Sierra County advocate. [volume] (Kingston, N.M.) 1884-1960, 1894-04-06
KINDS OF ROCKS IN WHICH
GOLD PRINCIPALLY OC-
OURS.
ARTHUR LAKES, LATE PROFESSOR
SCHOOL OF MINIS, colo.

SCHOOL OF MINES, colo.
Apart from ITS occurrence il
fragmental placers, gold favor
more especially the crystallix,
rocks, though it is occosionall,
found in others OF a fragmenta
and non-clystslizs structure. These
crystallixe rocks have all passed
through q certain amount Of heat
hot water and chemical action
Some OF them such as lavas and
porphyries, are of true molten.
heat origin; others, like quartzites,
marbles, schists and gneisses, have
passed through a less excessive
heat, an squeoigneous heat, which
has however changed them into a
crystalline condition. Unaltercd
rocks such as common limestones
and shales, are not commonly favor
ties OF gold. In unaltered sand
stones, gold is sometimes found,
because these are formed of the
debris OF older crystalline rocks
bearing gold; they are consolidated
gold bearing iron sands. In coarse
conglomerates, too, gold is often
found, for these are only gold
bearing placers, consolidated, and
in some cases, as In California,
protected from being washed away
by cap of lava. Limestones be.
ing of marine organic origin,
would not be likely to sontain
gold, and shales which often repre-
sent the consolidated mud of the
bottom OF the ocean, would not be
either likely TO carry gold, unless
it were in the finest state of
division, because these rocks by
their origin, far out at sea, and in
deep water, would not receiye
much g0ld-bearing detritus, from
mountain ranges or other gold
bearing rocks. OF course, under
certain circumstances, when either
OF these rocks are penetrated by
eruptlve rocks, or by quartz veins,
gold is likely to be found; bu, in
these cases, nearly ALWAYS, meta.
morphic action will be found to
hava taken place, and the lime
stone is considerably altered, some.
times into marble, and the shale
into states. Thus the old creta-
csous sbales, sandstones and lime.
stones of California are gold bear
ing, because they have passed
through an ordeal Of heat and
mstamorphic action.
In Colorado, apart from the
plaeers, the gold so far discovered
is confined to the crystalline rocks,
these are GRANTEES, gseisses, schists,
etc, quartzites or altered sand.
stones, and ingeoas eruptive rocks,
such as perphyriss, diorites, etc.
1t may be, that new attention 10 80
much directed to gold. some OF
our beds OF hreccis, and conglom-
crate, especially those capped with
lava. ss in the southern part of
the State, and in New Mexico, will
be found on examination to be
gold. bearing. Some sandstoncs,
too, may prove auriferous, and gold
may be found IN many rocks and
places, where 1t was hitherto but
little expected. At the same time
1t is observable that our lime
stones and shalss, have so far
proved unproductivs.
Il the I.eadyille and Aspen
regions, very little gold is found in
the deposits in the limestone,
which have 30 long and 30 vastly
been exploited, nearly all ore on
these that is merchantsble is silver
and lead. The few gold deposits
of the Leadville REGION are in
great dykes and extensive sheets
of quartz porphyry, such for ex-
ample ss the Antioch mine, which
is wide open quarry In huge
mass of porphyry impregnatsd
with free gold. The gold mines OF
Breckenridge, South Park, are in
rotten dykes OF porpnyiy. YHR
celebrated DeLsmar gold mine OF
Idaho state, is in a dyke OF por-
phyry, and so several gold mines
in Arizona and throughout the
West. In fact it is fair to say
that in the West our gold is con-
tanned in quartz veins and granite
rocks, or else in more or less rot
ten, decompossd dykes and sheets
OF ingenious rock or porphyry.
Those that occur in quaItIItes,
such as the gold at ouray and
Red Cliff, in saverneus deposits,
are rather exceptions, and even in
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