|Figure 1: Fossil Hunting on Bell Island, Conception Bay, Newfoundland.|
The most memorable stop (for me) on a recent McGill grad student trip that took us around the whole of Newfoundland was Bell Island, in Conception Bay. The discovery of iron ore in the late 1800s led to the an industry boom on the island that lasted until 1966 (Bell Island Mining History). We were fortunate enough to tour the Number 2 Mine (now a museum) and learn about the island's history and geology. The thing that stuck with me the most was that the story of Bell Island's mining history was one of pride and more or less, a happy story. This seemed unusual as most stories about mines in the news seem to usually involve accidents, death, or oppression of the mine workers. Our tour guide's father, grandfather, and great grandfather all worked in the mine. Her tour was filled with pride and a conveyed the bravery of the miners.
|Figure 2: Photo courtesy of VirtualMuseum.ca|
The iron ore is found in a gently dipping Ordovician (Bhattacharrya and Kakimoto, 1982) sedimentary bed in the Wabana Fm. This bed was mined out floor to ceiling leaving 40% in the form of large support columns. This ore was mined across the island, following the bed down-dip until the miners hit the cliffs on the north side of the island. Then the miners did something remarkable. They mined vertically down, and then out and, following the bed beneath the bay for miles. Now that the mine was submarine, the ratio of ore mined to support columns was changed to 40% mined, 60% support.
|Figure 3: Iron ore daylighting in the cliffs on the coast. Debris on the right of the photo is shales that were used to close up the mine shafts after the mine was decommissioned.|
|Figure 4: Iron ore bed daylighting.|
Being geologists, we were all asking questions about the nature of the ore. Hand lens examination showed that the ore was made of iron-oxide ooids. This presented an interesting conundrum of imagining the paleoenvironment with conditions allowing the precipitation of iron around siliciclastic sand grains.
We were all curious about how iron ore of this nature could form (especially on this scale). The papers we had on hand offered little explanation for the formation conditions. To add to the riddle I found a piece of ore down by the cliffs containing a shell fossil (Figure 6). Could this creature have been precipitating CaCO3 in an environment that was actively precipitating hematite?
|Figure 6: Oolitic Hematite with fossilized shell|
There is little consensus about the formation of ironstone ooids. Explanations include crystalization-precipitation, a process not unlike modern day calcitic oods, and subaqueous diagenisis of Al-Si hydroxygel precipitates from detrital clay-Fe hydoxide colloid coagulates (Bhattacharrya and Kakimoto, 1982).
Bhattacharyya and Kakimoto  conducted an SEM study of the fabric of ironstone ooids and concluded that the ooids formed from a dissolution and re-precipitation connected with mechanical accretion of suspended particles around a nucleus grain. Replacement of CaCO3 has also been proposed. Nothing I found was very conclusive.
|Figure 6: Inside the mine.|
|Figure 7: Looking out over Conception Bay from our camp site.|
"Bell Island Mining History." Virtual Museum of Canada. Virtual Museum, n.d. Web. 9 Oct 2011. <http://goo.gl/ahSpk>.
Bhattacharyya, Deba P., and Paula K. Kakimoto. "Origin of Ferriferous Ooids: an SEM study of ironstone ooids and bauxite pisoids." Journal of Sedimentary Petrology. 52.3 (1982): 0849-0857. Print.