STRUCTURAL GEOLOGY
Please download the General Geological Regional Photo courtesy of OFR 6192 Link Below:

http://johnduff13.myphotoalbum.com/view_photo.php?set_albumName=album01&id=McFaulds_aeromagneticOFR6192

Since this is a rather cold evening, with not much News out on McFaulds, I thought you might enjoy reading and catching up with James Bay, McFaulds Regional Geology…

Below are excerpts FROM OFR 6192 GSC Scott, Rainsford 2006, including above noted Photo, full credits given/detailed in my previous post…

I’ll briefly point out those facts that struck out at me, which may be of importance as Geological Setting Of McFaulds…The first of course is the INDENTOR like feature underlying James Bay Lowlands flanked by Faults…the Second is the merging of greenstone belts of Uchi domain and Oxford–Stull domain under the James Bay Lowland…the third is that the both the Meso and Neo Archean , including apparently McFaulds,were formed without significant imput from adjacent OLDER Terrains… Domains are described as those marginal parts of terrains or superterranes that are thought to have been largely added autochthonously or for which sparse evidence exists (e.g., Marmion domain) to treat them as separate Terrains…..

Let me opine and try to address some of these findings..The first striking finding is that McFaulds appears to be much younger than the surrounding terrains, by about 150 Million Years…autochthonous means of rocks, deposits, etc.; found where they and their constituents were formed, which means Mcfaulds is in the state wherein it was originally formed, and there appears NOT to be any significant imput from Older surrounding Terrains, or metamorphic events.. This would mean that McFaulds forming from “Subduction Zones” can be set aside for the time being…

The Fact that McFaulds is younger than the surrounding area, may mean that McFaulds “grew”/widened “ through cracks on the Earth’s crust wherein new Magma ascended for millennia onto the then surface…This Geological Process is sometimes termed as a “RIFT” …What will be exceedingly difficult, especially at this point with so little Geological information, is what caused these massive cracks in the Earth’s crust…Meteor Impact or Natural Geological Processes or something else…As I stated in previous, the “cause’ of the these cracks, is not really important for the purposes of the known the mineralization processes that followed, since the reaction of the Earth’s Geological responses would be very similar……

Since the evidence of this OFR Report indicates that the Oxford Stull Domain and the Uchi domain merge underneath McFaulds, then continue Eastward to Quebec, may indicate that at some point, the McFaulds terrain was “added on top” to the Oxford+Uchi Terranes…So it seems from this limited Geological data that McFaulds was a separate Domain that ended up on the Oxford Stull Domain, or perhaps a “Rift” extension about 150 Million years after the OSD was formed…

I am/have been in the process of preparing a Geological Hypothesis on the Mineralization Events at McFaulds based on a new Geological Map of this area in December-2007…

IMCO

JD*

Excerpts From OFR 6192

Figure 13.1. (facing page) This map displays a composite of the bedrock geology of the northern portion of the Archean Superior Province in Ontario. Some features to note:-
(1) The merging of greenstone belts of Uchi domain and Oxford–Stull domain under the James Bay Lowland;
(2) A large indentor- like feature underlies the James Bay Lowland, flanked by faults;

In this respect, it is noteworthy that a discontinuous chain of greenstone belts, extending from the Uchi domain, wraps around and joins the OSD, east of the McFaulds Lake belt (see Figure 13.3). Overall, both the Meso- and Neoarchean supracrustal belts of the OSD appear to be dominated by juvenile, oceanic crust formed without significant input from adjacent older terranes .

The eastern extent of the Uchi domain underlies the James Bay Lowland where, from high-resolution aeromagnetic images, it appears to merge with the OSD. The resulting merged greenstone–granite domain continues eastward under the James Bay Lowland on strike with the Eastmain greenstone–granite domain of Quebec.

REOGINAL PHOTO DESCRIPTION

Figure 13.3. Enlargement of Figure 13.2 showing the aeromagnetic expression of greenstone belts of Uchi and Oxford–Stull domains merging and wrapping around the east end of the Island Lake domain portion of the Sachigo superterrane. These domains continue eastward as a common greenstone-granite domain toward the Eastmain domain in Quebec. Location of the McFaulds Lake massive sulphide deposits and the diamond-bearing Victor kimberlite pipe are shown. The age of 2737 Ma for the McFaulds Lake felsic volcanic rocks (Rayner and Stott 2005) in the Oxford–Stull domain corresponds to the age of the Confederation assemblage in the Uchi domain wherein the South Bay Cu-Zn Mine as well as other mineral occurrences.

Domains are those marginal parts of terranes or superterranes that are thought to have been largely
added autochthonously or for which sparse evidence exists (e.g., Marmion domain) to treat them as
separate terranes…

Oxford–Stull Domain
At the northern margin of the Sachigo superterrane, the narrower, ribbon-like Oxford–Stull domain
(OSD) stretches from Manitoba to the James Bay Lowland (see Figure 13.1). In Manitoba, the OSD has
been best studied in the Oxford Lake–Knee Lake area where it includes several assemblages (ages are
compiled in Manitoba Geological Survey 2005) ranging in age from Mesoarchean (2870 to 2830 Ma) to
Neoarchean volcanism at 2722 Ma and detrital zircons in overlying sediments as young as 2707 Ma
(Corkery et al. 2000). Across the breadth of the OSD, there is a predominance of Neoarchean U/Pb zircon
ages derived through sensitive high-resolution ion microprobe (SHRIMP) analyses near the Manitoba–
Ontario border (as young as 2710 Ma) and farther east near the James Bay Lowland in Ontario (2737 to
2696 Ma) of volcanic and plutonic rocks, Neoarchean to Mesoarchean Nd model ages with negative åNd
values, consistent with relatively juvenile crustal growth (Skulski et al. 2000; Rayner and Stott 2005).

The OSD displays some evidence of Mesoarchean mid-ocean ridge basalt (MORB)-like sequences concurrent
with continental magmatic growth within Northern Superior superterrane and NCT margins to the north
and south, respectively. The southern contact of the OSD with the Island Lake domain of the NCT shows
a prevalence of Mesoarchean zircon ages and isotopic evidence for a shared constructive history across
the Stull–Wunnummin fault with the OSD.
At the edge of the James Bay Lowland in Ontario, the OSD includes a calc-alkaline metavolcanic
sequence containing volcanic-hosted massive sulphide deposits at McFaulds Lake, with a U/Pb zircon
SHRIMP age of 2737±7 Ma (Rayner and Stott 2005). This is comparable in age to the Confederation
assemblage in the Uchi domain. In this respect, it is noteworthy that a discontinuous chain of greenstone
belts, extending from the Uchi domain, wraps around and joins the OSD, east of the McFaulds Lake belt
(see Figure 13.3). Overall, both the Meso- and Neoarchean supracrustal belts of the OSD appear to be
dominated by juvenile, oceanic crust formed without significant input from adjacent older terranes except
close to the North Kenyon fault and the Northern Superior superterrane.