IAP2-22-399

Sulphur Landscapes: Isotopes and the Mining Environment (SLIME)

The sulphur isotopic δ34S signature of primary and hydrothermal sulphide is often around, or below 0‰. Sedimentary sulphide in UK coal bearing sequences (“Coal Measures”) can be much more variable, depending on the degree of openness or closure of the geochemical system during deposition and microbial sulphate reduction, and on post-deposition diagenesis and secondary mineralisation. On average, however, Coal Measures pyrite tends to exhibit a δ34S of between -10 and +10‰.

When coal is mined, Coal Measures pyrite is brought into contact with circulating water and oxygen. It is oxidised to intermediate hydroxysulphate minerals and ultimately to dissolved sulphate in mine water. Except under the influence of certain alkali- and brine-dwelling microbes (Pellerin et al. 2019), oxidation of sulphide is usually accompanied by negligible fractionation. It is commonly assumed that dissolved sulphate in mine water is derived from pyrite oxidation. If this were the case, it should also be characterised by a δ34S of between -10 and +10‰.

Pilot research carried out in the UK and Europe has indicated that shallow coal mine waters do indeed exhibit a dissolved sulphate δ34S within this range (Banks et al. 2020, 2022, Walls et al. 2022). However, it has also become apparent that deep minewater often exhibits much higher dissolved sulphate δ34S: above +20‰ and sometimes >30‰.

This project will test the following hypotheses:
1. That coal mine water sulphate is not exclusively derived from pyrite oxidation
2. That oxidation of pyrite to hydroxysulphates and dissolved sulphate is always accompanied by negligible fractionation.
3. That consideration of sulphate δ18O in addition to δ34S can elucidate the origin of sulphate.

Several sub-hypotheses can be put forward to explain the elevated sulphate-S isotopic signature of deep mine waters, although none seem to be universally applicable. The project will systematically consider and test these:

1. Dissolution of evaporites (gypsum, anhydrite) from adjacent strata
2. Infiltration of marine, lagoonal, sabkha or evaporite brines in the geological past
3. Fractionation by microbial sulphate reduction in the mine environment
4. Fractionation on oxidation by “exotic” micro-organisms

The research program will thus contribute to the IAPETUS focus on Earth Resources (coal, geothermal mine water) and Nutrient (sulphur) cycling.

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Image Captions

Dawdon Colliery shaft by David Banks,Sulphide oxidation minerals, Blast Beach by David Banks,Acidic mine waste pond, Blast Beach by David Banks,Colliery spoil “terrace”, Blast beach by David Banks,Colliery spoil, Blast Beach by David Banks

Methodology

The project will study Coal Measures stable isotopic landscapes and stratification at two scales:

(a) National: via Coal Authority-managed mine water discharges, pumping stations and treatment sites. (The Coal Authority manages around 75 treatment schemes in the UK – https://www2.groundstability.com/services/treating-mine-water/).
(b) Local: via study of the Blast Beach, Dawdon, Co. Durham anthropogenic coastal landscape. The beach contains colliery spoil containing pyrite; secondary sulphate minerals (tentatively identified as jarosite, alunite and sulphur), acidic sulphate lagoons, marine sulphate aerosols, marine water. Adjacent to the beach is the deep saline Dawdon colliery minewater environment, currently pumped and under consideration for use as a geothermal heat source.

The PhD student will link with the Coal Authority (CA) and develop a plan to visit (under supervision, where necessary) as many of the CA’s large minewater discharge sites, which comprise shallow gravity drainages, pumped deep collieries and intermediate overflows from adits, as practically feasible (with a target of 30-40), throughout England, Scotland and Wales. At each site, field parameters such as pH, electrical conductivity, alkalinity, temperature and redox potential will be measured, and samples of mine water will be collected. These will be analysed for:

1. Dissolved sulphate δ34S and δ18O at the NERC-funded SUERC / University of Glasgow isotope laboratory.
2. Water δ18O and δ2H also at SUERC.
3. Where the CA do not already routinely sample and analyse for hydrochemistry, major ion chemistry and selected minor ions (tentatively to include Ba, Sr, Br, Li, Fe and Mn) will be analysed at the hydrochemical engineering laboratory at the University of Newcastle.

The PhD student will also request access to the CA’s database of hydrochemical analyses of mine water to extend the data set, and will request access to the CA’s cores in order to compile a set of Coal Measures pyrite samples, analysed at SUERC to improve the UK data set on δ34S in Coal Measures pyrite (which is, at present, surprisingly sparse).

Selected coal mine waters with elevated δ34S values will be additionally sampled for analysis using metatranscriptomic techniques (c/o J Moreau) to examine whether expression of microbial sulphate reduction genes is occurring and, if so, which genes (bacteria, archaea). If a candidate with an appropriate microbiological background can be identified, rates of sulphate reduction using radioactive δ 35S labelling techniques can be investigated, contingent upon additional sources of funding being successfully sought within the University of Glasgow.

The PhD student will also visit Blast Beach, Dawdon. The beach has already been preliminarily characterised as part of the University of Newcastle’s (UoN) research programme (NERC Legacy Wastes in the Coastal Zone – https://research.ncl.ac.uk/legacywastes/). The student will systematically collect samples from all “compartments” of the beach’s sulphur isotope landscape: i.e. sedimentary pyrite in colliery spoil; secondary sulphate minerals, sea water, dissolved sulphate from acid lagoons, Dawdon deep mine water. Mineralogy will be characterised by X-Ray Diffraction (XRD) and the mineral sulphur content’s δ34S (and sulphate δ18O) will be characterised at SUERC.

Project Timeline

Year 1

Literature review. Review of data held by Coal Authority(CA). Site selection of CA sites. Preliminary visits to Blast Beach. Laboratory training at SUERC. Sampling / safety training with University of Newcastle (UoN) and CA.
First field season: regional mine water and Blast Beach sample collection commences.
Sample analysis commences.

Year 2

Sample preparation and completion of analysis of season 1 samples.
2nd field season: Complete sampling at Blast Beach and at CA sites. Sample analysis.
Sample collection and genomic analysis of water samples for evidence of microbial sulphate reduction.
Characterise mine water sampling sites in terms of geological / mineralisation history. Commence hypothesis testing.

Year 3

Completion of laboratory work. Data analysis and hypothesis testing. Initial dissemination of results at seminars and conferences.

Year 3.5

Completion of thesis. Authorship of scientific papers.

Training
& Skills

Training in sampling will be provided primarily by University of Newcastle (UoN) supplemented by University of Glasgow (UoG) and Coal Authority (CA).
Training in safety at CA sites will be provided by CA.
Training in isotopic sample preparation and analytical methodologies will be provided by UoG SUERC.
The PhD student will be expected to participate in national and international conferences to disseminate results.
The student will become part of the IAPETUS DTP, providing a multidisciplinary package of training

References & further reading

Banks, D., Boyce, A.J., Burnside, N.M., Janson, E. & Roqueñi Gutierrez, N.(2020). On the common occurrence of sulphate with elevated δ34S in European mine waters: sulphides, evaporites or seawater? International Journal of Coal Geology 232, 103619. doi: 10.1016/j.coal.2020.103619.

Banks, D. & Boyce, A. (2022). Dissolved sulphate δ34S and the origin of sulphate in coal mine waters; NE England. Submitted to Quarterly Journal of Engineering Geology and Hydrogeology.

Pellerin, A., Antler, G., Holm, S.A., Findlay, A.J., Crockford, P W., Turchyn, A.V., Jørgensen, B.B. & Finster, K. (2019). Large sulfur isotope fractionation by bacterial sulfide oxidation. Science Advances 5(7), eaaw1480. doi: 10.1126/sciadv.aaw1480.

Legacy Wastes in the Coastal Zone: https://research.ncl.ac.uk/legacywastes/newsevents/sitevisittolynemouthanddawdon.html

Walls, D.B., Banks, D., Peshkur, T., Boyce, A.J. & Burnside, N.M. (in press). Heat recovery potential and hydrochemistry of mine discharges from Scotland’s coalfields. Earth Science, Systems and Society.

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