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Mineral Reconnaissance Programme (MRP) reports 91–100

91 A geochemical survey of part of the Cheviot Hills and investigations of drainage anomalies in the Kingsseat area [2.77 Mb]

D G Cameron and others (1988)

A reconnaissance geochemical drainage survey in the Cheviot Hills of northern England identified anomalous concentrations of metals, which are, in general, related to (i) known mineral occurrences, (ii) hydrous oxide precipitation and scavenging processes, (iii) the relatively widespread occurrence of baryte, (iv) contamination, (v) tourmalinisation and other hydrothermal activity and (vi) high background levels in unmineralised rocks. Some anomalies may reflect hitherto unknown mineralisation. Anomaly groupings and regional variation patterns in the data are influenced by major structures such as the Gyle–Harthope fracture zone. In the Kingsseat area, rocks previously mapped as extrusive mica felsites are reinterpreted as a high level intrusion complex, named the Cock Law Complex, which contains five distinct types of porphyry. Many of the intrusive and extrusive rocks are highly altered. Metal enrichments were recorded in many of the analysed rocks. The greatest enrichments, for the widest range of elements, occur in samples taken from a gossanous structure, where the mineralisation has features in common with the epithermal precious–metal style of mineralisation associated with sub–aerial volcanism.

92 A mineral reconnaissance survey of the Llandrindod Wells/Builth Wells Ordovician inlier, Powys[6.85 Mb]

T R Marshall, R C Leake and K E Rollin (1987)

A reconnaissance drainage geochemical survey, supplemented by soil sampling, located several Pb and Zn anomalies, many of which appear to be associated with the outcrop of the main volcanic unit of the area. Samples collected from an area of old lead workings in the west of the inlier failed to provide evidence of further vein mineralisation beyond the limits of the workings. Elsewhere the biggest concentration of Pb and Zn anomalies and the greatest amplitude of anomaly (2000 ppm Pb) were located over the northern outcrop of the main unit of tuffaceous volcanic rocks, particularly in the vicinity of the farm Pen Rhiw Frank. A detailed geological, geochemical and geophysical survey of this area was carried out. The geophysical work revealed a zone of high resistivity with roughly coincident low amplitude chargeability maxima and a VLF crossover over part of the zone. There was a general association of this zone with Pb in soil anomalies and the presence of significant amounts of weathered pyrite in the limited outcrops. The Pb in soil anomalies broadly follow the local strike of the rocks. Four boreholes were drilled to test the down dip extension of apparently stratabound surface soil anomalies. Secondary Pb minerals occur within a soft clay–rich section 5.8m thick near the top of one of the holes. Lead levels up to 0.52% over 3.4m were found in this zone, which is located at the interface between a dacitic tuff and an andesitic lava.

93 Stratabound base–metal mineralisation in Dalradian rocks near Tyndrum, Scotland [1.01 Mb]

C G Smith and others (1988)

Stratabound zones of base–metal enrichment (sphalerite, with subordinate galena and chalcopyrite) occur in the Middle Dalradian Ben Challum Quartzite, a newly recognised horizon occcurring between the Ben Lawers Schist, at the top of which there is a horizon of cupriferous pyrite, and the Ben Lui Schist, at the base of which a chromiferous horizon is developed. The distribution of mineralisation over some 9km of strike length between Tyndrum and the upper Glen Lochay has been mapped at a scale of 1:10 000, and integrated geophysical, geochemical and mineralogical studies carried out. Four boreholes were sited on selected anomalies and the resultant core analysed.

94 Geochemistry of some heavy mineral concentrates from the island of Arran [4.32 Mb]

K E Beer (1988)

Chemical analysis of panned concentrates has indentified areas of possible mineralisation that merit further study. Moderate values of Sn and W in the Tertiary Goatfell granite suggest the possibility of disseminated low grade mineralisation. A cluster of anomalous values near the southern margin of the northern granite holds out some hope of zones of quartz–molybdenite veining associated with the marginal areas of the granite. Anomalous values for Ag are quite widely spread in the southern half of the island and appear to be associated with some of the basic minor intrusives. There are high Ba values in samples from the environs of the northern granite and over the Palaeozoic sediments east of Machrie Bay. Occasional very high values for Cu and Pb occur in lithologies which might well host sulphide mineralisation.

95 Mineral reconnaissance at Menear, St Austell, Cornwall [2.61 Mb]

K E Beer, B C Tandy and G S Kimbell (1988)

Geochemical soil sampling shows no evidence for a continuation of the Menear stockwork Sn mineralisation beyond the eastern rim of the old openwork, though there may be some extension westwards below areas of recent housing development. Elevated levels of Sn in soils are indicated to the north of Wheal Eliza, with above average values of Cu and Zn immediately to the south, over the site of that mine; VLF–EM anomalies delineate several possible mineral veins in this area. None of these metals are present at concentrations likely to be of economic interest.

96 Geochemistry of sediments from the Lui drainage, Braemar, Grampian [672 Kb]

K E Beer and M J Bennett (1988)

Stream sediments from the western headwaters of the Lui Water all contain markedly high amounts of Nb and some bear anomalous levels of Ce, Y, Th or Zr. Most of this compostion is attributable to the presence of a refractory mineral suite presumed to be derived from nearby granitic rocks. The tenor of these elements, however, offers little prospect of any significant concentrations of industrial or ore minerals.

97 Magnetic and geochemical surveys in the area between Geltsdale, Cumbria, and Glendue Fell, Northumberland [4.10 Mb]

A D Evans, P D Roberts and J H Bateson (1989)

A magnetic survey over the northwest corner of the Lower Carboniferous Alston Block revealed anomalies en–echelon along the line of an aeromagnetic feature. These may represent part of a major north–east–south–west structural feature extending to the northeast across Northumberland. The magnetic data indicate that the Whin Sill may be more extensive than suggested on the geological map, and additional evidence for this is provided by the geochemical data from the Thinhope Burn and Glendue Burn catchments immediately west of the River South Tyne. Geochemical stream and soil sampling confirm Pb–Zn mineralisation in the area.

98 Exploration for gold between the lower valleys of the Erme and Avon in the South Hams district of Devon [3.33 Mb]

R C Leake and others (1988)

A geochemical drainage survey within a poorly understood belt of Lower Devonian rocks, using panned concentrates, revealed gold anomalies which were subsequently followed up by overburden sampling, geophysical surveys and drilling. The geophysical data suggest that the upper crustal structure of the area and its relationship with the Start Complex to the south require re–interpretation. The multivariate statistical procedures of principal component analysis and cluster analysis, applied to the drainage geochemical data, facilitated recognition of geochemical patterns reflecting major geological boundaries and mineralisation of different types. Comparison of the analyses of different size fractions of the concentrate samples proved useful in detecting anomalies likely to be derived from contamination and in classifying anomaly types. The drainage data strongly suggest the presence of a major fault, trending around west–north–west, separating two entirely different sequences in the north–east of the area. The use of panned overburden samples from shallow pits in exploration for gold is described and compared with the results of conventional sieved soil samples. Mineralogical examination and chemical analysis of mineral grains from overburden concentrate samples led to the discovery of the very rare mineral potarite (Pd + Hg) and the recognition of several types of iron oxide, casserite and some secondary base–metal minerals. On average the diameter of gold grains in drainage is three times that in overburden grains, whether from background or anomalous sites. To account for this it is suggested that gold grain growth has occurred in head and perhaps in more recent alluvium in valley bottoms. The chemical composition of overburden gold grains from a number of sites has been determined by electron microprobe. Many grains have relatively silver–rich rims while the bulk of the grain is silver–poor, frequently containing a few percent Pd. Other grains are pure gold to the detection limit of the analytical procedure employed.

99 Base metal and gold mineralisation in north–west Anglesey, North Wales [1.44 Mb]

D C Cooper and others (1990)

Mineral exploration in northwest Anglesey, an area of complex geology with rocks ranging from Precambrian to Ordovician, has indicated the presence of hitherto unknown base metal mineralisation, accompanied locally by gold. Very low frequency electromagnetic ground survey data contain strong features related to mapped fault lines and steeply dipping geological boundaries. IP and soil survey data indicate the presence of anomalies related to mineralisation and more detailed surveys were carried out in the area between Carmel Head and Llanfairynghornwy. The sources of seven of the geophysical anomalies were investigated by fifteen boreholes ranging in depth between 32 and 122m. These boreholes showed that the anomalies were related to buried base–metal sulphide (Cu, Zn, Pb) mineralisation, locally accompanied by gold. The mineralisation is polyphase: syngenetic/diagenetic pyrite and disseminated pyritisation (possibly associated with sericite alteration) events are followed by hydrothermal mineralisation characterised by quartz ± carbonate ± chalcopyrite ± sphalerite ± galena ± pyrite veins and impregnations. This mineralisation occurs in at least five separate structures. Geochemical and geophysical anomalies not investigated by drilling suggest the presence of further mineralised structures and extensions to those intersected by drill–holes.

100 Molybdenum mineralisation near Chapel of Garioch, Inverurie, Aberdeenshire [4.18 Mb]

T B Colman and others (1989)

Molybdenum and tungsten mineralisation in quartz veins is associated with the Caledonian Middleton granite, a small stock apparently rooted in the buried roof of the large Bennachie pluton. The granite is emplaced in Dalradian schists. The veins are usually in granite, which is intensely sericitised (greisenised?); the alteration and mineralisation are believed to be coeval. Geophysical surveys were used to define the granite stock, an epidiorite body (a sill?) which caps the hill, and a late (Tertiary?) east–west basic dyke. Four short inclined boreholes were drilled in the Dalradian schists to the east of the granite stock and three into the granite itself. The drilling intersected minor quartz–molybdenite mineralisation in both schist and granite. Exposure is poor and neither the drilling nor base–of–drift geochemical sampling were effective in defining the distribution of the mineralisation.