Dunn Colin E. Biogeochemistry in Mineral Exploration

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‘plant’ – ‘phyton’) would be a more precise term to apply to the activities of the

‘biogeochemist’. In some countries, notably France and China, it seems that there is a

predisposition to use this as a more accurate term. For the purposes of this book the

terms ‘biogeochemistry’ a nd ‘phytogeochemistry’ are considered as synonymous.

Biogeochemical methods of exploration involve the chemical analysis of plant

tissues to assess the presence and na ture of underlying mineralization, bedrock

composition, bedrock structure (faults, joints and folds), and the chemistry of the

soil, surﬁcial sediments, and associated groundwater. By contrast, ‘geobotanical ex-

ploration’ relies on the recognition of the occurrence of a plant species (or plant

communities) with underlying mineralizati on and/or bedrock and groundwater. The

distinction can be summarized simply as follows:



Biogeochemistry is the chemical approach, whereas



Geobotany is the visual approach.

Consequently, they should be considered as closely associated but separate dis-

ciplines. With a modicum of training a geologist with some knowledge of geochem-

istry can soon learn the fundamentals required to effectively conduct a

biogeochemical survey. It is a much larger step that is required for a geologist to

become a geobotanist, because of the significant training in plant identiﬁcation that

geobotany demands. This step to geobotany is made more easily by a trained botanist.

Ideally, a geologist/geochemist needs to team up with a botanist/forester to optimize

the information that can be obtained from the distribution and analysis of vegetation.

Geobotanical clues are more subtle in temperate and boreal (i.e., northern) forests

than in tropical forests, because there is a lesser diversity of trees and shrubs in the

cooler regions, and plants are able to accumulate wide ranges of many elements

without exhibiting any visible clues. It is sometimes apparent that when a traverse

crosses major differences in composition of the substrate, such as granite to car-

bonate, some geobotanical signs might be evident, e.g., a change in dominant species,

a change in plant population densities, more vigorous growth, or health of a par-

ticular species. In Siberia, vegetation on kimberlites, as compared with that on sur-

rounding rocks, develops more profusely because of elevated levels of P in the

kimberlitic bedrock (Buks, 1963). Roses grow better in carbonate-rich soils, so the

presence of wild roses commonly indicates enhanced carbonate content to the soil

and/or underlying bedrock. Similarly, extensive studie s have been made of the ‘Ser-

pentine ﬂoras’ of the world (Br ooks, 1987), although more strictly these should be

referred to as the ‘ultramaﬁc’ ﬂoras, because they do not rely on serpentinization for

their development, just the over all bedrock composition with its rich sources of iron,

magnesium and calcium.

Most of the geobotanical ‘indicator’ plants of speciﬁc metals occur in the warm

parts of the world, notably in central Africa (Brooks et al., 1995; Brooks, 1998). Plant

development in cool and cold regions is controlled more by physical than chemical

conditions. As a result, there are far fewer species in cold areas than in warm and

Introduction

moist climates, where plant growth and diversity are not impeded by the harsh phys-

ical conditions. In the tropics, ground chemistry plays a more dominant role in the

distribution of plants, and some species adapt to a chemical niche. In the 1950s, some

of the best examples that guided many exploration activities are the copper/cobalt

ﬂora of the Democratic Republic of Congo (DRC) and the copper ﬂora of the Zam-

bian copper belt (Brooks and Malaisse, 1985; Brooks et al., 1995; Brooks, 1998;

Brummer and Woodward, 1999). Plants comprising these ﬂoral assemblages provide a

geobotanical indication of copper and cobalt, but they may or may not all be enriched

in these metals: certain species may develop barriers to copper/cobalt uptake, and

would therefore be poor choices for a biogeochemical survey.

Important characteristic ﬂoras summarized in Brooks et al. (1995) are as follows:

Calciphilous ﬂoras – characteristic of limestone.

Halophyte ﬂoras – characteristic of saline environments.

Serpentine ﬂoras – characteristic of ultramaﬁc environments.

Selenium ﬂoras – especially of the mid-western United States (Cannon, 1960).

European zinc (Galmei) ﬂoras – notably over base metals in western Germany and

Belgium.

Copper/cobalt ﬂoras of DRC – notably the Shaban Copper Arc.

Extensive bib liographies on geobotanical indicators and plant communities as ore

indicators are listed in Rose et al. (1974), Br ooks (1987), Brooks et al. (1995) and

Brooks (1998). Among the names frequently cited there are, in chronological order,

Helen Cannon (1953, 1956, 1957), S.V. Viktorov (1955),A.Chikishev (1965),

H. Wild (1965), N.G. Nesvetailova (1970), Monica Col e (1973, 1977), F. Malaisse

(Malaisse et al., 1978, 1979) and Brooks and Malaisse (1985). This list is by no means

exhaustive, but presents some of the authors within whose studies more details can be

found. For those familiar with the Russian language, there are many papers and a

number of books published only in Russian, that contain a considerable amount of

information on geobotanical indicators (e.g., Nesvetailova, 1970).

Biogeochemical surveys commonly rely on the analysis of tissues from trees or

shrubs (i.e., vascular plants), although they may involve the collection of any species

of plant life, depending on the distribution of that species and its propensity to

accumulate meta ls (e.g., lowe r-order plants such as lichens, mosses, fungi and sea-

weed). From a geochemical standpoint, plants can be considered as a ﬁltered above-

surface extension of the underlying soil and rock, since they contain elements drawn

from soil, sediment, rock, groundwater and gaseous compound s contained within the

substrate. Typi cally, there is not a one-to-one relationship between the chemistry of a

plant and that of the soil, because of barrier mechanisms established by plants to the

uptake of certain elements; hence the ‘ﬁltering’ of the elements from the ground into

the plant tissues. A simple biogeochemical response to changes in the substrate is

shown in Fig. 1-1, where sampling commenced on gneiss, traversed an ultramaﬁc

body, and ﬁnished in metasediments. As might be expected, the elevated levels of

Biogeochemistry in Mineral Exploration

Ni and Mg (typical of ultramaﬁc rocks) are evident, whereas conversely there is

concurrent depletion of Sr and Ba.

History of geobotany

The application of geobotany to assist in delineating mineralization has been used

for many centuries. By contrast, the history of biogeochemical exploration dates

back little more than a century, primarily because analytical technology and

100

200

300

400

500

0 100 200 300 400 500

Distance (m)

Ni ppm

Ni_ppm Mg_pct

1000

2000

3000

4000

0 100 200 300 400 500

Distance (m)

Sr ppm

200

400

600

800

1000

Ba ppm

Sr_ppm

Ba_ppm

Fig. 1-1. Response of vegetation chemistry to underlying bedrock – Baccharis trimera from

Cerro Mantiqueira, southern Brazil. Baccharis has many common names, notably ‘Thola’ and

‘carqueja’, and is widespread throughout much of South America.

4 Introduction

instrumentation were inadequate for accurately determining, at reasonable effort and

cost, the miniscule traces in plant tissues of many elements that are relevant to

mineral exploration.

The earliest of the geobotanical observations appears to be that of Vitruvius who,

in 10 BC, noted that certain species are restricted to marshy ground ( Brooks, 1983).

In India, the 6th century AD Sanskrit writings of Vara

hamihira record many re-

lationships among plants, minerals and (notably) groundwater (Prasad, 1980), even

listing the depths to aquifers that can be predicted by particular species. Many

subsequent studies dealing with geobotany focused on the relationship of plants and

plant communities to groundwater (abundance and quality).

In 1841, the Russian geologist Karpi nsky advanced the concept of a relationship

between plants and geological substrates by noting that a whole plant community

should be recognized in helping to characterize the relationship between plants and

underlying geology.

History of biogeochemistry

Whereas published accounts on the relationship of plant chemistry to mineralized

rock date back to the end of the 19th century, they are scarce until the late 1930s. In

an 1898 study at the Omai gold mine in Guyana, ash samples of Baromalli (genus

Catostemma, from the family Bombacaceae) and a species identiﬁed as ‘ironwood’

were foun d to contain 0.3 ppm Au and 3 ppm Au, respectively (Lungwitz, 1900).

Kovalevsky (1987) reports that work on biogeochemical exploration in the USSR

began in the 1920s when S.P. Aleksandrov discovered that, when compared to con-

centrations in plants outside of an ore zone, there were elevat ed levels of vanadium,

radium and uranium in ash of plants growing in the vicinity of a vanadium–uranium

deposit. Subsequently, in the 1930s V.I. Vernadsky supported the establishment of a

‘Biogeochemical Labor atory of the USSR Academy of Sciences’ to which A.P.

Vinogradov made significant contributions.

The ﬁrst published report of biogeochemical methodology was by the Russian

worker Tkalich (1938), who cited the discovery that a de posit of arsenopyrite in

Siberia could be traced by the iron content of overlying vegetation. At about the

same time Nils Brundin in Sweden related biogeochemical data to a vanadium de-

posit in Sweden and to tungsten in Cornwall, England. He was sufﬁciently enthused

by his ﬁndings that he ﬁled a patent on the use of vegetation in exploration, noting

that the method would be especially suited for locating ores of gold, silver, lead and

zinc (Brundin, 1939).

In the early 1940s, Professor Harry Warren commenced more than half a century

of biogeochemical studies from his base at the Unive rsity of British Columbia in

Canada. During the ﬁrst 30 years of his work, Warren and his associates did much to

document the relationships between plant chemistry and concealed mineralization,

and to raise the credibility of biogeochemistry from, as he declared, general disbelief,

Biogeochemistry in Mineral Exploration

through ‘benevolent scepticism’ to general acceptance that, when used properly, it

can be a viable exploration tool (e.g., Warren and Delavault, 1950; Warren et al.,

1968). Harry Warren rightly earned the distinction of ‘father of biogeochemistry’ in

North America, and it is an enlightening pastime to browse through his more than

200 publications to extract many little gems of information. Not only does he provide

many useful pieces of information, but also there are a good many historic data

from the analysis of trees over sites that have subsequently been developed as mines

(e.g., the Endako Mo mine and the Sullivan Pb/Zn mine, both in British Col umbia).

What can be more instructive than to look at analytical data from trees of virgin

forest, and then review the production data from a mine subsequently developed at

that site?

While Harry Warren was advancing the science in Canada, work was also under

way in the United States. In the mid-western states Harbaugh (1950) reported the

results of a base-metal study of soils and vegeta tion. Shortly afterwards, when there

was a significant push to ﬁnd deposits of uranium, a number of scientists at the U.S.

Geological Survey examined the geobotanical and biogeochemical expressions of

uranium roll-front deposits in Colorado and the surrounding states (Cannon, 1957,

1960, 1964). Concurrently, Hans Shacklette and his co-workers were conducting

laboratory and ﬁeld experiments on the metal uptake of plants, and they produced

a number of USGS publications on the biogeochemical behaviour of different

elements, and several compilations of baseline data on background concentrations in

vegetation (Shacklette, 1965; Shacklette et al., 1970).

Following on from his discoveries in the 1930s, Nils Brundin spearheaded the

Scandinavian investigations into biogeochemical methods. A monograph on trace

elements in plants from Finland provided v aluable semi-quantitative information on

the composition of a wide range of plants growing on different geological substrates

(Lounamaa, 1956). Baseline data were presented for lichens, mosses, ferns, conifers,

deciduous trees and shrubs, dwarf shrubs, grasses and herbs.

During this period in the former Soviet Union, numerous papers were published

(mostly in Russian, with only a few significant translations into English) that de-

scribed in general terms the methods that were being employed and resul ts of

biogeochemical surveys over various types of mineral deposit. Of importance to

the international community was the milestone publication of the ﬁrst book in

English that was devoted exclusively to biogeochemical prospecting for minerals

(Malyuga, 1963).

For almost 50 years, until the time of his death in 2001 , Alexander Kovalevsky,

from his base in Ulan-Ude, Siberia, published the results of a wide range of biogeo-

chemical studies. He produced many papers, some of which have been translated into

English. For those with a good working knowledge of Russian, there appears to be

an enormous amount of valuable information that can be learnt from the prodigious

volumes of tables, ﬁgures and text that he produced. Other leading Russian workers

on biogeochemical methods during this period included Vinogradov (1954), Tkalich

(1959, 1961, 1970), Polikarpochkin and Polikarpochkina (1964), Grabovskaya

Introduction

(1965), Vernadskii (1965) and Talipov (1966). The ‘landscape geochemistry’ studies

of Perel’man (1961, 1966) contributed, too, to the literature on biogeochemical

methods. It is fortunate that Robert Brooks understood Russian and was able to

interact with a number of the Russian workers to summarize the complex Russian

literature into easily comprehens ible English.

In 1960, Professor Robert Brooks (1926–2001) commenced 40 years of funda-

mental work in biogeochemical, geobotanical and phytomining studies from his base

at Massey University in Palmerston North, New Zealand. In 1972, he published the

ﬁrst book from outside the former Soviet Union dealing with geobotany and

biogeochemistry in mineral exploration (Brooks, 1972). Thi s was a significant

milestone in the science and provided the English-speaking world with an easy to

understand review and handbook of biogeochemical methods. It was superseded by a

second and expanded edition (Brooks, 1983). Amongst his biogeochemical interests

were geobotanical and botanical studies of the ﬂora endemic to serpentine substrates.

He initiated, organized and led ﬁve expeditions sponsored largely by the National

Geographic Society, to remote areas of ultramaﬁc rock outcrop where the ‘serpentine

ﬂora’ had bee n poorly documented. Thanks to these major efforts several species

new to science were discovered, and there are now greatly improved databases and

collections housed at several major herbaria around the world. In 1987, he published

another significant collation of information and data in his book ‘Serpentine and Its

Vegetation – A Multidisciplinary Approach’ (Brooks, 1987).

In the mid-1960s, the Geological Survey of Canada commenced investigations

into the use of biogeochemistry in mineral exploration. A trailer was ﬁtted out to be a

mobile biogeochemical laboratory containing basic analytical equipment, a mufﬂe

furnace, balances and an emission spectrograph. This was taken into the ﬁeld and the

analytical work carried out close to the survey areas (Fortescue and Hornbrook,

1967, 1969; Hornbrook, 1969, 1970a,b). These studies developed protocols for when

and how to sample, and suggested a systematic approach to biogeochemical research.

They recommended a ‘Visit’ lasting one or two days to assess plant distribution and

the environment in general (i.e., a brief orientation survey). If results looked prom-

ising, then this would be followed by either a ‘Pilot Project’ of up to 30 days to

conduct a comprehensive survey of an area; or, if mining was imminent, a ‘Quick

Project’ to obtain sample material prior to disruption and potential contamination of

an area by mining operations. These procedures remain sou nd advice for conducting

biogeochemical investigations today, and high credit should be given to these re-

searchers for their thoughtful and thorough planning that helped to advance biogeo-

chemical methodology in its application to mineral exploration.

The 1974 publication of Kovalevsky’s book ‘Biogeochemical Exploration for

Mineral Deposits’ was ﬁnally translated into English in 1979 (Kovalevsky, 1979). This

work provided new insight into the Russian experience and approach to the science,

along with a host of rather complex acronyms that were elegantly deciphered by the

translators, and by the biogeochemical/geobotanical group at the USGS – Hans

Shacklette, Jim Erdman and Gary Curtin – all of whom in their own right have added

Biogeochemistry in Mineral Exploration

valuable studies to the biogeochemical literature. Subsequently, a revised and ex-

tended second edition was published with further elucidation of the Russian terms

provided by Robert Brooks (Kovalevsky, 1987). As noted in the Foreword by

A.B. Kazhdan, ‘this second edition is a greatly expanded version of the ﬁrst

y [with] y discussion of principles governing the formation of biogeochemical

haloes for Cu, Hg, Mo, Pb and Zn, and y the biogeochemistry of 45 other indicator

elements’. Although many of the species listed are restricted to Siberia, there are very

useful analogies to similar species typical of the boreal forests and the cool dry areas

of the world. The 1987 edition is well worth browsing through, because it gives insight

as to the plant genera and species that might be worth considering for biogeochemical

exploration elsewhere. It should not be treated as a ‘cook-book’, but more of a guide,

because some broad generalizations are made, and it seems that results from the

Russian environment are not always paralleled by those from other parts of the

world. For example, a table indicates that the vast majority of plants have a very

low propensity to absorb U. This is partly true, but in certain U-rich environments,

such as around the uraniferous Athabasca Sandstone of northern Saskatchewan,

there are many plant species that can accumulate U (Dunn, 1981, 1983). Furthermore,

Kovalevsky’s 1987 text is 20-years old and significant advances have been made in the

interim – not least of which is the introduction of inductively coupled plasma mass

spectrometry (ICP-MS) analysis of dry tissues.

Kovalevsky wrote a third book that is as yet only available in Russian, therefore

its impact on the science is hard to evaluate for the non-Russian-speaking populace

(]NO!EOXNMNR PACTEHN[ – meaning ‘The Biogeochemistry of Plants’,

Kovalevsky, 1991). Some information contained in this book appeared in English in

book chapters (Brooks et al., 1995) and journal publications (Kovalevsky and

Kovalevskaya, 1989; Kovalevsky, 2001, shortly before his death).

During the 1980s, a resurgence of interest in biogeochemical methods of explo-

ration took place in North America, and especially in the south-western United

States. A conference held in Los Angeles in 1984 provided a useful ‘state-of-the-art’

summary of the science, bringing together expertise from a diversity of disciplines

(Carlisle et al., 1986). In the United States, big sagebrush (Artemisia tridentata)

became a common sample medium to assist in the exploration for uranium and

gold in the arid terrain of the southwest (Erdman and Harrach, 1981; Gough

and Erdman, 1980; Erdman et al., 1985; Erdman and Olson, 1985). The work by

S. Clark Smith and J.A. Erdman contributed significantly to the biogeochemical

database. In Canada, the preferred sample media were recognized as black spruce

(Picea mariana), balsam ﬁr (Abies balsamea), alder (Alnus spp.), Douglas-ﬁr

(Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and lodgepole

pine (Pinus contorta), among others (Dunn, 1981; Cohen et al., 1987; Dunn, 1989,

1995a).

There has been a tendency for significant advances in analytical instrumentation

to coincide with advances in biogeochemical exploration. In the mid-1970s, ICP-ES

and instrumental neutron activation analysis (INAA) were developed to provide

Introduction

accurate and precise multi-element data at low-element concentrations and remark-

ably low cost. The INAA, in particular, was a great break-through since many

elements could be determined at sub-ppm levels from a single irradiation of dry

vegetation. During heightened activity for discovering uranium deposits in the late

1970s, delayed neutron counting was used for determining uranium concentrations in

vegetation (Dunn, 1983a,b; Dunn et al., 1984), and as renewed interest for gold took

over from uranium in the 1980s INAA methods became routi ne for determination of

gold to 0.1 ppb in dry vegetation (Hoffman and Booker, 1986). Within the last 10

years, the most significant advance has been the application of ICP-MS to the anal-

ysis of small samples (typically 1 g) of dry plant tissues. This has provided new insight

into element concentrations and distributions in and among trees and shrubs, and

permitted the systemat ic examination of the distributions of elements rarely deter-

mined previously, because of the time-intensive procedures that were required. As a

result, there has been an exponential increase in biogeochemical knowledge, and

information, over the past decade.

In 1992, Robert Brooks compiled the book ‘Noble Metals and Biological Sys-

tems’ that covered a broad spectrum of cu rrent knowledge of these metals (Brooks,

1992). Three years later, Brooks was lead editor of the book ‘Biological Systems in

Mineral Exploration an d Processing’ (Brooks et al., 1995) that contains a wealth of

valuable information. The last book that he compiled focussed on those plants that

have the ability to concentrate metals to extraordinarily high levels, entitled ‘Plants

that Hyperaccumulate Heavy Metals’ (Brooks, 1998).

In China systematic biogeochemical studies began in the 1970s, and in recent

years it appears that the focus has been mainly on the search for deeply buried

mineralization in arid regions. Researchers claim that from the analysis of willow

twigs they can delineate Pb–Zn stratabound deposits beneath more than 100 m of

loess and over 100 m of redbeds. Few publications appear to come from China, and

when last consulted a few years ago, the Chinese considered that their biogeochem-

ical studies are still in the experimental stage.

In Australia, too, biogeochemical studies are enjoying renewed investigation. A

perceived problem in the past has been the complexities that arise in dealing with the

multitude of species comprising Australia’s two main genera of plant – the eucalypts

and the acacias. In Australia alone, there are about than 850 species of eucalyptus

(family Myrtaceae) and more than 1000 species of acacia (family Mimosaceae). As yet,

it has not been established if there are significant differences in metal uptake and

accumulation among all the species of each of these genera. If there are, then indeed,

there are problems in establishing the baseline information that is desirable for de-

termining which might be the preferred species for sampling. However, if differences

are quite minor among members of a genus or perhaps other grouping of species, then

it should prove possible to mix data from similar species without compromising a

survey. Furthermore, if an area has a particular species that is dominant (e.g., red river

gum, Eucalyptus camaldulensis – a species investigated by Karen Hulme at the Uni-

versity of Adelaide), then that species can be used since it is the spatial relationships of

Biogeochemistry in Mineral Exploration

element concentrations, rather than the absolute concentrations, that are the over-

riding dominant factors of value to biogeochemical exploration.

The Association of Exploration Geochemists (now renamed the Association of

Applied Geochemists) has been instrumental in disseminating biogeochemical ex-

ploration methods and data through sponsoring short courses and publishing the

course notes (Parduhn and Smith, 1991; Dunn et al., 1992c [which includes many

references to Clark Smith’s studies]; Dunn et al., 1993a; Dunn et al., 1995a).

In recent years, journal papers by many authors have provided case histories and

overviews of procedures and various sample media from a full range of environments

from around the world. Some of the best sources of information on the application of

biogeochemical methods to mineral exploration are the ‘Journal of Geochemical

Exploration’, ‘Applied Geochemistry’ and ‘Geochemistry: Explorat ion, Environ-

ment, Analysis’.

PLANT EVOLUTION AND CHEMISTRY

At about the end of the early Silurian Period, the ﬁrst vascular land plants ap-

peared. Cooksonia was a small fragile plant, just a few centimetres tall, comprising a

slender bifurcating stem topped with small spheres (sporangia) in which the repro-

ductive spores were formed (Fig. 1-2).

Over the ensuing 50–100 million years, this was the type of plant that grew in

suitably moist conditions while evolving into more complex entities. By the Car-

boniferous (360–300 million years ago), lush plant growth ﬂourished in equatorial

regions and huge trees prevailed – such as the fern-like but seed-bearing pterido-

sperms, the huge green-stemmed lycopods (Lepidodendron, Sigillaria, up to 35 m tall),

the giant Calamites (20 m) and the mangrove-rooted Cordaites (up to 45 m).

Cooksonia from the Lower Ludlow of Wales Reconstruction of Cooksonia b

C. Berr

(

Ludlow museum, UK

)

Fig. 1-2. Earliest form of plant life (Silurian). Source: http://www.xs4all.nl/steurh/engcook/

ecooks2.html#reco, May 2005.

10 Introduction

During their long period of evolution, plants have be come sophisticated in

adapting to their environments, both physical and chemical, and in order to survive

they have developed a requirement for certain elements. In addition to hydrogen,

oxygen and carbon there is general agreement that essential elements include nitro-

gen, phosphorus, potassium, calci um, magnesium, sulphur, boron, chlorine, iron,

manganese, zinc, copper, molybdenum and nickel. Other elements are considered

‘essential’ by some workers and/or ‘beneﬁcial’ by others and as research continues

the beneﬁcial effects of an increasing number of elements, often in very small con-

centrations, are being recognized. Kabata-Pendias and Pendias (1992) provide

many useful tables that summarize the role of metals in plants and the effects of too

much (toxicity) or too little (deﬁciency). As a consequence of these requirements for

metals, biogeochemical data should be viewed somewhat differently from those of

soils and rocks.

Laboratory experiments have demonstrated that the most basic of life forms –

bacteria and fungi – are capable of accumulating extraordinarily high concentrations

of several metals (Table 1-I).

Studies in the natural environment have recorded metal concentrations in macro-

fungi, such as the edible mushroo ms, that are significantly lower than in the lab-

oratory tests. However, they are still extremely high compared to the soils in which

they were growing that contained background concentrations of elements. This at-

tests to the ability of fungi to preferentially scavenge some metals (Table 1-II).

The efﬁciency of roots depends on the distan ce of their depth of penetration into

the soil and, more importantly, the surface area of roots that comes into contact with

the ground. Mycorrhizal fungal hyphae vastly increase the volume of surface area to

which roots have access. Not only do they absorb water and pass it into a plant, but,

TABLE 1-I

Concentrations of metals in primitive life forms (experimental data) – from Lepp (1992)

Bacteria Concentration (%) Fungi Concentration (%)

Ag Thiobacillus

ferrooxidans

35 Rhizopus arrhizus 5.4

Cd Zooglea ramigera 40 Rhizopus arrhizus 3

Co Zooglea sp. 25

Cr Rhizopus arrhizus 3.1

Cu Zooglea ramigera 40 Rhizopus arrhizus 1.6

Hg Rhizopus arrhizus 5.8

Ni Zooglea sp. 13

Pb Micrococcus

luteus

35 Rhizopus arrhizus 10.4

Zn Rhizopus arrhizus 2

11Biogeochemistry in Mineral Exploration