The Central Nevadan. [volume] (Battle Mountain, Nev.) 1885-1907, 1901-11-07
SECOND STAGE.

around Lander county, Nevada.
SECOND STAGE.
coNsoLID ALTON AND mETAnoRpHIsm.
During and after the subsistence of the
strata thus formed, and when gradually
exposed to increasing heat and pressure
the pressure of the original moisture ae-
CELEBRATES chemical activity, and new min.
eral combinations would form within
the various strata organic matter where
present causing a continued deposition
OF metallic sulphides through the mass.
The formation Of various silicates and
the gelatinizaton of the silica when
abundant in minute divisions
Most of the amorphoses acidic rocks
lwould become plastic and when earth
movements occurred occasioning fault
ing and folding with assuring and crush
ing Of harder strata the most plastic
portions of the rocks would move toward
the open spaces, the still more mobile
silica would carry with it much OF the
sulphides in suspension and solution.
Under the conditions then prevailing
the fissures caused by dynamic action
would be filled largely by the silica ex.
uding through the pores of the rock,
and also by other silicates and the crush
ed rock fragments would be recemented.
Beds Of gravel and even conglomerates
have under such stress and movements
lost their physical features and become
homogeneous tufts which have been con-
solidated into greenstones and fossilif
erous lmestones transformed into crys
talline marbles Superhcated steam
would form and exert active influence on
these processes, but it il not probable
that any bodies OF hot circulating water
from below could exist at great depths
the best evidence OF which is that the
deeper seated assures forming at this
and subsequent stages carried not hot
solutions but mineral matter in fusion.
Hot waters may however have been act
i've but they would be derived from the
assures reaching to considerable depths
and such waters as we'll as those Of low
er temperature may have carried silica
ms well as metallic salts into assures
these to be precipitated and solidified
A definition of the term secondary quartz
or silica often used seems necessary. The
term refers to quartz or silica formed
subsequent to and within an enclosing
rock OF whatever nature. Its general
formation results from exudation, inil-
tration Of silica from surrounding rock
or from soluble rock being replaced by
silica which takes place precisely in the
same manner as when buried tree is
petrihed. The term vein quartz is mis-
nomer. What is called is simply silica
which is nearly pure and has crystalized
slowly. 1t is found under all conditions
and everywhere among the metamorphic
rocks while hornstone or flinty silic, or
as some of the loc,l prospectors terms it
jasper, also forms the gangue Of many
metaliferous deposits. Not only the sed
imentary beds but the igneous masses
alternating with them would partake Of
the general metamorphism but the latter
in different manner and degree chiefly
owing to the fact that they carried less
free silica than the sedmentaries. In
most instances metamorphism would OBJ
literate all fossils in the sedimentary
rocks and their ore deposits specially
through the capitalization OF the lime
stones and only rare ms ances would oc-
cur in which stratifcation previous to
or during the first stages of subsidence
had rendered the fossils resistant to
physical and chemical forces and thus
in condition to be ultimately recognized
Under the conditions affecting the strata
during the second stage concentration
of metaliferous minerals would occur in
many sedimentary beds and their asso-
ciated igneous sheets and specially at
the junction of an igneous body with
sedimentary bed, shales and states would
be impregnated with metallic sulphides
and their compounds. Limestones would
take up magnesia and become dolomite
and limestones and dolomite both barren
and auriferous would be frequently
changed into quartz rr aphynites IN
which the latter occurs predominately
in this section by replacement. The re-
sultant ore deposits find their typical
representation in many large lodes in the
Shoshone and Toiyabe ranges running
parallel to each other especially 10 the
important groups of auriferous beds and
associated assures composed of the great
mineral zones and deposits in and
through Lander county and central Ne
vada. Fissures opening both in the ig-
! neons and sedimentary rocks would be