Several silicic plutonic bodies of Jurassic age have been mapped throughout the evaluation area. Several of these are described in some detail.

The Austin pluton, the largest plutonic body in Lander County, is exposed along the western margin of the evaluation area in the central Toiyabe Range. Septa of Paleozoic rocks, and Tertiary and Quaternary sediments, separate the pluton into three mappable masses with sharp and steeply dipping intrusive contacts (Stewart and McKee, 1977).

The Austin pluton is dominantly composed of fine to medium-grained, hypidiomorphic-granular, quartz monzonite composed of 30 percent plagioclase, 30 percent microcline and orthoclase, 20 percent quartz, and 10 percent biotite and hornblende. Accessory minerals include apatite, sphene, and zircon (Stewart and McKee, 1977). Steeply dipping joints are locally well developed in the pluton, and often localize dikes and veins of quartz, felsite, and aplite. A northwest-trending belt of intense alteration has developed a deeply weathered gruss that can be traced across the pluton (Stewart and McKee, 1977). K-Ar dating suggests the Austin Pluton is middle Jurassic (157 +/- 6 Ma) in age, and a small granitic body some 10 miles north of the northern portion of the Austin pluton is about 168 Ma (Krueger and Schilling, 1971).

The Clipper Gap pluton is exposed over about 12 square miles along the west flank of the Toquima Range, on the Lander-Nye County boundary (McKee, 1976b). The contact with the surrounding Ordovician Vinini Formation is sharp and steep with a contact metamorphic aureole about 0.25 miles wide containing aplite and diorite dikes. The country rock has been metamorphosed to a grade ranging from the hornblende hornfels facies near the contact to the albite-epidote hornfels faces a few tens of feet out from the pluton (McKee, 1976b). Both, closely-spaced, steeply-dipping (70-85 degree) joints, and widely-spaced, gently-dipping joints resembling bedding are pervasive throughout the pluton.

The Clipper Gap Pluton is fine to medium-grained hypidiomorphic granular biotite quartz monzonite composed of about 40 percent plagioclase, 30 percent microcline, 20 percent quartz, and 10 percent biotite. Smaller amounts of granodiorite and granite, and crosscutting alaskite dikes commonly about 10 feet in width, and 10 to 60 feet long are also present. The Clipper Gap Pluton is Middle Jurassic in age, about 151 +/- 3 Ma (Silberman and McKee, 1971). The crosscutting aplite dikes are probably Cretaceous, about 93 Ma, based upon fission track dating (McKee, 1976a).

Two genetically related, 150-160 Ma intrusives are exposed near the Clipper Gap Pluton. A small body of granite is exposed in the alluvium of Big Smoky Valley about 10 miles to the north of the Clipper Gap Pluton at Spencer Hot Springs (T.17 N., R.46 E.). This pluton, buried in large extent beneath the gravels of Big Smoky Valley, is composed dominantly of medium-grained porphyritic biotite quartz-monzonite with lesser amounts of biotite-hornblende quartz diorite and biotite quartz diorite porphyry (McKee, 1976b). The biotite quartz monzonite is composed of 30 percent plagioclase, 30 percent potassium feldspar, 25 percent quartz, and 15 percent biotite. Paleozoic rocks surrounding this body have been metamorphosed to hornfels and scheelite-bearing skarns up to 300 feet from the intrusive contact (McKee, 1976b). A small granitic stock about 10 square miles in area is also exposed about 10 miles to the south of the Clipper Gap Pluton (McKee, 1972).

The Mill Creek stock is exposed in the northernmost Toiyabe Range and southernmost Cortez Mountains, along the Eureka-Lander County line about two miles north of Cortez. This stock is dominantly a fine to medium-grained, locally porphyritic, biotite quartz monzonite that contains minor amounts of quartz diorite and alaskite. The Wenban Limestone and Hamburg Dolomite have been altered to marble and tremolitic hornfels. The Roberts Mountains and Fourmile Canyon Formations have also been baked to a hornfels along a narrow zone a few tens of feet from the intrusive contact (Gilluly and Masursky, 1965). The western half of the stock crosscuts the country rock, while the eastern half appears to be conformable and laccolithic in character (Gilluly and Masursky, 1965). Radiometric dating of biotite shows the intrusive to be Jurassic, about 151 Ma (Gilluly and Masursky, 1965).

The large Whistler Mountain stock, north of Devils Gate, is a fine-grained muscovite alaskite composed of quartz, feldspar, and muscovite, with tourmaline nodules up to 2 inches in diameter (Roberts and others, 1967). The stock intrudes the Vinini Formation with a narrow contact metamorphic aureole within a few tens of feet of the intrusive contact, and numerous 20 to 50 foot thick sills that intrude the Mississippian Chainman and Diamond Peak Formations along the southern margin (Roberts and others, 1967). K-Ar dating gives a Jurassic age of 154 Ma.

Late Jurassic plutons (about 140 Ma) of granodioritic and alaskite composition are present in the western Dry Hills, northern Cortez Mountains, and adjacent Pinon Range (Smith and Ketner, 1976; Muffler, 1964). The granodioritic plutons are light gray, highly altered, medium-grained and equigranular. The alaskites are pink to white, fine to medium-grained, and commonly porphyritic with highly altered quartz, albite and orthoclase phenocrysts (Smith and Ketner, 1976; Muffler, 1964).

The central portion of the Ruby Mountains is underlain by a large plutonic body dated at 160 Ma (Howard and others, 1979). This metamorphosed intrusive is composed of leucocratic, pegmatitic granite and gneiss, two-mica granite, and biotite quartz monzonite gneiss. Biotite granodiorite and alaskite bodies are scattered throughout the Jiggs Quadrangle, and are dated at 150 Ma by Armstrong and Suppe (1973). A similar quartz monzonite pluton of Jurassic age is present to the east in the Delcer Hills area.

In the southern portion of Elko County near White Horse Pass, the White Horse pluton is granodioritic to granitic in composition. About 80 percent of the pluton is characterized by pinkish-gray, medium-grained porphritic quartz monzonite (Messin, 1973). Phenocrysts are pink microcline and perthite and the principal mafic minerals are biotite and hornblende that give an age of 156 Ma (Messin, 1973; Armstrong, 1963).

Two Jurassic plutons are present in the northern Toana Range. The Silver Zone Pass pluton is dominantly a granodiorite, but varies from quartz diorite to quartz monzonite in composition. The intrusive contains hornblende and biotite, oscillatory zoned plagioclase, microcline or orthoclase and quartz, with accessory apatite, sphene, and zircon (Pilger, 1972). The Silver Zone Pass pluton is dated at 150 Ma by Coats and others (1965). The northern Toano Springs pluton intrudes the Prospect Mountain Quartzite. It is very coarse-grained granodiorite with abundant pegmatite and aplite dikes, and may be older than the Silver Zone Pass pluton (Pilger, 1972; Coats, 1985).

In the Bull Run Quadrangle, Decker (1962) described several small stocks along an easterly trend from White Rock Creek to Trail Creek. Several of these stocks are dioritic to quartz diorite in composition, with the stock at the head of Trail Creek being a granodiorite. The stock is undated and is not described in detail, but is considered Jurassic in age (Decker, 1962; Coats, 1985).

In the Mount Velma Quadrangle the Gold Creek pluton, in T. 44 N., R. 55 E., varies in composition from medium-grained hornblende biotite quartz diorite, to quartz monzonite which is the dominant phase (Coash, 1967). The pluton covers an area of just under 1 square mile and is dated on biotite at 152.1 +/- 5 Ma (Coats and McKee, 1972). Another pluton exposed along Beaver and Seventy Six Creeks in the northern Mount Velma Quadrangle, varies from diorite to granodiorite composition and is characterized by poikolitic biotite (Coats, 1985). A similar stock is poorly exposed in the northeastern portion of the Jarbidge Wilderness area (Coats and others, 1977; Coats, 1985).

The Contact pluton near Contact north of the HD Range, varies from quartz monzonite to granodiorite in composition with plagioclase and orthoclase, and minor quartz, hornblende and biotite, and accessory magnetite, sphene, apatite, zircon, and allanite (Gibbons, 1973). The Contact pluton has given a K-Ar age of 150 Ma (Coats and others, 1965).