Searching for Ancient Rivers in West Africa

PlacerGold Trip Reports February 15, 2022alluvial, artisanal, bedrock mapping, diamonds, geophysics, gold, gold mining, gold mining equipment, gold pan, mining, paleo-placer, paleochannel, placer, placer claim, seismic 0 Comment

In April 2021 West Coast Placer was hired to assist in exploration for a large-scale alluvial gold project in Sierra Leone, West Africa. This program took place in the Kono region of Sierra Leone which hosts diamonds as well as gold in their placer deposits. It was a great experience and it was really cool to see how they do things in West Africa compared to the West Coast of North America.

Sierra Leone is famous for its alluvial diamonds. We were working in the Kono district which is where the plot of the movie Blood Diamond took place. The region where Leonardo DiCaprio’s character died at the end (spoiler alert) is not far from the survey area that we were exploring.

Despite extensive diamond mining taking place in the region since the 1930s very little attention had been paid to the alluvial gold deposits. There are a lot of artisanal miners active in the area but their sole focus is diamonds and they often discard the gold that they dig up. That fact surprised me because even in Canada where the average income and standard of living is much, much higher nobody would ever throw gold back into a river. That’s one of many things that’s different in Africa.

The placer deposits in the Kono region are much older than anything in BC or the Yukon. Much of the bedrock is Precambrian (500 million to 4 billion years old) and hasn’t ever been glaciated. By contrast, the rock in BC is less than 200 million years old and has been bulldozed by large glaciers on at least 4 occasions. Despite the differences, some things are the same in pretty much every placer environment. Over time rivers and streams move and leave their gold deposits behind in ancient paleochannels. That’s what we were looking for. Our system is designed to map bedrock depth and show the location of paleochannels.

Ancient Channel Gold Map Africa — Actual Map from a survey in Africa in 2021

Travelling internationally during the covid-19 pandemic is quite an adventure. In April 2021 the vaccines weren’t available yet and travel restrictions were very tough. We had to do lots of covid tests at each leg of the journey and there were a few hiccups. One of our team members wasn’t allowed to board the flight to Belgium from Montreal because his test was taken too far in advance. He had to get another PCR test and catch a flight the next day. On the way back I almost had to stay in a covid hotel, fortunately, the Canadian government honored my essential service exemption.

It was interesting that Sierra Leone didn’t have a lot of covid restrictions. That’s because three years prior to the breakout of Covid -19 around the world West Africa was center stage to the worst ebola outbreak in history. When covid broke out in 2020 they knew what to do and locked the whole country down with no exceptions. By the time we arrived in 2021 the whole country had a total case count of 80 and zero deaths. With the intense screening protocols for international travellers they were able to keep infection rates to a minimum, something that wealthy western countries weren’t able to do, even with the advent of vaccines.

We spent a few nights in the capital city of Freetown and headed off to Koidu Town to begin our exploration. The bedrock mapping survey covered a large area that was chosen due to the prevalence of artisinal mining and topographic features that favoured the development of paleochannels. We had some knowledge of hard rock gold production in the area and anecdotal evidence from local artisanal placer miners.

excavator placer alluvial west africa — There’s no 6 month wait for permits in Sierra Leone

We had a crew of local laborers which included the son of the Paramount Chief. That was important for public relations since we didn’t speak the local language and it was important to explain to the villagers what we were doing. Having the chief on our side let everyone know that we were working along with local government and not just rolling in to take all the resources for ourselves.

Sierra Leone is ruled by a combination of federal government and chiefdoms. The mining claims are managed by both levels of government in a complex way. Without the support of the chief it would be hard to get the necessary permitting and support of the local community. Luckily for us, the local chief is a miner himself and we got along really well.

The artisanal miners do a lot of the work by hand. They often use gas-powered water pumps similar to what small-scale miners use in Canada. Mostly for dewatering though, they don’t have highbankers like we do back home. In Africa people carry everything on their heads, even the water pumps.

Most of the washing is done by hand using gem screens or large gold pans. The larger operations use a rudimentary hydrostatic jig. There are very few operations using heavy equipment but manpower is readily available in this area.

The local miners have a method of digging shafts that works really well in the clay-rich gravels in that area. They dig a shaft about 1 meter wide and dig out foot holds on the way down. In this way they can reach bedrock in a day or two and get really good samples from the bedrock interface. The company that we were working with hired a large crew of local miners to dig shafts instead of using a drill. The samples were better and expert shaft diggers were more than willing to work for $10 US per day.

shaft made by artisanal miners sierra leone — Shaft made by artisanal miners in Kono region

Getting supplies in a third world country can be an adventure in itself. We tried to bring everything that we needed with us but we counted on procuring some supplies locally. One thing that we need lots of was flagging tape. Since this is a mining area we thought it wouldn’t be too hard to find. It turns out that there is no flagging tape available for sale in the entire city of Koidu. Despite two full-scale kimberlite mines right next to the city. We had to buy fabric ribbon in bright colours and use scissors to cut it in order to mark our lines.

It turned out that the local kids like the fabric just as much as we did since they would come right behind us and pull all the ribbon off the lines as soon as we were done. Sometimes they wouldn’t even wait till we had completed the line which made a few sections really challenging.

Some of the more high tech mining devices in Africa are really cool. The company had some really efficient gold centrifuges for testing the gravels. They’re like a gravity concentrator that you see in North America but made to be economical and easy to deploy. One machine is called the Gold Kacha and works really well.

Centrifuges aren’t commonly used in placer mining in BC and the Yukon but that’s something that we should really consider. The gravity concentrators on the market are expensive in Canada but you can get a Gold Kacha out of South Africa for about the same price ad an average highbanker setup here in BC.

The local gold panning technique is quite different from what I’m used to. They use a large rounded bowl with handles on the sides. There are no riffles and the sides have a very gentle slope. My technique didn’t work to well with their pans. The local technique is to swirl the material in the pan while letting the lighter stuff wash over the sides. One of my crew members demonstrated the technique in the video below.

The bedrock mapping survey was a huge success. We identified a clear paleo-valley and an ancient river channel that spanned several kilometers. Much of the area that we identified with the seismic survey as an ancient channel had never been exploited by artisanal miners.

One great thing about working in Sierra Leone is you don’t need permits as you do in BC. We were able to start digging with an excavator right away. With a combination of bulk sampling with the excavator and teams of local shaft diggers sampling was completed in less than a month. The gold grades within the channel were excellent and alluvial diamonds were also present.

Exploring a new area is always a welcome experience. As explorers, we are constantly striving to search different areas and locate mineable gold deposits. This exploration program in West Africa did not disappoint. It was quite a contrast to use the latest technologies in an area where people are still living in mud huts and cooking with charcoal. Some of the ancient techniques used in Sierra Leone are very efficient, such as the shaft digging technique. If we could get hundreds of workers to dig shafts in Canada for $10 per day imagine the ground that could be explored.

We managed to locate a very rich placer deposit containing minable quantities of gold and alluvial diamonds. This project was developed with the support and mutual benefit of the local chiefdom and communities. It was a great experience to share knowledge of different mining and exploration techniques and learn a few new ones as well.

Hunting for Diamonds in the Arctic

PlacerGold Trip Reports December 7, 2015arctic, aurora, diamond mine, diamonds, geophysics, kimberlite, magnetometer, northern lights, showshoe 0 Comment

Back in 2010 I had the opportunity to work on a diamond exportation program in the Canadian Arctic. The camp was called Credit Lake and was located near Lac de Gras in the North West Territories. The Lac de Gras region was the epicentre of the 1990s diamond rush after the discovery of the Point Lake kimberlite pipe by Chuck Fipke. Today there are three operating diamond mines in the region Diavik, Ekati, and Snap Lake.

Diamonds are found in volcanic structures that are called kimberlite pipes. These are volcanic events that take place very rapidly. Most volcanoes take thousands or millions of years to develop. A volcanic pipe can develop and explode in less than a day. These volcanic explosions are charged by high pressure carbon dioxide and water vapour. And travel from the below the crust melting through rock at over 100km/h.

It is important that volcanic pipe events happen quickly if you want to mine diamonds. The environment where diamonds form is under intense heat and pressure. Once the pressure is removed diamonds will melt into graphite which is much less desirable. In kimberlite pipes diamonds are carried to the surface as the superheated kimberlite melts its way through the layers of the crust. When the pipe reaches the surface it releases its energy in a huge explosion and then quickly cools. The diamond crystals do not have time to melt, they cool with the rest of the pipe and stay in place.

The volcanic events that created the North West Territory kimberlite pipes took place millions of years ago. The surface has been subjected to many ice ages over the years and different continental ice sheets have scoured the surface like a bulldozer. To find a pipe today you look for the debris field left behind as the top of the pipe was scraped by ice sheets. As the glacial ice sheets retreated they left behind a trail of ground up rock and indicators for diamonds if you’re lucky.

My first stint at the camp was for six weeks in 2010. We were searching for diamonds as well as nickel. My role was to analyze pulverized rock samples from an R/C drill as well as preparing samples for assay and general exploration work. I returned in 2013 to conduct geophysical surveys including ground (snowshoe) magnetometer and HLEM. Both trips were in early spring when the temperature in the Arctic ranges from -50°C to -10°C. Show storms were frequent and the ice on the lake was five feet thick.

The camp is extremely remote, approximately 300km North of Yellowknife,NWT. Everything is brought in by ski plane or helicopter. In addition to exploration work we had to work together to keep the camp running. When a plane would arrive we would all pitch in to get the groceries, diesel drums, and any other supplies off the plane and into the camp. The same was true for getting water out of the frozen lake for showers, laundry and the kitchen. Water is always a challenge in remote areas when it is extremely cold.

While I was at the camp we experimented with several different water gathering techniques they all had their merits. What we ended up doing was using a chainsaw to cut out a section of the lake ice. Then used an ice auger to drill the final few feet (see video above). We used a snowmobile toboggan to transport pails up to the reservoir inside the kitchen.

To travel to and from the locations we were exploring we took a helicopter. We had a Eurocopter Astar B3 to shuttle people and move the heli-portable drill around. We also had a couple of snowmobiles and a GMC pickup truck that had tracks instead of wheels.

The RC drill is a super light weight drill that produces crushed rock instead of core. The RC stands for Reverse Circulation. The drill is air powered and behaves like a giant hammer drill, like the kind that you use for masonry work. The air returns from the bit carrying the rock chips to a hopper where samples can be collected. The advantage of an RC drill is that it doesn’t require water and breaks down for rapid transport. RC drilling is quicker and less expensive than diamond drilling.

After field samples were collected I conducted several tests on them inside our field lab. We had an X-ray fluorescence (XRF) analyzer which is a pretty cool instrument. It bombards the sample with high energy X-ray radiation and the atoms re-emit photons which gives information about their structure. XRF basically gives you a rapid geochemical assay. I also conducted magnetic susceptibility tests and identified the lithology of chip samples using a microscope.

The accommodations were first class. At least as far as small remote exploration camps go. We stayed in Weatherhaven dome tents which are heated by diesel stoves. As long as there is fuel in the stove you will be comfortable in any weather conditions. The stoves are prone to issues though and use half a drum of diesel per day when its super cold. Our beds are constructed out of 2×4 lumber that was flown in and everybody uses a sleeping bag for bedding. This camp was not a “dry camp” which means that alcohol was allowed. That is a huge plus when you’re stuck in the middle of nowhere for six weeks.

The high latitude makes for great northern lights viewing. That is actually my favourite thing about the Arctic. Interestingly the mechanism behind the glow of the Aurora Borealis is the same as the XRF machine. The molecules in the upper atmosphere are excited by a stream of radiation from the sun called the solar wind. When molecules are excited they reach an unstable electron configuration and rapidly release a photon as they return to a stable state. The different colours are due to different molecules being excited such as high altitude ozone, oxygen and nitrogen. The phenomenon is difficult to photograph but here are some of my best shots below. The best photo in the world doesn’t compare to seeing it in real life though.

The days out in the field can be pretty tough when the temperature drops. We built a survival shack that would travel with the drill. Other than that we were fully exposed until the helicopter arrived at the end of the day. The survival shack also made a great place to have lunch out of the wind.

In addition to drill sampling I conducted geophysical surveys to identify kimberlite pipes. We used two types of geophysical survey, magnetometer and HLEM. Magnetometer or “Walk Mag” is a sensor that measures changes in Earth’s magnetic field in very high precision. As you pass over different kinds of rock the sensor will record minute changes in the magnetic field. Once the survey is complete you can produce a map that looks like a topo map except that the you are showing magnetic field instead of elevation. Click here for a sample of a magnetometer map. Kimberlite pipes stick out as an anomaly because they have a different magnetic signature to the surrounding rock. You have to use the old school snow shoes because any metal will mess up the readings.

HLEM (Horizontal Loop Electomagnetic) works in a similar way except that there are two parts to the system. One provides a source field and charges up ore bodies. The receiver records the response signal from the rock. HLEM actually works the same way as a metal detector just on a larger scale and records actual data. The instrument is from the 1980s and is very uncomfortable, fortunately in the winter you are wearing lots of clothes.

I have always enjoyed working in the Arctic. Its not for everyone though. It is insanely cold in the winter and the summer has a lot of bugs. The wildlife is breathtaking I have seen Muskox, Wolverines, Caribou, different coloured bears, Narwhals, and other wildlife that you cannot see below the Arctic Circle. The Northern Lights shows are simply amazing. The people are different too. This kind of work attracts a different breed, those who are willing to travel to remote areas. Arctic explorers all share a strong sense of adventure.

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