Custer chronicle. [volume] (Custer City, Black Hills, D.T. [S.D.]) 1880-1890, 1885-12-26
Banca Tin Mines.

The cassiterite of Banca occurs in thin,
irregular veins in granite; in assures IN
the adjoining sandstones and quarzltes
in the unexpectedly d~i,integratcd
rocks, which everywhere cover the
granite; ana in the old river valleys.
The valleys are cut N the granite, their
beds are Of compact cay in quartz or
mica predominates, according to the
nature of the adjacent rocks. The strata
carrying the mineral rest upon the clay
bed, and have evidently undergone "a
species Of natural concentration, the
feldspar being changed to clay and car
ried away, and the cassiterite deposited
the larger grains near the valley-origin.
and the smaller further and further
down stream as their size diminishes.
Above the mineral bearing strata are
Alterations Of clay and sand, and finally
a black clayey or sandy soil in which
the modern river flows. The total ihick-
ness of the deposit rarely exceeds ten
metres, and the strata containing the
tin averages $40 $40 metre.
The minerals associated with the
cassiterite are quartz, clay, tourmaline,
mica, manganese minerals, sometimes Il
little gold pyrites, and menaccanite, and
in II deposite only %woIframite.
The deposits have been very carefully
mapped, and the Typographical work
has been accompanied by ~soundings,
from which the values of the deposits.
per square metre of deposit and per
cubic metre of earth removed, have
been deduced.
The soundings have proved that the
valleys are very far from being equally
rich, that there is little chance of sue
cess in the valleys ''ot yet exploited
and that the moment Is not far distant
when it will be necessary to mine the
stock-works which gave birth to the
a%lluvial deposits.
The mining is entirely done by Chi
nese, and is divided into annual tasks,
because this permits the most advan-
tageous use of the rainy season for
washing the mineral. The men, in com
panies proportional to the allotted
years task, work Immediate
~ after the Chinese New Year (Febru-
ary.l \ dixie is constructed up the river,
and the water is carried along the TANKS
of the valley by two canals. A third
canal is dug as deep as possible to re-
move the waste. When the deposite
has drained dry, a mark is made ON the
surf zee to show the intended limits OF
the years work. the vegetation is burn
ed, and the running waite: brought to
soften the earth, aud facilitate its re-
moval into the excavation Of the pre-
ceding year. When the first metre OF
soil has been removed in this way, the
water Is confined to wooden ~sluices, and
a dixie built between the two excava
tons; the earth is then raised in
baskets, thrown into the s%.uices, and
carried over the dixie by the water.
After the removal of the three upner
metres, over the entire years allotment,
the deposit is divided into small por.
tons which are in succession exploited
from top to bottom. The sterile earth
is simply thrown back into the neares,
excavation until the mineral is reached
The mineral is carried to the surface in
baskets suspended from each end of a
shoulder staff, and is there sifted 10
separate the coarser gravel. and washed
in rude sluices. The settings are re
washed in troughs, and a short time
before smelling are again washed.
The ore is reduced by charcoal with
out lux, on a rectangular hearth of
quartzose clay, set against a slightly
higher wall. The hearth proper il
semi-circnlar, and connects in iron.
with an exterior basin, the ,uyere 9
q little higher than the tap-hole, a. d
the blast is furnished by a very print
tive doub'e-actinc p~iatol.hei'oas