Active geothermal systems in New Zealand arise from the emplacement of magma intrusions in the upper crust, which discharge supercritical aqueous electrolyte fluids and heat. These fluids undergo phase separation and react with the surrounding host rocks (minerals) as they ascend buoyantly to interact with meteoric water and may eventually discharge at the surface. What we observe in the upper few kilometres of the Earth’s crust is to some appreciable extent, a manifestation of heterogeneous supercritical reactions occurring at near magmatic temperatures and pressures, and about which we have little rigorous chemical knowledge.
If we are to exploit the geothermal resources to deeper and more extreme (supercritical) conditions, a knowledge of the chemical environment becomes a fundamental requirement. The experimental study of chemical equilibria at supercritical conditions relevant to the deep geothermal environment will give new insight into poorly known processes operating in the Earth’s crust as well as providing information needed for the future exploitation of energy resources at supercritical conditions.
To carry out difficult experiments at extremes of temperature and pressure and obtain some elegant (hopefully) chemical data, which may then be applied to understanding of processes occurring in the Earth’s crust.
I shall focus on current or recent activities. With this in mind, I mention a recent publication, which germinated from experiments and computations carried out in other places at other times. The paper was some years “in the making” as our own thoughts evolved and we kept asking different questions.
Lemke, K.H. & Seward, T.M. 2018. Molecular Clusters and Solvation in Volcanic and Hydrothermal Vapors. Reviews in Mineralogy and Geochemistry, 84, 57-83.
What was the research finding?
The paper presents new and hitherto unavailable data on the molecular structure of steam and low density supercritical water and solutions. Of particular interest are our data on the pH of steam and low density supercritical water, which is the subject of only a handful of papers in the world chemistry/physics literature. Low density supercritical water is composed of nanodroplets or water clusters, the size of which is defined by the temperature and pressure (or density). We demonstrated that the solvated proton (or hydronium ion if you wish) sits on the surface of these water clusters, thus emphasising the reactivity of low density supercritical water/solutions. This is quite a different scenario compared to liquid water, in which ionic species (e.g. the proton) are “internally” solvated in the hydrogen bonded dielectric continuum that is water liquid.
Why is it important?
The data in the paper have important applications to understanding all aspects of the supercritical environment in the Earth’s crust, including, for example, the “complexing” and transport of metals in steam and low density supercritical water.
Where are you?
Sitting on the top of the island of Vulcano, one of the active volcanoes in the Aeolian Islands of Italy, on a sunny spring morning.
What are you doing?
Collecting high temperature gases from fumarole discharges on the rim and in the crater of the volcano. The aim was to study the abiogenic “organic” chemistry in the high temperature volcanic gases. The study (Schwandner et al., 2013) documented the enormous and complex carbon-based chemistry of the gas discharges, which included numerous halocarbons and CFC’s.
Read more about Terry's experience here.