YORK TIN REGION. 147 
prospecting was done that year, enough to show that the tin ore occurred in a much meta- 
morphosed acidic dike. The property was bonded, but reverted to the owners the next 
year (1904). During 1904 and 1905 prospecting continued, several more dikes carrying 
cassiterite were found, and several veins in the limestone were discovered. 
Should the lode deposits be shown to carry sufficient values to pay for exploitation, the T7 
will have many advantages over placer deposits, for they can be operated the entire year, 
while placer deposits can be worked only during the short open season and .even then 
there are frequent delays and inconveniences from storms, floods, lack of water, freezes, 
and other hindrances. Lode mining, being under cover, can be carried on without regard 
to weather. 
The entire Lost River basin lies within the Fort Clarence limestone. About a mile from 
Lost River, on Tin Creek (a tributary of Lost River, 5J miles from the sea), is a large boss 
of granite, half a mile in diameter and 1,000 feet high. Many acidic dikes cut the limestone, 
radiating in a general way from this boss, though but few can be traced directly to it. The 
dikes are usually but a few feet wide, 18 inches to 25 feet being the approximate limits, with 
local widening or narrowing. Acidic dikes, having no apparent connection with this com- 
plex, but with a character lithologically similar, cross the basin at other points. Near the 
coast are several dikes of diabase. The acidic dikes are probably of several ages and some 
contain none of the darker minerals and are of rather uniform texture, while others contain 
porphyritic orthoclase and quartz, resembling the granite of Cape Mountain. The dikes cut 
the limestone without reference to its bedding and the joint planes of the limestone some- 
times extend across the dikes. 
Close to the granite boss on Tin Creek, and near the dike in which tin was first discovered 
on Cassiterite Creek, portions of the limestone have been so metamorphosed that they would 
ordinarily be hardly recognized as such. The portion changed is from 1 to 3 or 4 feet wide, 
and takes a serpentine course through the unaltered limestone, with no apparent regard for 
bedding or jointing. The altered portion has a general green appearance and in places a 
weathered or polished face looks like an intensely crumpled schist, while in other places it is 
a mass of metamorphic minerals — epidote, vesuvianite, hornblende, calcite, fluorite, brown, 
red, and other garnets, quartz, magnetite, pyrite, and probably other minerals. 
ORE BODIES. 
At the time of the writer's visit (September 10-13, 1905) the only known deposits of cas- 
siterite were on the Crim, Randt, and O'Brien group of claims, and one other, Discovery 
claim, on a dike known as the Dolcoath lode. 
The Crim, Randt, and O'Brien deposits include those originally discovered and several 
veins and tin-bearing dikes found since. The original discovery was on a rhyoluic dike, called 
the Cassiterite lode, running from Cassiterite Creek across the mountain eastward to Tin 
Creek, a distance of about a mile. Developments to the end of the season of 1904 were 
described by Collier as follows: a 
A tunnel and a crosscut show an ore body about 60 feet long by 15 feet wide, the lateral walls of which 
are the well-defined contacts of the original dike matter with the limestone. The dike rock hi this shoot 
has been altered mainly to kaolin, though the original texture is partially preserved. Cassiterite in fine 
grains is rather uniformly distributed through this mass, but it is reported that the tin content dropped 
below 1 per cent at the end of the tunnel. 
A second tunnel, driven on the dike about 200 feet east and 200 feet higher on the hill, shows the por- 
phyry in a less kaolinized condition. Here it still contains some tin ore, although in smaller amounts. 
Samples taken from the croppings of the dike several hundred feet farther east were said to contain 
traces only of tin. 
The attempts to trace the dike westward were unsuccessful, though several prospect holes were sunk 
in the line of its extension west of the 60-foot tunnel noted above, seeming to indicate that the dike ends 
near this tunnel. 
a Collier, A. J., Recent development of Alaskan tin deposits: Bull. U. S. Geol. Survey No. 259, 1905, 
pp. 121-122. 
