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Growth of Silica Sinters: Laboratory and Field Studies

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Silica is a major component of most rocks. When high temperature waters circulate deep in the crust they can dissolve some of the silica from the rocks. If the hot water reaches the surface, it forms hot springs which usually contain high concentrations of dissolved silica (SiO2). As the hot spring water cools, the silica can no longer remain dissolved in solution. This causes it to drop out (a process called precipitation) to form silica sinter.

Silica sinter occurs around many hot springs worldwide including those in New Zealand. There is great textural variability in the sinter deposits. Much of this variability is due to difference in physical and chemical conditions in and around the hot spring. Yet, when we study sinters using microscopic techniques we find that they all contain extremophilic micro-organisms.

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The question that interests scientists is whether the growth of these textural types is in anyway determined by the presence of microbes, that is, are extremophilic microbes influencing the textural development of silica sinters.

At GNS Science we have been conducting field and laboratory experiments to study the growth and textural development of silica sinters. We are interested in their growth rates, their textural development, the influence of microbial communities and biofilms, and the preservation of physical microfossils in the silica sinters.

As all the sinter deposits we have studied from New Zealand contain microorganisms, it is difficult to conclude what textures are formed in their absence. This is where laboratory simulations are useful.

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Laboratory experiments have shown that the amount of silica precipitated is lower when microbes are not present. This is because the surfaces of microbes provide an extensive substrate for silica precipitation. This does not mean that the microbes are causing silica to precipitate only that they are providing surfaces for silica to cover. Also, when microbes are present, textural development is much more complex.

This research project is led by Bruce Mountain in collaboration with Liane Benning (Leeds University).

Reference: Mountain, B.W., Benning, L.G. and Boerema, J.A. (2003) Canadian Jour. Earth Sciences, v. 40, 1643-1667.