YUKON REGION
The vast Yukon region encompasses the entire drainage basin of the Yukon River in Alaska. It has the shape of a truncated wedge extending across central Alaska. The region is narrower (80 to 100 miles wide) along the west coast of Alaska at the mouth of the river and wider (200 to 300 miles) along Alaska's eastern border, where it includes the basins of the Yukon and one of its main tributaries, the Tanana. This has been by far the most productive of all the gold-producing regions, with a recorded total through 1959 of 12,282,250 ounces, most of it from placers.
Goodrich's detailed account (in Spurr and Goodrich, 1898, p. 103-131) of the early explorations, the discovery of gold, and the development of the first mining districts is the source of much of the material presented here.
The Yukon region had been traversed rather thoroughly after the 1840's by explorers and traders intent on establishing new posts and opening new country for the fur trade. A lively competition which developed among the Russians, the Hudson Bay Co., and the Americans was terminated by the purchase of Alaska by the United States.
In the 1860's small quantities of gold had been found at several localities in the Yukon basin, but credit for the discovery that led to intensive prospecting goes to George Holt, who made several trips to the Yukon in the 1870's and returned with glowing, if not entirely veracious, tales of gold in the interior. In 1881 a few prospectors panned some gold along the Big Salmon River, one of the tributaries of the Yukon River in the Yukon Territory, Canada. A year later, prospectors working up the Yukon from its mouth found gold in considerable quantities near what is now Rampart, in central Alaska. Discoveries in the 1880's along the boundary between Alaska and Canada in the Fortymile River area were developed rapidly, and by 1893 more than 300 men were working the gravels. Birch Creek in the Circle district next attracted attention and it soon rivaled the Fortymile district. Between 1890 and 1895 gold-bearing gravels were found along the Koyukuk River and additional discoveries were made in the Rampart area and in the adjacent Hot Springs district.
In 1902 gold was discovered in the Fairbanks district (Prindle, 1904, p. 64) which in the succeeding years developed into the leading producer in Alaska. The Fairbanks discoveries stimulated prospecting to the south in the foothills of the Alaska Range, and placers were found in the Bonnifield country in 1903 and the Kantishna district in 1906 (Prindle, 1907, p. 205).
At about the same time, commercial quantities of gold were found several hundred miles to the west in the gravels of the upper valley of the Innoko River and this led to discoveries on the adjacent Iditarod River. In about 1910 placers were found along Long Creek in the Ruby district, about 70 miles east of Koyukuk (Mertie and Harrington, 1924, p. 88, 89, 101). One of the most recently discovered placer districts in the Yukon region is the Tolavana district situated along the Tolovana River, a tributary which joins the Tanana River about 100 miles west of Fairbanks. Mining of these placers began in 1915 (Brooks, 1916, p. 201).
Most of the placer districts of the Yukon, basin remained active after World War II,, through 1959, though production decreased because of the constantly rising mining costs especially since 1950.
Only two districts—Fairbanks and Nabesna— have had; any significant lode production, but this is dwarfed by the placer output. The Yukon basin has yielded a total of 12,282,250 ounces of gold, of which 10,776,460 ounces is from placers, 305,560 ounces is from lode deposits, and 1,200,230 ounces is undifferentiated but presumably from placers. It may seem strange that from such a large region so few commercial vein deposits have been exploited; however, several factors must be considered in an analysis of this imbalance. First, the placers are amenable to large-scale dredging methods which means that low-grade material can be mined even at present high costs. Secondly, the remoteness of the areas containing the lode deposits demands large tonnages of high-grade ores for profitable mining.
It is difficult to summarize the geology of a region as large as the Yukon drainage basin, especially in view of the fact that the region has not been completely mapped and the areas that are mapped were done at different scales at different times and by numerous individuals. The upper part of the basin, the Yukon-Tanana area, was mapped first by Spurr (in Spurr and Goodrich, 1898) and then by Mertie (1937), but that part of the basin from the junction of the Yukon and Tanana to the mouth of the Yukon has been mapped in small parcels by individuals investigating only certain districts.
In the upper part of the basin, stratified rocks ranging in age from Precambrian to Recent are exposed. Representatives of every period except Jurassic are present (Mertie, 1937, p. 44-46). Mesozoic and Tertiary granitic intrusive rocks are the most important members of the igneous family in this area, and it is believed that the metalliferous ore deposits are related to them (Mertie, 1937, p. 46).
Farther downstream, in the Ruby area, greenstones and undifferentiated metamorphic rocks of Paleozoic age and older are the predominant country rocks (Mertie and Harrington, 1924, p. 12). In the Innoko and Iditarod districts, which may be considered the lower reaches of the Yukon, Mesozoic sedimentary rocks, chiefly Cretaceous in age, compose most of the country rock. These are inter-layered locally with basic igneous rocks. Granitic intrusions make up the mountain areas, and rhyo-lite dikes are scattered throughout the areas (Eakin, 1913, p. 295).
Throughout the Yukon basing large areas are covered with fluvial deposits that form flats tens of miles wide. The entire region has a complex geomorphic and structural history, much of which is fairly recent in age, but not enough work has been done in the region to interpret the many anomalous features of the present drainage (Mertie, 1937, p. 237).
BONNIFIELD DISTRICT
The Bonnifield district is between lat 63°30' and 64°50' N. and long 145°40' and 149°20' W. It extends from the Tanana flats on the north to the north slope of the Alaska Range on the south, and it is bounded on the west and east by the Nenana and Delta Rivers, respectively.
The first gold was mined from the gravels of Gold King Creek in 1903. During the early years there were high hopes that the Bonnifield would become a major district, but only small amounts of gold were produced annually, and after 1949 the district was idle. Total production through 1959 was about 36,600 ounces, all from placers.
The geology, as outlined by Capps (1912, p. 17-19), is as follows. The oldest rocks in the district are metasedimentary rocks of Precambrian or early Paleozoic age—the Birch Creek Schist, consisting of quartz and mica schist, phyllite, and quartzite. Mertie (1937, p. 46) considered the Birch Creek to be Precambrian in age. The Birch Creek Schist is overlain by quartz-feldspar schists forming the Totatlanika Schist of Silurian or Devonian age. A sequence of Tertiary sediments beginning with Eocene fresh-water deposits unconformably overlies the schists. The freshwater deposits are followed by the Nenana Gravel of middle Miocene to early Pliocene age (MacNeil and others, 1961, p. 1806) and Pleistocene and Recent glaciofluvial deposits. The schists are highly contorted, and as the Alaska Range rose in Tertiary time the Tertiary beds were subjected to considerable folding and faulting immediately after their deposition. Intrusive rocks of granitic to dioritic composition cut the schists at various localities. These bodies are older than Eocene and younger than Silurian or Devonian (Capps, 1912, p. 41-42).
The placer deposits are in the foothills between the Tanana Flats to the north and the high slopes of the Alaska Range to the south. Present streams have cut through valleys previously filled with alluvium and have reconcentrated and redeposited the detrital gold of the older alluvium.
CHANDALAR DISTRICT
The Chandalar district, between lat 67°00' and 68°10' N. and long 147°00' and 150°00' W., includes the upper drainage of the Chandalar River.
The Chandalar district, which began producing placer gold in 1906, is one of the small producers of the Yukon basin. Total placer production through 1959 was 30,708 ounces. Cobb (1962) indicated small but undisclosed lode production from the district.
Lode deposits, which have been known in the district for many years, have recently received renewed attention. In 1961 the Little Squaw Mining Co. reported blocking out an ore body worth $1,013,000 in gold (Mining World, 1961).The geology given here is generalized from a more detailed account by Mertie (1925, p. 223-252). Schists, resembling the Birch Creek Schist, of Precambrian or early Paleozoic age are the oldest rocks in the district and are found in the southern part. Other schists and phyllites of early Paleozoic age compose the bedrock in the central part of the district, north of the area underlain by Birch Creek (?) Schist. Silurian limestone and dolomite and Devonian slate occur still farther north. In the southwest corner, Devonian or Mississippian rocks unconformably overlie the schists, and a small patch of Upper Cretaceous sandstone caps the sequence. Igneous rocks in the district consist of granite, granodiorite, and basic lavas, that range in age from Late Silurian or Early Devonian to Tertiary.
The schists contain numerous small auriferous quartz veins and stringers that no doubt were the source of the gold in the placers. Both preglacial and postglacial gravels have been productive.
CHISANA DISTRICT
The Chisana district is between lat 61° 55' and 62°20' N. and long 141°40' and 142°35' W., in the drainage area of the Chisana River, a tributary of the Tanana River.
Gold lodes were known in this area before 1910, but were never developed; then in 1913 placer discoveries along Bonanza Creek started a stampede to the district (Capps, 1916, p. 89-92). The placers, however, were relatively small, and efforts to find and develop lode deposits were unsuccessful. Small amounts of placer gold were produced up to World War II, but since then the output has been insignificant. Total production from 1913 through 1959 was 44,760 ounces, all from placers.
The rocks of the district range in age from Devonian to Recent (Capps, 1916, p. 29-31). The oldest rocks are black shale, basic lava, and pyroclastic of Devonian age which are overlain by a great thickness of Carboniferous lava, tuff, breccia, agglomerate, and some limestone and shale. Shale and graywacke of Mesozoic age are faulted against the older rocks along an east-west line. Several small patches of Tertiary sediments unconformably overlie the Paleozoic rocks, and in the stream valleys considerable areas are covered with glacial debris and stream deposits interbedded with lava flows. Granitic intrusions cut the Devonian and Carboniferous rocks but the exact age of the igneous rocks is not known (Capps, 1916, p. 84-85).
Most of the placers occur in the area of Carboniferous pyroclastic rocks and the granitic intrusions. Capps (1916, p. 96-98) believed that the gold of the placers was eroded from veins in these Paleozoic rocks near their contact with the intrusives and that the present placers are a product of several previous reworkings of Tertiary auriferous gravels, first by streams, then by glaciers, then by the present streams reworking the glacial deposits.
CIRCLE DISTRICT
The Circle district is between lat 65° 15' and 66°00/ N. and long 144°00' and 146°00' W.
This is one of the older districts of the region, gold having been discovered along Birch Creek in 1893 (Prindle, 1906, p. 20). Production began the following year and was continuous through 1957. Hydraulic methods were used on nearly all productive streams, particularly along Mastodon Creek. Total production through 1959 was 705,660 ounces, all from placers.
The rocks, as summarized from Mertie (1932, p. 158-161), consist of schist, clastic sedimentary rock, limestone, and granitic rocks ranging in age from Precambrian to Mesozoic. Pleistocene and Recent unconsolidated deposits complete the sequence.
The Birch Creek Schist, the oldest rock, is of Precambrian or early Paleozoic age. Next youngest are lower Paleozoic metamorphic rocks—quartzite, phyllite, and slate—together with graywacke, arkose, limestone, and chert. The Crazy Mountains in the central part of the district are underlain in succession by Silurian or Devonian limestones, basic flows and sedimentary rocks of the Rampart Group of Early Mississippian age, and by a later Missis-sippian chert formation. Several small bodies of granite are intrusive into all the foregoing rocks, and the placer deposits are in the vicinity of the intrusive bodies. Alluvial deposits in the Circle district represent several erosional periods during Pleistocene and Recent time.
EAGLE DISTRICT
The Eagle district is between lat 64° 35' and 65° 15' N. and long 141°00' and 142°40' W., along Seventymile, American, and Fourth of July Creeks, all tributaries that enter the Yukon River near Alaska's eastern boundary.
Placer gold was first found in 1895 along American Creek, and production began the following year (Mertie, 1938, p. 190). Although it attracted few miners, the Eagle district maintained a small annual production even through the difficult post-World War II years. Production data before 1906 cannot be found and was probably reported under some other district. Total recorded production for the Eagle district from 1906 through 1959 is 40,220 ounces, all from placers.
The district is underlain in the southwest by a large mass of granite of Late Jurassic age that has intruded and thrust upward a series of Precambrian and Paleozoic sedimentary rocks that are now exposed in northwestward-trending bands in the central and northern parts of the district. Lower Cretaceous marine rocks are exposed in the northern part of the district and these are succeeded by a thick series of freshwater deposits of Late Cretaceous and Eocene age (Mertie, 1930, pi. 12). Post-Eocene uplift caused much of this covering to be removed. Unconsolidated deposits of sand and gravel of Pleistocene and Recent age are in the stream valleys. These sediments reflect a complex geomorphic cycle involving local glaciation, climatic changes, and changes in base level (Mertie, 1930, p. 147-148).
The gold placers are in present stream gravels. The gold in these deposits came originally from small veins related to the granitic mass in the southwest part of the area, but much gold also came from ancient placers in the Upper Cretaceous and Eocene elastics (Mertie, 1930, p. 161-162).
FAIRBANKS DISTRICT
The Fairbanks district, about 300 square miles between lat 64°40' and 65°20' N. and long 147°00' and 148° 10' W., has produced more gold than any other district in Alaska. It is predominantly a placer district, although it also ranks high among the lode districts.
Fairbanks was slow to develop. Placer gold was known in the area as early as 1878 (Mertie, 1937, p. 4), but the active districts of Fortymile, Rampart, and Circle kept all but the most restless away from the Fairbanks area. In 1901 the town of Fairbanks was founded as a trading post, not as a consequence of gold mining (Prindle and Katz, 1913, p. 86). The following year some workable placers were found along Pedro Creek. This discovery brought a rush of miners and prospectors to the district, most of whom became discouraged and left after learning that the rich, easily accessible placers were few and that the large, lower grade deposits were buried and required processing large volumes of material with special machinery. Large investments were needed to purchase and construct hoisting machinery, large dredges, and machinery for thawing the frozen overburden. But gradually, as the obstacles were overcome, it was found that the buried gravels could be mined profitably, and the district prospered as the dredges chewed through huge reserves of auriferous gravels on Dome, Ester, Vault, Cleary, and Chatanika Creeks. Production continued at a high level even after World War II, but in 1959, activity began to diminish. The Fairbanks Daily News-Miner reported (Sept. 15, 1959) that gold dredging was gradually ceasing in this area. Two dredges were closed in 1959 and a third was transferred to the Fortymile district.
Interest in lode mining began after the placers were developed. Small-scale operations were under way in 1910 in Skoogy Gulch and upper Cleary and Fairbanks Creeks (Hill, 1933, p. 51). The peak of lode mining was reached just before World War II. The Pedro Dome and Ester Dome areas contain the most productive lode deposits.
The total gold production of the Fairbanks district through 1959 was 7,464,167 ounces—7,239,696 ounces from placers, 224,471 ounces from lodes.
The Birch Creek Schist, of Precambrian or early Paleozoic age, underlies most of the district (Hill, 1933, p. 41). This includes a variety of rock types, among which quartz schist and quartzite are dominant. Masses of crystalline limestone are present locally. Small bodies of biotite granite and quartz diorite believed to be of Mesozoic age (Hill, 1933, p. 43) intrude the Birch Creek. In the northeast corner of the district is a small patch of Tertiary sandstone and conglomerate, and in the same general area are a few small isolated areas of Tertiary basalt (Hill, 1933, p. 42-43).
The lode deposits of the Fairbanks district are fissure veins in the Birch Creek Schist in the vicinity of bodies of intrusive rock. The trends of both the veins and intrusives seem to be controlled structurally, but the trends are not consistent throughout the district (Hill, 1933, p. 63-64). All the major intrusives trend eastward; the veins in the Pedro Dome area also trend eastward, but the veins in the Ester Dome area trend more northward. The veins consist of quartz with small amounts of the sulfides arsenopyrite, pyrite, sphalerite, jamesonite, and stibnite, and free gold which is associated either with quartz or with the sulfides. Cervantite is widespread as an oxidation product of stibnite, and its yellow-green stain is a guide to high-grade gold ore in this district (Hill, 1933, p. 64-73).
The gold placers occur along stream valleys in unconsolidated gravels. The most productive layer is normally a few inches to 8 feet above the bedrock ; the bedrock from 1 foot to several feet below the gravel is usually gold bearing. A thick mantle of barren material consisting of sands, clays, and muck covers the deposits (Prindle and Katz, 1913, p. 92-98).
FORTYMILE DISTRICT
The Fortymile district, between lat 64°00' and 64°30' N. and long 141°00' and 142°20' W., along the international boundary, includes the upper drainage of Fortymile River, one of the Yukon tributaries that joins the main stream in Canada. It is one of the oldest placer areas in the Yukon region and had uninterrupted output through 1959.
According to Mertie (1938, p. 157), gold was discovered in the district in 1886, but Smith (1933, p. 96) listed small production beginning in 1883. Discoveries of rich stream placers in 1893 in the Sixtymile River area, across the international boundary, drew many prospectors to the Fortymile district as well, and in a relatively short interval all the major gold-producing grounds in the Forty-mile district were found. The placers of Dome, Wade, and Chicken Creeks were all discovered during the 1890's (Mertie, 1938, p. 157). Large-scale mining methods—dredge and hydraulic—have been used with success, which is probably why the district was still active in 1959.
Total recorded gold production of the Fortymile district through 1959 was about 400,000 ounces, all from placers.
The most abundant country rock of the district, according to Mertie (1938, p. 148), is the Birch Creek Schist, but locally other rocks are present. In the Chicken Creek and Franklin Creek areas granite is exposed (Mertie, 1938, p. 171, 182). Small patches of Tertiary conglomerate, shale, and sandstone are known in the Chicken Creek and Napoleon Creek areas, and some lower Paleozoic greenstone and limestone is exposed along Napoleon Creek (Mertie, 1938, p. 184). Basalt, gabbro, and diabase, younger than the granite, are found in the central part of the Chicken Creek basin.
The productive deposits are in gravels of Pleistocene to Recent age. There are also ancient placers in the Tertiary deposits, but none of these contain gold in commercial quantities. On the other hand, these Tertiary deposits, where eroded, contributed their gold to the younger deposits. Quartz veins related to the granite intrusives are the ultimate source of the gold, according to Mertie (1938, p.154).
HOT SPRINGS DISTRICT
The Hot Springs district is between lat 65°00' and 65°20' N. and long 149°40' and 151°20' W. The drainages of Baker, Sullivan, and American Creeks are its major placer areas.
Gold-bearing gravels were discovered in 1898 on Baker and Eureka Creeks by a group of New Englanders known throughout the area as the "Boston Boys" (Mertie, 1934, p. 165-166). When the party returned in 1899 to the new settlement of Rampart, news of their discoveries leaked out and caused a rush to the Hot Springs area. The first production reported was in 1904 (Smith, 1933, table facing p. 96) ; a town was built a few years later (Mertie, 1934, p. 166).
The district maintained a steady output since mining began and was still active in 1959. Opencut, drifting, and hydraulic methods have been used in the mining. Total production through 1959 was 447,850 ounces, all from placers.
As the Hot Springs and Rampart districts are separated by only a narrow drainage divide, their geology can be summarized together.
Consolidated sedimentary rocks that range in age from pre-Ordovician to Tertiary and include sandstone, shale, conglomerate, chert, limestone, and coal-bearing rocks compose the bulk of the bedrock in these two districts (Mertie, 1934, p. 172-173). These are intruded locally by granite of Tertiary age.
Eakin (1915, p. 239) noted that the placers of the Hot Springs district were of several types— bench deposits, reworked bench deposits, irregular discontinuous bodies of auriferous gravel called "spots," and normal stream gravels containing pay streaks.
The gold of the placers was deposited during early and late Tertiary from lodes in and adjacent to granitic intrusives (Mertie, 1934, p. 223).
IDITAROD DISTRICT
The Iditarod district, between lat 62° 10' and 63°00' N. and long 157°30' and 158°30' W., along the upper drainage of the Iditarod River and its tributaries, ranks second among the gold-producing districts in the Yukon basin.
Gold was discovered in 1908 along Otter Creek, a tributary of the Iditarod River (Maddren, 1911, p. 238). Despite its remoteness, the district developed, and in 1910 production was reported at $500,000 (Smith, 1933, table facing p. 96). Productive gravels also were found on Flat and Willow Creeks. The placers have been mined by dredges, mechanical scrapers, and hydraulic equipment (Mertie and Harrington, 1924, p. 110). Total gold production through 1959 was 1,297,500 ounces; nearly all production was from placers.
The underlying bedrock of the district, as described by Mertie and Harrington (1924, p. 12-82), consists dominantly of sandstone, shale, and conglomerate of late Cretaceous and Eocene age. In the western part of the district, west of the Iditarod River, undifferentiated metamorphic rocks of Paleozoic and Precambrian age are exposed; in the central part there are a few small stocks of quartz monzonite and basic intrusives. Unconsolidated deposits of sand, gravel, and silt of Pleistocene and Recent age are in the stream valleys.
Placers are of two types—residual and stream (Mertie and Harrington, 1924, p. 111-115). The stocks of monzonite, which are sheared and mineralized, are the source of the gold for each type.
INNOKO DISTRICT
The Innoko district, in the upper drainage area of the Innoko River between lat 62°50' and 63°15' N. and long 156°10' and 156°50/ W., lies immediately northeast of the Iditarod River. The Beaver Mountains form the drainage divide between the Innoko and Iditarod Rivers.
Gold was discovered in the gravels of Ganes Creek in 1906, and despite its remoteness the new camp attracted permanent settlers (Maddren, 1911, p. 236) who began gold production in 1907 that continued uninterrupted through 1957. Most of the mining was in the Ophir, Spruce, Little, Ganes, and Yankee Creek areas (Maddren, 1911, p. 246). The Innoko is a placer district and through 1959 produced a total of 518,565 ounces of gold. Most of the placers are in the gravels of the present streams or in bench deposits.
Argillaceous beds of Late Cretaceous and Eocene age underlie most of the Innoko district, except for a small area in the northeastern part where several small bodies of quartz monzonite and basic intrusives cut the sedimentary rocks (Mertie and Harrington, 1924, p. 30, 62, 69, pi. 4).
KANTISHNA DISTRICT
The Kantishna district is an area of about 4,500 square miles, between lat 63°25' and 65°00' N. and long 149°00' and 151°10' W., that includes part of the Alaska Range foothills on the south and part of the Tanana lowlands on the north. It is bounded on the east by the Nenana River and on the west by the western tributaries of the Kantishna River.
The Tanana River valley became well populated by miners and prospectors during the early part of the Fairbanks rush, and soon the rich gravels in the Kantishna district were found. In 1904 gold was found along Toklat River and the following year a flood of hopeful gold seekers left Fairbanks for the new district (Capps, 1919, p. 75). Soon several thousand people swarmed into the area, nearly all streams were staked, and several towns were built. It soon became apparent that the deposits, though rich, were shallow and of small area, so that a dismal exodus began and the population of the district quickly dwindled to about 50 (Capps, 1919, p. 76). Those who remained were able to maintain small production from the placers, and the district was still active on that scale in 1957. In 1904-5 lode deposits of lead-silver and antimony were found, and in 1921 gold, copper, and mercury lode deposits were discovered. The antimony deposits were worked sporadically during 1936-55, but the other lode deposits never achieved any significance (Reed, 1961, p. 27-28).' Total gold production from the district from 1905 through 1957 was 45,925 ounces, all from placers. No activity was reported in 1958-59.
The oldest rock in the district is the Birch Creek Schist of Precambrian age (Wells, 1933a, p. 343). This schist is succeeded by younger schists, phyllites, and gneisses, composing the Totatlanika Schist of pre-Devonian age and the Tonzona Group of Devonian or Silurian age. Pre-Tertiary greenstone, Mesozoic limestone, a sequence of Tertiary fresh water sediments, tuffs, and flows, and Quaternary glacial, glaciofluvial, and fluvial deposits complete the sedimentary column in the district (Capps, 1919, p. 22-23). The pre-Tertiary and lower Tertiary rocks have been deformed into east-trending folds parallel to the axis of the Alaska Range to the south of the district (Capps, 1919, p. 22).
The productive placers of the district are along the streams that radiate outward from the higher parts of the Kantishna Hills. The gold was believed by Capps (1919, p. 79) to be derived from erosion of small quartz veins that cut the Birch Creek Schist.
KOYUKUK DISTRICT
The Koyukuk district, between lat 67°00' and 68°00' N. and long 149°00' and 150°50' W., drained by the north, middle, and south forks of Koyukuk River, is often considered to be one of the most northerly in the world.
Some time between 1885 and 1890 placer gold was first found in this district on the sand bars along the Koyukuk River. Maddren (1913a, p. 76) reported that by 1898 at least $4,000 in gold had been mined from them; however, Smith (1933, p. 96) did not report production from the Koyukuk district until 1900. Nearly all the upper reaches of the Koyukuk tributaries have been prospected, and the results have been rewarding. The district was still active in 1959, though only on a small scale. Total production from the district through 1959 was about 278,000 ounces, all from placers. Promising lode deposits of gold have not been found in this district.
The most abundant bedrock in the district is the ubiquitous Birch Creek Schist of Precambrian or early Paleozoic age. The schist is exposed in two belts—one in the southern part of the Endicott Mountains and the other in the Hodzana highland area, between the Yukon River and the Koyukuk valley. Numerous dikes and small intrusives of granitic composition, probably Mesozoic in age, cut the schist (Maddren, 1913a, p. 34-36). Exposed in the central and northern parts of the district are two sequences of Paleozoic rocks: one is of Devonian (?) age and consists of greenstone, slate, chert, and limestone; the other is a section of crystalline limestone and mica schist of Carboniferous (?) age. Underlying the western part of the district are Mesozoic sedimentary rocks represented by Cretaceous limestone and calcareous sandstone inter-bedded with basic flows and pyroclastics (Maddren, 1913a, p. 50-55).
Pleistocene gravel covers large areas in the district, including all the major stream valleys. Recent deposits include gravels along present stream courses.
The placer deposits are in present stream gravels and bench gravels; some of them are buried. Maddren (1913a, p. 83) considered that the gold in the placers was derived from the Birch Creek Schist. Auriferous pyrite occurs in carbonaceous phyllite facies and free gold is found in quartz veinlets and stringers that cut the micaceous quartz schist facies. The gold was transported by streams and glaciers and later concentrated by further stream action into the placer deposits.
MARSHALL DISTRICT
The Marshall district is between lat 61°40' and 62°00' N. and long 161°30' and 162°10' W., along the lower Yukon River.
During the early days, just after the discoveries at Nome, the port of St. Michael was the terminus and supply center for prospectors embarking on trips up the Yukon River or along the coastline of the Seward Peninsula. A portage to the upper Anvik River, one of the Yukon tributaries, greatly shortened the trip to the goldfields at Dawson and elsewhere on the upper Yukon by eliminating travel along several hundred miles of meanders on the lower Yukon River. Thus, except for a few itinerant prospectors and traders, the Marshall district was rather thinly settled and sparsely prospected.
In 1913, however, gold was discovered on Wilson Creek in the Marshall district (Harrington, 1918, p. 56). The usual rush followed. Additional placers were found on Willow Creek, and the first production was in 1914. Lode deposits were found in 1914, and a small shipment was made that same year (Harrington, 1918, p. 57). The quartz veins did not warrant extensive development; at any rate, lode production for the district is unrecorded.
After the first few years of near-bonanza placer production, activity slackened, was rejuvenated briefly in the late 1930's, then declined after World War II. In 1957 there was only small-scale activity in the Marshall district. Total recorded gold production through 1957 was 113,200 ounces, all from placers. The district was idle in 1958 and 1959.
Much of the bedrock in the Marshall district is greenstone and intercalated sedimentary rocks of Carboniferous age (Harrington, 1918, p. 22-26). These rocks are cut by several stocks and dikes of granite, quartz diorite, and dacite of possible Jurassic or Tertiary age (Harrington, 1918, p. 45-46). Cretaceous sandstone and argillite, somewhat metamorphosed, occur adjacent to the greenstone throughout much of the district. The most abundant rock type exposed in the district is the unconsolidated material deposited during Quaternary time by the debris-laden streams issuing from the huge glaciers of the interior of the Yukon River basin (Harrington, 1918, p. 36-44).
NABESNA DISTRICT
The Nabesna district is between lat 62° 10' and 62°30' N. and long 142°40' and 143°10' W.
Gold had been known in this district since 1899, but there was no significant production until 1931 when the first shipments were made from the Nabesna mine, the lone producer of the district. Credit for the discovery is given to a bear who exposed the moss-covered outcrop of the principal vein while digging out a gopher. The property was developed by C. F. Whithan, who formed the Nabesna Mining Co. in 1929 and began shipping ore in 1931 (Wayland, 1943, p. 176-177). By 1939, much of the vein was worked out and in 1940 production halted. Additional exploration and development work in the district apparently was unsuccessful for there has been no further production reported. In its brief history the Nabesna district produced about 63,300 ounces of gold, all from lodes.
The rocks in the vicinity of the mine consist of the Nabesna Limestone of Late Triassic age and basaltic lavas and shale of possible Permian age (Wayland, 1943, p. 177). A few small bodies of quartz diorite cut the limestone. The thick Wrangell Lava of Tertiary and Quaternary ages unconformably overlies these rocks. Moraine and fluvial sediments of Quaternary age are found in all the stream valleys.
The ore bodies are in contact-metamorphosed limestone near the largest of the quartz diorite in-trusives (Wayland, 1943, p. 183-191). Ore deposits are of three types: bodies of magnetite with pyrite, calcite, and some gold; veins and bodies of pyrrhotite with minor pyrite and gold; and gold-bearing pyrite veins in tactite or along intrusive contacts. The third type is the most important and has accounted for most of the production of the Nabesna mine.
RAMPART DISTRICT
The Rampart district, between lat 65°15' and 65°40' N. and long 149°40' and 150°40' W., joins the Hot Springs district on the north.
Gold was discovered in the gravels of Minook Creek and Hess River and their tributaries in 1882, but for the succeeding 10 years nothing was done to develop the placers. In the early 1890's more discoveries were made and finally in 1896 the first mining was done on Little Minook Creek (Hess, in Prindle and Hess, 1906, p. 26). Smith (1933, table facing p. 96), however, does not report any production until 1904. The district reached its peak of activity before 1910; after that time, production decreased, and in the 1950's only a few hundred ounces per year were mined. Total gold production through 1959 was 86,800 ounces from placers. There are no workable lode deposits in the district.
The geology of the district, as summarized by Mertie (1934, p. 172-173), is chiefly the same as that of the Hot Springs district. Consolidated sedimentary rocks—which range in age from pre-Ordovician to Tertiary and include sandstone, shale, conglomerate, chert, limestone, and coal-bearing rocks —compose the bulk of the bedrock. These are intruded locally by granite of Tertiary age. The major placers are along Minook Creek and its tributaries and along Quail Creek, one of the tributaries of Troublesome Creek.
Several prominent stream terraces containing low-grade gold deposits occur along the Minook Creek valley, but most production has come from gravels at present stream levels along Little Minook Creek (Mertie, 1934, p. 181).
RUBY DISTRICT
The Ruby district is between lat 63°40' and 64° 45' N. and long 154°40' and 156°20' W.
The first discoveries of gold in this district were made in 1907 along Ruby Creek (Mertie, 1936, p. 144). These placers were soon exhausted, but other discoveries in 1910 along Long Creek and in 1912 along Poorman Creek kept the district flourishing (Mertie, 1936, p. 145, 159). Underground drifting, sluicing, and hydraulic methods have been used to mine the gravels. Although production decreased somewhat in recent years, the district was still producing substantially through 1959. Total gold production through 1959 was 389,100 ounces, all from placers.
Undifferentiated metamorphic rocks, including schist, phyllite, slate, quartzite, chert, and limestone, are mainly of Paleozoic age and are the predominant bedrock types in the Ruby district (Mertie and Harrington, 1924, p. 12). A complex of greenstone derived from basic igneous rocks, be¬lieved to be Mississippian in age (Mertie and Harrington, 1924, p. 59), is exposed throughout the district. A few granite stocks of Mesozoic(?) age intrude both the Paleozoic rock units. The generalized structure is an anticline trending northeast and plunging to the southwest.
Numerous quartz veins are in the country rocks; some undoubtedly contain gold and could be regarded as the source of the gold in the placers. The distribution of the placers, however, does not directly coincide with areas of abundant veins, so that no clear relationship is apparent (Mertie and Harrington, 1924, p. 121). Nearly all the placer deposits are buried discontinuous bodies that occur mostly in fairly wide valleys. They were formed by streams older than those now occupying the valleys (Mertie, 1936, p. 144).
RICHARDSON DISTRICT
The Richardson (or Tenderfoot) district is between lat 64° 15' and 64°25' N. and long 146°00' and 146°40' W., about 60 miles southeast of Fairbanks, along the Tanana River.
This is a little-known district, about which only a few brief accounts have been written. According to Prindle (in Prindle and Katz, 1913, p. 141) gold was discovered in the gravels of Tenderfoot Creek in 1905 and for the following 4 years the gold production was probably "$300,000 or $400,000 annually." Smith (1933, table facing p. 96), however, reported a much more conservative figure. Productive deposits also were found along Buckeye and Democrat Creeks. Activity declined after the initial boom period and in recent years the production, which is low, has been combined with that of the Fairbanks district. Total recorded production for the district through 1959 was 64,300 ounces, all from placers.
Prindle (in Prindle and Katz, 1913, p. 140-141) noted that the bedrock in the district is Birch Creek Schist of Precambrian age (Mertie, 1937, p. 46). Numerous small quartz veins, some of which carry gold and sulfides, occur in the schist. Just west of the district are some large granitic masses (Prindle, in Prindle and Katz, 1913, p. 140-141). The placers are along present streams in the area.
TOLOVANA DISTRICT
The Tolovana district is between lat 65° 20' and 65°45' N. and long 147°50' and 149°00' W. in the upper drainage of the Tolovana River, a tributary of the Tanana.
Brooks (1916, p. 201) reported that placer gold had been found in this area as early as 1892 but that no interest was aroused until 1914, when placers along Livengood Creek were discovered. Mining began in 1915 and was substantially increased the following year with the development of the deposits on Livengood Creek and others on Gertrude, Ruth, Lillian, and Olive Creeks (Mertie, 1918, p. 256). The district continued to prosper and it was still productive on a small scale in 1959. Total gold production through 1959 was 375,000 ounces, all from placers.
The bedrock in the Tolovana district is distributed in several bands or belts that cross the area in a northeasterly direction. The oldest rocks in the district crop out in the southeast; the rocks become successively younger in a northwesterly direction. Briefly, the bedrock units consist of the Tatalina Group, of Cambrian or Precambrian age, Devonian and Silurian (?) sedimentary and igneous rocks, a chert unit of Devonian or Carboniferous age, and Carboniferous arenaceous and argillaceous units (Mertie, 1918, p. 230-256).
Igneous rocks, chiefly basic, occupy a considerable area in the northwestern part of the district. Small bodies of granitic intrusives are scattered throughout most of the district. In the stream valleys, unconsolidated deposits of sand and gravel were deposited during several stages in the Quaternary geomorphic cycle. The earlier of these are only remnants and are seen as benches along the valley walls (Mertie, 1918, p. 230-231).
Gold placers in the district are in bench and stream deposits (Mertie, 1918, p. 259). The bench deposits have been the more productive. The gold in the placers of Tolovana was derived from low-grade lode deposits at the heads of many of the tributary streams (Mertie, 1918, p. 274-275).
