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area for lodes and for placer accumulation and probably did in fact supply the gold of the Upper Cretaceous and Eocene conglomerates. The recent streams in this area have therefore obtained a part of their gold from the destruction of the old fossil placers and have reconcentrated it in the present drainage channels. But the streams southwest of the conglomerate belt-for example, the tributaries of the Seventymile River above Barney Creek-have probably derived a part of their gold directly from the original gold lodes.

It does not follow, however, that all the streams that drain the Upper Cretaceous and Eocene belt are favorable sites for gold placers, for three reasons: (1) Some of these old conglomerates may consist of gravel laid down by streams that did not head far enough to the southwest to have tapped mineralized zones. (2) Even where the ancient streams drained out of bodies of mineralized country rock the gold was probably irregularly distributed in the old placer bodies, just as it is in many present-day gold placers. (3) The Upper Cretaceous and Eocene rocks have been greatly folded and otherwise disturbed from their original nearly horizontal attitude; this feature alone would make for irregular distribution of gold, even if the ancient streams had developed long, continuous pay streaks.

Therefore, although some of the gold which came originally out of the Charley River batholith may be preserved in these old conglomerates instead of being widely dissipated into larger stream valleys like the Yukon, yet the present irregular distribution of gold in the conglomerate belt adds an element of uncertainty to the problem of prospecting in the streams draining it that is not unlike the uncertainty that attends prospecting in recent stream gravel in glaciated areas. In other words, prospecting can be done more intelligently in the part of the area southwest of the Upper Cretaceous and Eocene belt, where, as in the Fortymile precinct, the gold placers have been derived for the most part directly from the original gold lodes rather than by reconcentration from earlier placer deposits.

PLACER-MINING OPERATIONS

No extensive study of the gold placer-mining operations on the streams between Eagle and Circle has been made by the writer, but most of the placer-mining plants were visited in 1925, in order to obtain a general idea of the character of the placers and of mining conditions. On American Creek the Upper Cretaceous and Eocene rocks extend from the mouth upstream for about 4 miles, but the placer-mining operations were confined to a zone beginning about 4 miles farther upstream, where the bedrock consists of schist, serpentine, and other metamorphic rocks. At this point American Creek is joined by Discovery Fork, which enters from the southeast.

One operator, who owns Discovery claim at the forks and five claims below and six above Discovery claim, on American Creek, was preparing for hydraulic operations on a large scale. The stream gravel which was to be worked ranged in thickness from 3 to 10 feet. Three other men were operating small plants on Discovery Fork. The gold from American Creek is said to yield $17.25 to the ounce at the mint but is accepted at $16.70 commercially at Eagle.

On the Seventymile River the largest operating plant was at the upper end of Discovery claim on Crooked Creek. The bedrock on Crooked Creek belongs entirely to the Upper Cretaceous and Eocene sequence, and much or all of the gold in the present placers has probably been reconcentrated from the ancient conglomerates. The stream gravel that was being worked is from 5 to 6 feet thick in the center of the cut but becomes thicker toward the east valley wall. The pay streak, where worked in 1925, was 240 feet wide, but it is probably narrower upstream in the direction in which operations were being extended. The ground here averages about 13 cents to the square foot of bedrock, and the gold is of fairly high grade, yielding about $18 an ounce in Eagle. The largest nugget so far found was valued at $3.50. This ground was being mined by hydraulic operations, the gravel being moved by two 212-inch nozzles under a 100-foot head, and the tailings being stacked downstream by a 3-inch nozzle. The water for the nozzles was obtained from a ditch that taps Crooked Creek farther upstream, but as work progresses upstream a higher ditch will have to be dug in order to obtain the necessary head.

About 2 miles up the Seventymile River from Crooked Creek and on the same side of the river hydraulic placer-mining operations on a small scale were being carried on in 1925 at the mouth of a little creek called Broken Neck Creek, but this work proved unprofitable and was subsequently discontinued. The bedrock here, as on Crooked Creek, is the old conglomerate formation, and about 3 to 5 feet of gravel from 20 to 50 feet wide was being worked at the time of the writer's visit.

About 3 miles farther upstream, on the north side of the Seventymile River, another man was at work mining the river bars and prospecting. At this point the conglomerate formation lies to the northeast, and the country bedrock consists of quartzite schist, quartz-mica schist, amphibolite schist, and basalt and diabase of greenstone habit; but at one place along the river bank a piece of the conglomerate was seen faulted into the older schistose rocks. The Seventymile River at this point cuts through a short gorge in rapids which are known locally as "The Falls." The valley of the river here has a number of well-developed benches, one of which, about

12 feet high, shows well on the north side of the river and slightly on the south side. On the north side, at a level 4 to 5 feet higher than the 12-foot bench, a great flat extends to the hills. On the south side another prominent bench occurs about 125 feet above the river level. These benches, particularly the lower ones, are being prospected by hand methods.

Barney Creek, about 6 miles farther upstream and also on the north side of the Seventymile River, is an old placer-mining site, but no mining operations were being carried on there in 1925. This creek also flows entirely through the Upper Cretaceous and Eocene rocks, and the gold in the placers probably came from that source.

Two other mining plants were being operated still farther up the Seventymile River, on the south side, the uppermost of which, on Alder Creek, had been worked intermittently for many years. This is a hydraulic plant working stream gravel, but as the bedrock is composed entirely of the old schistose rocks, the gold has doubtlessbeen derived directly from original mineralization in the valley of Alder Creek, produced by the granitic intrusives. The other plant, on Nugget Creek, was worked on a small scale, mainly by hand methods.

Farther down the Yukon, south of Nation, Fourth of July Creek is the site of another good-sized hydraulic plant, which had been in operation for several years. The lower part of Fourth of July Creek cuts across the Tahkandit (Permian) limestone, but in the upper part, where the mining operations were being carried on, the bedrock is the same Upper Cretaceous and Eocene conglomerate strata seen on the Seventymile River and on American Creek. The pay streak is about 500 feet wide and the gravel is 10 to 15 feet thick, covered by 2 to 7 feet of black muck. The gold lies in the lower foot of gravel and in the bedrock, it being necessary at places to mine 2 feet of bedrock in order to obtain all the gold. The gravel in the placers ranges in size from 2 to 10 inches, but a few boulders as much as 212 feet in diameter are encountered. The pebbles of the conglomerate bedrock are mainly flint and quartzite, with some vein quartz and rarely a piece of greenstone, and naturally the stream gravel is similar in character. Curiously enough, no granitic pebbles were seen at this locality either in the bedrock or in the overlying gravel. The gravel at this plant ranges in value from 20 to 30 cents to the square foot of bedrock.

The July Creek Placer Co. owns nearly 3 miles of claims on Fourth of July Creek, from claim 10 to claim 21 above Discovery, and plans to continue its mining operations for a number of years. Two ditches have been built, a lower one 21/2 miles long, which taps the upper part of Fourth of July Creek, and an upper one 914 miles long, which takes its water from the head of Washington Creek. The discharge from

the upper ditch enters Ruby Creek, a headwater tributary of Fourth of July Creek, and helps to feed the lower ditch farther downstream. The pay streak, 500 feet wide, is mined in cuts 250 feet wide, working for a distance of 100 feet and then returning for the other half. The muck overlying the gravel is first ground-sluiced off, then three 21⁄2-inch nozzles under a head of 160 feet are used to move the gravel. A line of eight or ten 12-foot sluice boxes are used, with a steel shear board suspended longitudinally over them, thus making it possible to move gravel into the sluice boxes simultaneously from both sides of the boxes.

Little active mining is in progress on Woodchopper and Coal Creeks. The chief placer mining during the summer of 1925 was on Mineral Creek, a small right-hand tributary of Woodchopper Creek, about 5 miles from the Yukon. Here the baring of the bedrock by placer mining has revealed the contact between the lower Mississippian chert conglomerate and the Upper Cretaceous and Eocene conglomerate, the latter occurring upstream from the former. The pay streak is about 100 feet wide, and the gravel and muck are about 10 feet thick. Mining was being done by open cutting, aided by a small nozzle.

On Iron Creek, another eastern tributary of Woodchopper Creek, 2 or 3 miles above Mineral Creek, two men were at work in 1925, one on Discovery claim, at the mouth of Iron Creek, and another on claim No. 2 above Discovery. The work on Discovery claim was underground work done by winter drifting. The work on No. 2 above consisted of open cutting and shoveling in about 3 feet of gravel and 2 feet of muck, taking 8 feet on each side of the sluice boxes. The pay streak here is spotted and irregular, but the gold is coarse and of high grade, one sample sent to Seattle assaying $18.75 an ounce.

Three other men were at work farther up Woodchopper Creek, engaged in small-scale winter drifting and prospecting.

No placer-mining operations were in progress on Coal Creek at the time of the writer's visit in 1925, but this creek has been mined intermittently at a number of places in recent years. The bedrock at the mouth of Coal Creek and for 42 miles upstream is the Lower Cretaceous black slate, which is followed upstream for 31⁄2 miles by the lower Mississippian chert and chert conglomerate. Above this the Upper Cretaceous and Eocene rocks cross the creek. Two groups of claims on the creek are now held mainly by two men. The upper group lies at the lower end of the Upper Cretaceous and Eocene conglomerate, and the gold in these placers has probably been derived in part from the reconcentration of these ancient gold-bearing rocks. The lower claims lie mostly in the black-slate zone, and it seems likely

that the gold in these placers may have been derived from a mineralized zone in the creek itself, for this lower gold is brighter in color, coarser, and higher in grade than the gold from the upper claims. The pay streak on the lower claims is 100 feet wide and the gravel from 12 to 20 feet thick. The ground worked by the owner has not yielded less than 75 cents to the square foot of bedrock, although placers of lower grade than this are undoubtedly present. These two groups of claims, which together comprise 7 miles of placer ground on Coal Creek, should be thoroughly prospected and if possible should be mined as a unit. This should make a good hydraulic venture for some company, for Coal Creek always has plenty of water, and mining would therefore not be at a disadvantage, as it is on some of the smaller gold-bearing creeks tributary to the Yukon.

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