Geology topics

Preston E. Hotz

Publications and source records attributed to Preston E. Hotz.

5 recordsLinked to original sources

USGS1974

Mineral resources of proposed additions to the Salmon-Trinity Alps Primitive Area, California

A mineral survey of four areas totalling 80 square miles, not included during the 1968-70 examination of the proposed Salmon-Trinity Alps Wilderness, was made by the U.S. Geological Survey and U.S. Bureau of Mines in 1973. Geological Survey personnel mapped the geology and collected stream-sediment and rock samples for spectrographic and chemical analysis; Bureau of Mines personnel examined the known placer and lode claims. The areas examined include: (1) the upper drainage of Red Cap Creek in Humboldt County, adjoining the northwest part of the Salmon-Trinity Alps Primitive Area; (2) an area in Trinity County south of the Primitive Area including the drainage of Big French Creek and the canyon of North Fork Trinity River from Hobo Gulch Forest Camp to the junction with East Fork of North Fork; (3) an area, also south of the Primitive Area and in Trinity County, including East Fork of North Fork from Manzanita Flat to Squaw Gulch, and the drainages of Indian Creek, Squaw Gulch, lower East Branch, and lower Yellow Jacket Creek; (4) the drainage of St. Clair Creek in Siskiyou County north of the Primitive Area; and (5) a small area on New River from the junction of Slide and Virgin Creeks downstream to the mouth of Barron Creek that was previously mapped by the Geological Survey (Hotz and others, 1972) but had not been studied by the Bureau of Mines.

California↗

USGS1973

Blueschist metamorphism in the Yreka-Fort Jones area, Klamath Mountains, California

Blueschist is plentiful in the Yreka-Fort Jones area, eastern Klamath Mountains, adjacent to a belt of serpentinite that marks the boundary between two fundamental lithologic units, an eastern belt of early Paleozoic sedimentary and metamorphic rocks, and a western greenstone-chert assemblage of late Paleozoic and Triassic(?) age. The blueschists, which contain lawsonite and glaucophane or crossite, occur with phyllitic quartzite and siliceous phyllite of the Stuart Fork Formation, which is overthrust northwestward on the greenstone-chert terrane. The blueschist facies metamorphism probably was synchronous with Middle and Late Jurassic metamorphism of the Stuart Fork Formation. The blueschist-serpentinite terrane possibly marks the site of collision between the eastern Klamath plate and an oceanic western Paleozoic and Triassic plate.

California↗

USGS1968

Isotopic age of the Nevadan Orogeny and older Plutonic and metamorphic events in the Klamath Mountains, California

Several metamorphic and plutonic events have been recognized in the Klamath Mountains utilizing potassium-argon and rubidium-strontium mineral and whole-rock ages. The oldest known metamorphic event in the region produced the Abrams Mica Schist and the co-extensive Salmon Hornblende Schist. Strontium evolution diagrams indicate that the age of primary metamorphism of the Abrams Mica Schist is approximately 380 m.y. (Devonian). The Stuart Fork Formation of Davis and Lipman (1962), the schists of Condrey Mountain, and related schists were produced during a Middle and Late Jurassic metamorphic event. Granitic plutonic rocks are divided into four groups that are different in age and somewhat different in chemical characteristics. The oldest pluton, the Pit River stock, has a minimum age of 246 m.y. (Permian) and is grouped with the Castle Crags pluton. The other three plutonic groups are Middle and Late Jurassic and are characterized by the following ranges in isotopic age: 165 to 167 m.y., 145 to 155 m.y., and 127 to 140 m.y. The principal lode gold deposits in the California part of the Klamath Mountains seem to be related to the youngest group of plutons. If the Nevadan orogeny in this area is restricted to a Middle and Late Jurassic deformational, metamorphic, and plutonic event, the orogeny includes the emplacement of plutons of the three younger groups and the metamorphic development of the Stuart Fork Formation, schists of Condrey Mountain, and related schists.

California↗

USGS1964

Nickeliferous laterites in southwestern Oregon and northwestern California

Deposits of ferruginous nickeliferous lateritic soils formed by weathering in place of ultramafic rocks occur at several places in northwestern California and southwestern Oregon, mostly in the Klamath Mountains province. Most of the deposits have been derived from relatively fresh peridotite, although at least one deposit was formed on serpentinite. The accumulations of lateritic soil are on flat-lying to gently sloping surfaces in a terrain that has been extensively dissected and deeply entrenched.The thickness of the deposits ranges from a few feet to more than 50 feet, and may vary widely in any given deposit, for the bedrock surface is commonly highly irregular. The deposit at Nickel Mountain, Oregon, is unique, because it is the only one in which the nickel silicate, garnierite, is plentiful. At Nickel Mountain, garnierite, accompanied by abundant microcrystalline quartz, occurs in veinlike bodies and boxworks that lie at the base of the soil zone and persist in depth along joints and fractures into the underlying slightly weathered or fresh peridotite.Mineralogical studies and chemical analyses show that weathering of the ultramafic rocks destroyed olivine and much of the orthopyroxene and serpentine minerals. Secondary minerals formed are predominantly hydrated ferric oxides (goethite); minor amounts of a montmorillonite mineral, chlorite, and talc were also identified. The kaolin group and bauxite minerals were not found. Except for garnierite at the Nickel Mountain deposit, no nickel-bearing mineral was identified. Nickel may occur, however, in montmorillonite, chlorite, and talc where it substitutes for Mg to a limited extent; in serpentine minerals that were not destroyed by weathering; and possibly in combination with ferric hydroxides. Cobalt may also occur in the clay minerals and probably is associated with trace amounts of manganese oxide or hydroxides.The lateritic soils in northwestern California and southwestern Oregon are similar to soils formed by lateritic weathering of ultramafic rocks in Cuba, the Philippines, New Caledonia, and other tropical regions of the world. They have, however, a higher content of SiO 2 and MgO, and a lower content of Fe 2 O 3 than deposits formed in tropical climates. The California and Oregon deposits are considerably smaller and lower in average metal content which, because they are widely scattered in a rugged, relatively isolated terrain, makes them unpromising as likely reserves for commercial exploitation in the foreseeable future.Most of the deposits are regarded as having been formed by chemical weathering in a climate having alternating wet and dry seasons, probably similar to that prevailing today. Their age is uncertain but may range from post-Miocene to Pleistocene.

California, Oregon↗

USGS1953

Petrology of granophyre in diabase near Dillsburg, Pennsylvania

Small bodies of granophyre occur in the upper part of diabase bodies of Triassic age in southeastern Pennsylvania. One near Harrisburg was penetrated by a diamond-drill. Drill core specimens show a gradation from diabase to granophyre. New data include 10 chemical analyses, spectrographic determinations of trace elements, and the results of petrographic study of specimens from the drill core. The sequence, from diabase to granophyre, includes a chilled zone that represents an original magma of tholeiitic composition, normal diabase, pegmatitic facies of diabase, and granophyric diabase that is intermediate in composition and petrographic characteristics between diabase and granophyre, and finally granophyre. Alkalies and silica increase progressively from diabase to granophyre; iron increases to a maximum in transitional granophyric diabase, then decreases in the granophyre. It is concluded that crystal fractionation in a large sheetlike body of tholeiitic magma yielded a small amount of granophyre. Prior to complete solidification, a residual liquid rich in iron, alkalies, and silica accumulated locally in the upper part of the diabase sheet. In places volatile-rich iron-bearing solutions escaped into the overlying sedimentary rocks and deposited magnetite; the remaining liquid crystallized t o fine-grained granophyre.

Pennsylvania↗