Yellowjacket formation. Argillaceous quartzite interfingered with calcareous beds in lower part. Thickness 9,000+ feet. Base not exposed.
Type locality: town and mining district.

Source: GNC ID pre-Camb.-Quat. Corr. Chart, sheet 1, Sept. 1932.

Yellowjacket formation of Belt series. Dark-gray to greenish argillaceous quartzite with some calcareous beds and, rarely, lenses of limestone. Thickness probably nearly 9,000 feet. Underlies Hoodoo quartzite. Named from exposures at town of Yellowjacket, Casto region, Casto quadrangle, Lemhi County, southern central Idaho. Basal formation of Belt series. Age is pre-Cambrian (Belt; Algonkian). A.L. Anderson suggests (Idaho Bur. Mines. And Geol. Pamphlet, no. 34, p. 10, June, 1930) the rocks here named Yellowjacket formation and Hoodoo quartzite may correspond to lower and middle members of Prichard formation as identified by him in Orofino region.

Source: US geologic names lexicon (USGS Bull. 896, p. 2385).

Extended west into the Idaho primitive area of Lemhi, Valley, and Idaho Cos, ID in the Northern Rocky Mountain region as a formation in Belt Supergroup (formerly designated Belt series).

Source: GNU records (USGS DDS-6; Denver GNULEX).

Pg. 5-6. Yellowjacket Formation. In Lemhi Range, east-central Idaho, consists of medium- to medium-dark-gray fine-grained to very fine-grained feldspathic quartzite, and interbedded siltite. Thickness unknown, but possibly as much as 10,000 feet. Underlies Lemhi Group (revised). Age is Precambrian.

Source: Publication.

Three informal genetic units of Yellowjacket (A, B, and C) are described in vicinity of Blackbird Mine, west of Salmon in the Idaho cobalt belt, Lemhi Co, ID in the Northern Rocky Mountain region. The age of volcanic and subvolcanic rocks of "Unit B" at Blackbird Mine are dated at 1,670 m.y. to 1,700 m.y. (Early Proterozoic) by U/Pb method on zircons. Together with the older ("Unit A") and younger ("Unit C") units, Yellowjacket is considered Early to Middle Proterozoic in age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Pg. 1-4. Yellowjacket Formation. Consists of alternating thin beds of gray, very fine-grained, argillaceous quartzite, siltite, and dark-gray argillite. Thickness about 2,740 m. Base not exposed. Thought to correlate with basal part of Prichard Formation of Belt Supergroup. Underlies Hoodoo Quartzite. Age is Middle Proterozoic.
Principal reference section (Ross' 1934 section, p. 16): near Yellowjacket mining district, along Yellowjacket and Shovel Creeks, in T. 19 N., R. 17 E. (unsurveyed), about 2 mi (3.2 km) northeast of the mine and mill, Lemhi Co., southern central ID.

Source: Publication.

Yellowjacket Formation. In Idaho cobalt belt area, Lemhi County, southern central Idaho, subdivided into (1) lower unit, siltite and quartzite (Hoodoo Quartzite gradationally overlies and underlies the siltite beds of this unit); (2) middle unit, siltite and quartzite interbedded with argillite, about 2,000 m thick (hosts Co-Cu-Au deposit at Blackbird Mine); and (3) upper unit, feldspathic quartzite, about 200 m thick. Underlies Big Creek Formation of Lemhi Group. Age is Middle Proterozoic.

Source: Publication.

Yellowjacket Formation. Restricted to strata originally assigned to it by Ross (1934) and, along with the conformably overlying Hoodoo Quartzite and unnamed argillaceous quartzite of Ross, is areally restricted to exposures west of Iron Lake fault, Lemhi County, southern central Idaho. East of Iron Lake fault, in the Idaho cobalt belt, rocks previously included in the Yellowjacket are reallocated to (ascending) Apple Creek and Gunsight Formations of the Lemhi Group. Age is Middle Proterozoic.

Source: Publication.