by Hugo Serra, Project Geologist
In order to keep improving the geoscientific knowledge of Quebec, the Ministry of Energy and Natural Resources (MERN) of Canada deploys mapping teams throughout the territory during the summer period, since the weather and temperatures permit it from early June. The acquisition of this field data is primarily aimed at improving and updating the overall knowledge of the targeted area and secondly, at enhancing its mining potential (mines, quarries). Following a geological survey carried out during the summer of 2017, a new geological map of the Borgia Lake region (western zone of the Grenville Province) has been produced at the scale of 1:50 000, the mapping of the area was based on a systematic outcrop survey in a kilometer-spaced grid. The zone where the study has been conducted is situated 300 km (186.4 mi) North-West of Quebec City, in a controlled ecological zone made up of dense forest on hilly terrain dotted by numerous forest tracks, few main roads, rivers and lakes, and active wildlife during summer (moose, black bears, wolves, foxes, beavers, and a lot of various flying insects willing to drink your blood).
The Grenville Province characterizes the youngest geological entity accreted to the Canadian shield (Laurentia) around a billion years ago. The province represents a significant area of the North American continent, it is structured in a northeast/southwest orientation from Newfoundland to Mexico. Today, the region expresses the remains of a gigantic mountain range that was equivalent to the current Himalayas at the end of the Mesoproterozoic period, and it is now sufficiently eroded to allow the structures of the Precambrian middle crust to outcrop at the surface. The formation of the belt takes place in the Precambrian context of North America in which the continent-continent collision between the Archean/Paleoproterozoic cratons Laurentia and Amazonia (the South American shield) have formed the supercontinent Rodinia, between 1.26 and 0.90 billion years ago. The construction of the mountain range was structured by a succession of metamorphic thrust belts formed in medium to high-pressure regimes during the Grenvillian orogen. The region consists of pre-Grenvillian volcano-sedimentary rocks intruded by plutonic sequences metamorphosed from the amphibolite facies to the granulite facies then intruded by gabbroic and syenitic intrusions dated from the Grenvillian orogen until the post-Grenvillian period (1.09 to 0.99 billion years ago), eventually the whole sequence has been injected by pegmatitic dykes cross-cutting the older formations.
During the team meeting before dinner of the previous day, my project geologist Abdelali defined for myself and my field assistant Max an approximately 10 km (6.2 mi) long route oriented north/south in the middle of the forest where geological data was missing. Due to the predominant vegetation in the region, the bedrock exposure rate is less than 10%. Using a topographic map, I prepared the traverse by defining the best path along our transect in order to intersect the relief, increasing our chances of finding outcrops as much as possible. As the area mapped had no access road, we had to be dropped and picked up by helicopter, thus I had to find landing spots using a satellite map. I selected two swamps for the starting point, and I decided to extend our traverse by roughly 2 km (1.2 mi) north as a large river with meanders was cutting through the impenetrable forest, and the sand benches on the edges of rivers are a good landing zone while swamps can be trickier. After writing down the geographic coordinates of these three spots in Johann’s notebook (the pilot), it was time to have a good rest to make the best out of the next day.
I woke up early the next morning, as I was overexcited to spend a day of work in the world’s best office: the wilderness. After having a champion’s breakfast, I double-checked my backpack making sure I had all the geological equipment: Android tablet, GPS, geological compass, hammer, and chisel; and safety gear: ‘SPOT’ GPS tracker, walkie-talkie to help the helicopter pilot to find us during the pickup, foldable hand saw, first aid kit, 5 L (1.3 gal) of water, bear spray and bear banger, plus some extra survival equipment in case we must sleep on the field, and last but not least, lunch. All this equipment represented three-quarters of the volume available in my backpack (roughly 10 kg or 22 lb), knowing that we had to sample every lithologies of each outcrop (with 10 outcrops on average per day), thus it was necessary to have a good swing with the hammer to fit everything inside while making sure the sample size was decent enough to allow all the potential analyses.
Ready for the day, we sat in the helicopter, while Johann was typing the GPS coordinates of the arrival spot I wrote the night before and we took off. Why head to the arrival point first would you say? It allows the pilot to check and confirm that the landing zone is safe. If it isn’t, he just had to seek a better landing spot in the vicinity, and I would just have to change the GPS coordinates of the pick-up and voilà! After this step, we headed toward the starting point by overflying of the zone to be mapped, which is useful for geologists as it allows them to adjust the traverse after seeing the terrain for the first time. We landed on the grassy swamp that looked the safest for the helicopter and started the walk north.
The geological surveys carried out by the MERN involve the systematic filling of a ‘geofile’ for each outcrop, where the outcrop is identified (petrological and structural analyses), geolocated, photographed and sampled. The data entry, the photos, and the geolocation of the outcrop are done by using an Android tablet, and associated GPS data via Bluetooth. Publicly broadcasted via the Geomining Information System (SIGEOM website in Quebec), the content of each outcrop can thus be directly downloaded and compiled in the different geographic information systems (GIS). Before reaching the edge of the forest, we encountered a several-meter-wide stream blocking our progress, it was too deep to be crossed on foot, so we improvised a bridge of small trees we cut with the hand saw. We managed to cross the stream without falling and kept going. Several hundred meters further we found the first outcrop of the day, a beautiful 10 m (33 ft) high face of moss hiding a mangerite formation behind the vegetation. After cutting some squares of moss with my bowie knife, I started the geological analysis, as Max was sampling the outcrop.
After several hours of work, our bags started to get heavier while the forest was getting denser, slowing our progress. Luckily, we found an old track just before lunch and we followed it for a kilometer to catch up. We discovered another outcrop on the side of the track, we analyzed it, then we enjoyed a little rest and had lunch. During this break, I sent a message with the ‘SPOT’ GPS tracker to the project manager detailing our good progress.
Heading back into the pristine forest, we left the track behind for a steeper terrain heading north. The area was particularly complicated as tens of dead trees were lying on the abrupt slope, we probably spent half an hour to get through this 200 m (656 ft) wide obstacle due to the really slippery conditions of decaying trees, the weight of the backpacks, and the steep topography. After this little challenge, we found our eighth outcrop at the top of the mount and then progressed downhill until we reached the valley. After crosscutting some water bodies thanks to beaver dams, we found and analyzed our last two outcrops before going to the pick-up spot. Two chairs probably left by hunters were waiting for us on the sand bench allowing us to relax a bit after this hectic journey in the heart of the forest. I turned on the walkie-talkie and a short time after, heard the voice of Johann, I confirmed to him we were waiting for the pick-up while starting to hear the noise of the helicopter. With the strong wind created by the blades smashing sand into our faces, we took the equipment that we put in the side rack and flew towards the camp. Johann dropped us on the pad at the camp and kept going on his pick-up mission with the other pairs of geologists/field assistants still in the field. We emptied our heavy load and I took some time to double-check every geofile before transferring the data collected during the field day into the computer system. After a good shower and some time to unwind, we joined the team meeting for the next day, ready for another adventure, deep in the forest a call was sounding.
For more information get in touch with Hugo Serra on LinkedIn