ore inspiring moments in burkina faso · pdf fileore inspiring moments in burkina faso ......

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

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

Titanium ppm histogram

0 10000

Ti = 6,500 ppm

Zirconium ppm histogram

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

AS_PPM

100 100

200 200

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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ore inspiring moments in burkina faso · pdf fileore inspiring moments in burkina faso ......

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