，地表和地下岩石热液蚀变效应的研究为地热储层的表征和开发提供了重要的信息。一般来说，这些研究基于传统和可靠的方法，如岩石学(原生和次生矿物，蚀变等级)和地球化学(元素的流动性，元素质量和浓度的变化，以及流体包裹体)。近年来，除了这些已建立的方法外，一些基于地球化学蚀变指数(蚀变化学指数，CIA；Parkar风化指数，WIP；强热失量，LOI；和硫，S)和岩石磁性(磁化率，χlf；从属敏感性的百分比频率(χfd%)也被用于识别岩石是蚀变的还是新鲜的。

附：英文原文

Title: Hydrothermal alteration of the surface volcanic rocks at the Acoculco geothermal field, Mexico: a multi-parametric approach

Author: Garca-Soto, America Yosiris, Pandarinath, Kailasa, Santoyo, E., Gonzalez-Partida, Eduardo

Issue&Volume: 2024-04-08

Abstract: The studies on hydrothermal alteration-induced effects in surface and subsurface rocks provide useful information in the characterization and exploitation of a geothermal reservoir. Generally, these studies are based on traditional, and reliable methods like petrography (primary and secondary minerals, and grade of alteration), and geochemistry (mobility of elements, changes in mass and concentration of elements, and fluid inclusions). Recently, apart from these established methods, some methods based on the geochemical (Chemical Index of Alteration, CIA; Weathering Index of Parkar, WIP; Loss on Ignition, LOI; and Sulfur, S) and rock magnetic properties (magnetic susceptibility, χlf; and percentage frequency-dependent susceptibility, χfd%) are also being applied in the identification of whether a rock is an altered or a fresh one. The Acoculco Geothermal Field (AGF), Mexico, is characterized by high temperature and very low permeability, and it is considered a promissory Enhanced Geothermal System. The following changes are observed in the rocks as a result of an increase in hydrothermal alteration: (1) an increase in CIA, LOI, and S values, and a decrease in WIP; (2) an increase in quartz and quartz polymorph minerals (silicification), and clay minerals (argillization); and (3) decrease in χlf values. At AGF, the most altered surface acid rocks are characterized by entirely quartz and its polymorphs, and clay minerals. The present study also indicates the applicability of the binary plots of major elements (felsic vs mafic component) and rock magnetic parameters (χlf vs. χfd%). The rock with χfd% value of 2–10 and χlf value<0.5×10^-6m³kg^-1 indicate the presence of single domain and stable single domain grains, which in turn suggests that it is an altered rock. These methods are simple to apply, rapid, reliable, and have the potential to become effective tools for the identification of hydrothermally altered rocks during the initial stage of geothermal exploration.

DOI: 10.1007/s11631-024-00683-5

Source: https://link.springer.com/article/10.1007/s11631-024-00683-5