A. THIN SECTION OF LUXULIANITE FROM EAR MOUNTAIN. B. POLISHED SURFACE OF TIN ORE FROM LOST RIVER. a, Cassiterite; b, gray pyrite; c, zinnwaldite mica; d. fluorite; e, groundmass of fluorite and calcite; f, groundmass, chiefly kaolin. west is another granite area, smaller and much less prominent than that forming the Asses Ears.. These two localities are situated south of the Sound and, since they are not favorable places for placer gold, have been rarely visited. A third granite area makes up the central mass of the elevated watershed between Kiwalik and Buckland rivers. This range extends from Kotzebue Sound to within a few miles of Koyuk River, a distance of about 40 miles. Here the granites are found only in the higher central part of the mass, and are surrounded by later eruptives, including andesitic rocks and lavas which form the lower hills. These granites are all variable in their texture, and often have an extremely coarse, pegmatitic appearance. Twinned orthoclase feldspars, 2 or 3 inches in length and three-fourths of an inch thick, are not uncommon, and hornblende crystals of large size are found in places. Locally, quartz seems to be absent and the rock becomes syenitic in character. Fluorite was seen in joint planes in the granites northwest of the Asses Ears, suggesting the possible presence of tin ores such as occur with this mineral in the western part of Seward Peninsula. Dr. Cabell Whitehead, of the Alaska Banking and Safe Deposit Company, reports the presence of cassiterite in the form of fine sand in gold taken from Old Glory Creek, which heads up toward the limestone area in which the previously mentioned granite masses of the Asses Ears region occur. LOCALITIES WHERE STREAM TIN HAS BEEN FOUND. BUCK CREEK." Buck Creek was the scene of the first actual mining of tin ore in Alaska, and is the present center for tin-placer mining activities. This settlement is on the Arctic slope of Seward Peninsula, about 20 miles northeast from York, and 4 miles from tide water on Lopp Lagoon, an inlet from the Arctic Ocean. It is reached by a wagon road from York, which follows the bed of Anikovik River for 10 miles, then crosses a low divide to Grouse Creek and follows Grouse Creek to its junction with Buck Creek. This road is fairly good, except for 1 miles of soft tundra on the divide between Anikovik River and Grouse Creek, where it is almost impassable for heavy wagons. A good roadbed could easily be built here by bringing gravel from Anikovik River. Lopp Lagoon is not navigable for seagoing vessels and affords no harbor for such craft. It is a large, shallow body of water, sepa a This description of the tin placers of Buck Creek is based on the work of Mr. Frank L. Hess. b The Standard Dictionary gives the following definition of "tundra:" "A rolling plain of Russia and Siberia, covered with moss and at times very moist and marshy." "The 'tundras' of northern latitudes are frozen plains of which the surface is covered with arctic mosses and other plants.”— Archibald Geikie, Text-Book of Geology. rated from the Arctic Ocean by a low sand spit, on the seaward side of which the shallow water is reported to extend out about 2 miles from the coast, so that landing is difficult. For small, flat-bottomed boats, however, this lagoon is navigable, and it is possible that such boats might, but not probable that they ever will, convey tin ore from the Buck Creek mines, out through the inlet, to vessels lying offshore in the Arctic Ocean. It is reported that small boats can be brought up Mint River and Grouse Creek to within 1 mile of the mouth of Buck Creek. These streams, however, are shallow and crooked, and it is not probable that they can be used successfully for conveying ore from Buck Creek to the sea. The plateau already described extends northward from the town of York on the coast of Bering Sea to the Arctic Ocean. It has an elevation of about 600 feet near York, and slopes to sea level a few miles from the Arctic coast. Buck Creek and the other streams in its vicinity flow in comparatively new valleys cut in this plateau. Above the surface of the plateau there are several buttes, of which Cape Mountain and Potato Mountain" are the most prominent. Potato Mountain is a large, cone-shaped mountain, having an elevation of 1,370 feet. From this mountain a range of low hills extends northward for a distance of 3 or 4 miles toward Lopp Lagoon. Buck Creek is a small stream, about 5 miles in length, which rises in this range of hills and flows southeastward to Grouse Creek. Its waters are then carried northward through Mint River and Lopp Lagoon to the Arctic Ocean. About 1 mile from its mouth Buck Creek receives a large tributary from the south, called Sutter Creek, and about 4 miles above its mouth it again forks, the two branches being known, respectively, as Right and Left forks. Several smaller tributaries are received between Sutter Creek and these upper forks. The bed rock on which the York Plateau is developed, and in which Buck Creek Valley is incised, is a dark, slaty schist, which has been already described. Along Buck Creek it has the characteristic jointing described in the general discussion of the geology of this region. The mountains west of Buck Creek, including Potato Mountain, are composed of similar slates. They apparently contain no intrusive, igneous rocks, either of the greenstone or granite type. Near the mouth of Buck Creek bowlders and pebbles of greenstone occur in the gravel deposits. These have not been traced to their source, but they probably came from a group of hills on the east side of Grouse Creek before the present drainage was established. At a number of places along Buck Creek small quartz veins were found cutting across the bedding or running parallel with it through the slate. Some of these quartz veins are as much as 3 or 4 feet thick, a The name Conical Hill was applied to this mountain by Captain Beechey in 1826. It is said to have been called " Potato Mountain" by the Russians. On the topographic map, Prof. Paper No. 2, Pl. XII, the mountain is called "Cone Hill." Most and two of them can be traced for a quarter of a mile or more. of the veins are mere stringers, 1 or 2 inches thick and only a few feet long. In one instance a vein of nearly pure pyrite 6 or 8 feet wide was seen. Pebbles of pyrite 2 or 3 inches in diameter, oxidized on the outside, are found in the gravels below this vein. Mr. Edgar Rickard reports on this deposit as follows: The source of the cassiterite can be readily traced to the slate of the [Potato Mountain] range, where it undoubtedly occurs in countless small veins and yugs, sometimes associated with quartz and so thoroughly scattered through the mass that the action of the elements has washed it from the hillsides and concentrated it in the streams below in appreciable deposits. Though specimens obtained from the gravel show that this is true, no veins of this kind were seen by Mr. Hess nor by the number of prospectors who were actively engaged in a search for tin-bearing veins. It is of interest to note that no granitic rocks or acid intrusives of any kind have been found associated with the phyllites, nor have any pebbles of such rocks been found in the gravels. So far as the surface indications show, it appears that the tin ore has its source in veins which are of distinct origin from those found in association with granitic rocks. The gravel deposits in the bed of Buck Creek are from 10 to 150 feet wide, varying greatly in different parts of the creek. Cassiterite, in the form of stream tin, is distributed from the mouth of the creek to within a mile of its head, above which point little more than traces have been found. The ore varies in size from fine sand to pebbles weighing 13 or 14 pounds. Several pieces from 5 to 8 pounds in weight were seen by Mr. Hess, though the average size is much smaller. A few of the pebbles are perfectly rounded, but most of them are subangular. The ore from the claims near the mouth of Buck Creek is generally well rounded, while that from near the head is sharp and angular. In general the stream tin grows more angular as the head of the creek is approached. The color of the cassiterite varies from almost black to a light resin or amber; when crushed, however, it makes a light-colored resinous powder, by which it is readily distinguished from hematite or other iron minerals that are frequently mistaken for it, since they invariably give a distinctly red, brown, or black powder. A number of specimens were obtained with pieces of quartz and slate still attached to them, leaving no doubt as to the local origin of the fragments. Sometimes small pieces of cassiterite are found inclosed between fragments of slate, showing that the ore sometimes occurs as veinlets in the bed rock. Near the head of Buck Creek Mr. Edgar Rickard," in 1902, tested a Rickard, Edgar, Tin deposits of the York region, Alaska: Eng. and Min. Jour., vol. 75, 1903, p. 30. |