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

MINERAL OCCURRENCES

Three types of mineral deposits are found in the study area : disseminated sulfides, veins, and placers. Whereas these occurrences are numerous in the area, none seems to have sufficient tonnage and grade to be mined at this time.

DISSEMINATED SULFIDES

Disseminated sulfide deposits, tiny grains of sulfide minerals scattered through country rock, represent the most common type of mineral occurrence. The sulfides commonly weather to brown iron oxides, and the stained rock stands out from the adjacent unaltered rock.

Although zones of disseminated sulfides are found in many places in this area, the contained copper and molybdenite is insufficient to form submarginal ore bodies in most places. One known exception is the Weezie claim on Silver Creek, where the rock in an area 200 by 240 feet contains disseminated molybdenum and copper minerals. The grade of this deposit, which is described in a later section, is comparable to that of ore deposits that have been mined, but the deposit is too small to be mined successfully at the present.

Hundreds of zones of disseminated sulfides are known in the study area. They range in size from a few inches wide by a few feet long to one in Sulphide basin (fig. 10) that is 2.5 miles long by 0.3 mile wide. Pyrite and pyrrhotite are the principal sulfides. Copper and molybdenum in these zones is generally erratic and low in content. Higher values of the metals are from narrow zones, generally along joints.

Three zones of disseminated sulfides, in addition to the one in Sulphide basin, are more than 1 mile long. These are in the Bacon Peak area (fig. 9) (2.2 miles long by 0.3-0.9 mile wide), Red Face Mountain area (fig. 19) (1.4 miles long by 0.4 mile wide), and Pass Creek area (fig. 19) (1.3 miles long by 0.5 mile wide). Samples from the outcrop over the Sulphide basin zone (fig. 10) contain as much as 0.02 percent copper and lesser quantities of molybdenum. The copper content of samples from the other three zones is Bacon Peak (fig. 9), <0.0003-0.03 percent, average about 0.01 percent; Red Face Mountain (fig. 19), 0.0001-0.03 percent, average about 0.007 percent; and Pass Creek (fig. 19), 0.007-0.015 percent, average about 0.01 percent. Molybdenum, lead, and zinc either were not detected or were of very low values in the latter three areas.

Higher grade concentrations of sulfides are generally small and commonly form adjacent to or within joints or fractures in the country rock. A sample (362, pl. 2) from a small zone along a fracture on the west side of upper Big Beaver Creek yielded >0.50 percent copper, >0.20 percent molybdenum, and 1.5 ounces of silver per ton. Chip samples from four other narrow zones, none of which was more than 2 feet wide, all yielded 0.05 percent copper. Samples 1021, 1022, and 1023, from three disseminated zones 20-100 feet across on the southwest side of Copper Mountain, yielded 0.05, 0.02, and 0.015 percent copper and 0.01, 0.03, and 0.02 percent molybdenum, respectively. Samples 1013, 1015, and 1014, from three small altered zones 5-20 feet across on the northeast side of Silesia Creek, yielded 0.30, 0.10, and 0.07 percent zinc, respectively. Fourteen 1- to 2-foot-thick zones of disseminated sulfides bounding pyrite-rich veinlets were sampled on Easy Ridge. Three of these samples (852, 856, 857, pl. 2) yielded 0.15 percent copper and ranged from 0.003 to 0.03 percent molybdenum; a fourth (858, pl. 2) had 0.30 percent copper and 0.007 percent molybdenum.

Other than the Weezie property, the most favorable occurrences of disseminated sulfides are around the east cirque of Pass Creek (fig. 19) north of the large Pass Creek sulfide zone. Here near the contact of Custer Gneiss of McTaggart and Thompson (1967) with granodiorite are several small- to medium-sized zones that contain zinc, copper, and lead. Marble bands are found in several places in the gneiss. Adjacent to these bands are two small skarn bodies, one a layer 2 feet wide and the other an oval-shaped body 5 feet across, containing 0.70 and 0.50 percent zinc, 0.05 and 0.20 percent copper, and 1.0 and 0.07 percent lead, respectively. Two poorly exposed zones in Custer Gneiss adjacent to the creek yielded 0.30 and 0.15 percent zinc, 0.02 and 0.15 percent copper, and 0.10 and 0.007 percent lead. Two disseminated zones in gneiss on the cirque wall had 0.15 and 0.20 percent zinc, 0.02 and 0.07 percent copper, and 0.10 and 0.15 percent lead. The first of these two zones is about 60 feet wide and 100 feet long; the second is about 200 feet wide and more than twice as long. None of these occurrences are minable.

VEINS

Veins are relatively rare in the northern part of the North Cascades National Park. Those found are generally narrow, short, and, except for thin veinlets associated with disseminated zones, low in metal content. Many veins are of barren quartz; others contain minor amounts of copper, still others contain some lead and zinc, and a few contain molybdenum minerals. Conspicuous of the veins that contain molybdenum are those on two claims located on the east side of Sulphide basin.

A few quartz veins also contain base metal sulfides. The largest and highest grade of these were three found near the crest of the Picket Range south of Crooked Thumb Peak. The three veins are undulative and range from 1/8 to 5 inches in thickness. They were traced for 250, 150, and 175 feet. Metal content of the veins is highly variable; five samples of sulfide-rich rock from the three veins ranged from 0.002 to 0.12 ounce gold, 0.09 to 2.92 ounces silver, 0.05 to 2 percent lead, 0.07 to 1 percent zinc, and 0.03 to 1 percent copper.

PLACERS

We collected 64 panned concentrates (pl. 2; table 1) from 33 streams. All were analyzed spectrographically for 18 elements, and all were assayed for gold.

Gold was detected in measurable amounts in only 14 of the 64 panned concentrates. Only six contained more than 0.008 ounce of gold per ton. Where detectable gold was found, we made an effort to locate the source, but no lode deposits were found that contained gold in minable quantities.

The highest gold content found (0.64 ounce per ton of panned concentrate) was in sample 578, from Lonesome Creek, a tributary of Bald Eagle Creek, on the east side of Mount Blum. The stream drains rocks of the Chilliwack batholith, here mainly alaskite and biotite hornblende quartz diorite. The gold presumably was derived from rocks that contain disseminated sulfides. Samples of such rocks from the ridge crest to the southwest did not contain significant quantities of gold, and similar rocks at the head of Lonesome Creek crop out on a vertical cirque wall but could not be reached.

Of six panned concentrates collected in Big Beaver Creek drainage, only one, sample 391, contained measurable gold—0.24 ounce per ton. The source of this gold was not located.

Panned sample 836, from Brush Creek west of Whatcom Pass, contained 0.08 ounce of gold per ton. Brush Creek drains granodiorite of the Chilliwack batholith. Two more panned concentrates taken upstream from the gold-bearing sample on Brush Creek contained no detectable gold; thus this small amount of gold apparently comes from the lower part of Brush Creek basin.

A panned sample from a small east-flowing tributary of Silesia Creek and two panned samples from the West Fork of Silesia Creek contained measurable amounts of gold (table 1). The sources of this gold are believed to lie outside the National Park. One of these sources is in Winchester Creek basin, a tributary of West Fork, where veins have been known for many years. The other is from the east end of the ridge that contains the Red Mountain mine.

No other drainage basin produced samples that contain more than 0.008-ounce of gold per ton. Because of the small amount of gold found and the small proportion of heavy minerals concentrates found in our panning, we do not believe the northern part of the North Cascades National Park contains significant resources of placer gold.