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At least 1,333 records · Page 74Linked to original sources

USGS1989

Sulfide mineralization and magnetization, Cement oil field, Oklahoma

Geochemical, petrographic, and rock-magnetic studies were undertaken to investigate possible sources for reported positive aeromagnetic anomalies over the Cement oil field, Oklahoma. Ferrimagnetic pyrrhotite (monoclinic, Fe 7 S 8 ), intergrown with more-abundant, nonmagnetic pyrite (FeS 2 ), is present in well-cutting, core, and quarry samples at Cement, and it is the only identified source of possible enhanced magnetization in rocks over the field. Magnetite, found only in well cuttings from Cement, is contamination from drilling. Magnetite was considered previously by others to be the source of magnetic anomalies at Cement.

Oklahoma↗

USGS2024

Onset and tempo of ignimbrite flare-up volcanism in the eastern and central Mogollon-Datil volcanic field, southern New Mexico, USA

The Cenozoic ignimbrite flare-up (40–18 Ma) generated multiple volcanic fields in the southwestern United States and northern Mexico resulting from asthenospheric mantle upwelling after removal of the Farallon slab. The correlation of tuffs to one another and to source calderas within these volcanic fields is essential for determining spatiotemporal patterns in volcanism and magma geochemistry, which have been used to deduce migration of the Farallon slab at depth and associated mantle melting. However, the correlation of Eocene–Oligocene tuffs in the southwestern U.S. is difficult because of post-emplacement erosion and faulting. This study focuses on spatiotemporal patterns of the initial episode of ignimbrite flare-up activity (ca. 36.5–33.8 Ma) in the Mogollon-Datil volcanic field in south-central New Mexico, USA. We show that alkali feldspar major and trace element geochemistry is an effective tool for correlating tuffs when combined with high-precision, single-crystal 40 Ar/ 39 Ar geochronology and bulk-rock geochemistry. Using these data, we correlate several tuff units and differentiate other tuffs that have the same eruption age but very different geochemistry, and we conclude that there was a broadly northwestward migration in volcanism over time. The new tuff correlations are used to investigate spatiotemporal variations in magma geochemistry, erupted volumes, and recurrence intervals during the initial episode of Mogollon-Datil volcanic field volcanism. Early-erupted tuffs restricted to the eastern Mogollon-Datil volcanic field share similarities with western U.S. topaz rhyolites, which suggests that the silicic magmas were generated by partial melting of mafic lower crustal rocks. We also find differences in the compositions, crystallinities, and mineral assemblages between the early- and late-erupted tuffs. The early-erupted tuffs tend to have single-feldspar mineralogies, lower feldspar Or contents, large negative Eu anomalies, and low-whole–rock Ba concentrations. Conversely, late-erupted tuffs have two feldspar plus quartz assemblages, lesser Eu anomalies, higher whole-rock Ba concentrations, and feldspars have higher Or contents. Thus, we suggest that for some of the early eruptions, after magmas underwent crystal fractionation in the crust, the silicic melt largely separated from the crystalline mush prior to eruption, whereas late-erupted tuff magmas underwent crystal fractionation at near the eutectic minimum and were remobilized and erupted with a larger proportion of their crystalline mush. Using our new ages, correlations, and previously published data, we find that the initial phase of Mogollon-Datil volcanic field volcanism produced at least 15 eruptions between 36.5 Ma and 33.8 Ma, with a minimum total erupted volume of ~1350 km 3 and an average recurrence interval of 170 k.y. However, eruptions were generally smaller in volume (most <15 km 3 ) than in other coeval fields, and most eruptions (n = 11) occurred in the first 1.2 m.y. (ca. 36.5–35.3 Ma) of activity. Altogether, our work sheds new light on variations in the composition, timing, and migration of volcanism during the initial phase of Mogollon-Datil volcanic field activity and highlights the utility of feldspar geochemistry in both “fingerprinting” tuffs and elucidating magma evolution.

New Mexico↗

USGS2019

Tourmaline boron and strontium isotope systematics reveal magmatic fluid pulses and external fluid influx in a giant iron oxide-apatite (IOA) deposit

Tourmaline is a common boron-bearing mineral in hydrothermal system and has been widely used as a mineral probe to reconstruct geological processes because of its broad range in composition and resistance to metasomatic alteration. The origin of Kiruna-type iron oxide-apatite (IOA) deposits, commonly linked to andesitic subvolcanic or volcanic rocks, is highly controversial. Constraints on the evolution of these mineralizing systems are needed to advance understanding of the ore-forming process. In this study, we apply in situ elemental and combined B-Sr isotopic analyses of tourmaline to elucidate the nature and evolution of the subsurface hydrothermal system associated with IOA mineralization in the giant Taocun deposit, eastern China. Taocun is hosted at the top of a diorite intrusion and exhibits three stages of hydrothermal alteration that contain tourmaline: pre-ore Na alteration (Tur I), syn-ore magnetite formation and associated Ca-Fe alteration (Tur II), and post-ore Ca-Mg alteration with sulfide veins (Tur III). Compositional data for each stage of tourmaline plot along the “oxy-dravite”–povondraite join, which is indicative of precipitation from relatively oxidizing fluids. Ranges of Sr-isotopic compositions in Tur I (0.7065–0.7078) and Tur II (0.7068–0.7076) are identical to those of the igneous host rocks, indicating precipitation from magmatic-hydrothermal fluids. The range of B-isotopic compositions in Tur I (δ 11 B values of −6.3‰ to −1.2‰) is also consistent with a magmatic source. Higher δ 11 B values (−2.4‰ to 5.4‰) obtained from Tur II are mainly ascribed to Rayleigh fractionation in the magmatic-hydrothermal system as tourmaline precipitated. Post-ore Tur III has a wide range of mostly lower B-isotopic compositions (−8.5‰ to 0.8‰) that record another pulse of magmatic fluid input. This interpretation is supported by the enrichment of Na, Li, Be, W, Sn, V, and Ti in Tur III, relative to Tur I and II. However, the higher Sr-isotope composition (0.7076–0.7086) of Tur III and available O-isotope composition (−7‰ to 3.5‰) of fluids of this stage record the infiltration of meteoric ground water from adjacent sedimentary country rocks. The results suggest that the Taocun IOA deposit formed in a magmatic-hydrothermal system characterized by two (or more) pulses of magmatic fluid discharge from subvolcanic diorite intrusions, followed by the influx of external ground water as the system waned. This study highlights the utility of tourmaline as a robust geochemical and isotopic monitor of ore-forming processes in such systems.

Ningwu IOA district↗

USGS1952

Geology of the Quartz Creek Pegmatite District, Gunnison County Colorado

The Quartz Creek pegmatite district includes an area about 29 square miles in the vicinity of Quartz Creek in Gunnison County,. Colo. This area contains 1,803 pegmatites that are intruded into pre-Cambrian rocks. The rocks exposed in the district range in age from pre-Cambrian to Recent. The oldest pre-Cambrian rocks are chiefly quartzites interbedded with a few arkoses and conglomerates. These rocks are surrounded by more abundant hornblende gneiss and tonalite. A small body of biotite tonalite was intruded and two thin layers of dacitic pillow lava were extruded into this series. The hornblende gneiss and tonalite have the same composition and differ only in texture. The older material (hornblende gneiss) has a well-marked lineation, whereas the younger (tonalite) is equigranular. Subsequently, a large body of quartz monzonite was intruded along the northern boundary of the mapped area. Later, coarse-grained granite was intruded into the southern part of the area. Dikes of fine-grained granite cut the coarse-grained variety. The last period of intrusive activity in pre-Cambrian time is marked by a large number of pegmatites. The pre-Cambrian rocks were tilted and eroded, and the flatlying Jurassic Morrison formation was deposited on the irregular surface. This formation is conformably overlain by the Cretaceous Dakota sandstone. Faulting produced a vertical offset of 410 feet in the Mesozoic sediments along the only large fault in the area. At the end of Mesozoic time there was another period of erosion. Tertiary (?) tuff is exposed in small, scattered areas in the southern part of the district. It overlies both the Dakota sandstone and pre-Cambrian formations. Glacial till occurs along the edges of Quartz Creek and Wood Gulch. Quaternary alluvium fills the valley bottoms. Although the composition of the country rock has little effect on the shape of the pegmatites, the foliation imposed on this rock has a localizing effect and in part controls the ultimate shape of pegmatites. Zoned and related internal structures are not well developed in the pegmatites of this region. Many of the pegmatites are homogeneous and those that are zoned usually contain a large wall zone and small discontinuous cores. In addition to the more common homogeneous and zoned pegmatites, 7 percent of the pegmatites show a layered structure of textural and mineralogical units not repeated on the opposite side of the pegmatite. Other internal structural units include pegmatites which vary in composition along strike, multiple or “line-rock pegmatites” and fracture fillings. The mineralogy of the pegmatites is described in detail. Specific attention was given to most of the 27 observed minerals. A study of the index of refraction of 439 specimens of plagioclase showed that the variation from zone to zone and layer to layer is minor and that there is no systematic variation in respect to the entire district. No correlation could be found between the refractive index of plagioclase in the pegmatites and the type country rock, or the presence of various accessory minerals. Index of refraction determinations on 95 specimens of muscovite showed no constant variation from wall zone to core or from layer to layer. Curved muscovite has identical optical properties with the flat variety. The index of refraction was determined for 189 beryl specimens. The beryl in the pegmatites containing only a wall zone and a core showed no difference between zones, but in pegmatites that have intermediate zones, the indices of refraction of the beryl showed an inward increase in the alkali content from the contact. Beryl occurs with almost all of the pegmatite minerals and is not restricted in its mineral associations. Tourmaline, except the black variety, is associated with lepidolite. Dark green and blue tourmaline is found in the outer zones of pegmatites containing lepidolite, and the pink and light green varieties are found in direct contact with lepidolite. Lepidolite occurs in aggregates of fine grains, in flat plates, and in curved plates; the three varieties are optically identical. The lighter-colored varieties have higher indices of refraction and contain less lithia than the darker varieties. In addition, the occurrence of the following minerals is described in detail: perthite, quartz, martite, biotite, garnet, columbite-tantalite, monazite, microlite, topaz, gahnite, allanite, and an unidentified mineral. The lack of alteration in the wall rocks adjacent to the pegmatites is interpreted as indicating that the original pegmatite magma did not have an excess of materials such as B, OH-, and P that are needed to form alteration minerals. Because of their low concentration, the above materials were available only in the pegmatitic magma during its crystallization. Pegmatites that contain the rare minerals such as beryl, tourmaline, curved muscovite, biotite, magnetite, monazite, columbite-tantalite, cleavelandite, topaz, lepidolite, and microlite show a grouping in clusters within the district. Beryl-bearing pegmatites occur most abundantly in hornblende gneiss and are only rarely found in either granite or quartz monzonite. The types of minerals that form in a pegmatite appear to be determined by the character of the material segregated from the original magma and the period in which it segregated. The elements escape at one period and may be from only-a specific pocket in the magma. These liquids tend to form groups of pegmatites in which the later bodies contain a high proportion of volatiles. Inferred reserves of the district are estimated for beryl, scrap mica, both hand-cobbing and milling feldspar, lepidolite, columbite-tantalite, topaz, monazite, and microlite. No sheet mica was found. Reserves are small and transportation costs are high so substantial production of low-priced feldspar and scrap mica will depend on the adoption of economica milling techniques for recovering the large quantities of feldspar available. Beryl is irregularly distributed and its recovery as a byproduct will depend on the establishment of a stable market for feldspar and scrap mica. Lepidolite reserves are small low grade.

Colorado↗

USGS1990

The Ag-Mn-Pb-Zn vein, replacement, and skarn deposits of Uchucchacua, Peru; studies of structure, mineralogy, metal zoning, Sr isotopes, and fluid inclusions

Uchucchacua is an Ag-Mn-Pb-Zn vein, replacement, and skarn mineral district in the central Andes of Peru. Host rocks are massive Jumasha Formation shelf limestones of Turonian age that have been folded into an asymmetric northeast-verging anticline of Andean trend. Strata near the fold crest are cut by minor dacitic intrusions and have been displaced by a conjugate set of steep wrench faults that strike northwest-southeast and northeast-southwest. Most ore occurrences are restricted to host rocks that lie below marly limestone at the top of the middle Jumasha Formation. Vein ores located along the fracture system have formed by fissure infill and by replacement of limestone wall rocks. Larger sheetlike replacement orebodies are parallel and adjacent to a large fault. Replacement is in zones of brecciation adjacent to fault bends which were dilatent during sinistral slip of the master fracture. Such fracture belts may have been subject to paleokarst solution processes before mineralization.Four paragenetic stages have been identified. Fe, Mn, and Si were introduced at the exoskarn stage (I) as the anhydrous silicates ferroan tephroite, johannsenite, rhodonite, and bustamite. During the early main stage (II) ferroan tephroite was replaced by friedelite and magnetite under oxidizing conditions at a relatively low pH. Pb, Zn, Fe, Cu, and B were introduced; principal sulfides are pyrrhotite, Fe-rich sphalerite, Mn-rich wurtzite, alabandite, galena, chalcopyrite, and tetrahedrite. Pyrrhotite was replaced by other sulfides during later stage II. Main gangue minerals were calcite, kutnohorite, rhodochrosite, and quartz. Ag, As, and Sb were introduced during the late stage (III) in the form of sulfosalts, principally pyrargyrite. Redistribution of metals introduced at stage II resulted in the growth of Fe-poor sphalerite and alabandite accompanied by calcite gangue. Decreasing Fe contents of alabandite and sphalerite during late stage II and stage III, together with the appearance of pyrite, indicate an increase in sulfur fugacity and/or decrease in temperature over this period. The supergene stage (IV) affects the upper 30 to 150 m of most veins and involves the growth of Mn hydroxides, goethite, orpiment, marcasite, cerussite, and siderite.Distribution patterns of metal ratios and high metal values define ore bands, with a succession of antiforms and synforms. Ore-band locations are determined by vein width, itself a function of wall-rock reactivity, and fracture permeability. Metal ratio distributions in the Luz vein show symmetric dispersion of metals at right angles to the ore-band axis. Ag shows the least dispersion with progressively greater dispersion of Pb and Zn.Geologic considerations indicate mineralization at a minimum depth of 1,600 m. Most primary fluid inclusions in calcite of probable stage II origin were trapped over a temperature range of about 200 degrees to 337 degrees C (hydrostatic pressure) or about 225 degrees to 362 degrees C (lithostatic). Fluid inclusions from late stage II quartz were trapped at about 165 degrees to 205 degrees C (hydrostatic) or 190 degrees to 230 degrees C (lithostatic). Salinity ranged from 0.5 to 29.7 equiv wt percent NaCl-CaCl 2 with little relation to temperature. Calcite 87 Sr/ 86 Sr values of 0.70743 to 0.71122 extend well outside the range of values both determined for magmatic rocks of the region and estimated for the host limestones but are probably compatible with older sedimentary rocks of the mine district. Salinity levels and NaCl/CaCl 2 ratios are similar to basinal brines associated with Mississippi Valley-type deposits. It is concluded that basinal brine, expelled from the deforming Mesozoic sequence, was a significant component of the ore fluid. This fluid was probably heated by dacitic magmas or cooling dacitic intrusions; a polygenetic high-salinity magmatic-basinal fluid then rose along existing strike-slip fractures toward the mineralization site where it mixed with heated low-salinity ground water.

Uchucchacua↗

USGS2011

An approach to modeling coupled thermal-hydraulic-chemical processes in geothermal systems

Interactions between hydrothermal fluids and rock alter mineralogy, leading to the formation of secondary minerals and potentially significant physical and chemical property changes. Reactive transport simulations are essential for evaluating the coupled processes controlling the geochemical, thermal and hydrological evolution of geothermal systems. The objective of this preliminary investigation is to successfully replicate observations from a series of hydrothermal laboratory experiments [Morrow et al., 2001] using the code TOUGHREACT. The laboratory experiments carried out by Morrow et al. [2001] measure permeability reduction in fractured and intact Westerly granite due to high-temperature fluid flow through core samples. Initial permeability and temperature values used in our simulations reflect these experimental conditions and range from 6.13 × 10−20 to 1.5 × 10−17 m2 and 150 to 300 °C, respectively. The primary mineralogy of the model rock is plagioclase (40 vol.%), K-feldspar (20 vol.%), quartz (30 vol.%), and biotite (10 vol.%). The simulations are constrained by the requirement that permeability, relative mineral abundances, and fluid chemistry agree with experimental observations. In the models, the granite core samples are represented as one-dimensional reaction domains. We find that the mineral abundances, solute concentrations, and permeability evolutions predicted by the models are consistent with those observed in the experiments carried out by Morrow et al. [2001] only if the mineral reactive surface areas decrease with increasing clay mineral abundance. This modeling approach suggests the importance of explicitly incorporating changing mineral surface areas into reactive transport models.

Conference Paper↗

USGS1953

Radioactive deposits of Nevada

Thirty-five occurrences of radioactive rocks had been reported from Nevada prior to 1952. Twenty-five of these had been investigated by the U. S. Geological Survey and the U. S. Atomic Energy Commission. Of those investigated, uranium minerals were identified in 13; two contained a thorium mineral (monazite); the source of radioactivity on 7 properties was not ascertained; and one showed no abnormal radioactivity. Of the other reported occurrences, one is said to contain uraniferous hydrocarbons and 9 are placers containing thorian monazite. Pitchblende occurs at two localities; the East Walker River area, and the Stalin's Present prospect, where it is sparsely disseminated in tabular bodies cutting granitic rocks. Other uranium minerals found in the state include: carnotite, tyuyamunite, autunite, torbernite, gummite, uranophane, kasolite, and an unidentified mineral which may be dumontit. Monazite is the only thorium mineral of possible economic importance that has been reported. From an economic standpoint 9 only 4 of the properties examined showed reserves of uranium ore in 1952; these are: the Green Monster mine, which shipped 5 tons of ore to Marysvale, Utah, during 1951, the Majuba Hill mine, the Stalin's Present prospect, and the West Willys claim in the Washington district. Reserves of ore grade are small on all of these properties and probably cannot be developed commercially unless an ore-buying station is set up nearby. No estimate has been made of thorium reserves and no commercial deposits of thorium are known.

Nevada↗

USGS1975

Middle tertiary volcanic field in the southern Rocky Mountains

A widespread volcanic field covered most of the Southern Rocky Mountains in middle Tertiary time, 40 to 25 m.y. ago (approximately Oligocene time). This field covered an erosion surface that beveled structures formed during the Laramide orogeny in Late Cretaceous and early Tertiary time. The source vents from which the volcanic rocks were derived were largely restricted to the deformed area. Recognized volcanic centers lie mostly within a broad triangular area bounded on the east by the Rocky Mountain front, on the northwest by the northeast-trending Colorado mineral belt lineament, and on the southwest by the southern margin of the recurrently active Uncompahgre-San Luis uplift. Local volcanic centers existed also in the Never Summer Mountains and Rabbit Ears Range north of the mineral belt lineament. The resulting volcanic field thus consisted of a major southern segment covering all of south-central Colorado and adjacent New Mexico and a northern segment extending into the mountain areas of north-central Colorado. The two segments were linked along the trend of the Colorado mineral belt. Most of the volcanic field consisted of volcanic rock of intermediate composition derived from many widely scattered volcanoes. Extensive aprons of volcaniclastic rocks around these volcanoes coalesced to provide a virtually continuous cover of volcanic material. In places, the volcanic activity became more silicic with time, great ash-flow tuff sheets were erupted, and the source areas subsided to form calderas. The largest ash-flow field and most of the calderas formed in the San Juan Mountains. Other ash flows apparently were derived from areas in the Sawatch Range in central Colorado and the Never Summer Mountains in northern Colorado. Large near-surface batholiths were emplaced beneath the San Juan Mountains and beneath the region that extends northeastward from the Elk Mountains and Sawatch Range along the trend of the Colorado mineral belt as far as the Rocky Mountain front. These batholiths are manifested by two large gravity lows and by many exposed epizonal plutons that represent cupolas on the larger underlying bodies. The batholith in central Colorado probably consists of plutons of both Laramide (70 to 55 m.y.) and middle Tertiary (40 to 25 m.y.) ages.

Rocky Mountains↗

USGS2021

Mineral deposits of the Mesoproterozoic Midcontinent Rift System in the Lake Superior region – Metallogeny of the prolifically mineralized Keweenawan LIP

The Keweenawan large igneous province (LIP) of the Midcontinent Rift System (MRS) of North America is perhaps the most prolifically and diversely mineralized LIP known on Earth (Nicholson et al., 1992). The MRS is an approximately 2,200 km curvilinear continental rift that stretches from Kansas northeast to the Lake Superior region where it turns southeast and extends through lower Michigan (Fig. 1). Rocks of the MRS host a varied suite of magmatic and hydrothermal mineral deposits in the Lake Superior region of the United States and Canada where rift rocks are exposed at or near the surface. Historically, hydrothermal deposits, such as Michigan’s native Cu deposits and the White Pine sediment-hosted stratiform Cu deposit, were major MRS metal producers. On-going exploration for and potential development of Cu-Ni sulfide deposits hosted by the Duluth Complex of Minnesota and the opening of the Eagle Ni mine in Michigan indicate an expanding interest in MRS magmatic deposits. Many of the MRS hydrothermal and magmatic mineral deposits are significant past, present, and likely future providers of critical minerals. We have placed these deposits into a space and time metallogenic framework (Woodruff et al., 2020a) that is summarized here.

Iowa, Kansas, Minnesota, Michigan, Nebraska, Ontar↗

USGS1995

Porphyry copper and other intrusion-related mineralization in Mexico

Intrusion-related copper-bearing ore deposits in Mexico span a wide-range of deposit types and geological settings and formed from the mid-Mesozoic through the Holocene. These deposits include world-class copper porphyry and skarn deposits as well as a continuum of similar skarn, porphyry, vein, and replacement deposits that contain variable quantities of molybdenum, zinc, silver, lead, iron, gold, tungsten, tin, fluorine, and beryllium. Based on a new compilation, this paper reviews data on the full spectrum of intrusion-related deposits, concentrating on copper-rich systems, and attempts to place them in a generalized geological and petrological context. In Mexico, intrusion-related mineral deposits are primarily Mesozoic to middle Tertiary in age. Three broad periods are prominent in the mineralization record: the late Mesozoic, the Laramide, and the middle Tertiary. Jurassic to Late Cretaceous calc-alkalic batholiths with sparse volcanic rocks occur along the Pacific margin mainly on eugeoclinal crust, although locally on continental crust (for example, in Sonora). Latest Cretaceous to Early Tertiary ('Laramide') calc-alkalic batholithic, subvolcanic, and volcanic centers occur in an overlapping but somewhat more easterly band that extends with diminished intensity and somewhat younger ages into the Sierra Madre Oriental. Mid-Tertiary volcanism and local intrusive centers are widely developed, with the greatest abundance of calcalkalic felsic volcanics in the Sierra Madre Occidental and more mafic middle to late Tertiary arc volcanics in the Sierra Madre del Sur in southern Mexico and as a fringe of alkalic volcanic' and sub volcanic centers in northeastern Mexico. Over 600 copper-rich intrusion-related systems can be inferred from the literature; about 100 can be documented with some confidence. Copper-rich deposits occur with both intermediate (dioritic) and felsic (granodioritic) intrusive centers and show a corresponding variety of associated metals and alteration types. Styles include porphyry-type disseminated or stockwork mineralization, skarn, breccia pipes, and pegmatites. Multiple styles commonly occur in the same district. Porphyry copper deposits are best developed in association with the Laramide intrusive centers of northern Mexico and the mid-Tertiary intrusions in southern Mexico. Other intrusion-related deposit types occur within the same magmatic framework, but they have different temporal and spatial correlations related to their igneous composition and exposure level. The continuum of intrusion-related mineralization in Mexico can be divided by geological associations, metal contents, and styles of alteration. Although more than 1,500 intrusion-associated mineral deposits are known, the scarcity of data requires a simplified approach focusing on major districts. We distinguish the following overlapping groups of deposits based on their metal contents and igneous compositions: (1) porphyry or skarn Cu(-Mo-Zn) associated with intermediate to felsic granitoids, (2) porphyry or skarn Cu (-Au-Fe) associated with intermediate intrusions, (3) greisen, skarn, or pegmatite W(-Mo) associated with intermediate to felsic granitoids, (4) replacement or skarn Zn-Pb-Ag(-Cu-F) deposits associated with felsic intrusions, (5) volcanic-hosted vein Ag-Au(-Zn-F-Sn) deposits associated with hypabyssal felsic intrusions, (6) vein ± replacement Ag-Au(-Cu-Zn-Pb) deposits associated with intermediate stocks, (7) volcanichosted Au-Ag(-Cu) systems, (8) rhyolite-related F(-Sn-Be) deposits, (9) diorite-related Fe(-Au-Cu) skarns, and (9) rhyolite-related Fe deposits. Some inferences can be drawn from examination of these patterns: • Igneous compositions vary in time and space in Mexico, but multiple compositions commonly were emplaced at different times in the same region. Temporal variations (as in Sonora) are as important as differences in province (as between Sonora and southern Mexico). • Alteration and metal differences between alkaline and sub alkaline, felsic and mafic magma suites can be partly rationalized from equilibria among igneous minerals (for example, in terms of a Al 2 O 3 vs a CaO [vs a SiO 2 ]), fluid chloride and sulfur contents, and magmatic metal contents which reflect province and process. • Exposure and preservation filter observed Mexican metallogeny. Erosion of the Mesozoic arc superstructure in the west leaves mainly tungsten-skarns, burial of the Laramide arc in central Mexico interrupts porphyry copper patterns, and minimal exhumation of mid-Tertiary intrusive centers preserves distal vein or replacement systems. • The superimposed metallogenic patterns in Mexico have parallels with metallogenic patterns in the western United States in terms of the effects of preservation, process, and province. Future work should focus on increasing the basic geological data on mineral deposits and igneous rocks. Geochronology, petrology, and geochemistry would help better define the temporal, spatial, and compositional interrelationships between tectonism, magmatism, and mineralization.

Book chapter↗

USGS1954

Radioactive deposits of Nevada

Thirty-five occurrences of radioactive rocks had been reported from Nevada prior to 1952. Twenty-five of these had been investigated by personnel of the U. S. Geological Surveyor of the U. S. Atomic Energy Commission. Of those investigated, uranium minerals were identified at 13 sites; two sites contained a thorium mineral (monazite); the source of radioactivity on nine properties was not ascertained, and one showed no abnormal radioactivity. Of the other reported occurrences, one is said to contain uraniferous hydrocarbons and nine are placers containing thorian monazite. Pitchblende occurs at two localities, the East Walker River area, and the Stalin's Present prospect, where it is sparsely disseminated in tabular bodies cutting granitic rocks. Other uranium minerals found in the state include: carnotite, tyuyamunite, autunite, torbernite, gummite, uranophane, kasolite, and an unidentified mineral which may be dumontite. Monazite is the only thorium mineral of possible economic importance that has been reported. From an economic standpoint, only four of the properties examined showed reserves of uranium ore in 1952; these are: the Green Monster mine, which shipped 5 tons of ore to Marysvale, Utah, during 1951; the Majuba Hill mine; the Stalin's Present prospect; and the West Willys claim in the Washington district. No estimate has been made of thorium reserves and no commercial deposits of thorium are known.

Bulletin↗

USGS1950

Mineral constituents in water and their significance

Pure water does not exist in nature. Because water is a powerful solvent, every drop of rain water carries dissolved or suspended material - dust, pollen, and smoke, as well as the atmospheric gases, oxygen, nitrogen and carbon dioxide. When rain falls, the water running over the rocks and percolating through the soil gathers more and more mineral matter in solution. As the uses to which a water supply may be put depend primarily on its mineral content, information concerning the chemical characteristics of water is of importance to each of us. (available as photostat copy only)

Open-File Report↗

USGS1969

A ground-water reconnaissance of the Republic of Ghana, with a description of geohydrologic provinces

This report gives a general summary of the availability and use of ground water and describes the occurrence of ground water in five major geohydrologic provinces lying in the eight administrative regions of Ghana. The identification and delineation of the geohydrologic provinces are based on their distinctive characteristics with respect to the occurrence and availability of ground water. The Precambrian province occupies the southern, western, and northern parts of Ghana and is underlain largely by intrusive crystalline and metasedimentary rocks. The Voltaian province includes that part of the Voltaian sedimentary basin in central Ghana and is underlain chiefly by consolidated sandstone, mudstone, and shale. Narrow discontinuous bands of consolidated Devonian and Jurassic sedimentary rocks near the coast constitute the Coastal Block Fault province. The Coastal Plain province includes semiconsolidated to unconsolidated sediments of Cretaceous to Holocene age that underlie coastal plain areas in southwestern and southeastern Ghana. The Alluvial province includes the Quaternary alluvial deposits in the principal river valleys and on the delta of the Volta River. Because of the widespread distribution of crystalline and consolidated sedimentary rocks of low permeability in the Precambrian, Voltaian, and Coastal Block Fault provinces, it is difficult to develop large or event adequate groundwater supplies in much of Ghana. On the other hand, small (1 to 50 gallons per minute) supplies of water of usable quality are available from carefully sited boreholes in most parts of the country. Also, moderate (50 to 200 gpm) supplies of water are currently (1964) obtained from small-diameter screened boreholes tapping sand and limestone aquifers in the Coastal Plain province in southwestern and southeastern Ghana, but larger supplies could be obtained through properly constructed boreholes. In the Alluvial province, unconsolidated deposits in the larger stream valleys that are now largely undeveloped offer desirable locations for shallow vertical or horizontal wells, which can induce infiltration from streams and yield moderate to large water supplies. The principal factors that limit development of ground-water supplies in Ghana are (1) prevailing low permeability and water-yielding potential of the crystalline and consolidated sedimentary rocks that underlie most of the country, (2) highly mineralized ground water which appears to be widely distributed in the northern part of the Voltaian province, and (3) potential problems of salt-water encroachment in the Coastal Plain province in the Western Region and in the Keta area. On the other hand, weathering has increased porosity and has thus substantially increased the water-yielding potential of the crystalline and consolidated sedimentary rocks in much of central and northern Ghana. Also, with proper construction and development, much larger yields than those now (1964) prevalent could be obtained from boreholes tapping sand and limestone aquifers in the Coastal Plain province.

Water Supply Paper↗

USGS2026

Geochemical, mineralogical, and isotopic evidence for multi-stage genesis of the Hicks Dome REE + Y-HFSE-fluorite deposit, Illinois, USA

Hicks Dome hosts breccias enriched in rare earth elements (REE), Y, Th, F, Ba, Ti, Nb, and Be, alongside spatially associated lamprophyre dikes (ca. 271 Ma). Hicks Dome is located within the Illinois–Kentucky Fluorspar District, which hosts fluorite, Pb–Zn, and barite resources. This study investigates the genetic relationships between Hicks Dome mineralization in breccias, alkaline magmatism, and Illinois–Kentucky Fluorspar District mineralization. Lamprophyre dikes are light REE–enriched with chondrite-normalized abundances decreasing from La to Lu. The Host Breccia exhibits middle and heavy REE–enriched patterns that mirror those of the principal REE–Th host minerals, including fluorapatite, xenotime, and thorite. Textural evidence suggests recrystallization of phosphates, sulfates, and Ti–Nb oxides in the Host Breccia. U–Pb geochronology constrains multiple mineralizing events, with ages of 277 ± 18 Ma from low-Th apatite interpreted as main-stage mineralization, and 121.6 ± 9.7 Ma from high-Th apatite indicating later overprinting. O–H–C stable isotope data provide evidence for multiple stages of fluid-rock interaction and fluid mixing: (1) early magmatic fluids dissolved limestone country rock, (2) mixing between magmatic fluids and basinal brines led to main-stage mineralization in the Host Breccia, and (3) late-stage mineralization occurred following mixing of meteoric water and basinal brine. These results indicate that heavy REEs, high field strength elements, and fluorine precipitated proximal to its alkaline magmatic source because of fluid–rock interactions and fluid mixing. Subsequent fluid mixing drove late-stage recrystallization and additional fluorite formation, a process that may be similar to mineralization in the Illinois-Kentucky Fluorspar District.

Illinois↗

USGS1982

Map showing geochemical characteristics of rock samples from the Kalmiopsis Wilderness, southwestern Oregon

This report summarizes 1,307 semiquantitative chemical analyses of rocks collected to aid int he evaluation of the mineral resources of the Kalmiopsis Wilderness, Oreg. Chemical analyses and sample location maps are presented by Grimes, Leinz, and Speckman (1981). The area is located in the Kilamath Mountains geoporphic province of southwestern Oregon, and the area's location and boundaries are shown on the accompanying map. The geology of the study area is described by Page and others (1981), Gray (1980), and Ramp (1975). The rocks of the area cosist of dismembered ophiolite, island-arc, and sedimentary rock sequesnces that lie within the Western Jurassic belt of the Klamath Mountains. All units normally found within these assemblages are present; however, thrusting ans subsequent normal faulting have disrupted the geometric relations, producing a complexly faulted series of imbricate thrust slices.

Oregon↗

USGS2004

40 Ar/ 39 Ar Dating of Zn-Pb-Ag Mineralization in the Northern Brooks Range, Alaska

The 40 Ar/ 39 Ar laser step-heating method potentially can be used to provide absolute ages for a number of formerly undatable, low-temperature ore deposits. This study demonstrates the use of this method by determining absolute ages for Zn-Pb-Ag sediment-hosted massive sulfide deposits and vein-breccia occurrences found throughout a 300-km-long, east-west-trending belt in the northern Brooks Range, Alaska. Massive sulfide deposits are hosted by Mississippian to Pennsylvanian(?) black carbonaceous shale, siliceous mudstone, and lesser chert and carbonate turbidites of the Kuna Formation (e.g., Red Dog, Anarraaq, Lik (Su), and Drenchwater). The vein-breccia occurrences (e.g., Husky, Story Creek, West Kivliktort Mountain, Vidlee, and Kady) are hosted by a deformed but only weakly metamorphosed package of Upper Devonian to Lower Mississippian mixed continental and marine clastic rocks (the Endicott Group) that stratigraphically underlie the Kuna Formation. The vein-breccias are mineralogically similar to, but not spatially associated with, known massive sulfide deposits. The region's largest shale-hosted massive sulfide deposit is Red Dog; it has reserves of 148 Mt grading 16.6 percent zinc, 4.5 percent lead, and 77 g of silver per tonne. Hydrothermally produced white mica in a whole-rock sample from a sulfide-bearing igneous sill within the Red Dog deposit yielded a plateau age of 314.5 Ma. The plateau age of this whole-rock sample records the time at which temperatures cooled below the argon closure temperature of the white mica and is interpreted to represent the minimum age limit for massive sulfide-related hydrothermal activity in the Red Dog deposit. Sulfide-bearing quartz veins at Drenchwater crosscut a hypabyssal intrusion with a maximum biotite age of 337.0 Ma. Despite relatively low sulfide deposition temperatures in the vein-breccia occurrences (162°-251°C), detrital white mica in sandstone immediately adjacent to large vein-breccia zones was partially to completely recrystallized. The 40 Ar/ 39 Ar age spectra and inverse isochron plots of the multicomponent whole-rock sandstone samples are more complex than those of single minerals. However, different minerals have different Ca/K and Cl/K ratios and closure temperatures, and these properties were used to identify portions of spectra dominated by argon release from specific minerals. 40 Ar/ 39 Ar laser step-heating analyses of Late Devonian sandstone whole rocks produced spectra that record a two-stage resetting history: a Carboniferous hydrothermal event first and later Mesozoic to Tertiary events, which are in agreement with geologic constraints. The 40 Ar/ 39 Ar ages and the similar mineralogy, lead isotope composition, and relative stratigraphic positions support the interpretation that the shale-hosted massive sulfide deposits and most vein-breccia occurrences are temporally and genetically related, and that they are different expressions of Carboniferous basinal dewatering.

Alaska↗

USGS2007

Geology and origin of epigenetic lode gold deposits, Tintina Gold Province, Alaska and Yukon

More than 50 million ounces of lode gold resources have been defined in the previous 15 years throughout accreted terranes of interior Alaska and in adjacent continental margin rocks of Yukon. The major deposits in this so-called Tintina Gold Province formed around 105 to 90 million years ago in east-central Alaska and Yukon, and around 70 million years ago in southwestern Alaska, late in the deformational history of their host rocks. All gold deposits studied to date formed from CO 2 -rich and 18 O-rich crustal fluids, most commonly of low salinity. The older group of ores includes the low-grade intrusion-related gold systems at Fort Knox near Fairbanks and those in Yukon, with fluids exsolved from fractionating melts at depths of 3 to 9 kilometers and forming a zoned sequence of auriferous mineralization styles extending outward to the surrounding metasedimentary country rocks. The causative plutons are products of potassic mafic magmas generated in the subcontinental lithospheric mantle that interacted with overlying lower to middle crust to generate the more felsic ore-related intrusions. In addition, the older ores include spatially associated, high-grade, shear-zonerelated orogenic gold deposits formed at the same depths from upward-migrating metamorphic fluids; the Pogo deposit is a relatively deep-seated example of such. The younger gold ores, restricted to southwestern Alaska, formed in unmetamorphosed sedimentary rocks of the Kuskokwim basin within 1 to 2 kilometers of the surface. Most of these deposits formed via fluid exsolution from shallowly emplaced, highly evolved igneous complexes generated mainly as mantle melts. However, the giant Donlin Creek orogenic gold deposit is a product of either metamorphic devolatilization deep in the basin or of a gold-bearing fluid released from a flysch-melt igneous body.

Alaska, Yukon↗

USGS2002

Epigenetic lead, zinc, silver, antimony, tin, and gold veins in Boulder Basin, Blaine and Custer Counties, Idaho: Potential for economic tin mineralization

Boulder Basin is in a northwest-trending belt of allochthonous Paleozoic rocks in the Boulder Mountains of central Idaho. Regional Tertiary extension resulted in widespread normal faulting and coeval emplacement of shallow-level intrusions and extrusive rocks of the Challis Volcanic Group. Epigenetic lead-zinc-silver-antimony-tin-gold vein deposits formed during Tertiary extension and are hosted within Paleozoic strata. The major orebodies are in the lower plate of the Boulder Basin thrust fault, in massive quartzite of the Middle Pennsylvanian to Lower Permian Wood River Formation. Anomalous concentrations of tin are present in the base-metal mineral assemblage of the Boulder Basin ore deposits. The tin-bearing veins in Boulder Basin are strikingly similar to Bolivian tin deposits. The deposit model for Bolivian tin deposits identifies buried tin porphyry below the tin-bearing vein system.

Idaho↗