About 4,000 feet south from the Imperial lode there is a mine of unusual
character and interest, called the Tiptop. Originally a silver mine, it
is now producing a high-grade copper ore, which is being shipped to
Swansea, Wales.
The Tiptop was discovered in 1890, by the strong outcrop of an ore
shoot. The country rock on both sides of the vein is quartz porphyry,
similar to that inclosing the Imperial lode. The ore occurs along a
fault plane, or rather a series of parallel faults, as the result of
substitution of ore for the original rock. The faulting of the rocks has
resulted in an extensive crushing and breaking up of the porphyry along
the line of fracture, exposing large surfaces of rock, thus facilitating
the deposition of mineral. As mentioned above, the faulting seems to
have consisted of several fractures, nearly or quite parallel, between
which the rock was crushed or ground to powder. In places this ore body
would seem to possess well-defined walls, but moving in either direction
along the strike of this zone the “wall” proves to be simply a faulting
plane, beyond which ore again occurs. The result of these parallel
fractures is to give to the deposit an appearance of banded structure,
like that sometimes noticed in simple fissure veins. This apparently
banded structure is entirely due to the planes of displacement.
[Illustration: _CROSS SECTION
OF
TIPTOP MINE_]
Doubtless this faulting extends to great depth, though the
mineralization is not continuous along the surface for more than 150
feet. At some distance, however, and in line with the strike of the
displacement, other ore bodies appear. The ore body where the discovery
was made is heavily mineralized with iron oxides, of red, yellow, and
black colors.
Much of the original rock has become silicified and bleached to snowy
whiteness in the lower part of the deposit, but such masses contain only
finely disseminated iron pyrites, low grade in silver. The once
sulphuretted ores are so thoroughly oxidized in this surface deposit
that they are very porous.
The ores carry on an average about 30 ounces of silver, and for the most
part are very free-milling. At the time of my visit an estimate of this
silver ore on the dump and in the mine placed its value at,
approximately, $20,000. In one portion of this rather remarkable ore
deposit considerable quantities of native sulphur occur, associated with
a brownish iron oxide and silicious gangue material. As depth is
attained the oxidation is less marked, and at 80 feet has apparently
given place entirely to sulphuretted ores and silicious rock, low in
silver.
The strike of this shoot of ore is north 50° west, dipping northeast at
an angle of 70°. At the depth of 65 feet below the croppings, in sinking
a winze, which in its downward course follows a slip northward but is
vertical as compared with the dip of the vein, a bunch of high-grade,
partly oxidized copper ore was discovered. Further development
discovered other pockets or bunches of copper ore carrying usually about
15 ounces in silver per ton. When a depth of 120 feet had been reached a
crosscut tunnel was run in 235 feet. The course of this tunnel is north
5° west. The face, however, had not reached a line representing the dip
of the surface shoot. The tunnel has been connected by winze with the
upper workings, and considerable other development accomplished.
By means of these workings the peculiarities of the mine have been
exposed. The series of faults which have resulted in the deposit of a
considerable quantity of silver ore have been accompanied by another
series of fractures which, while independent of the former, were,
perhaps, contemporaneous. The second series exhibit no parallelism, but
strike in various directions. Along these fault planes occur bunches of
copper ore, principally variegated pyrites (bornite), chalcopyrite, and
a black “earthy” sulphide, having a shining streak, not sectile,
probably a variety of copper glance.
These ores are sometimes associated with iron sulphide, but most of this
class may be easily sorted. One class of ores occurs intermingled with
the gangue containing about 15 per cent copper. This ore can be
separated on any concentrating machine such as a jig, the resulting
product being high grade. The ore shipped to Swansea has averaged over
33 per cent copper and 15 ounces silver per ton.
[Illustration: _LONGITUDINAL SECTION OF TIPTOP MINE
LAVA BEDS DISTRICT SAN BERNARDINO CO._]
The Tiptop consists of two claims. The easterly one, the Kenton, has
little or no development, though copper carbonates have been discovered
on the ground. All of the workings of the Tiptop that are in copper ore,
it should be remembered, are in the country rock on the foot wall side
of the series of faults in which the silver ore occurs, and no drift or
crosscut had been run into that zone below 80 feet from the surface. The
face of the drift on the third level had exposed about 6 feet of good
ore at the time of my examination. The drift at that point was 160 feet
from the surface. It is not likely, should a crosscut be run under the
silver ore shoot from the lower levels of the mine, that oxidized ore
will be found at that level, but it will be interesting to know what
sort of ore may be found there. Indications of copper on the surface are
very slight. In a few places stains and thin seams of copper carbonates
occur in the fracture joints of the country rock, but there is nothing
to lead one to believe that ore lies beneath that will bear shipment to
Europe and return a handsome profit to the owners of the mine, yet such
is the case.