Friday, 30 November 2012

Geological Society of Zimbabwe Summer Symposium



Today is the annual conference of GSZ and as usual an interesting mixture of industry and academic presentations. As has become the case in recent years, there were very few classic geological presentations, with academic papers mainly on applied earth sciences like hydrogeology, environmental geology and geomedicine. Development of our understanding of Zimbabwean geology moves slower than it did in the 1990s.

In an overview from chamber of mines, it was emphasised that apart from diamonds and platinum, our mines are operating well below capacity. Income in the sector was spent on imports and expenses, 15% wages, 17% taxes and royalties and 11% profits. Within the mining sector, gold, platinum and diamonds each contribute around a quarter of exports, against gold generating around half in the 1990s and platinum around half at the turn of the century.

OJ Maponga spoke on the Zimbabwean coal industry and gave a fascinating overview of the history of Hwange colliery. Lubimbi coal has excellent properties for conversion to petrol and diesel (like Sasol).

Sharad Master presented on the Magondi Supergroup,  a classic geology paper with new SHRIMP geochronological data. Lomagundi carbon isotope anomaly is now the type locality for such anomalies worldwide and their paper won the Phaup Award. The team, using funds they sourced on the basis of the award, have now redated the Magondi using U-Pb SHRIMP. Maximum age of the Deweras volcanic 2235 Ma. Deweras clastics maximum age 2171 Ma. Lomagundi tuff maximum 2070 Ma. Godzi volcanics in Piriwiri maximum 2051 Ma. Nyagari volcanics inconclusive. Older zircons show Zimbabwe Craton is basement to Magondi.

Master also reported on recent work on the Limpopo Belt, challenging its original as an orogenic belt from the collision of the Zimbabwe and Kaapvaal Cratons. Recent precise  baddeleyite dating of dyke swarms suggests proximity of the Zimbabwe, Superior and Karelia Cratons, but not the Kaapvaal. This challenges the classic interpretation of the Limpopo Belt. The Kaapvaal and Zimbabwe Cratons only share dukes from after 2000 Ma - post Bushveld. This suggests the two Cratons only came together after 2000 Ma not 2600 Ma. Masters suggests the Zimbabwe Craton lay just off the Superior Craton with the Magondi Supergroup and Labrador Trough lying between the two Cratons. Piriwiri volcanics are post rifting off Superior as collision with the Kaapvaal at 2000 Ma. But couldn't the Kaapvaal be just off the Zimbabwe Craton on the other side? 

I gave a talk on my preliminary work on the geology associated with Hwange pans. I got two useful questions: does the current game water supply drilling programme provide any data? The South African council for geoscience has published a SubKalahari map that will also assist. 



Two fascinating presentations on Ground Penetrating Radar by Dumisani Mapundu and Ed Magan - including latest developments from the Russian space programme. Mobile system (100 kg), can do from 1 more to 200-270 more depth.  Good for tracking intrusions and also palaeochannels, deep alluvium, deep weathering etc. Some application in gold mining also. Excellent applications in groundwater - system was designed to find water on Mars - and groundwater chemistry.


Hillary Gumbo spoke on the use of geophysics in small mining projects and claims. Expectations can be very broad and some service providers give out unrealistic results abusing the data to claim they can show gold grades!  This is akin to giving a patient an injection - any injection - because that is what I have in my toolbox. Geophysics has its specific place in exploration and is not the whole programme by itself.

Gayle Hanssen spoke on her recent visits to Ethiopia and Iceland. The actual cracks at the spreading zone in the Danakil triple junction can be seen in the field. The three rifts and their junction can be seen. They are planning geological National Parks.

Tendai Njila made a presentation of the background to the geomedicine research programme that UZ is starting in Zimbabwe. Key elements are As Cd Hg Se F Pb and Cr. He mentioned high levels of Cd in the Pungwe River - this is interesting in the context of what we saw in the Limpopo Basin.

Prof. Isidro Manuel presented on artisanal gold mining in Mozambique. Of interest in addition to the typical impacts of ASM as reported in the MMSD work, is a major problem with child labour. Access to formal credit is a problem for the miners, as is often the case with small scale rural livelihood strategies. In addition to the environmental and social problems, and lack of management structures, ASM in Manica is unsustainable due to lack of knowledge of reserves hence lack of proper planning.

Bornwell Mupaya presented on the diamond deposits of the Umkondo Supergroup: Marange type, associated with basal arkosic conglomerates of the Calcareous Series. The contact to weathered basement is gradual. The diamonds are brown and with a completely worn primary surface.  Chikwakwa type is similar to Marange but in a matrix-supported conglomerate with fewer clasts.  The Chimanimani deposit is hosted in conglomerates in the lower argillaceous series. The cement is quartz rather than feldspar. The deposit also has the classic suite of heavy minerals, unlike Marange. The diamonds are well formed and in many cases polycrystalline. They have a wide range of colours.
 

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