The weekly miner. [volume] (Butte, Mont.) 1878-1881, 1879-12-09
HOW TO MINE.
Some Important Laws Affecting the &C.
c~urrence and the Richness OF Metal.
IiferOus Veins.
n. Y. Mining Record.

/. MetdIliferOus veins occur mostly in dis
turbed and highly-metamorphic regions, where
the strata are tilted, and followed, and meta
morphosed. The fitting and folding are nee
essary to the formation of assures and the
conditions under which m~etamorphism takes
place seem necessary for the subsequent
filling with mineral matter. Mineral veins,
and in the vicinity of more Or less obvious
evidence Of igneous agency. Lead veins
seem to be an exception to this rule. They
are eftet found in undisturbed regions, where
the rocks are. entirely unchanged. The rich
lead mines eS Illinois, Iowa and Missouri are
notable examples, the country rock being
horizontal, fossiliferous limestone of the Pal
aeozoic era.
@. MetdliTerouS veins occur mostly IN the
older rocks. In Great Britain, for example,
no profitable veins occur above the Trias.
This rule, which was regarded as one of
great Importance by the older biologists, is
not so regarded now. There seems to be no
close connection between the occurrence of
metalliferous veins and simple age alone the
connection is rather with metamorphism.
Metamorphism is most common in older
rocks, and becomes more and more excep-
tional as we pass upward. The occurrence
of metalliterous veins follows the same law.
But when the newer rocks are metamorphic,
they are as likely to contain veins as are rocks
of the older series. The netalliferous veins
of California occur in Jurassic, Cretaceous,
and even Tertiary strata but these strata are
there highly metamorphic, and strongly
folded. In Bohemia, also, and elsewhere,
metalliferous veins occur in the higher series.
phillips 10,549).
3. Parallel veins are apt to have similar
metallic contents, while veins running in diff
ferent directions (unless at right angles), are
apt to contain different metallic contents. "
= The auriferous VEINS of California are
parallel to each other and to the Sierras, eX-
cept a few smaller ones, which are at right
angles to these. The reason Of this rule is,
that parallel assures belong to the same sys-
TEN, and were therefore formed at the
same time, broke through the same strata,
and were filled under similar conditions, and,
thefore, with the same materials while fis-
sures running in different directions, unless
in some cases at right angles, were probably
formed at different times, broke through diff
ferent strata, and were filled under different
conditions. Thus, the east and west veins of
Cornwall break only through the Trias, while
the north and south veins break through the
Cretaceous. The auriferous veins of Califor-
MIA all break through the Jurassic they, or
their assures, were all produced at the same
time, viz: at the time of the pushing up of the
Sierras.
4. A change of country rock of o%utcropping
veins is apt to determine some change, either
in the contents or in the richness of the vein.
Nevertheless, there is not that close connec-
ton between the nature of the country rock
and the vein contents which obtains in infil-
trative veins. The reason is, that infiltrative
veins derive their contents entirely from the
wall rock on either side, while assure veins
derive their contents from all the strata
through which they break, even to great
depths, and especially from the deeper strata.
The nature of the surface or country rock is,
therefore, only one factor determining the
vein contents. u
5. Metallic veins are usually richer near
their points of intersection with granite OF
with an igneous dyke, especially if the strata
have suffered metamorphism. This shows
the influence of such heat as is present in
metamoiphism, in determining the metallic
contents.
g. If two veins cross each other, especially
If at small angles, one or both are apt to be
richer at the point of crossing. No sufficient
reason has been given for this law. It IL
probably due to the reaction of water bearing
different materials circulating in the two ifs.
sures.
I. Since the veins are the filling of assures
they are often slipped by each other or b.
dykes By simple untitled assures. If a metal
iissrous vein Is thus slipped, according to thu