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

DESCRIPTION OF MINERALIZED AREAS
(continued)

SULPHIDE BASIN AREA

Sulphide basin is underlain mainly by phyllite and greenschist of Mount Shuksan, which has been intruded by two small quartz diorite stocks of the Chilliwack batholith (fig. 10). On top of the ridge that bounds the east side of Sulphide Creek is a small area of volcanic breccia of the Hannegan Volcanics. The basin is drained by several tributaries of Sulphide Creek which, in the headwaters area, cascade down near-vertical-walled cirques. Access to the basin from the end of the road up Baker River is by 3 miles of low-gradient trail to the mouth of Sulphide Creek and then 1 mile without trail up the creek.

The Dead Goat claim was located by Lester McCullough, Ben Hinkle, and Clarence Keplinger on a prominent westward-flowing tributary of the east branch of Sulphide Creek at an elevation of 1,600 feet. At the claim site a small quartz diorite stock intrudes black phyllite. Along the contact is a zone, at least 80 feet wide, which consists of fragments of a dark-gray diorite and partly assimilated phyllite surrounded by cream-colored quartz diorite. The zone is visible for only 30 feet along the watercourse. In this contact zone are numerous quartz veins as much as 2 inches thick. These veins have a variable but generally northward trend and dip 10°-30° E. Massive seams of molybdenite as much as three-fourths inch thick are found along these veins. Small flakes of molybdenite also were seen in the rock between the veins, but no molybdenite was seen in the water-scoured streambed. An 80-foot chip sample (675, pl. 2) that was taken across the entire contact zone between the veins contained 0.09 ounce of silver per ton and a trace of gold, but no detectable molybdenum, copper, lead, or zinc. Two other samples taken by the claim owners in the lower third of the zone, in rock that did not have any obvious molybdenite, yielded 0.015 and 0.03 percent molybdenum and 0.04 and 0.02 percent copper. Even including the molybdenite-rich veinlets, the average tenor of the contact zone is very low.

The Molly claim is about 2,500 feet north of the Dead Goat prospect and lies across the east branch of Sulphide Creek. This claim has molybdenite-rich quartz veins similar to those of the Dead Goat prospect, but the occurrence appears to he less promising.

Many claims are staked on a large U-shaped iron oxide-stained zone that curves around the east branch of Sulphide Creek. This zone is 2.5 miles long and has an average width of about 0.3 mile (fig. 10). Much of this zone is exposed in the steep cliffs that form the headwalls of this tributary. Staining is due to oxidation of abundant disseminated pyrite and pyrrhotite. Chalopyrite and molybdenite were seen in a few places. Two of the three small pits found in Sulphide basin occur on the old Union claim in an upper basin at the head of the east fork of Sulphide Creek at an elevation of about 3,040 feet. Two pits were dug in a highly iron oxide-stained part of the zone (fig. 20). At this locality a pod of massive pyrite, 3-10 inches thick, is exposed for 7 feet in the lower pit (fig. 20). A 7-foot sample (637, fig. 20) cut along the pod did not contain any detectable gold, silver, lead, zinc, or molybdenum. A chip sample (638, fig. 20) across a pyrite-rich quartz vein exposed in the upper pit assayed 0.015 percent copper but no gold, silver, molybdenum, or zinc.

FIGURE 20.—Union Prospect in Sulphide basin. (click on image for an enlargement in a new window)

A total of 18 chip samples taken of the large disseminated zone contained minor but varying quantities of copper, molybdenum, silver, and gold. Copper content of two samples (640, 643, pl. 2) was as much as 0.05 percent, but the average indicated by the samples is probably near 0.02 percent. Molybdenum was not detected in most samples, although one sample (653) had 0.02 percent. A trace of silver was found in most samples; several had 0.04 ounce per ton. Gold was not detected in most samples, although several had a trace, and one (646) had 0.30 ounce per ton. The lack of access to large parts of this disseminated sulfide zone resulted in inadequate sampling of these areas. The general tenor of the samples taken, however, is so low that there is little indication of the presence of any minable deposits.

Near the crest of a ridge to the northwest of the large disseminated zone, about N. 60° E. of Sulphide Lake, is a 6-inch-wide vein containing manganese oxides and rhodonite. This vein is in a wide shear zone, in contorted phyllite, that strikes north and dips 60° S. From near the top of the ridge, the shear zone can be seen angling up the steep craggy ridge for about 150 feet; it probably extends to the west side of the ridge. Samples (650, 651, pl. 2) of the vein contained 4.2 and 7.8 percent manganese, but no detectable gold, silver, copper, or molybdenum.

Another prospect is on a small quartz vein on the crest of the steep ridge east of Sulphide Creek basin and a half mile south-southeast of Seahpo Peak. It consists of a small pit, 6 feet wide, 8 feet long, and about 1 foot deep, that has been dug in black phyllite. Along the back of the pit is a flat-lying iron oxide-stained quartz vein that has a general strike of N. 5° W. and a dip of about 15° NE. This vein, which is 0.1-0.8 foot thick, is exposed for about 20 feet. A channel sample (637, pl. 2) across the quartz vein in the back of the pit did not yield any detectable gold.

Panned samples were taken between the mouth and the main forks of Sulphide Creek, but no gold was found in them. The stream gravels contain less than 5 pounds of black sand per cubic yard. The black sand consists of pyrite, magnetite, garnet, epidote, and generally a few flakes of molybdenite.

DEPOT CREEK AREA

Sediment samples were collected from most of the tributaries that enter Depot Creek, which drains the north side of Mount Redoubt and flows north into Canada. Samples from two tributaries about 1-1/2—2 miles below the headwaters had anomalous amounts of cold copper. Samples (736-739, pl. 2; table 1) from a tributary on the southwest side of Depot Creek contained as much as 30 ppm cold copper. This tributary drains a part of the big Redoubt Glacier. Several small, widely spaced, half-inch-thick veins of pyrite with a little chalcopyrite were found just below the glacier. Scattered glacial boulders in the same area contain disseminated pyrite and pyrrhotite, and several iron oxide-stained zones can be seen above the glacier on the near-vertical northeast fact of Mount Redoubt. The cold copper in this tributary probably comes from both the small veins and the disseminated zones on the cliff.

Samples (732-734, pl. 2; table 1) from a tributary on the northeast side of Depot Creek yielded 50-500 ppm cold copper. Several iron oxide-stained zones of disseminated sulfides crop out on the mountain above. Five chip samples (724-726, 729-730, pl. 2; table 1) were taken on the largest zone, which is about 1 mile long and lies mainly north of the area drained by the tributary containing the samples with the higher copper values. Samples from this large zone yielded 0.0003-0.005 percent copper. Molybdenum was detected in only one sample. Another chip sample was taken on a smaller disseminated zone directly east and above the tributary containing the high cold copper values. This sample (731, pl. 2) had 0.01 percent copper and 0.01 percent lead. The difference between the copper content of much higher stream samples and that of the rock samples suggests that part of the disseminated zone contains considerably more copper than the site that was sampled.

Nine other chip samples of disseminated sulfide zones were taken downstream in the Depot Creek drainage. These contained 0.0015.-0.015 percent copper and <0.001-0.03 percent lead. Two samples (748, 749, pl. 2; table 1) that contain 0.01 and 0.03 percent lead came from west of a small lake that is 1.4 miles northwest of the top of Mount Redoubt. These two samples were among five collected from disseminated zones along and adjacent to a northeast-trending fault. The highest value came from a zone lying across a small fault.

BEAR CREEK AREA

Bear Creek flows down a heavily wooded valley and drains steep bare ridges that form the northeast side at Mount Redoubt and the southwest side of Bear Mountain. Sediment samples were collected from all flowing tributaries of Bear Creek, and anomalous amounts of copper and molybdenum were found in two areas. One of these is from near the middle part of Bear Creek, where samples from several tributaries on the northeast side of the creek contained 10-15 ppm cold copper and molybdenum. Iron oxide-stained zones, 1-180 feet wide, of disseminated pyrite occur on the ridge northeast of the sample localities. Most of these rocks contain only minor amounts of copper (0.002-0.01 percent) and molybdenum (<0.0005-0.0007 per cent). One small iron oxide-stained zone, approximately 2,800 feet south-southwest of a peak at an altitude of 7,365 feet, lies adjacent to a quartz vein that cuts biotite-quartz diorite. This vein is 0.2 foot thick, is exposed for about 40 feet, and contains a few small scattered molybdenite crystals. Chip samples were taken of the quartz vein and of the adjacent iron oxide-stained country rock. Sample 763 (pl. 2; table 1) of the vein contained 0.004 percent molybdenum; sample 764 of the adjacent country rock, however, yielded 0.07 per cent molybdenum, 0.03 percent copper, and 0.20 ounce of silver per ton.

The other anomalous area is near the upper end of Bear Creek, where several tributaries that drain the north side of Bear Mountain contain 15-20 ppm cold copper and 20-50 ppm molybdenum. These tributaries receive their high metal content from disseminated sulfide zones high on the northwest side of Bear Mountain. One of the largest of these is triangular in shape, roughly 150-200 feet on the sides. Sulfide content of this zone is erratic and is higher in the narrow borders along joints in granodiorite than in the rest of the zone. A chip sample (777, pl. 2; table 1) taken at random across the larger of the disseminated zones contained 0.015 percent total copper and 0.002 percent molybdenum. An 8-inch sample (778) across a joint within the larger zone contained 0.03 percent copper, 0.02 percent lead, and 0.01 percent molybdenum. Seven other samples taken across narrow disseminated zones, 1-1/2—6 feet wide, yielded 0.007-0.03 percent copper and <0.0005-0.015 percent molybdenum.

INDIAN CREEK AREA

Indian Creek drains a deep valley between Bear Mountain on the north and Red Face Mountain on the south. All the Indian Creek drainage is discussed here except the tributary that drains Lake Reveille, which was included in the discussion of the Red Face Mountain area. Sediment samples from six tributaries that drain the south side of Bear Mountain contained anomalous amounts of cold copper or molybdenum, or both. Nine of these sediment samples (796, 798, 802, 805-807, 810-812, pl. 2; table 1) contained 7-70 ppm cold copper and 3-20 ppm molybdenum. The source of this anomalous metal content is a number of small iron oxide-stained zones in the granodiorite country rock. These zones are rarely more than 2 feet wide. Some are exposed for a length of only 15 feet or less, although a few are exposed for as much as 200 feet. Two chip samples (813, 814, pl. 2; table 1), one each from two of the longest of these narrow zones, just south of Bear Mountain, had 0.05 percent copper. In addition, one sample (813) contained 0.003 percent molybdenum, 0.06 ounce of silver per ton, and 0.003 ounce of gold per ton, and the other (814) yielded 0.44 ounce of silver per ton and 0.10 ounce of gold per ton. Two chip samples (794, 795, pl. 2; table 1), one each from two other small iron oxide-stained zones, contained 0.05 percent total copper. These samples were from adjacent pyrite-bearing zones along joints about half a mile west of the top of Bear Mountain. In addition to copper, one sample (794) contained 0.03 percent lead, 0.001 percent molybdenum, and 0.87 ounce of silver per ton; the other (795) yielded 0.007 percent lead, 0.0007 percent molybdenum, and 0.20 ounce of silver per ton.

The Packsaddle placer claims lie along the central part of Indian Creek, about 3 miles above its mouth and 2,000 feet east of its junction with a tributary that drains Lake Reveille. This property is reached by a narrow trail along the northeast side of Indian Creek that leaves the Chilliwack River trail at the Indian Creek shelter. Unconsolidated alluvium was placered in a sluice built in a high-water channel. Sand panned from a sandbar produced one-half ounce of heavy mineral concentrate from three 16-inch-diameter pans. This concentrate (808, pl. 2) did not yield any detectable gold. Sand samples 793 and 790 (pl. 2; table 1), panned about 1-1/2 and 3 miles below Packsaddle placer claims, yielded 0.002 and 0.001 ounce of gold per ton, respectively.

EASY RIDGE

Easy Ridge is a broad, fairly flat topped, steep-sided ridge that trends northwest from Whatcom Peak to the Chilliwack River, a distance of about 5 miles. The ridge is underlain by granodiorite that is cut by numerous north-trending alaskite dikes and a few small diorite bodies. Several narrow zones that contain pyrite either in disseminated cubes or in veinlets occur in an area about 1-1/2 miles long on the top of this ridge in the vicinity of Easy Peak. In a few places a little chalcopyrite is present in the zones. Although these zones contain abundant pyrite, the rocks were fresh and unstained. Fourteen samples of these zones (pl. 2) contained 0.005-0.30 percent copper and <0.0005-0.03 percent molybdenum. Of the six samples with the highest copper and molybdenum content, one (852), from near the top of Easy Peak, was cut across a 1-inch-wide pyrite veinlet and the adjoining silicified alaskite. This sample yielded 0.15 percent copper, 0.03 percent zinc, and 0.003 percent molybdenum. An adjacent sample (853, pl. 2; table 1) of silicified alaskite with disseminated pyrite had 0.007 percent copper, <0.02 percent zinc, and 0.03 percent molybdenum. About 1,400 feet southeast along the ridge from the top of Easy Peak, two other samples were collected from pyrite veinlets and the adjacent pyritized diorite. Both of these samples (856, 857, pl. 2; table 1) contained 0.15 percent copper, <0.02 percent zinc, and 0.007 percent molybdenum. The other two copper-rich samples came from an area 260 feet east of the two samples just described. One was cut across 2 feet of pyrite-bearing diorite and a 1/4-inch-thick pyrite veinlet; the other was a sample of another area with a pyrite veinlet and accompanying pyrite-rich wallrock, about 2 feet from the first sample. These two samples, 858 and 859 (pl. 2; table 1) had 0.30 and 0.05 percent copper, <0.02 and <0.02 percent zinc, and 0.007 and 0.003 percent molybdenum, respectively. Although the copper content of these disseminated zones is one of the highest found in the study area, the individual zones are small, for they generally consist of rock containing disseminated sulfides that extends only a few feet from a small sulfide veinlet.

EASY CREEK AREA

Easy Creek is a northwestward-flowing 2-mile-long tributary of the Chilliwack River that heads in a cirque between Easy Peak and Mineral Mountain. Five sediment samples (837, 839, 841-843, pl. 2; table 1) collected from tributaries around the head of the cirque had 10-20 ppm molybdenum. Sample 842, which came from one of the two tributaries that drained Mineral Mountain, also had 15 ppm heavy metals; sample 843, from another tributary, had 10 ppm cold copper. We did not attempt to trace the source of the two samples from the tributaries that drain Mineral Mountain, for the tributaries cascade off a series of cliffs on the steep southwest face of the cirque, but the streams head 1 mile or less from the sample localities. The tributaries that drain the northeast side of the cirque flow for most of their courses down the thick talus that forms the west side of Easy Ridge. No samples of mineralized rock were collected in this area.