Absolute fixing of tide gauge benchmarks and land levels : the BGS contribution to a report on a study of the London and Thames estuary region

This report comprises material submitted as the British Geological Survey (BGS) contribution to the final report of a project measuring changes in land and sea levels using high precision global positioning system (GPS) surveying, absolute gravimetry (AG), persistent scatterer interferometry (PSI) and tide gauge records. Data was collected during the period 1997 to 2005 for a National study of changes around the coast of Great Britain, and a Regional study of changes along parts of the Thames Estuary and the River Thames at London. Since 2003, the national study has been funded by the Joint DEFRA/EA Flood and Coastal Erosion Risk Management R&D Programme, and a regional study, funded by the Environment Agency Thames Estuary 2100 project. The national study was carried out jointly by the Proudman Oceanographic Laboratory (POL) and the University of Nottingham’s Institute of Engineering Surveying and Space Geodesy (IESSG). The regional study was led by IESSG and carried out jointly by IESSG, POL, Nigel Press Associates Ltd. (NPA) and the British Geological Survey (BGS). The item in the project research plan relevant the main BGS input is Objective 08: ‘The estimates of changes in absolute ground level for the regional network of 13 GPS stations and a few thousand PSI points (output from 07) will be analysed, and geological interpretations presented using the geological database and other available information’. The final project report includes a condensed version of this material, with only a few of the figures. That is due to be published as Environment Agency R&D Technical Report FD2319/TR. The geological setting of the London region is described in a report for the EA/NERC CONNECT B project (Bingley et al., 1999), and by Ellison et al. (2004)

Mineral exploration in the Cockermouth area, Cumbria. Part 2: follow-up surveys

This report describes the results of geochemical, geological and geophysical surveys across three small areas of Carboniferous and Lower Palaeozoic rocks along the northern margin of the English Lake District. The areas were chosen from the appraisal of regional-scale survey data described by Cooper et al. (1991). In two of the areas, Ruthwaite and Tallentire, the objective was to provide more information on the extent and magnitude of fracture-controlled epigenetic baryte and base metal mineralisation. In the third area, at Whitrigg, brief surveys were carried out to aid the interpretation of unexplained geochemical and geophysical anomalies found during two projects carried out under the Mineral Exploration and Investment Grants Act (MEIGA). At Ruthwaite, where a mine formerly worked baryte from a fault separating Lower Palaeozoic and Carboniferous rocks, surface indications of further baryte mineralisation were found. Soil analyses indicated that mineralisation may be present along the continuation of the faultline worked at Ruthwaite and in the Eycott Volcanic Group rocks to the south of it. In this area relatively small, but in some circumstances perhaps economically attractive, deposits of baryte may be present under drift cover. In the Tallentire Hill area, geological mapping followed by traverse-based soil sampling showed that fracture-controlled mineralisation is widespread in the Carboniferous (Dinantian and Namurian) rocks. The fracture fillings consist dominantly of baryte, often accompanied by carbonate, with traces of copper and mercury. Where seen at surface the fracture fillings are too small, patchy and low-grade to be of any economic importance. Baryte mineralisation also occurs locally as patchy impregnations in sandstones. These are considered to be epigenetic deposits related to the fracture-controlled mineralisation. Trial geophysical surveys suggested that electrical methods may be useful in determining the extent of the mineralised sandstone. There is a possibility that more extensive baryte deposits may be present in the limestone succession underlying the mineralised sandstones. In the Whitrigg area, Carboniferous rocks are separated from Lower Palaeozoic rocks of the Eycott Volcanic Group by the easterly-trending Boundary Fault and north-westerly-trending Bothel Fault. Evidence from an old mineral working and the results of a soil survey indicate that patchy, epigenetic, fracture-controlled baryte and base metal mineralisation occurs along the Bothel Fault and, locally, in the adjacent rocks. A feature of this mineralisation is the presence of mercury, which is most abundant in a sample of brecciated and altered rock from the Eycott Volcanic Group. Prominent base metal in soil anomalies discovered by MEIGA-funded projects near Stangerhill are not associated with barium anomalies. It was concluded that these soil anomalies are most likely to be caused by secondary concentration in overburden, and that the source of metals may be a sub-cropping metalliferous horizon within the Carboniferous succession or, more probably, fracture-controlled mineralisation. Trial geophysical surveys carried out in all three areas indicated that in ground free of artificial sources the VLF(EM) and conductivity mapping methods could be useful for tracing faults beneath drift and providing information on drift thickness. Closely-spaced soil sampling proved effective for detecting mineralisation in areas where the drift cover is thin, and a trial soil-gas survey showed that this technique could also be useful for tracing faults beneath drift

A preliminary interpretation of Tellus airborne magnetic and electromagnetic data for Northern Ireland

An airborne geophysical survey of the whole of Northern Ireland was flown in 2005 and 2006 as part of the Tellus project. This project was funded by the Northern Ireland Department of Enterprise Trade and Investment and by the Rural Development Programme through the Northern Ireland Programme for Building Sustainable Prosperity (www.tellus.detini.gov.uk). The aircraft used was a De Havilland Twin Otter which carried magnetic, electromagnetic and radiometric sensors. It was operated as a joint venture between the British Geological Survey (BGS) and the Geological Survey of Finland (GTK). Survey lines were spaced 200 m apart and orientated NNW or ESE (165 and 345º). The flying height was 56 m above ground (185') in rural areas rising to 240 m over urban areas. This report presents a preliminary interpretation of the airborne magnetic and electromagnetic data and shows examples of the types of geological feature that can be identified from the data on a regional scale. A few comments on the radiometric results are also included together with a brief evaluation of the mineral potential of Northern Ireland based on the airborne geophysical data. For the preliminary interpretation many high resolution images of the magnetic, electromagnetic and radiometric data were generated and analysed in a GIS system along with existing regional gravity, digital geological mapping and mineral occurrences data. The main structural elements were identified and digitised and a structure map produced. The Tellus data have provided a wealth of new information about the geology, regional structure and mineral potential of Northern Ireland and the GIS has proven a powerful tool for analysing these data at both regional and local scales. The strong magnetic signature of the Antrim basalts allows their surface extent to be mapped accurately in areas of poor exposure, and within the basalt outcrop lineaments associated with bounding faults of sedimentary basins have been identified. The margins of the Tyrone Igneous Complex and the internal structure of the complex itself are revealed in stunning detail and many new faults and sheared rocks identified. Within the adjacent Dalradian rocks arcuate linear magnetic anomalies related to fold structures and several important magnetic marker horizons have been revealed. The full extent of the dyke swarms that cross Northern Ireland has only now come to light with the new Tellus magnetic data. Dykes reveal regional stress fields, and those that are offset can be used to measure post Palaeogene fault displacements. The margins of the major intrusive centres of the Newry Igneous Complex, Mourne Mountains, Slieve Gullion and Carlingford and their internal structure have also been delineated by the magnetic and gravity data. The rocks that make up Northern Ireland show a considerable variation in their electrical properties and where contrasts between geological formations are sufficiently large their geological distribution can be mapped. The main mineral prospectivity target in Northern Ireland lies within the area covering the Upper Dalradian rocks of the Sperrins area, the Omagh Thrust Fault and the sheared rocks of the Tyrone Igneous Complex where this area shows the greatest degree of shearing and faulting. Magnetic anomalies depict a series of arcuate structures within which mineralisaton is located in a series of distinct belts and appears to be spatially related to shearing and faulting. A prospectivity study of this area is highly recommended

Exploration for stratabound mineralisation in the Argyll Group (Dalradian) of north-east Scotland

The Mineral Reconnaissance Programme (MRP) identified several horizons of stratabound mineralisation within the Argyll Group during investigations of the Dalradian Supergroup in Scotland between 1973 and 1987. These included the multi-million tonne Aberfeldy baryte deposits. Most of the discoveries were made in the central and south-western Scottish Highlands, where the Dalradian succession is well recognised. The Dalradian of north-east Scotland, because of its poorer exposure and greater complexity, did not receive the same level of attention. The project reported here was set up to assess the potential of the Argyll Group in north-east Scotland for stratabound mineralisation, based on the geological models developed in the central Highlands. An initial desk study involved the digitisation (where necessary), integration and review of the following datasets: (i) geological mapping, including the results of new BGS mapping, (ii) BGS airborne aeromagnetic data, (iii) BGS geophysical ground survey results, (iv) BGS Geochemical Baseline Survey of the Environment drainage data, (v) existing MRP data, (vi) BGS traverse-based soil sampling results, and (vii) datasets collected by Exploration Ventures Ltd, principally detailed airborne and ground geophysical information. Assessment of these datasets identified three broad areas which contained geochemical, geophysical and geological features that merited examination to determine their sources and indicate the potential for economic stratabound mineralisation. These areas were Ballater-Strathdon, Upper Deveron and Huntly-Portsoy. Geochemical and geophysical ground surveys were carried out in parts of all three of these areas and followed-up locally by pitting and trenching to clarify, the sources of individual anomalies. The studies indicated that the areas with the most potential for stratabound mineralisation occur to the east of the Portsoy Lineament and/or in rocks which cannot be easily correlated with Argyll Group rocks elsewhere. These rocks tend to be lithologically different from the typical Argyll Group sequence and are generally more fractured, sheared, brecciated and altered. The most promising area for the discovery of stratabound mineralisation is considered to be in the Upper Deveron area at Wellheads. Here, high levels of lead and zinc in overburden are probably enhanced by hydromorphic processes, but the source of the lead has been traced to quartzites and the zinc to adjacent pelites within the Corinacy Pelite Member of the Blackwater Formation. The predominantly lead-zinc mineralisation is similar to that at Glenshee and Dericambus. Detailed VLF EM and IP surveys are recommended to assist in defining trenching and drilling targets. Lead and coincident IP anomalies at Succoth-Gouls also merit follow-up investigation. In the Ballater-Strathdon area a large EM and magnetic anomaly on Creagan Riabhach, although apparently low in base-metal content, merits further investigation on the grounds that: (1) a significant amount of sulphide mineralisation is present at shallow depth, (2) there is good evidence for stratabound mineralisation, and (3) the rocks are thought to be similar to the Ben Lawers Pyrite, where copper mineralisation occurs sporadically. In the Upper Donside part of the Ballater-Strathdon area several lead-zinc anomalies have been identified from drainage sampling, but very little mineral-exploration work has been carried out over the c. 10 km strike length of the Argyll Group metasedimentary rocks. The Glenbuchat Graphitic Schist Formation has a volcanic component here, providing the potential for hydrothermal mineralisation. In the Glen Avon part of the area lead and zinc drainage anomalies have been identified and their potential is enhanced by proximity to the Lecht mineralisation

Exploration for volcanogenic mineralisation in south-west Wales

South-west Wales has extensive and voluminous extrusive and intrusive volcanic rocks of Grdovician age interbedded with black shales and other sedimentary rocks, a sequence which has proved to contain economic base-metal deposits in other areas of the British Isles and elsewhere. No significant mineral deposits are known in the area apart from a small lead mine at Llanfymach which was abandoned in the last century. The Mineral Reconnaissance Programme has completed several projects in the area in the past 20 years and this report is a compilation of data collected during the programme but not previously published, together with data from additional new investigations in the Treffgame, Crosswell and Llangynog areas. Regional interpretations of the geophysics (gravity and aeromagnetics), lithogeochemistry and petrogenesis are presented in the report. These include the physical properties of many of the rock types and a study of the rare-earth-element (REE) contents of examples of the volcanic rocks to determine their origin and their potential for volcanogenic massive sulphide (VMS) and preciousmetal mineralisation. More detailed investigations were carried out in the Treffgame area, following on from earlier MRP work which included the drilling of three cored boreholes. The published summary report (Brown et al., 1987) contained little data as these were in a separate unpublished dataset which was later released on open file. The current report publishes some of the results of the earlier work, including details of the drilling. No sulphides other than pyrite were found during the earlier survey but up to 8.6% Ba (as baryte) was found in rhyolite lavas and tuf& in Borehole 1 on Dudwell Mountain. This prompted further investigations, described in this report, which included additional soil geochemistry coupled with geophysical techniques not used in the earlier survey. The aim was to investigate the possibility that volcanogenic mineralisation at depths of up to 100 m may occur between the widely spaced lines of the initial survey. Geophysical methods included gravity, electromagnetic (EM) and self-potential (SP). Although no signi&ant base-metal mineralisation was located, massive baryte and disseminated pyrite were found in a metre-wide zone of hydrothermal alteration in Rock Farm Quarry at the western end of the Roth Rhyolite Group. Work in the Crosswell area showed anomalous levels of Ba in soil (exceeding 2000 ppm). There, coincident strike-parallel EM conductors are associated with black shales overlying volcanic rocks of the Fishguard Volcanic Group. A regional lithogeochemical survey demonstrated that the Sealyham Volcanic Group contains acid volcanic rocks with similar intensity of alteration to that observed in the Treffgarne area; it may also be prospective for volcanogenic mineralisation. Further work is recommended in a number of districts including the ground from Plumstone Mountain to Rock Farm Quarry in the Treffgame area, the Crosswell locality and parts of the Sealyham Volcanic Group

Gold in the Ochil Hills, Scotland

Mineral reconnaissance drainage sampling in the late 1970s identified gold in heavy mineral concentrates collected from a number of localities in the Ochil Hills. Subsequent detailed sampling of these localities showed that alluvial gold is present over a large area of the central Ochils and extends eastwards to the Firth of Tay. The most anomalous catchment, Borland Glen, near Glen Devon, was the focus for further integrated geological, geochemical, and geophysical studies. The geology of Borland Glen comprises a series of Lower Devonian andesitic lavas and pyroclastics intruded by a diorite body and porphyry dykes. Minor hydrothermal alteration is visible at surface. A large induced polarisation anomaly was found near the watershed between Borland Glen and Coul Burn and was interpreted as a steep-sided zone of disseminated pyrite with associated hydrothermal alteration. Overburden sampling proved gold and mercury anomalies over the same area. Seven boreholes were drilled to a maximum depth of 102 m to investigate the source of the IP and overburden geochemical anomalies. Intense hydrothermal alteration and brecciation were found to have affected the lavas and pyroclastics in the central, IP-anomalous zone and were accompanied by major pyritisation with associated minor base metal sulphides. Gold values in the drillcore reach a maximum of 505 ppb Au and it is concluded that the bedrock source of the alluvial gold has not been proved. However, the intense hydrothermal alteration in the setting of an evolved calcalkaline volcanic complex is indicative of a large epithermal system, and a more fertile source may yet be discovered in the area. Other gold sources are indicated in the central Ochils and further detailed investigations are thought to be warranted

Revealing deep structural influences on the Upper Cretaceous Chalk of East Anglia (UK) through inter-regional geophysical log correlations

New borehole geophysical log interpretations between Wiltshire and north Norfolk show detailed lateral changes in the spatial relationships of Chalk Group marker beds. They show how marker beds in the Turonian and Coniacian Chalk Group in East Anglia pass laterally into their correlatives further west, and reveal unusual lateral thickness changes affecting stratigraphical intervals in the East Anglian succession. Newly enhanced regional gravity and magnetic data indicate that these thickness changes are probably related to WNW to ESE trending structural lineaments in the Palaeozoic basement rocks of the buried Anglo-Brabant Massif. The later part of the Mid Turonian and early part of the Late Turonian succession across East Anglia is greatly thickened, and shows almost no lateral variability. These relatively soft, smooth-textured chalks equate with thinner, hard, nodular beds formed in both shallow marine and deeper basinal settings elsewhere in southern England. Since it seems unlikely that there was greater sediment accommodation space across East Anglia at this time compared to basinal areas, this thickening may reflect a localised coccoliths productivity pulse, or perhaps a sheltered palaeogeographical position that protected the area from sediment-winnowing marine currents