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USGS1968

The non-colloidal origin of 'colloform' textures in sphalerite ores

" Colloform " ores have generally been considered to have been deposited as colloidal sulfide gels, and even transported as colloidal "sols." However, studies of doubly polished plates of " colloform " sphalerite -wurtzite assemblages from various deposits reveal crystal growth features that cannot have been formed by crystallization from gels, and indicate that most, and perhaps all, grew directly as minute druses of continuously euhedral crystals projecting into an ore fluid. Each of the many textural criteria proposed for recognizing colloidal deposition is shown to be invalid, ambiguous, or inapplicable to these samples, and perhaps also to most other " colloform " mineral samples.Four conclusions pertinent to ore research are derived from this study: (1) Primary fluid inclusions in " colloform " samples are believed to represent the original ore fluid, not merely a residual fluid from the crystallization of a gel. (2) Although euhedral crystals may possibly grow directly from a sol, several features make a noncolloidal (true solution) ore fluid more probable. (3) Maintenance of the large number of crystal nuclei responsible for the " colloform " texture is attributed to relatively high supersaturation, and hence relatively high nucleation and growth rates, for the temperatures involved. (4) Remarkably uniform, regular compositional microbands, traversing many crystals in samples from the east Tennessee, Aachen, and particularly the Pine Point deposits, are tentatively interpreted as annual "varves." No actual growth rates have been determined, but each "varve" consists of a dark and a light band, outlining sharply euhedral former crystal growth patterns and suggesting an annual change in the ore fluid due to dilution with surface waters of varying volume or chemistry (e.g., oxygen or organic content).

Economic Geology↗
USGS1968

Minor epigenetic, diagenetic, and syngenetic sulfide, fluorite, and barite occurrences in the central United States

Metallic sulfides, fluorite , barite , and celestite are widespread in the sedimentary rocks of the central United States . Many occurrences are epigenetic concentrations either in known major mineral districts or in clusters of deposits that warrant further exploration for potential ore. Evaluation of trace-element composition, of fluid inclusions, of depositional temperature, and of isotopic composition of sulfur may help discriminate potentially economic deposits from even more widespread, probably noneconomic, syngeneic occurrences . Known major mineral districts and many promising sulfide occurrences are located along complex major fault systems and particularly over structural domes at intersections of fault systems. Economically promising sulfide deposits occur along a west-trending fault system crossing Kentucky and Missouri near the 38th parallel, particularly at associated cryptoexplosion structures along it, at the intersection of the fault system with the Cincinnati arch. Elsewhere in the central United States , promising sulfide occurrences are located along the crest of the Findlay arch, near Serpent Mound, Ohio, along the northwest-trending Mount Carmel fault in southwestern Indiana, and buried at depth in oil fields of west- central Kansas.Other types of deposits that are productive or may have some future economic interest are locally economic and possibly syngenetic red-bed copper occurrences in Oklahoma, Texas, Kansas, and Pennsylvania. Most widespread are the black shale and pyritic sandstone beds, some of which have been a source of pyrite for sulfur and sulfuric acid in conjunction with coal mining. Bedded barite deposits of possibly diagenetic origin have been mined in Arkansas. Diagenetic siderite concretions containing sulfides and barite were widespread sources of iron in the 19th century.

Economic Geology↗
USGS1968

Chronology of intrusion, volcanism, and ore deposition at Bingham, Utah

Potassium-argon dates for major igneous rock types in the Bingham mining district, Utah, range from 39 to 32 m.y. and suggest that:(1) Plutonism, volcanism, and hydrothermal activity were sequential stages in a magmatic history of about 7 m.y. duration.(2) Latitic volcanic rocks, in part, postdate emplacement of the Last Chance and Bingham stocks.(3) Sulfide mineralization and hydrothermal alteration followed emplacement of the monzonitic stocks and extrusion of at least the earliest units in the volcanic sequence; the time interval between intrusion and alteration was probably less than 1 m.y.(4) The rhyolites of Shaggy Peak, which may represent terminal differentiation products in a comagmatic series, are the youngest igneous rocks in the area.

Utah↗
USGS1968

Mineralogy of sulfides from certain Hawaiian basalts

Polymineralic sulfide grains, composed principally of Fe sulfide and Fe-Cu sulfide, with magnetite, have been studied mineragraphically and by electron probe, and interpreted in terms of experimental data for the system Fe-Ni-Cu-S. The three main phases are monosulfide solid solution, a Cu-Fe sulfide (solid solution) with composition near cubanite, and Ti-free magnetite. The grains are believed to represent phases unmixed from an immiscible liquid phase in the basalt magma. Compositions of the two main sulfide phases suggest quenching below 700 degrees C. Most of the Ni has been retained in the monosulfide solid solution by rapid quenching.

Hawaii↗
USGS1968

Distribution of minor elements in ore and host rock, Illinois-Kentucky fluorite district and Upper Mississippi Valley zinc-lead district

This paper presents data on the distribution of minor elements in ore and gangue minerals and in adjacent host rock from the Illinois-Kentucky fluorite district and Upper Mississippi Valley zinc-lead district. Comparisons are made of the minor-element abundances between districts and within the paragenetic sequence in individual districts.The ore of the Illinois-Kentucky fluorite district is characterized by greater abundance of minor elements than in other Mississippi Valley deposits, by large fractionation of silver between galena and sphalerite, and by a low ratio of antimony to silver in galena. Silver and antimony are concentrated in the galena and show a marked zonal pattern within the district. Sphalerite is high in cadmium, gallium, and germanium.The Upper Mississippi Valley zinc-lead district differs markedly from the Illinois-Kentucky fluorite district in minor-element concentrations and distribution. The minor elements are much less abundant, and silver is slightly more concentrated in sphalerite than in galena.Several analyses of minor elements in ore minerals from the Southeast Missouri lead district are given for comparison.It is concluded that the minor elements were largely leached from the basement by convective circulation of heated oilfield brine.

Illinois, Kentucky↗
USGS1968

Experimental evidence that fluid inclusions do not leak

The possibility of leakage of fluids into or out of fluid inclusions subjected to large pressure gradients has always been considered a serious problem in the interpretation of inclusion data. As previous experimental evidence on leakage was contradictory, new experiments were performed. Inclusion vapor bubble diameters in twelve quartz crystals (≤ 3 mm; 8 localities), not sawn, ground or polished, were measured. The samples were run at Pa-.o,-4,000 bars, at T u 100°-410° C, for ≤ 17 days total, and remeasured after each run. Similar experiments at ≤ 155° C were made on sphalerite and calcite. Most inclusions in most samples (even those only 5am under the surface in quartz) showed no change in bubble diameter, hence no leakage. A few exceptions, mainly among inclusions homogenizing at T « Tru, had P internal » P internal , hence they ruptured and lost liquid during the 410° C run. From this work and a review of the literature, we conclude that most inclusions have not suffered major leakage. Some previous experiments indicating leakage may be explained by microfractures introduced during sample preparation. The present work does not , however, preclude the possibility of diffusion of small but chemically significant amounts of substances such as hydrogen in or out of inclusions .

Economic Geology↗
USGS1968

Uranium deposits in the Jackpile Sandstone, New Mexico

Ultimate sources of uranium are believed to be either fluids from Morrison volcanoes (not demonstrable) or labile constituents in the Jackpile Sandstone. Petrographic studies indicate considerable pre-Dakota diagenesis, which would have made uranium in feldspars, heavy minerals, and volcanic debris available. Deposition of uranium occurred while host sandstone was near the surface during the pre-Dakota hiatus. Sedimentary permeability was the principal factor in distribution of ore and of the organic decomposition products that precipitated it.

New Mexico↗
USGS1968

A lead isotope study of galenas and selected feldspars from mining Districts in Utah

The leads in feldspars from the main Tertiary intrusive bodies in each of three mining regions in Utah are isotopically similar to the lead deposits immediately associated with them. These deposits are the largest and also the least radiogenic in each region, whereas the smaller deposits are more radiogenic. Throughout each region the 'ore leads appear to be mixtures in various proportions of lead derived from the intrusive magma and a radiogenic lead component derived from the upper crustal rocks through which the mineralizing fluids passed. Linear relationships are exhibited between the lead isotope ratios within each mining region, and these enable the ages of the upper crustal basement rocks to be determined. A simple tvo-stage model theory for the development of the lead ores yields the folloving data: Oquirrh Mountains region, t 1,650 4-150 m.y., p-Cottonwood-Park City region, t = 2,415 4-30 m.y., p- = 8.87. Tintlc region, t 2,075 4-30 m.y., Milford region, t 1 765 4-70 m.y., p-T ( Us ) = , = 8.83. An alternative "mixing" model is also proposed which requires only 1,650-m.y. and 2,400-m.y. events in these regions. In either case these ages confirm and supplement our present geochronological knowledge of the basement rocks of Utah .

Utah↗
USGS1968

Borax solution at Kramer, California

Material of obscure structure that forms part of the hanging wall of the great sodium borate ore body at Kramer, Kern County, Calif., is interpreted herein as collapsed insoluble claystone layers left where interbedded borax has been dissolved. Nodular ulexite in such collapsed material is secondary; relationships between primary borax and contemporaneous ulexite or other syngenetic borate minerals remain unestablished. The effects of solution also leave unestablished the original limits of borax deposition. It is suggested that collapsed claystone layers containing ulexite might be used as an indicator of proximity to borax elsewhere in the district.

California↗
USGS1968

Lead and strontium isotope studies of the Boulder Batholith, Southwestern Montana

The isotopic composition of lead in feldspar varies widely from pluton to pluton of the Late Cretaceous Boulder batholith, encompassing the following ranges in isotopic values: 16.9-18.1 for Pb 206 /Pb 204 ; 15.4-15.7 for Pb 207 /Pb 204 ; and 37.7-38.5 for Pb 205 /Pb 204 . Although each pluton has a characteristic isotopic composition, the fact that Pb 206 /Pb 204 for the Butte Quartz Monzonite varies by 1.3 percent, compared to a range of about 8.6 percent for the batholith as a whole, suggests that perfect isotopic mixing of the magma was not always attained. Whole rock initial Sr 87 /Sr 88 for the entire batholith ranges from 0.705 to 0.710, comparable to ranges for the Sierra Nevada and British Columbia batholiths. Ore leads of the Butte district are isotopically very similar to feldspar leads of the host Butte Quartz Monzonite. This isotopic similarity was interpreted by Murthy and Patterson (1961a) to indicate complete mixing of independently derived feldspar lead and ore lead rather than close genetic relationship. However, detailed study of the only sample in the present investigation, from the Donald pluton, that clearly has mixed leads shows significant differences in lead isotopic composition between megacryst K-feldspar and both the groundmass K-feldspar and plagioclase, indicating that isotopic mixing of leads is not complete, even within a single hand specimen. Spatial relations of isotopic differences among the various plutons strongly suggest that complete mixing of leads of different isotopic composition from the magma did not occur in the Butte Quartz Monzonite nor in any other pluton of the batholith, and that the isotopic similarity between Butte ore and feldspar lead of the host rock indeed stems from a genetic association. Lead and strontium isotope ratios generally behave in a similar way; that is, the more radiogenic the lead in a rock, the more radiogenic the strontium. The source of the lead which could produce the isotope variations observed for the batholith is calculated to have a mean age of about 2,200 m.y., which is compatible with ages of Precambrian crystalline rocks in the region, and an isotopic makeup with U 238 /pb 204 <9, Th/U > 4, and Rb/Sr of 0.03-0.09. However, no large volumes of prebatholith rocks exposed in the Boulder batholith region are of the required isotopic composition, which is typical of basaltic-gabbroic or quartz dioritic chemical composition. Models involving complete melting of possible source materials to account for the isotope variations are considered and rejected. Mechanisms involving par.tial melting of lower crustal or upper mantle source material appear to be the most viable in explaining the observed isotopic compositions. Assimilation of upper crustal material (i.e., the Precambrian Belt and pre-Belt rocks, in which the lead and strontium are more radiogenic than in the batholith rocks) may have accompanied partial melting of the lower crust or upper mantle and indeed must have played a major role if the source material had a composition isotopically comparable to that observed for oceanic tholelites (i.e., low Th/U, U 238 /Pb 204 and Rb/Sr), but would be relatively unimportant if the source material were sufficiently radiogenic to begin with as might be expected from basalt, gabbro, or quartz diorite compositions 2,200 m.y. old. © 1968 Society of Economic Geologists, Inc.

Montana↗
USGS1969

Massive sulfide deposits and volcanism

Massive sulfide deposits, consisting of pyrite and/or pyrrhotite and various ratios of chalcopyrite, sphalerite, and galena, are commonly associated with volcanic rocks that accumulated in eugeosynclines. Later deformation may leave an imprint of regional metamorphism. Two-thirds of the deposits mentioned in this review are about equally divided between silicic and mafic volcanic host rocks, and the remainder occur in tuffaceous sedimentary rocks interbedded with volcanics. Little compelling evidence is available to relate genetically most of these deposits to granitic rocks, whereas considerable evidence supports a complex genetic relationship to volcanic rocks that accumulated in a submarine environment. Some deposits apparently formed during or soon after emplacement of the volcanic rocks, and possibly involved early deposition of pyrite that was followed later by the addition of base metals. The transporting agents of the base metals and some of the sulfur are heated solutions probably of different origins containing alkali chlorides as well as alkali chloride brines. Pyrite and base metals may have been deposited during the accumulation of the volcanic and associated rocks, or later during diagenesis, regional metamorphism, or intrusion of granitic plutons. The source of the base metals may have been: (1) early metal concentrations distributed through the volcanic pile, (2) trace quantities in the silicate minerals in the volcanics, or (3) later crystallizing magma.

Economic Geology↗
USGS1969

Unstable sulfur compounds and the origin of roll-type uranium deposits

Anomalous concentrations of iron sulfides found at roll fronts are believed to result from limited oxidation and mobilization of reduced sulfur species from earlier formed pyrite within the more extensively oxidized core of the roll. Laboratory experiments and chemical theory suggest that the reactions need not be biogenic, and that the sulfur of the reconstituted pyrite could be isotopically indistinguishable from biogenic sulfur. Sulfite formed by limited oxidation slowly decomposes to sulfate and sulfides, and because the sulfate-producing reaction is irreversible at low temperature, only the reduced sulfur species are available for further oxidation-reduction reactions.

Economic Geology↗
USGS1969

Determination of gold in waters in the nanogram range by anion exchange and atomic absorption spectrophotometry

A method has been developed whereby nanogram amounts of gold in waters can be accurately determined. The development of the method involves determination of optimum conditions for the complete recovery of gold from water using an anion exchange resin column, quantitative elution of gold from the resin, and final measurement of gold by atomic absorption spectrophotometry following MIBK (methyl isobutyl ketone) extraction of gold from a nitric acid solution.

Economic Geology↗
USGS1969

Micromineralogy of silver-bearing sphalerite from Flat River, Missouri

Detailed mineralogical and chemical study of sphalerite-rich lead ores from Flat River, Mo., confirms the presence of anomalous amounts of silver in the sphalerite. Although silver is closely associated with chlorine and no silver sulfide minerals were identified, geochemical considerations indicate the silver may be in the form of discrete submicron-size grains of sulfide rather than chloride. However, the close correlation between abundance variations in silver, chlorine, cadmium, iron, and minor lead suggests the possible existence of submicron-size grains of a complex chloride or oxychloride. Results from detailed chemical study of sphalerite show: (1) chlorine is present in areas containing silver and changes in abundance of both elements are similar; (2) the mole ratio of chlorine to silver varies from approximately 3:1 to 6:1 with an approximate average of 5:1 and the total content of each element varies widely between grains and within the same grain; (3) taking total silver in any analysis and calculating the amount of chlorine required for silver chloride leaves an excess of chlorine; (4) in chlorine-deficient areas the amounts of iron and cadmium substituting for zinc in the sphalerite structure vary widely; and (5) in areas containing chlorine, changes in abundance of iron and cadmium vary directly with that of chlorine. The fine-grained dusty opaque inclusions characterize sphalerite from this area; they were identified as mainly galena with lesser amounts of pyrite and cassiterite. Galena is silver-free (<0.02 weight percent Ag) and is essentially pure lead sulfide. Other sulfides identified include pyrite, a cobalt-nickel-iron sulfide of composition Co (sub 0.55) Ni (sub 0.25) Fe (sub 0.20) S (sub 2.00), and an iron-cobalt-nickel sulfide containing 22-28 weight percent Fe, 10-15 weight percent Co, and 3-5 weight percent Ni. Anomalous amounts of tin present as cassiterite are associated with the gangue minerals quartz, potash feldspar, a kaolinite-type clay, and trace amounts of cuprite. Carbonate gangue minerals include calcite, dolomite, ankerite, magnesite, and minor amounts of cerussite. Chemical analyses were made of many minerals and physical and textural relationships examined.

Missouri↗