This post is a summary of the excellent recent paper on the above topic in Economic Geology: Jeffrey W. Hedenquist, Antonio Arribas; Exploration Implications of Multiple Formation Environments of Advanced Argillic Minerals. Economic Geology 2022;; 117 (3): 609–643. https://doi.org/10.5382/econgeo.4880
Introduction
Hydrothermal ore deposits are associated with alteration minerals, and one such alteration type is “advanced argillic,” found in relatively shallow geological environments where minerals like alunite, kaolinite, dickite, and pyrophyllite indicate the presence of reactive fluids. This term encompasses a range of minerals, including sericite, quartz, alunite, pyrite, tourmaline, topaz, and more. Some of these minerals are shared with other alteration types, like the kaolinite, dickite, and halloysite clays of the argillic term.
Recognition and interpretation of advanced argillic minerals have increased during mineral exploration in recent decades, facilitated by SWIR spectrometry. This extensive mineralogical information provides insights into the formation environment and its relation to potential mineral deposits.
Understanding advanced argillic and related alteration types is essential for mineral exploration and assessment. The provided framework guides exploration efforts and the study of alteration mineralogy across a wide range of hydrothermal settings, from subaerial to submarine, and varying depths and temperatures.
Executive Summary
- Advanced argillic minerals include alunite, anhydrite, aluminosilicates (kaolinite, halloysite, dickite, pyrophyllite, andalusite, zunyite, and topaz), and diaspore. Advanced argillic minerals are key indicators of specific geological alteration environments and are commonly associated with hydrothermal systems and volcanic activity.
- The formation of these minerals is closely tied to the pH levels, depths, and geochemical conditions of their respective environments.
- These minerals form in five distinct geologic environments of hydrolytic alteration, with pH ranging from 4 to less than 1, often at depths below 500 meters.