GOLD DEPOSITS. 71 
decomposition through weathering has taken place along the sides of the dike, a zone of 
alteration is present and is characterized by the softness of the rock, formation of limonite, 
and development along joints of minute crystals of gypsum. But this has nothing to do 
with the dike itself. Moreover, the diabase, with the exception of atmospheric decompo- 
sition, is perfectly unaltered where it cuts either the ore bodies or the barren rock. Little 
or no pyrite is present and no evidence of the action of vein solutions is seen. Such condi- 
tions would be almost impossible if the diabase were as old or older than the ore. The 
distribution of the ore bodies with respect to the dikes argues strongly against this hypoth- 
esis. Instead of being parallel to the dikes, as would be expected according to this supposi- 
tion, they occur only at intervals, separated by lean or barren spaces, and have their long 
directions transverse to the dikes. The ore body at the Colossus mine is said to extend 
several hundred feet away from the dike on each side. In the Haile mine some of the best 
ore has been found at a considerable distance from the dikes. The writer is not aware 
that the ore is richer near the dikes at the Colossus mine; and at the Brewer, mining has 
not been conducted along or on the dike, if indeed a dike is present. Finally, the ore body 
at the Colossus mine is said to be faulted along an unsheared diabase dike, showing that 
the dike is later than the ore. There is also evidence of a fault in the vein along a diabase 
dike at the Wallis mine in York County, S. C. 
At the Haile mine, furthermore, several narrow, decomposed diabase dikes, called by the 
miners "clay" dikes, are cut by and are consequently older than the large dikes which 
are commonly considered to have brought in the ore. It would be natural to expect, 
therefore, that these small older dikes would be converted into ore like the surrounding 
tuffs, or at least would show some effect of the ore-bearing solutions. But all the evidence 
obtainable indicates that these older dikes are themselves younger than the ore. Neither 
where most decomposed nor in the fresh cores, which can be found here and there, is more 
than a trace of pyrite present, and these traces are not ore — so far as the writer is aware 
they carry no gold whatever, even where in the midst of a large ore body. 
It is apparent, therefore, that all these diabase dikes are younger than the ore, and had 
no connection with its formation. 
2. Several facts argue against the theory that increased deposition of ore was caused 
by different solutions contained in the fissures now occupied by the dikes, at their inter- 
section with the ore-bearing channels. Outside the ore bodies there is no evidence of the 
action of solutions along these dike fissures except the slight induration caused by the 
dikes and the later decomposition which has gone on in some places. The distribution 
of the rich portions, as noted in (1), is likewise against this supposition. Moreover, if these 
cross fissures existed when the ore was formed, the ore would naturally extend along them 
for at least a short distance beyond the general limits of the ore body, but such is not the 
case, and the fissures now occupied by the dikes are probably of later formation than the 
ore. Finally, it is an unwarranted assumption that a fracture existing in pre-Cambrian 
time, the probable date of vein formation, should still be a prominent plane of weakness 
when the diabase was intruded, probably in Jura-Triassic time. 
3. Even if it is granted that there has been secondary enrichment of the deposits, the 
relation of the ores to the dike fissures is not decidedly marked and the tenor of the ore 
remains fairly constant for such distances away from these fissures that it seems improbable 
that they have exerted much more influence in the enrichment of the ore than have other 
fractures, crevices, and joints. 
If it is true, as sometimes stated, that the ore within a few feet of the dikes is of lower 
grade than that a little farther away, it is possible that leaching of the gold has taken place 
along the decomposed zones bordering the dikes and that secondary deposition has gone 
on below. There is no satisfactory evidence of such phenomena, however. 
4. The only alternative remaining is that the ore deposition, preceding the formation 
of the dike fissures, is in no way related to them. The only places where increased rich- 
ness in the vicinity of the dikes has been noted is where the dikes cut across about the mid- 
dle of the ore body. But that is just the place where a replacement deposit is apt to be 
