Other
names have been connected with other claims around Turquoise Hill, but
some of these claims are said to hare lapsed through want of assessment
work. Litigation due to claims dating back to a Spanish land grant of
1728 has tied up the development cf many of these turquoise deposits,
especially the Tiffany mine. A decision of the court has ruled that
some of the deposits lie outside of the Spanish land grant, but there
is still some question about others, and development is accordingly
being delayed. Active operations have been suspended at the Tiffany
mine for several years, but assessment work has been kept up by James
P. McNulty, superintendent, for the American Turquoise Co. of New York.
The workings consist of numerous pits, open cuts, shafts, tunnels,
drifts, and stopes. Some of these openings are ancient, and old stopes
have been encountered in the modern tunnels. Two of the larger tunnels,
450 and 225 feet long, respectively, have been driven within the last
year or two. They were started about 3C0 feet east of the company's
camp and about 195 feet apart, and were driven in a north of east
direction, connecting with shafts and other previous workings.
Crosscuts were made from them along promising cross veins. The depth to
which the ancient workings had been carried could not be ascertained,
but was evidently as much as 100 feet, if not more.
The
rock encountered in the workings is probably all monzonite porphyry,
which presents different aspects according to the amount of alteration
it has undergone. The less altered rock is dark speckled gray and very
tough, and that which is more decomposed is light-gray to nearly white,
with white spots. The following minerals were observed in a thin
section of the less altered rock: Ihenocrysts of plagioclase and
orthoclase, much clouded with kaolin; abundant epidote; a very little
biotite, magnetite, apatite; and abundant patches of calcite. The
groundmass was also clouded with kaolin. The epidote is secondary and
probably formed from augite. Apatite occurs rather plentifully for that
mineral in stout prisms and laths.
The
rock has been strongly fractured and jointed and decomposition with
kaolinization has been extensive along some of the joint systems.
Turquoise has been found in veinlets, seams, and segregations, filling
these fissures, joint planes, and fracture zones. The mine workings
have followed two sets of veinlets of turquoise striking north of east
and west of north with steep dips. Smaller branch veinlets were found
to extend from these a few feet into the surrounding rock. The
turquoise-bearing streaks of badly decomposed rock are many feet thick
in parts of the mine. A few veinlets of quartz and seams of limonite
stain are associated with the decomposed rock. The greater part of the
turquoise occurs in seams and veinlets but there are some segregations
in nodular masses in badly fractured and decomposed rock. There is also
a tendency to lens and nodular structure in some of the streaks of
turquoise. Ihe turquoise seams range from a small fraction of an inch
up, and some an inch thick have been found. The rock in the tunnel and
a drift about 40 yards east of the turquoise-bearing zone is stained
blue and green with copper minerals.
The
best turquoise from the Tiffany mine has a fine dark sky-blue color
with an even texture. It is about 6 in the scale of hardness, and has a
smooth to conchoidal fracture. Pale-blue and greenish-blue turquoise
also occurs. Asa rule the best color is found in small seams
