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

DESCRIPTION OF MINERALIZED AREAS

Principal mineralized areas are described in this section of the report. For convenience, the mineralized areas are discussed by individual drainage basins. Some large zones of disseminated sulfides that lie in parts of several drainage basins are described under a single heading such as the name of an easily identified peak or ridge.

The description of each drainage basin or ridge may include not only a discussion of zones of disseminated sulfides and veins present but also a consideration of significant stream sediment anomalies. Zones of disseminated sulfides, which contained only iron sulfides, are not described, nor are drainage basins without known geochemical anomalies or evidence of mineralization.

SILVER CREEK AREA

Silver Creek flows for 6 miles down a deep, wide valley from its headwaters in a glacial tarn to its mouth on Ross Lake. Several prospects are known in the Silver Creek area, of which the Weezie, or Silver Creek, prospect is the most promising. In addition to the Weezie, other areas of interest are (1) the south side of the creek, where other prospects are reported, (2) an area of anomalous sediment samples west of the Weezie prospect, (3) two trenches on the ridge north of the west part of Silver Creek, and (4) a series of quartz veins containing chlorite, tourmaline, and sericite that are exposed for 1.5 miles along the ridge on the south side of the creek.

The Weezie claim lies on the north side of Silver Creek about 1.5 miles by steep trail from Ross Lake at an approximate elevation of 2,900 feet. Six claims were located in this general area in 1927 (Shideler, 1965, p. 83). Later four claims were relocated in this area, and in 1954 they were held by Roy Davis, George Hunt, and A. E. Blockberger (Purdy, 1954, p. 87). Between 1956 and 1958 the area was owned by the Coronado Copper Co. of Idaho (Shideler, 1965, p. 83). In 1965 seven claims were relocated by Robert Grant with the name Weezie No. 1 given to the one covering the principal disseminated sulfide deposit. This property was sold in 1966 to the Inland Cooper Co. of Washington.

Workings on the Weezie No. 1 claims (fig. 18) consist of an 80-foot adit and two groups of cuts on separate outcrops. The first group of cuts is adjacent to and north of the adit, and the second group is along a small ridge 200 feet to the west. Several diamond-drill holes were drilled during 1966 and 1967, but data on the holes were not available. The workings are mainly in a massive gray volcanic breccia of the Skagit Volcanics, which is cut to the northwest and to the north east by quartz diorite of the Chilliwack batholith (fig. 18). Small dikes of quartz diorite cut the volcanic breccia in several places, and biotite granodiorite intrusive is exposed in the adit (fig. 18). Breccia near the northwest contact of the volcanics consists of fragments of volcanic rock enclosed in a quartz diorite matrix.

Disseminated sulfides, principally chalcopyrite and pyrite, occur erratically in areas outlined roughly by the workings and separated by a covered area. Rough dimensions of this total area is 200 by 240 feet. Molybdenite is common locally, and bornite and covellite were seen in a few places. In some pyrite-rich spots the rock is heavily stained with iron oxides. Kaolinite also occurs in places and is most common in a northerly trending zone north of the portal of the adit.

Chip samples 35 and 36 were taken in the adit, and five other chip samples (33, 34, 37, 43, 45, fig. 18; table 1) of the sulfide-bearing volcanic breccia were taken from small cuts in the adjacent (eastern) outcrop. The copper content of these samples ranged from 0.15 to 2.26 percent and averaged 0.72 percent, and the molybdenum content ranged from 0 to 0.5 percent and averaged 0.11 percent. Sample 35, which came from near the face of the adit, contained the most copper (2.26 percent), but it contained only 0.03 percent molybdenum. In five chip samples (32, 38, 42, 44, 46) taken from cuts in the western outcrop the copper content ranged from 0.09 to 0.15 percent and averaged 0.14 percent, and the molybdenum content ranged from a trace to 0.04 percent and averaged 0.007 percent. A fault southeast of the adit separates mineralized volcanic breccia from nonmineralized volcanic breccia. Two samples (39, 40) were taken along this fault, and both contained a trace of copper but no molybdenum. A sample (41) of quartz diorite taken 100 feet northwest of the volcanic breccia contact also yielded a trace of copper but no molybdenum.

FIGURE 18.—Workings on the Weezie claim on Silver Creek. Mapped by R. M. Van Noy and E. C. Pattee, August 1967. (click on image for an enlargement in a new window)

Although the grade of parts of this disseminated body is comparable with the grade of deposits that have been mined, the available data indicate that the deposit is too small to be economic and that the cost of mining would he more than twice the value of the mineralized material.

Molybdenum and copper minerals have been reported (Purdy, 1954, p. 87; Shideler, 1965, p. 84-85) on the south side of Silver Creek. Shideler (1965, p. 84) described the locality as being 300 feet south of Silver Creek and south of the Weezie adit. Although we searched this area, we were unable to find the deposits. The following brief description therefore is taken from Purdy (1954, p. 87):

The deposits consist of 1/4—1-inch stringers of quartz containing scattered chalcopyrite and clusters of molybdenite. The stringers, striking a few degrees west of north, are in granodiorite close to its contact with volcanic rock. At the outcrop the distance across the strike of the quartz stringers is about 10 feet. How far they may be traced along their strike is a question that could not be answered at the time of the examination because of the overburden and brush.

Five stream-sediment samples collected on tributaries upstream from the Weezie property contained 10-20 ppm cold copper. Three of these samples (29, 30, 31, pl. 2; table 1) were collected from tributaries on the north side of the creek, and two (25, 26) from the south side. The samples from the north side came from the three tributaries just west of the one that drains the Weezie property. All three tributaries drain a tongue of quartz diorite that intrudes the Hannegan Volcanics. By contrast, the next tributary to the west does not drain the quartz diorite, and it yielded a sample that contains only 5 ppm cold copper. Pyrite is found in the float of the volcanics from above the quartz diorite contact in the western two tributaries, and one sample (28) of this material contained 0.015 percent total copper. Samples 25 and 26, anomalous samples from the south side of Silver Creek, are from tributaries that also flow across a quartz diorite-volcanic rock contact. The north-facing slope is densely forested, and no attempt was made to trace the anomalous copper samples to their source.

Two trenches in light-greenish-gray welded tuff of the Skagit Volcanics are near the top of the ridge on the north side of Silver Creek 2.9 miles northeast of Glacier Peak. These trenches are probably the discovery pits on the Gold Top and Silver King claims. The Gold Top was located in 1918 by Ed Marshall and P. A. De Fries. Its north boundary is 40 feet southwest of Boundary Monument 69. A small north-trending trench 4 feet wide by 10 feet long is near the south end of this property, about 200 feet south of the ridge crest. In the trench, an iron oxide-strained zone 8 feet long by 7 feet wide contains disseminated pyrite and pyrrhotite. Chip samples 7 and 8 (table 1) from this zone were low in copper, molybdenum, lead, and zinc, but sample 8 contained 0.02 ounce of gold per ton and a trace of silver.

The Silver King claim, which is south of the Gold Top claim, was located in 1918 by C. J. Howlett and Irie Town. A 5-foot-long trench been dug 200-300 feet downslope from the trench on the Gold Top exposing a small quartz vein. A sample (9, table 1) from this vein contained no gold, silver, copper, or molybdenum. About 1,000 feet downslope from this trench, an iron oxide-stained zone, which is exposed in the bottom of a gully, is cut by a quartz vein that contains disseminated pyrite. Two samples (10, 11, table 1) of this vein were collected at localities 8 feet apart. One contained 0.60 ounce of silver per ton, and the other 0.06 ounce; both contained a trace of gold, but no other metals were found.

On the main ridge south of Silver Creek, 2.2-3.5 miles east-southeast of Glacier Peak, we found seven localities (13, 16, 17, 18, 19, 20, 22, pl. 2) in which one or more steeply dipping northeast-trending quartz veins occurred. One vein had been tested by a small prospect pit. These veins strike N. 10°-50° E. and dip 80° SE. to 75° NW. Their thickness ranges from a fraction of an inch to 10 feet and averages about 1 foot. Outcrops in this area are poor, and exposed vein lengths between scree and snow cover are 20-70 feet. All the veins contained, in addition to quartz, some limonite, and most of them also contained minor amounts of sericite, chlorite, pyrite, or tourmaline. All the veins are in quartz diorite except the easternmost vein (loc. 22) which is near the center of a 2,000-foot-wide roof pendant of Custer Gneiss of McTaggart and Thompson. Seven chip samples (13, 16, 17, 18, 19, 20, 22, table 1), taken across the width of the veins, contained 0.005-0.05 percent copper and <0.003-0.003 ounce of gold per ton. The sample from locality 22 also contained 0.02 percent lead and 0.03 ounce of silver per ton. The sample from locality 20 yielded 0.02 percent tin.

PASS CREEK AREA

Pass Creek flows south into Little Beaver Creek about 3 miles east of Red Face Mountain (fig. 19: pl. 2). Custer Gneiss of McTaggart and Thompson (1967) is the dominant rock exposed in the Pass Creek drainage, but granodiorite intrudes the gneiss near the head of the stream. Sulfide minerals are disseminated in the gneiss east of the creek and in the cirques at its head. Weathering of the sulfides to iron oxides causes them to be readily visible. The largest iron oxide-stained zone, 1.3 miles long by 0.5 mile wide, lies east of the central part of Pass Creek (fig. 19). The staining, which is not uniform, is strongest where pyrite is most common, along joints and in plagioclase porphyry dikes that cut the gneisses. Six chip samples (95-99, 103, pl. 2) of some of the more strongly stained parts of this one yielded trace amounts of copper and molybdenum.

FIGURE 19.—Sample localities, stream-sediment analyses, and general geology of the Red Face Mountain and Pass Creek areas. (click on image for an enlargement in a new window)

Two smaller iron oxide-stained zones north of the large zone contain visible scattered pyrrhotite and sphalerite in the gneiss. Chip samples 87 and 93 (pl. 2), from these two zones, had 0.15 and 0.30 percent zinc, 0.10 and 0.007 percent lead, and 0.15 and 0.02 percent copper, respectively.

Several marble bands in the gneiss have been metamorphosed to a epidote-garnet skarn near the granodiorite. Some of the skarn contains sulfide minerals. Two north-trending marble layers are high on the cirque wall northeast of the largest disseminated zone and interlayered with hornblende and biotite gneisses. The easternmost layer is about 100 feet wide and consists of coarse white grains of calcite with scattered nodules of andradite. A chip sample (83, table 1) of this marble yielded 0.10 percent zinc, 0.02 percent lead, 0.025 percent copper, and 0.06 ounce of silver per ton. In the marble is an oval body of skarn 5 feet wide by 8 feet long. Ten feet west of the oval body is a 0.5—2-foot-thick layer about 10 feet long of similar epidote-andradite rock. Two skarn bodies have chrysocolla along fractures, and the layer contains visible galena, chalcopyrite, pyrite, and sphalerite. A 5-foot-long chip sample (84, table 1) across the oval body and a 1-foot-long chip sample (85, table 1) across the layer of epidote-andradite rock contain 0.50 and 0.70 percent zinc, 0.07 and 1.0 percent lead, 0.20 and 0.05 percent copper, and 0.06 and 0 ounce of silver per ton, respectively.

The western layer of marble is similar in mineralogy to the eastern layer, but no sulfides are visible; a chip sample (81, table 1) across the western layer contains insignificant amounts of metals.

Pyrite and pyrrhotite are disseminated through the rocks in several areas on the cirque wall in Pass Creek. Some chip samples across these sulfide-bearing rocks (82, 86, table 1) contain small amounts of lead, zinc, copper, and silver; others (73, 79, 80, 101, 102, table 1) contain trace amounts of copper, zinc, and molybdenum.