4E - Exploration - INAA, Total Digestion - ICP, Lithium Metaborate/Tetraborate Fusion - ICP
INAA Portion
A 1 g aliquot is encapsulated in a polyethylene vial and irradiated with flux wires and an internal standard (1 for 11 samples) at a thermal neutron flux of 7 x 10
12
n cm
-2
s
-1
. After a 7-day decay 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, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. The standard present is only a check on accuracy and is not used for calibration purposes. From 10-30% of the samples are rechecked by re-measurement. 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 samples are provided.
The method is described by Hoffman, E.L., 1992. Instrumental Neutron Activation in Geoanalysis. Journal of Geochemical Exploration, volume 44, pp. 297-319.
Total Digestion ICP Portion
A 0.25 g sample aliquot is digested with HClO
4
-HNO
3
-HCl-HF at 200°C to fuming and is then diluted with aqua regia. This leach is partial for magnetite, chromite, barite and other spinels and potentially massive sulphides.
Major Elements by Fusion ICP/OES, Trace Elements by ICP/MS
Samples are prepared and analyzed in a batch system. Each batch contains a method reagent blank, certified reference material, and 17% replicates. Samples are mixed with a flux of lithium metaborate and lithium tetraborate and fused in an induction furnace. The molten melt is immediately poured into a solution of 5% nitric acid containing an internal standard, and mixed continuously until completely dissolved (~30 minutes). The samples are then run for major oxides and selected trace elements (Code 4B) on a combination simultaneous/sequential Thermo Jarrell-Ash ENVIRO II ICP.
For the ICP analysis, reagent blanks with and without the lithium borate flux are analyzed, as well as the method reagent blank. Interference correction verification standards are analyzed. Calibration is performed using multiple USGS and CANMET certified reference materials. Two of the standards are used during the analysis for every group of ten samples. This standard brackets the group of samples. The sample solution is also spiked with internal standards and is further diluted and introduced into a Perkin Elmer SCIEX ELAN 6000 ICP/MS using a proprietary sample introduction methodology. Calibration is performed using USGS and CANMET certified reference materials.
Code 4E-exploration
Fusion ICP
|
Oxide
|
Detection Limit
|
|
SiO
2
|
0.01%
|
|
Al
2
O
3
|
0.01%
|
|
Fe
2
O
3
|
0.01%
|
|
MgO
|
0.01%
|
|
MnO
|
0.01%
|
|
CaO
|
0.01%
|
|
TiO
2
|
0.005%
|
|
Na
2
O
|
0.01%
|
|
K
2
O
|
0.01%
|
|
P
2
O
5
|
0.01%
|
|
Loss on Ignition
|
0.01%
|
Code 4E-exploration
Trace Elements and Detection Limits (ppm)
|
Element
|
Detection Limit
|
Upper Limit
|
Reported By
|
|
Element
|
Detection Limit
|
Upper Limit
|
Reported By
|
|
Ag
|
0.5
|
100,000
|
|
|
Nd
|
5
|
10,000
|
INAA
|
|
As
|
2
|
-
|
INAA
|
|
Ni
|
1
|
10,000
|
|
|
Au
|
5 ppb
|
30,000 ppb
|
INAA
|
|
Pb
|
5
|
5,000
|
|
|
Ba
|
3
|
30,000
|
|
|
Rb
|
20
|
-
|
INAA
|
|
Be
|
1
|
10,000
|
|
|
S
|
0.001%
|
20%
|
|
|
Bi
|
2
|
10,000
|
|
|
Sb
|
0.2
|
10,000
|
INAA
|
|
Br
|
1
|
-
|
INAA
|
|
Sc
|
0.1
|
-
|
INAA
|
|
Cd
|
0.5
|
5,000
|
|
|
Se
|
3
|
-
|
INAA
|
|
Ce
|
3
|
10,000
|
INAA
|
|
Sm
|
0.1
|
10,000
|
INAA
|
|
Co
|
1
|
10,000
|
INAA
|
|
Sr
|
2
|
-
|
|
|
Cr
|
2
|
100,000
|
INAA
|
|
Ta
|
1
|
10,000
|
INAA
|
|
Cs
|
0.5
|
|
INAA
|
|
Tb
|
0.5
|
-
|
INAA
|
|
Cu
|
1
|
10,000
|
|
|
Th
|
0.5
|
10,000
|
INAA
|
|
Eu
|
0.1
|
-
|
INAA
|
|
U
|
0.5
|
10,000
|
INAA
|
|
Hf
|
0.5
|
|
INAA
|
|
V
|
5
|
-
|
|
|
Hg
|
1
|
-
|
|
|
W
|
3
|
10,000
|
INAA
|
|
Ir
|
5 ppb
|
-
|
INAA
|
|
Y
|
1
|
10,000
|
|
|
La
|
0.2
|
10,000
|
INAA
|
|
Yb
|
0.1
|
-
|
INAA
|
|
Lu
|
0.05
|
-
|
INAA
|
|
Zn
|
1
|
10,000
|
|
|
Mo
|
2
|
10,000
|
|
|
Zr
|
2
|
-
|
|
Typical ICP Analysis of some USGS and Canmet Standards (%)
|
Std.
|
SiO
2
|
Al
2
O
3
|
Fe
2
O
3
|
MnO
|
MgO
|
CaO
|
Na
2
O
|
K
2
O
|
TiO
2
|
P
2
O
5
|
|
SY3
|
59.51
|
11.62
|
6.47
|
0.32
|
2.54
|
8.25
|
4.17
|
4.23
|
0.14
|
0.52
|
|
MRG1
|
39.43
|
8.59
|
17.93
|
0.17
|
13.74
|
14.77
|
0.73
|
0.18
|
3.78
|
0.07
|
|
DNC1
|
46.91
|
18.46
|
9.76
|
0.15
|
10.05
|
11.27
|
1.99
|
0.24
|
0.47
|
0.07
|
|
BIR1
|
47.78
|
15.43
|
11.52
|
0.17
|
9.70
|
13.75
|
1.86
|
0.02
|
0.95
|
0.02
|
|
W2
|
52.58
|
15.35
|
10.72
|
0.16
|
6.37
|
10.98
|
2.31
|
0.64
|
1.05
|
0.12
|
|
G2
|
68.72
|
14.95
|
2.65
|
0.03
|
0.71
|
1.87
|
4.08
|
4.48
|
0.48
|
0.13
|
|
STM1
|
59.64
|
18.07
|
5.24
|
0.22
|
0.07
|
1.09
|
8.87
|
4.24
|
0.13
|
0.1
|
Code 4E-exploration Options
4E-XRF
The trace elements analyses are done on pressed powder pellets made from 6 g of sample. Spectral interferences are corrected from pre-calculated interfering factors. Because of the trace level (< 1,000 ppm) of the analytes, only the mass absorptions are corrected for matrix effects. The mass absorption coefficients are derived from measuring the
Compton
scatter of the Rh-tube (e.g., Nisbet et al., 1979. Fortschr. Miner., volume 57, pp. 264-279). The background and mass absorption corrected intensities are then calculated against the calibrations constructed from 24 international geological reference materials. In general, the limits of detection are between 1 to 5 ppm.
Option 4E-XRF
Elements and Detection Limits (ppm)
|
Element
|
Detection Limit
|
Upper Limit
|
|
Ga
|
5
|
10,000
|
|
Pb
|
5
|
1,000
|
|
Sn
|
5
|
10,000
|
|
Nb
|
1
|
10,000
|
|
Rb
|
2
|
20,000
|
|