46 ALASKAN MINERAL RESOURCES TN 1905. 
on Chichagof Island, was made during the summer of 1905, and developments are in prog- 
ress at this point. 
At Conclusion Point , on the southeast side of Baranof Island, several prospects have been 
located which are reported to give good assay values. 
COPPER. 
In the deposits of copper the high-grade enrichment zone, which plays such an impor 
tant role in the western mining camps, is practically absent, probably having been removed 
by erosion during the recent glacial period. As a consequence the belt of weathering and 
oxidation extends only a short distance below the surface and the ores are chiefly unaltered, 
unenriched sulphides. Leaching near the surface is not pronounced, and experience has 
shown that the values obtained a short distance below the surface approximate those at 
greater depths. A possible exception to this statement is at Copper Mountain, where 
surficial copper carbonates form the pay ore. 
The copper deposits occur almost without exception as irregular lenses and masses, 
either as replacement or contact deposits or as heavily impregnated portions of schists. 
Their irregularity is SO pronounced that in their exploitation the rule to observe is to 
follow the ore and not to drive long crosscul tunnels expecting to undercut the deposit in 
depth. The chief copper ore is chalcopyrite and cupriferous pyrite, accompanied by mag- 
netite, pyrrhotite, and various other minerals. On Kasaan Peninsula the deposits may 
lie described as bodies of magnetite and chalcopyrite averaging about 40 per cent metallic 
iron and containing 0.7 to 10 per Cent metallic copper. A magnetic or mechanical sepa- 
ration of this ore has not been found practicable and it is shipped directly from mine to 
smelter. 
KETCHIKAN DISTRICT. 
The principal copper deposits of southeastern Alaska are located on Prince of Wales 
[sland, m the Ketchikan district. (See map, PL XI.) The conditions of their occurrence 
\ar\ with the deposit, though in a general way they are similar. This is especially true 
of the copper bodies on Kasaan Peninsula and Tolstoi Bay. The geologic relations at 
Skowl Arm. Niblack, and Copper Mountain are noticeably different and will be discussed 
separately. 
KAsAA.N PENINSULA. 
Kasaan Peninsula is on the cast side of Prince of Wales Island and extends in a south- 
easterly direction as a promontory 12 mile- long and several miles wide into Clarence Strait. 
Its hills range from ."00 to 3.000 feet in elevation, and are made up essentially of eruptive 
rocks, with occasional areas of sedim< utaty strata, all of which have suffered intense metal 
morphism. The bedded rocks include Paleozoic limestone.-, and chloritic greenstone schists, 
intricately folded and faulted and cut by intrusive masses and dikes of diorite, diabase, 
andesite, and felsite. The ore bodies occur as flat-lying lenses, either in conjunction with 
magnetite, limestone, and felsite masses, or with garnet, epidote, and crystalline limestone 
m the contact aureole of intrusive granite-diorite bosses. The formation of both types 
of deposits is thought to be due primarily to pneumatolitic emanations from the intru- 
sives, influenced perhaps by underground waters. In the special descriptions below only 
the salient features of each deposit will be emphasized, the details being left for the more 
complete report. 
The Mamie mine, located on one of a group of claims owned by the Brown Alaska 
Company, is situated \\ miles from Hadley. Considerable advance has been made during 
the last year at this mine. Diamond drills have been used in exploratory work and are 
said to have given encouraging results. In tunnel Xo. 2 a shaft 100 feet deep has been 
sunk and many drifts and crosscuts extended. The ore bodies belong to the low-grade 
chalcopyrite-magnetite type and contain besides these minerals pyrite, epidote, horn-: 
blende, chlorite, calcite, and quartz. They occur as flat -lying lenticular masses 100 to 
200 feet long, incased in bands of limestone and various types of greenstone, and are cut 
