Sunday, August 05, 2012

Trotting in the Bog - for Iron Ore (1)

Although the focus of DARC's recent interpretive program at L'Anse aux Meadows NHSC was not iron smelting (unlike 2010), we did take the opportunity of being in Northern Newfoundland to do some searching for primary bog iron ore.

Readers have heard me expound upon natural iron ore formation before :

Finding Primary Bog Ore?

To be clear, what I am referring to here is as I defined 'primary bog iron ore' in my paper 'Adventures in Early Iron Production' (2006):
 " There is considerable confusion among the current generation of North American iron smelt enthusiasts about exactly which material the term 'bog iron ore' refers to. The term has come to describe materials with a wide range of physical and chemical properties, and seems to be applied regionally to describe any iron rich material, not obviously a rock ore, that is found in lumps near water. The term 'primary bog ore' is therefore proposed to describe ... material which:
- is newly formed
- is a product of the chain of iron rich bedrock, leached by tannic acid bog water then deposited via the action of bacteria along the margins of small streams immediately below the source bog. "
This is hardly the only deposit method for a natural bog iron ore. The sheets of clay like material that forms in plates on the bottom of shallow lakes and bog pools being another type widely used historically in places like Sweden. In earlier visits to the L'Anse aux Meadows area, I had spent a little time 'prospecting' for primary bog iron ore. One wrinkle is that gathering of any kind of raw materials is *not* permitted on Parks Canada grounds.

One of our group is a geologist, so had an interest in looking at the actual chemistry involved in iron ore formation. To that end, we did secure permission to take some water samples along the course of Black Duck Brook. This is the small stream which cuts down from the upland bogs through the centre of the LAM archaeological site.

Finding a viable deposit of primary bog iron ore is 'easy' - but very time consuming. The physical arrangement of the primary elements (rock, bog, stream) have to be just right. The best way is to wander along the course of a stream, every so often reaching down the side of the bank and running your hands along the interface between the upper vegetation layer and the sterile gravel soil underneath. The bacteria involved is anaerobic, so if the organic layer is too thick, you can not easily reach the deposit locations.  At LAM this level is down roughly 12 - 18 inches. Your best chance is along the outside edge of a bend in the stream flow.

When I was part of the week long research group for Parks Canada in 2001, archaeo-metallurgist Arne Espelund had shown us some tips for finding possible stream edge deposits. One had forgotten was 'check just downstream of a spruce close to the bank'. Staff interpreter (and the blacksmith in the Norse Encampment) Mark Pilgrim would remind me of that tip later.
'Some lovely filth down here...'
For the exploration at LAM itself, we would start where the brook is cut by the entry road to the Visitor's Centre. The road roughly runs along the height of land point, marking the flatter land containing the bogs, and the start of the downward slope that forms the bowl running down towards the archaeological area (on the shore). This line is also roughly the original treeline of 1000 AD. Black Duck Brook curves back and forth across this descending bowl of bog, which is dotted with small clumps of stunted black spruce.

The image above shows Marcus and myself searching along the creek bank, just down from the road. (At the end of an interpretive day, so we are still in VA costume!) The material we found along the upper reaches of the brook was a dark, almost black colour. I had been told in 2001 by Espelund that this was a sign of slight amounts of Manganese present. Breaking open a nodule would reviel the red iron oxide layers.

The joke involved here is that Marcus is just about to check a spot where I had found the first traces of a bog ore deposit. There were some small fragments at that location, most about the size of a peanut. As he had never collected the material in the field before, he was a bit uncertain of just what to look for. I had moved along another 3 metres or so further downstream to check again. Marcus would hold up a couple of small pieces, "Is this it Darrell?". Meanwhile, the second spot proved excellent. "Yea Marcus, it looks like this", says I, holding up a lump about the size of my fist! Moving another 3 metres down further and the deposit tapered out yet again.

The lesson there is that the exact conditions required for a thick deposit of primary bog iron ore are very specific. There is a combination of the conditions within the bog itself, then some variable of distance, elevation, volume, motion within the draining stream. I think I might be developing some kind of visual and experiencial feel for this, but with only a few attempts at prospecting (and finding!) bog ore, this might be an illusion.

The next day, Mark took me off to show me the 'secret special spot' where he gathers small amounts of ore to show to visitors to the site. Guess where?

Note to my readers:
Just home from DARC to LAM 2012 - and off in a few hours to a week at Goderich Celtic. My internet connections, and available time, has been spotty at best. I do have a number of pieces in mind based on the LAM trip especially. Bear with me and I will get some new materials here as quickly as I can manage.

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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