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Douglas M. Sheridan

Publications and source records attributed to Douglas M. Sheridan.

15 recordsLinked to original sources
USGS1977

Preliminary data on some Precambrian deposits of zinc-copper-lead sulfides and zinc spinel (granite) in Colorado

Precambrian sulfide deposits in the Southern Rocky Mountains in Colorado are being studied and re-evaluated according to geologic concepts which were developed in recent years in other parts of the world during successful research regarding economic massive sulfide deposits. These studies, initiated in 1974 in Colorado by the U.S. Geological Survey, have indicated that a new look at areas containing long dormant mines and prospects may well lead to the discovery of minable Precambrian sulfide deposits. The zinc, copper, and lead contents of ores investigated to date, supplemented by silver and gold contents, indicate that many long-forgotten deposits are minable in terms of grade. The deposits occur in Precambrian rocks metamorphosed to the lower amphibolite facies in one major region and to the upper amphibolite facies in other regions. Field studies have provided ample evidence indicating that the search for commercial tonnages can he facilitated by using newer concepts of economic geology regarding ore-host rock associations as prospecting guides and by using structural considerations aimed toward learning how metamorphism and folding have modified the shapes and distribution of the ore bodies. A newly recognized concept, originating from the current studies by the U.S. Geological Survey in Colorado, concerns the potential economic significance of gahnite, a zinc spinel. The field and laboratory data indicate that gahnite can be used by geologists as a prospector's guide to ore and can be considerd by mining engineers as a potential major ore mineral, contributing significant amounts of zinc to the sulfide ores in many of the deposits. Studies to date indicate that the Gunnison area, the Salida area, and the Guffey area are particularly favorable to the search for minable deposits, and the potential is equally present in many other areas.

Colorado↗
USGS1968

Rutile and topaz in Precambrian gneiss, Jefferson and Clear Creek Counties, Colorado

Disseminated rutile and major amounts of topaz have been identified in Precambrian topaz-quartz gneiss northwest of Evergreen, Colo. The rutile occurs in quartz-topaz-sillimanite gneiss that forms a stratigraphic unit which is 11 to 100 feet thick and is identified along strike for more than 7,000 feet. Three composite chip samples taken across this unit contain 2.2 to 4.2 percent of rutile, by weight, in grains averaging from 0.1 to 0.3 millimeter in size. The topaz content, by weight, in the same samples ranges from 23 to 67 percent.

Circular↗
USGS1956

Geology of the Ralston Buttes district, Jefferson County, Colorado: a preliminary report

The Ralston Buttes district in Jefferson County is one of the most significant new uranium districts located east of the Continental Divide in Colorado. The district is east of the Colorado Front Range mineral belt, along the east front of the range. From November 1953 through October 1956, about 10,000 tons of uranium ore, much of which was high-grade pitchblende-bearing vein material, was shipped from the district. The ore occurs in deposits that range in size from bodies containing less than 50 tons to ore shoots containing over 1,000 tons. The only other mining activity in the area has been a sporadic production of beryl, feldspar, and scrap mica from Precambrian pegmatites, and quarrying of dimension stone, limestone, and clay from sedimentary rocks. Most of the Ralston Buttes district consists of complexly folded Precambrian metamorphic and igneous rocks - gneiss, schist, quartzite, amphibolite, and granodiorite. Paleozoic and Mesozoic sedimentary rocks crop out in the northeastern part of the district. These rocks are cut by northwesterly-trending fault systems of Laramide age and by small bodies of intrusive rocks that are Tertiary in age. The typical uranium deposits in the district are hydrothermal veins occupying openings in Laramide fault breccias or related fractures that cut the Precambrian rocks. Pitchblende and lesser amounts of secondary uranium minerals are associated with sparse base-mental sulfides in a gangue of carbonate minerals, potash feldspar, and, more rarely, quartz. Less common types of deposits consist of pitchblende and secondary uranium minerals that occupy fractures cutting pegmatites and quartz veins. The uranium deposits are concentrated in two areas, the Ralston Creek area and the Golden Gate Canyon area. The deposits in the Ralston Creek area are located along the Rogers fault system, and the deposits in the Golden Gate Canyon area are along the Hurricane Hill fault system. Two geologic factors were important to the localization of the uranium deposits: (1) favorable structural environment and (2) favorable host rocks. The deposits in each of the two major areas are located where a northwesterly-trending Laramide fault system splits into a complex network of faults. Also, most of the deposits appear to be localized where the faults cut Precambrian rocks rich in hornblende, biotite, or garnet and biotite. The ore controls recognized in this relatively new uranium district may have wider application in areas of similar geology elsewhere in the Front Range.

Colorado↗
USGS1955

Geology and beryl deposits of the Peerless pegmatite, Pennington County, South Dakota

The Peerless pegmatite, half a mile south of Keystone, Pennington County, S. Dak., has been a large source of scrap mica and beryl. Feldspar, amblygonite, tantalite-columbite, and cassiterite also have been recovered. The pegmatite is intrusive into Precambrian quartz-mica schist. Much of the schist contains staurolite and chlorite. Staurolite has been partly altered to mica, quartz, and chlorite, especially near pegmatite contacts. The pegmatite is generally discordant with the schist, but in many places secondary schistosity has been developed parallel to the contact. Tourmaline and muscovite, presumably introduced by pegmatitic solutions, are characteristic of the wall rock near discordant contacts. At the surface the pegmatite is tadpole-shaped and is 580 feet long and 360 feet wide. In cross-section the pegmatite has an anticlinal form that suggests control of the intrusion by fractures bearing N. 30°W. and dipping 45°NE. and SW. Dike-like apophyses extending from the main pegmatite have various attitudes. The Peerless pegmatite is a complex pegmatite consisting of seven zones, two replacement units, and two types of fracture-fillings. These are: Zone 1, quartz-muscovite-plagioclase pegmatite (border zone); Zone 2, albite-quartz-muscovite pegmatite (wall zone); Zone 3, cleavelandite-quartz-muscovite pegmatite (first intermediate zone); Zone 4, perthite-cleavelandite-quartz pegmatite (second intermediate zone); Zone 5, clevelandite-quartz pegmatite (third intermediate zone); Zones 6a and b, quartz-microcline pegmatite and quartz pegmatite (fourth intermediate zone); Zone 7, lithia mica-cleavelandite pegmatite (core); lithia mica-cleavelandite-quartz replacement unit; muscovite-cleavelandite replacement unit; quartz fracture-fillings; and tourmaline-quartz fracture-fillings. Zones 1 and 2 consist of alternating layers of different texture and mineralogy that are parallel to the contact. The layers contain differing proportions of quartz, plagioclase, muscovite, perthite, and accessory minerals. Sugary albite-quartz aggregates are important constituents of some layers. Layers of similar composition may occur two, three, or perhaps more times. The overall mineralogic composition of Zones 1 and 2 is similar to the composition of wall zones in many other Black Hills pegmatite, Zones 3 to 7 are in the normal sequence of zones in Black Hills pegmatites. The structural, textural, and mineralogic data confirm previously published evidence from other Black Hills pegmatites that indicates crystallization of a magma-like fluid from the wall inward. Repetition of layers in Zones 1 and 2 indicates changes in composition of the fluid at the crystallizing face. These changes may have been caused by addition of new material from below, by loss of material to the wall rocks, or by failure of convection to maintain equilibrium throughout the fluid in the pegmatite chamber. Zone 3 to 7 are in the normal sequence of zoned pegmatites that indicates crystallization from a restricted or nearly closed system. The lithia mica-cleavelandite replacement unit, which extends outward from the core, shows that in, the very late stages of crystallization a pneumatolytic or hydrothermal fluid escaped outward and replaced previously crystallized pegmatite. Accessory minerals of the pegmatite include tourmaline, beryl, apatite, amblygonite (variety, montebrasite), lithia mica, cassiterite, tantalite-columbite, garnet, spodumene, svanbergite, loellingite (?), vivianite (?), triploidite (?), dahllite, and vari-colored phosphate minerals of the lithiophilitetriphylite group and their alteration products. The chemical composition of the pegmatite has been determined by estimating the mineral, constitution of the various units and by calculating the tonnage of these units by use of successive geologic sections. The principal constituents are: SiO 2 (77.0 percent), Al 2 O 3 (13.7 percent), Na 2 O (5.0 percent), and K 2 O (1.7 percent). Chemical composition has also been determined for four subdivisions of the pegmatite: (A) Zones 1 and 2, (B) Zones 3 and 4, (C) Zone 5, and (D) Zones 6 and 7 and the replacement units. The content of Si0 2 increases and the content of Al 2 O 3 decreases from the outer pan of the pegmatite inward. Na 2 O forms only 0.4 percent of the inner subdivision (D), but 4 .7 to 6.5 percent of the other subdivisions. K 2 O forms 4.0 percent of subdivision (B), but only 0.7 to 1.3 percent of the other subdivisions. Zone 3, the principal minable unit, contains 1. 7 percent beryl and 28 percent scrap mica. Beryl also constitutes more than 1 percent of parts of the wall zone, especially albite-rich layers of the inner part of the unit in the upper part of the pegmatite. Beryl is a less important constituent of other units of the pegmatite. Potash feldspar is mined chiefly from Zone 4. Clevelandite that can be hand-cobbed and sold as soda-feldspar occurs in Zones 3, 4, and 5. Amblygomlte forms between 0.5 and 1.0 percent of Zone 5. Reserves of beryl, scrap mica, potash feldspar, and amblygonite are one to six times past production.

South Dakota↗
USGS1953

Geology, of the High Climb Pegmatite, Custer County, South Dakota

The High Climb pegmatite, Custer County, S. Dak., belongs to the series of pegmatitic and granitic rocks that characterize the Harney Peak region of the southern Black Hills. It intrudes pre-Cambrian metamorphic rocks consisting chiefly of quartz-mica schist. The country rock has been altered to a tourmaline-rich schist along part of the pegmatite contact. The structure of the pegmatite, in general is concordant with the westward-dipping schistosity of the country rock, but locally the pegmatite is crosscutting. The main part of the pegmatite is an irregularly shaped pipe that plunges 45° N. 40° W., parallel to the average plunge of rolls in the foot wall. A small northern extension of the pegmatite has a lenticular shape and crosscuts the schist at a low angle. Rolls in this part of the pegmatite have an average plunge of 28° N. 25° W. One large, north-trending crestal roll divides the outcrop of the northern segment of the pegmatite into two parts. The pegmatite has a well- defined internal structure consisting of five zones. A fine-grained wall zone, consisting of albite-quartz pegmatite, and a medium-grained first intermediate zone, consisting of albite-quartz-muscovite pegmatite, form incomplete concentric shells. Perthite-quartz-albite pegmatite (second intermediate zone) forms a hood-shaped unit between the outer units and the third intermediate zone along the crest and hanging-wall of the pegmatite. A concentric shell of quartz-cleavelandite pegmatite (third intermediate zone) surrounds a lenticular core of quartz pegmatite that contains altered spodumene, in addition -to the five zones, a fracture-filling unit of quartz-perthite-muscovite-albite-pegmatite and a possible sixth zone (or replacement unit?) of very fine-grained muscovite pegmatite were recognized. The essential minerals of the pegmatite include microcline-perthite, quartz, albite, and muscovite. Accessory minerals include tourmaline, beryl, amblygonite (variety, montebrasite), apatite, columbite-tantalite, loellingite, altered spodumene, numerous unidentified dark-colored phosphate minerals, a manganese-bearing carbonate, garnet, and chalcopyrite. An explanation of the origin of the pegmatite requires fractional crystallization and incomplete reaction in a restricted system. The concentric zonal structure and the general increase in grain size from the wall zone to the core suggest that the pegmatite units crystallized in order from the walls inward, without any true replacement stages. Industrial minerals that have been produced at the High Climb pegmatite are beryl, amblygonite, potash feldspar, columbite-tantalite, scrap mica, and sheet mica.

South Dakota↗
USGS1952

Results of exploration at Lost Creek schroeckingerite deposit, Sweetwater County, Wyoming

The U. S. Geological Survey, on behalf of the Atomic Energy Commission, from July 1951 to February 1952, explored the Lost Creek schroeckingerite deposit, Sweetwater County, Wyoming, by means of auger- drilling, trenching, and bucket-drilling. This report presents an estimate of the inferred ore reserves obtained during this exploration. The inferred reserves are presented under three schedules. Schedule A is the reserves calculated for the main schroeckingerite-bearing area; Schedule B is the reserves for the smaller schroeckingerite-bearing area to the north of the main area. The grade and tonnage estimates for both Schedule A and Schedule B are divided into two groups--data for selective mining, and data for bulk-mining. Schedule C presents reserve estimates for a semi- selective mining method and was calculated for four selected blocks in the western half of the main schroeckingerite-bearing area. The inferred reserves of schroeckingerite available for bulk-mining in the area of Schedule A are about 3,000,000 tons that contain 0.005 percent uranium, or about 140 tons of metallic uranium. By bulk-mining, 900,000 tons containing 0.005 percent uranium, or U£ tons of metallic uranium, are available in the area of Schedule B. The inferred reserves available for selective mining in the area of Schedule A are 100,000 tons of schroeckingerite deposits that contain 0.030 percent uranium, or 30 tons of metallic uranium. By selective mining, 35,000 tons of schroeckingerite deposits that contain the 0.030 percent uranium, or 10 tons of metallic uranium, are available in the area of Schedule Bo Semi- selective mining in the four areas of Schedule C will yield about 650,000 tons of rock containing O.008 percent uranium, or 50 tons of metallic uranium.

Wyoming↗