By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Southeastern Alaska, the panhandle of Alaska, is the narrow coastal strip that extends southeastward from the main peninsula and is bordered on the north, east, and southeast by Canada. Important gold-producing districts in this region are Juneau, Chichagof, Ketchikan-Hyder, and Porcupine. For the purpose of this report, the Yakataga district, which lies just to the northeast of what is usually considered to be the Southeastern Alaska region, is included in this section.
Gold was known in this region in the days of Russian ownership of Alaska, but no mining was done until 1870-71 when about $40,000 was produced from placers at Windham Bay and on nearby Powers Creek at Sumdum Bay in the Juneau district (Buddington and Chapin, 1929, p. 8). The important discoveries in the Juneau district were not made until the period 1880-85. During the 1890's and early 1900's lode gold mines began significant production in the Ketchikan and Chichagof districts, and beach placers were mined in the Yakataga district.
The Alaska Juneau mine in the Juneau district yielded the bulk of the gold produced in the Southeastern Alaska region. When this mine closed in 1944, the production of the entire region dropped accordingly to only a few hundred ounces annually.
Total gold production through 1959 for Southeastern Alaska was 7,788,514 ounces, of which 7,614,791 ounces was from lode deposits, 138,503 ounces was from placers, and 35,220 ounces was a byproduct from copper ores from the Ketchikan-Hyder district.
This is an extremely mountainous region with complex geologic structures and varied bedrock types. Dominant among the geologic features are the intrusive rocks of Late Jurassic or Early Cretaceous age that occupy much of the mainland area of this region. These rocks range in composition from gabbro to granite and are believed to be related to the great composite Coast Range batholith (Buddington and Chapin, 1929, p. 173-253). Adjacent to the intrusive rocks on the west is a belt of low-rank metasedimentary rocks comprising the Wales Group of early Paleozoic age. Other sedimentary rocks in this region represent every period from Ordovician to Cretaceous and have an aggregate thickness of about 50,000 feet. Tertiary clastic rocks and lavas accumulated in a trough between the major mountain ranges. A few sills and dikes of basalt and andesite cut the Tertiary rocks (Buddington and Chapin, 1929, p. 260-275). Quaternary deposits are of minor areal extent and consist mostly of marine gravels, delta deposits, basalt, and tuffs (Buddington and Chapin, 1929, p. 275-281).
The Chichagof district comprises an area of about 4,500 square miles and includes Baranof, Chichagof, Kruzof, and Sitka Islands.
The first attempts at lode mining in Alaska, under American rule, were made near Sitka in 1871 (Knopf, 1912, p. 8). These ventures and others in the succeeding few years failed, and mining in the Sitka area lapsed into a period of dormancy until the lode discoveries were made at Klag Bay on Chichagof Island in 1905. The Chichagof mine soon became the big producer here, with a production from 1906 through 1938 of $13,784,710 in gold (Reed and Coats, 1941, p. 89). The Hirst-Chichagof mine, which went into production in 1922, produced $1,702,624 in gold through 1938 (Reed and Coats, 1941, p. 104). In succeeding years production from these mines dwindled, and the Chichagof district was operating on a very small scale in 1959. The total recorded production for the district through 1959 was 770,000 ounces, all from lode mines.
The general geology of Chichagof and Baranof Islands has been described by Knopf (1912, p. 11-21), and according to him the oldest rocks are chert and quartzite which are overlain by cherty limestone of Silurian age. Devonian limestone and tuff, Mississippian limestone, Permian or Triassic gypsiferous limestone, Mesozoic graywacke, and postglacial lavas and tuffs complete the stratified rock sequence. The central parts of the islands are composed of masses of granitoid rocks, dominantly quartz diorite of late Mesozoic age. In the Klag Bay area of Chichagof Island masses of greenstone and greenstone schist of possible Triassic age (Reed and Coats, 1941, p. 14-22) occur between the diorite and graywacke. The stratified sedimentary rocks lie on the west bank of an anticlinorium, the axial part of which in this district is occupied by the diorite. Many northwest-trending high-angle faults cut the bedded rocks (Reed and Coats, 1941, p. 64).
The ore deposits are in plunging quartz bodies along the faults. Quartz is the main constituent of these lodes, but calcite may be present. Sulfides, in conspicuously minor amounts, consist of pyrite, arsenopyrite, galena, sphalerite, and chalcopyrite. Gold is present as specks in the quartz and in the sulfides (Reed and Coats, 1941, p. 78-80).
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