Injection of somatostatin‐14 (SS‐14) at 5 ng g−1 body mass (BM) into rainbow trout Oncorhynchus mykiss decreased (P < 0·05, cubic, r2 = 0·54) levels of growth hormone (GH) (1·5 ± 0·9 ng ml−1v. 6·6 ± 0·6 ng ml−1) over time when compared to controls. Somatostatin‐14 at 50 ng g−1 BM also decreased (P = 0·064, quadratic; r2 = 0·30) levels of GH (3·6 ± 2·1 ng ml−1v. 6·6 ± 0·6 ng ml−1) over time compared to controls. In a second study, passive immunization against SS‐14 (1 : 25 dose) increased (P = 0·10, cubic, r2 = 0·12) levels of GH (11·0 ± 4·8 ng ml−1v. 5·2 ± 1·4 ng ml−1) over time. Passively immunizing against SS‐14 (1 : 50 dose) increased (P < 0·05, cubic, r2 = 0·10) levels of GH (8·2 ± 2·3 ng ml−1v. 5·2 ± 1·4 ng ml−1) over time compared to controls. Overall, in the active immunization study there was no difference (P > 0·10) in specific growth rate (G) or feed conversion ratio (FCR) between the three treatment groups during the 9 weeks of the study. Only four of the fish immunized against SS‐14, however, developed antibody titres against SS. Compared to controls, these fish exhibited a G of 0·89 ± 0·09 v. 0·56 ± 0·09% per 3 weeks and FCR of 0·80 ± 0·04 v. 1·20 ± 0·05 g g−1. In SS‐14 immunized fish, levels of GH decreased (P < 0·05) by day 63 while levels of insulin like growth factor‐I (IGF‐I) increased (P < 0·05) by day 42 and 63. These results indicate the hypothalamic hormone SS‐14 regulates GH secretion similarly in rainbow trout as it does in mammals. Active immunization against SS‐14 could improve growth performance in rainbow trout but enhanced G and FCR is dependent upon generation of antibody titres.

The increased availability of digital geoscience information and major improvements in data handling technology between the 1980s and the late 1990s have had a significant effect on mineral exploration. Geographical information systems (GIS) are being applied increasingly to the integration of geoscience data sets so that more reliable and objective exploration methods can be developed. The MIDAS project was concerned with the development of such an approach for gold exploration on the basis of studies of the Caledonian and Variscan orogenic belts of western Europe, which have a range of types of gold mineralization in different tectonic settings. Participants in the MIDAS programme included members of the academic, commercial and government sectors in Britain, France, Ireland, Portugal and Spain. Parts of the study related to the British Caledonides. A description is given of the regional geochemical, geophysical and tectonic settings of the zones of the British Caledonides in which gold mineralization is concentrated and examples are presented of the detailed data compiled for selected occurrences of gold mineralization of mesothermal lode and epithermal-porphyry types. GIS techniques for the display and analysis of multi-variate data sets are applied to the data, allowing the development of metallogenic models for gold exploration from the reconnaissance to the local scale. The application of knowledge-based methods to the mapping of gold prospectivity is discussed.

This research, which has taken part of the time of the author over a period of more than ten years, has been rewarding in the sense that insight has been gained in what turned out to be a complex problem. It is hoped that this work can be of assistance to the dredging contractors and consulting engineers involved in rock dredging contracts. Being aware of the geological factors involved in the mechanical excavation of rock is the most important notion that can benefit and improve the quality of site investigation reports.

The British Caledonides contain a range of mineralization styles, including a world-class stratiform, sediment-hosted, SEDEX Ba-(Pb-Zn) deposit and mesothermal and epithermal gold mineralization. The British Geological Survey's regional geochemical database (G-BASE) has been used to identify the regional-scale geochemical patterns associated with the various mineral deposit types and to examine the extent to which their distribution reflects the presence of long-lived metallogenic provinces in the crust. The geochemical data have been analysed in relation to regional geology by image-analysis methods to provide new insights into the setting of mineralization, geochemical constraints on tectonic models for Caledonide evolution and the evidence for terrane amalgamation and for large-scale processes that have affected the distribution of chemical elements in the crust. There is evidence that much of the mineralization reflects the presence of long-lived metallogenic provinces, which have a distinctive geochemistry that reflects their origin as zones of crustal extension and lithospheric thinning. In the case of the Upper-Middle Dalradian SEDEX deposits the relationship between geochemistry and the tectonic setting is direct. In other cases rocks deposited in extensional zones in the crust appear to have acted as crustal reservoirs of ore-forming elements, which were concentrated further during later mineralizing events.

Heavy metal concentrations have been determined in topsoils (0-15cm) in the London Borough of Richmond-upon-Thames, a non-industrial, mainly residential area of approximately 56 km(2), and Wolverhampton an industrial city in the West Midlands of 70 km(2). Soil samples were taken on a grid basis at a density of four per km(2) and analysis for 25 elements was carried out by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Topsoils in Richmond were found to have significantly higher concentrations of heavy metals in developed locations compared to areas of open space, whilst in Wolverhampton topsoils a greater degree of contamination with Zn was found than with Pb. GIS-based mapping techniques used in conjunction with statistical analysis of the data have highlighted the influence of land-use on the heavy metal content of topsoils in these two urban areas. The highest concentrations of Pb in Richmond-upon-Thames ( > 1000 mu g/g) tend to occur close to major road junctions on roads with high traffic densities. High levels of Pb (approx. 500 mu g/g) also occur in the areas where the oldest housing is located (> 100 a). In Wolverhampton the highest concentrations of heavy metals, Zn in particular, are generally located to the east of the city in areas of both historical and contemporary industrial activity. Copyright (C) 1996 Elsevier Science Ltd

Concentrations of Pt, Pd, Rh and Au in soils and road dusts taken from areas of high and low traffic flows in the London Borough of Richmond and from a section of the Kingston bypass (A3) at New Malden, Surrey, have been measured. High concentrations of platinum are associated with high traffic densities. Samples taken from streets of lower traffic flows were found to contain the lower concentrations of the ranges. These values correlated well with the levels of lead which were also high at roundabouts. If the preliminary results obtained in this study apply more generally throughout the UK, then the potential for exposure to enhanced levels of Pt would appear to be higher for road users and for those living in urban environments or along major highways.

The Southern Uplands terrane is an early Palaeozoic accretionary thrust system that formed during closure of the Iapetus Ocean. The initial (late Ordovician to early Silurian) thrust slices contain turbidite strata probably derived from a back-arc environment, whereas the later (mid-Silurian) thrust sequence propagated southwards as a foreland-basin thrust belt across the suture zone that was formed by mid-Silurian continental collision. Arsenic and lead are regionally enriched in stream sediment derived from the northern (back-arc) sector, but the highest As value's occur in southwest Scotland over a compound Permian horst that is defined by northwest-southeast faults. Subdivision of the horst into blocks of different structural depths is possible hom a consideration of the fabrics within a major Caledonian shear zone that trends northeast-southwest across the area. The broadest part of the shear zone occurs within the horst and contains textures that are indicative of deformation around the brittle-ductile transition at depths of about 10-12 km and a temperature of about 300 degrees C. The shear zone has also acted as a focus for the intrusion of minor dioritic bodies and the shear fabrics appear to have a pre- to syntectonic relationship with the 392-m.y. Cairnsmore of Fleet granite pluton. Thus, in southwest Scotland three factors combine to recommend the area as having potential for gold mineralization: As-rich greywacke country rock, felsic intrusives and a major shear zone. Sediment from streams that drain the area of the shear zone was analysed for gold using lead fire assay with ultra-pure flux and inductively coupled plasma-mass spectrometry finish. Six localities were identified where Au levels are significantly above the regional background. The gold enhancements (up to about 90 ppb in <150-mu m sediment) have distinct characteristics that can be related to the local geological environment. Very high As and low platinum-group element (PGE) levels are associated with gold adjacent to a granodioritic intrusion. Gold associated with moderate As levels and with high PGE is derived fi om an andesitic volcanic-rich greywacke, whereas gold associated with lower Pt, no detectable Pd and low As levels is derived from quartzofeldspathic greywacke. Such variations reinforce the concept of a sedimentary reservoir for gold within the older greywacke formations of the Scottish Southern Uplands. The As (and, by association, Au) was preconcentrated in the back-arc sector of the Southern Uplands and was then remobilized into the brittle-ductile transition zone during deformation, where it was precipitated.

The simultaneous determination of Pt, Pd and Au at sub-part per billion concentrations has recently been made possible by the development of Pb fire assay with inductively coupled plasma-mass spectrometry (ICP-MS), marking a significant advance in analytical geochemistry. This offers the opportunity to expand the scope of systematic geochemical mapping to include Pt, Pd and Au, thus providing information on crustal levels of these economically important elements on a routine basis. A pilot study was carried out as part of the Geochemical Survey Programme (GSP) of the British Geological Survey to evaluate the application of Pb fire assay with ICP-MS in regional geochemical mapping. Stream-sediment samples collected from the northern-most Shetland Islands, Unst and Fetlar, were analysed for Pt, Pd and Au as well as 38 trace and major elements. The geology of the study area comprises an obducted ophiolite complex that has been thrust on to a gneissose metamorphic basement. Localized exploration for platinum-group elements (PGE) in recent years, which has been hampered by the use of inadequately sensitive analytical methods, has primarily targeted their potential association with chromitite pods in harzburgite and dunite in the northern parts of the ophiolite outcrop. The presentation of geochemical data for precious metals as single-element maps demonstrates the suitability of this highly sensitive analytical method for regional geochemical mapping of PGE; the maps for Pt and Pd exhibit particularly coherent and well-defined patterns that are clearly controlled by the underlying geology. Levels of precision are comparable with those for trace-element determinations by established multielement analytical techniques, such as inductively coupled plasma-emission spectroscopy and X-ray fluorescence, which are commonly employed in regional geochemical surveys, where absolute elemental abundances are typically four to five orders of magnitude higher. Above-background levels of both Pt and Pd occur along the outcrop of the dunite cumulate unit of the ophiolite, giving a regional perspective on the occurrence of PGE in the complex that has not previously been available. Relationships with other elements in the different ophiolite lithologies indicate a dominant primary igneous control on Pt and Pd distribution. Within the dunite cumulate both Pt and Pd show the strongest correlation with Cu in preference to either Cr or Ni, and there is evidence of laterally extensive enrichment associated with the upper, pyroxene-rich part of this unit. No high levels of Pt or Pd are encountered on basement lithologies. In contrast, the distribution of Au is not so closely related to lithology, and anomalous levels occur over both the basement and the ophiolite. However, Au is present in slightly higher abundance over the dunite, in common with Pt, Pd and other chalcophile elements. The regional data define new exploration targets, and, when used in conjunction with data for other elements, provide the basis for developing an increased understanding of PGE metallogenesis. On the basis of this work the cost-effective determination of Pt, Pd and Au by Pb fire assay with ICP-MS in systematic regional geochemical surveys represents a successful new development for mineral exploration.

Synopsis Regional geochemical data from the Southern Uplands of Scotland and the Windermere Group of the English Lake District are assessed in terms of the underlying greywacke-dominated lithostratigraphical units. Stratigraphical (time-related) trends apparent in a number of elements continue from the Southern Uplands, across the Iapetus Suture, into the Windermere Group of the Lake District. The principal geochemical break occurs within the central Southern Uplands coincident with a major strike-parallel fault, the Moffat Valley Lineament. To the north of this structure a late Ordovician to early Silurian back-arc basin sequence has elevated Pb and As levels and feldspar-related element (Rb, K, Sr) abundances compatible with derivation of the greywackes from a granodioritic provenance. The mineralization potential of this sequence is stressed. To the south of the Moffat Valley Lineament a mid to late Silurian foreland basin sequence spans the Iapetus Suture with relatively lower Pb and As levels and feldspar element abundances suggestive of a moderately-evolved provenance. Development of such a foreland basin requires the effective closure of the Iapetus Ocean by the early Wenlock.

The production of geochemical maps of the world as proposed by the International Geochemical Mapping project (IGM) will require sampling of new areas at low densities and amalgamation of new data with existing geochemical data to ensure map production within reasonable time scales and budgets. Assuming compatibility in sampling and analytical techniques, two important considerations regarding sample density are: (i) how far can sample densities be reduced before meaningful geochemical patterns are lost, and (ii) how can datasets of different sample density be amalgamated? These considerations are examined in the present study by applying two methods of computational data reduction simulating low density sampling to the British Geological Survey's high precision, high resolution (1 sample per 1.5 km(2)) stream sediment datasets for Northern Britain, exemplified by Ni and B.A series of grids with grid squares of 25 km(2), 100 km(2), 500 km(2) and 160000 km(2) corresponding to sample densities recommended elsewhere for IGM (Table 1) are superimposed on the data. For each grid square the data are reduced by (i) selecting a single sample at random, and (ii) calculating the median value. Results are presented as a suite of image processed maps contoured with similar percentile levels enabling comparisons of element distributions to be made.The maps demonstrate that geochemical patterns become distorted at sample densities lower than 1 per 25 km(2) using the random selection method. Random sub-sampling of existing datasets with high sample densities is therefore unlikely to be successful. Employing the median value method, geochemical patterns are maintained with a reasonable degree of accuracy to densities as low as 1 sample per 500 km(2). The optimum reduced sample density for the Northern Britain datasets for Ni and B is 1 per 25 km(2). The size of the geological feature(s) and the magnitude of the geochemical variation are the principle factors controlling the resolution of geochemical patterns at low sample densities. Hence it is unrealistic to recommend an optimum sample density suitable for geochemical mapping throughout the world. Additional factors which influence the choice of sample density include the objectives of the survey (eg, regional reconnaissance, mineral reconnaissance, environmental monitoring), logistical controls on sampling (access, vegetation, climate etc.) and funding constraints. A sample density structure based on grid sizes of 25600 km(2), 6400 km(2), 1600 km(2), 400 km(2), 100 km(2) (Garrett, pers. commun., 1992) and 25 km2 which takes account of these various factors and allows surveys of different sample densities to be related to each other, is therefore proposed for the International Geochemical Mapping project.

The stream water hydrogeochemical database, prepared by the British Geological Survey's Geochemical Survey Programme, in conjunction with databases for stream sediments, soil samples and mineral concentrates, has recently been enhanced for a range of economic and environmental objectives. The density of systematic stream water sampling and analysis has been increased to one sample per km2 and a broader spectrum of determinands introduced. An orientation suite of hydrogeochemical maps has been produced from water samples collected at 1279 sample sites in North Wales to test the methodology. Preliminary results indicate that bedrock geology and mineralisation are the most important variables which influence the surface water chemistry. The primary control by geological parameters is variously modified by secondary influences which include geomorphological factors (especially altitude) atmospheric (climatic and coastal effects), and anthropogenic (agriculture, urban and industrial developments). Regional hydrogeochemical stream water maps have a wide range of economic and environmental applications, especially when interpreted in conjunction with geological data. Results obtained so far indicate that interpretation is likely to be further enhanced in the future by intercomparison with regional stream sediment, hydrogeological, geomorphological, pedological, agricultural, landuse, climatic and remotely sensed datasets in a GIS environment. Hydrogeochemical sampling and analysis represents a cost-effective addition to the Regional Geochemical Survey of the UK.

The results of orientation studies for a regional geochemical survey of Jamaica and the CARICOM countries of the Caribbean region are described. The survey is designed to provide systematic geochemical information for a wide variety of applications and, especially, to form a basis for agricultural development in the region. The programme is modelled on the Geochemical Survey Programme (GSP) being carried out in Great Britain by the British Geological Survey (BGS), which is preparing, in digital form, a high-resolution geochemical database suitable for a range of environmental and economic investigations. The application of rock, soil, stream-sediment and water sampling to define the regional geochemistry of Jamaica is described with particular reference to sources of error and the modification of trace-element patterns in different surface environments. Contrasts on the island are marked, with approximately 70% of the land area underlain by an Eocene to mid-Miocene platform-limestone cover with bauxite deposits. The remainder, which mainly comprises a Cretaceous basement complex, outcrops as a series of inliers that are exposed in a central, east-west-trending chain of mountains. Studies of sampling and sub-sample preparation methods indicate that soil samples of particle size less-than-or-equal-to 150-mu-m (100 BSI mesh) provide the optimum sampling medium for a regional geochemical survey of Jamaica. They contain a higher proportion of fine-fraction material than stream sediments, particularly in the mountainous areas of the Central and Blue Mountains Inliers; they also provide a better and more consistent means of differentiating rock types and occurrences of metalliferous mineralization while, unlike stream sediments, showing minimal variation of element concentrations in relation to particle size. Soil samples thus provide a robust sample type, with trace-element levels that are unaffected by variations in the proportions of different size fractions arising as a result of operator error, geomorphology or temporal climatic changes. Studies of the dispersion of elements in six catchment basins that were selected to represent the main rock types and environments of the island suggest that a sampling interval of one soil sample per 5 km2 is adequate to define anomalous metal concentrations and that regional variation can be represented on the same interval. The primary geochemistries of most rock types and of occurrences of metalliferous mineralization in Jamaica have been intensely altered as a result of surface processes. Intense leaching of elements of low ionic potential (Ca, Mg, K, Rb, Ba and Sr) and U has occurred (although U is frequently resorbed by iron oxides in bauxite and terra rossa soils). In contrast, other elements, such as Mo, As and, to a lesser extent, Cr, Ni, Co, Fe and Mn, are strongly enriched in soils (and stream sediments) relative to bedrock. Enrichment is attributed to the formation of secondary ferric/manganic (Mo, As, Cr, Ni and Co) and phosphatic (As) phases. Only the content of high field strength elements, such as Zr, Hf, Th and the rare-earth elements, can be used to deduce bedrock chemistry. A more complex dispersion model is thus required for Jamaica than those developed previously for tropically weathered terrains, such as Australia-where landscapes are frequently more than 10 m.y. old.

An understanding of the Ordovician—Silurian development of the Southern Uplands accretionary thrust belt is an essential precursor to reconstructing the British sector of the Appalachian—Caledonian orogen. The British Geological Survey (BGS) has now extended its regional geochemical database to cover this controversial area. Integration of the new geochemical data with results from the current geological resurvey allows fresh insights into the provenance patterns of the Southern Uplands' greywacke sequences and constrains the extrapolation of geological boundaries.

Regional geochemical data for the gold pathfinder elements As, Sb and Bi prepared by the British Geological Survey over the Grampian Highlands of Scotland and the English Lake District are discussed with particular reference to models for gold mineralization. In both regions known gold mineralization and anomalous levels of the gold pathfinder elements are associated with granitic intrusions or lineament systems that cut metasedimentary or volcanic sequences and contain high background levels of gold pathfinder elements and, probably, gold. In the Grampian Highlands the enriched sequences comprise the Upper Middle and Upper Dalradian rocks, whereas in the Lake District high background levels of As, Sb and Bi occur over the Skiddaw Group and the Eycott and Borrowdale Volcanic Groups. Hence, in both regions shale-turbidite sequences in tectonically controlled extensional basins appear to have acted as crustal reservoirs for later ore-forming processes for gold, while in the Lake District the Ordovician volcanic rocks also appear to have fulfilled a similar role. Elsewhere in the United Kingdom high levels of As occur over metasedimentary sequences that have subsequently been intruded by granites; these include, for example, the high levels of As that occur over Devonian-Carboniferous rocks intruded by the Cornubian batholith in southwest England, where new evidence of Au mineralization has recently been identified. The Grampian Highlands and English Lake District evolved as part of the American and European continental plates, respectively, and were separated by the Iapetus Ocean until they were tectonically juxtaposed during the late stages of the Caledonian orogeny. The similarity in the controls of the distribution of gold pathfinder elements and gold mineralization in the two regions thus provides important information for understanding the genesis of gold deposits in comparable tectonic settings elsewhere. The data presented are inconsistent with models that invoke a juvenile source of gold or its pathfinder elements. Instead, they support a model whereby gold and its pathfinders were initially concentrated in volcano-sedimentary sequences in rapidly subsiding, tectonically controlled basins and in associated volcanic rocks. Remobilization and mineralization occurred subsequently, probably as a result of an increase in oxygen fugacity associated with the influx of granite magmas into the crust and the establishment of hydrothermal convective circulation systems.

Regional geochemical data from the classic mining districts of Southwest England, the Pennine orefields of Central England, and the Dalradian belt of Scotland, with its important occurrences of gold, are considered as a basis for understanding metallogenic provinces. The deposit types are granite-associated Sn-U, Mississippi Valley Type Pb-Zn-Ba-F and vein Au. It is suggested that crustal reservoirs, enriched in ore-forming elements, were important in the genesis of the examples of Sn-U and Au mineralisation studied. The reservoirs comprise evolved subalkaline granites and carbonaceous sulphur-enriched turbidities in listric faulted orogenic basins, respectively. In the case of the Pennine base-metal deposits, the reservoirs from which the ore-forming fluids were derived, comprise sedimentary basins approximating in composition to average shale and ore deposition mainly reflects the nature of basin evolution.The regional geochemical data used in the study were derived from geochemical atlases produced for different purposes and to different standards. Nevertheless, simple trace-element plots normalised, for example, to average crustal abundances can be used together with geological and geophysical criteria to summarise key characteristics of the crustal reservoirs identified and to develop methods suitable for screening spatially related data sets using Image Analysis or Geographical Information Systems.