80 GOLD AND TIN DEPOSITS OF SOUTHERN APPALACHIANS. 
Several dikes of diabase close to the mine workings strike north-northwesterly across the 
foliation of the schist. (See map, fig. 8.) These are approximately vertical. A small 
decomposed diabase dike east of the Bumalo pit has a northerly strike and a steep dip to the 
east, and a narrow dike of diabase, also decomposed, exposed in the Beguelin cut, is parallel 
to the foliation of the surrounding rocks. (See PL VI. ) In the description of the ore bodies, 
these dikes will be referred to and designated by their width, which is given on the map. In 
the Haile pit, as has been said, the ore has been mined away from the 27-foot dike, leaving it 
standing up as a partition between the two sides of the pit. In the new pit a side fully 150 feet 
square is exposed (PI. IV) . Near the surface this exposure affords a good example of the for- 
mation of residual soil. In the lower portion the dike has an uneven wall, the surface being 
billowed and looking shriveled or folded, much like an elephant 's skin. The larger irregulari- 
t ies are rudely parallel corrugations and indicate the dip of the inclosing schists. The appear- 
ance of the dike suggests that it was intruded when the surrounding rocks were in a plastic 
condition, which certainly was not the case. Along the walls of these diabase dikes the miners 
find a layer of soft, muddy material which they term a " binder," and which doubtless repre- 
sents an outer zone of decomposition. This binder is removed at the same time as the ore. 
It may be that the varying thickness of this decomposed portion has caused the irregularities 
in the surface of what remains, but if that is the case it is difficult to understand why these 
irregularities correspond with the dip of the schist. It seems more probable that the frac- 
ture through which the molten diabase came was influenced by the structure of the rocks in 
which it formed and hence did not develop along a perfect plane, but as an undulating crack. 
A petrographic description of the diabase of the region is given on page 23. 
Where crosscuts and drifts penetrate these dikes away from the ore bodies, there is little 
alteration of the quartz-sericite schist at the contact with the diabase. The schist is baked 
or hardened a little for a few inches from the dike and shows a slight sheeting parallel with 
and close to the dike. Surface waters have been able to follow the crevice between dike and 
schist and have oxidized both rocks to a small extent. The diabase has usually suffered 
most in this respect. Small crystals of gypsum occur in the joints of both rocks where this 5 
oxidation has been moderate. Where the dikes cut the silicificd schist of the ore bodies, the 
changes which they cause are even less marked and are practically negligible. There is no 
noticeable difference in the character of the diabase where it cuts the barren, unsilicified 
schist and where it breaks through the silicified rock of the ore bodies. 
CHARACTER AND OCCURRENCE OF THE ORE. 
The ore bodies of the Haile mine typify the class of replacement deposits previously 
described. They consist of large lenses of altered tuff which has been subjected to certain 
changes in composition. This alteration is of comparatively simple nature, consisting 
mainly of a silicification and pyritization of the porous tuffs. In most cases these two, 
processes appear to have gone on simultaneously, so that although the pyritc is the mineral 
which carries the greater portion of the gold, the degree of silicification usually corresponds 
so closely to the degree of pyritization that it is commonly accepted as a rough measure oq 
the richness of the ore. Soft, unsilicified schist is an unwelcome discovery, while rock so' 
silicified that it will strike fire under the hammer is always looked on as a favorable indi- 
cation. In general, the distribution of these replacing minerals is fairly uniform, producing 
a hard, bluish ore, usually with a lustrous fracture, due to the sericite, and containing dis- 
seminated pyrite, of which much is too fine in grain to be readily seen. Under the micro- 
scope this ore is seen to consist' mainly of small polygonal grains of quartz with swarms of 
minute pyrite crystals, both cubes and octahedrons, scattered all through; sericite shreds 
and occasional fragments of biotite and remnants of a feldspar individual occur between 
the quartz grains. The rock which lias suffered most intense silicification is a fine-grained 
aggregate of quartz and pyrite, with sparing fibers of sericite. 
Here and there the replacement of the original rock has not gone on evenly. Light- 
colored veinlets, occurring either singly or in numbers, closely spaced, probably represent 
