Details of Award
NERC Reference : NE/I02349X/1
Transport of Lithophile Elements in Magmatic-Hydrothermal Fluids
Grant Award
- Principal Investigator:
- Professor DM Sherman, University of Bristol, Earth Sciences
- Co-Investigator:
- Professor JD Blundy, University of Oxford, Earth Sciences
- Co-Investigator:
- Dr RA Brooker, University of Bristol, Earth Sciences
- Co-Investigator:
- Professor M Walter, University of Bristol, Earth Sciences
- Grant held at:
- University of Bristol, Earth Sciences
- Science Area:
- Earth
- Overall Classification:
- Unknown
- ENRIs:
- Natural Resource Management
- Science Topics:
- None
- Abstract:
- It has long been recognized that H2O-rich (aqueous) and CO2-rich (carbonic) fluids play a fundamental role in a wide range of geological processes. Of particular importance is the ability of such fluids to selectively transport chemical components, such as metals, from one geological reservoir to another. As a consequence, aqueous and carbonic fluids play a key role in the formation of some of the most economically important ore deposits in the world. Magmatic-hydrothermal ore deposits result from the cooling and phase-separation of volatile-rich magma bodies in the shallow crust. The chemistry of the fluids depends on the nature of the magma from which they exsolved, which in turn is influenced by the tectonic setting of the magmatism. Magmatism associated with destructive plate margins tends to be dominated by aqueous fluids, whereas carbonic fluids are more prevalent in intraplate magmatism. Fluids also contain a variety of anions (e.g. F, Cl, S etc) or anionic complexes (CO3, SO4 etc) which play an important role in metal transport. Despite the universal recognition of the importance of fluids in ore formation, we have surprisingly little understanding of their physical chemistry, which in turn limits our ability to predict how and where ore deposits may form. A large part of our ignorance stems from the experimental difficulties of studying high-temperature aqueous or carbonic fluids. Unlike silicate or carbonate melts, fluids do not quench to a solid at room temperature and pressure, making it difficult to characterise them chemically or physically. We have pioneered a novel experimental approach to this problem, in which a laser is used to drill through the walls of a frozen experimental capsule, directly analysing the frozen fluid, without risk of contamination during sectioning. Coupling the laser to an ICP-MS apparatus means that we can analyse the frozen fluid for a wide variety of trace elements. The coexisting silicate or carbonate melt can be quenched and retrieved from the capsule for subsequent analysis. We can systematically vary the composition of the fluid and its concentration, allowing us to explore the key controls on how metals are complexed in fluids. By looking at the variations in melt-fluid partitioning with fluid composition we can hypothesise about the types of metal-ligand complexes that are present. We cannot, however, directly observe these at pressure and temperature. To do this, we have developed an alternative experimental methodology in which a small droplet of fluid of known composition is held between the flattened tips of two diamonds in a resistance-heated diamond anvil pressure cell. The diamonds are transparent to synchrotron-generated X-rays, meaning that the solution can be studied in situ at elevated pressure and temperature. This approach allows us to evaluate the predictions made on the basis of the partitioning experiments. Finally, we can use computational quantum chemistry (classical and ab initio molecular dynamics) to predict the hydration and complexation of cations in fluids at at elevated pressure and temperature. Recent implementations of a technique call metadyanamics enables us to derive free energies and, hence, equilibrium constants, for the formation of metal complexes from molecular dynamical simulations. In summary, we are approaching the problem of metal transport from three quite different, but complementary directions. In its own right, each approach has limitations; in combination these approaches will enable us to generate a comprehensive picture of aqueous and carbonic fluids under precisely the same physical conditions as ore bodies form. We will begin by studying an important, but relatively simple, class of metals, the alkalis, alkaline earths and rare earths, although our methodology can ultimately be extended to encompass the entire range of economically important metals.
- NERC Reference:
- NE/I02349X/1
- Grant Stage:
- Completed
- Scheme:
- Standard Grant (FEC)
- Grant Status:
- Closed
- Programme:
- Standard Grant
This grant award has a total value of £306,366
FDAB - Financial Details (Award breakdown by headings)
| DI - Other Costs | Indirect - Indirect Costs | DA - Investigators | DI - Staff | DA - Estate Costs | DA - Other Directly Allocated | DI - T&S |
|---|---|---|---|---|---|---|
| £23,892 | £105,979 | £29,228 | £103,883 | £38,360 | £1,806 | £3,217 |
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