bkooks] STREAM TIN IN ALASKA. 93 
The stream tin is concentrated on the bed rock with other heavy 
minerals, and was found by the miners in the sluice boxes. A sample 
of the concentrate in one of the sluice boxes was examined by Mr. 
Arthur J. Collier, and yielded the following minerals: Cassiterite, 
magnetite, ilmenite, limonite, pyrite, fluorite, garnets, and gold. 
The determination of percentage by weight was as follows: 90 per 
cent tin-stone; 5 per cent magnetite; other minerals, 5 per cent. The 
cassiterite occurs in grains and pebbles, from those microscopic in 
size to those half an inch in diameter; they have subrounded and 
rounded forms. In some cases there is a suggestion of pyramidal and 
prismatic crystal forms. The cassiterite varies in color from a light 
brown to a lustrous black. 
A second locality of this mineral was found on the Anikovik 
River about half a mile below the mouth of Buhner Creek. Here the 
cassiterite was also found with the concentrates from the mining 
operations. One pebble of stream tin obtained from this locality was 
about 2 inches in diameter. 
It will be necessary to make a more detailed examination of this 
region to determine where this mineral occurs in the bed rock. The 
facts obtained by the writer point toward the conclusion that its 
source was in the quartz and calcite veins in which the gold was found. 
No cassiterite was, however, found in this vein material. 
No evidence was found that this cassiterite is in any way connected 
with granitic intrusions, which is its usual association in other regions. 
As far as known there are no intrusives of such rocks within the 
drainage basins of streams where the tin was found. The nearest 
known granitic rock is the biotite-granite stock which forms the 
promontory of Cape Prince of Wales and which is at least 10 miles 
distant. 
This discovery of stream tin has, at present, scientific rather than 
commercial interest. No developments have been made which would 
warrant the conclusion that valuable tin deposits exist in the York 
district. It is worth while, however, for the prospectors who visit 
this region to familiarize themselves with the physical properties of 
the mineral, so as to be able to recognize it if found. By this means 
deposits carrying values may be discovered, and the cassiterite will 
probably be traced to its source in the bed rock. 
