10 research outputs found
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
Gold potential in the Dalradian rocks of NW Northern Ireland : prospectivity analysis using Tellus data
Gold potential in the Dalradian rocks of NW Northern Ireland: GIS-based prospectivity analysis using Tellus data
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
Data arising from drilling investigations of the Knock Intrusion at Claymires, north-east Scotland
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