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‘The gift of fantasy has meant more to me than my talent for absorbing positive knowledge.’ Albert Einstein

The papers in the Journal section selected from the Tomography Symposium focus on slurries and mineral processing and some aspects of extraction metallurgy. They are somewhat specialized but the review papers included provide a window onto a much wider field of applications. The sophistication in the medical field, for example, has been spectacular and I am sure way beyond the fantasies of the early pioneers. I thought it would be interesting to reminisce to illustrate many concepts being explored, but it is only in the last few decades that the potential in mining and metallurgy are beginning to mature into sophisticated systems available for routine work implants and mines. I have the feeling that there are steep learning curves ahead.

For me, it has been fascinating to have been involved from the ‘prehistoric’ days when tomography was an obscure word in a technical dictionary and desk top computers had kilobyte capacities. But the concept of using X-rays, microwaves (called radar) and even neutrons to delve into the unseen components of solids, rocks, and geological formations were much in evidence. My first association with a tomographic problem was initiated by the credulity of a post-war mining magnate who was talked into purchasing a Miles Hi-Volt Neutron Generator on the basis that it would resolve the problem of ‘unassayable gold.’ There was some excuse for the belief that such a form of gold could exist, since the mine call factors on many mines operating at that time were inexplicably low, of the order of 70% or less.

Soon the neutron generator was delivered to the basement of one of the palatial buildings in Hollard Street ready for action. In the light of the penetrating and lethal properties of neutrons, I was instrumental in having it removed to a high density concrete bunker at the Nuclear Physics Institute at Wits where the NIM and the physicists could pursue the experiments in safety. It proved to be pretty useless in winkling out unassayable gold but had some use in providing neutrons to show there was some promise in using them to look into bulk samples to investigate properties and composition. This prompted the National Institute for Metallurgy to investigate methods that would complement the laboratory scale X-ray diffraction and fluorescence methods for analyses to extend them to mineral processing plant for control and sampling purposes. Almost all the post-war research laboratories within the mining houses were involved in exploration with measuring absorption, reflection, and dispersion using just about every portion of the electromagnetic spectrum from short wave radar, microwaves, infrared, X-rays and some others such as neutron beams ultrasonics, and gamma rays.

A lot of work was done by the Chamber of Mines to develop an Xray fluorescence method to identify the gold bearing reefs on stope faces but the fantasy of being able to generate images of what lay behind the rock faces or in deposits underground remained elusive— until the medical researches showed what high capacity computers could do using tomographic scanning methods to provide in effect three-dimensional representation of what the inside of human beings looked like without opening them up, CT X-ray, and NMR scans became household words. Perhaps the first sensational scientifically established results of tomographic techniques in the minerals industries were in the geological characterization of ore bodies using microwave. I recall my amazement when witnessing a computer printing a multi-coloured ‘slice’ of the cross-section of a copper orebody.

This application is well documented in the geological literature. Of course the mine planning protocols have benefited from these geological advances. The concepts of establishing what lies underground have moved from fantasy to pragmatic application. Other applications in mining and extraction metallurgy are still being developed and expanding rapidly as is evident in the papers. Some of the potential future uses, mentioned in the presentations, are enticingly interesting and important. Space permits me to refer to only one or two. I am beginning to think that, with the help of the X-Ray micro tomographic technique (XMT) described by Williamson et al., the final chapter may be written in the saga of ‘The mystery of the missing gold between stope face and surface plant’. According to Zaniewski’s publications on the carbon leader reef at the Kopanang Mine, the losses are a function of rock ‘fragmentation’ and there seems to be a number of tomographic techniques to get a handle on this characteristic, particularly in the micron dimensions.
Maybe this final chapter might well be entitled, ‘What happened at the big bang?’ Is the gold converted to a gaseous compound, or melted into a refractory solid or conveyed out of the mine as ultra fine particles? Maybe some controlled explosions on samples of the carbon leader reef with tomographic analysis, before and after, with collection and similar studies on all the products, should be enlightening. The resources of the carbon leader reef types still available at depth well justify a concerted national effort to get another 30% gold recovery from future carbon leader reef mining is not to be sneezed at. The second reference that caught my eye was to the use of neutron techniques to measure the porosity of sandstone mineral strata. This is the critical topic of what I believe should be the highest priority national research undertaking in our country. It forms part of the method of carbon capture and storage (CCS) systems.

If these prove to be reasonably feasible technically and costwise, it will enable us to continue with the profligate use of coal for motor fuels and power generation without incurring carbon penalties. The concept is to pump the carbon dioxide into the huge sandstone strata of the Karoo system. The extent to which these sandstones can accommodate and retain the carbon dioxide in its critical state depend on what happens to the material previously present in the pores. How does it disappear and why does the gas/liquid carbon dioxide not follow it once pressure is released? Moreover if, as is postulated, the carbon dioxide reacts with the silicates in the sandstone, what happens to the silica solid formed by the reaction and how does it affect the porosity? These and many other aspects seem to be readily answerable by the neutron and the Xray diffraction tomographic facility at Pelindaba, as described by De Beer in his review of the facilities at this centre.

Here again if this fantasy can be turned into fact the financial benefits are immense, in the trillion order of magnitude. But to end my fantasy to fact theme, and as a glimpse into the future, I must refer in passing to what is one of the most esoteric fantasies that seems utterly impossible to bring to a pragmatic fact. This is that we will be able to read people’s thoughts and interpret them for practical applications. I have just read a podcast from Australia recited by Dr Graham Clarke, who I firmly believe will soon be a recipient of the Nobel Prize, for his development of the cochlear Implant. He is now heading up a group at Melbourne in Human Bionics. In this podcast, he refers to his latest work, in which using what are essentially tomographic procedures, he has been able to get a quadriplegic person to move the cursor on a remote computer monitor to the left, right or up or down using thought processes alone. These are the first faltering steps in perhaps enabling such persons to paint a picture or even drive a motor car without moving a muscle or uttering any sound. This will be the ultimate in converting fantasy to fact.  R.E. Robinson October 2008