The Arizona sentinel., 1879-05-24
Orc BIancO and Arivaca.

to the mining districts of Orc Blanco
and Arivaca, was much interested in the
geological formation, and the mineralogi
cal character of that section. The Ari
vaca district is about Sixty miles south
southwest from Tucson and has an eleva
ton of 1000 feet. Tae formation is clay
slate, aud quartz porphyry: the SLATE
predominates in the valleys and low hills
and is strewn in many directions, produ
ced doubtless by lateral pressure, during
the Plutonic Porphyry period. This slate
carries no fossil rests, and appears to De-
long to the azoic, or primitive formation
It is evident the slate is intersected by the
quartz porphyry. This quartz porfhyr'
seldom intersects younger fornaIio"s'
than the palaezoic graywacke iornat'oh'
and therefore this slate is OF older aaIe'
The mineral veins are in this character
of porphyry and run in various directions
forming net work. Many of them crop
at the surface, and can be traced for long
distances, and appear to be well defined.
Wherever shafts have been sunk the
walls appear solid and the veins increase
in width. The matrix of the veins is
generally quartz. In few cases how
ever, Gale and brown spar was found with
quartz. This may be regarded as favora-
bic for high grade ores. The character
of the ores at or near the surface, are
oxides OF iron, manganese, and copper
stains, and in some cases chlorides and
bromides of silver. Galena, iron and cop
per pyrites are found at greater depths,
and give to the ores their base character.
In some instances free ores are found.
From the general character of the ores
there can be no doubt but that they will
have to be treated by smelling or lixiva-
ton, and as they do not contain now
sufficient lead for smelling, and as lead
mines are not found in the district, the
only safe and economical method for their
treatment in my Judgment in the lixlvia-
ton process.
The Orc Blanco District joins the Ar-
vaca on the south. The elevation is about
$500 feet. The country is well wooded
with sufficient water for all mining pur-
poses. The formatian is porphyry, two
varieties of which are plainly distinguish
able, one is called the "Orthoklas," quartz
and consists of felsitic elemen
tary dense matter quartz and feldspar),
with quartz and feldsrar crystals. The
other is syenitic porphyry. The dark
greenish elementary matter conists of
horneblende aad chlorite, with large field
spar crystals, which German authors call
porphyrite The syenltic porphyry fire.
9uently intersec.s the quartz. porphyry,
granite, gneiss, states, &c, in which large
of rock found there is felsite, or petrosi-
lex, or what the miners in Sweden call
" hallefinta;" il is hard stone matter of
a grayish color, quite =, hard as feldspar
with conchoidal fracture. The mineral
veins in this district are frequently found
between these varieties of porphyry.
They are, as rule, large and well defined
and show good ore to the extent of t.eir
present development. At or near the sur
ACE the character If the ore is oxides of
ron and manganese, copper and carbon
ltes of lead. At greater depth, they
show their respective sulpturets, the py-
rites and galenas. There are, however,
some mines which give free ores, but the
general features of the ores are base, and
need to be treated in the same way rs
those of the Arivaca District. Besides
the azo.c or primitive gneiss and slate for.
nations, with their contemporary eruptive |
of porphyry, GRANTEES, diroites |
and syenites, are the transition formations |
with their Gray,0acke states and sand |
stones, silica states and quartz:tes. are |
those in which all kinds of ore are found |
The porphyry eruptions during the azoic |
and transition periods seem to have pro- |
duced great influence in the formation OF
the multifarious veins, and there is no
doubt that the azoic hills in which the
mineral veins are found in Orc BlaIco,
now only wait the sturdy hand of the mi
ner to bring to the surface immense
treasure In this formation are found the
rich mines of Mexico, Peru. and Chile,
which have attracted the attention of the
civilized world for their immense amounts
of gold, silver. copper, lead, &C., &c. The
same may be said Of all the rich mines of
the world. B. SALAzAR.