BIOGEOCHEMISTRY

Humus and vegetation has been used very successfully to discover buried mineralization.

The trees act as mini drills with their root structures sampling very large volumes of soil and in the case of phreatophytes the root structure searches out the water table and may extend hundreds of metres below the surface. The choice of package depends on the elements and detection limits required.

Humus (Decaying Surface Vegetation) – The material is dried below 60oC and then macerated with a cutting mill with a 1mm internal sieve. The ground material can be compressed into a briquette for INAA or ashed and analyzed by digestion and ICP or ICP-MS.

Ground humus samples weighing 6 to 15 g are compressed under 30 tons of pressure to form a briquette (smaller samples are weighed in vials). Smaller samples will be weighed into vials. Briquettes are stacked with flux wires and two internal standards (up to 28 samples) and irradiated along with flux wires at a thermal neutron flux of 7 x 10 12 ncm-2 s-1. After a 7-day period to allow Na-24 to decay the samples are counted on a high purity Ge detector with resolution of better than 1.7 KeV for the 1332 KeV Co-60 photopeak. Using the flux wires and control standards, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. For values exceeding the upper limits, assays are recommended. Duplicates are analyzed when sample material is available.

Required Preparation: B1 (drying and blending humus)

Elements and Detection Limits (ppm)

ElementDetection Limit
Ag2
As1
Au1 ppb
Ba100
Br1
Ca0.5%
Ce1
Co1
Cr1
ElementDetection Limit
Cs0.5
Eu0.2
Fe0.05%
Hf0.5
Hg0.5
Ir5 ppb
La0.1
Lu0.1
Mo0.5
ElementDetection Limit
Na100
Nd3
Ni10
Rb20
Sb0.1
Sc0.1
Se2
Sm0.1
ElementDetection Limit
Sr100
Ta0.5
Tb0.2
Th0.5
U0.1
W1
Yb0.1
Zn20

Reference:

Hoffman, E.L., 1992. Instrumental Neutron Activation in Geoanalysis. Journal of Geochemical Exploration, volume 44, pp. 297-319.

Vegetation (dried and ground in a cutting mill to homogenize it. Then can be analyzed by compressing into a briquette, by ashing and analysis of ash, or analysis on unashed material.

Ground humus samples weighing 6 to 15 g are compressed under 30 tons of pressure to form a briquette (smaller samples are weighed in vials). Smaller samples will be weighed into vials. Briquettes are stacked with flux wires and two internal standards (up to 28 samples) and irradiated along with flux wires at a thermal neutron flux of 7 x 10 12 ncm-2 s-1. After a 7-day period to allow Na-24 to decay the samples are counted on a high purity Ge detector with resolution of better than 1.7 KeV for the 1332 KeV Co-60 photopeak. Using the flux wires and control standards, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. For values exceeding the upper limits, assays are recommended. Duplicates are analyzed when sample material is available.
Required Preparation: B2 (drying and macerating vegetation in a Retsch mill with sieving to 1 mm)

Elements and Detection Limits (ppm)

ElementDetection Limit
Ag0.3
As0.01
Au0.1 ppb
Ba5
Br0.01
Ca0.01%
Ce0.1
Co0.1
Cr0.3
ElementDetection Limit
Cs0.05
Eu0.05
Fe0.01%
Hf0.05
Hg0.05
Ir0.1 ppb
K0.01%
La0.01
Lu0.001
ElementDetection Limit
Mo0.05
Na1
Nd0.3
Ni2
Rb1
Sb0.005
Sc0.01
Se0.1
Sm0.001
ElementDetection Limit
Sr100
Ta0.05
Tb0.1
Th0.1
U0.01
W0.05
Yb0.005
Zn2

Reference:

Hoffman, E.L., 1992. Instrumental Neutron Activation in Geoanalysis. Journal of Geochemical Exploration, volume 44, pp. 297-319.

Vegetation Ash

A 1g aliquot is encapsulated in a polyethylene vial and irradiated along with flux wires at a thermal neutron flux of 7 x 10 12 ncm-2 s-1. After a 7-day period to allow Na-24 to decay the samples are counted on a high purity Ge detector with resolution of better than 1.7 KeV for the 1332 KeV Co-60 photopeak. Using the flux wires and control standards, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. For values exceeding the upper limits, assays are recommended. One standard is run for every 11 samples. One blank is analyzed per work order. Duplicates are analyzed when sample material is available.
Required Preparation: B3 (ashing of vegetation in dedicated kilns at 475°C for 18-24 hours)

Vegetation Ash-INAA Elements and Detection Limits (ppm)

ElementDetection Limit
Ag2
As0.5
Au5 ppb
Ba50
Br1
Ca0.20%
Ce3
Co1
Cr1
ElementDetection Limit
Cs0.5
Eu0.01
Fe0.05%
Hf0.5
Hg1
Ir2 ppb
K0.05%
La0.1
Lu0.05
ElementDetection Limit
Mo2
Na10
Nd5
Ni50
Rb5
Sb0.1
Sc0.1
Se2
Sm0.1
ElementDetection Limit
Sr300
Ta0.5
Tb0.5
Th0.1
U0.1
W1
Yb0.05
Zn50

Reference:

Hoffman, E.L., 1992. Instrumental Neutron Activation in Geoanalysis. Journal of Geochemical Exploration, volume 44, pp. 297-319.

2 grams of vegetation samples are ashed at 475°C. The ash sample is digested with aqua regia for 2 hours at 95°C and analyzed by ICP using a Varian 735 ICP. Ashing is included in this package.
Required Preparation: B3 (ashing of vegetation in dedicated kilns at 475°C for 18-24 hours)

Vegetation Ash-ICP Elements and Detection Limits (ppm)

ElementDetection LimitUpper Limit
Ag0.2100
Cu110,000
Mn1-
Mo110,000
Ni110,000
Pb15,000
Zn110,000

Vegetation samples are ashed at 475°C over a 36 hour period. A proprietary acid digestion is used on the ash. Digested ash samples are diluted and analyzed by Perkin Elmer Sciex ELAN 6000, 6100 or 9000 ICP/MS. A matrix blank and digested blank are each run every 35 samples. Two digested standards are run every 35 samples. Instrument is recalibrated every 70 samples. Duplicates are digested and analyzed every 14 samples. Results are reported on an ash weight basis. If Au, Pd, Pt are required please use Code 2E.
Required Preparation: B3 (drying and ashing at 475°C in dedicated kilns)

(Vegetation Ash-ICP/MS) Elements and Detection Limits (ppm)

ElementDetection Limit
Ag0.2
Al2
As1
B5
Ba3
Be0.005
Bi0.05
Ca0.10%
Cd0.01
Ce0.01
Co0.01
Cr1
Cs0.001
Cu0.2
Dy0.001
ElementDetection Limit
Er0.001
Eu0.001
Fe0.01%
Ga0.1
Gd0.01
Ge0.1
Hf0.01
Ho0.001
In1 ppb
K0.01%
La0.002
Li0.5
Lu0.001
Mg0.01%
Mn0.1
ElementDetection Limit
Mo0.1
Na0.01%
Nb0.005
Nd0.002
Ni5
Pb0.1
Pr0.002
Rb0.01
Re0.1 ppb
Sb0.02
Sc0.5
Se1
Si0.20%
Sm0.001
Sr0.1
ElementDetection Limit
Ta0.001
Tb0.001
Te0.01
Th0.001
Ti1
Tl0.001
Tm0.001
U0.001
V1
W0.5
Y0.001
Yb0.001
Zn1
Zr0.5

Samples are ashed at low temperature in dedicated ovens at 475oC for 24 hours. 0.25g of ash is digested in aqua regia at 95oC for 2 hours. Digested ash samples are diluted and analyzed by Perkin Elmer Sciex ELAN 6000, 6100 or 9000 ICP/MS. A blank is run every 69 samples. Two digested controls are analyzed every 69 samples. Duplicates are digested and analyzed every 14 samples. Instrument is recalibrated every 69 samples. Results are reported on an ash weight basis. On request results can be computed on a dry weight basis.
Required Preparation: B3 (dry and ash at 475°C in dedicated vegetation kilns)

Elements and Detection Limits (ppm)

ElementDetection Limit
Ag0.2
Al2
As3
Au5  ppb
B5
Ba3
Be0.08
Bi0.05
Ca0.10%
Cd0.01
Ce0.01
Co0.01
Cr10
Cs0.001
Cu0.2
Dy0.001
ElementDetection Limit
Er0.001
Eu0.001
Fe0.01%
Ga0.1
Gd0.01
Ge0.1
Hf0.01
Ho0.001
In1 ppb
K0.01%
La0.002
Li0.5
Lu0.001
Mg0.01%
Mn0.1
Mo0.1
ElementDetection Limit
Na0.01%
Nb0.005
Nd0.002
Ni5
Pb0.1
Pd3 ppb
Pr0.002
Pt2 ppb
Rb0.01
Re0.1 ppb
Ru10 ppb
Sb0.02
Sc0.5
Se10
Si0.20%
Sm0.001
ElementDetection Limit
Sn1
Sr0.1
Ta0.001
Tb0.001
Te0.01
Ti1
Th0.001
Tl0.001
Tm0.001
U0.001
V10
W0.5
Y0.001
Yb0.001
Zn1
Zr0.5

Vegetation Un-Ashed

Ground vegetation samples are digested in an aqua regia matrix at 95°C. The solution is concentrated on an ion exchange resin and then eluted for analysis on a high resolution Thermo Finnegan Element 2 magnetic sector ICP-MS.

Preparation required: B2 – dry and grind vegetation in a Retsch cutting mill.

Elements and Detection Limits (ppb)

ElementDetection Limit
Ir0.2
Pt0.2
Pd0.1
Rh0.1
Ru0.2

Raw vegetation samples are digested in aqua regia at 95°C for 2 hours. Resultant sample solutions are diluted and analyzed on a Finnegan Mat Element 2 High Resolution ICP-MS (HR-ICP-MS).
Required Preparation: B2 (dry and macerate vegetation in a Retsch cutting mill with internal 1 mm sieve)

Elements and Detection Limits (ppb)

ElementDetection Limit
Ag1
As5
Au0.1
B200
Ba1 ppm
Be0.1
Bi1
Ca2 ppm
Cd0.1
Ce0.5
Co0.5
Cr10
Cs0.1
Cu20
Dy0.05
Er0.05
ElementDetection Limit
Eu0.1
Fe0.5 ppm
Ga0.5
Gd1
Ge10
Hf2
Hg5
Ho0.01
In0.1
K10 ppm
La0.2
Li5
Lu0.2
Mg0.5 ppm
Mn10
Mo1
ElementDetection Limit
Na10 ppm
Nb0.5
Nd0.2
Ni0.1 ppm
Pb10
Pd2
Pr0.5
Pt0.1
Rb10
Re0.1
Ru0.5
Sb0.2
Sc1
Se0.2 ppm
Sm0.1
Sn40
ElementDetection Limit
Sr15
Ta0.1
Tb0.02
Te1
Th5
Ti20
Tl0.5
Tm0.05
U1
V10
W5
Y0.2
Yb0.4
Zn0.2 ppm
Zr5

Raw vegetation samples are digested in aqua regia at 95°C for 2 hours. Resultant sample solutions are diluted and analyzed on a Perkin Elmer Sciex ELAN 6000, 6100 or 9000 ICP-MS. A blank is run every 69 samples. Two digested controls are analyzed every 69 samples. Duplicates are digested and analyzed every 14 samples. Instrument is recalibrated every 69 samples.
Required Preparation: B2 (dry and macerate vegetation in a Retsch cutting mill with internal 1 mm sieve)

Elements and Detection Limits (ppb, except where noted)

ElementDetection Limit
Ag3
Al4 ppm
As10
Au0.2
B1 ppm
Ba100
Be30
Bi2
Ca25 ppm
Cd6
Ce15
Co4
Cr100
Cs0.2
Cu50
Dy0.5
ElementDetection Limit
Er0.4
Eu0.2
Fe3 ppm 
Ga4
Gd0.4
Ge3
Hf0.4
Hg2
Ho0.2
In0.2
K10 ppm
La10
Li10
Lu0.5
Mg2 ppm
Mn100
ElementDetection Limit
Mo10
Na5 ppm
Nb2
Nd5
Ni50
P4 ppm
Pb50
Pd0.2
Pr1
Pt0.2
Rb10
Re0.2
Sb10
Se10
Sm1
Sn50
ElementDetection Limit
Sr40
Ta0.2
Tb0.2
Te8
Th2
Ti150
Tl1
Tm0.1
U1
V10
W25
Y2
Yb0.4
Zn400
Zr20