Silicic plutons of various Tertiary ages are exposed in small and large intrusive masses throughout the evaluation area. The following discussion addresses many of these plutons, although some of the smaller and poorly studied bodies are not described.

Several small, medium to coarse-grained, granodioritic to quartz monzonitic intrusives, mainly less than 1 square mile in area, occur within the Shoshone and northern Toiyabe Ranges. These plutons are Oligocene to Eocene with ages of 35-38 Ma. The largest of these is the Granite Mountain stock which covers about 6 square miles in the northern Shoshone Range. The 38 Ma Granite Mountain stock is a granodiorite, composed of about 47 percent plagioclase, 24 percent quartz, 15 percent K-feldspar, 10 percent biotite, and 5 percent hornblende. Small amounts of quartz monzonite, quartz diorite porphyry, and aplite dikes are also present (Gilluly and Gates, 1965; Stewart and McKee, 1977).

The small pluton at Jacobs Peak (Sec. 24, T. 25 N., R. 54 E.) in the high portion of the northern Diamond Mountains is a light gray, fine to coarse-grained, quartz monzonite to granodiorite. It is probably Oligocene (45 +/- 10 Ma) based upon lead-alpha ratios from zircons (Schilling, 1965). The hornblende-biotite granodiorite is composed of about 55 percent plagioclase, 20 percent quartz, 10 percent orthoclase, 10 percent biotite, and 5 percent hornblende. Orthoclase, plagioclase, and quartz form phenocrysts. A narrow contact metamorphic aureole extends a few tens of feet out from the intrusive contact (Haworth, 1979). A similar pluton is present along Wood Cone Peak in the Fish Creek Range.

In northern Elko County along the western border of the Wild Horse Quadrangle, a small-undated stock of alaskitic granite intrudes the Miocene Jarbidge Rhyolite. The rock is principally composed of quartz, sanidine, and plagioclase and is devoid of mafics. The stock is miarolitic with tridymite and glass lining the cavities and indicating abrupt quenching (Coats, 1985).

West of Tuscarora in the Mount Blitzen Quadrangle, the Mount Neva pluton varies from a hornblende-biotite granodiorite to granodiorite porphyry, and has a K-Ar age of 38.4 +/- 1.5 Ma (Coats, 1985; Coats and McKee, 1972). To the southeast in the southern Independence Mountains, the crescent-shaped Lone Mountain (Nannies Peak) pluton is a 4-mile long composite stock. It is composed of quartz monzonite porphyry with biotite, hornblende and cummingtonite, and also contains light gray, biotite quartz latite, altered diorite, and quartz monzonite along the eastern flank of Lone Mountain (Lovejoy, 1959). The dike-like Lone Mountain pluton is dated at about 38 Ma (Coats, 1985).

To the south of Lone Mountain at the southern end of the Independence Mountains, the Swales Mountain pluton is composed of biotite quartz monzonite with phenocrysts of quartz, plagioclase and potassium feldspar, and biotite-hornblende monzonite porphyry with plagioclase, biotite and hornblende phenocrysts up to half an inch long (Evans and Ketner, 1971). Limestones near the intrusive contact have been metamorphosed to a pyroxene-garnet hornfels. Biotite from this intrusive gives a K-Ar age of 38 +/- 1.3 Ma (Evans and Ketner, 1971).

Northwest of Eureka, Mount Hope and the two hills to the north in Eureka County are plugs of rhyolite porphyry with surrounding rhyolite sills and dikes which give an age of 35.6 Ma (Roberts and others, 1967).

Several plutons of granite, quartz monzonite, and quartz diorite, with fine to medium-grained hypidiomorphic granular to porphyritic texture are present in the Railroad mining district of the Carlin-Pinon area (Smith and Ketner, 1976). These intrusives are assumed to be Oligocene and coeval with the Bullion stock, which has given radiometric ages of 35.4 +/- 1.1 Ma and 36.8 +/- 1.1 Ma (Smith and Ketner, 1976). Sedimentary rocks near these intrusives are metamorphosed in some cases such as near the Bullion stock, and are not altered in others such as along the large body in Secs. 27 and 34, T. 29 N, R. 53 E (Smith and Ketner, 1976).

The large Harrison Pass pluton, exposed in the southern portion of the Ruby Mountains, creates a transitional boundary between high-grade metamorphic rocks to the north and low-grade to unmetamorphosed sediments to the south. The pluton is Oligocene and has given a K-Ar radiometric age of 36 Ma (Howard and others, 1979; Snoke and Lush, 1984). The pluton is dominantly composed of porphyritic biotite-hornblende granodiorite or monzogranite, biotite-muscovite granite, and alaskite-pegmatite phases which are characterized by large microcline phenocrysts (Snoke and Lush, 1984). The Harrison Pass pluton is penetratively deformed and is locally mylonitic.

A small, elliptical, light-gray quartz monzonite stock is exposed to the south of the Ruby Mountains on the south flank of Bald Mountain in T. 24 N., R. 67 E. (Rigby, 1960; Hose and Blake, 1976), and just to the east along the northern tip of Alligator Ridge. These intrusives are cut by numerous light gray to green aplite dikes and are Oligocene in age.

In the southern White Pine Range, two medium-grained quartz monzonite stocks, the Railroad and Silver Springs stocks are exposed in Secs. 5, T. 11 N., R. 58 E., and in Secs. 36, T. 12 N., R. 58 E. They have been dated at 31 +/ 5 Ma and 36 +/- 5 Ma respectively (Armstrong, 1970). To the south, in the southwestern Grant Range, several medium-grained granitic and quartz monzonitic bodies intrude Cambrian and Ordovician sediments between Irwin Canyon and Little Meadow Creek. The Troy Canyon Quartz Monzonite in T. 6 N., R. 57 E. has been dated at 23 +/- 4 Ma (Lumsden, 1964; Armstrong, 1970). Farther south in the northern Quinn Canyon Range, three small bodies of quartz monzonite porphyry intrude Cambrian and Ordovician rocks near Willow Creek (Kleinhampl and Ziony, 1985). One of these stock gives a K-Ar date of 26.8 +/- 0.5 Ma (Kleinhampl and Ziony, 1985).

A series of discontinuous exposures of porphyritic and aplitic quartz monzonite, which probably form a continuous intrusive body of batholitic dimensions, are present along the eastern flank of the northern Egan/southern Cherry Creek Ranges. The largest of these bodies is near Cherry Creek and Warm Springs and several smaller bodies are also present on the western flank of the northern Egan Range. Several of these plutons have been described by Adair (1961) in his treatment of the Cherry Creek district, primarily a gold, silver, and tungsten producer.

In general these monzonitic intrusives are deeply weathered and show no obvious evidence of contact metamorphic effects. Sericitic, propylitic and argillic alteration are displayed throughout most of the intrusives, and hydrothermal alteration left some of the surrounding Cambrian limestones vuggy and rusty in color. The margins of the intrusive masses are irregular both in shape, and dip, which varies from almost flat to about 60 degrees (Adair, 1961). In many cases however these bodies are nearly horizontal and are, according the Fritz (1968) intruded along flat faults, which he felt were Mesozoic thrusts. These faults are interpreted in this evaluation to be Tertiary low-angle normal faults. K-Ar dates on biotite within these intrusives are Oligocene and range from 32.1 +/- 0.6 Ma about 5 miles south of Cherry Creek, 36.2 +/- 0.7 Ma in the northern Egan Range in Sec. 9, T. 20 N., R. 63 E., and 33.6 +/- 0.7 Ma at Heusser Mountain (Armstrong, 1970).

A small hornblende-biotite adamellite or quartz monzonite intrusive body is present on the White Pine/ Elko County line in the southern Kingsley Mountains (Buckley, 1967). The Kingsley stock has been dated by Armstrong (1970) at 33.4 +/- 0.7 Ma.

A small body of pink fine-grained and equigranular Miocene granite is exposed over an area of about 1 square mile along the eastern flank of the Bristol Range (Ekren and others, 1977; Tschanz and Pampeyan, 1970). The only other intrusive body exposed within the evaluation area in Lincoln County is a small circular body of intrusive, pink to blue-gray, crystal-poor rhyolite on Burnt Peak at the southernmost tip of the Schell Creek Range (Ekren and others, 1977).