Dunn Colin E. Biogeochemistry in Mineral Exploration

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shows a typical proﬁle of Ni in top twigs from a helicopter-borne ﬂight over a known

geophysical conductor.

Niobium (Nb) (Fig. 9-41)

Precision for Nb is poor at the concentrations usually present in vegetation.

Occasional spikes in controls and fair to poor replication of ﬁeld and laborat ory

duplicates considerably compromise the value of the Nb data. Interpretation of Nb

results should be treated with caution, since the controls indicate that false anomalies

may arise.

Niobium has low mobility in the natural environment. Kabat a-Pendias (2001)

reports that Nb may be relatively mobile under humid conditions, but notes that

there is no evidence offered to support this contention. Kovalevsky (1987) stated that

the low mobility of Nb over Nb-bearing ores results in low availability to plants

except over ‘cryog enic taiga-type [waterlogged] soils’, which is interpreted to mean

permafrost or discontinuous permafrost, and is likely to refer to studies in the arctic

conditions of the Kola Peninsula where significant Nb ores occur.

Determinations of Nb can assist in the exploration for Nb/Ta deposits. Near Nb

mineralization on the Kola Peninsula concentrations of up to 10 ppm in dry tissues of

several species (notably the arctic raspberry Rubus arcticus) have been reported

(Tiutina et al., 1959). At the Bernic Lake rare metal dep osit in Manitoba various

tissues of jack pine, black spruce, alder, poplar (Populus tremuloides) and paper birch

(Betula papyrifera) were collected at eight sites near the mine. Niobium was deter-

mined by ICP-MS at the Geological Survey of Canada laboratories. The pine bark

had, on average, the highest concentrations with an average of 4.3 ppm Nb. The

spruce bark had 2.2 ppm Nb, the spruce twigs 1.5 ppm Nb and the pine twigs 1.2 ppm

Nb. All of the remaining samples yielded o0.2 ppm Nb. A few co mparisons of

needles from spruce and pine indicated that the pine had twice as much Nb as the

spruce, but both were substantially lower than in the twigs or bark.

Nb ppm

V17 NIST 1575a

Target

Mean

Std. Dev.

RSD %

0.02

0.01

No data

0.004

0.003

0.01

0.02

0.03

0.04

0.05

0.06

V17 - 22 samples among 440 samples

Concentration

Detection

Fig. 9-41. Niobium – Precision and accuracy on dry tissues – V17 and NIST 1575a (see

Fig. 9-1).

282 Biogeochemical Behaviour of the Elements

At Bernic Lake the Nb concentrations were probably somewhat enhanced by Nb-

bearing dust from the mine workings, but the data serve to demonstrate that the

conifer bark and twigs would be the preferred sample media for conducting a

biogeochemical su rvey for Nb. These ﬁndings are in accord with those of Kovalevsky

(1987) who considered that the external layers of bark or suberized cones from the

forest ﬂoor are the most informative indica tors of Nb.

Kimberlites commonly have elevated Nb values, and some enrichment of Nb at

the margins of kimberlites has occasionally been found. The volcanic-facies kimber-

lite at Sturgeon Lake, Saskatchewan, yielded weakly anomalous levels of Nb in twigs

of trembling aspen (Populus tremuloides) using an ICP-MS method developed to

determine ultra-trace levels of selected elements (Hall et al., 1990b). Background

concentrations in ash were 0.2 ppm Nb (0.006 ppm Nb dry weight), with a maximum

adjacent to the kimberlite outcrop of 1.3 ppm Nb (0.02 ppm dry weight) (Dunn,

1993).

Osmium (Os)

See ‘Platinum and the Platinum Group Elements’.

Palladium (Pd)

See ‘Platinum and the Platinum Group Elements’.

Phosphorus (P) (Fig. 9-42)

Since P is an essential element for plants, concentrations are always well above the

detection limit. Precision is excellent. There is a considerable volume of literature on

P %

V6 NIST 1575a

Target

Mean

Std. Dev.

RSD %

0.046

0.045

0.003

0.11

0.13

0.006

0.01

0.02

0.03

0.04

0.05

0.06

V6 - 30 controls among 600 samples

Concentration

Detection

Fig. 9-42. Phosphorus – Precision and accuracy on dry tissues – V6 and NIST 1575a (see

Fig. 9-1).

283Biogeochemistry in Mineral Exploration

the role of P in plants; it is a component of various proteins, sugars and starches, and

it is critical for energy transfer. The general ratio of C:N:S:P in terrestrial plants is

790:7.6:3.1:1 (Bolin et al., 1983). The P content of Markert’s (1994) ‘reference plant’

is 0.2%, which is close to the average of 0.24% in foliage samples from the Eden

Project. Twigs contain less P (gener ally about 0.05–0.15% P) and in conifer bark

concentrations are lower still at 0.01–0.03% P.

With respect to exploration, the P content of plants occasionally assists in de-

ﬁning the location of mineralization. Phosphorus is sometimes enriched with U de-

posits, in which case anomalous P concentra tions can occur in plants. However, U is

a mobile element and U is a better indicator of U than P.

Some kimberlites have elevated levels of P. In these situations plants growing over

the kimberlites can generate positive P anomalies. In central Alberta, a white spruce

sampling programme found enrichments of several elements in the ash of the top

stems, including a good response from P over most of the known kimberlites of

which only one had an outcrop and the remainder were concealed beneath several

metres of overburden (Fig. 9-43).

Over kimberlites from elsewhere P responses in vegetation are usu ally more subtle

or absent. Several kimberlites from South Africa yielded no positive P response in the

overlying vegetation, whereas others had a modest response. Similarly, there was a

1.4

3.2

3.6

metres

K14

TQ155

BH225

K252

Kimberlite

0 2000 4000

Sample site

Max. 6.5% P

Contours at

70, 80, 90th

percentiles

PHOSPHORUS

in ash of

White Spruce

Top Stems

Fig. 9-43. Phosphorus in the ash of top stems from white spruce (Picea glauca). Buffalo Head

Hills, Alberta, Canada.

284 Biogeochemical Behaviour of the Elements

positive response in leaves of dwarf birch from over some of the kimberlites in the

Ekati diamond ﬁelds of Canada’s Northwest Territories, and a subtle response in

twigs of poplar from adjacent to the volcanic facies Sturgeon Lake kimberlite in

Saskatchewan (Dunn, 1993). Commonly, positive signatures of P in plants growing

over kimberlites are complem entary to stronger signatures of other elements.

Platinum (Pt) and the platinum group elements (PGEs) – palladium (Pd), iridium

(Ir), osmium (Os), rhodium (Rh) and ruthenium (Ru) (Figs. 9-44 and 9-45)

These are among the rarest of the elements and, although instrumental detection

limits are now in the low-ppb range, the PGEs are infrequently detected in dry plant

tissue from areas remote from cities. Of these elements only Pd and Pt are detected by

ICP-MS without analysis by high-resolution instrumentation or the introduction of

methods to pre-concentrate the PGEs (e.g., NiS ﬁre assay). If traces of Pd or Pt are

reported in dry tissue, results should be veriﬁed by re-analysis and carefu l consid-

eration of the environment from which the samples were collected, always bearing in

mind that modern vehicles have catalytic convert ers than emit Pt and Pd. Samples

from close to highways are likely to be contaminated with small amounts of Pt and/

or Pd. For example, Dongarra

et al. (2003) recorded up to 102 ppb Pt and 45 ppb Pd

V7 (ash) NIST 1575a

Target

Mean

Std. Dev.

RSD %

∼ 80 ppb

No data

Pd (ppb) in Control Ash V7

100

120

Chronological Sequence: n=45 controls among 900 samples

Fig. 9-44. Palladium – Precision and accuracy on ashed tissues – V7 (see Fig. 9-1).

V7 (ash) NIST 1575a

Target

Mean

Std. Dev.

RSD %

∼ 50

No data

Pt (ppb) in Control Ash V7

100

150

200

250

300

Chronolo

ical Sequence: n=46 controls amon

900 samples

Fig. 9-45. Platinum – Precision and accuracy on ashed tissues – V7 (see Fig. 9-1).

285Biogeochemistry in Mineral Exploration

in pine needles from the urban area of Palermo, Italy. From SEM studies they found

Pd bound to micron-sized silica particles, probably in the form of a halogenat ed

compound.

For PGEs other than Pt and Pd, HR-ICP-MS, INAA, GFAAS or special tech-

niques are required for determining the very small traces present in plant tissues.

Iridium is included in most INAA packages, with detection as low as 0.1 ppb Ir in dry

tissue, but even so concentrations are nearly always below detection. Any positive

values reported should be queried with the laboratory to ensure that appropriate

corrections have been made. For all practical exploration purposes, at the present

time only Pd and Pt need to be determined in plant tissues and any requirement for

the other PGEs should be discussed with the analyst.

At this time there is no commercially available PGE standard for dry vegetation.

The quality control charts for Pd and Pt shown above are data from the analysis of

an unusually PGE-rich ash (designated V7) and they demonstrate precision that is

quite good for Pd but poor for Pt. In ﬁeld samples it is rare to obtain Pd values as

high as these and precision at lower ppb Pd level s is likely to be considerably inferior.

V7 has yielded extreme variability for Pt with a RSD of 86%. This level of variability

does, of course, cast doubt on the validity of the data from ﬁeld samples. However, if

analytical duplicates are reasonably repeatable and the patterns of Pt distribution are

similar to those of Pd and other typical pathﬁnder elements (e.g., Te, Se), there is

good reason to more fully investigate their significance with regard to the potential

presence of PGE-rich deposits.

Palladium determinations by ICP-MS are prone to a variety of complex inter-

element interferences requiring many corrections by the analyst. Platinum gives a

much cleaner signal, but like Au it exhibits the classic ‘nugget’ effect such that it

appears to be highly heterogeneously distributed within plants. In conducting a

biogeochemical survey for PGEs, the reduction of tissues to ash by controlled ig-

nition is an effective way to preconcentrate them so that concentrations are appre-

ciably above the instrumental detection limits. There are, however, some potential

problems with respect to Pd, because the usual ashing temperature is about 475

and at this temperature studies have indicated that Pd may create a poorly soluble

oxide bond that does not breakdown until much higher temperatures are attained

(Table 9-VI). Excellent agreement was shown between the ICP-MS method and lead

ﬁre assay (FA)/ICP-MS for twenty samples collected in bulk in the vicinity of the

Rottenstone Deposit, Saskatc hewan (Hall et al., 1990a).

Table 9-VI shows that the total Pd content of the samples was not obtained until

samples were heated to about 850

C. However, an appreciable amount of the Pd

could be recovered from ash obtained from controlled ignition at 470

C demon-

strating that, for exploration purposes, meaningful inter-site distribution patterns

could be obtained provided all samples were ashed at the same controlled temper-

ature. It could be argued that in PGE exploration all samples should be ashed to at

least 850

C. However, this would involve an extra cost and at that temperature other

elements will have partially volatilized and others may have formed complex bonds

286

Biogeochemical Behaviour of the Elements

creating new problems in interpreting a multi-element data set. Whereas it is desir-

able to release all of an element into solution, for exploration purposes this is not a

requirement, because it is the spatial relationships of element concentrations that

provide focus for exploration acti vities. Controlled conditions are the critical factors

to be maintained.

In dry tissues, background levels of Pd, the most abundant of the PGEs, are in the

sub-ppb range, and the other ﬁve PGEs (Pt, Rh, Ir, Os and Ru) occur as only a few

parts per trillion (Dunn et al., 1989). Palladium in plants of the western United States

has been studied in some detail by Kothny (1979, 1987, 1992), who found that plants

growing in soils containing 40 ppb Pd had from 15 to 110 ppb Pd in ash. The highest

levels were in California white oak (Quercus lobata), red pine (Pinus resinosa) and

bearberry (Arctostaphylos nummularia). Seasonal variations determined mostly from

samples of black walnut (Juglans hindsii) were similar to those reported elsewhere for

gold, with highest concentrations occurring in the early summer (Kothny, 1992).

Under most na tural conditions Pd is more mobile than the other PGEs, behaving

in a similar manner to base metals. Studies show that Pd can migrate either as a true

solute or in colloidal form (Pogrebnyak et al., 1986) whereas this has not been

demonstrated for Pt. It can be expected, therefore, that a biogeochemical halo

around PGE mineralization will be larger for Pd than Pt. Of all the PGEs, Pd is that

which is likely to provide the best biogeochemical signature of underlying PGE

mineralization. In sulphide-hosted PGE mineralization, Pd is commonly the most

abundant of the PGEs. In oxide-hosted PGE mineralization, Ir may be relatively

abundant and can be determined as part of a routine multi-element INA analysis.

The low detection obtained by INAA (2 ppb Ir in ash and 0.1 ppb Ir in dry tissue)

provides a simple ﬁrst appraisal of the presence of PGEs in vegetation and, by

inference, in the underlying substrate.

From a biogeochemical exploration perspective it is important to consider the

anticipated type of mineralization that may be hosting PGEs. The biogeochemical

response to PGE mineralization is strongly dependant on whether the host minerals

are sulphides or oxides. Sulphide-rich mineralization (Ni and Cu-rich) may generate

a good biogeochemical response, whereas PGEs locked tightly in crystal lattices, such

TABLE 9-VI

Effect of ashing temperature on the recovery of Pd (ppb) in black spruce using ICP-MS. Values

normalized to ash weight at 470

C (Hall et al., 1990)

Tissue Ignition temperature (

470 700 800 850 870 900

Black spruce twigs

Pd (ppb)

810 890 958 1390 1428 1410

Black spruce needles

Pd (ppb)

91 117 170 220 230 228

287Biogeochemistry in Mineral Exploration

as chromite, are not readily released and are therefore absorbed only weakly by

plants to give a subtle biogeochemical response.

In the Arctic tundra, gossans rich in Pt and Pd occur near Ferguson Lake within a

suite of metamorphic rocks dominated by hornblende-rich gneiss, amphibolite and

granitic gneiss. They are volcanic and sedimentary rocks of the Archaean Kaminak

Group that were metamorphosed during the Hudsonian orogeny. Copper–nickel sul-

phides form narrow, massive lenses and disseminations, and the metallic minerals

collectively contain 1.2–3.3% combined copper and nickel. Grab samples have yielded

up to 590 ppb Pt and 2500 ppb Pd (Coker et al., 1991). A study of several arctic shrubs

and lichens reported less than 50 ppb Pt, but up to 913 ppb Pd in ash of Diapensia

lapponica from a gossan (Lee, 1987). This circumpolar alpine-arctic species is a small

cushion-forming evergreen perennial shrub, up to 15 cm in height. A second study in

the same area examined the PGE content of dwarf birch (Betula glandulosa), and

Labrador tea (Ledum palustre) and reported maxima of 1350 ppb Pt, 3071 ppb Pd and

124 ppb Rh in ash from stems (Coker et al., 1991). The dry tissue equivalent concen-

trations of these values are approximately 25 ppb Pt, 55 ppb Pd and 2.4 ppb Rh. The

ashed stems of the birch and Labrador tea had substantially more Pt, Pd and Rh than

the leaves, with Rh showing the greatest stem to leaf contrast of more than 15:1 in ash.

The Stillwater Complex of Montana contains North America’s largest known

reserves of PGEs. Platinum, Pd and Ni sulphides of the braggite-vysotskite solid

solution series are hosted by layered maﬁc to ultramaﬁc rocks. Fuchs and Rose

(1974) collected two samples of limber pine (Pinus ﬂexilis) which yielded maxima of

56 ppb Pt and 285 ppb Pd in twig ash. Ten years later, prior to the commencement of

mining operations, Riese and Arp (1986) collected twigs and needles of Douglas-ﬁr

(Pseudotsuga menziesii) from 65 sites along several traverses over the Howland Reef

part of the complex. Samples were reduced to ash at 550

C and analysed by ICP-ES

after a proprietary double MIBK-based extraction method. Twigs (5–7 years growth)

were reported to contain remarkably high maxima of 3000 ppb Pt and 15,000 ppb Pd

in ash. Conce ntrations were approximately one order of magnitude higher in the

Douglas-ﬁr twigs than in the soils, and biogeochemical anomalies were displaced a

few tens of metres down slope from a known zone of mineralization. Platinum had

the lowest signal-to-noise ratio, and it was concluded that Pt in vegetation was the

preferred geochemical exploration method for this area.

The small ultramaﬁc body comprising the Hall deposit at Rottenstone Lake in

Saskatchewan was mined from 1965 to 1968 to extract PGE-rich violarite (Ni) and

chalcopyrite (Cu). The deposit yielded 4779 ppb Pt and 3920 ppb Pd that was con-

tained mostly in sperrylite (PtAs2), moncheite (PtTe2) and kotulskite (PdTe). Sub-

sequently, PGE-rich phases of several mineralized boulders have yielded up to

38,000 ppb Pt, 13,000 ppb Pd, 270 ppb Rh, 180 ppb Ir, 200 ppb Os and 140 ppb Ru

(Hulbert and Slimmon, 2000). Although the ore body was only 50 m by 50 m by 10 m,

it was richer in PGEs than any other nickel–copper deposit in Canada.

The Rottenstone area is located in pristine boreal forest, far from any road or all-

weather trail and as such comprises a ‘natural biogeochemical laboratory’ from

288

Biogeochemical Behaviour of the Elements

which collections have been made on numerous occasions between 1983 and 2006.

Samples have been analyse d for all the noble metals, and they show that twigs and

outer bark of black spruce accumulate PGEs more than the other tissues that were

examined (Table 4-VII). Labrador tea is also sensitive to the presence of most of

these elements. During that time span plants were naturally seeded after cessat ion of

mining operations, yet species have maintained a similar PGE composition – the

precise locations visited in 1983 to collec t samples were re-sampled in 2006.

Platinum group meta ls within the Alaskan-type Tulameen Complex of southern

British Columbia occur mostly in chromite-rich pods within serpent inized dunite.

Platinum and Ir are the dominant PGEs, with no detectable Pd in the chromites, but

weak Pd enrichment in the clinopyroxenite, hornblendite and the rare sulphide

phases. Platinum-iron alloys, sperrylite (PtAs2), and irarsite (IrAsS) are the most

abundant PGE-bearing minerals, and all other PGE minerals reported are Pt-bear-

ing. They occur either as euhedral to subhedral grains in chromite, or as anhedral

grains interstitial to chromite. The recovery of platinum has been solely from placer

operations. In view of the nature of the mineralization and the resistance of chromite

to weathering, the PGEs tend to remain tightly bound in crystal lattices. Conse-

quently, analyses of various trees have yielded only low concentrations of PGEs.

However, most rock types comprising the complex do contain total PGE concen-

trations of at least a few tens of ppb demonstrating a regional enrichment of PGEs.

At Tulameen, plant cover is sparse on the steep slopes and on top of the ser-

pentinized body that rises steeply from the moist wooded valley of the Tulameen

River. Samples of trees and shrubs from a 6 km transect along the Tulameen valley

(down-slope from known chromite pods on Grasshopper Mountain) yielded only a

few ppb PGEs. Iridium was detected in only two of 70 ash samples: 15 ppb Ir in

Douglas-ﬁr (Pseudotsuga menziesii) twigs, and 5 ppb Ir in twigs from a yew (Taxus

brevifolia). None of the 34 samples from sites close to chromite pods on the mounta-

inside yielded over 2 ppb Ir or Rh in ash, but they contained o2 – 29 ppb Pt and o2

– 21 ppb Pd. Ash of Douglas-ﬁr twigs had 17 ppb Pt and 7 ppb Pd, and bark had

7 ppb Pt and 18 ppb Pd. Highest concentrations in ash of the samples tested were

29 ppb Pt in outer bark of lodgepole pine (Pinus contorta), and 21 ppb Pd in bark of

Whitebark pine (Pinus albicaulis)(Dunn, 1992, 1995a; Fletcher et al., 1995). Earlier

unpublished work by Prof. H.V. Warren (pers. comm., 1989) noted some preferential

uptake of Pt by the small ‘umbrella plant’ (Eriogonum ovalifolium), and analysis of a

sample collected later conﬁrmed his observation, yielding a relatively high level of

21 ppb Pt in ash. Several species of this plant occur on mountain slopes of western

North America, especially on ultramaﬁc rocks and, de spite its irregular distribution,

it could be used to provide an indication of the PGE potential of the substr ate.

A biogeochemical component was included in a range of geochemical surveys

conducted by the Minnesota Geological Survey over a 1000 km

area that encom-

passed the Duluth Gabbro (Buchheit et al., 1989; summarized in Dunn, 1995a).

Among the objectives of the programme was to explore for PGEs by determining

distribution patterns of Pt and Pd using the ﬁve most common species of tree and

289

Biogeochemistry in Mineral Exploration

shrub. In ash, maxima of 40 ppb Pt in white spruce twigs, and 52 ppb Pd in balsam ﬁr

twigs were recorded. Maps that accompany the report show that the few samples

with detectable levels of Pt did not relate to any particular rock type or structure. The

Pd data, however, showed weak clustering of higher values at several locations.

The Coryell alkalic intrusion near Grand Forks, in south-central British Colum-

bia, has associated Cu mineralization with Au, Ag and PGEs that was worked almost

a hundred years ago. Ore shipped out in 1915 had an average grade of 9.6% Cu,

230 ppm Ag, 0.68 ppm Au and 8.9 ppm PGEs. Fifty tissue samples from common

trees, shrubs and herbs collected mostly from a site near the base of the mountain

over shonkinite pyroxenite failed to yield an Ir analysis above the detection limit of

2 ppb in ash, and Pt and Pd were present in amounts similar to those found at

Tulameen (Dunn, 1992).

In Siberia, over many years Kovalevsky (2001) analysed more than 25,000 plant

samples, mostly rotted pine stumps, for PGEs resulting in the discovery of several

new types of PGM mineralization in weathered bedrock. Maximum concentrations

were reported to be 5000 ppb Pt in ash, with data obtained by a ‘sensitive emission

spectrographic method’. An initial survey involving extremely dense sampling inter-

vals revealed twelve biogeochemical anomalies, 1–10 m wide, with concentrations of

50–500 ppb Pt in ash. Subsequent trenching disclosed seven types of PGM miner-

alization.

It is to be concluded that the value of biogeochemical methods to explore for PGE

mineralization is low for most PGE-bearing rocks except sulphide-rich systems where

a strong response can occur. For PGEs hosted by other rock types the biogeochem-

ical signature is likely to be very subtle unless there has been considerab le degra-

dation of host minerals (e.g., chromite) through weathering processes.

Praseodymium (Pr)

See Lanthanum and the Rare Earth Element s.

Praseodymium is a REE that has no known biological role. In V6 it exhibits good

precision with a mean of 0.19 ppm Pr. Databases are very limited, but Pr is usually

concentrated in plants at levels close to its de tection limit by ICP-MS of 0.02 ppm Pr.

In South Africa, foliage of Acacia mellifera (Black thorn) has yielded up to 2.7 ppm

Pr adjacent to a kimber lite. Stems from this species had concentrations 50–70%

lower. Dwarf birch leaves from over kimberlites in the Ekati area of the Northwest

Territories of Canada yielded concentrations consistently below detection.

Promethium (Pm)

This rare earth element has no stable isot opes. It is radioactive and there are no

known measurements of Pm in plants.

290

Biogeochemical Behaviour of the Elements

Potassium (K) (Fig. 9-46)

Concentrations of this essential macronutrient element for plants are typically

well in excess of the detection limit. Precision is excellent and concentrations in ﬁeld

samples can be plotted with conﬁdence that they are not analytical artefacts. Trends

in K enrichm ent can sometimes be attributed to bedrock alteration, particularly

where K feldspar has been degraded due to weathering, or there has been some K

metasomatism. In the latter situation plants may be useful indicators of metalliferous

porphyry environments. In a survey over a Mo–Cu porphyry in the Amazon, fronds

from tree ferns had high K levels (up to 2.86%) that corresponded to the locations of

highest Mo con centrations. In this situation, whereas the Mo data were the more

useful for deﬁning areas of mineralization, the K data were supplementary in that

they helped support the interpretation that Mo was associated with K-rich rocks.

Potassium data from foliage collected in the Eden Project show concentrations

ranging from 0.38% K in bamboo to 5.09% in wild coffee.

Radium (Ra)

Most of the work on Ra in plants that has been directed towards mineral ex-

ploration has been undertaken in the former Soviet Union (Kovalevsky, 1972, 1973).

Kovalevsky (1987) reported that of 139 plant tissues tested 100% showed no barrier

to Ra uptake, and there is no other element that exhibits this non-barrier property.

He noted that ‘samples with anomalous alpha activity are subjected to radiochemical

analysis of radium and thorium (via radon and thoron), to determine the nature of

their radioactivity’. He later concluded that mosses and lichens are reco mmended for

prospecting for ores whose indicator element is Ra (i.e., U).

Essentially all naturally occurring radium is present a s radium-226. The concen-

tration of Ra in plants is typically about 3% of that in soil . It seems that the only

K %

V6 NIST 1575a

Target

Mean

Std. Dev.

RSD %

0.09

0.01

0.42

0.44

0.022

0.02

0.04

0.06

0.08

0.1

0.12

V6 - 30 controls among 600 samples

Concentration

Detection

Fig. 9-46. Potassium – Precision and accuracy on dry tissues – V6 and NIST 1575a (see

Fig. 9-1).

291Biogeochemistry in Mineral Exploration