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J. E. Gair

Publications and source records attributed to J. E. Gair.

At least 19 recordsLinked to original sources
USGS1984

Deformation, geochemistry, and origin of massive sulfide deposits, Gossan lead district, Virginia

The Gossan Lead district is a 28-km-long, northeast-trending belt of discontinuous massive sulfide deposits in the Blue Ridge province of southwestern Virginia. The deposits, hosted by the Ashe Formation of late Proterozoic age, consist of strata-bound lenses and layers of massive pyrrhotite, minor chalcopyrite, sphalerite, and pyrite, and rare arsenopyrite and galena. Deposits were mined principally in the Iron Ridge and Betty Baker segments, respectively, at the southwestern and northeastern ends of the belt. Detailed mapping of the Gossan Howard, Huey, and Bumbarger pits in the Iron Ridge segment indicates that the deposits occur at one horizon and have been variously folded and brecciated after sulfide deposition. The Gossan Howard consists of a single, gently dipping lens of sulfide. The Huey deposit is complexly folded and locally contains tectonically thickened ore. The Bumbarger deposit is a lens as much as 40 m thick--the thickest known in the district. This deposit contains abundant coarse breccia fragments of wall rock around which the massive sulfide has flowed (during deformation and metamorphism), probably thickening the original deposit significantly. In the northeastern part of the district, drill holes intersect several sulfide layers that possibly are structurally repeated.The Ashe Formation in the district is a sequence of metasedimentary rocks and local conformable lenses of amphibolite and actinolite-chlorite schist. The metasedimentary rocks include metapelite, quartz-feldspar granofels (metagraywacke), and minor quartzite and carbonaceous schist, and are interpreted as marine turbidites. The amphibolites and other mafic rocks have chemical compositions similar to low Ti tholeiitic basalt, with a high Y/Nb (>10) and high average contents of Co (40 ppm), Cr (403 ppm), Ni (211 ppm), and V (247 ppm). Immobile trace element signatures (Ti-Y-Zr; Th-Hf-Ta; Ti-Cr) suggest a magmatic affinity with midocean ridge basalt (MORB); rare earth elements (REE) have low abundance levels (10X-15X chondrite), broadly flat patterns [(La/Yb) N = 0.7-1.1], and a slight depletion in the light elements similar to midocean ridge basalts. An amphibolite from a much higher stratigraphic level, south of the district, differs significantly from the mafic rocks closer to the sulfide zone in having the chemical signature of a transitional, slightly alkalic tholeiite with high TiO 2 (3.87 wt %), Fe 2 O 3 (16.4 wt %), and P 2 O 5 (0.56 wt %), low Y/Nb (3.3), and a highly fractionated rare earth element distribution [(La/Yb) N = 3.9] similar to continental basalt.Some silicate wall rocks of the deposits are mineralogically and chemically unusual, and differ substantially from the clastic metasediments of the Ashe Formation. Such rocks are composed mainly or wholly of plagioclase feldspar, biotite, chlorite, muscovite, or spessartine-rich garnet. The unusual lithologies form local strata-bound lenses in the footwall and/or hanging wall of the deposits, typically within 10 m of massive sulfide. The plagioclase rocks (3.4-7.6 wt % Na 2 O) consist largely of granoblastic albite-oligoclase (Ab (sub 78-90) ) with minor quartz and biotite; rare earth elements are highly fractionated [(La/Yb) N = 6.8-7.1] and their patterns resemble those of the quartz-feldspar granofels (metagraywacke) from the district.The biotite schists, locally monomineralic, have FeO/(FeO + MgO) = 0.5 and contain high phosphorus (1 wt % P 2 O 5 ) and fluorine (0.5 wt % F), present in fluorapatite. The chlorite schist is essentially all ripidolite; rare earth elements are highly fractionated, and have a large negative Eu anomaly. The spessartine-rich rocks (6.3-8.9 wt % MnO) are in places interlayered with the other unusual wall rocks and consist of abundant Mn-rich garnet (Sp 50 Al 23 Gr 19 Py 8 ) and minor quartz, plagioclase, pyrrhotite, and biotite. The distinctive mineralogy and chemistry of these rocks suggest that they represent metamorphosed alteration zones and/or intermixed chemical and clastic sediments.The sulfide deposits are interpreted as syngenetic in origin but modified in form by deformation which accompanied metamorphism. The great length of the mineralized district parallel to the regional strike and the flyschoid (turbidite) nature of the host rocks suggest that sedimentation and initial sulfide deposition took place in a deep, elongate marine basin or graben overlying a crustal rift zone. A rift underlying the sedimentary pile is consistent with the occurrence of mafic metavolcanic rocks of midocean ridge basalt affinity and could also have served as the feeder system for a line of hydrothermal vents on the sea floor that generated the sulfide deposits.

Economic Geology↗
USGS1984

A special issue devoted to massive sulfide deposits of the Appalachian-Caledonian orogen. Preface.

This issue of Economic Geology (pp 1425-1758) adds 17 reports to those earlier published by a nine-year project (No. 60) of the International Geological Correlation Programme (IGCP) on the Correlation of Caledonian Stratabound Sulphides (CCSS). The contents of the 17 reports are noted and briefly discussed in relation to one another and to stratiform ores as a whole. From this preview, it is concluded that geological mapping appears to be still the best way to find strata-bound sulphide deposits.-G.J.N.

Economic Geology↗
USGS1982

Massive sulfide deposits of the Southern Appalachians central Virginia volcanic-plutonic belt as a host for massive sulfide deposits

Strata-bound massive sulfide deposits of the central Virginia Piedmont occur in a volcanic- plutonic belt composed of Lower Cambrian(?) metamorphosed volcanic rocks and locally of pre-Upper Ordovician, low potassium granitoid rocks. The belt, interpreted as an ancient island arc, begins about 50 km south of Washington, D. C, and extends some 175 km south- westward. The volcanic rocks within the belt are located along the flanks of the Quantico- Columbia synclinorium and the Arvonia syncline. The Chopawamsic Formation, a western facies of the belt, consists of volcanic rocks that have the geochemical features (rare earth and immobile elements) of a tholeiitic island-arc suite; it also contains calc-alkaline components. Tholeiitic amphibolites of the Ta River Metamorphic Suite on the eastern side of the belt form an oceanward facies of the island arc, coeval with the Chopawamsic. This distribution suggests an underlying westward-dipping Cambrian(?) subduction zone. Contrasts in stratigraphy, geochemistry, and magnetic and gravity features indicate that the central Virginia volcanic- plutonic belt is not related to the Carolina slate belt as has been proposed in the past. Known sulfide bodies in the Chopawamsic and its coeval units total about 13.5 million tons. The Mineral district on the northwest flank of the Quantico-Columbia synclinorium has the largest deposits and contains about 10 million tons. Sulfide bodies in the belt consist largely of pyrite with minor sphalerite and chalcopyrite; Zn and Pb are important in a few of the smaller deposits. There are local concentrations of sphalerite and other base metal minerals within the major pyritic deposits (Zn = 1-12.5%; Cu - 1-2%; Pb as much as 5%). The dom- inantly sphaleritic deposits are found in and northward for about 15 km from the Mineral district. Sulfide mineralization is found in all types of volcanic rock, but the large sulfide bodies on the northwest flank of the Quantico-Columbia synclinorium are in felsite. Am- phibolite, containing local beds of iron-formation, is abundant on the southeast flank of the Arvonia syncline; however, most sulfide mineralization there took place in felsitic to intermediate layers. Mineralization, attributed to submarine volcanic exhalation, took place during formation of the island arc.

Economic Geology↗
USGS1979

Geochemical data for Cohutta Wilderness, Georgia-Tennessee

Trace-element data obtained from stream-sediment, soil, and rock-chip samples by semiquantitative spectrographic and atomic absorption analyses. Geochemical data are grouped alphabetically by letter prefix and arranged in numerical order within the lettered groups. The listed data were obtained from samples collected in 1977 and 1978 by Jacob E. Gair and John F. Slack, assisted by Andrew Grosz, Richard Ketelle, Donald Henry, Thomas Hanley, Ann Stevens, and Gregory R. Morley. The spectrographic and atomic absorption analyses were done in laboratories of the Branch of Exploration Research, U.S. Geological Survey, Denver. The spectrographic analyses were done by David F. Siems and Elwin L. Mosier; the atomic absorption analyses, by Allen L. Meier. Data retrieval from the computerized storage file of the U.S. Geological Survey was made by Nancy A. Wright.

Georgia, Tennessee↗
USGS1976

Compositional variations in wolframite from the Hamme (Tungsten Queen) mine, North Carolina

A microprobe study of wolframite from the Tungsten Queen mine, Hamme district, North Carolina, proves it to be almost pure huebnerite. Concentric zoning, which shows up as light-brown and dark-brown bands, indicates small variations in the content of FeO. There is no apparent correlation between the small variations in the composition of the wolframite and its position in the mine. The Fe/Mn ratio of the wolframite is not indicative of the temperature of crystallization.

North Carolina↗
USGS1970

A revision of stratigraphic nomenclature for middle precambrian rocks in Northern Michigan

The name Marquette Range Supergroup is proposed to supplant the term Animikie Series for middle Precambrian strata of the Northern Peninsula of Michigan and adjacent areas of Wisconsin. The Marquette Range Supergroup consists of the Chocolay, Menominee, Baraga, and Paint River Groups, as defined in previous literature. We feel that this new name to apply to Northern Peninsula rock units is appropriate, as continued investigations have failed to show unequivocal correlation between middle Precambrian rocks of Michigan and the Huronian Supergroup of Ontario. Although the equivalence of the Animikie Group in Ontario and Minnesota with parts of the Michigan rocks is likely, the Stratigraphic complexity of the Michigan sequence requires supergroup rank. The inherent confusion of an Animikie Group in Ontario and Minnesota, and an Animikie Supergroup in Michigan, makes a local name such as Marquette Range Supergroup preferable to Animikie for the middle Precambrian rocks of Michigan. © 1970, The Geological Society of America, Inc.

Michigan↗
USGS1965

Aeromagnetic map of parts of Marquette, Dickinson, Baraga, Alger, and Schoolcraft Counties, Michigan, and its geologic interpretation

The U. S. Geological Survey, in cooperation with the Geological Survey Division of the Michigan Department of Conservation, is conducting a comprehensive restudy of the iron-bearing districts of Michigan. The use of aeromagnetic data is one of the fastest and most reliable methods for outlining the areal distribution of magnetic iron-formation and thus is of material value in assessing the iron resources of the United States. As part of this program of restudy, aeromagnetic surveys of approximately 4,500 square miles of the Northern Peninsula have been made. The results of several of these surveys have been presented by Balsley and others (1949) and by Wier and others (.1953). This report is about a survey made in 1950, over an area of about 1,400 square miles in Marquette County and ad-· joining strips in northern Dickinson and northeastern Baraga Counties, and a later survey flown in 1961, over about 500 square miles in parts of Marquette, Alger, and Schoolcraft Counties. The Marquette iron range extends in an east-west direction across approximately the west-central part of the area, and iron districts of lesser importance are located at Republic, in the southwestern part of the area, and near Gwinn, in the south -central part of the area. Aeromagnetic surveys were flown along north-south lines spaced at intervals of one-quarter mile in the western part of the area and at intervals of from about 1 to 3 miles in the eastern part. Lines were flown at approximately 500 feet above the surface or at elevations of 1,100 to 2,400 feet above sea level. The flight path of the aircraft was recorded by a gyrostabilized continuous-strip camera, and elevation was continuously recorded by a radio altimeter. Magnetic measurements were made by an AN/ASQ-3A fluxgate magnetometer. Compilation of aeromagnetic data was by standard methods, described by Balsley ( 1952 ), under the supervision of John Kirby and Frank Petrafeso. The aeromagnetic contours are relative to an arbitrary datum. Magnetic properties of rocks were measured by W. E. Huff. At the time the earlier aeromagnetic survey was flown, the only base maps available were planimetric maps such as the Helena NW quadrangle and county road maps. Small errors, therefore, may exist in the location of flight lines and specific aeromagnetic a nomalies. The major magnetic anomalies and broad areas that have characteristic magnetic patterns are correlated herein with geology as determined from published reports and from mapping done since 1957 by the U. S. Geological Survey in the eastern part of the Marquette iron range. The geology north of the Marquette iron range and west of the line between R. 25 W. and R. 26 W. is based mainly on a compilation made by Robert Reed of the Geological Survey Division of the Michigan Department of Conservation from data in the files of the State Survey. In addition some aeromagnetic features have been checked by ground magnetometer in selected localities and correlated directly with the rock types. A few oriented samples have been collected for measurement of the magnetic properties of the major rock units, but many hundreds or thousands of samples would be required to obtain a full range of values of the magnetic susceptibility and remanent magnetization of the rocks over such a large area. Although the geology of much of the area is still imperfectly known, the available aeromagnetic data together with the best obtainable geologic data are presented at this time, rather than awaiting the eventual extension or completion of the present mapping program, because the combined data provide much information on the extent and location of magnetic iron-formation and other major rock units where concealed beneath glacial, vegetative, and alluvial cover.

Michigan↗