Finding Primary Bog Ore?

This is a response I drafted for the ArchMetals discussion list (where I many lurk and post infrequently). The original question was a request for some advise on how to find primary bog iron ore - in Ireland.

My experience on trudging through bogs is limited. A couple of days in Newfoundland. A lot more searching around middle Ontario without a lot of luck. A lot of talk about sources in Denmark with the smelting enthusiasts there.

Now, what I know about this I learned from Arne Espelund. The comments here are based on the physical geography of 'Mid North' Canada - which is likely much different than your situation in Ireland! Forgive me for this more practical advise, this will certainly not be given in the language of geologists.

In Newfoundland (and on the Canadian Shield in the Mid North) the organic top layer is relatively thin. The bog ore accumulates in the boundary between this top organic layer, and the sterile sub soil underneath. In the places I have searched, the boundary was from 12 - 18 inches down from the surface.
First thing to look for here is a chain of iron bearing rock with shallow upland bog pools over it. Then you find a small stream that empties out one of those bogs, ideally with enough drop in elevation that there is a 'babbling brook' kind of effect to tumble the water (introducing more oxygen). Then what you do is reach down along the edge of the bank, where the water has eroded the top vegetation layer away. If you run your hand along the boundary line, you can feel lumps of the accumulated bog ore. The stuff feels about the consistency of a hard window putty, or quite hard clay. At first you think its gravel, but it does not cut into your hands. The pieces I have gathered from sizes ranging from about pea size to some about the size of a dog turd. The amount of ore accumulated along a given bog and stream combination varies significantly. One stream I followed had only small traces over a kilometre of checking - then in one section of about 10 metres I found enough to gather two 20 litre pails worth in about twenty minutes.

Primary Bog Iron Ore, sample from St Lunaire, Newfoundland (after roasting)

There is no doubt that this is just one of several types of deposited primary bog iron ores. I did find a small amount of a form of 'lake ore' along the margins of larger bog pools down at the southern end of Newfoundland as well. This is maybe more like the stuff that you might find in Ireland?
One note of caution here! I was on my own, and at one point lost my balance while leaning over on hands and knees at the edge of a pool. I put my arm out to catch myself - only to find my hand quite rapidly sinking down into the goo. With images of Ancient Irish 'Bog People' flashing through my mind, I gave a massive jerk to throw my body back away from the water (at my chin by that point). Obviously I didn't end up a discovery for some future archaeologist, but it was a near thing. I keep to stream deposits now.

One other tip (blame Arne). You can roughly check the relative purity of the bog ore in the field - by eating it! Take a small (half pea) size piece and put it in your mouth. As it dissolves, the iron oxide component will turn into a fine powder and wash into your spit. The organics (like bits of grass) and most importantly the silica, as sand, will remain. By comparing how much sand is left from the starting lump, you get at least a rough idea how 'pure' the sample is. Not perfect to be sure, but good enough to keep you from hauling out kilograms of ore that later proves to be mostly sand.

Readers (who have not seen it) might also be interested in our work here to develop a bog ore analog. We are mixing powdered potters iron oxides with sand and flour (as a binder) to create a good working material. We have been able to match our mixes to roughly duplicate specific natural primary bog iron ores. (Our focus is the Viking Age smelt at L'Anse aux Meadows, but we are working some 3000 km away in Central Ontario.)

Table of Ores Used
L'Anse aux Meadows Smelt - Ore Analog