Arc Minerals in Zambia

As a disclaimer, I should state that what is posted here is purely my own interpretation of the data we have available to us. It is not to be taken as THE interpretation but it is one that fits the pieces of the puzzle together in a way that makes sense to me. 

Some Background

First, I think it's worth having a look at the topography of our licenses and the surrounding areas:

The colour scale is white through to blue indicating high to low altitude. A couple of things jump out immediately;

•  Large scale faulting around the dome which is one of the main factors affecting the location of sulphide deposits, creating pathways for the migration of mineral rich brines. The nearby Sentinel and Enterprise deposits are on fault zones, as are most of Arcs major targets.
• The boundary of Arcs license areas is quite clearly defined in the topography, particularly in the south and east. This corresponds to a change in geology, which is another key factor in understanding where deposits might form.

Here is the topographic map of Arcs licenses with geology overlaid on it. The most important things to understand about the geology are that; 

• The red band which surrounds much of our area is Lower Roan rock. This is the rock from which metals were dissolved by briny fluids and later deposited higher in the geological sequence. Although we only see a band of Lower Roan at surface, in fact it is continuous across most of our licenses below surface. This is key to understanding where mineralisation may have come from.
• The area within the red band is Upper Roan, which overlays the Lower Roan. It is within these rocks that the fluids migrated, travelling via fractures and natural pathways in the rock. Chemical reaction between the fluid and certain rock types caused the metals to drop out of solution. 

I'm not a geologist and I suspect that most of you aren't either so I won't attempt to go into more detail on the geology, but if you do want to know more, I would recommend viewing this video by David Wood, a senior geologist with Anglo American and previously involved in the discovery of the nearby Sentinel deposit when with First Quantum Minerals:

It is very much a talk by a geologist for geologists but there is some very relevant information, particularly toward the end.

A comprehensive campaign of soil sampling was carried out across the licenses over several seasons. Here is a map of the copper in soil concentrations:

You can see several large areas of anomaly highs (in pink) as well as anomaly lows (in blue). The blue corresponds to the Lower Roan rock and is the first indication that metals have been stripped from these rocks.

An airborne electromagnetic survey was also carried out during this time:

Again you can see in blue the Lower Roan rocks which indicate low level electromagnetic response. This map is more complex to interpret and I'll come back to this shortly with my own interpretation.

During the Exclusivity Agreement with Anglo American they requested that soil samples from the original sampling campaign were re-assayed using a technique called 4 acid digest. This uses the fact that some elements are not taken into solution by the brines when others are. In this case scandium is chemically stable whereas copper is not, so by testing the ratio of copper to scandium in the soil samples it is possible to map where copper has been leeched and where it has been enriched relative to the background level.

There is a research paper written by David Wood and others where they describe this method and how it was used in the mapping of Sentinel.

Copper Scandium mapping

Here is the Copper Scandium ratio map for Arcs licenses:

Normal background level is indicated by light blue to green. Dark blue indicates copper depletion with respect to scandium and enrichment is shown in yellow-to-pink. Again you can see depletion of copper in the Lower Roan around the whole of the license area.

Initial shallow drilling (150m max) has been guided by the surface copper anomalies revealed by the soil sampling. As Remy has said (during his 2020 Indaba presentation), they were going for the most obvious low hanging fruit. This drilling has been successful in finding high grade oxides at Fwiji, Cheyeza East and also evidence of deeper sulphides at those locations as well as Muswema. A deeper drilling campaign last year has shown more evidence of deep sulphides at both Fwiji and Cheyeza East although the drilling campaign was impacted by external events which limited the amount of drilling which could be done.

Here is a depth plot of the shallow drill results at Cheyeza East which include an area of roughly 200mx200m with very high oxide grades, some of the best ever seen in the Zambian Copperbelt. You can see there is also evidence of sulphide mineralisation below the oxide cap. 

The limited drilling at Fwiji showed some even higher grades particularly in one drill hole which showed 1m of sulphides at more than 7% Cu eq.

My Interpretation (take with a pinch of salt or two)

First I want to go back to the airborne electromagnetic (EM) map which I think has some interesting things to tell us. Imagine that you were able to remove all of the overlying rock from our licences, just leaving the Lower Roan. If you did another airborne survey what you would expect to see is a map that is for the most part blue in colour, because metals have been stripped from those rocks across the entire area. David Wood mentioned in his video presentation that this isn't a localised process but one which has been mapped for hundreds of square kms across the Domes region.

So what can we understand by looking at the EM map:

• Any areas which are blue in colour are showing that no mineral deposition has occurred in the rocks above the Lower Roan in that area.
• Any areas which are NOT blue are indicating that mineral deposition HAS occurred in the rocks above that area.
• There is one proviso to the above in that shallow / surface mineralisation does not show up on the EM map. I presume this is by design in order to see what is happening at depth although I don't know that for sure.

Lets first take a look at the area around Lumbeta and Muswema:

What I think we are seeing here is the path of the brines (indicated with the arrows) as they followed the major fault line down the side of the dome, then spreading out as they got to the foothills. I believe that this is likely to be the main source of the mineralisation that we see at Muswema and Lumbeta. 

One interesting comparison is the deposit at Barrick Golds Lumwana mine, which has formed up against an L-shaped outcrop of Lower Roan in much the same way as the Muswema anomaly does:

 

Now lets take a look at the area from Cheyeza / Fwiji to Nyambwezu in the North East:

My interpretation of what is happening here is that the area around Nyambwezu is an area of fluid flow from the Lower Roan (in blue) to the Upper Roan. The large red anomaly may be a fluid trap which has become mineralised. The whole area from Nyambwezu to Cheyeza is showing a strong EM response, indicating that this whole area MAY be mineralised as fluids have flowed down towards Cheyeza.

I noticed that in the RNS on 29th April, Nick made reference to "targeting the contact between this unusual basal magnetic unit and the overlying rock formation" I believe this may be what he was referring to.

I've always thought that Nyambwezu has the potential to be another major find although it hasn't been the focus of attention to date. In the RNS from 12th April 2019 notes were made on each of the targets and Nyambwezu was noted to have an intense EM anomaly and intense copper-cobalt anomaly. The only target where intense was used in the description.

I've marked a line which follows surface fault lines. It's noticeable that above Cheyeza this faulting seems to act as a barrier to fluid flow or creates a pathway to the surface. It is along this line that the high grade oxides were located. Further North, between Cheyeza and Fwiji, the fluid flow seems unaffected by the faulting, continuing further West. It's possible that the mineralisation at Cheyeza West was via this route:

The EM interpretation map certainly indicates that there are two distinct areas at Cheyeza (labelled CM4 and CM5 above).

Here is the topographic map and the EM anomaly map for the area between Fwiji and Cheyeza. When you see it like this, it's pretty clear that the anomalies (in red) are closely related to the fault line running between Fwiji and Cheyeza. I think that all of these anomalies are potentially targets for drilling.

 

And here is a closer view of the area around Cheyeza, showing the previous and planned drilling and the shallow oxides, located on the boundary between the mineralised and non-mineralised areas (blue).

A slideshow view is a bit easier to see how features line up:

And here is the area around Muswema and Lumbeta. The fractures at Muswema again seem to fit well with the EM anomalies.