Piute County Research Articles

Basin-range uplift and canyon cutting in 3 million years, Kingston Canyon, Piute County, southwestern Utah

The Sevier Plateau is a gently east-tilted, block-faulted range in the High Plateaus transition zone of southwestern Utah. Part of this range underwent basin-range deformation, including at least 6000 feet (1800 m) of uplift, in a 3-million-year time span. The north-south range, whose southern end is just north of Bryce Canyon National Park, was uplifted and tilted by the Sevier fault zone along the western side. Kingston Canyon is a deep, east-west antecedent canyon that cut through the range and maintained itself during uplift. The deformation took place between 8 and 5 Ma, constrained by isotopic dating of pre-uplift rhyolite flows (8 Ma), now exposed on the crest of the range, and a post-canyon-cutting rhyolite dome (5 Ma), now in the bottom of Kingston Canyon. This episode of uplift and canyon cutting represents the most closely constrained example known in the Great Basin and adjacent transition zone of main-phase uplift by basin-range faults.

The black skarns of Pine Canyon, Piute County, Utah

A small micromonzonite pluton intruding Miocene extrusives of the Marysvale volcanic field of southern Utah has undergone a sequence of explosive brecciation, syenite veining, rheomorphism, calcium metasomatism and zeolitization. Skarn-like occurrences of magnetite and Al-spinel-rich feldspathoidal rocks within the outcrop are of two main types: (1) an olivine-bearing variety with occasional REE-rich minerals (zirconolite) occurs as veins and seams in desilicated latite screens and xeno-liths.; (2) an aluminous, corundum- and hibonite-bearing variety with accessory zirconolite, perovskite and armalcolite occurs mainly as fillings to the micromonzonite breccias. The chemically disparate types are interpreted as having initiated as propylitic, and argillic/alunitic, alterations of latite country rock in the early hydrothermal system of the pluton. Subsequent intrusion of the micromonzonite to higher levels has incorporated these products into the igneous complex, in which they have experienced varying degrees of nephelinization, pyrometamorphism, rheomorphism and veining.

Vein formation and distribution, Ohio and Mt. Baldy districts, Marysvale, Piute County, Utah, USA

The Ohio and Mt. Baldy mining districts near Marysvale, Utah, are situated within a calc-alkalic rock assemblage of the Bullion Canyon Volcanics. The assemblage is divisible into three portions: 1) a lower laharic sequence of epiclastic breccias and autobreccias, 2) a middle portion containing mostly lava flows, including a dacite flow with cupola magma characteristics, and tuff and lapilli breccias, and 3) an upper portion containing a local volcanic vent complex and the ash-flow Delano Peak Tuff Member.

Origin and structural implications of upper Miocene rhyolites in Kingston Canyon, Piute County, Utah

Kingston Canyon is one of the deepest antecedent canyons in the High Plateaus subprovince of the Colorado Plateaus. Here the East Fork of the Sevier River flows westward transversely across the gently east tilted Sevier Plateau, which is developed on a basin-range fault block uplifted more than 1,500 m along the Sevier fault zone on the west. Upper Tertiary rhyolites, uncommon in southwestern Utah, occur both on the northern rim and in the bottom of Kingston Canyon. Those on the northern rim consist of lava flows and volcanic domes of the rhyolite of Forshea Mountain, dated by K-Ar methods at 7.6 m.y. old. Those in the bottom of Kingston Canyon, the rhyolite of Phonolite Hill, are especially well exposed and provide spectacular examples of a pyroclastic cone whose base is about at river level and a steep-sided volcanic dome emplaced into and through these deposits. The pyroclastic deposits, formerly 500 or more metres thick, consist of airfall, mudflow, and ash-flow(?) material of rhyolite and foreign lithic fragments, especially olivine basalt. The dome consists of flow-banded, mostly devitrified rhyolite as much as 500 m thick; it has been dated by K-Ar methods at 5.4 m.y. In addition to the rhyolites, a dome and lava-flow complex, the rhyodacite of Dry Lake, occurs near the northern rim and is considered to postdate the rhyolite of Forshea Mountain and predate the rhyolite of Phonolite Hill. The rhyolite of Forshea Mountain was deposited near basin-range faults, before the uplift of the Sevier Plateau and before the cutting of Kingston Canyon. Before uplift, a river flowed across the site of the present Sevier Plateau toward the east-southeast and perhaps also across the Awapa and Aquarius Plateaus to the east. The rhyodacite of Dry Lake was deposited during uplift and perhaps before canyon cutting. During uplift, the river maintained itself and cut Kingston Canyon. The rhyolite of Phonolite Hill was deposited in this canyon, blocking the river flow, which probably formed new outlets to the east. The Awapa and Aquarius Plateaus later were uplifted along faults, disrupting the eastern part of the river segment. The topography then took on its present appearance, and drainage was re-established through Kingston Canyon. There has been little deepening since the reopening of Kingston Canyon.

The uranium deposits near Marysvale, Piute County, Utah

The uranium deposits are ore zones in igneous rocks chiefly in an intrusive of quartz monzonite. The zones consist of quartz-fluorite-calcite-pyrite veins and veinlets commonly of similar strike and dip. Pitchblende occurs as very thin seams or as grains in and between the veins. Weathering extends to at least 200 feet and has resulted in secondary schroecking-erite, autunite, torbernite (and their meta modifications) and a uranophane-like mineral. The mineralization is of late Tertiary age.