Determination of stream sediment background concentrations in mineralised catchments impacted by mining using Tellus data from Northern Ireland : final project report

Palumbo-Roe, B.; Ander, E.L.; Cave, M.R.; Johnson, C.C.. 2013 Determination of stream sediment background concentrations in mineralised catchments impacted by mining using Tellus data from Northern Ireland : final project report. Nottingham, UK, British Geological Survey, 56pp. (CR/14/021N) (Unpublished)

Before downloading, please read NORA policies.

Preview

Text
CR14021N.pdf
Download (2MB) | Preview

Abstract/Summary

Background metal(loids) concentrations, intended as concentrations of naturally occurring substances rather than anthropogenic, are more often integrated in the assessment of water and sediment quality. This approach allows that ecosystems may be adapted or acclimatised to certain concentrations of metals in surface water and sediments as a result of their natural abundance. Background values of metal(loids) have long been recognised to be higher in mineralised catchments than those in unmineralised, and this is in fact the same as the central precept of geochemical exploration for economic ore deposits. From the environmental perspective, these mineralised zones should be considered as a separate baseline unit from that of the unmineralised formation. Information on the baseline conditions of catchments prior to mining is needed to better understand what restoration goals are achievable in mining impacted catchments. The geochemical baseline data also provide a reference point against which changes can be measured and can be used both by industry and regulators in future mine applications. In this project an approach for deriving pre-mining baseline sediment concentrations using systematically collected survey geochemical data is demonstrated using the mineralised area associated with the Ordovician-Silurian rocks in southern Co. Armagh in Northern Ireland as study area. The Tellus geochemical survey data for sediments were used for this scope. International literature has usefully provided methodologies and examples of deriving ‘background’ concentrations in mineralised catchments. Statistical methods in use to distinguish between anomalous and background concentrations in geochemical exploration of mineral deposits all converge on various methods of discriminating outliers and making estimates of central tendency, spread and identification of upper thresholds of background. The statistical method used in this project is the method of Sinclair (1976a) and applied using the ‘PROBPLOT’ code (Stanley, 1987), reproduced in an ‘R’ script environment. This method chooses threshold values between anomalous and background geochemical data, based on partitioning a cumulative probability plot of the data. Data analysis has primarily focused on elements for which there are sediment quality standards derived in other jurisdictions, which may be adopted in the UK regulatory framework in future. Probability distribution plots of stream sediment lead (Pb) zinc (Zn), arsenic (As), chromium (Cr) and nickel (Ni) concentrations have been partitioned in the respective contributing populations and population statistics derived (mean and standard deviation). Interpretation of the significance of the resulting groupings of data and understanding different background populations has then been achieved through analysis of the spatial distribution of the groups in a GIS framework. Where data exceed environmental quality standards, these populations can assist in identifying where natural background concentrations (due to mineralogical variations in the catchment geology) may contribute to the exceedance. This is designed to aid the decision-making process in relation to why quality standards may have failed, or if there is any merit in ‘remediation’ of a natural ecosystem. Separation of the more widespread, potentially natural, high concentrations from the data populations which reflect very high concentrations (more likely to arise from anthropogenic sources) could also help in targeting key sites for further investigation.

Item Type:	Publication - Report
Funders/Sponsors:	British Geological Survey, European Union, Tellus
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed, but not externally peer-reviewed. Report made open by author in December, 2021.
Date made live:	13 Dec 2021 15:09 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/531541

Item Type:

Publication - Report

Funders/Sponsors:

British Geological Survey, European Union, Tellus

Additional Information. Not used in RCUK Gateway to Research.:

This item has been internally reviewed, but not externally peer-reviewed. Report made open by author in December, 2021.

Date made live:

13 Dec 2021 15:09 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/531541