During the first week of July 2022, 10 iMAGE-CREATE students travelled to St John’s to take part in an 8-day fieldtrip that focused on the large-scale geology and tectonics of Newfoundland. The trip focused on the pre-, syn- and post-collisional sequences related to the closure of the Iapetus Ocean and the Taconic Orogeny which included visiting world-class exposures of pillow basalts at Sleepy Cove, ophiolitic units around Betts Cove, and Moho transition in the Bay of Islands. The students learned how to identify key lithologies and field relationships that mark the transition from one tectonic regime to another, and synthesize this information to better understand how collisions develop over time. The following is a day by day report that synthesizes the observations and main objectives that the student attendees were responsible for.
Day 1: Twillingate – Moreton’s Harbour
Morning (written by Brittany Pegg)
To kick off the field course, we explored outcrops in the Twillingate islands. These outcrops represent oceanic arc and back-arc igneous activity during the early Ordovician. Tectonically, they are part of the Notre Dame subzone of the Dunnage Zone, which is separated from the Exploits subzone by the Red Indian Line, a major structure related to the closing of the lower Paleozoic Iapetus Ocean.
The first stop visited was a hike up to the northernmost edge of Twillingate, at Sleepy Cove. Here, exposures of metamorphosed Cambrian mafic pillow lavas and bimodal volcanics from the Sleepy Cove group were seen along the edges of the cliffs. The majority of the rocks were metamorphosed to greenschist/amphibolite facies, and are locally mylonitic. The pillows are sheared, locally rich in amygdules infilled with calcite and chlorite, with abundant NE-trending faults. Rocks adjacent to the faults are locally carbonated with minor pyrite mineralization. These features however were nearly impossible to observe, as they could only be viewed up close to the cliff face.
The second stop visited was Jenkins Cove, located just southeast of Sleepy Cove. Observed here is the Twillingate pluton, composed of trondhjemite and tonalite; the pluton overlays the pillows as seen in Stop 1 and is the lithology that is the most exposed across the Twillingate islands. The most notable feature at this stop was a large 30cm wide black lamprophyre dyke, containing numerous phenocrysts of biotite and strikes to the north. The lamprophyre is undeformed, unlike the Twillingate pluton, and is interpreted to represent the tensional environment related to the breakup of the North American Margin.
The final stop visited in the morning was the Chanceport Fault, which is exposed just before the causeway leading to the Twillingate Islands. This fault is a 2km long thrust fault striking NE/SW. To the north of the fault is the Twillingate trondhjemite whereas the mudstone, graywacke and pillow lava with red chert of the overlying Chanceport Group are located south to the fault. The Chanceport Fault in this case is used interchangeably with the Red Indian Line. The southernmost unit of the Chanceport Group is the only unit exposed at this locality; indicated by the presence of numerous pillow lavas as well as small exposures of jasper. Unlike the Twillingate pluton, the unit is well preserved and unmetamorphosed, as well as being very structurally complex.
Afternoon (written by Jessie Kehew)
In the busy afternoon of Day 1, we saw various pre-, syn- and post-accretion lithologies of the closure of the Iapetus Ocean. The purpose of these stops was to see the wide variety of lithologies that are involved in ocean closure. We first visited the pre-accretion Moretons Harbour island arc sequence. The Moreton’s Harbour Group (late Cambrian to mid Ordovician) is located north of the Chanceport Fault and is a sequence of volcanic and volcaniclastic rocks. It hosts mineralized veins that were explored and mined for Arsenic in the late 19th – early 20th centuries. These are epithermal deposits, associated with felsic sub-volcanic volcanism.
Our first stop was the Stewart’s Mine in the Little Harbour Formation, which hosts all the mineralization in the Moretons Harbour Group. We found the mine’s ore dump, which was rich in pyrite and arsenopyrite, however, we could not locate the trench to view the diabase dyke which hosts the mineralized veins, or the nearby felsic dyke which served as the fluid source for the veins.
The next stop was Hayward’s Cove Formation, the youngest formation in the Moretons Harbour Group, where we saw the extrusive equivalent of the felsic dykes associated with the mineralization. These felsic extrusive rocks are predominantly massive quartz-feldspar crystal tuffs, but we also observed bedded tuffs that appeared to be rafted or slumped units.
The syn- and post-accretion lithologies visited for the rest of the day recorded initial tectonic instability causing the movement of giant blocks, a period of quiescence once the island arc activity stopped, a flysch sequence deposited in a foreland basin near the end of accretion, and the intrusion of a post-tectonic batholith. These were all roadside outcrops.
We then drove south over the Chanceport Fault to view lithologies recording the syn-accretion history. The first stop was the Boyd’s Cove Dunnage Mélange, an early to middle Ordovician olistostrome that indicates tectonic instability interpreted to be associated with the Taconian Orogeny. This unit is a polymictic conglomerate with clasts ranging from cobbles to 1 km in an argillite matrix. We viewed small clasts and rafted units on the ground to the northeast and southwest of the Reach Run Causeway.
Next, we stopped at the Loon Bay Granite, the granitic portion of the Loon Bay Batholith (Devonian). This unit is post-tectonic, which can help to provide a minimum age of deformation for the surrounding rocks. Further down the road we encountered the Caradocian chert and shale, a late Ordovician unit associated with a period of quiescence following the cessation of an island arc. In the roadside outcrop we saw argillaceous cherts and intruding dykes, as well as stratiform pyrrhotite, pyrite and magnetite – exhalative sulfides that are present throughout the entire section.
The final two stops record a flysch sequence of the late Ordovician to early Silurian, deposited during the Taconian Orogeny. The Samson Greywacke is at the base of the sequence, consisting of sandy turbidites, and up stratigraphy interbeds of conglomerate increase in frequency, transitioning into the Goldson Conglomerate. The Goldson Conglomerate is a polymictic conglomerate with volcanic, plutonic and sedimentary clasts. The two lithologies were viewed at roadside outcrops, and due to limited exposure, sedimentary structures were not apparent.
Day 2: Buchans
Morning (written by David Summer)
During our Day 2 excursion, we left the Newfoundland coastal areas and headed into the Newfoundland interior to the town of Buchans. Tectonically, this region is part of the Dunnage Zone—vestiges of volcanic and sedimentary terranes formed during the closure of the Iapetus Ocean and the collision of the continents of Laurentia and Gondwana. More specifically, the town of Buchans lies within the Annieopsquotch Accretionary Tract, which is the most westward series of Ordovician arc and backarc volcanic-sedimentary stratigraphy and associated ophiolite sequences within the Notre-Dame Sub-zone (peri-Laurentian origin; ~480-458 Ma). The northeast-southwest trending Red Indian Line, the suture between Laurentia and Gondwana lies directly east of Buchans.
The geology in the vicinity of Buchans is interpreted to be a mature volcanic-sedimentary arc sequence formed during the subduction of the oceanic margin of Gondwana from the southeast (~473-468 Ma). The stratigraphic sequence is classified collectively as the Buchans Group and is contiguous with the Roberts Arm volcanic suite visited the following day (Day 3). The significance of the Buchans-Roberts Arm Group is that it is host to a number of volcanogenic massive sulphide (VMS) deposits, including Buchans, one of the largest Zn-Pb-Cu-Au VMS deposits ever mined in Canada. The VMS deposits of Buchans-Roberts Arm are interpreted to have formed during arc extension in which metal-bearing fluids were channelled along normal faults and deposited at the seafloor of submarine volcanos. About half of the ore deposition at Buchans are interpreted to be in-situ exhalative deposits while the other half are interpreted to be transported deposits, having been entrained in mass movement events such as caldera collapse or debris flows. A shift to transpressional tectonics during terrane accretion and continental collision reactivated these faults, resulting in a fold-thrust belt with fault-bounded ore deposits being found within stacked duplex structures.
The Day 2 excursion began with a visit to Ski Hill, which provides a panoramic view revealing the local physiographic expression of various regional lithologies as well as the location of the mined ore bodies. The lithology at this site is the characteristic mafic breccia of the Ski Hill Formation, which lies in the stratigraphic footwall of the ore horizon. At the next few stops, we saw the pillow breccias and resedimented pyroclastic conglomerates of the youngest stratigraphic unit of the Buchans Group, the Sandy Lake Formation. The significance of these outcrops is that they contain clasts from the oldest Buchans stratigraphic unit, the Lundberg Formation, providing evidence for caldera collapse and/or debris flows resulting from exposure of the deeper stratigraphy along the margins of graben structures in an extensional setting. Next, we visited outcrops of the Sandy Lake arkosic sandstone along the Buchans River, which indicates a transition to terrestrial setting. Our final stop was the discovery site of the Old Buchans Orebodies, within the structural hanging wall of the Buchans River Fault. The discovery site is within the felsic rocks of the Buchans River Formation which contains most of the ore bodies in the Buchans area.
Afternoon (written by Michael Ryan)
In the afternoon of the third day on the Newfoundland field course, members of the mining company Buchans Resources were kind enough to host an afternoon session with the iMAGE-CREATE attendees at the town of Buchans. During the session, Paul Moore (VP of Exploration) and Marina Schofield (Senior Geologist) provided a presentation on the mining history at Buchans, the local geology, as well as some of the current company initiatives.
Following the presentation, the attendees were given a guided tour of the company facilities, including a run through of some of the various and significant drill core sections from across the company property. This provided the attendees with a good overview of the localized stratigraphy, the complex structural history of the area, as well as an idea of what the mineralized orebodies look like. Additionally, this allowed attendees to gain first hand experience on the processes of exploration within the industry.
After the tour at the company facilities, Paul and Marina provided the group with access to one of the Newfoundland provincial core shacks that is housed in Buchans. The provincial core shack houses thousands of meters of preserved and historic drill core, dating back to the earliest stages of exploration and production from the mines at Buchans. This core storage library represents one of six that are maintained by the Mines Branch in the Department of Natural Resources of the Newfoundland Government.
Day 3: Pilley’s Island – Robert’s Arm
Morning (written by Sabrina Chan)
During the morning of day 3 we explored the Buchans – Robert’s Arm volcanic belt. Pilley’s island and the Robert’s Arm group consist of a felsic centre related massive volcanogenic sulphide deposit. During this portion of the trip, we were exposed to the Robert’s Arm Group, and the Springdale Group.
The Robert’s Arm Group represents a section of Llanvirn (476 – 463 Ma) island arc volcanics within the Buchans-Roberts Arm mature volcanic arc system, which is associated with the closing of the Iapetus Ocean and the subduction of Laurentia. The volcanic belt is located within the Notre Dame subzone of Central Newfoundland.
We spent time mapping the dacite dome and the related sulphide deposit on Pilley’s Island. We were able to study, identify, and interpret the eruption and alteration processes of the different units associated with the dacite dome. We saw excellent exposures of pyritized and highly silicified pillows, dacite lava flows and breccias overlaying the pillows, dacite dyke intrusions, varying levels of sericite alteration throughout the dome, and the hydrothermally deposited massive sulphides.
Afternoon (written by Ryley Penner)
In the afternoon of day 3, we continued our excursion of the Roberts Arm volcanic belt along a highway stretch that provided a cross-section of the northern part of Robert’s Arm Group. Outcrops of mafic volcanics viewed on these stops represent some of the best exposures of pillow lavas in central-Newfoundland. Pillow breccias, alteration zones, and sulfide mineralization shown at the next stops provided local geological context of the exposures at different levels of the VMS system (from bottom to top).
A visit to the Mills Cove mine site allowed us to observe disseminated and stringer pyrite mineralization hosted by chloritized schist, a part of the Lushs Bight Group known for its prolific mineralization that we examined in further detail at the Little Bay deposit the following day.
We gained an understanding of the Robert’s Arm volcanic rock units at a regional-scale that are equivalent to the volcanic rocks and at Buchans and Pilley’s island. Linking the outcrops observed in this area allowed us to conceptualize where we were situated in the Llanvirn mature island-arc complex in the northern part of the Cambro-Ordovician Iapetus Ocean that was undergoing arc-rifiting and extension during accretion to the Dunnage Zone oceanic rocks on the Laurentian Continental Margin.
Day 4: Lush’s Bight – Baie Verte
Morning (written by Jonathan Umbsaar)
Day 4 highlighted the transition from oceanic rocks of the Notre Dame Subzone onto the continental margin of Laurentia. At the first stop, the group hiked into the Little Bay Mine site, hosted within the Lush’s Bight group. Here, mineralization occurred as massive lenses, pods, veins and veinlets between highly chlorotized and epidotized pillow basalts. Though the gloryhole was fenced off, excellent exposures of wallrock illustrated how mineralization was most concentrated within a section of highly deformed chlorite schist.
We then continued the mineralization tour with a stop at the Hammerdown Au project, accommodated by Maritime Resources. After a short hike, and a primer on Silurian alkaline magmatism in the Catchers Pond Group we found quartz feldspar porphyry dykes associated with gold bearing quartz-suplide veins. The surface exposure was minimal, though the number of drill collars on the property indicated strong interest in this deposit.
Finally the last stop for the morning was along the beach of Nickey’s Nove Cove where after lunch the group walked down the beach to where pillow lavas have undergone extensive epidotization and interpillow jasper is common.
Afternoon (written by Dan Stepner)
The afternoon began near directly on the continental suture as represented by the Baie Verte Line. 2 stops along highway 410 illustrated the degree of deformation which occuring during the Salinic and Acadian orogenies, where ultramafic protoliths have metamorphosed into quartz-magnesite-fucshite schists with abundant asbestiform actinolite and serpentine.
Then after a short drive to Ming’s Bight we spoke of the Point Rouse Ultramafic complex and late Ordovician to early Silurian alkaline magmatism found across the Baie Verte Peninsula. As examples that highlight the complicated geotectonic setting which was the Laurentian margin during the closure of the Iapetus Ocean, day 4 put a strong point on the variety of rock types which comprise both the accreted compacted arc and back-arc assemblages and the continent-ocean suture zone.
Day 5: Bett’s Cove
Full Day (written by Taylor Tracey Kyryliuk)
On the fifth day of the field course, iMAGE-CREATE trainees visited Bett’s Cove, an abandoned mining town famous among geologists for its excellent exposure of a well-preserved ophiolite sequence. Ophiolites are oceanic crust that has been thrust onto a continental shelf. In the case of Bett’s Cove, these ophiolites are believed to have formed in the fore-arc of the Laurentia-Iapetus Ocean subduction zone soon after subduction initiation. This is due to the presence of boninites, rocks that are depleted in incompatible, non-soluble trace elements. These rocks give us a snapshot of the oceanic crust at the beginning of the closure of the Iapetus Ocean. The relatively undeformed state of the Bett’s Cove Ophiolites is attributed to their distance from the Baie-Verte Line.
Our time at Bett’s Cove consisted of a day long hike and mapping exercise. Bett’s Cove was abandoned when the mine collapsed, a stop along the way included visiting this spot, where the collapsed glory holes were now filled with water. We observed plenty of alteration in this area. The closer we were to the mine location, we observed increasingly chloritized basalt pillows with quartz stringers. We began to see rust staining on the rocks, a sign of pyrite. At the mine site, we saw pyrite schist, light gray in colour with a sandy texture. These rocks were soft enough to break apart in your hands. These signs of hydrothermal alteration all pointed to the history of the chalcopyrite deposit that was mined for copper here in the late 1800s. Along our hike, we also observed dark brownish-red ultramafic rocks, gabbros and sheeted dykes that were part of the ophiolite sequence. The gabbros are late intrusions that were the heat source for the hydrothermal convection cell that would have created the deposit.
Despite a forecast for rain, we had nothing but sunshine, perfect weather for scaling the steep rocky terrain created by these ancient late-Cambrian/early-Ordivician rocks. Visiting this unique and remote landscape is a rare opportunity and we are very lucky to have had the chance to experience it.
Day 6: Gros Morne National Park – Tablelands
Full Day (written by Alicia Escribano)
Wet and windy day – didn’t dampen the spirits of the participants. This day involved a trip to Gros Morne National Park, which included a short hike to look at the exposures of the mantle rocks and layered peridotites of the Bay of Islands ophiolite sequence. Students also observed the melange zone underneath the Woody Point lighthouse at Bonne Bay, as well as the supercrustal rocks along the road exposure. High levels intrusions were then observed along the Green Garden Trail within the Tablelands.
Day 7: Bay of Islands
Full Day (written by Alan Baxter)
Wonderful coastal exposures at Little Port and Bottle Cove. Students mapped the pillow basalts and overlying sediments. They learned how to correlate these rocks across the Cove and to propose depositional environments and emplacement mechanisms for the sequences.
Looked at some of the melange units underneath the Bay of Islands ophiolite. Large coastal sections of apparently intact lithologies, that looked in situ, were discovered to be melange blocks.
The afternoon was taken up looking at the world-class exposures of the Bay of Islands ophiolite, including a cliff section where the Moho meets the Ocean.