Comments on biogeochemical prospecting at the Shawangunk Mine; discussion
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New York↗
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A gold-scheelite-cinnabar placer in Humboldt County, Nevada
Gold, scheelite, and cinnabar in amounts that might be profitably extracted are found in a placer deposit in the Dutch Flat mining district in north-central Nevada. These materials are the products of at least two and possibly three stages of metallogenic activity recorded in the district. The gold and perhaps most of the scheelite were derived from quartz veins that cut a small granodiorite stock and lower Paleozoic sedimentary rocks. Part of the scheelite may have been derived from contact-metamorphic deposits associated with the granodiorite stock. The cinnabar came from a shear zone that is later than the quartz veins. The proximity of the placer to the source of the minerals is the factor that made a significant concentration of these minerals possible. Incomplete sampling of the placer indicates an average value of $1.50 per cubic yard in combined gold, tungsten, and mercury based on the price of these metals in August 1954.
Nevada↗
Salt-water encroachment as induced by sea-level excavation on Angaur Island
Angaur, southwesternmost of the Palau Islands, 800 miles southwest of Guam, has an area of 3.2 square miles and consists of reef limestone of Pliocene through Recent age. In the northwestern part of the island a basin is formed by a ringlike ridge that has a maximum altitude of 150 feet. To the east and south a series of arc-shaped lower ridges and intervening depressions are concentric with the ring ridge. Beyond these, a low plain with shallow swales composes the remaining two-thirds of the island. The ridges are composed of indurated limestone, whereas the plain is underlain chiefly by unconsolidated coralline fragments. Phosphate has been mined from the three types of topographic depressions since 1908. When power equipment was introduced, excavations were extended below sea level. Lakes formed in these excavations and, despite an annual rainfall of 110 inches, contamination of fresh-water supplies and of agricultural land by salt water resulted from tidal pulsations through the fissured rock. As a result, stoppage of mining was imminent unless remedial measures could be devised. Angaur provides a model of the operations of a Ghyben-Herzberg fresh-water lens on an oceanic island. At numerous lakes, wells, and test holes, continuing observations were made on water levels; amplitude and lag of tidal fluctuations; and mineral content, pH, and temperature of the lens. These observations guided the selection of constantly adjusted remedial measures, which included partitioning of lakes, and bottom filling or back filling of compartments that failed to freshen because of fissures connecting them with the sea. © 1955 Society of Economic Geologists, Inc.
Angaur↗
Geochemistry of sphalerite from the Star Mine, Coeur d'Alene district, Idaho
Forty sphalerite samples from the Star mine, Coeur d'Alene district, Idaho, and 19 sphalerite samples from other Coeur d'Alene mines have been quantitatively analyzed by spectrographic methods for Fe, Cu, Pb, Cd, Ga, Ge, In, Mn, Co, and Hg. The samples from the Star vein were collected over a strike length of 2,000 feet and a vertical distance of 5,300 feet.It is believed that Star mine sphalerite formed in equilibrium with Fe; consequently, following Kullerud's work, the Fe content may be used as a relative temperature scale. Relative Fe temperatures suggest that the lower portions of the Star ore body formed at lower temperatures than the upper portions of the ore body.Distribution of the minor elements in sphalerite is random within the ore body. Also, there is no correlation of Fe with minor elements other than Mn; therefore we believe temperature has had no influence on the distribution of minor elements, except Mn, in this ore body.The principal reason for this seems to be that equilibrium concentrations of the minor elements were not reached. Minor-element concentrations in sphalerite from the Coeur d'Alene district are similar to those in other districts throughout the world; consequently, the writers suggest that in general the minor-element content of sphalerite, other than perhaps Mn, cannot be an indicator of formation temperatures because equilibrium concentrations are rarely, if ever, attained.The average minor-element content in a district is probably that of the ore-forming solutions. Specific minor-element content in sphalerite is random.
Idaho↗
Uranium deposits of the northern part of the Boulder Batholith, Montana
Uranium minerals and radioactivity anomalies occur in many silverlead veins and chalcedony veins and vein zones in the Boulder batholith of southwestern Montana. Pitchblende has been identified in a few silverlead veins. These silver-lead veins occupy shear zones along which there is no evidence of large-scale lateral displacement. The wall rock adjacent to the veins is intensely silicified and sericitized quartz monzonite and granodiorite. The veins have yielded substantial quantities of lead, silver, zinc, and gold. The silver-lead veins consist principally of galena, sphalerite, tetrahedrite, chalcopyrite, and pyrite in a gangue of light- to dark-gray quartz, altered rock, gouge, and subordinate chalcedony and carbonate minerals. No anomalous radioactivity nor uranium minerals have been found in similar veins in prebatholithic rocks of the area.Chalcedony veins and vein zones, some of which are uraniferous, are distinctly different from the silver-lead veins and, with a single exception, are known only in the batholith. The chalcedony vein zones consist of one or more discontinuous stringers or veins of chalcedony and microcrystalline quartz in silicified and sericitized quartz monzonite and granodiorite, and in less strongly altered alaskite. Only small amounts of silver ore have been produced from these chalcedony veins and vein zones. All of the veins are early Tertiary in age, but the silver-lead veins probably are older than the chalcedony veins. Uranium is closely associated with chalcedony and microcrystalline quartz in both types of veins. This association suggests that all of the uranium in the area is of the same age. If so, some of the silver-lead veins must have been re-opened during the period of chalcedony vein formation.
Montana↗
Some limitations on the possible composition of the ore-forming fluid
The activity ratios of various important anions (S (super =) , CO 3 (super =) , SO 4 (super =) , OH (super -) , F (super -) , and Cl (super -) ) in hydrothermal solutions at the time of deposition are evaluated using a simple thermodynamic technique. The ratios are interpreted in the light of the mineralogy of ore deposits and limits are placed on the variability of each ratio in hydrothermal solutions. All of the calculations are made for 25 degrees C and cautious extrapolation to higher temperatures seems justified; however, additional data for elevated temperatures and pressures are needed before more than approximate values may be assigned to these ratios in the ore-forming fluid.The calculated partial pressure of CO 2 in the ore fluid is generally less than one atmosphere, which suggests that a dense CO 2 phase cannot be considered an important ore fluid for most deposits. The partial pressure of H 2 S is usually less than 10 (super -4) atmosphere, which makes it extremely difficult to defend the theory that metals (other than the easily complexible mercury, arsenic, antimony, and perhaps gold and silver) are transported in quantity as complex sulfides or hydrosulfides. The sulfate to sulfide ratio is such that the oxidation potential at the time of deposition is defined by the following equation: Eh (in volts) = 0.22 + or - 0.04 - 0.059 pH.
Economic Geology↗
Ezcurrite (2Na 2 O.5B 2 O 3 .7H 2 O), a new sodium borate from Argentina; occurrence, mineralogy, and associated minerals
Describes ezcurrite from a pluglike deposit of recrystallized borax at the Tincalayu mine in Salta, Argentina, and attributes its origin, together with that of associated kernite which it closely resembles, to crystallization from solutions released by dehydration of borax at elevated temperatures during deformation.
Tincalayu↗
Occurrence of selenium in sulfides from some sedimentary rocks of the western United States
Investigations of the minor- and trace-element content of sulfides associated with uranium ore deposits from sandstone-type deposits have shown that selenium commonly substitutes for sulfur. The Morrison formation and Entrada sandstone of Jurassic age and the Wind River formation of Eocene age seem to be seleniferous stratigraphic zones; sulfides deposited within these formations generally contain abnormal amounts of selenium. The selenium content of the pyrite, marcasite, and chalcocite is much greater than that reported in previously published data.Under the prevailing temperatures and pressures of formation of the Colorado Plateau uranium deposits the maximum amount of Se substituting for S in the pyrite structure was found to be 3 percent by weight. Ferroselite, the iron selenide (FeSe 2 ), was found in two deposits on the Colorado Plateau and it was also established that galena (PbS) forms an isomorphous series with clausthalite (PbSe) in nature.During oxidation of the selenium-bearing sulfides and selenides from the Colorado Plateau and Wyoming, the selenium forms pinkish crusts of either monoclinic or hexagonal native selenium intergrown with soluble sulfates, suggesting that under "normal" oxidizing conditions native selenium is more stable than selenites or selenates. The above-normal selenium content of these sulfides from sedimentary rocks of Mesozoic and Tertiary age is significant. The high selenium in these sulfides is related to periods of volcanic and intrusive activity penecontemporaneous with the formation of the containing sediments.
Arizona, Colorado, New Mexico, Utah, Wyoming↗
A definition of coal
In reply to critical discussion, restates and clarifies the definition of coal given in a glossary of terms pertaining to coals, bitumens, and related carbonaceous materials.
Economic Geology↗
Minerals of the cassiterite-bearing veins at Irish Creek, Virginia, and their paragenetic relations
Major rock types of the Irish Creek district are gneisses and schists, intruded by granodiorite. All these rocks are believed to be Precambrian. The ore deposits are fissure veins consisting largely of quartz veins bordered by greisen, and enriched by recurrent deposition. From field and microscopic evidence six stages of mineral formation have been deduced: 1. Crystallization of the granodiorite with the formation of hypersthene, augite, hornblende, andesine, orthoclase, microcline, and quartz; and accessory apatite, rutile, ilmenite, titanomagnetite, and zircon. 2. Metamorphism of the granodiorite and gneiss with formation of uralitic actinolite, epidote, and sphene. 3. A period of fracturing and formation of quartz veins. 4. Greisenization of the host rock producing first: coarse muscovite, brown biotite, cassiterite, beryl, wolframite, and quartz; then producing a second group of minerals-fluorite, green biotite, chlorite, phenakite, siderite, ankerite, parisite, sphalerite, sulfides, including aikinite and galeno-bismutite, leucoxene, fine muscovite, and quartz. 5. Formation of late vein minerals, clinozoisite, calcite, nontronite, and montmorillonite. 6. Formation of surficial alteration products, kaolinite, vermiculite, hematite, limonite, and scorodite. The italicized mineral names indicate the minerals heretofore unreported from Irish Creek; parisite, aikinite, and galenobismutite are new minerals for Virginia. Included in the detailed descriptions of all the minerals is a chemical analysis of beryl.
Virginia↗
The environmental control of sedimentary iron minerals
An Eh-pH stability diagram is developed for hematite, magnetite, siderite, pyrite, and iron sulfide that indicates the relative position of their stability fields in a normal sea water system. With the exception of the magnetite-siderite relationship, Eh is much more critical than pH. In general terms, hematite is stable under oxidizing conditions, siderite and magnetite under intermediate to moderately reducing conditions, pyrite under moderate to strongly reducing conditions, and iron sulfide under still stronger reducing conditions. Because of numerous variables involved the relative positions of the stability fields are stressed rather than their limits on the Eh and pH scales. The inclusion of a magnetite field suggests that magnetite should be much more important as a primary or diagenetic mineral in sedimentary rocks than has been commonly recognized. This is in accord with numerous recent suggestions to that effect. The importance of thermodynamic equilibrium is stressed and it is suggested that differences in rates of formation of the various minerals and the persistence of some metastable phases are among the commonest causes of lack of equilibrium.
Economic Geology↗
Design of simple punched card systems with reference to geochemical problems
A number of critical factors should be considered in the design of files using marginally punched cards. These factors are discussed in general terms and exemplified by reference to a system developed for use in geo-chemical studies.
Economic Geology↗
Nickel-gold ore of the mackinaw mine, Snohomish County, Washington
The Mackinaw mine ore is of an unusual or unique type, consisting chiefly of niccolite, maucherite, pentlandite, chalcopyrite, cubanite, and magnetite in an altered peridotite. Valleriite, gold and sphalerite are minor primary minerals; chalcocite and violarite or bravoite are supergene minerals. Pyrrhotite and pyrite are absent. From the textural relations it is inferred that a complex copper-nickel-iron sulfide was deposited early. On cooling, the sulfide unmixed into two different complex sulfides, one of which in turn unmixed into chalcopyrite and cubanite, the other into chalcopyrite and pentlandite. The latter exsolution relationship has not been previously reported. Valleriite either exsolved from, or replaced, chalcopyrite. Late solutions altered the niccolite to maucherite, and introduced gold and magnetite. The gold is almost always with maucherite.
Washington↗
Titaniferous sedimentary rocks in the Cuyuna district, central Minnesot
The ore-yielding main iron-formation of the Cuyuna district is strati-graphically overlain by approximately 300 feet of titaniferous sedimentary rocks, and a field test for titahia has been an effective supplement to customary stratigraphic studies. The titanium is in leucoxene. The sedimentary rocks of the district are highly folded, and the main iron-formation serves as the reference for relative stratigraphic position. The strata older than the main iron-formation are light-gray argillite and siltstone with local lenses of quartzite near the upper contact; the older strata contain about 0.5 percent titania. The main iron-formation is a persistent layer of chemically precipitated ferruginous sediments that contain about 0.2 percent titania. The strata younger than the main iron-formation are gray or black argillite, partly carbonaceous, partly ferruginous, and are transitional into lenses of lean upper iron-formation. At the base of the younger strata, 250-350 feet of argillite and slate contain 1-3.7 percent titania and average 2.0 percent. This titaniferous argillite is similar to argillite higher in the younger sequence which contains less than 1.5 percent titania and averages about 1 percent. There are weathered rocks interpreted as tuffs and basalt flows locally interlayered near the bottom of the titaniferous zone. The basalt contains 1-2 percent titania. The high titania content of the 250-350-foot zone suggests a volcanic origin; the argillite probably is reworked basaltic pyroclastics. A few titaniferous bodies have been found in rocks below, within, and above the main iron-formation and thin titaniferous argillaceous layers occur within the main iron-formation.
Minnesota↗
Limestone aquifers of Maryland
Limestone rocks are an important source of ground water in the Piedmont and Appalachian areas of Maryland. The major limestone aquifers are the Cockeysville and Wakefield marbles and the Silver Run, Tomstown, Frederick, Grove, Waynesboro, Elbrook, Conococheague, Beekmantown, Stones River, Tonoloway, Helderberg and Greenbrier formations. Drilled and dug wells and springs are common sources of water supply in the limestone areas. The depths of 298 limestone wells range from 8.7 to 1,800 feet and average about 150 feet. The yields of these wells range from 0.1 to 575 gpm. Specific capacities, or yield per foot of drawdown, range in 137 wells from 0.1 to 43 gpm per foot. Springs are common in the limestone areas and their flow varies widely at different times. Most of the known springs are of the 5th magnitude or lower, and therefore have a mean flow of less than 100 gpm. The quality of water from the limestone aquifers is satisfactory for most purposes, but is commonly hard and slightly alkaline. The limestone aquifers are large essentially untapped ground-water reservoirs whose hydrologic character is only partially understood.
Maryland↗