Search USGS⌕ Search

Geology topics

A.F. Trites

Publications and source records attributed to A.F. Trites.

5 recordsLinked to original sources
USGS1955

Uranium deposits at the Jomac mine, White Canyon area, San Juan County, Utah

The Jomac mine is in the White Canyon area. San Juan County, Utah, about 13 miles northeast of the town of White Canyon, Utah. The mine is owned by the Ellihill Mining Company, White Canyon, Utah. Mine workings consist pf two adits connected by a crosscut. Two hundred feet of exploratory drifting and 2,983.5 feet of exploratory core drilling were completed during 1953 by the owners with Defense Minerals Exploration Administration assistance. Sedimentary rocks exposed in the area of the Jomac mine are of Permian to Late Triassic age, having a combined thickness of more than 1,700 feet. An ancient channel, from 200 to 400 feet wide and about 4 feet deep, enters the mine area from the southwest, swinging abruptly northwest near the mine workings and continuing to the northern tip of the Jomac Hillo This channel was cut into the upper beds of the Moenkopi formation and filled in part by Chinle and in part by Shinarump sediments. This channel is marked by depressions that apparently were scoured into its floor; a tributary channel may have joined it from the southeast at a point near the mine workings. Chinle beds Intertongue with Shinarump beds along the southwestern part of the channel. After the main channel was partly filled by siltstone of the Chinle formation, the stream was apparently diverted into the tributary channel, and scours were cut into the Chinle siltstone and filled by Shina'rump sandstone, conglomerate, and siltstone. Statistical study of wood orientation in the beds of the Shinarump conglomerate further indicates a channel trend of about N. 23° W. Basal siltstoned-pebble conglomerates appear to mark the edge of channels and scours. Jomac Hill is on the crest of a southwest-plunging fold that is on the west flank of a larger syncline. The area surrounding the hill is broken by intense faulting, but no faults were noted in the vicinity of the mine. The major fractures in the mine workings strike N. 70° to 80° E. and are steeply dipping. Secondary steeply dipping fractures strike N. 40° to 60 °E., and N. 10° E. to N. 10° W. The fractures are believed to be related to the anticlinal structure rather than the faults. Most of the uranium is contained in coa!5 associated with jarosite and gypsum in sandstone, conglomerate, or sandy siltstone near the base of the Shinarump conglomerate. Uranium occurs ill a fibrous green secondary mineral, metazeunerite, an unknown fibrous yellow mineral, and an unknown massive yellow mineral. Secondary copper minerals including malachite azurite, and chalcanthite occur locally with the uranium minerals. Principal ore guides at the Jomac mine are channels, and scours at the bottom of these channels coal-bearing sandstone or conglomerate at the base of the Shinarump conglomerate, coal, and jarosite.

Utah↗
USGS1952

Geology of the Quartz Creek Pegmatite District, Gunnison County Colorado

The Quartz Creek pegmatite district includes an area about 29 square miles in the vicinity of Quartz Creek in Gunnison County,. Colo. This area contains 1,803 pegmatites that are intruded into pre-Cambrian rocks. The rocks exposed in the district range in age from pre-Cambrian to Recent. The oldest pre-Cambrian rocks are chiefly quartzites interbedded with a few arkoses and conglomerates. These rocks are surrounded by more abundant hornblende gneiss and tonalite. A small body of biotite tonalite was intruded and two thin layers of dacitic pillow lava were extruded into this series. The hornblende gneiss and tonalite have the same composition and differ only in texture. The older material (hornblende gneiss) has a well-marked lineation, whereas the younger (tonalite) is equigranular. Subsequently, a large body of quartz monzonite was intruded along the northern boundary of the mapped area. Later, coarse-grained granite was intruded into the southern part of the area. Dikes of fine-grained granite cut the coarse-grained variety. The last period of intrusive activity in pre-Cambrian time is marked by a large number of pegmatites. The pre-Cambrian rocks were tilted and eroded, and the flatlying Jurassic Morrison formation was deposited on the irregular surface. This formation is conformably overlain by the Cretaceous Dakota sandstone. Faulting produced a vertical offset of 410 feet in the Mesozoic sediments along the only large fault in the area. At the end of Mesozoic time there was another period of erosion. Tertiary (?) tuff is exposed in small, scattered areas in the southern part of the district. It overlies both the Dakota sandstone and pre-Cambrian formations. Glacial till occurs along the edges of Quartz Creek and Wood Gulch. Quaternary alluvium fills the valley bottoms. Although the composition of the country rock has little effect on the shape of the pegmatites, the foliation imposed on this rock has a localizing effect and in part controls the ultimate shape of pegmatites. Zoned and related internal structures are not well developed in the pegmatites of this region. Many of the pegmatites are homogeneous and those that are zoned usually contain a large wall zone and small discontinuous cores. In addition to the more common homogeneous and zoned pegmatites, 7 percent of the pegmatites show a layered structure of textural and mineralogical units not repeated on the opposite side of the pegmatite. Other internal structural units include pegmatites which vary in composition along strike, multiple or “line-rock pegmatites” and fracture fillings. The mineralogy of the pegmatites is described in detail. Specific attention was given to most of the 27 observed minerals. A study of the index of refraction of 439 specimens of plagioclase showed that the variation from zone to zone and layer to layer is minor and that there is no systematic variation in respect to the entire district. No correlation could be found between the refractive index of plagioclase in the pegmatites and the type country rock, or the presence of various accessory minerals. Index of refraction determinations on 95 specimens of muscovite showed no constant variation from wall zone to core or from layer to layer. Curved muscovite has identical optical properties with the flat variety. The index of refraction was determined for 189 beryl specimens. The beryl in the pegmatites containing only a wall zone and a core showed no difference between zones, but in pegmatites that have intermediate zones, the indices of refraction of the beryl showed an inward increase in the alkali content from the contact. Beryl occurs with almost all of the pegmatite minerals and is not restricted in its mineral associations. Tourmaline, except the black variety, is associated with lepidolite. Dark green and blue tourmaline is found in the outer zones of pegmatites containing lepidolite, and the pink and light green varieties are found in direct contact with lepidolite. Lepidolite occurs in aggregates of fine grains, in flat plates, and in curved plates; the three varieties are optically identical. The lighter-colored varieties have higher indices of refraction and contain less lithia than the darker varieties. In addition, the occurrence of the following minerals is described in detail: perthite, quartz, martite, biotite, garnet, columbite-tantalite, monazite, microlite, topaz, gahnite, allanite, and an unidentified mineral. The lack of alteration in the wall rocks adjacent to the pegmatites is interpreted as indicating that the original pegmatite magma did not have an excess of materials such as B, OH-, and P that are needed to form alteration minerals. Because of their low concentration, the above materials were available only in the pegmatitic magma during its crystallization. Pegmatites that contain the rare minerals such as beryl, tourmaline, curved muscovite, biotite, magnetite, monazite, columbite-tantalite, cleavelandite, topaz, lepidolite, and microlite show a grouping in clusters within the district. Beryl-bearing pegmatites occur most abundantly in hornblende gneiss and are only rarely found in either granite or quartz monzonite. The types of minerals that form in a pegmatite appear to be determined by the character of the material segregated from the original magma and the period in which it segregated. The elements escape at one period and may be from only-a specific pocket in the magma. These liquids tend to form groups of pegmatites in which the later bodies contain a high proportion of volatiles. Inferred reserves of the district are estimated for beryl, scrap mica, both hand-cobbing and milling feldspar, lepidolite, columbite-tantalite, topaz, monazite, and microlite. No sheet mica was found. Reserves are small and transportation costs are high so substantial production of low-priced feldspar and scrap mica will depend on the adoption of economica milling techniques for recovering the large quantities of feldspar available. Beryl is irregularly distributed and its recovery as a byproduct will depend on the establishment of a stable market for feldspar and scrap mica. Lepidolite reserves are small low grade.

Colorado↗