Geological Survey Bulletin 1359 Geology and Mineral Resources of the Northern Part of the North Cascades National Park, Washington

DESCRIPTION OF MINERALIZED AREAS
(continued)

RED FACE MOUNTAIN AREA

Red Face Mountain (fig. 19) derives its name from the iron oxide stained zone 0.4 mile wide and 1.4 miles long that caps it. The north side of this mountain is generally precipitous, but the south side is somewhat gentler, with several small tarns scattered along a discontinuous bench high on the side of the ridge. Pyrite is disseminated in varying proportion throughout this zone, impregnating the country rock, which is mainly granodiorite but also includes dikes and irregular bodies of alaskite and plagioclase porphyry. In the 18 chip samples that were taken of this iron oxide-stained zone, the copper content ranged from 0.001 to 0.03 percent and averaged about 0.007 percent. Only one sample (120, table 1) contained as much as 0.002 percent molybdenum. One small boxwork of quartz veinlets (122, pl. 2) and three quartz veins (123, 128, 130, pl. 2) cut the iron oxide-stained rocks. These veins vary in thickness, but have an overall range of from 0.1 to 3 feet. The largest is exposed for a little more than 100 feet. They have diverse strikes and steep dips. Chip samples (122, 123, 128, 130, table 1), which were cut across the veins, did not yield any detectable gold or silver.

North of this large iron oxide-stained zone, on the east flank of Indian Mountain, is a similar but smaller zone (fig. 19). Four samples (106-109, table 1) from this zone contained 0.005-0.03 percent total copper and <0.0005-0.005 percent molybdenum.

A stream that drains both of these altered areas flows into Lake Reveille. A stream-sediment sample (153, table 1) taken at the outlet of this lake (fig. 19) contained 300 ppm cold copper and 50 ppm molybdenum. These values, especially the one for cold copper, suggest that portions of the altered zones contain more copper and probably more molybdenum than was obtained in our sampling.

South of the large iron oxide-stained zone on Red Face Mountain are several small scattered zones (fig. 19) that contain small amounts of copper (133, pl. 2).

Another zone of disseminated sulfides is indicated on the lower part of the south slope of Red Face Mountain by a stream-sediment sample (143, pl. 2) taken near the mouth of a tributary of Brush Creek. Sample 143 contains 150 ppm cold copper, whereas sediment samples (141, 142) taken 1,000-2,000 feet upstream contained only 10-20 ppm cold copper (fig. 19), suggesting a separate source of copper on the heavily wooded area between them.

A highly fractured iron-oxide-stained zone containing abundant pyrite extends for 2,000 feet northeastward from lower Middle Lakes (fig. 19). Several chip samples (168-171, table 1) along it were low in copper and molybdenum. Water seeping through this fractured zone has leached out iron which has been redeposited, in an area 270 by 210 feet, as a yellowish-brown bog iron deposit in the swale on the east side of the stream that drains lower Middle Lake. Two chip samples (173, 174, table 1; pl. 2) of this limonite yielded only 0.0005 percent copper and <0.0002 percent molybdenum.

Several zones of disseminated sulfides occur near East Lakes. The largest one is on cliffs several hundred feet high southeast of the lower of the two lakes (fig. 19). This zone is made up of fractured, iron oxide-stained granodiorite with abundant pyrite and, locally, traces of molybdenite; however, two chip samples (183, 184, pl. 2) contained no detectable molybdenum and only very small amounts of copper and lead. Specks of molybdenite that were noted in another part of this zone indicate an erratic distribution of the element. On the steep mountainside on the west side of East Lakes, two other disseminated zones were sampled. Chip samples 167 and 180 (pl. 2), from these two zones, contained 0.005 and 0.02 percent total copper and <0.0002 and 0.02 percent molybdenum, respectively. The zone with the higher molybdenum content is about 1,000 feet west of the lower lake and is an irregular zone about 150 feet across. This zone contains disseminated pyrite, which is most concentrated adjacent to and along joints. Several pieces of molybdenite, as large as 1 inch across, were found erratically distributed on a few fracture planes.

Three quartz veins and a mineralized dike were examined on the ridge north of Middle Lakes and East Lakes. The three quartz veins (162, 163, 165, pl. 2) have a N. 15°-40° E. strike and a steep dip, and two of the three veins are branched. These veins are irregular, range in thickness from 0.15 to 6 feet, and have a maximum exposed length of 150 feet. They cut granodiorite; quartz was the only mineral noted. Maximum gold content of chip samples across the three veins is 0.0006 ounce per ton.

The previously mentioned mineralized dike is near the top of the south side of a ridge west of Pass Creek and 500 feet west-southwest of peak 6861 (187, pl. 2). Here a dark irregular poorly exposed dike that strikes N. 75° E. cuts mafic granodiorite. At its principal exposure, the dike is 3-6 feet thick; at its only other exposure, 150 feet to the southwest, it is only a few tenths of a foot thick. This dike is heavily stained with iron oxides and contains scattered pyrrhotite. A 5-foot chip sample (187, table 1) yielded 1.0 percent zinc, 0.05 percent lead, 0.20 ounce of silver per ton, and 0.009 ounce of gold per ton.

LITTLE BEAVER CREEK AREA

Little Beaver Creek, one of the largest streams in the area, meanders down a wide, U-shaped, densely forested valley about 14 miles from Whatcom Pass to Ross Lake. In contrast to the main stream, the tributaries are generally small and plunge down cliffs and steep valley walls. As might be expected in a large stream, sediment samples from Little Beaver Creek did not yield anomalous amounts of metals. Anomalous values were obtained, however, from tributaries flowing into Little Beaver Creek from three areas (pl. 2): (1) the upper 3-1/2 miles of Little Beaver Creek, (2) the north side of Little Beaver Creek west of the mouth of Perry Creek, and (3) the lower 2 miles of Little Beaver Creek. Sediment samples from near the mouth of tributaries on the north side of the upper part of Little Beaver Creek (fig. 19) contained 2-100 ppm cold copper and 2-30 ppm molybdenum. These tributaries drain brown iron oxide-stained areas that have been discussed. Sediment samples from near the mouths of the tributaries along the south side of Little Beaver Creek contained 5-50 ppm cold copper but only <2-5 ppm molybdenum. In the headwaters of Little Beaver Creek a chip sample was taken of talus from a zone of iron oxide-stained quartz diorite on the cliff above. This sample (195, pl. 2) contained 0.02 percent copper and 0.015 percent lead. A stream-sediment sample (199, pl. 2) from the stream below the glacier west of Wiley Lake had 100 ppm cold copper. Iron oxide-stained quartz diorite float along this stream contained chalcopyrite along the joints.

Stream-sediment samples from near the mouths of tributaries that drain the north side of Little Beaver Creek west of the mouth of Perry Creek had 5-100 ppm cold copper and 3-15 ppm molybdenum. Sediment samples taken farther up the steep south-facing mountainside contained as much as 300 ppm cold copper and 70 ppm molybdenum (239, pl. 2). These tributaries drain a poorly exposed area of quartz diorite and Custer Gneiss of McTaggart and Thompson. In several places in the eastern part of this area, joints in the quartz diorite are coated with pyrite and a little chalcopyrite. In the Custer Gneiss, just west of the quartz diorite contact, we found several small zones of disseminated sulfides. Nine chip samples (60, 61, 218-224, pl. 2; table 1) from these zones contained small amounts of copper and insignificant amounts of other metals. Two other chip samples (216, 217; pl. 2) were taken from a layer of pyrrhotite and magnetite-bearing biotite gneiss. This layer is 18 feet thick and can be traced for several hundred feet in a N. 70° W. direction. Pyrrhotite, quartz, and a little chalcopyrite are found in the upper 8 feet of the layer, and magnetite and quartz are abundant in the lower 10 feet. A grab sample (216, table 1) of pyrrhotite-rich material from the upper part contained 0.50 percent copper; a grab sample (217, table 1) of the lower part yielded only 0.05 percent copper.

Three sediment samples (245, 248, 249, pl. 2) that had from 10 to 30 ppm cold copper were collected from tributaries near the mouth of Little Beaver Creek. These tributaries all drained greenstone of the Hozomeen Group of Cairnes. Similar values for cold copper have been obtained in several other places that drained this greenstone. In the other localities the source of the copper had been many widely scattered, small, irregular zones of disseminated sulfides that formed along shears in the greenstone.

ARCTIC CREEK AREA

Sediment samples taken in two areas along Arctic Creek, which flows east into Ross Lake (pl. 2), were found to be high in cold copper, heavy metals, and molybdenum. One of these areas is on the south side of Arctic Creek 1-1/2—2-1/2 miles above its mouth. Samples 276-282, 285, 287, and 288 (pl. 2), collected from tributaries in this area, contained 5-15 ppm cold copper, 3-30 ppm heavy metals, and 3-10 ppm molybdenum. The fact that the metal content does not increase upstream suggests a broad diffuse source of the metals. Greenstone, which is drained by these tributaries, contains small scattered zones of disseminated sulfides. Samples of greenstone with minor pyrite have only 0.005-0.007 percent copper. Similar anomalies were also found in the greenstone east of Ross Lake, where they were caused by many small scattered weakly mineralized zones and veins.

The other anomalous area on Arctic Creek is in its headwaters. Samples from seven small rivulets that cascade down a cirque wall into the southwestern branch of this creek contain 1-700 ppm cold copper, 5-200 ppm heavy metals, and 10-70 ppm molybdenum. These rivulets all drain a zone of disseminated sulfides that lies on the near-vertical cirque wall close to the top of the ridge. This zone, which has a northwest trend, is about 200 feet wide and can be traced for about a quarter of a mile. The disseminated zone is in an irregular tongue of gneiss that is surrounded and metamorphosed—mostly to skarn—by quartz diorite of the Chilliwack batholith. The disseminated zone, which is marked by brown staining, contains as much as 5 percent sulfides, most of which are pyrite and pyrrhotite. A dark mineral, believed to be chalcocite, was noted in one place. In nine samples (250-252, 260-265, pl. 2; table 1) taken in this zone, the copper content ranged from 0.0007 to 0.05 percent and averaged about 0.016 percent, and the molybdenum content ranged from <0.0005 to 0.01 percent and averaged about 0.0025 percent. The copper and molybdenum contents are very erratic, as indicated by the sample data and by the cold copper analyses of a few of the stream-sediment samples collected from very small tributaries that are higher in copper than any of the sulfide-bearing rocks sampled. The most likely reason for this discrepancy is that material in the small tributaries came from a part of the zone that was a higher grade than that sampled. The total size of these richer zones, however, is probably not large, for a sediment sample taken 1-1/2 miles downstream from the samples from the small tributaries in the cirque did not contain anomalous cold copper.

Small disseminated zones are scattered around the upper end of the cirque on the southeast branch of Arctic Creek. Six samples taken from five of these zones (266-270, 273, pl. 2; table 1) in the central and western part of the cirque contained 0.001-0.01 percent total copper. A sample (271, pl. 2; table 1) from an irregular disseminated zone 80 feet across on the ridge along the east side of this cirque contained 0.05 percent total copper.