Noront Resources

Dr. Jim Mungall – AGM

I’m just going to say a few words about the geological model that we’re using to guide our exploration program in the lowlands, and really, it’s a fairly simple conceptual model. It’s the assimilation of iron formation by komatiite. So, komatiite is a magma type which doesn’t form on the earth anymore, but they were relatively common in the Archean , 3 billion years ago. They’re extremely hot magmas which came up out of the mantle, much hotter than magmas that you see in the earth today. Hot enough so that you can take just about any type of crustal rock and chuck it in there, and it’ll melt and dissolve, and it’s the assimilation of other crustal rocks which causes the formation of the ore deposits that we’re interested in.

Iron formations were a fairly common type of sedimentary rock in the Archean, they’re sediments which are unusually rich in iron, either as magnetite or sulphide minerals, or even as silicate minerals. And depending on the flavour of the iron formation that goes into the komatiite, you get different types of deposits. The form of deposit like Eagle 1, which is a magmatic massive sulphide deposit, it’s necessary for the komatiitic magma to dissolve iron formation which is rich in iron sulphide minerals. And when that occurs, an immiscible sulphide melt forms. That means that that sulphide liquid is like a separate magma which doesn’t actually dissolve in the silicate in the ultramafic magma but they’re like oil and water. And the droplets of sulphide melt scavenge the nickel, copper, platinum, palladium, gold and so on from the magma and concentrate it, the same way as a fire assay concentrates those metals in the laboratory. And because the sulphide melt is dense, and it’s immiscible, it forms a separate pool on the lowest point of whatever intrusion you happen to be dealing with.

But we looked for accumulations of dense sulphide minerals at the bottoms of (ultra?)mafic intrusions which represent what’s left of these komatiitic magmas.

In the case of chromite deposits, we’re still looking at the same magma type and in fact we can form both kinds of deposits in the same intrusion but in this case it seems that the key process which precipitates chromite, is the assimilation of silica and magnetite, which are also components of these iron formations. So when you add silica and magnetite to the komatiite, it becomes over-saturated in this mineral chromite, Mg or Fe Cr2O4 . Chromite is a dense mineral and like the sulphides, it wants to go to the bottom, but unlike sulphide, it’s a solid, it’s not a liquid so it can’t trickle down and collect at the very bottom. Instead, it falls to the bottom of wherever the melt reacts (sic?) with the other crystals are forming, to form layers. So we’re looking for layers of chromite on the bottom of flat-lying intrusions, and we’re looking for pools of sulphide liquid at the very lowest points of the intrusions that we’re dealing with.

And the way that we can use this kind of model with the geophysical data which is available to us is to consider how these different types of ore deposits respond to geophysical methods. So the sulphides are very magnetic, the mineral pyrrhotite and magnetite are both magnetic, so we can use magnetometers to detect them but what’s more useful for the sulphides is they’re very good conductors. They’re like electric wire buried in the ground, so if you fly over them with a transmitter receiver arrangement, like an AeroTem system or VTEM system, you can actually detect the presence of these conductive bodies deeply buried beneath overburden. So that’s the third way of exploring for the sulphide deposits.

The ultramafic rocks that host the deposits are also very magnetic, they contain a lot of magnetite and so we can detect large intrusions which may be the host of ore bodies of magmatic sulphides just by looking for big blobs of highly magnetic rock. So we can use magnetometer surveys for that as well.

And the chromite deposits don’t have those same kinds of geophysical responses, they’re not magnetic, and they’re not conductive but what they are is dense. We’re looking at rocks which are 50, 60, 70 percent chromite and chromite is a dense mineral so we can use gravity surveys to detect large concentrations of chromite. And we’ve had some success with that, and that’s our preferred method going forward to find more chromite.