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

DESCRIPTION OF MINERALIZED AREAS
(continued)

LITTLE FORK OF THE CHILLIWACK RIVER AREA

The Little Fork of the Chilliwack River, which is only a little more than 3 miles long, flows down a densely wooded valley that drains a quartz diorite terrain. Sediment samples were collected at the mouths of 20 tributaries that flow into this river (pl. 2). In the central and lower parts of the valley, sediment samples (870, 871, 873, 874, pl. 2; table 1) from four tributaries yielded 7-20 ppm cold copper, and a sample from a fifth tributary (869) yielded 500 ppm cold copper. The tributary from which the highest copper sample was obtained was traced up a heavily wooded mountainside, on which exposures are meager and widely separated. Iron oxide staining was not observed on any of the outcrops or on pieces of quartz diorite float. Three chip samples were taken at different elevations up the mountain from float specimens that contained scattered pyrite. In order of increasing elevation the samples, 866, 867, and 868 (pl. 2; table 1), contained 0.015, 0.007, and 0.015 percent total copper and 0.002, 0.0005, and 0.015 per cent molybdenum, respectively. Although these zones undoubtedly furnished some copper, the higher value obtained at the tributary's mouth indicates that the principal source of the copper was not found.

At the headwaters of the Little Fork of the Chilliwack River, samples (861-863) from three tributaries draining the east and south sides of the valley contained 10-20 ppm molybdenum. As all these tributaries have a small flow and are 1 mile or less in length, the source of the molybdenum is most likely small or low grade. All three tributaries drain thickly forested slopes; therefore, no attempt was made to locate the source of the anomalous samples.

CHILLIWACK RIVER AREA

The Chilliwack River heads near Hannegan Pass and flows north into Canada. It is the major drainage in the northwest part of the study area, and many streams flow into it, including the previously mentioned Depot, Indian, Bear, and Easy Creeks and the Little Fork of the Chilliwack River.

Stream-sediment samples were collected from the small tributaries that enter the Chilliwack River. Chip samples of iron oxide-stained zones were also collected wherever found on the valley sides and ridges. Only a few stream sediment and chip samples contained anomalous amounts of metals. Three areas are of particular interest: the area on the ridge east of the Chilliwack River near the Canadian border and the areas west of the mouths of Indian and Easy Creeks.

In the first area, which is on a ridge crest 1-2 miles south of the Canadian border, eight iron oxide-stained zones, 1-4 feet wide, occur near the contact between granodiorite of the Chilliwack batholith and the Custer Gneiss of McTaggart and Thompson. The northern two zones are in the granodiorite; the other six are in the gneiss. All are along shears or small faults that strike N. 45° E. to east and dip 50°-60° S. Chip samples (893, 894, 896-898, 901-904, 906, pl. 2; table 1) across seven of these zones yielded 0.003-0.03 percent copper. A sample (895) across the third zone from the north had 0.10 percent copper (pl. 2). This zone, which is 2 feet wide, could be traced for about 200 feet. The northernmost sample (893), which was also across a 2-foot-wide zone, had 0.015 percent lead. Molybdenum was low in all samples.

The second area is a small tributary west of the mouth of Indian Creek (pl. 2). A sediment sample (919, pl. 2; table 1) from the mouth of this tributary, which flows over quartz diorite, had 50 ppm cold copper. A sediment sample (917) taken from a spring issuing out of the bank about a third of the way up the mountain had 200 ppm cold copper. Sediment samples 916 and 918, taken on the main tributary above this spring, contained 15 and 30 ppm cold copper, respectively. The source of the copper coming from the spring is not known.

The third area that contains anomalous amounts of metal is west of the mouth of Easy Creek, where sediment samples (928, 929, 935, 938, pl. 2; table 1) from the mouths of four small tributaries to the Chilliwack River contained 15-500 ppm heavy metals. These samples are unusual in that they have a low cold copper content. The lower part of the small tributary from which the sample (935) that contained 500 ppm heavy metals was obtained flows down a steep bouldery water course between forested, soil-covered banks. A sediment sample (937) taken where the stream starts cascading down rock outcrops showed 70 ppm heavy metals; thus the source of much of the heavy metals is beneath the cover on the hillside. Samples (935, 929) taken at the mouths of two other tributaries contained 50 and 70 ppm heavy metals; these tributaries were traced upward into steep rocky gorges cut into alaskite. The alaskite is in places sheared and faintly stained with iron oxides. Two samples taken of the iron oxide-stained rock in each gorge had <0.02 percent zinc. Samples (931, 932) from the easternmost gorge had 0.001 percent lead; samples 943 and 940, from the westernmost gorge, had 0.003 and 0.015 percent lead, respectively. Sediment samples from the tributaries, above the faint iron oxide-stained zones, were not anomalous in heavy metals. As the lower limit of detection of the spectrographic analysis for zinc is high (200 ppm) and that for combined heavy metals by our geochemical method is relatively low (1 ppm), the presence of anomalous amounts of zinc below 200 ppm in the sheared iron oxide-stained rocks might be sufficient to account for the anomalies found in these two tributaries.

HANNEGAN PASS-RUTH MOUNTAIN AREA

The Hannegan Pass-Ruth Mountain area lies along the main north-trending ridge on the west boundary of the study area between Hannegan Peak and Ruth Mountain (pl. 2). This is one of the most easily reached parts of the area studied, for the principal east-west trail in the western part of the area crosses the ridge at Hannegan Pass, and hence it is one of the more thoroughly prospected areas. The Hannegan Pass group of six claims was located in and near Hannegan Pass in 1895, and several other claims were located in the vicinity between 1897 and 1909. Several sloughed pits and two adits, one of them caved, were found on the mountain on the north side of Hannegan Pass; another small adit lies to the west and 500 feet vertically below the pass.

This area for the most part is in the Hannegan Volcanics, although a small tongue of quartz diorite of the Chilliwack batholith is exposed within Hannegan Pass (pl. 1). The workings on the north side of Hannegan Pass are in quartz diorite near its contact with the volcanics. Several trenches, as much as 30 feet long, and an adit were dug in the lower soil-covered part of this slope. These workings are now sloughed in, but iron oxide-stained quartz diorite debris on the dumps indicates that bedrock was reached in most of them. Six grab samples (962, 963, 965, 966, 968, 969, pl. 2; table 1) were taken from dumps of the sloughed workings. Several samples yielded traces of gold and silver, but none contained anomalous copper or molybdenum. Above the trenches a 6-foot-long adit is driven into an outcrop of iron oxide-stained quartz diorite. A sample (961) containing disseminated pyrite from the back of this adit and three other samples (960, 964, 967) from this same iron oxide-stained outcrop did not yield any gold, silver, copper, or molybdenum.

The adit west of Hannegan Pass is on a small creek that drains a little meadow some 500 feet below the pass at an approximate elevation of 4,550 feet. The adit, which is only 6 feet long, is between two small waterfalls in an 80-foot-wide silicified iron oxide-stained zone that contains disseminated pyrite. This zone, which is in quartz diorite, trends N. 45° E. One chip sample (971, pl. 2; table 1) was taken along the sides and back of the adit, and another (970) was taken across 20 feet of the iron oxide-stained zone where it crosses the trail above the adit. Gold was not detected in either sample.

Several old claims are reported in the county courthouse records as being on or in the vicinity of Ruth Mountain. The descriptions of some of these claims, however, indicate that the name Ruth Mountain was used in the late 1890's and early 1900's for a different mountain, a peak on the ridge on the north side of Ruth Creek, west of the study area. Nevertheless, a careful examination was made of Ruth Mountain, as presently shown on the maps, and we found several iron oxide-stained zones in the Hannegan Volcanics. Samples were taken of zones on the north, west, and south flanks of this mountain (pl. 2). None contained anomalous amounts of gold, silver, or molybdenum. One sample (976, pl. 2; table 1) of a 2-inch-thick iron oxide-stained zone along a fracture on the north flank of Ruth Mountain had 0.03 percent copper.

SILESIA CREEK AREA

Silesia Creek is the major stream that drains the northwest part of the area. Thirty-six sediment samples were taken from tributaries that flow into this stream (pl. 2). Only samples from two tributaries that drain the west side of Copper Mountain were anomalous for copper or molybdenum, and these samples (1025, 1035, table 1) had 50 and 1 ppm cold copper and 30 and 50 ppm molybdenum, respectively. About a quarter of the way up the more northern of the two tributaries, we found several zones containing disseminated pyrite. A chip sample (1022) from the lowest of these zones, which is about 50 feet across, had 0.02 percent copper and 0.03 percent molybdenum. Just above this zone is a second zone, which is exposed for 100 feet up the creek bottom. A chip sample (1023) from this bleached zone, which is cut by drusy quartz seams, yielded 0.015 percent copper and 0.02 percent molybdenum. Farther upstreamn were irregular patches of iron oxide-stained quartz diorite cut by several alaskite dikes as much as 20 feet thick. Within the dikes were scattered pods of sulfides, mainly pyrite, but including some molybdenite. A chip sample (1021) of the iron oxide-stained quartz diorite contained 0.05 percent copper and 0.01 percent molybdenum. A stream-sediment sample on the tributary above this last sample was low in copper (pl. 2); thus the disseminated zones sampled are possibly the source of the copper and molybdenum obtained at the mouth of the tributary.

A sediment sample (1016, pl. 2; table 1) from a large tributary draining the northeast side of Silesia Creek yielded 15 ppm heavy metals. Six zones of iron oxide-stained rock were sampled (1010-1015, pl. 2; table 1) on the ridge north of this tributary. All were either in quartz diorite of the Chilliwack batholith or in the adjacent metamorphosed arkosic sandstone of the Chuckanut Formation. Three of these samples (1013-1015) contained 0.07 percent or more zinc. The sample (1013) with the highest zinc content, 0.30 percent, came from two small adjacent iron oxide-stained zones totaling about 5 feet across in sandstone inclusions surrounded by quartz diorite. The next highest sample (1015), which yielded 0.10 percent zinc, was a composite sample from several small irregular zones 2 inches to 20 feet across that lie adjacent to the north side of the tributary. Sample 1014, which had 0.07 percent zinc, was from a small iron oxide-stained zone, 5 by 15 feet in size, on the west end of the ridge. Although these zones are small, their zinc content is relatively high.

Several small calcite veins were found at two localities near the top of the high ridge on the southwest side of Silesia Creek between peaks 6839 and 7035 (pl. 2). The most northerly of these veins is 2,400 feet south of peak 6839 and 200 feet below and to the east of the top of the pinnacles that cap this part of the ridge. Here a calcite vein cuts sheared biotite-hornblende-quartz diorite. This vein strikes N. 42° E. and dips vertically. It is 0.3 feet thick and is exposed for approximately 40 feet. On either side of the vein is a 4-foot-wide zone of iron oxide-stained quartz diorite. A 0.3-foot channel sample (1004, pl. 2; table 1) was cut across the vein, and an 8-foot chip sample (1005) was taken of the altered rock on either side of the vein. Neither sample contained anomalous amounts of copper, lead, zinc, molybdenum, silver, or gold. The second locality is 800 feet south-southeast of the first zone and at about the same elevation. Several branching white calcite veins cut biotite-hornblende-quartz diorite on a cliff face area of 10 by 25 feet at this locality. These veins generally strike N. 35° E. and dip 75° NW.-75° SE. The quartz diorite on either side of these veins is bleached and stained with iron oxide. Three samples were taken from this exposure: (1) a 0.6-foot channel sample (1006, pl. 2; table 1) across a 0.3-foot calcite vein and the altered country rock adjacent to it at the south side of the exposure, (2) a 1-foot channel sample (1007) of a 0.3-foot calcite vein and the altered rock adjacent to it at the north side of the exposure, and (3) a 2-foot chip sample (1008) across several small veins and the intervening country rock in the center of the exposure. All three samples contained 0.02 percent zinc, but were low in other metals.

WEST FORK OF SILESIA CREEK AREA

The West Fork of Silesia Creek lies along the west boundary of the study area, but tributaries on its east side drain a ridge within the study area. Samples (1052, 1053, 1061) from three west-flowing tributaries about 1—1-/2 miles above the mouth of Winchester Creek contain 7-10 ppm heavy metals. Sample 1053 bad the highest heavy metals value, and the tributary from which this sample was taken was traced upward. In the three sediment samples (1054, 1056, 1058, pl. 2; table 1) that were taken along this tributary, heavy metals increased to 30 ppm. Chip samples (1055, 1057, table 1) were also taken from several small iron oxide-stained areas along the way. None contained anomalous amounts of lead, zinc, copper, or molybdenum. Above the last sediment sample near the ridgetop, however, several small iron oxide-stained areas were found along joints in a dacite flow. A composite chip sample (1060, table 1) from a few of these areas bad 0.02 percent lead.