Methodological studies

Soil Geochemical
Survey
Selecting the proper method and
analysis

Tested at Namtenga and Zandkom
19-Jul-10 2HRG- Monthly Technical Meeting

Tested for
• Depth of sampling
• Magnetic response
• Soil Gas Hydrocarbon (SGH)
• Mobil Metals Ion (MMI-M)
• Enzyme Leach

Methodology
At each sampling point, the following samples and measurements
were taken:
•At 10 cm from the surface a 20 g sample was taken for Soil Gas
Hydrocarbon determination (SGH).
•At 15 cm a measurement of the magnetic intensity was preformed.
•At 25 cm from the surface two samples of 200 g each were taken, one
for a multielement Mobile Metal Ion analysis (MMI-M) and a second
one for multielement Enzyme Leaching analysis.
•At the same depth (25 cm) a 20 g sample was taken for (SGH).
•Also at this depth (25 cm) a magnetic measurement was taken.
•Finally, at 50 cm depth, another two samples of 200 g each were
taken (MMI-M and Enzyme Leaching).
•Also at this depth (50 cm) a magnetic measurement was taken.

Namtenga Au vs Magnetics

Namtenga Ore location vs Magnetics

Zandkom Au vs Magnetics

Zandkom Ore location vs Magnetics

Conclusions of the Magnetic Survey
• In every case we can observe that there is a spatial
correlation between the actual locations of the ore
body with the lowest magnetic values along the
profile. The deeper is the measurement; the better is
this spatial correlation.
• Results are especially interesting for Zandkom, were
the thick cuirass completely blocked the geochemical
signature from gold, but not the magnetic signal.
• I assume that on top of the ore body are relatively
more sulphides then outside the ore body, and thus
the magnetic signal is weaker there.

Soil Gas Hydrocarbon

SGH Conclusions
• At depths of 25 cm, the SGH method was very
successful in locating the ore body, especially
over cuirass, where the gold response was nil.
There is also a clear spatial relationship between
our magnetic lows and the SGH targets.
• But the sole proprietorship status of the
technology, and the limitation imposed by the lab
in regards as they being the only one capable of
providing this interpretation, is a strong hurdle in
the path to consider the wide use of this
technology at this present time.

MMI-M Namtenga

MMI-M Zandkom

MMI-M Conclusions
• Our test clearly shows the ineffectiveness of
the MMI-M in our geochemical environment
to identify the location of the ore body.
Further application of MMI is not
recommended.

Compositional Data Analysis (CoDa)
• When dealing with multielement analysis, the
following modeling sequence was applied:
• Transformation of the raw data using Centered
Logratio Transformation (CLR).
• Determination of the distribution laws using the test of
Asymmetry and Excess.
• Determination and treatment of statistical outliers.
• Correlation analysis.
• Factor analysis.
• Determination of the Mineralization Coefficients.
• Interpretation of the results.

Correlation analysis (RCC)
Since the use of Range Correlation Coefficients (RCC) is not a common
practice, I will explain in more detail the methodology for their selection from
the significant correlations. This a three step process. We start by ranging all
correlations from the highest positive to the lowest negative correlation.
•First, using Excel Find option, find all the correlations for each important
element (in our case I used Au, Ag, and Cu) and write the coefficient using
only the significant correlations (in our case I used the correlations higher
and lower than 4). You put the positive correlations on the nominator of the
coefficient and the negative correlations in the denominator.
•Step two consists on eliminating elements that get repeated in other
coefficients, being in the nominator or the denominator. This way we obtain
the RCC that characterizes the specific element we are modeling.
•The last step consists in creating a “general or total” RCC that will
characterize the mineralized zone. We obtain this by adding all the previously
obtained coefficients.

Enzyme leach
• A 0.75 g sample of -60 mesh B soil horizon
material is leached in enzyme matrix
containing glucose oxidize solution at 30o
C for
1 hour. The enzyme reacts with amorphous
MnO2dissolving it. The metals are complexed
with the gluconic acid present. The solution is
then analyzed by ICP-MS.

Namtenga at 25 cm

Namtenga at 50 cm

Zandkom at 25 cm

Zandkom at 50 cm

Conclusions on Enzyme Leach
• This method, combined with the proper
elaboration of the multielement suite by
compositional data analysis is extremely
successful in the location of targets. It is also
worth to mention that it is possible to get a
gold response even though the thick lateritic
cover at Zandkom.

Conclusions and Recommendations
On the basis of this study, we can see that SGH and Enzyme leaching
give the best possible response to locate the ore body. Also negative
magnetic anomalies are very useful to define potential targets of
mineralization. For the future soil sampling works, the following is
recommended:
•Take samples from 50 cm depth.
•Measure the magnetic signature at each sampling point, directly from
the ground or from the sample.
•Analyze the sample for multielements with enzyme leach extraction
procedure.
•Process the data using compositional data analysis (CoDa).
•Determine the Range Correlation Coefficient (RCC) of the most
probable mineralized association.
•Use Factor Analysis (FA) if there is a known target to calibrate the
coefficient.

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