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USGS1968

The synthesis of ferroselite from an aqueous solution at low temperature

Ferroselite , FeSe 2 , is commonly associated with sandstone-type uranium deposits. Although it has been previously synthesized, the conditions of synthesis were not applicable to the natural system, and the literature did not provide any information on the formation of natural ferroselite . The U. S. Geological Survey's Ambrosia Lake study, however, was concerned with the formation of ferroselite under more natural conditions. Thus, in this work, the synthesis of ferroselite was restricted to conditions more nearly approaching the conditions of the formation of sandstone-type uranium deposits-a low temperature and an aqueous environment. A solution of sodium seleno-sulfate, Na 2 SSeO 3 , stood in contact with freshly precipitated iron sulfide, FeS, for 10 days under an inert atmosphere at 80° C. The final product was identified by its diffraction pattern and consisted of FeSe 2 mixed with about 10 percent FeS.

Economic Geology↗

USGS1987

Structural reinterpretation of the Ajo mining district, Pima County, Arizona, based on paleomagnetic and geochronologic studies

The Ajo mining district of southern Arizona is divided into two main structural blocks by the Gibson Arroyo fault. The eastern Camelback Mountain block contains the Late Cretaceous-early Tertiary porphyry copper deposit which has been previously thought to be associated with the displaced apex of a large intrusion exposed by deeper erosion in the western Cardigan Peak block. However, unpublished U-Pb data support a mid-Tertiary age for the western intrusion. Paleomagnetic and geologic evidence indicates that the ore deposit has been tilted to the south a total of approximately 120 degrees : 68 degrees before and another 55 degrees after emplacement of the overlying Locomotive Fanglomerate and Ajo Volcanics. The Ajo Volcanics have K-Ar ages (24-25 m.y.) slightly older than those from the large intrusion of the Cardigan Peak block (20-23 m.y.). Paleomagnetic directions are consistent with the southward tilting of the volcanic rocks, but they suggest that the remanent magnetization and perhaps the K-Ar dates of the western intrusion were reset by the emplacement of dikes younger than the Locomotive Fanglomerate and Ajo Volcanics. These and other geologic relations indicate the following sequence of mid-Tertiary events in the district: (1) emplacement of the western intrusion, (2) movement along the Gibson Arroyo fault, (3) unroofing and perhaps tilting of the pluton [asymp] 70 degrees to the south along with the Camelback Mountain block, (4) syntectonic depositions of the Locomotive Fanglomerate and the Ajo Volcanics, (5) continued uplift and tilting to the south totaling 40 degrees to 60 degrees , (6) intrusion of the youngest dikes with attendant alteration and remagnetization of the host rocks, and (7) minor (?) oblique movement along the Gibson Arroyo fault.

Economic Geology↗

USGS1986

Geology and geochemistry of the Deer Trail Pb-Zn-Ag-Cu manto deposits, Marysvale District, west-central Utah

Strata-bound sulphide replacement bodies in the Deer Trail mine are sinuous pipes in carbonate beds, approximately localized by an anticlinal axis, and radiate from a fault across the lower part of the Permian Toroweap formation. Indistinct sericitic envelopes provide a K/Ar age of 14 m.y., correlative with barren, altered volcanic rocks above a hypothesized intrusion, 1 km to the west. Lead and sulphur isotope data imply an igneous source. Inclusion data and deuterium and oxygen isotopes imply a magmatic fluid progressively diluted with meteoric waters. The deposits are the outer zone of a volcanic hydrothermal system. -G.J.N.

Utah↗

USGS1992

Predicting sizes of undiscovered mineral deposits; an example using mercury deposits in California

A critical part of the exploration for mineral deposits or of quantitative mineral resource assessments is the estimation of how large undiscoveredeposits might be. Typically, this problem is addressed using grade and tonnage models in which a major source of variation in possible sizes is accounted for by the differences in types of deposits (Cox and Singer, 1986; Mosier and Page, 1988; Bliss, 1992). It is clear from studies of petroleum exploration that larger oil fields tend to be found early in the process (Arps and Roberts, 1958). If the same behavior exists in mineral exploration, then tonnage models constructed from local data may be biased estimators of the tonnages of any remaining undiscoveredeposits in the area. Although Singer and Mosier (1981) showed that larger porphyry copper deposits should be found earlier than smaller deposits in a given geologic and exploration environment, there are no definitive studies that we could find which actually test the hypothesis that larger mineral deposits are discovered early in the exploration of a region. In this paper the hypothesis that larger mineral deposits are discovered early in the exploration of a region is tested by examining the relationship between discovery order and size of known mercury deposits in the California Coast Ranges. We then present a new maximum likelihood approach to modeling the size distribution of undiscovered mineral deposits by examining the sizes of the mercury deposits discovered early in the exploration process.

Economic Geology↗

USGS1961

Uranium migration and geochemistry of uranium deposits in sandstone above, at, and below the water table; Part 2, Relationship of uranium migration dates, geology, and chemistry of the uranium deposits

The time of U migration in deposits in sandstone can be determined by correlating apparent age calculations, based on radiochemical analyses, with the geology of a particular deposit. Data were obtained from U ore samples representing deposits above the water table, deposits just above and below perched water tables, and deposits at least 250 ft. below the water table in the Hulett Creek area, Wyoming. The first U deposition occurred more than 250,000 years ago for the deposits now at or above the water table. Approximately 60,000 to 80,000 years ago these deposits were oxidized, leached, and locally enriched. Accumulation of U in the deposits below the water table probably did not start before 180,000 years ago and has continued to the present.

Montana, South Dakota, Wyoming↗

USGS1951

Antimony ore in the Fairbanks district, Alaska

Antimony-bearing ores in the Fairbanks district, Alaska, are found principally in two areas, the extremities of which are at points 10 miles west and 23 miles northeast of Fairbanks; and one of two minor areas lies along this same trend 30 miles farther to the northeast. These areas are probably only local manifestations of mineralization that affected a much broader area and formed antimony-bearing deposits in neighboring districts, the closest of which is 50 miles away. The ores were exposed largely as a result of lode gold mining, but at two periods in the past, high prices for antimony ore warranted an independent production and about 2500 tons of stibnite ore was shipped. The sulfide deposits occupy the same fractures along which a gold-quartz mineralization of greater economic importance occurred; and both are probably genetically related to igneous rocks which intrude the schistose country rock. The sulfide is in part contemporaneous with some late-stage quartz in which it occurs as disseminated crystals; and in part the latest filling in the mineralized zones where it forms kidney-shaped masses of essentially solid sulfide. One extremely long mass must have contained nearly 100 tons of ore, but the average of the larger kidneys is closer to several tons. Much of the ore is stibnite, with quartz as a minor impurity, and assays show the tenor to vary from 40 to 65 percent antimony. Sulphantimonites are less abundant but likewise occur as disseminated crystals and as kidney-shaped bodies. Antimony oxides appear on the weathered surface and along fractures within the sulfide ore. Deposits containing either stibnite or sulphantimonite are known at more than 50 localities, but only eighteen have produced ore and the bulk of this came from the mines. The geology of the deposit, and the nature, extent, and period of the workings are covered in the detailed descriptions of individual occurrences. Several geologic and economic factors, which greatly affect prospecting and mining for stibnite ore in the area, are outlined. The principal available ore and reserves are considered to be ores earlier mined but never shipped, ore minable from near-surface deposits, and ores recoverable as a by-product of future gold mining. The outlook for stibnite production in the district is very uncertain. Apparently the greater portion of stibnite ore has already been recovered and present operations will strip the two principal areas of the district. This conclusion is based on the scanty discoveries since the last war and the fact that the areas are so pock-marked with prospects that there is little likelihood that any other large near-surface bodies remain to be discovered. Future prospecting would essentially be limited to attempts to seek the continuation of lodes previously having high yields of stibnite.

Open-File Report↗

USGS1982

Geologic estimates and future costs of strip mining coal

Geologic coal-resource appraisals, which typically describe the location and general characteristics of coalbeds, do not generally provide enough information to estimate the cost of developing the resource or to predict the escalation of costs expected to result from physical depletion. This paper considers the nature of data and methods of appraisal required to provide this cost information to policymakers. Illinois is used as a prototype area for analysis because of its long history of coal mining and its demonstrated coal reserve base of strippable coal that exceeds all but two of the States in the United States. Evidence of gradual depletion of Illinois strippable coal reserves is provided by declining labor productivity, decreasing average mine size, and increasing overburden depth. The procedures used to estimate the costs of mining remaining deposits indicate that the physical characteristics that will affect mining costs most significantly are depth of overburden, thickness of coal seam, and areal extent of coal of the minable reserve blocks. Findings presented here provide guidelines for the collection of economic and geologic data in order to improve coal appraisals, particularly those currently in progress in the Western United States.

Energy Systems and Policy↗

USGS1961

Copper, vanadium, and uranium deposits in sandstone-their distribution and geochemical cycles

Deposits of copper , vanadium , and uranium in nonmarine sandstones are numerous and widespread. Copper deposits , with or without uranium , are mainly resident in first-generation arkosic sandstones derived from granitic rock terrains; deposits rich in vanadium , with or without much uranium , are dominantly in second-generation sandstones derived from sedimentary rocks; and the uranium deposits with little or no vanadium or copper are in either first- or second-generation sandstones, many of which are associated with beds containing volcanic debris. All three metals are dispersed in igneous rocks but not in close association. Copper and uranium enter the hydrothermal environment, but the record of vanadium in hydrothermal solutions and veins is scant. Some of the uranium and most of the copper minerals in igneous rocks and veins oxidize readily and the metals go into surface- and ground-water solutions, but the vanadium in igneous rocks is not so easily mobilized-under normal geologic conditions, conceivably it may require diagenetic reactions and a second period of weathering to solubilize much vanadium . All three metals precipitate from solutions in the presence of a reducing agent, such as carbonaceous material or associated sulfide ions, either in sediments as they accumulate or in existing rocks. These geochemical habits permit the concept that copper and uranium are made available by weathering of igneous rock terrains and hence might accumulate in first-generation sediments, whereas vanadium would be commonly available only after a second period of weathering. Perhaps the oxidation or devitrification of volcanic debris may contribute uranium to ground waters as does the weathering, of igneous rocks.

Economic Geology↗

USGS1999

Lead isotope compositions of Late Cretaceous and early Tertiary igneous rocks and sulfide minerals in Arizona: Implications for the sources of plutons and metals in porphyry copper deposits

Porphyry copper deposits in Arizona are genetically associated with Late Cretaceous and early Tertiary igneous complexes that consist of older intermediate volcanic rocks and younger intermediate to felsic intrusions. The igneous complexes and their associated porphyry copper deposits were emplaced into an Early Proterozoic basement characterized by different rocks, geologic histories, and isotopic compositions. Lead isotope compositions of the Proterozoic basement rocks define, from northwest to southeast, the Mojave, central Arizona, and southeastern Arizona provinces. Porphyry copper deposits are present in each Pb isotope province. Lead isotope compositions of Late Cretaceous and early Tertiary plutons, together with those of sulfide minerals in porphyry copper deposits and of Proterozoic country rocks, place important constraints on genesis of the magmatic suites and the porphyry copper deposits themselves. The range of age-corrected Pb isotope compositions of plutons in 12 Late Cretaceous and early Tertiary igneous complexes is 206 Pb/ 204 Pb = 17.34 to 22.66, 207 Pb/ 204 Pb = 15.43 to 15.96, and 208 Pb/ 204 Pb = 37.19 to 40.33. These Pb isotope compositions and calculated model Th/U are similar to those of the Proterozoic rocks in which the plutons were emplaced, thereby indicating that Pb in the younger rocks and ore deposits was inherited from the basement rocks and their sources. No Pb isotope differences distinguish Late Cretaceous and early Tertiary igneous complexes that contain large economic porphyry copper deposits from less rich or smaller deposits that have not been considered economic for mining. Lead isotope compositions of Late Cretaceous and early Tertiary plutons and sulfide minerals from 30 metallic mineral districts, furthermore, require that the southeastern Arizona Pb province be divided into two subprovinces. The northern subprovince has generally lower 206 Pb/ 204 Pb and higher model Th/U, and the southern subprovince has higher 206 Pb/ 204 Pb and lower model Th/U. These Pb isotope differences are inferred to result from differences in their respective post-1.7 Ga magmatic histories. Throughout Arizona, Pb isotope compositions of Late Cretaceous and early Tertiary plutons and associated sulfide minerals are distinct from those of Jurassic plutons and also middle Tertiary igneous rocks and sulfide minerals. These differences most likely reflect changes in tectonic setting and magmatic sources. Within Late Cretaceous and early Tertiary igneous complexes that host economic porphyry copper deposits, there is commonly a decrease in Pb isotope composition from older to younger plutons. This decrease in Pb isotope values with time suggests an increasing involvement of crust with lower U/Pb than average crust in the source(s) of Late Cretaceous and early Tertiary magmas. Lead isotope compositions of the youngest porphyries in the igneous complexes are similar to those in most sulfide minerals within the associated porphyry copper deposit. This Pb isotope similarity argues for a genetic link between them. However, not all Pb in the sulfide minerals in porphyry copper deposits is magmatically derived. Some sulfide minerals, particularly those that are late stage, or distal to the main orebody, or in Proterozoic or Paleozoic rocks, have elevated Pb isotope compositions displaced toward the gross average Pb isotope composition of the local country rocks. The more radiogenic isotopic compositions argue for a contribution of Pb from those rocks at the site of ore deposition. Combining the Pb isotope data with available geochemical, isotopic, and petrologic data suggests derivation of the young porphyry copper-related plutons, most of their Pb, and other metals from a hybridized lower continental crustal source. Because of the likely involvement of subduction-related mantle-derived basaltic magma in the hybridized lower crustal source, an indiscernible mantle contribution is probable in the porphyry magmas. Clearly, in addition, Pb was contributed from the local country rocks. This is most evident in sulfide minerals in veins that are late stage, hosted in Proterozoic gneiss, and/or peripheral to the porphyry copper deposit.

Economic Geology↗

USGS2025

Anatectic origin of Mississippian spodumene-bearing pegmatites in western Maine during orogenic plateau collapse

Spodumene pegmatites are an important lithium source, but the processes and tectonic settings in which they form are poorly understood. The Rumford pegmatite district surrounding Plumbago Mountain, western Maine, is host to numerous spodumene pegmatites, including the Plumbago North pegmatite (a world-class spodumene resource). Competing petrogenetic models for these spodumene pegmatites include (1) highly fractionated melts of the Mooselookmeguntic igneous complex and (2) anatexis. We tested these hypotheses by constraining the geologic, magmatic, metamorphic, and tectonic history of the Plumbago Mountain area with detailed geologic mapping and U-(Th)-Pb geochronology. The Silurian Rangeley Formation records initial isoclinal folding prior to, and contact-related metamorphism synchronous with, the intrusion of the 417 ± 4 Ma Plumbago Mountain pluton. Peak amphibolite facies metamorphism and crustal melting occurred during the ca. 410 to 400 Ma Acadian orogeny. Pulsed emplacement of the Mooselookmeguntic igneous complex occurred between ca. 389 and 356 Ma. Cassiterite U-Pb dates of spodumene pegmatites (333–327 Ma) are ≥23 m.y. younger than nearby granitic plutons, strongly arguing against the fractional crystallization model. Metamorphic monazite and xenotime (346–328 Ma) and 330 to 308 Ma 40 Ar/ 39 Ar hornblende dates indicate metamorphism coeval with spodumene pegmatite emplacement, supporting anatectic models. Reheating, anatexis, and spodumene pegmatite emplacement occurred during collapse of the 380 to 330 Ma Acadian orogenic plateau. Lithium enrichment may be linked to one or more stages of partial melting of metasedimentary and plutonic rocks during the formation, tenure, and collapse of the Acadian altiplano and emphasizes the role of anatexis in producing spodumene pegmatites of economic significance.

Maine↗

USGS1960

The chief oxide-burgin area discoveries, East Tintic district, Utah; A case history

The Burgin shaft is in the Chief Oxide area of the E. Tintic district, Utah, and is about a mile E. of any previously known ore bodies; workings from it are currently developing a substantial amount of commercial Pb-Zn ore in several blind ore bodies that lie in folded Paleozoic carbonate rock concealed beneath a blanket of Eocene lava. This area was mapped by Tower and Smith of the U.S. Geological Survey in 1897 and again by Lindgren and Loughlin in 1911, but no detailed work was done until after 1943 when a field party headed by T.S. Lovering began a study of the entire E. Tintic district. The history of the development of exploration concepts is summarized under Historical Summary. The E. Tintic mining district is in the E.-central part of a N.-trending fault-block mountain range near the eastern margin of the Great Basin; dominant structures of the range are a N.-trending syncline on the W. and a less well exposed anticline on the E. Both folds are cut by an intersecting system of transcurrent strike-slip faults and by minor thrust faults and normal faults of moderate displacement. A strong W.-dipping thrust fault cuts the anticline a short distance E. of the fold axis, but is hidden by Eocene lava throughout the E. Tintic district. The pre-Tertiary rocks range from Lower Cambrian to Upper Mississippian and exceed 7,000 ft. in total thickness; they are dominantly marine limestone and dolomite except for a thick basal Cambrian quartzite. The Tertiary rocks are chiefly dacitic lavas and pyroclastic deposits that are intruded by moderately persistent dikes and irregular bodies of monzonite and quartz porphyry. Nearly all the faulting and folding took place before the extrusion of the lavas on a rugged Eocene erosion surface. At about the time of the intrusion of monzonitic magma, many of the faults in the Paleozoic rock were re-opened and in the overlying lava some fracturing took place which was later accented by hydrothermal alteration. Most of the ore mined in the E. Tintic district has come from Pb-Zn-Ag replacement bodies in shattered Jasperoidized hydrothermal dolomite at the intersection of low angle faults and steep mineralized NE.-trending cross fractures. The U.S. Geological Survey studies of 1943 to 1957 concentrated on detailed mapping of geology and alteration in the E. Tintic district, together with field and laboratory studies of the relation of alteration to stages of mineralization and ore deposition. Trenching and core drilling were carried on after World War II to aid in interpreting the subrhyolite geology, and the Chief Oxide area was 1 of 4 localities tested by drilling. Study of the fossils, lithology, and alteration shown here in a deep drill core, together with the knowledge of the regional geology, led to an essentially correct interpretation of subrhyolite structure in the strongly discordant underlying Paleozoic rocks in which a mineralized tear fault cuts a strong thrust fault, and to the conclusion that ore stage mineralization was present in substantial amounts in the Paleozoic rocks below the Chief Oxide alteration patch in the quartz latite lava. Subsequent geothermal and geochemical work strengthened this conclusion, and the recent development work of the Bear Creek Mining Company, which sank the Burgin shaft, has shown the presence of Pb-Zn-Ag ore of commercial grade in substantial amount in blind ore bodies below the lava blanket in the Chief Oxide area.

Utah↗

USGS1981

The possible role of sulfate-reduction kinetics in the formation of hydrothermal uranium deposits

Sulfate is known to be an active oxidizing agent at high temperatures; however, both experimental and geologic evidence indicate that as a hydrothermal solution cools (to about 200 degrees C, depending on pH) kinetic factors slow the rate at which sulfate enters into redox reactions. This retardation of sulfate reduction diminishes the effectiveness of sulfate as an oxidizing agent. Consequently, as cooling proceeds, the reducing effect of H 2 S (and other reduced species) is not balanced with the oxidizing effect of SO (super -2) 4 to the same extent as at higher temperatures. The result is a progressively more reducing solution, which is precisely what is needed to precipitate reduced uranium minerals and to generate the paragenetic sequence observed in these deposits. The same mechanism may apply to other types of epithermal deposits.

Economic Geology↗

USGS1986

Platinum-group element resources in podiform chromitites from California and Oregon

Rock samples from about 280 podiform chromite deposits in California and Oregon were analyzed for Pt, Pd, Rh, and Ir by fire assay-atomic absorption and spectrographic techniques to estimate by-product platinum-group element potential of chromite mining. These deposits include ophiolites from the Sierra Nevada, Klamath Mountains, Coast Ranges, and the Canyon Mountain Complex; the deposits vary from Paleozoic to Mesozoic age and vary in size, shape, texture, and degree of metamorphism. The maximum platinum-group element contents (in ppm) measured for chromitites are: Pt, 2.53; Pd, 0.2; Rh, 0.14; Ru, 4.93; and Ir, 2.93.Correlations between Pt and Rh (0.60), Rh and Ir (0.64), Rh and Ru (0.71), and Ir and Ru (0.85) are significant at the 1 percent level. Relatively small but significant differences in platinum-group element content exist between geologic terranes. Chromite production from California and Oregon amounts to about 692,000 metric tons (1914-1985); the mean contained platinum-group element amounts in troy ounces are: Pt, 850; Pd, 100; Rh, 260; Ru, 4200; and Ir, 1,700, using estimated grades. Previous investigators have suggested that relatively few samples can represent the platinum-group element content of a podiform chromite deposit; therefore, these analyses are assumed to approximate "grades." Total world resources of platinum-group elements in podiform chromite deposits are estimated in troy ounces to be: Pt, 210,000; Pd, 25,000; Rh, 64,000; Ru, 1,000,000; and Ir, 420,000.

Economic Geology↗

USGS1957

Application of punched cards to geologic data concerning uranium deposits in sandstone

The punched card has been chosen for use in compiling the great mass of geologic data concerning uranium deposits in sandstone into permanent file. The most valuable uses of the punched-card file are as a multiple index to data and as a means of correlating different data. By using the punched card, uranium deposits in sandstone can also be compared to other metalliferous deposits in sandstone.Besides the geographic location of the deposit, about 120 different items can be punched on the sides of the card. In the center of the card more detailed data and a summary of the report are given. Although the card is designed for data on a single deposit or group of deposits, topical data on many studies such as chemistry, geobotanical prospecting, and geophysics can be summarized on the card.

Economic Geology↗

USGS1981

The Lasky cumulative tonnage-grade relationship; a reexamination

The need for interdisciplinary research on resource appraisal techniques was recognized by Samuel G. Lasky, a U.S. Geological Survey geologist, more than 30 years ago. His efforts to devise an appraisal technique that incorporated many attributes of mineral resources resulted in a cumulative tonnage-grade relationship that has been referred to as "the arithmetic-geometric (A/G) ratio" or "Lasky's law" by later writers. A review of subsequent studies of the increases in available metal to be expected as grade decreases indicates that Lasky's work has at times been misinterpreted. Lasky's relationship is shown to be consistent with studies of the correlation between average grades and tonnages of mineralized material in ore deposits. The projection of Lasky's analysis to lower grades is limited because the mathematical formulation predicts physically impossible situations below some limiting grade.

Economic Geology↗

USGS1989

Constraints from fluid inclusions on sulfide precipitation mechanisms and ore fluid migration in the Viburnum Trend lead district, Missouri

Measurements on fluid inclusions in hydrothermal dolomite cements place constraints on sulfide precipitation mechanisms and on the thermal-hydrologic processes which formed the Viburnum Trend Mississippi Valley-type lead district. Homogenization temperatures and freezing point depressions were determined for fluid inclusions in Bonneterre Dolomite-hosted dolomite cements in mine samples, as well as drill core from up to 13 km outside of the district. A well-defined cathodoluminescent zonation distinguishes dolomite growth zones in the Vi-burnurn Trend as older or younger than main-stage mineralization (octahedral galena) and facilitates correlation with other dolomites outside the Viburnum Trend.Homogenization temperatures and salinities in samples from mines are not systematically different from those of samples outside of the district. Medians of homogenization temperature distributions differ by not more than 25 degrees C, so that a temperature gradient, if present, should not have exceeded approximately 25 degrees C within the study area. These observations are interpreted to indicate that the Viburnum Trend was not strongly thermally anomalous with respect to surrounding country rock and that fluid flow occurred on a broad scale through not only the Lamotte Sandstone but through the overlying Cambrian carbonates as well.The absence of a significant, recognizable decrease in temperature either vertically within the section or east-west across the district, coupled with the minor amount of silica in the district, argues against cooling as a primary cause of sulfide precipitation. Fluids whose primary aquifer was the Lamotte Sandstone, predominantly a quartz arenite, should have been in equilibrium with quartz. Quartz in the Viburnum Trend occurs as a minor, drusy, vug-lining phase, but the district lacks the intense silicification found in other Mississippi Valley-type districts such as Tri-State (Oklahoma, Kansas, Missouri). Quartz solubility is strongly temperature dependent and, under equilibrium conditions, a decrease of 10 degrees C or more should have precipitated at least as many moles of silica as galena (assuming a galena solubility of between 1 and 10 ppm). Clearly this is not the case, as galena is far more abundant than quartz in the Viburnum Trend.Ice final-melting temperatures (T m ) in fluid inclusions generally range from -14 degrees to -27 degrees C for primary dolomite-hosted inclusions. Using these T m values and cation ratios for the inclusion fluids, absolute concentrations for the individual cations and chloride were calculated using the thermochemical model of Spencer et al. (1990). The corresponding high but variable salinities, 3.9 to 5.9 chloride molality, are evidence for the presence of more than one distinct fluid during mineralization.In a reduced sulfur mineralization model with Pb carried as chloride complexes, dilution is also a possible sulfide precipitation mechanism. The difference in Pb solubility (for an equal quantity of reduced sulfur) in the extremes of the chloride concentration range, 3.9 vs. 5.9 molal, reaches 1 ppm only for pH values below approximately 4.5. Accepting 1 ppm as a minimum metal concentration for a viable ore-forming fluid, dilution only appears capable of precipitating sulfides in a fluid with pH near the lower limit of values considered geologically reasonable or attainable.Dolomite cements hosting warm (approximately 105 degrees -125 degrees C) saline fluid inclusions are ubiquitous in the porous dolomitic facies of the Bonneterre Dolomite. Based on stratigraphic reconstructions, however, it is unlikely that the Bonneterre was buried deeper than 1.5 km. The distribution of warm inclusions beyond the Viburnum Trend district implies that fluid migration was regional in scale. Fluid inclusion temperatures inconsistent with typical basement heat-flow-controlled geothermal gradients (25 degrees -35 degrees C/km) may be explained by long-distance migration of warm, basin-derived brines. Elevated temperatures observed in fluid inclusions at shallow stratigraphic depths are consistent with a gravity flow hydrologic system characterized by rapid flow rates and the capacity for advective heat transport.

Economic Geology↗

USGS1940

Ground water in the Oklahoma Panhandle

An investigation begun in 1937 by the United States and the Oklahoma Geological Surveys, has shown that the depth to the water table in the Oklahoma Panhandle ranges from less than 25 feet in parts of major valleys to about 3oo feet in parts of the uplands. In 8 upland areas the depth is between 50 and 100 feet. The thi kness of the zone of saturation differs widely in these areas, the most promising of which totals about 80 square miles in northeastern Texas County. The pervious sands and gravels of the Ogallala formation, of Pliocene age, furnish most of the ground water, and one well yielding 960 gallons a minute from them has been used for irrigation since x937. The formation ranges from less than xoo to more than 500 feet thick, the differences being due to relief on the pre-Ogallala topography and to post-Ogallala erosion. The alluvium is also an important source of water, as are the Dakota and Cheyenne sandstones, of Cretaceous age. A few wells yield water of variable quality from Jurassic and Triassic rocks, and many wells in the valleys of the eastern part of the area yield small supplies of highly mineralized water from Permian red beds. © 1940 Society of Economic Geologists, Inc

Oklahoma↗

USGS1985

The timing of ore formation in southeast Missouri: Rb-Sr glauconite dating at the Magmont mine, Viburnum trend

Seven Bonneterre and Davis Formation glauconite samples from the Magmont mine area, Viburnum Trend, southeast Missouri, yield a 359 + or - 22-m.y. Rb-Sr isochron with an initial 87 Sr/ 86 Sr ratio of 0.7234 + or - 0.0273 (2 sigma). Gangue calcite from the ore zone has an 87 Sr/ 86 Sr ratio of approximately 0.7112. The isochron age for the Magmont glauconite samples is about 30 percent younger than the age of their Cambrian host rocks.The Rb/Sr ratios for Magmont glauconite samples are typical of many early Paleozoic glauconites but distinctly lower than ratios for glauconites from unmineralized localities in basinal Bonneterre facies, some distance from the Vibrunum Trend. Because the Rb-Sr data from Magmont glauconite samples define an isochron, it appears that the glauconites behaved as a cogenetic suite which was isotopically homogenized 359 m.y. ago. It is very unlikely that episodic or incomplete loss or exchange of radiogenic strontium, or the addition of rubidium, would result in the formation of an isochron. Addition of common strontium (mixing) will lower and produce a greater spread in Rb/Sr ratios but will not significantly change the calculated Rb-Sr isochron age for the glauconites. Because the total thickness of stratigraphic cover in the southeast Missouri region has never exceeded a kilometer, it is unlikely that the anomalously young glauconite isochron age resulted from heating associated with deep burial. Mississippi Valley-type ore fluids offer a hot, chemically reactive medium which could promote isotopic homogenization in glauconites. Therefore, the 359-m.y. age probably reflects a real geologic event, most likely the time of ore formation in southeast Missouri. A review of other attempts at dating early Paleozoic glauconites from the midcontinental United States indicates that all Rb-Sr and K-Ar glauconite ages are 10 to greater than 30 percent younger than their known stratigraphic ages. These glauconites are from Paleozoic formations on the stable craton, and again, resetting due to burial metamorphism is unlikely. Because there was no immediately obvious explanation for the discordant young ages, early Paleozoic glauconites were simply considered to be unsuitable geochronometers. It is suggested that the anomalously young radiometric ages for early Paleozoic glauconites record disturbances in the Rb-Sr and K-Ar isotopic systems, the result of Mississippi Valley-type fluid migration in the midcontinent region.

Economic Geology↗