Hot-springs through time, and how to find them

Hot-springs have fascinated geologists including James Hutton for centuries. Here we synthesise data collected over timescales from centuries to days to reveal rules governing hot-springs, including where and when they occur. Data reveal waters dominantly sourced from the surface (either meteoric or seawater) and circulated through faults and fractures systems. Heat comes from magmatic sources (active plate margins) or from the geothermal gradient. Silica-precipitating springs tend to be hotter than carbonate-precipitating springs, and spring vent temperatures are generally near-constant over historical timescales. An exploration of the geological record reveals a few additional known cases of ancient hot-springs formed around impact craters. Given the number of active hot-spring sites, and decades of astrobiologically-driven research, the geological record of hot-springs is more populous than commonly reported but still sparse. One Archaean example, three reported Palaeoproterozoic examples and one Ediacaran example are known in the Precambrian. Eight Palaeozoic and at least ten Mesozoic examples have also been reported. This contrasts with thousands of known Recent examples, implying that many ancient deposits have not been preserved, while many others are yet to be found. Guidelines emerging from this synthesis will hopefully assist in the search for more ancient hot-spring lagerstatten sites.