
ORE-FORMATIONS 257 

Further down the lode was found to consist of massive sulphide ore— 
an intimate mixture of argentiferous galena and zinc-blende, containing 
5 to 36 ounces of silver and 2 or 3 pennyweights of gold per ton. The 
Broken Hill lode is the largest of the kind hitherto encountered. “In 
the widest part of the oxidised zone it contained payable ore for nearly 
three hundred feet in width, and at the present time (1900) the lode is 
being worked for a width of about four hundred and fifty feet (consisting 
of solid sulphide ore).” 
If this great “reef” really occupies what was originally a cavity 
formed during the folding of the rocks—the crustal deformation could 
hardly have been deep-seated, otherwise the space ought to have been 
obliterated by the crushing-in of the compressed rock-masses. It is 
perhaps just conceivable that, if the folding was a very protracted process, 
ascending ore-bearing solutions may have been gradually introduced, 
deposition taking place Jari fassu with the formation of the cavity. It 
is doubtful, however, if the ore-formation in question is really of the 
nature of a “saddle-reef.” It ought to be added that intrusions of 
granite and diorite traverse the schistose rocks with which the silver-lode 
is associated. | 
It must not be supposed that the ore-formations here 
described as “bedded-veins” are always so sharply marked-off 
from the rocks amongst which they occur, as in the examples 
given. Often enough the ore-bed opens out, as it were, and 
so shades off gradually into overlying and underlying beds. 
In many cases, indeed, it is obvious that a so-called “bedded 
vein” or quasi-bedded ore-formation is merely a schistose 
rock which has been so highly impregnated with ore, that it 
can be advantageously mined. 
It must be admitted that it is often very difficult to dis- 
tinguish between such ore-bearing schists and those which 
have been described (see p. 234) under the head of syngenetic 
ore-formations. Probably not a few of the quasi-bedded ore- 
bodies associated with crystalline schistose rocks are largely 
of syngenetic origin—their original character having been 
more or less obscured by subsequent modifications brought 
about by epigenetic action. Amongst the quasi-bedded ores 
occurring in schists are both oxides and sulphides, but 
particularly the latter— such as zinc-blende, iron-pyrite, 
enaleopyrite, galena, etc. The precise origin of many of 
these ore-bodies, as already remarked, is obscure. In 
some cases they may be the result of metasomatic action, 
and thus replace pre-existing beds. That many of the ores, 
however, are true impregnations and disseminations cannot 
R 
