Breaking cover– How Kavango Resources is surveying beneath the surface in Botswana

How dense is the rock beneath your feet?

In some cases, this might seem like a strange question. After all, the rock beneath your feet might in turn lie beneath several hundred metres of soil or sand. And when “cover” is this deep, it can often present a significant obstacle to effective exploration.

Author, Alexander Crossing

This is the case with the targets Kavango Resources has identified across the Kalahari Suture Zone (“KSZ”) in Botswana. Indeed, the thickness of the cover at the KSZ is one of the key reasons why no-one has been able to turn the various attractive indications at the project to serious account.

Until now, that is.

Indeed, advances in the surveying technology enabling explorers to examine rock deep beneath the earth’s surface have been enormous in the years since the KSZ was first identified as prospective. And while the ones Kavango is now employing have been known about for some time, their accuracy has only increased even further in recent years.

Let’s take a look…

Gravity surveys

Hence – how dense is the rock beneath your feet?

An exploration company could be interested in establishing the density of subsurface rock for a variety of reasons, but one of the most common is a desire to identify alteration or intrusion.

Mineralisation is often found where rocks have been altered by volcanic activity, or where magma has intruded directly into host, or ‘country’, rock. If such intrusions or alterations are present, they will show up as a gravity anomaly­–effectively an area of different density to the country rock.

While this is not necessarily conclusive of anything in itself, a gravity anomaly is a clear sign that exploration is on the right track.

The specific gravity of what’s underground varies greatly. It stands at between 1.2 and 1.5 for unconsolidated alluvium, between 2.5 and 3.5 for hard igneous or metamorphic rocks, and between 3 and 5 for massive metallic minerals. Meanwhile, a void has a density of zero, but if filled with water or mud, the figure is likely to rise to around 1 to 1.5. The specific gravity of water is 1.0.

The results of recent gravity surveying by Kavango in the KSZ were released in January, with the firm carrying out work from two drillholes to run seven lines of gravity data each 13 kilometres long.

In total, the company ran five north-south lines at an 800-metre spacing and two east-west tie lines at 2,0000-metre spacing, with stations spaced at roughly 200 metres along each line.

The result was the detection of a strong ~30 miliGal Bouguer anomaly at the area of the KSZ known as the Great Red Spot.

Electromagnetic surveys

Electromagnetic surveys can be run both from the air–most typically via helicopter–and from the ground–either at surface, or, where possible, underground.

The principle here is relatively straightforward: an electromagnetic pulse is sent into the ground, and the conductivity it meets is measured.

Electromagnetic surveying is particularly effective at helping to identify sulphide deposits. After all, there is a large contrast between the conductivity of sulphides and country rock and, handily, this shows up well in results.

Sometimes, the reasons sulphides light up so well is because they actually host significant amounts of metal, and this–of course–is the holy grail of the exploration company.

Because Kavango is now beginning to undertake a significant amount of actual drilling on the KSZ, it now also has the added opportunity of conducting underground electromagnetic surveys from inside its own drillholes.

These are commonly referred to as down-hole electromagnetics; sometimes abbreviated to DHEM.

Towards the end of 2021, Kavango utilised this method in hole KSZDD002 to a depth of 350 metres above the Great Red Spot anomaly. The readings taken from electromagnetics at this depth showed that the already-identified B1 Conductor target below actually had far greater conductance than had previously been thought.

Following this, in March 2022, DHEM surveying of the completed KSZDD002 hole was able to confirm the existence of two targets in the B1 area–one with a conductance of 16,000 Siemens consistent with possible nickel/copper massive sulphides, and one with a conductance of 2,500 Siemens consistent with the presence of possible nickel/copper net textured sulphides.

Meanwhile, earlier in the season, downhole magnetics identified the upper edge of a conductive anomaly in the Proterozoic gabbro even deeper down at the KSZ, and this initial find was eventually broadened out into the identification of a 30-kilometre strike length of distinct magnetic Proterozoic gabbro.

The bottom line is, thanks to DHEM, Kavango has been able to establish numerous high-priority exploration targets and target areas for the detection of possible large-scale mineralisation.

Author, Alexander Crossing

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