Definition
Alteration is any mineralogic change to a preexisting rock through chemical reaction caused by hot circulating hydrothermal fluids.
Introduction
Hydrothermal fluids , owing to temperature and pressure gradient, travel within a rock’s primary or secondary porosity. They react with country rock, alter original mineralogy, and produce new minerals. Hydrothermal fluids can be magmatic, meteoric, marine, or sedimentary (connate) in origin. They carry mobile elements, large ion lithophile elements (Li, Be, B, Rd, Cs), alkalies, alkali earths, and volatiles (Guilbert and Park 1986).
Alteration Processes
The fluids responsible for inducing alteration of minerals may eventually deposit ore minerals as a result of thermal and chemical changes. Therefore, mapping alteration halos is key to discovering hydrothermal mineral deposits that may or may not outcrop on the surface. Alteration is common with porphyry, skarn, and orogenic/magmatic vein-hosted,...
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References
Doyle, Mark G (2001) Volcanic influences on hydrothermal and diagenetic alteration: evidence from Highway-Reward, Mount Windsor Subprovince, Australia. Economic Geology 96(5):1133–1148
Guilbert JM, Park CF Jr (1986) The geology of ore deposits. W.H. Freeman and Company, New York, p. 985
Harris JR, Wilkinson L, Grunsky EC (2000) Effective use and interpretation of lithogeochemical data in regional mineral exploration programs: application of Geographic Information Systems (GIS) technology. Ore Geol Rev 16(3):107–143
Van Ruitenbeek FJ, Cudahy T, Hale M, van der Meer FD (2005) Tracing fluid pathways in fossil hydrothermal systems with near-infrared spectroscopy. Geology 33(7):597–600
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Admassu, Y. (2016). Alteration. In: Bobrowsky, P., Marker, B. (eds) Encyclopedia of Engineering Geology. Encyclopedia of Earth Sciences Series. Springer, Cham. https://doi.org/10.1007/978-3-319-12127-7_13-1
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DOI: https://doi.org/10.1007/978-3-319-12127-7_13-1
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