16 TIN DEPOSITS OF THE YORK REGION, ALASKA. [no. 229. 
ECONOMIC GEOLOGY. 
GENERAL STATEMENT. 
Tin is known to be irregularly distributed in the York region over 
an area of about 4:50 square miles, embracing the western end of the 
peninsula. Its occurrence in alluvial deposits has been verified by the 
United States Geological Survey at three localities, and the existence 
of tin-bearing lodes has been observed at two points. The extreme 
points known are 25 miles apart. In addition to these, prospectors 
report the occurrence of tin at a great many other places, either in 
lode or placer form, and though it has not been possible to confirm 
these reports, there is reason to believe that the} 7 indicate a more 
extensive distribution of the tin ores. Many of the reported discov- 
eries lie beyond the limits of the York region and indicate that the 
tin districts extend 100 miles or more to the northeast. 
The tin ore is almost all cassiterite (tin oxide), though some stan- 
nite (sulphide of tin, copper, and iron) has been found. In the bed 
rock two essentially different types of deposits are represented. The 
ore occurs in veins cutting phyllites or metamorphic slates, and is dis- 
seminated through more or less altered granitic dikes. The lode 
deposits of the latter t} T pe give promise of commercial importance. 
Lode deposits of the former type have not been discovered in place, 
but the occurrence of tin- bearing quartz veins in slates is inferred 
from the distribution of the placer tin and from pebbles of slate con- 
taining small tin-bearing quartz veins, which have been observed in 
the gravels. It should be noted that no granite has been found in the 
slate area, and there is no positive evidence that the tin there has 
any genetic relation to granite intrusives. 
No discussion of the genesis of these various ore bodies w r ill be pre- 
sented in this report, since the field work lias all been of a reconnais- 
sance character. From a comparison of the evidence at hand with 
the facts known with regard to the older tin-bearing districts, it seems 
to be at least possible that the tin lodes of both types are connected 
with intrusive granite bodies, some of which have been exposed b}^ 
erosion, while others are still deeply buried. These granites, which 
probably were all intruded at about the same time, mark a zone of 
plutonic activity extending from the Diomede Islands northeastward, 
parallel with the Arctic coast, for 100 miles or more. The localities 
from which tin ore has actually been obtained by United States Geo- 
logical Survey parties and which have been examined in some detail 
will be described under the headings "Lost River," "Cape Moun- 
tain," "Buck Creek," "Buhner Creek," and "Anikovik River." The 
streams from which placer tin is reported by prospectors will be men- 
tioned under the heading "Reported occurrences of stream tin," and 
