Post from the field: Termite mound sampling?

Today I am writing from the field, connecting with the fastest, most rural internet connection I have every had the privilege of connecting to! And what a day it was! The site where I am currently working is one of the few near-equatorial, semi arid regions in the world and is far from anything and everything, they way I love it! Apart from a very short rainy season, the rest of the year is blistering hot and dry. From about 10 am the temperature starts flirting with 40C and then it only goes up. I made the mistake of mapping the largest mountain in the region over the heat of the day and at one point had a real fear that my heart was going to explode! Most of the way was through thorn thicket and wood land, looking for fresh outcrop, a rare commodity in these parts.

The view from the top of the mountain.

The view from the top of the mountain.

This brings me to the topic of my post. While in the field today, on of the field technicians, did something that reminded me of something that I had read about a while ago. At one point while on the mountain slope we wandered into a savannah-type field with tall grass stretching above our heads. The chances of finding fresh outcrop in such a field are small. Just before leaving the grass field, the technician bent down and scratched open a small ant hill, maybe 15cm in diameter. The inside of the ant mound revealed lots of quartz and some feldspar grains which had been brought to the surface by the ants. They had obviously scavenged them from the saprolite/ weathered rock below the soil visible to us. Interestingly, it gave us an immediate indication of what the rock type beneath was. In this case, a felsic gneiss common in the area.

A termitaria on the trunk of a tree. If you are a good entomologist, maybe you can guess the location!

A termitaria on the trunk of a tree. If you are a good entomologist, maybe you can guess the location!

This was interesting to me because I had in the past done a little research on the topic of termite mound sampling as an exploration tool. I was prompted to it when I read this article which I have referenced in a previous post. Another article in Cosmos magazine also makes reference to this practice. Merrex Gold Inc, a Canada-based junior gold explorer used termite sampling at their Siribaya project in Mali and had the following to say about the results:

A detailed geochemical survey of termite mounds has been completed over the ten kilometre strike length of the Siribaya mega-structure. The termite mound survey has identified new gold-anomalous zones that were not evident from prior surface sampling and confirmed previous surface geochemical survey results and prior RAB drilling results.

An interesting map of the Siribaya project showing termite mound gold geochemistry.

An interesting map of the Siribaya project showing termite mound gold geochemistry.

A recent study by CSIRO (Australia) looked at the possible sources of anomolous gold concentrations in termite nests at Moolart Well, Western Australia and what the possible implications for exploration could be. Their conclusion is as follows:

These results suggest termite-driven local soil heterogeneity and termite mounds being a consistent geochemical and mineralogical sample medium for the discovery of ore deposits beneath weathered cover and shallow sediments.”

In the past, some have been more skeptical. Robert R. Brooks wrote a paper on “Geozoology in mineral exploration” in 1983 and started the chapter on termite mound sampling by stating that “The direct use of insects for mlneral exploration has no advantage over soil or vegetatlon sarnpling, which is easier and more reliable”. Brooks however does end the paper with a positive conclusion:

“Nevertheless, two techneques do stand out as having potential for further work. Perhaps the most promising of these is the sampling and analysis of termitaria. A very large part of Africa (and arid parts of other tropical or semi-tropical regions such as Australia and South America) is covered with aeolian sands which effectively blanket outcrops and render mineral exploration an expensive and tedious business. the discovery that termites can penetrate this blanket and bring ore minerals to the surface has exciting applications for future work.”

So how do termites concentrate elements? In their search for water they tend to bore down into the soil horizon and exploit natural fissures in the bedrock (where water also usually is found). They get contaminated with ore material in these fissures which they then bring to the surface. Opinion on the depth to which these little guys can go vary between 3 and 230 meters.

A collection of one very big and some smaller termite mounds close together in the field

A collection of one very big and some smaller termite mounds close together in the field

As some historic studies suggest, along with other more recent ones, and importantly after today’s experience my opinion on termite and ant mound sampling is that it can be a very effective and inexpensive exploration tool when used in the right context. That context is at geological occurrences where the bedrock is covered predominantly by soil that is not derived from the same bed rock, ie. transported soils and gravels from a different source rock. In such situations, standard soil sampling is ineffective and does not lend itself to discovery of buried deposits. The reason why this context is important is due to the fact that under normal weathering soil conditions, soil sampling would be the most effective tool, no less effective than termite mound sampling.

Even though it was written a long time ago, the aforementioned paper by Brooks gives a very good review of studies conducted up until publication of his work. If you are interested in this method I suggest reading his entire paper. He also includes work done on sampling other biological features such as honey, pollen, even the insects themselves as well as the use of sniffer dogs in exploration! The more recent study by CSIRO is also a valuable read. Have a look. Have you had any experience in this area? Please share your thoughts or opinions by commenting!

Finally, I would like to thank Mr Jack Caldwell for his gracious reference of my blog on his “I THINK MINING” blog. Thank you for your well wishes and encouragement Sir.

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