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James J. Rytuba

Publications and source records attributed to James J. Rytuba.

44 records · Page 3Linked to original sources
USGS1979

Zeolite-clay mineral zonation of volcaniclastic sediments within the McDermitt caldera complex of Nevada and Oregon

Volcaniclastic sediments deposited in the moat of the collapsed McDermitt caldera complex have been altered chiefly to zeolites and potassium feldspar. The original rhyolitic and peralkaline ash-flow tuffs are included in conglomerates at the caldera rims and grade into a lacustrine series near the center of the collapse. The tuffs show a lateral zeolitic alteration from almost fresh glass to clinoptilolite, clinoptilolite-mordenite, and erionite; to analcime-potassium feldspar; and finally to potassium feldspar. Vertical zonation is in approximately the same order. Clay minerals in associated mudstones, on the other hand, show little lateral variation but a distinct vertical zonation, having a basal dioctahedral smectite, a medial trioctahedral smectite, and an upper dioctahedral smectite. The medial trioctahedral smectite is enriched in lithium (as much as 6,800 ppm Li). Hydrothermal alteration of the volcaniclastic sediments, forming both mercury and uranium deposits, caused a distinct zeolite and clay-mineral zonation within the general lateral zonation. The center of alteration is generally potassium feldspar, commonly associated with alunite. Potassium feldspar grades laterally and vertically to either clinoptilolite or clinoptilolite-mordenite, generally associated with gypsum. This zone then grades vertically and laterally into fresh glass. The clay minerals are a dioctahedral smectite, a mixed-layer clay mineral, and a 7-A clay mineral. The mixed-layer and 7-A clay minerals are associated with the potassium feldspar-alunite zone of alteration, and the dioctahedral smectite is associated with clinoptilolite. This mineralogical zonation may be an exploration guide for mercury and uranium mineralization in the caldera complex environment.

Open-File Report↗
USGS1979

Uranium, thorium, and mercury distribution through the evolution of the McDermitt Caldera complex

The McDermitt caldera complex developed over a period of 5 m.y. years during which ash-flow tuff sheets anomalous in mercury, uranium, and thorium were emplaced. The moat portions of the caldera complex were subsequently filled with tuffaceous sediments. Late in the caldera development near-surface intrusives and domes were emplaced along the margins of the complex and mineralized with uranium. Seven large hydrothermal systems developed at this time and formed large areas of alteration within the caldera-fill volcanics and sediments. Five of the altered zones are associated with economic concentrations of uranium, and or mercury.

Nevada, Oregon↗
USGS1979

Relation of mercury, uranium, and lithium deposits to the McDermitt caldera complex, Nevada-Oregon

The McDermitt caldera complex, located along the Nevada-Oregon border, is a Miocene collapse structure 45 km in diameter. Large-volume rhyolitic and peralkaline ash-flow tufts were erupted from 17.9-15.8 m.y. ago, leading to the formation of overlapping and nested calderas. Emplacement of rhyolitic ring domes, located primarily along the western margin of the calderas, represents the last phase of volcanic activity.

Nevada;Oregon↗
USGS1978

Lithium in the McDermitt caldera, Nevada and Oregon

Anomalously high concentrations of lithium in fluviatile-lacustrine sediments near McDermitt, Nevada, may constitute a potential resource. These sediments are associated with a caldera about 45 km in diameter that is a result of volcanic activity, subsidence and sedimentation chiefly of Miocene age. The sediments originally were vitroclastic and now consist chiefly of authigenic zeolites, clay minerals, feldspar and quartz. Calcite occurs as thin beds, nodules and cement Gypsum is presnt but sparse. Most of the clay beds in the caldera contain 0.01–0.1% Li and have well above the average Li concentration for continental clays (0.006%) (Ronov et al. 1 ). Individual smectitic clay samples from the western and southern part of the caldera contain as much as 0.65% Li and are associated with analcime and K-feldspar. Two beds, each 0.6m thick, contain 0.35% Li. Clay samples from the northern part of the caldera contain as much as 0.36% Li, and are associated with clinoptilolite and erionite. The clay beds are thinner in the north; in one section a bed 0.3 m thick contains 0.36% Li, and in another section a bed 0.1 m thick contains 0.30% Li. Lithium is probably derived from volcanic material and then incorporated into the clay beds during alteration.

Nevada, Oregon↗
USGS1978

Relation of Mercury, Uranium, and Lithium Deposits to the McDermitt Caldera Complex, Nevada-Oregon

The McDermitt caldera complex, located along the Nevada-Oregon border, is a Miocene collapse structure 45 kilometer in diameter. Large-volume rhyolitic and peralkaline ash-flow tuffs were erupted from 17.9 to 15.8 m.y. ago, leading to the formation of overlapping and nested calderas. Emplacement of rhyolitic ring domes, located primarily along the western margin of the calderas, represents the last phase of volcanic activity. The complex is the site of large deposits of mercury, an are deposit and several occurrences of uranium, and widespread occurrences of lithium. Mercury deposits at Cordero, McDermitt, Bretz, Ruja, and Opalite occur along ring fractures in sedimentary rocks that fill the calderas. Near the deposits the rocks are altered to zeolites and within the ore zones to potassium feldspar and silicate minerals. Although the mercury deposits contain anomalous concentrations of uranium, the most important uranium occurrences are restricted to rhyolitic ring domes emplaced along the western margin of the calderas. Lithium occurrences are located in tuffaceous rocks that are altered to zeolites and potassium feldspar. Concentrations of lithium ranging from 0.1 to 0.68 percent are associated with the clay mineral hectorite. The rhyolitic rocks erupted from the McDermitt caldera complex are enriched in mercury, uranium, and lithium and are likely source rocks for these elements in the ore deposits. Tuffaceous caldera fill-sediment averages 0.29 ppm mercury, 22 ppm uranium, and 236 ppm lithium; large-volume ash-flow tuffs contain up to 0.26 ppm mercury, 20 ppm uranium, and 300 ppm lithium.

Open-File Report↗
USGS1976

Geology and ore deposits of the McDermitt Caldera, Nevada-Oregon

The McDermitt caldera is a Miocene collapse structure along the Nevada-Oregon border. The oval-shaped caldera is bounded by arcuate normal faults on the north and south and by rhyolite ring domes on the west. Precollapse ash-flow tuffs exposed within the south caldera rim consist of three cooling units and are peralkaline in composition. Refractive indexes of nonhydrated glasses from basal vitrophyres of the. units range from 1.493 to 1.503 and are typical of comendites. Post-collapse intracaldera rocks consist of tuffaceous lake sediments, rhyolite flows and domes, and ash-flow tuffs. Within the caldera are the mercury mines of Bretz, Cordero, McDermitt, Opalite, and Ruja and the Moonlight uranium mine. The mercury mines are adjacent to ring fracture faults, and the uranium mine and other uranium occurrences are located within rhyolite ring domes. Fluid inclusions in quartz indicate a deposition temperature of 340?C for the uranium deposit and 200?C for the mercury deposits. The mercury deposits formed at shallow depth by replacement of lakebed sediments and volcanic rocks.

Open-File Report↗