40 TIN DEPOSITS OF THE YORK REGION, ALASKA. [no. 229. 
Specimens of the ore rained in the York region, which were tested in 
this office, gave specific gravities from 5.15 to 6.06. Since cassiterite 
is heavier than most of its associated minerals, it can usually be sep- 
arated from them by crushing and panning. The most satisfactory 
test for cassiterite that can be made in the field is with the blowpipe, 
as follows: The mineral, crushed and finely powdered, is mixed with 
about equal amounts of powdered charcoal and soda, and heated gently 
in the reducing flame. Metallic tin is readily obtained in small globules 
scattered through the assay, but it is more difficult to collect the metal 
into one globule, and in attempting it an unskilled operator will 
usually reoxidize the tin. 1 
Stannite, or tin pyrites, is sulphide of tin, copper, and iron with 
some zinc. Some varieties contain silver, lead, or antimony. Stan- 
nite resembles pyrites and other metallic sulphides, and is not easily 
distinguished in the field. The blowpipe tests are unsatisfactory, since 
it is impossible to obtain a tin globule from it. This ore, when pure, 
contains only 27 per cent tin, and is not mined except in conjunction 
with other ores. It has been found on Tin Creek in the York region. 
ASSOCIATED MINERALS. 
In the York region the most common minerals accompanying tin 
are quartz, tourmaline, epidote, garnet, rutile, fluorite, wolframite, 
magnetite, hematite, limonite, and ilmenite. Of these, tourmaline, 
garnet, rutile, wolframite, magnetite, limonite, and quartz have often 
been mistaken for tin ore. 
Tourmaline. — This is a complex silicate of boron and aluminum. 
In the York region it occurs in slender three, six, or nine sided prisms, 
brownish black and bluish black in color. These prisms are often 
arranged in radiating groups. Tourmaline is distinguished from 
cassiterite by its crystallization and by its specific gravity, which 
varies from 2.98 to 3.20. Before the blowpipe the tourmaline of the 
York region is fusible without fluxing, while cassiterite is infusible. 
Garnet. — In the York region garnet often occurs in massive, granu- 
lar aggregates, which greatly resemble tinstone. To the experienced 
eye they are readily distinguishable by slight differences in color. 
Garnet has a specific gravity from 3.15 to 4.30; in other words, it is 
a little more than half as heavy as tinstone. It crystallizes in the 
isometric system, and never forms elongated prisms. Like tourmaline, 
it fuses before the blowpipe. 
But ilc. — Titanium dioxide, or rutile, occurs in crystals, which in 
hardness, specific gravity, and crystallization resemble cassiterite. 
The crystals, however, are usually slender prisms, striated or furrowed 
lengthwise. The streak is pale brown. This mineral has not been 
found in the ledges, but in alluvial deposits it has often been mistaken 
for tinstone. 
