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Ore inspiring moments in Burkina FasoRoderick Carlson – AMC Principal Geologist

November 2015

AIG – pXRF Friday Seminar

www.amcconsultants.com

Thanks

1. Co-conspirator Ann Ledwidge – ex Orbis Gold Exploration Manager

2. Michel Crevier SEMAFO Inc. VP Exploration and Mine Geology for permission to present

3. Richard Roy SEMAFO Exploration Manager for providing data and presentation feedback

2


Introduction

Source: Orbis Gold presentation


Regional Geology

Source: SEMAFO 43-101 report March 2015


Cross section and long section



Mineralised horizon orthogonal view

Source: Orbis Gold presentation


So what is the problem?



Gold only assays – pick the zone?


Logging

BSZBSZ

and gold assays


Grade wireframe?


Innov-X Omega elements and detection limits


pXRF being collected on lab pulps

- Innov-X Omega series- Calibration using standards

(NIST2702, NIST2781 and SiO2)


Calcium ppm histogram

0 100,000


Rubidium ppm histogram

0 100


Titanium ppm histogram

0 10000

Ti = 6,500 ppm


Zirconium ppm histogram

0 80

Zr = 28 ppm


Principal Components Analysis

F1 – Fe, Ni, Mn, Mo, V, Bi, Cr, Co..Ti

F2 – Rb, K, Hg, S

F3 – As, Cd, S, Ca….+-Au..Ti

Eigenvectors:

F1 F2 F3Lab_Au_ppm ‐0.006 0.178 0.181S_ppm 0.008 0.312 0.326Cl_ppm ‐0.085 0.070 ‐0.196K_ppm ‐0.109 0.430 0.089Ca_ppm 0.114 ‐0.171 0.281Ti_ppm 0.165 ‐0.236 0.177V_ppm 0.304 ‐0.007 ‐0.028Cr_ppm 0.260 0.152 ‐0.239Mn_ppm 0.324 ‐0.057 0.060Fe_ppm 0.335 ‐0.144 0.091Co_ppm 0.226 ‐0.152 ‐0.031Ni_ppm 0.331 0.140 ‐0.135Cu_ppm 0.217 0.134 ‐0.048Zn_ppm 0.073 ‐0.096 0.224As_ppm 0.019 0.278 0.384Se_ppm 0.084 0.024 0.311Rb_ppm ‐0.090 0.426 0.064Sr_ppm ‐0.100 0.154 ‐0.265Zr_ppm ‐0.054 0.043 ‐0.227Mo_ppm 0.316 0.150 ‐0.216Ag_ppm 0.073 0.004 ‐0.065Cd_ppm 0.101 ‐0.175 0.329Hg_ppm 0.218 0.359 0.119Pb_ppm 0.256 0.054 ‐0.070Bi_ppm 0.307 0.103 ‐0.125

On un-domained dataset


Principal Components Analysis

F1 – Fe, Co, Mn, Ti, Ca, Zn

F2 – Ni, Zr, Cr, Sr

On lode flagged samples

0

0

10000

10000

20000

20000

AS_PPM

AS_PPM

0 0

100 100

200 200

AU_PPM

AU_PPM

rho=0.331


Downhole pXRF – Sharp contact

Zr = 28 ppm

MAM – AmphiboliteGDI – DioriteBSZ – Boungou Shear ZoneVRH – RhyoliteGGD - Granodiorite

Au FA/AAS


Downhole pXRF – Mislogged?

Zr = 28 ppm

Ti = 6,500 ppm



Downhole pXRF – HW grade

Zr = 28 ppm

Ti = 6,500 ppm



How best to model the grade distribution in an unbiased way?

BSZBSZ


pXRF lithogeochemistryKAu Zr Ti KAu Zr Ti

Upper unitLower unit


ModellingKAu Zr Ti

?Wireframe too high?


Modelling confidence

?


Structural discontinuities


3D Natougou mineralised lode wireframe


Conclusions

• Some pXRF elements showed bimodal element distribution.

• Examination of correlations showed mafic and alteration associations, but no global gold correlation.

• Recognition that K, Rb, Ti, Zr all helped to define BSZ.

• Modelling used geology (from photographs), pXRF multi-element trends and finally gold grade.

• Gold is present in a shear at or near the contact between two mafic units distinguishable by their multi-element signatures.


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