Pennine Orefield Research Articles

A revised age, structural model and origin for the North Pennine Orefield in the Alston Block, northern England: intrusion (Whin Sill)-related base metal (Cu–Pb–Zn–F) mineralization

Mineralization and associated fluid migration events in the c . 1500 km 2 North Pennine Orefield (NPO) are known to be associated with tectonic activity, but the age of these tectonic events and origins of the base metal sulfide mineralization remain unresolved. New fieldwork in the Alston Block shows that mineralization post-dates a weakly developed phase of north–south shortening consistent with far-field Variscan basin inversion during the late Carboniferous. New observations of field relationships, coupled with microstructural observations and stress inversion analyses, together with Re–Os sulfide geochronology show that the vein-hosted mineralization (apart from barium minerals) was synchronous with a phase of north–south extension and east–west shortening coeval with emplacement of the Whin Sill ( c . 297–294 Ma). Thus the development of the NPO was related to an early Permian regional phase of transtensional deformation, mantle-sourced hydrothermal mineralization and magmatism in northern Britain. Previously proposed Mississippi Valley Type models, or alternatives relating mineralization to the influx of Mesozoic brines, can no longer be applied to the development of the NPO in the Alston Block. Our findings also mean that existing models for equivalent base metal sulfide fields worldwide (e.g. Zn–Pb districts of Silesia, Poland and Tennessee, USA) may need to be reassessed.

Regional variations in fluid formation and metal sources in MVT mineralization in the Pennine Orefield, UK: Implications from rare earth element and yttrium distribution, Sr-Nd isotopes and fluid inclusion compositions of hydrothermal vein fluorites

The Pennine Orefield is one of the most important ore fields for Pb-Zn-Ba-F mineralization in Great Britain. It is subdivided into the Northern Pennine Orefield (NPO), consisting of the Alston and Askrigg Blocks, and the Southern Pennine Orefield (SPO). The Alston Block is underlain by the early Devonian Weardale Granite and the Askrigg Block by the coeval Wensleydale Granite. The potential relationship between the batholiths and the mineralization is a matter of debate. We here studied the rare earth elements and Y (REY) geochemistry, Sr-Nd isotopes and fluid inclusion (FI) compositions of fluorites from the two structural blocks in the NPO and found that the fluorite mineralization in these blocks differ substantially. The REY in Askrigg fluorites show features that are characteristic for leaching of adjacent Lower Carboniferous limestones. In contrast, Alston fluorites have significantly higher REY concentrations, lack REYSN limestone signatures and show a decoupling of redox-sensitive Eu from its trivalent REY ‘neighbours’. Neodymium isotopes indicate a similar crustal source of REY in both blocks, but higher REY concentrations and lower Y/Ho ratios suggest Lower Carboniferous shales as potential REY source in the Alston Block. The fluids that precipitated the Alston fluorites experienced temperatures > 250 °C prior to mineral formation, as evidenced by Eu geothermometry. Fluorite formation, however, occurred at much lower temperatures, as suggested by homogenization temperatures in FI, that fall within ranges of 105–159 °C in Alston and 99–160 °C in Askrigg fluorites. Mineralization of the Mississippi-Valley Type usually lack association with igneous activity. We show that some of the fluids responsible for the NPO mineralization were influenced by magmatic sources. The REY systematics in Alston fluorites may be linked to an interaction of the Permian-age Whin Sill dolerite with the basement granite, which heated fluids and focussed fluid flow into the overlying sedimentary rocks. In the Askrigg Block, where such a dolerite intrusion was not described, fluorites lack any positive EuSN anomalies, indicating that these fluids had never been subjected to temperatures exceeding 200–250 °C.

Mineralization of the South Pennine Orefield, UK—A Review

This review of the South Pennine Orefield (SPO) draws together the findings from many years of underground field observations and petrographical study. Mineralization is of the Mississippi Valley-type (MVT) and is concentrated within an area of some 200 km 2 , mainly along the eastern margins of a large inlier, the Derbyshire High, in Carboniferous platform carbonate host rocks. The inlier covers some 390 km 2 , forms an up-dip promontory of a larger structure, the East Midlands Shelf, and is surrounded by shales and sandstones of the Millstone Grit and Pennine Coal Measures groups. Mineralization probably began during the late Westphalian (Moscovian, Mid Pennsylvanian), when subsidence due to thermal sag resulted in the limestone being buried to depths of c. 4 km beneath younger strata. A palaeohydraulic reconstruction is presented from analysis of mineralized palaeokarst features, which are interpreted as representing hypogenic or deep-seated karst formed by the interstratal circulation of hydrothermal water in a mostly confined hydrodynamic setting. It is reasoned that Variscan inversion of N–S faults to the east of the SPO resulted in erosion of Namurian and Westphalian (Upper Mississippian–Middle Pennsylvanian) rocks and created a hydraulic gradient inclined towards the south-west. Acidic F-Ba-Pb-Zn enriched fluid evolved in the Namurian basinal rocks and migrated into fractured limestone. The resultant wall-rock dissolution along existing wrench faults led to the formation of a maze of stratiform mineral deposits (flats) and more irregular spongework-shaped structures (pipes). The presence of hydrocarbon accumulations in the limestones and evidence from fluid inclusions indicates that the mineralizing fluids were chloride/fluoride-rich and compositionally typical of oilfield brine. Isotope evidence demonstrates a sulphate evaporite source of sulphur, mainly from the Chadian (Visean, Middle Mississippian) Middleton Anhydrite Formation. By the late Cenozoic, karstification of exposed carbonate rocks began and the current pattern of epigenic karst drainage started to develop as the regional hydraulic gradient reversed, assuming its present eastward inclined attitude. The mineralized hypogenic karst was overprinted by later drainage systems as the hydraulic gradient changed, and placer deposits were formed from the erosion of existing mineralization. This was accompanied by circulation of meteoric water and resulted in the supergene weathering of the sulphide ore minerals. Eastward underflow of meteoric groundwater also exploited the same mineralization flow paths. There is evidence that pre-mineralization hypogenic karst was also significant in the formation of orebodies in the North Pennine Orefield and the Halkyn–Minera Orefield of NE Wales.

The geochemistry and mineralogy of high-S coals, with examples mainly from the East Pennines Coalfield in Yorkshire and Nottinghamshire, UK: an overview

Over a number of years, coals have been analysed in the geochemical laboratories of the University of Sheffield. Much of this work has been published and this paper presents an overview and, in some cases, a reinterpretation of the data. Most of the coal samples were obtained from seam sections in the Yorkshire and Nottinghamshire coalfields (now included in the East Pennines Coalfield), and from the Parkgate Coal in particular. Sulphur variations are essentially due to pyrite. In individual plies of the seam, lateral variation in total sulphur is thought to be due to the availability of sulphate at the time of deposition. Access of sulphate into the coal swamp environment can be directly related to river channels, many of which are known to have been long-lived features. The pyrite is of concern because of S emissions, but in addition it is the location in the coal for Hg, Tl, Pb, As and Se, all of which are of major environmental concern. Concentrations were determined by direct and indirect methods. The most common of the latter methods is statistical, and some of the potential problems are reviewed. Also contained within pyrite, but not exclusively so, are Cd, Ni and Sb. Trace element concentrations from different pyrite samples are similar, strongly suggesting a common source. Comparable trace element enrichment patterns for coals and marine shales provide evidence of a seawater origin. The chloride concentration in the coals is high and can also be linked to seawater. The two elements, S and Cl, differ in that Cl is conservative, is not involved in diagenetic reactions and is retained in the coal in residual pore fluids. Illite and kaolinite are the main clay minerals present, with subsidiary chlorite and mixed-layer illite-smectite. In most coals, the clay minerals are dominantly detrital, but in low ash coals, kaolinite of diagenetic origin can be detected. In some samples from the Barnsley Coal, the source of this kaolinite, based on the trace element geochemistry, is dispersed volcanic ash (basaltic). It is also highly likely that organic matter contributes small amounts of Si and Al in the coal, and phytoliths are one potential source. However, the detrital sediment is a major contributor to the major and trace element geochemistry of the coals. Trace elements with a dominantly detrital origin are Rb, Cs, Cr, Ga, Th, Nb and Li. Trace elements are also associated with the organic matter to a greater or lesser extent. Germanium is mainly associated with organic matter, but V is also present in the clays. These elements are mainly contained in vitrinite, although Ge concentrations are more variable, suggesting some mobility during diagenesis. This is borne out by Ge, V and Be showing enrichment at the margins of the the Parkgate Coal, following ‘Zilbermints Law’. Mobility during diagenesis is also demonstrated by the mineral infill of the cleat (joints). Stages of cleat mineralization have been recognized and related to diagenetic stages in siliciclastic sequences. Although there is evidence of element mobility after deposition in the coals, this is not thought to be related to the mineralizing fluids in the Pennine Orefields.

Westgarth Forster’s Strata – a reappraisal of a geological pioneer

In 1809, Westgarth Forster, an agent in the Northern Pennine lead mines, published his only book. Entitled ‘A Treatise on a Section of the Strata…etc.’, it is more usually known simply as his ‘Section of Strata’. Although some contemporaries doubted its originality, the reputation of this work has grown since its publication and Forster is now widely regarded as one of the pioneers of northern England geology. This paper gives an overview of Forster’s life and unsuccessful career before closely examining the text of his work. It shows how most of Forster’s text was copied without acknowledgement from earlier authors and was not drawn from observations made in the Northern Pennine Orefield. Reference is made to earlier sections of strata from mines in the north of England, and Forster’s ‘Strata’ is shown to be drawn mainly from these. Westgarth Forster should not be seen as a pioneer of the geology of northern England, but as an author who pieced together his book very largely from the work of others.

A 3300-year atmospheric metal contamination record from Raeburn Flow raised bog, south west Scotland

There is now a plethora of records of atmospheric metal deposition across Europe based on total concentrations and calculated enrichment factors. However, to place such records into an archaeological context and to identify anthropogenic contamination signals more accurately, it is important to separate the signals derived from anthropogenic activities from those of a natural origin. This study presents a new 3300-year record from a bog in the vicinity of Hadrian's Wall and the Northern Pennine orefield in order to generate a new atmospheric metal deposition record for this archaeologically important part of the British Isles. For this purpose multi element geochemistry was undertaken to apportion the contribution of trace metals (lead, zinc, copper, arsenic and mercury) and sulphur as a result of mining/metallurgy and/or geogenic processes. To extract the different contributions through time we used total concentrations and enrichment factors (EF), and applied principal component analysis (PCA) to the dataset. The PCA extracted 7 components: at least two components are necessary to elucidate the trace metal distribution. Zinc, arsenic and lead are mostly related to atmospheric pollution, while mercury and copper appear to be more closely associated with organic matter. Based on these results four phases of lead contamination have been identified that date to: I, c. 2350–1500 cal BP; II, c. 1050–700 cal BP; III, c. 500–350 cal BP and IV, 250 cal BP–present. Copper enrichment also occurs during the Bronze Age (c. 3150–2800 cal BP). Peaks in other metals do not always correspond with lead and they may have been caused by other land use changes or processes that operate internally within the bog. Although the lead can be attributed to both anthropogenic and geogenic sources, its down profile pattern is in accordance with contamination records elsewhere in Britain and Europe, and the lead enrichment recorded at Raeburn Flow suggests that the Northern Pennine orefield was exploited for metals during the late Iron Age and Roman period.

Mine water geochemistry and metal flux in a major historic Pb-Zn-F orefield, the Yorkshire Pennines, UK

Recent studies have shown up to 6 % of rivers in England and Wales to be impacted by discharges from abandoned metal mines. Despite the large extent of impacts, there are still many areas where mine water impact assessments are limited by data availability. This study provides an overview of water quality, trace element composition and flux arising from one such area; the Yorkshire Pennine Orefield in the UK. Mine drainage waters across the orefield are characterised by Ca-HCO3-SO4-type waters, with moderate mineralization (specific electrical conductance: 160-525 μS cm(-1)) and enrichment of dissolved Zn (≤2003 μg L(-1)), Ba (≤971 μg L(-1)), Pb (≤183 μg L(-1)) and Cd (≤12 μg L(-1)). The major ion composition of the waters reflects the Carboniferous gritstone and limestone-dominated country rock, the latter of which is heavily karstified in parts of the orefield, while sulphate and trace element enrichment is a product of the oxidation of galena, sphalerite and barite mineralization. Contaminant flux measurements at discharge sites highlight the disproportionate importance of large drainage levels across the region, which generally discharge into first-order headwater streams. Synoptic metal loading surveys undertaken in the Hebden Beck sub-catchment of the river Wharfe highlight the importance of major drainage levels to instream baseflow contamination, with diffuse sources from identifiable expanses of waste rock becoming increasingly prominent as river flows increase.

Plumbogummite from Upper Teesdale, County Durham, Northern Pennines, UK

Summary The uncommon, lead-aluminium phosphate hydroxide mineral plumbogummite is reported here, for the first time in the Pennine orefields, derived from a highly oxidized lead-rich vein at Grasshill mines, Upper Teesdale, Co. Durham. The plumbogummite is undoubtedly supergene in origin, but whether it formed along with associated pyromorphite through natural, in situ weathering, or is a post-mining, dump-formed alteration product is unclear.

Reply to discussion on ‘Hyper-permeable granite: lessons from test pumping in the Eastgate Geothermal Borehole, Weardale, UK’ by P.L. Younger and D.A.C. Manning

We are very grateful to F.W. Smith for his thoughtful consideration of the brief speculation we included in our paper about the origins of the permeable features encountered at 411 m depth in what is now known as the Eastgate No. 1 Borehole (Younger & Manning 2010). His remarks are very enlightening, and add significantly to the published record on the structural geology of the North Pennine Orefield. Dr Smith's comments actually penetrate a point of amicable difference between the two of us, with Younger being in favour of a predominantly structural interpretation, whereas Manning was more inclined to an explanation that also involved deep weathering. As it happens, further work undertaken at the site in 2010 has since shed further light on the matter, and would tend to support Dr Smith's suggestion that the empty voids found at 411 m depth in Eastgate No. 1 are essentially …

Radon concentrations in abandoned mines, Cumbria, UK: safety implications for industrial archaeologists

Abstract. This paper presents a number of surveys performed in a geographical area of the UK, part of which until recently was considered low radon risk. The Cumbrian region was identified by the Building Research Establishment (BRE) in its 1999 guide as an area without a significant radon problem in the built environment. The geology of the region, which includes the Northern Pennine Orefield is varied, but consists of granites, andesites, tuffs, carbonates, sandstones and shales. Mineralisation has taken place (mostly lead and copper ores) primarily along fault and fracture zones, one example being Copper Valley, northwest of Coniston village. This work quantifies the risk of exposure to radon in a number of abandoned mine environments. High radon levels, up to 28 589 Bq m−3, have been measured in parts of one mine. This study demonstrates that industrial archaeologists (such as the Cumbrian Amenity Trust Mining History Society or CATMHS members) and explorers of abandoned mines can be at risk from radon exposure and it proposes a management scheme to allow industrial archaeologists to continue exploration whilst minimising the risk to health from radon.

The North Pennine batholith (Weardale Granite) of northern England: new data on its age and form

SUMMARY A three-dimensional gravity model of the North Pennine batholith is interpreted to show that it comprises five contiguous steep-sided plutons. The North Pennine batholith was previously referred to as the Weardale Granite, but this term is now restricted to the largest, most central pluton, which was proved by the Rookhope Borehole in 1961. The surrounding plutons are the Tynehead and Scordale plutons in the west, and the Rowlands Gill and Cornsay plutons in the east. A new U–Pb zircon age of 399.3±0.7 Ma demonstrates an unequivocal Early Devonian (Emsian) age of emplacement for the Weardale Pluton. The similarity of the forms of the four unsampled plutons to the body beneath Rookhope, and to other Devonian granites in northern England, strongly suggests that they are also of Devonian age. Seismic reflection evidence supports a contrast between relatively deep-seated Devonian granites and tabular Ordovician granites in northern England. The most conspicuous magnetic anomalies over the North Pennine batholith are associated with the Early Permian Great Whin Sill, but there is also evidence of magnetized basement rocks or denser magnetic intrusive phases on the flanks of the non-magnetic, low density plutons. A long-wavelength magnetic low can be explained in part by the granite puncturing a deep magnetic basement, although the demagnetized zone may extend beneath the batholith. A spatial correlation between the vein systems in the Northern Pennine Orefield and the form of the batholith suggests that the granite masses played a significant role in focussing mineralizing fluids into the overlying Carboniferous rocks. The highest temperature mineralization occurs over the Weardale and Tynehead plutons, where there is also the clearest evidence for the channelling of mineralizing fluids through the batholith. The other plutons are generally associated with a lower intensity of mineralization, which occurs on their flanks rather than above their roofs. The Rookhope and Tynehead areas may therefore mark the location of convective ‘chimneys’ which were important in focussing the fluid circulation responsible for the mineralization. The coincidence of the ‘chimney’ zones with the minimum of the long wavelength magnetic low suggests that the hydrothermal system may also have played a role in modifying crustal magnetization.

Regional lead isotope study of a polluted river catchment: River Wear, Northern England, UK

High precision, lead isotope analyses of archived stream sediments from the River Wear catchment, northeast England (1986–88), provide evidence for three main sources of anthropogenic lead pollution; lead mining, industrial lead emissions and leaded petrol. In the upper catchment, pollution is totally controlled and dominated by large lead discharges from historic mining centres in the North Pennine Orefield ( 208Pb/ 206Pb, 207Pb/ 206Pb ratios range from 2.0744–2.0954 and 0.8413–0.8554 respectively). In the lower catchment, co-extensive with the Durham Coalfield and areas of high population density, pollution levels are lower and regionally more uniform. Isotope ratios are systematically higher than in the upper catchment ( 208Pb/ 206Pb, 207Pb/ 206Pb ratios range from 2.0856–2.1397 and 0.8554–0.8896 respectively) and far exceed values determined for the geogenic regional background. Here, the pollution is characterised by the atmospheric deposition of industrial lead and petrol lead. Lead derived from the combustion of coal, although present, is masked by the other two sources. Recent sediments from the main channel of the River Wear are isotopically indistinguishable from older, low order stream sediments of the North Pennine Orefield, indicating that contamination of the river by lead mining waste (up to several 1000 mg/kg Pb at some locations) continues to pose an environmental problem; a pattern that can be traced all the way to the tidal reach. Using within-catchment isotope variation and sediment lead concentrations, estimates can be made of the discharges from discrete mines or groups of mines to the overall level of lead pollution in the River Wear. As well as providing information pertinent to source apportionment and on-going catchment remediation measures, the database is a valuable resource for epidemiologists concerned with the health risks posed by environmental lead.

Hydromagnesite and dypingite from the Northern Pennine Orefield, Northern England

SUMMARY The rare basic hydrated magnesium carbonate minerals hydromagnesite and dypingite are reported from low temperature hydrothermal Pb–Zn deposits in the Alston Block of the Northern Pennine Orefield. Both minerals occur as very late stage constituents of deposits rich in barium carbonates. Apparently similar though uncharacterized magnesium carbonates are noted in very small amounts from elsewhere in the orefield.

Direct evidence of fluid mixing in the formation of stratabound Pb–Zn–Ba–F mineralisation in the Alston Block, North Pennine Orefield (England)

The North Pennine Orefield Alston Block has produced approximately 4 Mt Pb, 0.3 Mt Zn, 2.1 Mt fluorite, 1.5 Mt barite, 1 Mt witherite, plus a substantial amount of iron ore and copper ore from predominantly vein-hosted mineralisation in Carboniferous limestones. However, a significant proportion of this production (ca. 20%) came from stratabound deposits. Though much is known about the vein mineralisation, the relationship between the veins and the stratabound mineralisation is not well-understood. New petrographic, isotopic and fluid inclusion data derived from samples of stratabound mineralisation allow us to present a unified model that addresses the genesis of both the vein and stratabound styles of mineralisation. The mineralisation can be considered in terms of three episodes:

Realities and histories: ‘In search of a hidden landscape’

The intersection of geological and human histories in a northern Pennine landscape, covering the metalliferous mining areas of County Durham, Cumbria and Northumberland (formerly the counties of Cumberland and Westmoreland) known as the Northern Pennine ore field. On 11 December 1998 Bob and Joe Forster worked the final shift on the 260 East Level at Frazer's Hush fluorspar mine in the Vale of Rookhope, County Durham. In July 1999 the long history of hard-rock mining in the Northern Pennines ended with the closure of the Firestone Dib (decline) at Groverake Mine a half-mile east of Frazer's Hush. In an area now designated a landscape of outstanding natural beauty and granted European geo-park status in 2003 the residue of this industrial heritage is all that remains of an extraordinary convergence of geological and human histories. The specific focus of this article relates to the extensive history of metalliferous mining that has taken place in the region possibly since the Romano-British period, having a documented history from the twelfth century and which actively ceased on the last day of July 1999.

Geological controls on the sulphur content of coal seams in the Northumberland Coalfield, Northeast England

The sulphur content of coal is an important consideration when developing reserves for exploitation, driven by emission limits from power stations becoming more stringent. Variations in the sulphur content of Westphalian A and B coals from the predominantly freshwater Northumberland Coalfield, Northeast England, were studied according to their regional, stratigraphic and in-seam location. The observed variation in sulphur content spatially increases towards the source area away from more marine influenced areas, with increased sulphur content through time linked to changes in the general depositional environment as conditions became more marine-influenced. A model of basinal surface water and groundwater flow driven by post-depositional source area tectonism is thought to have played only a minor role in contributing secondary sulphur to the coal. However, the isotopic composition of coal pyrite shows a similar range in composition to that of pyrite and other sulphides from the North Pennine Orefield along the southern margin of the coalfield, suggesting an additional potential source of secondary sulphur, as sulphur-rich fluids were expelled northwards through the coal measures during early Permian Variscan transpression from the south. The Westphalian A and B are interpreted as third-order depositional sequences, defined by third-order maximum flooding surfaces. Each sequence is made up of several coal-bearing fourth-order parasequences, which tend to be more brackish to marine in character, on either side of the third-order maximum flooding surfaces when base level was relatively high. The lowest sulphur coals are confined to the lower to middle, relative low stand part of the Westphalian A third-order base level curve and the lowest part of the Westphalian B third-order base level curve. This difference is attributed to a more rapid rise of base level in the Westphalian B. The stratigraphic and spatial distribution of coal sulphur has been used as a guide to prediction of reserve identification for surface mining operations.

Tracing element sources of hydrothermal mineral deposits: REE and Y distribution and Sr-Nd-Pb isotopes in fluorite from MVT deposits in the Pennine Orefield, England

Fluorite from Mississippi Valley Type (MVT) deposits in the South Pennine Orefield, England, displays significantly different distributions of rare earths and yttrium (REY) compared to fluorite from similar MVT deposits in the North Pennine Orefield. Samples from the South Pennine Orefield display negative Ce and positive Gd and Y anomalies but lack any Eu anomaly, indicating that the REY were mobilized from relatively pure marine sedimentary carbonates. In marked contrast, fluorite from the North Pennine Orefield lacks any Ce and Gd anomalies but shows a pronounced positive Eu anomaly, suggesting that the REY were provided by different source rock(s), that the mineralizing hydrothermal fluid had experienced higher temperatures prior to fluorite precipitation, and that it was derived from deeper crustal levels in the north compared to the south. The isotopic composition of Sr in Blue John fluorite from the South Pennine Orefield suggests that Sr was mobilized from Lower Carboniferous (Tournaisian) limestones, whereas Pb isotopes suggest that in contrast to REY and Sr, Pb was derived from aluminosilicate rocks. Neither Nd nor Sr or Pb isotopes can be used to radiometrically date the formation of Blue John fluorite. All isotope systems studied indicate that the limestone host rock of this fluorite mineralization did not contribute to the trace element budget of the hydrothermal fluid. Our results show that different solutes in a natural water (hydrothermal fluid, groundwater, etc.) may be derived from different sources, and that the study of a small set of elements or isotope ratios may not provide full insight into the genesis or history of a mineralization or a hydrothermal fluid. Our data provide evidence for the uncoupling of Sr, Nd and Pb during fluid-rock interaction and fluid migration, and show that the use of plots such as 87Sr/86Sr vs. eNd. to learn about mixing relationships (as is commonly done in igneous geochemistry) is unreliable when applied to natural waters and their precipitates.

Metal contamination of active stream sediments in upper Weardale, northern Pennine Orefield, UK.

In the Upper Weardale area the headwaters of the River Wear bisect the Northern Pennine Orefield, where Pb-Zn-F-Ba vein-type mineralisation has been exploited since the Roman Conquest. The area contains evidence of open pit, underground and hydraulic mining of base metal ores, associated mineral processing and smelting, exploitation of ironstones during the industrial revolution, recent extraction of fluorite and active quarrying. The aim of this study was to determine the extent of modern sediment contamination arising from these past activities. Samples of active stream sediments were collected from all major drainage channels at 1 km intervals. The sediments were analysed for Pb, Zn, Ba, Mn, Fe, Co, Ni, Cu, Cr, As, Sb, Ag and compared to data from earlier regional geochemical surveys of low order drainage samples using ArcView software. The significance of contamination levels was assessed using the Ontario aquatic sediment quality guidelines. Our results indicate widespread contamination of some major drainages by Pb, Mn, Zn and As at concentration levels anticipated to significantly affect use of the sediments by benthic organisms. Furthermore, Pb contamination shows persistence in stream sediments downstream towards agricultural areas of the floodplain and drinking water abstraction points, above which interaction with colliery mine water discharges may occur.

Hydrothermal Fluid Origins in a Fluorite-Rich Mississippi Valley-Type District: Combined Noble Gas (He, Ar, Kr) and Halogen (Cl, Br, I) Analysis of Fluid Inclusions from the South Pennine Ore Field, United Kingdom

The South Pennine (Peak district) ore field, United Kingdom, is host to several fluorite-rich Mississippi Valley-type deposits and was chosen for study as an analogue to the Illinois-Kentucky fluorspar district, United States. The study was undertaken to test the idea that the large-scale carbonate dissolution and fluorite-rich mineralogy, characteristic of both districts, may require a magmatic source of HF. The data also provide constraints for water-rock interactions and potential fluid sources relevant to the local geology of the South Pennine ore field. Samples were studied from two of the largest and most economically important deposits within the South Pennine ore field, the Hucklow Edge and Dirtlow rakes. In vacuo crushing of irradiated calcite samples released inclusion fluids that were analyzed for noble gas isotopes ( Ar, Ar, Kr) and the halogens (Cl, Br, I). This was achieved simultaneously by noble gas mass spectrometry (Ar-Ar methodology) and was combined with fluid inclusion thermometric salinity data to determine noble gas concentrations. In addition He isotope analyses were obtained from unirradiated fluorite. The He/ He ratio of the Pennine ore fluids (≤0.1 Ra, where Ra = atmospheric He/ He ratio of 1.4 × 10 ) is significantly lower than the maximum value recorded in the Illinois-Kentucky fluorspar district (0.35 Ra: Kendrick et al., 2002, this volume), indicating a crustal fluid source and supporting existing basinal brine models. The low Ar/ Ar ratios with most 50 to 60 percent halite dissolution water (Br/Cl mol ratio = 0.57-0.92 × 10 ). The salinity of fluids included in the main stage of the Hucklow Edge mineralization (avg of 22 wt % NaCl equiv) places an upper limit on the extent of meteoric recharge at 15 vol percent. A secondary vein present at Hucklow Edge has a lower salinity of 40 m.y., a time scale compatible with models in which fluids were derived from small local basins such as the Widmerpool and Edale Gulfs.

Hydrothermal Fluid Origins in a Fluorite-Rich Mississippi Valley-Type District: Combined Noble Gas (He, Ar, Kr) and Halogen (Cl, Br, I) Analysis of Fluid Inclusions from the South Pennine Ore Field, United Kingdom

Hydrothermal Fluid Origins in a Fluorite-Rich Mississippi Valley-Type District: Combined Noble Gas (He, Ar, Kr) and Halogen (Cl, Br, I) Analysis of Fluid Inclusions from the South Pennine Ore Field, United Kingdom