The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1918-05-02
Features to Be Considered in Deter
mining the Valuation of Prospect

VI q ! IOSPCN>
post or the outcrop of prospect pla,
so important a part 1t seems advis.
able that few suggestions along thi,
line be mentioned
In practically all cases the vein oil
ore body is made up of different rocks
and minerals than that of the country
rock surrounding 1t. This being the
case, 1t usually has different colol
than the country rock, which differ
ence of color can be noticed at a
distance when not apparent at short
range. Also the vegetation covering
the district may have a snghtly diff
ferent shade where 1t grows on OF
close to the deposit from that growing
on the country rock.
One of the most common indications
Of outcrops is the different rate OF
weathering of the country rock and
the rocks or minerals making up the
outcrop, due to the difference in COM
position. For example, a thick, hard
slow weathering quartz vein in con-
tact -metamorphia deposits will appear
after long weathering as small ridges
or knobs above the general level of a
softer, quicker weathering country
rock, and can be traced very easily
along its surface.
Where the minerals making up the
deposit are more easily eroded than
the country rock surrounding it, the
reverse Is true, and instead of ridge,
la depression or gully marks the de-
posit.
Some of the geological factors which
have more or less influence on the val
uation are surface indications, such as
the commonly known iron cap" iron
stained, honeycombed vein matter or
heavily iron stained disintegrated gos-
san. These indicate that the vein
matter before erosion contained iron
as pyrites or in some other form,
with possibly other valuable minerals
upon weathering these broke down. the
Igangue being carried away Chemical
ly), stained the outcrop the character
istic iron rust color. Since most OF
the large mines of the world have
been found under or as extensions of
outcrops so colored. the prospectors
look very favorably upon these fac
tors as good indications of mineral.
Likewise If the iron stained disin-
tegrated is in contact metamorphic
deposit, 1t indicates that there may
have been values of more easily leach
ed metals present, such as copper.
which were leached out as the outcrop
Weathered and eroded, carried down
in solution and redeposited at a lower
level. The concentration of values
known as a zone of secondary enrich
ment and this as accomplished by
this action produces what is common
ly part of the deposit where the best
values are found usually. This zone
OF secondary enrichment extends to
the permanent water level, and the
depth and values found in 1t depend
not only upon the values which were
present in the original ore body, but
also on the efficiency of the action
which accomplished the concentration
of values.
Another good indication for copper
deposit Is surface showing heavily
stained with copper carbonate. This,
like the above, may reasonably be as
sumed to indicate that the values in
copper viii improve with depth. The
stain indicates that copper is present
and was probably originally present in
the form of sulphides which have wea-
thered to carbonates or some other
soluble form. These soluble copper
salts are taken up in. solution in the
same manner as explained above.
Below the permanent water level is
the zone Of unaltered primary sui
phides, where the copper minerals exist
as they were originally deposited, and
therefore are usually of lower value
than the enriched secondary sulphides
of the deposit. For this reason the
distance from the top of the secondary
sulphides to the permanent water level
is important.
Phyllite schists, as found In and
around Jerome and Humboldt, repre-
sent another form of outcrop below
which copper in commercial qualities
is found at depth. The same theory
of deposition applies to these deposits
as for the above mentioned deposits.
except that in some of these there
are found patches of primary sulphides
above or mixed with the secondary
sulphides. This Is due to the fact
that the solutions carrying the copper
values down passed through the
cracks of the schist and did not come
In direct contact with the primary
sulphides found in these patches. In
this way they We're not acted upon
by the solutions, but remained in their
original form. 1t will be seen that
deposits Of minerals such as copper, |
which are easily leached and precip-
tated out of solutions at a lower |
lepth, thus being concentrated and |
orming a zone of secondary enrich |
nent, are looked upon as better risks
han deposits Of low-leaching min
rails, such as gold. The only concen-
ration of values which takes place