The Goldfield news. [volume] (Goldfield, Nev.) 1904-1911, 1905-07-14


ovaI-shaped, flared on top like n vene-
tian vase, and evidently as bottomless
as a true fssure vein, while they be-
come more oblong in descent and may
prove in depth to be filed assures. Like
assure veins these pipes open through
all kinds of rocks. The rocks in the
Kimberley region are mainly horizon
tai. The first, or upper, material of the
pipes is called yellow ground, and is
friable to a depth of 20 or $50 feet,
where a stratum of hard blue ground
is met with. Underlying this is the
softer blue ground that constitutes the
milling of all further depths so far
reached, which in instances are about
$500 feet.
The blue ground was first encoun-
tered in the Kimberley mines, and be-
ing unlike anything mentioned in text
Books was named Kimberlite. The %
~stituents of the blue aod yellow ground
are identical, the yellow being simply
blue ground weathered and oxidized.
The ~"country' rocks enveloping the
pipes are mainly lime tufa under a
few feet of red sand, or the tufa may
form over considerable area on top
from 2 to Is feet thick. Beneath these
surface deposits, some 100 feet of dol
critic, then shales or chistose rocks to
a thickness of 800 feet, then 10 to 20
feet of stratum of conglomerate over
lying malaphyre, an amygdaloridal dia-
base 400 feet hick. Then a somewhat
disturbed ferruginous quartzore is met
18th which forms the walls of the low
er workings to present depth of most
of the Kimberley mines. The enclos-
ing rocks of the mines vary c%onsidera-
lily, while the yellow and blue ground
are in appearance and general charac-
ter the same throughout the Kimber-
ley and Orange River regions, as well
as in the district of Pretoria, Trans
vaal. Granite is unknown on the sur-
face in the Kimberley region, while
granite rocks. form the surface country
rock of the famous "Premier, ; the
greatest diamond mine in the world,
situated among other diamond produc-
ers IA miles northeast of the city of
Pretoria. The new district of Preto-
ria, discovered about two years before
the Boer war in search of coal, bids
fair to eclipse Kimberley and Orange
River diamond fields combined. The
Kimberlite (blue ground) is said by
some to be basic eruptive rock, by
others to be a sort of mud forced up
by hydrostatic pressure through the
strata with more or less volcanic en-
ergy.
inally volcanic mud or a true intrusive
ingenious rock, opinion is divided, but
evidences through investigation are in
favor of the latter. Fragments of en-
/ closing rocks are imhedded in the kim
berthe alike in Kimberley and Preto.
TE
ria mines.
CHARACTERISTICS, ETC.
To the optical properties of dia-
monds they owe their great charm and
beauty. The diamond crystal belongs
to the Isometric group, with cleavage
octahedral, and is more brilliant by
artificial than natural light. The octa-
hebron (8-sided solid) and dodecahed-
ron (12-sided solid) are the most com.
mon forms of this diamond, though
found in many others. In any form
form the extreme hardness and ada
mantion lustre distinguishes it from
all other crystals. 1t is the hardest
known substance Oh. 10Y with specific
quality, 3.5. To the Roentgen rays
the diamond is extremely transparent,
whereas glass limitations are opaqua,
This affords obvious means of detect
ing spurious goods.
"Flats" and ''mackles'' are names
given in South Africa to a somewhat
common form of diamonds. The for
mer is a distorted octahedra and the
latter are fiat triangular crystals which
are in reality twins and bear some re-
semblapce to the white sapphires min
ed near Helena, Mont, at the head wa
tiers of the Missouri river.
There are three distinct varieties of
diamonds, viz: the Gem Bort and Car
bonado. Bort is more or less spher-
ical and somewhat harder and tougher
than the gem. Corbonado is a black
massive variety found in Brazil and
usually harder and tougher than the
Bort, and is mainly used for settings
in bits for drilling exploration holes
in the ground in search of water or
minerals, and the process is known as
diamond drilling.