From geochemical prospecting to international geochemical mapping:a historical overview

R.G. Garrett1, C. Reimann2, D.B. Smith3 & X. Xie4

1Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8, Canada (e-mail: garrett@NRCan.gc.ca)2Geological Survey of Norway, N-7491, Trondheim, Norway (e-mail: clemens.reimann@ngu.no)

3US Geological Survey, PO Box 25046, MS 973, Denver, CO 80225, USA (e-mail: dsmith@usgs.gov)4Institute of Geophysical and Geochemical Exploration, 84 Jinguang Road., Langfang, 065000 Hebei, P.R. China

(e-mail: xuejing_xie@126.com)

ABSTRACT: This paper provides a history of the development of regionalgeochemical mapping. Modern geochemistry was born in the Soviet Union in the1930s, and the basic methodologies for regional mapping had been developed bythe late 1960s, with important extensions being made in the 1980s. The paper recordsthe development of regional geochemical surveys, or mapping, in the context ofspatial scale and transition from a mineral exploration and resource assessment toolto an environmental mapping exercise supporting multi-disciplinary research. Atten-tion is drawn to the role of the International Geological Correlation Program’sProjects 259 and 360, and the continuing role of the International Union ofGeological Sciences, in providing an international focus and dimension to globalgeochemical mapping. The paper closes with a section on some of the currentresearch issues, opportunities and challenges for regional geochemical mapping.

KEYWORDS: geochemistry, regional, global, mapping, history, IGCP, Project 259, Project 360, IUGS

INTRODUCTION

The primary purpose of geochemistry is to determine quanti-tatively the chemical composition of the Earth and its parts, andto discover the laws that control the distribution of theindividual elements (Goldschmidt 1937; 1954). Applied geo-chemistry is the application of this knowledge to societalbenefit, whether for discovering mineral resources, protectingthe surface environment that sustains life, improving theefficiency of agriculture and animal husbandry, or studyingthe behaviour of elements in the food-chain and their healtheffects on humans (epidemiology) and other biota. All of these,to varying extents, depend upon knowledge of the spatialdistribution of the elements in and on the Earth.

The first regional geochemical surveys, if they can be calledthat, were undertaken by prospectors panning for heavy min-erals many centuries ago. Much later, perhaps a carbon blockand blowpipe were used to ‘chemically’ identify some of theminerals retained in the pan. As an improvement on thistechnique, Russian geologists used ‘spot tests’ for the samepurpose (Sergeyev 1936). For cassiterite (SnO2), identificationwas easy with a piece of zinc sheet and some hydrochloric acid– the nascent hydrogen reduced the SnO2 to metallic tin and theshiny grains could easily be counted. For gold, the trained eyewas, and still is, sufficient, and the presence of alluvial gold andcassiterite in panned concentrates has led to the discovery ofmany of the world’s great hardrock gold and tin camps (Hawkes& Webb 1962). However, these surveys, as thoroughly as theprospectors may have carried them out, were not organized inany systematic fashion.

Regional geochemical surveys require coordination of field,laboratory and office activities on a scale that can only be

undertaken by governmental or industrial organizations, or withtheir financial support. In a historical context, stream sedimentswere the dominant sample medium reported in early publica-tions. In many, but not all, environments they convenientlyprovide a composite sample of the weathered material, bedrock,glacial sediments or soils, in the catchment basin upstream fromthe sampling point.

Early surveys were generally high-density (multiple samplesites per square kilometre), one-sample-material exercises.Currently, regional geochemical surveys employ a wide varietyof sampling densities. These range from 1 sample site per 1 to15 km2 for mineral exploration purposes to extremely lowdensities, e.g. 1 sample site per 2500 to 10 000 km2, fornational- and international-scale mapping projects. Further-more, these latter mapping exercises are commonly multi-mediato provide knowledge on the source, transport and fate ofelements in the biogeochemical cycle (e.g. Reimann et al. 2001).

TWENTIETH-CENTURY DEVELOPMENT OFGEOCHEMICAL PROSPECTING

Geochemical prospecting methods were first developed in theSoviet Union, where central decision-making led to a focus onmineral resource exploration to support economic growth. The1920s and 1930s saw the development of chemical methods,especially optical spectroscopy, and their application to geologi-cal problems. In the context of prospecting, Russian scientistsled the way with the work of Vernadsky, his co-workers, andFersman (1939), who themselves acknowledge the fundamentalcontributions made by V.M. Goldschmidt (see Mason 1992).The Russian geochemists referred to their work as ‘metallo-metric surveys’, reflecting its quantitative nature; studies appear

Geochemistry: Exploration, Environment, Analysis, Vol. 8 2008, pp. 205–217 1467-7873/08/$15.00 � 2008 AAG/ Geological Society of London

to have started in 1932 (Sergeyev 1941) and by 1935 they hadperfected optical spectrographic methods (Borovik 1939) thatwould support routine geochemical survey work (Hawkes &Webb 1962). Some 17 field projects were undertaken between1935 and 1939 and are described in some detail by Sergeyev(1941); seven of these depended on spectrographic analysis fortin (Hawkes & Webb 1962). Hawkes (1976) states that the firstever publication on geochemical prospecting was by Flerov(1935) and concerned the search for bedrock tin deposits bystannometric surveys. These first investigations were onmining-camp scales with the objective of finding extensions ofknown ore-bearing systems.

This new prospecting technology spread from the SovietUnion to Scandinavia, which was fertile ground due to thepresence of ex-students of Goldschmidt, and thence to otherparts of Europe and North America. In Norway, Vogt at theNorwegian Technical University, Trondheim, undertook, onthe inspiration of Goldschmidt’s work, soil-plant and otherstudies around the Røros copper deposits in 1939–1944(Brotzen et al. 1967). In Sweden, both the Boliden Companyand the Swedish Prospecting Company, realizing the potentialof geochemical prospecting, played important roles (Hawkes1976). Brundin and Palmqvist, two of Goldschmidt’s formerGöttingen students working for the Swedish ProspectingCompany, successfully applied biogeochemical methods inCornwall and Wales, UK, in 1936 (Boyle 1967). Lundbergintroduced geochemical methods to Canada and Newfoundlandin 1938 and carried out initial studies in the Buchans areaof central Newfoundland until 1940 (Brummer et al. 1987;Lundberg 1940a, b, 1941, 1948). Interestingly, Lundberg sawgeochemical methods as a complement to geophysical surveys,a tool to assist decision-making in how to proceed in explora-tion; as such, this must be amongst the first examples of anintegrated exploration strategy. It was at a meeting withLundberg in 1940 that Hawkes, who had worked previously asa field assistant for Lundberg in Newfoundland, learnt aboutLundberg’s geochemical studies. Lundberg’s enthusiasm aboutgeochemistry was one of the factors that got Hawkes interestedin trace elements as ore-guides (Hawkes 1976). FollowingWorld War II, Hawkes and Lakin commenced investigationsinto geochemical exploration at the US Geological Survey in1947 (Hawkes 1976). It had taken some 15 years, with six yearsof intervening global conflict, for the ideas and proceduresdeveloped by Russian geoscientists to become widely known inthe rest of the world.

FROM MINING CAMPS TO REGIONALRECONNAISSANCE, THE 1950S AND 1960S

These various mining-camp studies in the Soviet Union, Europeand North America laid the groundwork for the first regionalgeochemical surveys. Hawkes & Webb (1962) report that thefirst regional surveys were undertaken by Russian scientistssearching for uranium using hydrogeochemical methods (seeVinogradov 1956). Vinogradov stated, ‘In recent years, wide usehas been made in the Soviet Union of the hydrogeochemicalmethod of prospecting for uranium deposits’, and later, ‘It isvery simple and enables preliminary explorations of largeterritories to be carried out’. Miller (1956) described systematicregional geochemical mapping, metallometric surveys, in centralKazakstan. These involved sampling soils on a 500 � 50 mgrid, using semi-quantitative optical spectroscopy to determinea suite of trace elements, and presenting the data at 1:50 000scale. This approach was later extended and integrated with1:200 000 scale geological mapping, with soil sampling beingundertaken on a 2000 � 200 m grid, with less success (Miller

1956). Ginzberg (1960) reports that between 1940 and 1960,25 million sites were sampled, and samples presumably ana-lysed, of which 11 million were in central Kazakhstan. Thesemight be described as ‘brute force’ geochemical surveys usinghigh sample densities over very large areas. The Russiandevelopments during this time period are described in theintroduction of Ginzberg (1960), who mentions a ‘highlydetailed and circumstantial provisional manual’ written bySofronov, Miller, Sergeev and Solovov in 1951.

In 1952, Riddell was experimenting with hydrogeochemicalsurveys using Huff’s (1948) field test for heavy metals in water.He sampled many of the streams flowing off the Gaspé(Québec) central highlands along the coastal perimeter, some320 km, and up some of the streams (Riddell 1952). In the nextyear, he joined Hawkes and Bloom in applying the ‘Bloom coldextractable heavy metal’ test to stream sediments in the NashCreek area of northern New Brunswick (Hawkes & Bloom1956). Over the following two years, 4937 reconnaissancestream-sediment samples were collected over 69 940 km2 of theGaspé and New Brunswick regions (Hawkes et al. 1960). Thesuccess of this geochemical prospecting campaign brought thebenefits of regional geochemical stream-sediment reconnais-sance surveys to the attention of the exploration community.Hawkes (1976) notes that one outcome of the 1954–1955regional reconnaissance survey was the recognition of ‘geo-chemical relief’ as a spatial attribute. The areas of high relief,reflecting geochemical heterogeneity, contained practically allthe known base metal deposits of the surveyed region (Hawkes1976). The enormous impact that this had on the application ofgeochemical methods to mineral exploration in Canada hasbeen extensively documented by Brummer et al. (1987). Recon-naissance stream-sediment surveys were being widely applied bythe mid- to late 1950s and into the 1960s by both governmentagencies and mineral exploration companies. The same tech-niques were being applied on other continents, and Sovietgeochemists introduced geochemical methods to geochemistsin the People’s Republic of China in 1951 (Xie et al. 1997).Research on various aspects of exploration geochemistry com-menced in 1951, and in 1956 the Soviet soil metallometricprocedures were implemented. Later, the utility of stream-sediment surveys as an exploration tool were investigated,which led to the first full-scale regional stream-sediment surveyin 1958 (Kang et al. 1961) and further developments in the1960s (Xie et al. 1997).

Lessons learnt in Africa

Several important developments in regional reconnaissancemethodology were made in Africa in the 1960s. In 1959,Webb at the Geochemical Prospecting Research Centre(GPRC), Imperial College, London, was donated a suite of<80-mesh (<177 µm) active stream sediment, and somedambo (seasonal swamp) samples collected in 1957 byNamwala Concession Ltd. for the 7770 km2 Livingstone-Namwala Concession area in southern Zambia (then northernRhodesia) (Webb et al. 1964; Davis 1986). The original studyhad indicated that Cu, Zn and Ni levels appeared to have arelationship with the underlying lithologies. Following someorientation studies (Watts et al. 1963; Harden & Tooms 1965),the full suite of samples was itself sampled at a density of 1site per square mile, with preference being given to first- andsecond-order streams, to yield c. 3000 samples. These sampleswere analysed in 1961–1962 (I. Nichol, pers. comm.) for 15elements by optical spectroscopy, Zn by colorimetry follow-ing a potassium pyrosulphate fusion, and both cold extract-able (Cx) Cu and Zn. The Geological Survey of Zambia

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(1964) published maps for ten elements (Cx Cu, Cu, Pb, Zn,Co, Ni, Cr, Ti, V and Mn). In 1963 Nichol returned to thefield and resampled selected areas; the analyses of thesesamples indicated that the geochemical results were stableover a six-year period, 1957 to 1963 (I. Nichol, pers. comm.;Webb et al. 1964). This multi-element regional geochemicalreconnaissance revealed that:

(1) major geological/lithological units were associated withcharacteristic patterns of level and relief, and in someinstances geochemical differences could be observed inunits mapped as a single lithology;

(2) the presence of sub-economic mineralization gave rise tomore or less extensive patterns of abnormally high elemen-tal contents and all known strongly mineralized areas laywithin or close to these anomalous areas; furthermore,readily extractable Cu gave more contrasting patterns thattotal Cu;

(3) in general, the analysis of rocks, soils and stream sedimentsfrom the same areas revealed similar metal patterns in allthree sample media;

(4) the degree of weathering and the nature of the surfacedrainage system are more or less related to topography,itself related to the underlying lithologies; and

(5) rock and soil samples were generally representative of asmall area in the vicinity of the sample site, while the streamsediment sample represented an approximation for thecatchment area (Webb et al. 1964).

These findings demonstrated the value of geochemical surveysas a mapping tool capable of supporting a wide range ofgeological survey activities.

Subsequent to the Namwala Project, Webb’s group contin-ued research studies in Sierra Leone, Ireland and the UK, withNichol supervising many of the graduate students. It was inSierra Leone that the utility of regional geochemical mappingwas confirmed and the next advance was made to broader-scaleand lower-density mapping. The geology of Sierra Leone isdominated by a Precambrian granitic basement hosting green-stone (schist) belts of Birrimian age (2100 Ma) that were knownto have potential for base- and precious-metal deposits.Between 1960 and 1963, Viewing and James completed amulti-element regional geochemical stream sediment reconnais-sance of the Sula Mountains and Kangari Hills schist belt(1600 km2) at an average sampling density of 2.5 to 3 samplesper km2 using procedures similar to those for the NamwalaProject (Nichol et al. 1966a). The results helped define the Moand Au potential of the region, the latter by using As as apathfinder element for Au. Away from mineralization, thegeochemical patterns reflected the various bedrock lithologiesin the stream catchment basins, though in some cases similarlymapped lithologies exhibited significantly different geochemicalsignatures. These latter differences were related to soil devel-opment, the presence of indurated laterites, duricrust (ferricrete,canga), and trace element differences in bedrock not reflectedin its obvious mineralogy and therefore field mappingidentification.

In 1963, as the work on the Sula Mountains and KangariHills was being completed, Garrett joined the GPRC tocomplete the geochemical reconnaissance of the remainingthree schist belts in the Precambrian basement complex, theNimini, Kambui and Gori Hills. Similar field and analyticalprocedures were employed as in the Sula Mountains andKangari Hills. In a review of the data, it became apparent thatthere were major differences in geochemistry, independent ofsoil formation processes, between lithologies mapped withsimilar names in the different schist belts. A comprehensive

suite of archival samples was recovered and re-analysed, and thedifferences confirmed.

At that time computing facilities became available at ImperialCollege (Nichol et al. 1966b). Whitten (1959), in an applicationof polynomial surface fitting (a technique rarely used today),described how through surface fitting modal analyses, theoriginal sedimentary structure of the Donegal granite prior togranitization could be elucidated. Garrett hypothesized that thesame procedure should work over the 38 650 km2 of thePrecambrian basement using, instead of modal analyses of thinsections, the geochemistry of suitably sized stream catchmentbasins. In November and December 1964, a suite of 215stream-sediment samples, together with rock and soil samples,was collected along the road network and by extended foottraverses. Prior to the fieldwork, a study of available geologicalmaps had indicated that at a scale of 190 km2 the graniticbasement was relatively lithologically homogeneous. Similarly,study of the stream-sediment geochemical data had shown thatstreams with catchment sizes of 13–18 km2 were the bestcompromise between the adverse effects of elutriation of thefine (geochemically informative) fraction in increasingly largecatchment basins and sampling a catchment basin with as largean area as possible (Garrett 1966). The 215 sample sites did notrepresent 100% of the basement area but some small fractionbetween 7 and 10%. It was hypothesized that any systematicbasement-scale variability would be revealed by that low sampledensity, together with any features related to the presence ofmetallogenic provinces, metallotects, etc.

Polynomial surface fitting and rolling-mean (moving-average)maps were required to elucidate the systematic component inthe basement data. This demonstrated that for elements such asCo, Cr and Ni, the eastern schist belts, the Nimini, Kambui andGola Hills, lay in a basement region higher in those elementsthan the Sula Mountains and Kangari Hills. The most convinc-ing data were for Cr, where the basement survey data clearlyoutlined a chromite metallogenic province in southeasternSierra Leone (Garrett & Nichol 1967) where chromite had beenmined in the North Kambui Hills and chromite lenses can beobserved as the last remnants that resisted granitization in thebasement migmatities.

The success in identifying a metallogenic province in SierraLeone led to a study in Zambia by Armour-Brown. This 1967survey of 207 220 km2 in central Zambia (Armour-Brown &Nichol 1970) used the same field and analytical procedures ashad been employed in Sierra Leone, i.e. an average sampledensity of 1 site per 190 km2. Armour-Brown and Nichol state‘The clearly defined variation of background metal contents instream sediments associated with the major metallogenic zonesis clear evidence of the application of wide interval streamsediment sampling as a method for identifying such areas inconditions similar to those in Zambia’, and furthermore, ‘Thedistribution of the minor elements in the drainage sediments isto a large extent controlled by a limited number of featuresincluding local bedrock types, surface environment or miner-alization’.

In the late 1960s, Reedman & Gould (1970) undertook asimulated low-density survey by sampling the data from geo-chemical surveys undertaken in an 18 130 km2 area of north-eastern Uganda. They subdivided the survey area into c.200 km2

squares (a quarter of each quarter degree topographic mapsheet) and selected the data for the most northeasterly samplewith a catchment basin size of c. 16 km2. This led to theselection of data for 100 sites of the original 10 000 sampled.Reedman & Gould reported, ‘The low sample-density basedrolling-mean maps show marked similarities with the highsample-density based maps’. Subsequently a suite of some 875

Historical overview of geochemical mapping 207

stream sediment samples were collected from streams withc. 25 km2 catchments at a density of 1 stream per 200 km2

across Uganda (c. 230 000 km2). The <80-mesh (<177 µm)fraction was retained and analysed by optical spectrographic andcolorimetric methods. The resulting maps were published bythe Geological Survey and Mines Department of Uganda (1973)in what is probably the first-ever national geochemical atlas, andcertainly the first based on low-density sampling.

An even lower-density regional survey in the USA

Some countries are almost continental in size. One such is theUSA that constitutes c. 40% of the North American continent.In 1961, Shacklette commenced a study at the US GeologicalSurvey with the purpose of collecting data across the conter-minous United States (i.e. excluding Alaska and Hawaii) in orderto determine the range of elemental concentrations in largelyundisturbed surficial materials and in plants growing on them.The analyses of the surficial materials would provide a measureof the total amounts of elements present, and the plant analysesa measure of what amount was bioaccessible to the plants(Shacklette & Boerngen 1984). The conterminous USA has anarea of c. 7 840 000 km2 and the task of sampling such a largearea was daunting, so Shacklette requested that his colleaguescollect samples for him according to a provided protocol duringtheir travels to and from their field projects, meetings, etc.When these were added to the samples he had collected himself,this led to a network of samples collected at c. 80-km intervalsproximal to the highways travelled along. The first results of thisactivity were published in 1971, ten years after inception, andconsisted of determinations for 35 elements, mostly throughoptical spectroscopy (Shacklette et al. 1971). The availability ofthese data and an increasing awareness of environmental issuesled to the reanalysis of the original sample suite, together withcollection of additional samples of surficial material.

This activity continued until 1975 by which time satisfactoryregional coverage had been obtained for the conterminousUSA. The complete data set of determinations for 50 elementsin the 1323 sample suite, equivalent to 1 site per c. 6000 km2,were plotted as maps and form the basis of the Shacklette &Boerngen (1984) publication. Subsequently, these data werereprocessed to generate a series of colour maps due to theincreased interest in continental-scale and low-density geo-chemical sampling and mapping in the 1990s (Gustavsson et al.2001). To complete the US continental coverage, Gough andcolleagues collected a suite of 265 surficial samples from Alaskaduring the late 1970s and early 1980s. These were analysed for47 elements, and ash yield and soil pH were determined (Goughet al. 1988; 2005).

Studies in Europe

In Germany, the Institute for Geosciences and NaturalResources (BGR) commenced studies of the application ofgeochemical prospecting in 1958. Activities in France, led bythe Bureau de recherches géologique et minière (BRGM),commenced at about the same time with a strong focus onuranium exploration. The work undertaken in Ireland and theUK by the Applied Geochemistry Research Group (AGRG),renamed from the GPRC in 1965, broadened the focus ofregional geochemistry to agricultural and veterinary issues(Webb & Atkinson 1965; Webb et al. 1966; 1968a, b; Thorntonet al. 1966). These and other studies (e.g. Nichol et al. 1967) ledto the stream-sediment sampling of Northern Ireland(13 500 km2) in 1967 (Butt & Nichol 1979) and the publicationof a provisional geochemical atlas (Webb et al. 1973). In 1969,

AGRG undertook the stream sediment sampling that led to theWolfson Geochemical Atlas of England and Wales (Webb et al. 1978,1979). In Scotland, the British Institute of Geological Sciences(now the British Geological Survey, BGS) commenced orien-tation studies in 1968 for stream-sediment and water surveys(Plant 1971) in parallel with starting regional geochemicalmapping in Caithness.

WIDESPREAD APPLICATION OF GEOCHEMICALMAPPING, 1970S TO 1990S

With the publication of the first national-scale geochemicalmaps by Shacklette et al. (1971) and atlases by Webb et al. (1973)and the Geological Survey & Mines Department of Uganda(1973), interest in geochemical mapping widened. The avail-ability of these publications did much to encourage nationalagencies to consider geochemical mapping data as a valuablecomponent of their national geoscience knowledge base. As aresult, the 1970s and 1980s saw the application of geochemicalmapping at a variety of densities over a range of areal extents byboth national agencies and mineral exploration companies.Additionally, multi-media surveys were undertaken so that thebiogeochemical cycle could be studied on a regional scale andelemental sources, sinks and transport mechanisms identified.For mineral exploration and resource evaluation purposes, thedensities were often high, more than one site per 13 km2, andover areas defined as a function of national boundaries andanticipated mineral potential. During this time period, theimportance of geochemical knowledge to support environ-mental studies and the establishment of the range of naturalbackground was recognized. To cover some very large areas,low-density surveys were undertaken in order to provide aframework for the selection of smaller areas warranting moredetailed mapping for whatever reason was driving the activity.

In the UK, the BGS extended their systematic high-densitystream-sediment and water coverage from Caithness north-wards to the Shetland and Orkney islands. Following that, theyprogressed southwards to cover all of Scotland, Wales and mostof England and Northern Ireland. The first atlases for northernScotland were published in 1978 (Johnson et al. 2005). AtImperial College (AGRG), the Wolfson Geochemical Atlas ofEngland and Wales (Webb et al. 1978; 1979) was prepared forpublication.

In the western part of Germany (former Federal Republic ofGermany), a systematic multi-element stream-sediment andstream-water survey was commenced in 1977 to supportmineral exploration and to establish environmental baselinesagainst which future change, including contamination, could beassessed (Fauth et al. 1985). The survey was completed in 1983following the collection of c. 80 000 stream-sediment and watersamples. The Geological Survey of Austria commenced adetailed stream-sediment and water survey in 1978 (Thalmannet al. 1989); c. 37 600 samples were collected and the analyses of29 717 of them were presented in the resulting geochemicalatlas of Austria.

Scandinavia was the site of much geochemical mappingactivity during the 1980s. The Swedish Geological Survey(SGU) commenced a national biogeochemical survey in 1980using organic stream material consisting of aquatic mosses andthe roots of higher aquatic plants at an average sample densityof 1 site per 7 km2 (Lax & Selinus 2005). This sample mediumreflects the trace element concentrations of the stream watersand provides a time-averaged measure that avoids the seasonalvariations commonly observed in stream water data. The SGUand state-sponsored commercial interests also systematicallysampled soils and glacial tills at the same sample density over

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most of Sweden east of the Caledonian mountain range duringthe 1980s.

The Geological Survey of Finland’s main objective at thistime was to provide regional geochemical data to supportmineral exploration, and sampling and analytical techniqueswere chosen to meet that objective. A department of geochem-istry was established at the Survey in 1973 (Koljonen 1992). Asa result of their work, there exists a whole series of geochemicalatlases covering the whole country. The first Finnish geochemi-cal atlas, the groundwater atlas, was based on a data set of 3500dug wells and 1000 drilled wells with the samples collectedbetween 1978 and 1982 (Lahermo et al. 1990). The secondvolume reports the results of systematic till sampling at adensity of 1 site per 300 km2 (c. 1100 points), planned as earlyas 1984 (Koljonen 1992). This is an exemplary geochemical atlasthat no doubt belongs in any serious scientific library. The thirdvolume, published in Finnish with an English summary, coversstream-sediment and stream water collected at the same lowdensity (Lahermo et al. 1996). Finally, the whole country wascovered by till sampling at a density of 1 site per 4 km2; in total,82 062 samples were collected. The results were published in aseries of 1:400 000 scale maps (Salminen 1995). Throughoutthis work, considerable effort was put into building a nationaldatabase (ALKIMIA) and developing data presentation proce-dures and software (Björklund & Gustavsson 1987; Gustavssonet al. 1994; 1997).

The international Nordkallot project was established in 1980through the Nordic Council of Ministers and ran in parallel withactivities already underway. The project involved the participa-tion of the Geological Surveys of Norway, Sweden and Finlandin a stream-based multi-media mapping project for the areanorth of 66�N. The project ran until 1986 (Bølviken et al. 1986),after which time a wide range of maps and reports werepublished by the participants.

In Norway, Ottesen et al. (1989) investigated the use ofoverbank sediments as a sample medium for low-densitygeochemical mapping because of a concern that in mountainousareas ’traditional’ active stream sediments were not a reliablesample medium. Their work had demonstrated seasonal varia-bility in active stream sediment data and a tendency for samplematerial to be derived from a limited number of active erosionalsites. They proposed that this could be overcome by samplingthe finer sediments accumulated adjacent to streams duringflood events. A suite of 690 samples was collected from acrossNorway (320 000 km2) at an average sample density of 1 site per460 km2, and it was proposed that this medium be consideredfor use in any global geochemical mapping projects.

Regional geochemical maps were also prepared using data fornon-traditional media for geologists. Based on a joint Danish–Swedish project in 1980, the Nordic Council of Ministerssponsored a moss survey to monitor the atmospheric deposi-tion of metals across the Nordic countries in 1985 (Rühling et al.1987). The average sample density of this survey was 1 site per300 km2. Because mosses gain their nutrients from atmosphericdeposition, the assumption was that the spatial distribution oftrace elements would map the extent of contaminants releasedfrom anthropogenic sources to the atmosphere.

Well into the 1970s, the focus of Russian geochemists wasgeochemical mapping to support mineral exploration anddevelopment at a wide range of scales as low as 1:1 000 000. Ingeneral, these mapping programmes collected samples at adensity such that on the map being prepared there was 1 site persquare centimetre of map (Koval et al. 1995). This inferssampling densities for maps of 1:50 000, 1:200 000 and1 000 000 scales of 4 samples per km2, 1 site per 4 km2 and1 site per 100 km2, respectively. By 1976, interest was growing

in environmental issues related to contamination from industrialsources and urban development. The birth of landscape geo-chemistry, a holistic approach to geochemistry in the biologicaland physical environments, took place in the Soviet Union inthe 1950s (e.g. Perel’man 1955; 1966). This was a naturalconsequence of the interest of early Russian geochemists (e.g.Vernadsky) in biogeochemistry. As a result, landscape geo-chemical concepts had been widely adopted by the 1970s, andwere championed in the English language by Fortescue (1980).By the end of the 20th century, landscape geochemistry hadbecome a central paradigm for applied geochemical studiesglobally (for a review see Fortescue 1990).

In China, the Regional Geochemistry – National Reconnais-sance (RGNR) project was approved in 1978 and commencedimmediately (Xie et al. 1989; 1997; Xie & Ren 1991). Now,28 years later, c. 6.7 million km2 of the Chinese mainland havebeen mapped. The distinguishing feature of this project is theclose linkage of mapping with mineral exploration and thedevelopment of a cost-effective, low detection limit, multi-element, multi-method analytical scheme (Xie 1995; Xie et al.1997). Stream-sediment samples are collected at a density ofc. 1 sample per km2, and four samples are composited, sothat one composite represents on average 4 km2, prior tochemical analysis. With geochemical surveys being undertakenin agencies and laboratories in some 40 provinces, standardiz-ation of field and analytical protocols, together with rigorousquality control procedures, is an important concern. Bothworld-recognized primary certified reference materials andcomplementary secondary reference materials are used in orderto ensure that data are not only comparable between laborato-ries in China, but also globally (Xie et al. 1985; 1989; Xie 1995).

An important contribution to the discussion of whetheroverbank sediments (fine-grained sediment accumulated adja-cent to low-order streams during floods), floodplain sediments(fine-grained sediment accumulated adjacent to higher-orderstreams during floods), or traditional active stream-sedimentsamples were most suited to continental-scale mapping wasmade by Chinese geochemists. The China National Environ-mental Centre undertook a national soil geochemistry surveyemploying floodplain sediments in the 1980s (NationalEnvironmental Protection Agency of the People’s Republic ofChina 1994). The spatial features in maps prepared from thisactivity agreed well with the more detailed maps generated byMinistry of Geology geochemists from the RGNR data avail-able at that time. As a result, the feasibility of using floodplainsoil samples was investigated in the Environmental Geochemi-cal Monitoring Network (EGMON) project (Cheng et al. 1997;Xie & Cheng 1997; 2001). An orientation survey was carried outin Zhejiang Province where 13 floodplain samples were col-lected and the results of these compared with the RGNR resultsfor the province. The results were very encouraging (Xie &Cheng 1997), and in 1993 a truck-borne reconnaissance of thewhole of China was undertaken, with a necessarily lower sampledensity in mountainous and desert regions (Cheng et al. 1997).This resulted in the collection of floodplain soils from depths of5–25 cm and 80–120 cm from 529 sites in major river drainagesacross China. The geochemical maps prepared from theEGMON data are remarkably similar to those obtained fromthe high sample density RGNR surveys. Xie & Cheng (2001)concluded that due to logistical advantages, i.e. rapidity and easeof access on major highways, floodplain sediments could berecommended as a first choice for a global sampling medium inorder to obtain an initial global-scale geochemical overview.

In Canada, the logistics problems of working in the CanadianShield led to the development of lake-sediment surveys.Near-shore sub-aqueous frost boils were sampled rapidly by

Historical overview of geochemical mapping 209

float-equipped helicopters in permafrost tundra areas (Allanet al. 1973a, b). In boreal forests, centre-lake-bottom sedimentsampling was developed for use in this unique environment,first in Newfoundland and later in Saskatchewan (Hornbrook &Garrett 1976). The ‘energy crisis’ of the mid-1970s saw arevitalized interest in uranium exploration, which led to majoractivities in many parts of the world. In Canada, in 1975, theUranium Reconnaissance Program (URP) grew from ongoingcentre-lake-bottom and stream-sediment regional geochemicalsurveys. Some three years later, this work was subsumed intothe National Geochemical Reconnaissance (NGR) programme(Friske & Hornbrook 1991). The NGR continues today,c. 83 500 lake sediments and 85 300 stream sediments have beencollected, covering c. 2.4 million km2 of Canada’s 9.7 millionkm2 landmass, and data and maps released to the public. In1975, the National Uranium Resource Evaluation Hydrogeo-chemical and Stream Sediment Reconnaissance (NURE HSSR)programme commenced in the USA, leading to the productionof much geochemical data released as Open File documents(e.g. Smith 1997). However, one atlas was generated for Alaska(Weaver et al. 1983) and the NURE data have seen continuinguse in combination with comparable data from Canada’s NGRto compile a map of the As geochemistry of North America(Grosz et al. 2004).

TOWARDS A UNIFIED APPROACH

By the late 1970s and early 1980s, continental- and global-scalegeochemical mapping was being discussed. One forum was theWestern European Geological Surveys (WEGS) organizationfor work in Europe. The concept of a world geochemical mapwas discussed by a group of uranium explorationists meetingunder the auspices of the International Atomic Energy Agency(IAEA) in Sweden in late 1984. The WEGS proposal eventuallyevolved into the geochemical survey of Europe conducted bythe agency members of the Forum of European GeologicalSurveys (FOREGS) (see Bølviken et al. 1996; Salminen et al.1998; 2005; De Vos et al. 2006).

By the 1980s, and in the light of the recognition of globalchanges to the Earth’s environment, the necessity of consistentcontinental-scale international geochemical baselines was beingrecognized. In April 1987, Arthur Darnley made a proposal tothe International Geological Correlation Program (IGCP), ajoint programme of the United Nations Educational, Scientificand Cultural Organization (UNESCO) and the InternationalUnion of Geological Sciences (IUGS), to support an inter-national geochemical mapping project. This initial proposalwas rejected and an international workshop was held at the12th International Geochemical Exploration Symposium atthe BRGM in Orleans, France, in April 1987 to discuss thesubmission of a new proposal (Darnley 1990). The secondproposal to IGCP was successful, and Project 259 (Inter-national Geochemical Mapping) under Darnley’s leadershipwith an International Steering Committee, was approved andcommenced in February 1988. The International Geosphere-Biosphere Program on Global Change also endorsed the projectthat same year (IGBP 1989). The objective of the project was tomake a comprehensive review of geochemical mapping activi-ties worldwide and to prepare recommendations for carryingout an internationally consistent geochemical mapping effortleading to global coverage. Low-density coverage was proposedthrough the collection of a suite of c. 5000 composite samplesrepresenting the terrestrial environment. The recommendationsof the project were published in 1995 (Darnley et al. 1995).

The IGCP project was a catalyst for many research projects.For example, in Fennoscandia, Eden & Björklund (1994, 1996)

further investigated the utility of overbank sediment samples.They sampled 49 catchment basins in Finland and Sweden thatranged in size from 500 to 7000 km2 at an ultra-low density ofan average of 1 catchment basin per 23 000 km2. They con-cluded that in comparison with composite samples of glacial till,the dominant soil parent material, overbank samples wererepresentative for sampling at ultra-low densities. Furthermore,in the context of natural, i.e. uninfluenced by human activities,background levels, as measured by total analyses, deep over-bank samples represented the pre-industrial geochemistry ofFennoscandia.

Project 360, whose objective was to implement the recom-mendations of IGCP 259 through a programme of internationalco-operation and to seek funding from international agencies tosupport a global geochemical mapping programme, followedIGCP Project 259. Many organizations applauded the projectand gave it ‘moral support’; however, none came forward withfunds (Darnley 1997). In 1996, IGCP Project 360 terminatedand the focus of activities moved to the Task Group on GlobalGeochemical Baselines under the auspices of the IUGS and theInternational Association for Geochemistry and Cosmochem-istry (IAGC) (Darnley 1997). Since that time, activities havecontinued with national support, or groups of countries haveco-operated regionally to prepare continental- and sub-continental-scale geochemical maps consistent with the recom-mendations of IGCP Projects 259 and 360. The role that ArthurDarnley played in focusing the attention of geochemists andnational and international agencies on continental- and global-scale geochemical mapping cannot be overestimated. Hisactivities were, and those of the current IUGS task group are,the ‘glue’ that binds applied geochemists in their internationalgeochemical mapping activities.

A COLLECTION OF GEOCHEMICAL ATLASES

By the late 1970s, the first geochemical atlases were appearing,the1980s saw their numbers increase, by the 1990s a largenumber were available, and publication continues. The invest-ments governments and institutions had made in sampling,analysis and map preparation were bearing fruit. The list ofatlases in Table 1, though incomplete, will provide an impres-sion of the resources that have been committed to geochemicalmapping and atlas preparation.

THE ROLE OF MULTI-MEDIA GEOCHEMICALSURVEYS

Starting with the Nordkallot Project (Bølviken et al. 1986), anew era in geochemical mapping in Scandinavia emerged. Dueto the high cost of geochemical sampling in areas with difficultaccess, and with different organizations traditionally usingdifferent sample materials, it was hard to agree on one optimalsampling material for such an international co-operationproject. Thus, for the Nordkallot Project, four different samplematerials were collected: till, stream sediments, stream organicmatter and stream moss. The geochemical maps revealed thatthe different media often reflect different geochemical processesand complement one another rather than duplicating theresults.

The advent of IGCP Projects 259 and 360 brought on anincrease in the implementation of multi-media surveys thatfitted into the landscape geochemistry concept. In Russia, thiswas exemplified by the introduction of a new ‘MultipurposeGeochemical Mapping’ (MPGM) programme (Koval et al.1995; Burenkov et al. 1999). This was a collaborative effortamongst major Russian geochemistry institutions in Moscow,

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St. Petersburg, Irkutsk and Khabarovsk to develop proceduresfor regional geochemical mapping at scales of 1:1 000 000,1:200 000 and 1:50 000. The higher density (1:50 000 scale)mapping provided for the detailed study of features discoveredin less detailed (1:1 000 000 scale), low density exercises. One ofthe primary objectives of the MPGM programme was tomonitor the distribution of chemical elements in differ-ent media of the environment, related to both natural andanthropogenic processes.

The approach of collecting a diversity of sample materials inthe field was further refined during the Kola Project (Reimannet al. 1998), where four sample materials were carefully selectedfor geochemical mapping to reflect different compartments ofthe ecosystem (Reimann et al. 2001). Terrestrial moss (Hyloco-mium splendens and Pleurozium schreberi), and the O-, B- andC-horizon of Podzol profiles were collected at the same samplesites and analysed with comparable methods in the samelaboratory. The project covered an area of almost 200 000 km2

at a density of 1 sample site per 300 km2. The project led to abetter understanding of the origin, cycling and fate of chemicalelements in the terrestrial environment. It was recognized thatbiological processes need far more attention than had oftenbeen given to them when interpreting the distribution ofchemical elements at the Earth’s surface. The Geochemical Atlasof Eastern Barents Region (Salminen et al. 2004) continued in thistradition. Here the analytical results of moss, stream water,organic soils and mineral soils were mapped and compared. Theproject area covered more than 1 000 000 km2 at a sampledensity of c. 1 sampling site per 1000 km2. In the meantime,much of Europe was covered by a low-density, multi-media,multi-element geochemical survey and the results presented inthe Geochemical Atlas of Europe (Salminen et al. 2005). Reimann

et al. (2007a, b, c) have recently demonstrated the power of themulti-media approach to aid the interpretation of geochemicalprocesses on a more detailed scale.

In the agriculturally and industrially developed regions ofeastern and central China, the China Geological Survey andnearly all the provincial governments have jointly implementedmulti-purpose geochemical mapping projects since 2002 (Xi2007). These projects provide geochemical data for environ-mental assessments, land-use planning, and to supportagronomy actions that will increase agricultural productivity.These areas are underlain by Quaternary sediments, and soilshave been the primary sampling medium. Additionally, lakesediments, near-shore sediments, stream- and well-watersamples have been collected; and vegetable and crop sampleshave been collected in selected areas for specific studies. Soilsare collected at two depths, 0–20 cm and 150–200 cm, in orderto study any anthropogenic influences on the surface layers.Surface samples are collected at a density of 1 site per km2, andsamples at depth at a density of 1 site per 4 km2. The analyticalprogramme comprises the determination of 52 elements andpH, and locally, dependent on requirements, the determinationof available amounts of elements, organically bound elements,and organic contaminants. To date these projects have covered1.26 million km2 (C. Hangxin, pers. comm.)

CURRENT RESEARCH ISSUES AND FUTURECHALLENGES

The science and ‘art’ of regional geochemistry has beendeveloping for some 70 years. By science is meant the knowl-edge and understanding of biogeochemistry, in its widest sense.This knowledge permits projects to be planned on the basis of

Table 1. Geochemical atlases.

Year of publication Author Atlas title

1978 Webb et al. The Wolfson Geochemical Atlas of England and Wales

1978 Institute of Geological Sciences Regional Geochemical Atlas Series, Shetland and Orkney volumes(see Johnson et al. 2005, for a list of subsequent volumes)

1983 Weaver et al. The Geochemical Atlas of Alaska

1985 Fauth et al. Geochemischer Atlas Bundesrepublik Deutschland

1985 Institute of Geophysical and Geochemical Exploration Provisional Geochemical Atlas of Northwestern Jiangxi

1986 Bølviken et al. Geochemical Atlas of Northern Fennoscandia

1987 Bolivar et al. Geochemical Atlas of San Jose and Golfito Quadrangle, Cost Rica

1989 Thalmann et al. Geochemischer Atlas der Republik Österreich

1989 Tan The Atlas of Endemic Diseases and Their Environments in the Republic of China

1990 Lahermo et al. The Geochemical Atlas of Finland, Part 1: Groundwater

1992 Koljonen The Geochemical Atlas of Finland, Part 2: Till

1992 McGrath & Loveland The soil geochemical atlas of England and Wales

1994 National Environmental Protection Agency of thePeople’s Republic of China

The Atlas of the Soil Environmental Background Value in thePeople’s Republic of China

1995 Lalor et al. A Geochemical Atlas of Jamaica

1995 Lis & Pasieczna Geochemical Atlas of Poland

1996 Lahermo et al. Geochemical Atlas of Finland, Part 3: Environmental Geochemistry stream waters andsediments

1996 Mankovská Geochemical Atlas of Slovakia: Forest Biomass

1996 Rapant et al. Geochemical Atlas of Slovakia: Groundwater

1998 Reimann et al. Environmental Geochemical Atlas of the Central Barents Region

1999 Aurlík & Šefcík Geochemical Atlas of the Slovak Republic Part V: Soils

1999 Kadunas et al. Geochemical Atlas of Lithuania

1999 Li & Wu Atlas of the Ecological Environmental Geochemistry of China

1999 Rank et al. Bodenatlas des Freistaates Sachsen

2000 Ottesen et al. Geochemical Atlas of Norway. Part 1: Chemical Composition of Overbank Sediments

2003 De Vivo et al. Geochemical environmental atlas of Campania Region (in Italian)2003 Reimann et al. Agricultural Soils in Northern Europe: A Geochemical Atlas

2004 Imai et al. Geochemical Map of Japan

2004 Salminen et al. Geochemical Atlas of Eastern Barents Region

2005 Salminen et al. Geochemical Atlas of Europe

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a sound scientific understanding of the potential sources ofelements, their transport from one location to another byfluvial, aeolian and gravitational processes, and their fate in, andpossible effects on, some repository, whether geological (e.g.soils or sediments) or biological (plants and animals). By ‘art’ wemean the experiential knowledge gained in the execution ofregional geochemical mapping programmes that has beengained and shared by applied geochemists over the years(Reimann 2005).

The following paragraphs outline some of the currentresearch issues and challenges that the authors consider worthyof attention (see also Garrett 2003). Some of the issuesdiscussed below are not directly applied geochemistry as theconcept has developed in the Association of Applied Geochem-ists over the last 40 years. However, it is the applied geochem-ists’ appreciation of regional-scale features, interest in thenatural world, logistical abilities gained through years of runningand managing regional surveys, and interest in societal issues,whether economic, ecological, agricultural or health-related,that permits them to contribute to these issues.

Geochemical mapping in urban environments will becomeincreasingly important as a larger proportion of the world’spopulation moves into cities, and those environments becomestressed with possible health implications to the occupants(Wong et al. 2006). In this context, children’s health is a majorissue in many countries, as exemplified by the concern over Pbin urban soils and its impact on the development of children’smental potential (Mielke et al. 1999). Remediation is costly, bothfinancially and in terms of community disruption (Mielke et al.2006). The identification and selection of areas requiringremediation is a task that requires mapping (Birke et al. 1994;Ottesen & Langedal 2001). Concerning remediation, geochemi-cal knowledge of the transport and fate of chemical elementsand their species is a key knowledge requirement for planningeffective and efficient remediation procedures. There are cur-rently both research activities and remediation programmesunderway in many nations. However, there is a lack of commonmethodologies that will permit comparison between the resultsof studies and the development of a common shareableknowledge base.

Human health is a major societal concern worldwide. Låg& Bølviken (1974) were among early workers to point outthe potential links between geochemistry and health. Theamount of attention that has been focused on the links betweengeoscience and medicine in the last 30 years may be measuredby the recent publication of Geology and Health: Closing theGap (Skinner & Berger 2003) and Essentials of Medical Geology(Selinus et al. 2005). The relationship of geochemical mappingdata for soils, sediments and waters to biomonitoring data, forexample the analysis of hair, urine and blood, collected by themedical community and public health agencies is an area withgreat potential for societal benefit and research (Davies et al.2005; Plumlee et al. 2006). It may be possible to detect potentialhealth problems when they are at sub-clinical stages, leadingto recommendations by health practitioners of appropriatemicro-nutrient or other strategies to improve the quality oflife. However, many complex interactions are present in thetransfer of trace elements across biological barriers, withelements other than the ones of initial interest having synergisticor antagonistic effects. Attention needs to be paid to develop-ing partial extraction procedures that measure the bio-accessible fractions of trace elements in sample materials(Oomen et al. 2002; 2003). The traditional near-total and totalanalytical data generated by geochemists have severe limitationsin studies of source and transport in the biogeochemicalcycle.

The major pathways for trace elements into biota, includinghumans, are through the food-chain. Our food, except for fish,largely reaches us through grains, fruits and vegetables grown inthe soil, or through animals, both domestic livestock and wildgame, dependent to a large extent on plants grown in the soilfor their existence. Thus, understanding soil–plant relationshipsis an extremely important field of research. The study of theserelationships has largely been the domain of agronomists andsoil scientists; however, applied geochemists can bring theirparticular skills to bear in these studies (e.g. Garrett et al. 1998).It is important to understand the abundance and spatialdistribution of elements in soil at all scales from local to globaland to understand the relationships between crop compositionand soil composition (e.g. Holmgren et al. 1993). It is also vitalto understand the complex biogeochemistry of the rhizosphereadjacent to plant rootlets where the plants interact with the soil(Huang & Gobran 2005). It is here that plants acquire thenutrients they need and pass on to the animals, includinghumans, that consume them (Combs 2005; Welch 2005), and, insome cases inadvertently take up elements with deleteriousconsequences to those that consume the plants (e.g. Chaneyet al. 2004). Again, as in animal systems, availability or unavail-ability, of other trace elements with antagonistic or synergisticeffects can influence the uptake of the elements of primeinterest (Alloway 2005). In all of this work, a key issue is thedevelopment of analytical methods to determine bioaccessibleamounts of elements in the media under study (Sauvé 2002).

The relevance of the comments in the previous two para-graphs to regional geochemical mapping is that once appropri-ate analytical protocols to determine the relevant bioaccessibleamounts have been developed, they can be applied to archivalsample suites, assuming the samples have been collected andarchived using appropriate protocols. Knowledge of the spatialdistribution of the bioaccessible amounts of elements thathave deleterious, or beneficial, effects on life will be of widebenefit.

To date, other than in some urban studies and for specificcompounds determined in oil and gas exploration, there is littleknowledge of the regional distribution of organic compounds.One reason for this neglect is the high cost of analyses. Whatwould encourage attention in the field is the availability ofinexpensive analytical procedures to determine compounds ofhealth concern, such as polycyclic aromatic hydrocarbons(PAHs) and polychlorinated biphenyls (PCBs). The main con-cern is in urban areas where people live and where industrialactivity may have released substances to the environment and‘beyond the fence’ (Andersson et al. 2004; Jensen et al. 2007).Both PAHs and PCBs are lipophilic (i.e. tend to be associatedwith fats in animals), as are many organic compounds of interestand concern, which has implications for the pathways theyfollow to enter humans. The food-chain is an importantpathway, as demonstrated by the transfer of PCBs from Arcticmarine mammals into women and into the breast-milk theyprovide to their children (Dewailly et al. 1996). While thecontent of organic compounds in freshwaters is of interest, it istheir long residence time in soils where they accumulate becauseof very slow rates of biodegradation that may be of greaterconcern (Chaudry & Chaplamadugu 1991).

The availability of large regional sample sets for soils opensup a new area for collaboration with agricultural and healthscientists – the quantification of the presence of pathogens insoils. Examples are Brucella abortus (cattle), Bacillus anthracis(cattle, with a risk of transfer to the human population) andCryptosporidium parvum (humans). Some of the measurementprotocols require special sampling and sample preservationtechniques; testing for anthrax spores is one that does not.

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Various ‘prion diseases’ or transmissible spongiform encepha-lopathies, such as ‘mad-cow disease’, in animals and humans arebecoming an increasing concern because of their devastatinglong-term health effects. If a simple and cost-effective protocolcould be developed to detect and quantify the presence ofprions in soils, this would be of benefit to society.

In the above paragraphs the matter of developing suitable,sensitive and cost-effective analytical protocols has been men-tioned. These are analytical methodology problems that are atthe frontier of research. For some elements there is still thechallenge of reducing detection limits so that they are one totwo orders of magnitude below average concentration levels inthe various sample media (environmental compartments)studied. There are elements that have not been studied exten-sively, such as the halogens, the rare earths, platinum groupmetals, rare and dispersed elements, and anions in solid samplematerials. All of them may have bearings on plant and animal,including human, life. In many problems involving bioaccessi-bility and toxicity, knowledge of the amounts of differentspecies of polyvalent elements and different complex cationsand anions, and their mineralogical hosts, is critical (Hall &Pelchat 1999). Little is known about the regional distribution ofelemental isotopes, other than where they have been used in oregenesis studies; the multi-collector ICP-MS is now available forsuch work. In this context, knowledge of the natural distri-bution of isotopes may help in ‘forensic’ studies, such as tracingthe sources of contamination, food, or other natural products.The provision of suitable methods to support regional-scaleinvestigations is a challenge, and solutions to these challengeswill provide data that has the potential to reveal to us much thatis important about our environment.

To meet the needs of applied geochemistry in the 21stcentury, there need to be continuing efforts nationally andinternationally to harmonize sampling and analytical methods.Harmonization of sampling procedures is of great importance ifcontinental- and global-scale geochemical maps are to beprepared. There has to be consistency, and we have to berecognizing the same material for sampling (e.g. Salminen et al.1998). The debate continues over the relative merits of activestream-sediment sampling and overbank-sediment sampling(Ottesen et al. 1989). The objectives of a geochemical mappingprogramme and the size of the area under study are major issuesthat bear on the choice for any specific project. It is quiteapparent from the work in China that overbank-sedimentsampling of floodplains adjacent to major rivers, a form of soilsampling, can yield informative geochemical maps for very largeareas in a time- and cost-effective manner (Xie et al. 1997). Theappropriateness of overbank-sediment sampling for higher-density mapping of smaller areas is a remaining issue. There islikely to be no one simple answer; there will be regionallyappropriate choices where sedimentological and geomorpho-logical conditions will have to be taken into account (e.g.Macklin et al. 1994; Bølviken et al. 2004).

It is clear that there is an increasing need for appliedgeochemists to work in collaboration with other natural andhealth scientists to solve the increasingly complex ecologicaland health problems that face societies in the 21st century(Garrett 2003). Applied geochemists can make important con-tributions on the basis of their knowledge of the source,transport and fate of elements as they pass through biogeo-chemical cycles that range in scale from site-specific to global.There is a further benefit to working in multi-disciplinary teams.Applied geochemists are expert at mapping regional geochem-istry, as evidenced by the number of atlases and map productsthat have been, and are being, generated. However, it is notunfair to say that, as a group, applied geochemists have not

always been as successful in interpreting the story those mapstell, especially from non-geological perspectives. Improvedinterpretations will follow a greater understanding of thephysical and chemical processes involved in the transport andfate of elements. Notable advances have been made in thiscontext in glaciated areas, with better understanding of glacialtransport processes (e.g. Kauranne et al. 1992), and the role ofphysical and chemical processes in ancient tropical terrains suchas Australia, Africa and South America (e.g. Butt & Zeegers1992). The interpretation of regional geochemical maps anddata by multi-disciplinary teams from a broader ecologicalperspective will likely lead to the recognition of geochemicalfeatures that are influencing other physical and biologicalprocesses. That can only benefit applied geochemistry as ascience and society as a whole.

Regional geochemical data are increasingly being used byindustry and government agencies to address regulatory issues,for example current work in Europe using the FOREGS datain metal risk assessments, and in Canada for the federalContaminated Sites programme. The importance of biogeo-chemistry is being recognized by requests to define ‘metallo-regions’ or ‘biogeochemical domains’ (see Fairbrother &McLaughlin 2002; Reimann & Garrett 2005) where similaritiesin the major aspects of elemental source, transport and fate, andtherefore bioaccessibility, define coherent spatial units. A chal-lenge is to determine how best to delineate such units bygeochemical mapping, at whatever scale is appropriate. Withinsuch spatial units, procedures can be established for definingthe natural or ambient range of background concentrations,effectively monitoring the environment, and undertakingremediation efficiently and cost-effectively if required. Withreference to monitoring, there is increasing interest in the use ofcritical load models to manage metal and other releases to theatmosphere. It is essential that these models take into accountthe transport and fate of metals in the biogeochemical cycle(Lofts et al. 2007). Working in collaboration with public health,regulatory agencies, risk assessment and management agenciesis becoming increasingly important (Chapman 2008). Appliedgeochemists need to bring their maps and data to play in theseimportant areas. However, it is important that the maps anddata are accompanied by expertise so that the data are used andinterpreted appropriately. Working closely with such expertswill also have the benefit of providing feedback to regional,local and urban geochemical mappers so that relevant observa-tions and measures that will improve the utility of thegeochemical data are collected.

Care over the usage of the terms ‘baseline’ and ‘background’needs to be taken, particularly in the context of non-geochemistusers of geochemical data, such as environmental regulators.While the term ‘baseline’ is convenient and frequently used, itimplies to many people a single known value against whichother values may be compared. This hides a fact that isrecognized by the very execution of national, sub-continentaland continental geochemical mapping programmes, i.e. thatgeochemical baselines and background vary spatially (e.g.Salminen & Tarvainen 1997). Why else map them? The term‘baseline’ also hides the fact that geochemical background is arange within which most observations will fall (Reimann &Garrett 2005). The ‘background’ has an average value that maybe used as a ‘baseline’, but that single value hides an importantfeature of the geochemical reality. It is important in environ-mental and ecological contexts to recognize that what has to beestablished are the scales and range of natural or ambientbackground (or baseline) variation in different environmentsacross the Earth’s terrestrial surface. Only then can situations berecognized that merit further attention for whatever reason.

Historical overview of geochemical mapping 213

A related issue is scale (Xie & Yin 1993). Geochemicalbaselines and backgrounds refer to a specific sample suite, i.e.number of samples of a particular sample medium in a given;therefore all these parameters need to be explicitly defined.Geochemical data, like so many others in the natural sciences,are fractal, i.e. self-replicating, (Bølviken et al. 1992). A graphicexample of this can be seen in Darnley et al. (1995, plate 3-1),which consists of a copper geochemical map of St. Lucia (WestIndies) and a nickel microprobe map of a Pt-group mineralgrain; they are almost identical, but differ in scale by a factor of1010. This implies that there will continue to be a necessity toundertake geochemical mapping exercises at a variety of scalesdepending upon purpose. Dependent upon the size of a studyor survey area relative to the scale of the sources and factorsinfluencing geochemical dispersion, different controlling factorswill be of differing influence. Prime examples of such factorsare geology and lithology, topography, proximity to oceans,climate, broad changes in vegetation, and contamination fromanthropogenic sources. In continental-scale surveys many ofthese will be influencing, often simultaneously, the observedelemental spatial patterns.

Returning to the roots of many readers in mineral explora-tion, what is the relationship of the patterns seen oncontinental-scale maps to mineral potential? What is the rela-tionship between geochemical provinces and metallogenicprovinces? This is an area of fundamental interest and aresearch challenge (Reimann & Melezhik 2001). Ultra-lowdensity surveys are extremely unlikely to directly discover a newmineral deposit; the spatial probability odds are too low. Butthrough a knowledge of the relationships between geochemicaland metallogenic provinces, attention can be efficiently focusedon the areas of greatest mineral potential and lead to newdeposit discovery (Reimann et al. 2007; Wang et al. 2007). As inso many aspects of applied geochemistry, the application ofappropriate geochemical analysis techniques has much to offer.By using analytical methods that focus on the forms, chemicaland mineralogical, of the elements released by weathering andtransported away from their sources, information of directrelevance to mineral search can be provided (Hall 1998).

When Arthur Darnley first proposed an international pro-gramme to foster international geochemical mapping, globalchange was just becoming of wide interest and public concern.But if change is to be detected, it has to be measured relative tosome range of baseline values. Some countries and continentshave made great strides in establishing regional geochemicalbaselines, others are still working towards that objective.However, if change is to be measured, sites or regions have tobe revisited and measurements undertaken using the same orsufficiently similar field and analytical protocols, at regularintervals. In order to reliably measure the changes, samplingintervals of between 10 and 25 years may be appropriate formedia such as soils, stream sediments and overbank sedimentssampled as soils in major river floodplains. A much shortersampling interval may be needed when monitoring changes inthe geochemistry of surface or ground waters. Some countrieshave even started to do this, e.g. China and the UK (Bellamyet al. 2005). Agencies and governments will have to be con-vinced of the continued importance of funding monitoring,which may be seen as costly and having the ability to revealunwelcome truths which then need to be addressed.

Finally, Arthur Darnley’s vision was for global-scale geo-chemical maps and data that could be used for environmentaland resource management. We have progressed significantlytowards that end since the start of IGCP Project 259 in 1988.The IUGS/IAGC Task Group on Global Geochemical Base-lines, of which Arthur Darnley was the Honorary Chairman,

continues as the international focus point. As applied geochem-ists we need to keep his vision before us and strive to completethe task along the path that he started us on.

The senior author wishes to express his sincere thanks to the staff ofthe Earth Sciences Information Centre (the Geological Survey ofCanada Library), Ottawa, and in particular P. Minter and L. Simpson,for tracking down and obtaining copies of some of the publicationscited. We also express our thanks to A. Golovin of IMGRE,Moscow, for providing notes on the development and progression ofapplied geochemistry in the Soviet Union and Russia. Finally, wethank our colleagues A. Rencz and R. Klassen for their reviews of thetypescript and their suggestions.

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