Hardolph Wasteneys reported that the long-simmering resource nationalism in Tanzania heated up in early March this year with a sudden export ban on ore concentrates by Tanzanian President John Magufuli who was quoted as saying: “Based on the information that I have, if I say what is really inside these containers, it could make any patriotic Tanzanian cry…. From now onwards, no mineralised sand will be exported from Tanzania… There is no country being robbed of its mineral wealth like Tanzania”. It then erupted in June with the release of reports by 2 presidentially appointed committees alleging that gold miner Acacia Mining PLC was defrauding the Tanzanian government of tax revenue and royalties by substantially under stating the value of its exported concentrates.
The committee reports confirmed the president’s position and were enthusiastically amplified by Tanzanian Swahili newspapers, but solidly refuted by Acacia and even international observers sympathetic to the cause of resource nationalism. However, one Tanzanian weekly, Wawio, stepped out of line by examining the role of past-presidents in resource deals and was promptly shut down for 2 years by Magufuli under his recent Media Services Act. This activity was then upstaged by the rapid revisions to the Tanzanian Mining Act dramatically increasing royalties, government ownership, and prohibiting external arbitration and then subsequently, by hitting Acacia with a $190 B (USD) tax and penalty bill. However, the original source of controversy was the first committee report, considered to be technical in nature, that came up with the disputed numbers. It specifically cited ranges and averages of concentrations of Au, Cu, Ag, S, Fe, Ir, Rh, Yb, Be, Ta and Li that it measured in 44 of 277 impounded concentrate shipping containers and concluded that they were understated or undeclared in Acacia’s concentrate assays. The most striking were for gold, which they claimed ranged from 671 ppm to 2375 ppm and with an averaged 1400 ppm gold that was about 10 times higher than the 164 ppm that Acacia’s rigorous concentrate sales assays showed. Acacia, SGS (assay lab) and the smelter company (MRI Group) defended the veracity of the original assays, but this large discrepancy raised a question in my mind of exactly how the committee had analysed the concentrates, about which a rough translation from Swahili showed no indication. The confidence or lack of qualification with which the numbers were stated suggested that they were not just a theoretical committee consensus and instead must have come from an analytical source.
The unsupported high gold reminded me of a situation in 2006 when I was running a drill program at Granduc in NW BC. As part of our core logging routine we scanned the core with a handheld Niton XRF unit (the only manufacturer at that time following the Mars Rover missions) to produce a numerical log of copper and iron contents of the iron formation hosted chalcopyrite-pyrrhotite mineralization. The numbers supplemented our visual estimates and helped overcome backlogs at the geochem labs that were common in that era. The numbers looked good and were posted on the company website and were eventually corroborated by routine ICP analyses. The XRF unit was also extremely handy for elements like Ti and Zr, which would have required expensive whole rock analyses.
One day I found an arsenopyrite vein that I thought might be gold prospective, but was astounded when the XRF unit reported 2% gold. Repeated analyses with longer count times corroborated the high gold values, but my excitement ebbed when I realized that I could not see a trace of gold in the sample when at 2% it should have been smeared all over the surface. Concerned, I delved into the XRF analysis routine by downloading the raw data and energy dispersive spectral plot onto a computer and found that the characteristic fluorescence gold peaks within the spectral range (the Au- Lα and -Lβ) were buried under a mountainous arsenic Kα peak at 10.5 keV (gold K-lines which might have been uncompromised are actually at 68.88 keV, far above the limits of the X-ray source). The signals that were being measured at the Au L-line energies were just part of the slope leading up to the major arsenic peak and this was eventually confirmed by lab analysis of the rock which returned nil gold.
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