Ore inspiring moments in Burkina FasoRoderick Carlson – AMC Principal Geologist
November 2015
AIG – pXRF Friday Seminar
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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
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Introduction
Source: Orbis Gold presentation
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Regional Geology
Source: SEMAFO 43-101 report March 2015
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Cross section and long section
Source: SEMAFO 43-101 report March 2015
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Mineralised horizon orthogonal view
Source: Orbis Gold presentation
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So what is the problem?
Source: SEMAFO 43-101 report March 2015
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Gold only assays – pick the zone?
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Logging
BSZBSZ
and gold assays
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Grade wireframe?
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Innov-X Omega elements and detection limits
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pXRF being collected on lab pulps
- Innov-X Omega series- Calibration using standards
(NIST2702, NIST2781 and SiO2)
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Calcium ppm histogram
0 100,000
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Rubidium ppm histogram
0 100
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Titanium ppm histogram
0 10000
Ti = 6,500 ppm
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Zirconium ppm histogram
0 80
Zr = 28 ppm
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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
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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
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Downhole pXRF – Sharp contact
Zr = 28 ppm
MAM – AmphiboliteGDI – DioriteBSZ – Boungou Shear ZoneVRH – RhyoliteGGD - Granodiorite
Au FA/AAS
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Downhole pXRF – Mislogged?
Zr = 28 ppm
Ti = 6,500 ppm
MAM – AmphiboliteGDI – DioriteBSZ – Boungou Shear ZoneVRH – RhyoliteGGD - Granodiorite
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Downhole pXRF – HW grade
Zr = 28 ppm
Ti = 6,500 ppm
MAM – AmphiboliteGDI – DioriteBSZ – Boungou Shear ZoneVRH – RhyoliteGGD - Granodiorite
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How best to model the grade distribution in an unbiased way?
BSZBSZ
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pXRF lithogeochemistryKAu Zr Ti KAu Zr Ti
Upper unitLower unit
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ModellingKAu Zr Ti
?Wireframe too high?
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Modelling confidence
?
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Structural discontinuities
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3D Natougou mineralised lode wireframe
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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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