AbstractThe mineralisation which occurs within the Central Wales Orefield (CWO) is of historical importance, as the area was once one of the major producers of silver in the United Kingdom. In comparison to the other ore districts situated in the British Isles however, surprisingly little research has been undertaken in the CWO in recent years. This thesis redresses this issue by examining, in conjunction with Pb isotope analysis, the geochemical variation in three sulphide minerals (galena, sphalerite and chalcopyrite), collected from six mineralised lodes located in the Afon Clarach catchment; a small river system situated in the northern region of the CWO, north of Aberystwyth. Although the Pb-Ag mines in the CWO have been abandoned for over 100 years, many of these sites continue to have a legacy of pollution, which under the Water Framework Directive (2000/60/EC) now require remediation. By characterising the trace metal and Pb isotope fingerprints of the six mineralised lodes situated in the Afon Clarach catchment, this thesis successfully identifies those mine sites which continue to contaminate the river sediments of the Afon Clarach with trace metals and therefore require remediation.
Variations in the Pb isotope ratios and the concentrations of Sb, Tl and Hg identified in the Pb-ore and Tl, In, Fe, Mn and Cu in the Zn-ore collected from the six lodes have successfully differentiated the two periods of mineralisation previously identified in the CWO by Mason (1994) and dated by Fletcher et al. (1993). The Camdwr, Cwmerfyn, Cwmsymlog and Daren Lodes are dominated by the older phase of mineralisation (Group 1) whereas the Hafan Lode is dominated by the younger phase (Group 2). In contrast, the Goginan Lode contains ore minerals which were precipitated during both stages of mineralisation. In addition to differentiating the two periods of mineralisation, subtle variations in the concentrations of Ag, Cd, Co, Cu, Fe, Ni, Pb and Sb in the Pb-ore; Cd, Cu, Ga, Fe, Hg, Ni, Pb, Sb, Tl, In and Zn in the Zn-ore and Cu, Fe, Ga, Hg, In, Pb, Sn and Zn in the Cu-ore differentiate those lodes assigned to the older Group 1.
It is possible to use the chemical and isotope signatures of the lodes, to trace the metal contamination, particularly that of Pb, Zn, Cu and Sb, into the river sediments and identify those sites which are continuing to contaminate the Afon Clarach. The priority mine sites identified in the study include Bwlch Mine, Cwmsymlog Mine, Daren Mine and Cwmerfyn Mine, all of which are located along the Nant Silo, one of the four main tributaries of the Afon Clarach. The inclusion of Bwlch and Cwmerfyn Mines in this list is of some concern as these sites have already undergone some remediation work during the early 1990‟s. In addition, mines including Llety-Hen, Willowbank and Pen-y-Cefn are also introducing some metal contamination into the Afon Stewi. The remaining two tributaries of the Afon Clarach (the Bowstreet Brook and the Afon Peithyll) are less affected by metal contamination. The spoil tips located at Mynydd Gorddu Mine, situated on the Bowstreet Brook, however do pose a threat to the local environment with high mean concentrations of Pb (4.21 %), Zn (4.02 %) and Sb (221 g/g) found in the tailings and high concentrations of soluble Zn (7.3 mg/L) found in the water draining the spoil tips
|Date of Award||2010|
|Supervisor||Bill Perkins (Supervisor) & Nick Pearce (Supervisor)|