MINERALOGY OF BLACK LAKE AREA. 
19 
has a brecciated character, and subangular blocks and fragments are 
connected by stringers, veins, or wider bands of dyke material. The 
cementing material in many such cases is not granite at all, but either 
compact diopside or vesuvianite, which has resulted from the pneu- 
matolytic action following or accompanying the granite intrusions, as 
discussed in an earlier section (p. 11). 
It may be noted here that the observations of the writers lead them 
to believe that many of the dykes associated with the chromite, as well, 
perhaps, as some of those cutting the peridotite and other rocks in the 
Black Lake area, which have generally been referred to as "granite” or 
"granitic,” will be found on closer inspection to be composed of compact 
diopside, grossular garnet, or vesuvianite; Cirkel, 1 for instance, in describ- 
ing the dykes of the Montreal chrome pit (Plates VI and VII) says: 
"Another feature of the granitic dykes in the Montreal pit worthy 
of attention is the peculiar colour which some of them exhibit. Small 
dykes have a distinct pink colour, and samples of the dyke granite analy- 
sed showed traces of chromium and manganese. However, as chromium 
with alkali (of the feldspar) gives a distinct purple colour, it is fair to 
assume that the purple colour of the kaolinized granite is simply due to 
the presence of chromium.” 
It is quite certain that the dykes to which reference is here made are 
those composed of lilac vesuvianite, and described elsewhere (p. 51), 
but had it not been for their exceptional colour there would be nothing 
in the description to warrant one in regarding them as anything but 
granite. Many vesuvianite "dykes,” however, as well as all those 
composed of diopside and grossularite are white or pale in colour, and 
so closely resemble aplite that, unless examined individually, they might 
easily be mistaken for such in the field. 
The shattering and brecciation of the ore have been accompanied 
by faulting and stickensiding, and in some cases entire ore-bodies have 
been cut off along the planes of such movement. 
While claiming that the chromite is in the main primary, Dresser 2 
qualifies this statement by adding: 
"Subsequent solution and redeposition may have taken place to 
some small extent; but of this there seems, as yet, to be no certain proof, 
since the small vein-like bodies of chromite, which are occasionally 
found, show no internal structure to distinguish them from ultra basic 
offshoots of chromite-bearing portions of the intrusive rock.” 
The view that there may have been locally a partial re-solution of the 
chromite would seem to be confirmed by the occurrence of deep emerald- 
green chrome vesuvianite (and also of a crystal of ouvarovite) at the 
* Op. dt., p. 27. 
* Op, dt-, p. 90. 
