From PRB Board
in response to
by
posted on
Jul 04, 2009 03:14PM
NI 43-101 Update (September 2012): 11.1 Mt @ 1.68% Ni, 0.87% Cu, 0.89 gpt Pt and 3.09 gpt Pd and 0.18 gpt Au (Proven & Probable Reserves) / 8.9 Mt @ 1.10% Ni, 1.14% Cu, 1.16 gpt Pt and 3.49 gpt Pd and 0.30 gpt Au (Inferred Resource)
As I posted the map earlier, all discoveries (Eagle one & two, Blackbird one & two, AT12, Big Daddy, Black Thor) were found on the Ultramafic rock band that is narrow in width and stretched from Eagle two at south end to the jv claim block at north end.
The recent Noront news release suggests new zones below this known Ultramafic rock and it could triple the high-grade Ni-Cu PGE Mineralization at Eagle one.
The narrow ultramafic band to which you refer is the edge-on view of what was a very large sill structure. Sills are planar intrusions which take advantage of weaknesses in layers of pre-esisting rock. In this case, that weakness was likely the contact between the gradiorite pluton intrusive to the north, and the older Archean rocks to the south. The upwelling pressures associated with the granodiorite has later flipped the ultramafic sill on its side, exposing a cross section of it at today's surface. But that didn't happen all in one shot. At the time the overturning occurred, significant uplifting also took place, forming foothills, if not mountains. All of the elevated portions, during the last two billion years or so, have been eroded away. That's what exposed the band, the cross-section of the sill.
Here is a major implication of this scenario (if it is correct)....Anything that was north of the present day magnetic high that defines this ultramafic band has been lost to erosion. Anything to the south of the line has been plunged into the ground. When they're drilling down at Eagle 1, they're actually drilling sideways into the intrusion, as it was originally oriented.
In my opinion, maybe 75-80% of the original deposit at Eagle 2/Blackbird has been eroded away. Maybe 70% at Big Daddy. Perhaps 60% at Black Thor. You can actually see some of the funnel shape of the intrusion on the mag maps of the FWR claim, but the central upwelling part has been lost. The whole district has an eastward plunge, so more of the original structure is retained as you go east along the southern rim of the ROF.
Eagle 1 was a conduit, which as Mungall has noted, carried a huge volume of magma, from somewhere, and to somewhere else. Because the sulphide melt had already partitioned the nickel and copper and PGEs and gold, it is reasonable to assume that its place in the magmatic flow sequence places it above a large magma chamber. However, because of erosion, that chamber is simply gone. Yes, as originially placed, it would have been north of Eagle 1, but everything north is missing today. Back to the conduit; Eagle 1 was going somewhere. That could mean another chamber. If Eagle 1 continues on at depth on the same trend as the piece we've found, that could mean significant depth.
Our minds tend to simplify things. We think of conduits like pipes, and pipes are straight. Anything is possible with these structures, however. They zig. They zag. They form little pockets here or there. Or big pockets. They follow the weakness in the country rock. We just don't know enough to predict much more than what I've already described. I repeat, anything is possible.
I'm not trying to dismiss your enthusiasm. I'm hoping to offer you some context for it. Yes, Probe and Noront needed to settle those claim disputes, and it needed to be settled before significant discoveries were made on them. You can understand that with financial disputes, the dispute magnifies with the size of the financial stakes. So, everyone agreed to just settle it, so that unencumbered progress could be made.