The Goldfield news. [volume] (Goldfield, Nev.) 1904-1911, 1909-10-02

Development work has now given a better understanding of the
geology of the Goldfeld district, and with this more intimate knowl-
edge of the formation and the origin of the n deposits, has come full
proof Of the persistency of values with depth, and to a certain extent
a reconstruction of theories and mining endeavor Ore bodies of
almost inconceivable extent and richness have been opened in entire
y unexpected places, but these surprises have shown more conclusive
" the wonderful possibilities Of the naturalization area Nearly all of
the important ore bodies yet discovered in the Goldfeld district are in
the dacits formation, and the more fully the mining operators r.
coming to realize that fact, the greater effort is made to confne ope-
rations to that zone. In many leases where hundreds y ieet Oh oe-
yelopment has been done in the everything andesite with disappointing
results, operators ire sinking to greater depths to get through
the andesite and into the dacite, which they have learned is almost
invariably the cradle OF the ore.
AS is set forth in Frederick L. Ransome's recent report on the
geology and ore deposits of Goldfeld, description of the shape Of
the Gold6eld or bodies is difficult because the r bodies themselves
arr inherently vague The pay shoots a IS a rule nave nothing TO as
tmeuish Them structurany from barren ledge matter. They have
10 boundaries other than the invisible limits beyond which the assay
ers returns show stopping to be Improbable. The change from very
rich ore to practically barren ledge matter may take place within a
very short distance, but it is nearly always a graduation, not a definite
boundary. The size of pay shoots, and to some extent their shape Also
densnd. therefore upon conditions which determine the grade of ore
that can be proftably treated at any given time. If the economic
h,,,da,v between ore and waste be placed at $25 a ton, a given ore
body will have a definite shape and size. If the limiting value be
re.aced to $40 a ton, the same r body will be larger. We may as
same that its shape will be somewhat similar to that defined by the
m.ner value. but beyond this we cannot go without such detailed and
systematic exploration of pay shoots as is hardly ever practicable IN
this district.
Pay Shoots Show Many Freaks.
4In general the pay shoots are fully as irregular a S the lodges
vth wbiah hev r. associated. Some of them r roughly eq,n,men-
siosal masses others n lenticular, some are approximately spindle
shaped, with the large axis nearly vertical, and still others ae tabular
or ulatelike although such sheets of ore r often curiousy twisted
! warped. The striking features of the or bodies a $ a whole is the
absence OF, rather than the approximation to- any regularity u form.
While many Of the pay shoots conform to n tren u Tn enclosing
ledge, others do not.
Although metosomaic replacement has played no small part in
the formation Of the oe deposits IS a whole, that process the
ores themselves are very closely controlled by assuring. Such m
plete replacement Of rock by masses of sulphides as takes place in
some imestones, q replacement which in that rock may extend for
oons;dsr.hle distances from the assures supplying the active solutions,
is NOT found at Goldfeld. There assuring, 10 relative solubility II
chemical instability Of the country rock has determined the shape
Of ore deposits. The irregularhy OF the bodies, like that OF the