AN  INTEGRATED PETROLEUM  EVALUATION OF NORTHEASTERN  NEVADA


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LEACH CANYON TUFF

Type Section Information

The Leach Canyon Tuff was named by Mackin (1960) for exposures along the south side of Leach Canyon, in the Desert Mount Quadrangle, Iron County, southwestern Utah.

Geologic Age

The Leach Canyon Tuff is Lower Miocene (22 to 24 Ma) in age (Ekren and others, 1977). It rests on a various Paleozoic and Cenozoic rocks and is commonly overlain by the Condor Canyon Formation (Cook, 1965).

General Lithology

At its type locality in Utah, the Leach Canyon Tuff is described by Mackin (1960) as a single ash-flow tuff sheet consisting of gray to pink welded tuff with strongly developed compaction foliation. About 10 percent of the unit is made up of lithic clasts of felsite, pumice, and other rocks, and broken phenocrysts of quartz, feldspar and biotite. A basal black vitrophere several tens of feet thick is commonly present at the base of the Leach Canyon.

In the evaluation area the Leach Canyon Tuff contrasts with surrounding ash-flow tuffs as it is commonly a nonwelded to partially welded, grey to red crystal-lithic tuff which forms rounded cliffs and soft slopes, and is only rarely densely welded (Ekren and others, 1977). Phenocrysts form about 20 to 35 percent of the tuff on average with about 35 percent quartz, 25 to 50 percent alkali feldspar, 15 to 50 percent potassium feldspar, 3 to 5 percent biotite, and traces of hornblende, orthopyroxene, and sphene (Ekren and others, 1977). It also contains abundant angular red and brown aphanitic volcanic fragments, which are often surrounded by thin cream colored alteration haloes (Cook, 1965: Ekren and others, 1977). A black glass zone is present at the base of many Leach Canyon sections (Cook, 1965).

Modally and megascopically similar tuffs about 500 feet in thickness are exposed along the flanks of the Quinn Canyon Range, and have been informally named the Tuff of Quinn Canyon Range by Ekren and others (1977). Although the Tuff of Quinn Canyon Range (Ekren and others, 1977) is more densely welded and lacks accessory sphene, it is here considered equivalent to the Leach Canyon Tuff.

Average Thickness

The Leach Canyon Tuff varies from 100 to 800 feet in thickness across the evaluation area with the thickest sections in the Wilson Creek Range (Ekren and others, 1977; Cook, 1965).

Areal Distribution

The Leach Canyon Tuff is exposed in several of the mountain ranges in western Utah. In the evaluation area it is present in the Wilson Creek, Fortification and Quinn Canyon Ranges.


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