Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Economic Geology”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources
USGS1966

Stratified deposits of the oxides and carbonates of manganese

Compared with the stratified deposits of iron minerals, those of manganese minerals have received little attention until recent years. Before 1930, students of the stratified deposits of manganese minerals have generally concluded that the contained manganese was derived from the decomposition of the rocks that formed the borders of the basins. Only in a few places have geologists recognized that if these rocks were the principal source of the contained manganese the basins should contain also enormous quantities of iron minerals, whereas most of the large deposits of manganese contain little iron. Even though more than 100 years ago some geologists proposed that the iron contained in some deposits of stratified iron minerals was probably derived from hydrothermal waters related to centers of volcanism, not until about 1930 was this source of manganese in similar deposits seriously proposed. This mode of origin was given the name "volcanogene sedimentaire" by French geologists working in Morocco. Since then, other names, such as "exhalative sedimentaire," have been used by geologists working in several European districts. Because of the development of new techniques for the study of the chemical and physical features of the minerals, and because close attention to the lithologic environments of the beds is being given more and more during recent years, it has seemed advisable to review the features of stratified deposits of the manganese minerals in many parts of the world and over a wide range in age. This study indicates that at least three sources may have contributed the manganese in the large deposits of iron-free oxides and carbonates : (1) the rocks that form the borders of the basins, either marine or continental; (2) the nearby underlying sediments, largely of igneous origin, decomposed by warm waters largely derived from depth; and (3) waters of hydrothermal origin derived from great depths during epochs of volcanism from which iron minerals with little manganese are deposited in deep zones, then minerals with much iron and more manganese at intermediate depths, and, finally, manganese minerals with little iron near the surface. As the hot waters of many thermal springs contain more manganese than iron, such waters could yield the pure manganese oxides and carbonates found in stratified deposits . Several kinds of evidence indicate that most of the manganese in the large stratified deposits of the oxides and carbonates of manganese in many parts of the world has been derived from hydrothermal waters from depth related to centers of volcanism. Obviously, manganese derived from decay of the rocks on the lands adjacent to large basins-marine and continental -may have been added to that derived from centers of volcanism to form the sedimentary deposits found in the basins.

Economic Geology↗
USGS1966

Preliminary investigation of the source of lead and strontium in deep geothermal brines underlying the Salton Sea geothermal area

A radiogenic tracer study has been made of lead and strontium in deep geothermal brines , salt from brine , and the upper Quaternary rhyolite domes near the Salton Sea in the Imperial Valley, California. The data on the brines and rhyolite glasses are compared to those from Quaternary Colorado River and Tertiary sediments of the area . The brines sampled contain '-'100 ppm Pb, sufficient for consideration as a possible ore-forming fluid. The isotopic data indicate that 80-100 percent of the strontium and 50-100 percent of the lead in these brines were acquired from the associated sediments. The isotopic compositions of lead and strontium in the Quaternary rhyolite glasses are distinctly different from those of the sediments and brines . The strontium data suggest that the rhyolite glasses were derived from basaltic or gabbroic material but may have attained as much as 40 percent of their strontium from upper crustal rocks such as the sediments analyzed.

California↗
USGS1966

Isotopic study of galenas from the upper Mississippi Valley, the Illinois-Kentucky, and some Appalachian Valley mineral districts

Analyses of lead isotopes in galena in carbonate rock ore deposits collected from several mineralized districts in the Central and Eastern Interior of the United States support previous studies in establishing that the galena is anomalously radiogenic ("J"type")- This study , using care-fully selected samples to test some géologie relationships, shows region-wide and distrietwide systematic variations in isotope ratios. The genetic implications of thèse variations are discussed. Two mechanisms of origin are considered to explain thèse variations in isotopic ratios. One involves mixing of leads from multiple sources, the other calls for variable lead-isotope ratios originating from a single source. Several source materials for the lead ores have been suggested; whether a single source has predominated, or two or more main sources have predominated is still unresolved. Slopes from Pb206/Pb204 versus Pb207/Pb204 plot are compatible with a contribution of lead by the 1300 ± 300 m.y. basement rocks that underlie the deposits. The spatial relationships of alkaline igneous rocks to several of the minerai districts in the Mississippi Valley région suggest a possible mag-matic source for the lead. Isotopic analyses of galenas closely associated with several of the intrusive rocks are similar in isotopic composition to adjacent ore leads, but genetic implications are ambiguous. Galena oc-curring in shales in the Mississippi Valley région outside mineralized districts contains ordinary lead. Théories that call upon such shales to be the major source of the lead in the depoaits of the Mississippi Valley type must explain this distinct différence in isotopic compositions. Galena collected from districts within the Appalachian Ridge and Valley Province contains notably less radiogenic lead than that from the Mississippi Valley minerai districts , and the lead is of the ordinary type.

Illinois, Kentucky↗
USGS1966

Dawsonite in the green river formation of Colorado

Dawsonite NaAl(OH)2C03 is a rare mineral that occurs in relative abundance over hundreds of square miles in the Piceance Creek Basin of northwestern Colorado, as a rock-forming constituent of the oil shales in the green River Formation. In some specimens it makes up 25 percent by weight of the shale. Containing 35 percent of acid-soluble A1203, it has been viewed as a potential ore of aluminum. The dawsonite extends through 700 feet of continuous section of high-grade oil shale (averaging 25 gallons per ton), which may be as much as 1,500 feet in thickness. Its distribution, areally and stratigraphically, is reviewed; methods for its identification, and for its quantitative determination in the oil shale, with special reference to X-ray diffraction procedures are described; and the geochemistry of dawsonite, as it relates to the origin of the mineral, is considered. The scattered literature on dawsonite is briefly summarized. © 1966 Society of Economic Geologists, Inc..

Colorado↗
USGS1966

Sulfide-mineral zoning in the basal nonesuch shale, Northern Michigan

A zone, 1 to 50 feet thick, at the base of the Nonesuch Shale , is relatively rich in copper, chiefly as chalcocite. Pyrite is the characteristic sulfide mineral of the overlying 400 to 600 feet of the formation. The boundary of the cupriferous zone with the pyrite zone regionally transgresses both stratigraphic layering and fades gradations indicative of ancient environmental boundaries. The top of the cupriferous zone is marked by the upward sequence, chalcocite-bornite-chalcopyrite-pyrite, and by the cadmium sulfide , greenockite. The sulfide zoning does not appear to be syngenetic. The regional configuration of the cupriferous zone suggests, instead, that the copper was introduced after deposition of the entire 50-foot sequence of strata. The area in which the top of the cupriferous zone is stratigraphically highest is related spatially, and probably genetically, to a zone of wedging in the underlying Copper Harbor Conglomerate.

Michigan↗
USGS1967

Silver-bearing black calcite in western mining districts

The name black calcite has been applied from time to time to a dark gray to black variety of calcite or aragonite in metalliferous ore deposits in the Western States. Most of the material shows curved, roughly rhombic cleavage. The color is due to dispersed minute grains of one or more oxides of manganese, so dispersed that they rarely show any relation to cleavage surfaces or outward crystal forms.Recent study shows that the black calcite from numerous metalliferous deposits in the Western States contains small amounts of several metals, especially zinc, lead, and silver; in places, the crude black calcite contains as much as one percent silver and the black residue remaining after solution of the calcite as much as 1,500 ounces of silver to the ton. Black calcite is recognized in some deposits of Late Cretaceous to early Tertiary age where the host is Paleozoic carbonate rocks; thus far, this variety contains the larger amounts of silver. It is also present in some vein deposits where the host is generally volcanic rocks of middle Tertiary age; these are known in many districts in the southwest and even though the lead and zinc content is noteworthy, the silver content rarely exceeds one ounce to the ton (8).By studying polished sections of black calcite from the Aurora mine, White Pine County, Nevada, three silver-bearing manganate minerals have been recognized; (1) an argentian chalcophanite containing 7.5 percent silver (Ag 2 O), to which, in a following paper, the name aurorite is given; (2) argentian todorokite containing 3.9 percent silver (Ag 2 O), and (3) hydrous silver-bearing lead manganese oxide, containing 1.18 percent silver (Ag 2 O).

Nevada↗
USGS1967

The porphyry copper deposit exposed in the Liberty open-pit mine near Ely, Nevada; Part 2, The formation of hydrothermal alteration zones

In the southwest part of the Liberty pit a large porphyry body exhibits a zonal alteration pattern related to fissures and pyrite-bearing veins. The outermost zone contains unaltered K-feldspar, kaolinite after plagioclase, and black biotite after hornblende. An intermediate zone contains reconstituted K-feldspar, phlogopitic biotite, and muscovite or muscovite plus K-feldspar replacing only plagioclase. In the innermost zone the only silicates are quartz and muscovite. In some places an alteration band of K-feldspar after plagioclase separates kaolinite and muscovite.The widespread association of kaolinite and K-feldspar in hydrothermal alteration zones suggests that these two minerals were stable together at the time of formation. Experimental data show that, where quartz controls the activity of silica in solution, kaolinite and K-feldspar should react to form muscovite. However, calculations predict that, at 15,000 psi, solutions with silica activities compatible with amorphous or gelatinous silica could stabilize K-feldspar and kaolinite relative to muscovite at temperatures below about 250 degrees C. The rapid decomposition either of plagioclase feldspar or montmorillonite is considered a prime cause for the attainment of such high activities of silica in pore solutions of rock. The supersaturation of pore solutions with silica is a transient condition; quartz precipitates where kaolinite and K-feldspar react to give muscovite. Thus, the zonally distributed alteration at Ely is considered to have taken place after the rock had cooled to below 250 degrees C. In contrast, the diffusely distributed muscovite and montmorillonite found in another portion of the pit probably commenced at 600 degrees to 700 degrees C with only minor formation of alteration products below 250 degrees C.

Nevada↗
USGS1967

Sulfides associated with the Salton Sea geothermal brine

Concentrated saline brine tapped by a deep well drilled for geothermal power near the Salton Sea, California, deposited metal-rich siliceous scale at the rate of 2 to 3 tons per month. The iron-rich opaline scale contains an average of 20% Cu and up to 6% Ag present in bornite, digenite, chalcopyrite, a new dense polymorph of chalcocite, stromeyerite, and native silver.The brines are in equilibrium with an assemblage of sulfide minerals in the reservoir rocks. Sphalerite containing 16.6 mol % FeS is in equilibrium with the brine in which the activity of sulfur (a (sub s 2 ) ) is estimated at 10 (super -10.2) at 325 degrees C. This is in good agreement with the projected high-temperature data of Barton and Toulmin (2) for the system Fe-Zn-S. Other sulfides identified in the reservoir rocks are pyrite, pyrrhotite, chalcopyrite, and galena.The heavy metals in solution are apparently derived from the sediments of the brine reservoir, being released from the silicate minerals in which they occur in trace amounts, as metamorphism of the sediment proceeds. Although the total of the heavy metals in solution greatly exceeds the sulfur, on a molal basis, the brine is saturated with respect to sulfide components and addition of more sulfide ion would only cause precipitation of sulfides.

California↗
USGS1967

The Fe-Pb-S system

The phase relations in the ternary system Fe - Pb - S were determined by quenching and differential thermal analysis experiments in rigid silica-glass tubes. The solubilities of FeS in galena and in liquid Pb and the extent of solid solution of PbS in pyrite and pyrrhotite at 700° C are too small to be determined by the methods employed and are probably less than 0.1 wt. percent. Less than 1 wt. percent S is soluble in liquid Pb at 700° C. Ternary compounds do not occur in this system . An invariant point involving galena, pyrite, sulfide liquid, liquid sulfur, and vapor occurs at 716° C. The ternary liquid at this temperature contains about 60 wt. percent Pb , 13 wt. percent Fe , and 27 wt. percent S , and is thus situated slightly on the sulfur side of the PbS-FeS2 join. At 719° C tie lines between galena and pyrite are replaced by sulfide liquid-pyrrhotite tie lines in an invariant reaction involving vapor. The sulfide liquid field expands rapidly and intersects the PbS-FeS2 join at 723° C. At 848° C the ternary liquid field intersects the FeS-PbS join. Diagrams are presented to illustrate changes in phase relations from 700° to 1,115° C. The experimental results demonstrate that mixtures of galena (about 70 wt. percent) and pyrite (about 30 wt. percent) can crystallize directly from a liquid at 716° C. Additional components may lower this temperature so that it appears possible that pyrite-galena ores may melt at temperatures below 700° C when exposed to thermal metamorphism.

Economic Geology↗
USGS1967

The fort gouraud, Mauritania, iron ore deposits

In connection with a paper by Baldwin and Gross on the localization of residual hematite ore (for reference, see this Bibliography Vol. 31, No. 7, 02 E67-05748), inaccuracies in the citations from the literature used for purposes of comparison are pointed out, particularly those on Brazilian deposits.

Economic Geology↗
USGS1967

Closed system differentiation of sulfides in olivine Diabase, Missouri

Two small bodies of Precambrian basic intrusive rock in southeastern Missouri show uninterrupted differentiation of olivine diabase that produced ferrogabbro. Olivine diabase , foliated gabbro and coarse gabbro constitute the major textural rock types. Gravitational settling of plagio-clase, olivine and Fe-Ti oxides occurred in both intrusives and iron enrichment is a conspicuous feature. Plagioclase ranges from An58 to An35 and olivine varies from Fa36 to Fa57. Because these rocks were intruded into volcanic rocks at a substantial depth and were slowly cooled in an apparently closed system , they afford an opportunity to trace the differentiation trends exhibited by the disseminated sulfides . Pyrrhotite, chal-copyrite, pentlandite, sphalerite and cubanite are the most abundant sulfides deposited initially as unmixed sulfide solid solutions which were essentially coprecipitates with the major silicates. Paragenesis and abundance of primary sulfides are directly related to the differentiation parameters shown by the silicates. The extreme fractionation of these intrusives did not lead to a large concentration of any of the sulfides at any stage during consolidation.

Missouri↗
USGS1968

Exploration possibilities in the Western Chagai District, West Pakistan

A northerly-trending group of quartz diorite stocks that cut Cretaceous, Eocene, 01igocene(?) and Pleistocene( ?) sedimentary rocks near Saindak, West Pakistan , contain oxidized disseminated copper minerals which may occur in commercial concentrations at depth. The stocks are enclosed by an aureole of albite-epidote hornfels about 4 miles wide that locally is cut by veins containing sparse lead and copper minerals. Within the contact aureole the few thin beds of limestone and lenticular limestone reefs have been metasomatically replaced by iron sulfide or iron oxide. The sulfide is largely oxidized near the surface. The areas of metamorphosed rocks to which the veins are mostly restricted can be recognized on panchromatic aerial photographs and from a considerable distance on the ground by their rugged topography, dark color, and by the local abundance of dikes, thus greatly reducing the area requiring field examination during a prospecting program. The red and yellow soils mantling the sulfide-rich rocks are easily recognized from short distances on the ground, but cannot be differentiated from the unmetamorphosed rocks on conventional aerial photographs. Color photography or limited-spectral photo techniques probably can be used to reveal these distinctive soils and thus define the areas of sulfide mineralization.

west Pakistan↗
USGS1968

Environments of generation of some base-metal ore deposits

The origin of the ore fluids, their dissolved constituents, the force that drives them, and the causes for deposition of their constituents are reviewed for five districts: Providencia, Mexico; Mississippi Valley (Pb-Zn); Salton Sea geothermal system; Red Sea geothermal system; Nonesuch Shale, Michigan. The compositions (chemical and isotopic) and temperatures, determined directly for brines and from fluid inclusions for ancient deposits, reveal significant differences between the Providencia deposit (close magmatic affiliations) and the others, in which connate water and constituents dissolved from country rock appear to be important. Deposits formed by complex processes, with multiple sources for materials, may well be more common than simple 'end-member' deposits.

Economic Geology↗
USGS1968

Environment of ore deposition at the Mex-Tex deposits, Hansonburg District, New Mexico, from studies of fluid inclusions

These deposits , in Pennsylvanian limestone and shale, contain barite, fluorite, low-silver galena with "J-type" lead, and quartz, and only minor amounts of other minerals. Mineralization occurs in veins, in blankets of bedded, rhythmically banded "coontail" ore , and in vuggy, coarsely crystalline open-space fillings in tectonic and solution channels in limestone adjacent to faults. Except for widespread silicification, the mineralization is very similar to that of the southern Illinois deposits . The main stages of hypogene mineralization are: 1) sphalerite, pyrite, galena and chalcopyrite; 2) five easily recognizable substages of fluorite with intermittent quartz and barite; and 3) late calcite.More than 500 primary and 2,500 pseudosecondary inclusions , mainly from fluorite, were studied on the freezing and heating microscope stages. Some primary inclusions contain organic matter. Gross supercooling indicates slow ore - fluid movement. Recognizable planes of pseudo-secondaries (each containing 20-200 inclusions ) yield data essentially identical with coeval primaries, but the few planes of presumed secondaries do not.The first three substages of fluorite formed from fluids that were essentially constant in temperature at 186°-205° C (assumed pressure correction +10° C), but increased in salinity from aproximately 10 up to 15 weight percent salts. Succeeding substages formed at gradually decreasing temperatures (to about 140° C) and increasing salinity (maximum 17%), with breaks marking several individual substages. A few inclusions in an early barite have anomalously low homogenization temperatures. Coarse selenite has primary inclusions full of fresh water and hence is presumed to be supergene.These data do not prove any given theory or origin for the fluids or the deposits , but they do place some limits on possible mechanisms of origin.

New Mexico↗
USGS1968

Hypogene veins of gibbsite, pyrolusite, and lithiophorite in Nye County, Nevada

Gibbsite, lithiophorite, pyrolusite, and goethite, plus discrete mixtures of gibbsite and lithiophorite and of gibbsite and iron oxide, occur as replacement veins in limestone. Minor accessories are barite, alunite, opal. Minerals of wall-rock alteration are garnet, idocrase, K-feldspar, prehnite, sericite, and quartz. These silicates formed at higher temperature than the vein minerals, but the whole sequence is considered to be a product of the same solutions, of deep-seated origin, deposited over a long period of time.

Nevada↗
USGS1968

Temperature, salinity, and origin of the ore-forming fluids at Pine Point, Northwest Territories, Canada, from fluid inclusion studies

Although the Pine Point ore is relatively poor in useable fluid inclusions, some sphalerite crystals from replacements, vugs, and from " colloform" crusts were found to contain primary or pseudosecondary liquid-gas inclusions adequate for study . Most (132 of 133) of these had low freezing temperatures, indicating exceedingly saline brines. The 112 inclusions suitable for filling- temperature determination homogenized at +51° to +97° C. A very small pressure correction must be added to obtain the trapping temperature .Dolomite crystals from some of the same vugs contain large numbers of primary inclusions, many of which have leaked. The twenty-three that presumably have not leaked had filling temperatures of 90°-100° C, but somewhat lower salinities. Inclusions in late calcite appeared to have similar gas-liquid ratios, but had still lower salinities.The significance of these data lies in the limitations they place on the choice of possible mechanisms of origin of these large deposits. This choice, in turn, may influence the success in prospecting for blind ore bodies. There is general agreement that the deposits are of Mississippi Valley type. Although the high salinities may reflect solution of salts from evaporites, as are now found to the south, the elevated temperatures seem to require deep circulation, perhaps through known faults in the underlying Pre-cambrian. The densities of these brines, even at their elevated temperatures, are well above that of fresh, cold surface water, thus restricting the possible modes of circulation during ore deposition.

northwest Canada↗