Geologic controls on the composition of natural waters and mine waters draining diverse mineral-deposit types
No abstract available.
Reviews in Economic Geology↗
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Silica-carbonate alteration of serpentine: Wall rock alteration in mercury deposits of the California Coast Ranges
Chemical, isotopic, and thermodynamic properties have been measured of CO 2 -rich ground waters in the central California Coast Ranges. The acidic CO 2 -rich waters react with serpentine to form silica-carbonate rock, the host rock of many mercury deposits in the Coast Range of California. In part the waters are of a metamorphic origin and in part the waters are locally derived meteoric waters. The CO 2 is entirely derived from metamorphic reactions at depth. Depending on the relative importance of several reactions, the relative abundances of silica and carbonate minerals vary in the silica-carbonate rock. If the CO 2 -rich fluids react directly with peridotite or dunite, massive magnesite deposits may form. © 1973 Society of Economic Geologists, Inc.
California↗
Application of seismic-refraction techniques to hydrologic studies
During the past 30 years, seismic-refraction methods have been used extensively in petroleum, mineral, and engineering investigations, and to some extent for hydrologic applications. Recent advances in equipment, sound sources, and computer interpretation techniques make seismic refraction a highly effective and economical means of obtaining subsurface data in hydrologic studies. Aquifers that can be defined by one or more high seismic-velocity surfaces, such as (1) alluvial or glacial deposits in consolidated rock valleys, (2) limestone or sandstone underlain by metamorphic or igneous rock, or (3) saturated unconsolidated deposits overlain by unsaturated unconsolidated deposits, are ideally suited for applying seismic-refraction methods. These methods allow the economical collection of subsurface data, provide the basis for more efficient collection of data by test drilling or aquifer tests, and result in improved hydrologic studies. This manual briefly reviews the basics of seismic-refraction theory and principles. It emphasizes the use of this technique in hydrologic investigations and describes the planning, equipment, field procedures, and intrepretation techniques needed for this type of study. Examples of the use of seismic-refraction techniques in a wide variety of hydrologic studies are presented.
Open-File Report↗
Geological Survey research 1976
This U.S. Geological Survey activities report includes a summary of recent (1976 fiscal year) scientific and economic results accompanied by a list of geologic and hydrologic investigations in progress and a report on the status of topographic mapping. The summary of results includes: (1) Mineral resources, Water resources, (2) Engineering geology and hydrology, (3) Regional geology, (4) Principles and processes, (5) Laboratory and field methods, (6) Topographic surveys and mapping, (7) Management of resources on public lands, (8) Land information and analysis, and (9) Investigations in other countries. Also included are lists of cooperating agencies and Geological Survey offices.
Professional Paper↗
Geological Survey research 1978
This U.S. Geological Survey activities report includes a summary of 1978 fiscal year scientific and economic results accompanied by a list of geologic and hydrologic investigations in progress and a report on the status of topographic mapping. The summary of results includes: (1) Mineral and water resources, (2) Engineering geology and hydrology, (3) Regional geology, (4) Principles and processes, (5) Laboratory and field methods, (6) Topographic surveys and mapping, (7) Management of resources on public lands, (8) Land information and analysis, and (9) Investigations in other countries. Also included are lists of cooperating agencies and Geological Survey offices. (Woodard-USGS)
Professional Paper↗
Application of seismic-refraction techniques to hydrologic studies
During the past 30 years, seismic-refraction methods have been used extensively in petroleum, mineral, and engineering investigations and to some extent for hydrologic applications. Recent advances in equipment, sound sources, and computer interpretation techniques make seismic refraction a highly effective and economical means of obtaining subsurface data in hydrologic studies. Aquifers that can be defined by one or more high-seismic-velocity surface, such as (1) alluvial or glacial deposits in consolidated rock valleys, (2) limestone or sandstone underlain by metamorphic or igneous rock, or (3) saturated unconsolidated deposits overlain by unsaturated unconsolidated deposits, are ideally suited for seismic-refraction methods. These methods allow economical collection of subsurface data, provide the basis for more efficient collection of data by test drilling or aquifer tests, and result in improved hydrologic studies. This manual briefly reviews the basics of seismic-refraction theory and principles. It emphasizes the use of these techniques in hydrologic investigations and describes the planning, equipment, field procedures, and interpretation techniques needed for this type of study. Further-more, examples of the use of seismic-refraction techniques in a wide variety of hydrologic studies are presented.
Techniques of Water-Resources Investigations↗
SHRIMP U-Pb ages of xenotime and monazite from the Spar Lake red bed-associated Cu-Ag deposit, western Montana: Implications for ore genesis
Xenotime occurs as epitaxial overgrowths on detrital zircons in the Mesoproterozoic Revett Formation (Belt Supergroup) at the Spar Lake red bed-associated Cu-Ag deposit, western Montana. The deposit formed during diagenesis of Revett strata, where oxidizing metal-bearing hydrothermal fluids encountered a reducing zone. Samples for geochronology were collected from several mineral zones. Xenotime overgrowths (1–30 μm wide) were found in polished thin sections from five ore and near-ore zones (chalcocite-chlorite, bornite-calcite, galena-calcite, chalcopyrite-ankerite, and pyrite-calcite), but not in more distant zones across the region. Thirty-two in situ SHRIMP U-Pb analyses on xenotime overgrowths yield a weighted average of 207 Pb/ 206 Pb ages of 1409 ± 8 Ma, interpreted as the time of mineralization. This age is about 40 to 60 m.y. after deposition of the Revett Formation. Six other xenotime overgrowths formed during a younger event at 1304 ± 19 Ma. Several isolated grains of xenotime have 207 Pb/ 206 Pb ages in the range of 1.67 to 1.51 Ga, and thus are considered detrital in origin. Trace element data can distinguish Spar Lake xenotimes of different origins. Based on in situ SHRIMP analysis, detrital xenotime has heavy rare earth elements-enriched patterns similar to those of igneous xenotime, whereas xenotime overgrowths of inferred hydrothermal origin have hump-shaped (i.e., middle rare earth elements-enriched) patterns. The two ages of hydrothermal xenotime can be distinguished by slightly different rare earth elements patterns. In addition, 1409 Ma xenotime overgrowths have higher Eu and Gd contents than the 1304 Ma overgrowths. Most xenotime overgrowths from the Spar Lake deposit have elevated As concentrations, further suggesting a genetic relationship between the xenotime formation and Cu-Ag mineralization.
Montana↗
Pb-Sr-Nd isotopes in surficial materials at the Pebble Porphyry Cu-Au-Mo Deposit, Southwestern Alaska: can the mineralizing fingerprint be detected through cover?
The Cretaceous Pebble porphyry Cu-Au-Mo deposit is covered by tundra and glacigenic sediments. Pb-Sr-Nd measurements were done on sediments and soils to establish baseline conditions prior to the onset of mining operations and contribute to the development of exploration methods for concealed base metal deposits of this type. Pebble rocks have a moderate range for 206 Pb/ 204 Pb = 18.574 to 18.874, 207 Pb/ 204 Pb = 15.484 to 15.526, and 208, Pb/ 204 Pb = 38.053 to 38.266. Mineralized granodiorite shows a modest spread in 87 Sr/ 86 Sr (0.704354–0.707621) and 143 Nd/ 144 Nd (0.512639–0.512750). Age-corrected (89 Ma) values for the granodiorite yield relatively unradiogenic Pb (e.g., 207 Pb/ 204 Pb <15.52), low values of 87 Sr/ 86 Sr, and positive values of ɛNd (1.00–4.52) that attest to a major contribution of mantle-derived source rocks. Pond sediments and soils have similar Pb isotope signatures and 87 Sr/ 86 Sr and 143 Nd/ 144 Nd values that resemble the mineralized granodiorites. Glacial events have obscured the recognition of isotope signatures of mineralized rocks in the sediments and soils. Baseline radiogenic isotope compositions, prior to the onset of mining operations, reflect natural erosion, transport and deposition of heterogeneous till sheets that included debris from barren rocks, mineralized granodiorite and sulfides from the Pebble deposit, and other country rocks that pre- and postdate the mineralization events. Isotopic variations suggest that natural weathering of the deposit is generally reflected in these surficial materials. The isotope data provide geochemical constraints to glimpse through the extensive cover and together with other geochemical observations provide a vector to concealed mineralized rocks genetically linked with the Pebble deposit.
Alaska↗
The environmental control of sedimentary iron minerals
An Eh-pH stability diagram is developed for hematite, magnetite, siderite, pyrite, and iron sulfide that indicates the relative position of their stability fields in a normal sea water system. With the exception of the magnetite-siderite relationship, Eh is much more critical than pH. In general terms, hematite is stable under oxidizing conditions, siderite and magnetite under intermediate to moderately reducing conditions, pyrite under moderate to strongly reducing conditions, and iron sulfide under still stronger reducing conditions. Because of numerous variables involved the relative positions of the stability fields are stressed rather than their limits on the Eh and pH scales. The inclusion of a magnetite field suggests that magnetite should be much more important as a primary or diagenetic mineral in sedimentary rocks than has been commonly recognized. This is in accord with numerous recent suggestions to that effect. The importance of thermodynamic equilibrium is stressed and it is suggested that differences in rates of formation of the various minerals and the persistence of some metastable phases are among the commonest causes of lack of equilibrium.
Economic Geology↗
Comparison of platinum, palladium, and rhodium distributions in some layered intrusions with special reference to the late differentiates (upper zone) of the Bushveld Complex, South Africa
The Stillwater, Fiskenaesset, and Bushveld Complexes are all composed of layered ultramafic and mafic rocks in which the cumulus phases generally appear in a regular order, which have similar petrologic and chemical characteristics, which are all Precambrian in age, and which contain platinum-group elements that vary widely in their abundances and relative proportions. Two of the complexes, the Stillwater and Bushveld, contain platinum-group element enriched horizons not yet found in the Fiskenaesset. The ratio of Pt/(Pt + Pd) in rocks from the Stillwater tends to increase from the basal zone to the middle of the ultramafic zone, decreases to the beginning of the banded zone, and then increases again through the banded zone; many fluctuations, however, are superimposed upon this generalized trend. The trends of Pt/(Pt + Pd) ratios appear to show a positive correlation with the Mg/(Mg + Fe (super +2) ) ratio in olivine. In the Fiskenaesset Complex, the Pt/(Pt + Pd) ratio increases rapidly from 0.3 to 0.7 from the lower gabbro and ultramafic units through the leucogabbro units, then increases slowly through the anorthosite and upper gabbro unit. Superimposed on this generalized trend are increasing and decreasing patterns within each unit.Analyses of platinum, palladium, and rhodium for 69 rocks from the main and upper zones of the eastern Bushveld from the Roossenekal area show generally low concentrations of less than 1 ppb Pt; 0.1 ppb Pd; and 0.1 ppb Rh, but larger amounts occur in some magnetite layers and sulfide-bearing zones. Within the main zone up to the pyroxenite marker, from the pyroxenite marker to below lower magnetite layer 2, and in the upper zone, the Pt/(Pt + Pd) ratio decreases with stratigraphic position, although with minor fluctuations in these intervals. The concentration levels of the platinum-group metals appear to be directly related to the amount of sulfide material present and the proportion of intercumulus material. Variations in Pt/(Pt + Pd) ratios in the Bushveld and Fiskenaesset Complexes are presumably related to changes in major mineral compositions as they are in the Stillwater Complex.
Economic Geology↗
Genesis of the Questa Mo porphyry deposit and nearby polymetallic mineralization, New Mexico, USA
The Oligocene Latir magmatic center in northern New Mexico is an exceptionally well-exposed volcanoplutonic complex that hosts a variety of magmatic-hydrothermal deposits, ranging from relatively deep, F-rich porphyry Mo mineralization to shallower epithermal deposits. We present new whole-rock chemical and isotopic data for plutonic rocks from the Latir magmatic center, including extensive sampling of drill core samples of intrusive rocks from the Questa porphyry Mo deposit. These data document temporal chemical trends of porphyry-related mineralization that occurred after caldera-forming magmatism and during postcaldera batholith assembly. Silicic magmas were generated multiple times throughout the history of the Latir magmatic center, but few are associated with the formation of a mineral deposit. Whole-rock trace element ratios and Sr, Nd, and Pb isotope compositions vary throughout the protracted history of silicic magmatism. The caldera-forming ignimbrite and early phase of postcaldera intrusions are unmineralized, more enriched in high field strength elements, and generally contain less radiogenic Sr and Pb and more radiogenic Nd than later intrusions. The Questa porphyry Mo deposit formed immediately after the most isotopically primitive phase of the batholith was assembled, ruling out simple reworking of juvenile mantle-derived crust as the source for mineralizing magmas. Rhyolite dikes associated with polymetallic sulfide deposits intruded ~800 k.y. after Mo mineralization, and Nd isotope data indicate that these dikes are associated with different batches of magma and are unrelated to the Mo-mineralizing intrusions at the Questa mine. Together, these data indicate that the source of magmas changed significantly throughout the 10-m.y. history of the magmatic center. We assess multiple genetic models for porphyry-related magmatism against this data set, favoring models with discrete periods of magma genesis from a deep hybridized zone in the lower crust giving rise to the punctuated periods of mineralization. These observations suggest that the formation of mineral deposits within a central magmatic locus is likely the result of the piecemeal assembly of individual hydrothermal-magmatic systems, and that distal and younger polymetallic mineralization commonly observed near known porphyry deposits represents decoupled processes.
New Mexico↗
Geochemistry of quartz and fluid inclusions associated with gold, tungsten, and antimony in the Stibnite-Yellow Pine district, Idaho
Deposits in the historic Stibnite-Yellow Pine district in east-central Idaho were mined for Ag, Au, Hg, Sb, and W. Ore is hosted in breccia and fault zones along NE-striking faults that transect the Atlanta lobe of the Late Cretaceous Idaho batholith and metamorphosed Neoproterozoic to lower Paleozoic rocks. Geochronological studies have delineated five superimposed and zoned hydrothermal events in the mining district which range in age from Late Cretaceous to the Eocene. They formed the following consecutive assemblages: (1) vein and disseminated pre-ore milky quartz (± calcite), muscovite, and brassy pyrite with minor molybdenite and base metal sulfides; (2) vein and disseminated quartz, calcite, sericite, auriferous-pyrite, and arsenopyrite; (3) potassium feldspar, quartz, dolomite, and calcite with vein and disseminated scheelite ± pyrite and arsenopyrite; (4) Au-Ag veins that contain adularia; and (5) breccia, vein, and disseminated quartz, calcite, and stibnite with minor Ag sulfosalts and distal zones of cinnabar and realgar at Fern and Hermes mines. In this study, the pressure, temperature, and composition of ore-forming fluids were measured in Au-, W-, and Sb-bearing samples collected from drill core and surface exposures. Using optical petrography, scanning electron microscopy cathodoluminescence (SEM-CL) and electron microprobe cathodoluminescence (EMPA-CL) imaging, as well as electron microprobe (EMP) and laser ablation-inductively coupled plasma-mass spectrometry trace element analyses, four major overprinting generations of hydrothermal quartz are defined. Fluid inclusion assemblages (FIAs) in each generation of quartz were characterized by microthermometry and laser Raman spectroscopy. Quartz and fluid inclusion paragenesis are as follows: (Qi) altered and overprinted Qi with no coeval FIAs that formed before or during event 1; (Q1) early veins as well as disseminated quartz with dull gray SEM-CL and H 2 O-NaCl-CO 2 FIAs that formed at minimum temperatures and pressures of 281° to 358°C and 1346 to 1789 bar during event 2 (Au); (Q2) vein and disseminated quartz, often euhedral, with H 2 O-NaCl ± CO 2 ± CH 4 FIAs that formed at minimum temperatures and pressures of 183° to 213°C and 72 to 602 bar during event 3 (W); and (Q3) euhedral and disseminated quartz with H 2 O-NaCl FIAs that formed at minimum temperature and pressures of 156° to 161°C and 5 to 6 bar during event 5 (Sb). Stibnite hosts H 2 O-NaCl FIAs trapped at minimum temperatures and pressures of 150° to 189°C and 5 to 12 bar that are similar to those of Q3-hosted FIAs. The quartz paragenetic history in the district follows a progressive temporal path from Tienriched quartz deposited by a relatively deep and higher temperature aqueous-carbonic fluid to a Li, Al, and Sb enriched quartz precipitated from a lower temperature aqueous fluid. Gases in fluid inclusion extracts from ore and gangue minerals were analyzed by mass spectrometry. Noble gas isotope analysis of fluid inclusion extracts revealed three signatures. Pre-ore Qi has R/R A (the isotopic ratio of the sample 3 He/ 4 He to atmospheric 3 He/ 4 He (1.384 × 10 −6 )) values that reflect the composition of the crustal melt-derived Atlanta lobe of the Idaho batholith. Quartz (Q1) and auriferous arsenian pyrite of hydrothermal event 2 have 20 Ne/ 4 He and R/R A values that plot along the air-crust mixing line, and these gases were likely introduced by metamorphic fluids derived from metasedimentary rocks. Stibnite with associated quartz (Q3 ± Q2) have 20 Ne/ 4 He and R/R A values that extend from the air-crust mixing line to the air-mantle mixing line, showing a shift from a crustal signature to an overprinting mantle signature. Late calcite has 20 Ne/ 4 He and R/R A values that extend from air toward the mantle end member, which suggests that magmatic volatiles condensed into meteoric groundwater late in the paragenesis. A mantle volatile source is also supported by high 20 Ne/ 22 Ne ratios. The Stibnite-Yellow Pine district is similar to other Au-W-Sb districts around the world in ore fluid chemistries, with late-stage stibnite being a product of cooling. The fluid pressure-temperature-composition (P-T-X) estimates and the crustal source of He during hydrothermal event 2 gold mineralization are characteristic of orogenic Au deposits, and the observed inclusion reequilibration textures indicate that trapped fluid inclusions were deformed during transitions between the brittle-ductile environment. Scheelite was deposited during event 3 with Q2 quartz and is overgrown by Q3 quartz and stibnite. Our interpretation of the quartz texture, chemistry, and fluid inclusion P-T-X data suggest that Au, W, and Sb mineralization occurred as hydrothermal fluids evolved from H 2 O-NaCl-CO 2 at >300°C and depths of ~4 to 6 km near the ductile to brittle transition to H 2 O-NaCl at ~150°C and epithermal depths as the Idaho batholith was exhumed. Geochronology indicates that from the Late Cretaceous to early Eocene, overprinting hydrothermal events formed deep orogenic Au, intermediate W, and shallow epithermal Au-Ag and Sb. Without comprehensive geochronologic constraints, our fluid inclusion data and textural observations could be interpreted as a single evolving hydrothermal system, as has been done in many other mining districts with similar mineralization.
Idaho↗
Germanium redistribution during weathering of Zn mine wastes: Implications for environmental mobility and recovery of a critical mineral
Germanium (Ge) is a metal used in emerging energy technologies, communications, and defense, and has been deemed critical by the United States due to its essential applications and scarce supply. Germanium is recovered as a byproduct of zinc (Zn) sulfides, and mining and processing of these materials lead to waste that could act both as a source of extractable Ge and a source for exposure to humans and ecosystems. Yet the distribution, speciation, and mineral hosts of Ge in mining-impacted areas are poorly understood. The Tar Creek Superfund Site, a former Zn mining area and Ge producer, is a natural laboratory to understand the environmental behavior and economic implications of Ge in mine wastes. We studied the distribution and behavior of Ge in solid wastes at the Tar Creek Superfund Site using bulk and microanalytical techniques. In wastes at this site we find that Ge has been redistributed from its original host, sphalerite (ZnS), to the fine-grained weathering product hemimorphite (Zn4Si2O7(OH)2·H2O), which impacts germanium's mobility, bioaccessibility, and potential for recovery. We provide chemical and mineralogical evidence of this redistribution, along with an evaluation of the oxidation state and molecular-scale substitution of Ge into sphalerite, hemimorphite, and quartz. Geochemical modeling shows that hemimorphite is more stable than sphalerite in waste piles and provides a stable secondary repository for Ge. However, hemimorphite is fine-grained, and if ingested or inhaled is readily soluble, with the potential to release Ge. Lastly, we discuss other sites internationally where similar behavior may be important. This study shows that weathering can have a significant impact on the distribution, speciation, and mineral hosts of Ge in mine wastes; directly influence mobilization from waste piles and subsequent availability to humans and ecosystems; and dictate metallurgical strategies to target Ge for recovery.
Oklahoma↗
Environmental characteristics and utilization potential of metallurgical slag
Slag, an abundant byproduct from the pyrometallurgical processing of ores, can be an environmental liability or a valuable resource. The most common environmental impact of slag is from the leaching of potentially toxic elements, acidity, or alkalinity that may impact nearby soils and surface water and groundwater. Factors that influence its environmental behavior include physical characteristics, such as grain size and porosity, chemical composition with some slag being enriched in certain elements, the mineralogy and partitioning of elements in more or less reactive phases, water-slag interactions, and site conditions. Many of these same factors also influence its resource potential. For example, crystalline ferrous slag is most commonly used as construction aggregate, whereas glassy (i.e., granulated) slag is used in cement. Also, the calcium minerals found in ferrous slag result in useful applications in water treatment. In contrast, the high trace-element content of some base-metal slags makes the slags economically attractive for extraction of residual elements. An evaluation tool is used to help categorize a particular slag as an environmental hazard or valuable byproduct. Results for one type of slag, legacy steelmaking slag from the Chicago area in the USA, suggest the material has potential to be used for treating phosphate-rich or acidic waters; however, the pH and trace-element content of resulting solutions may warrant further examination.
Book chapter↗
Aeromagnetic map of the Powderhorn wilderness study area and Cannibal Plateau Roadless Area, Gunnison and Hinsdale counties, Colorado
The Powderhorn Wilderness Study Area (51,000 acres or 20,640 hectares) and the contiguous Cannibal Plateau Roadless Area (29,500 acres or 11,959 hectares) are on the Gunnison County-Hinsdale County boundary, approximately 50mi (80 km) southwest of Gunnison and a few miles east of Lake City, Colo. Part of the area has been known as the Powderhorn Primitive Area. The mineral resource potential of the study area has been assessed by the U.S. Geological Survey and the U.S. Bureau of Mines; this assessment involved, besides the geologic study and economic appraisal (Sharp and others, 1983), a geophysical survey (this report) by the Geological Survey, and a geochemical survey (Sharp and Lane, 1983) by the Geological Survey and the Bureau of Mines.
Colorado↗
Geology of the Jabal Al Qarah Quadrangle, Sheet 20/43 C, Kingdom of Saudi Arabia
The Jabal al Qarah quadrangle (sheet 20/43 C) is a 30-minute quadrangle mapped at 1:100,000 scale in the southern Najd Province of Saudi Arabia. The quadrangle is located between lat 20°00'N. and 20°30'N. and long 43°00'E. and 43°30'E. It is underlain by volcanic, volcaniclastic, and plutonic rocks of late Precambrian age. Most of the quadrangle consists of a large, asymmetric gneiss dome that extends far to the north and south of the quadrangle. Parallel with the eastern border of the quadrangle, part of the extensive, serpentinite-bearing, Nabitah fault zone probably represents a major suture between crust of Jiddah age to the west and younger crust of Halaban age to the east. An excellent section of the Halaban-age crust is exposed in and adjacent to the gneiss dome. At the eroded top of the section to the east, calc-alkalic volcanic rocks of the Halaban group are dominantly andesite but range from basalt to dacite. Beneath the volcanic rocks, comagmatic, subvolcanic plutonic rocks include predominantly diorites but range from gabbro to trondhjemite. These rocks were formed during island-arc volcanism and plutonism from about 780 m.y. to 720(?) m.y. ago. About 725 m.y. ago this primitive crust was thickened by emplacement of large intermediate-crustal depth plutons of hornblende tonalite and hornblende granodiorite. Compressional tectonism produced folds and faults with northern trends and accompanying greenschist metamorphism. Granitic plutonism began 625 m.y. ago, perhaps in response to a major continental collision between the Halaban crust and a continental mass to the east. Granodiorite-monzogranite comprising the Wadi Musayrah batholith formed the core of the Jabal al Qarah gneiss dome as the dome rose. The low-density, intermediate-depth, plutonic rocks of the Halaban crust were converted to orthogneisses as they rose. Strong compression resulted in a large west-directed thrust, the Nabitah fault zone, containing serpentinite. Subsequently, plutons of monzogranite, syenogranite, and alkali-feldspar granite intruded the eroding crust at progressively shallower levels until about 600 m.y. ago. After this time the polymictic conglomerate of the Murdama group was deposited over the youngest granite--the alkali-feldspar granite at Jabal ash Shawhatah al Hamrah; the conglomerate was subsequently deformed. Continued compression of the now relatively thick continental crust resulted in the Najd faulting event about 570 m.y. ago. Two northwest-trending faults in the quadrangle have left-lateral displacement; one has 7 km of offset. These two faults are small but are characteristic of the large Najd fault zones farther north. Throughout the quadrangle, northwest-trending Najd fracturing was pervasive and many of these secondary fractures were filled with diabase dikes of Najd age. The diabase dikes and the deeper, non-exposed mafic plutons induced small-scale, but widespread hydrothermal convection and alteration that produced small quartz veins locally mineralized with gold. Quartz-vein gold was mined on a small scale by ancient miners in several areas. An extensive gold placer was worked about 2,600 years ago in a 50 km 2 area at Jabal Mokhyat. None of these deposits are economical by present-day standards.
Jabal Al Qarah Quadrangle↗
Mineralogy of oil shale in the upper part of the Parachute Creek member of the Green River formation in the Eastern Uinta Basin, Utah
The relative abundance and distribution of major and minor minerals have been determined by X-ray diffraction for samples of Green River Formation oil shale in three drill cores from the eastern part of the Uinta Basin, Utah. The samples in each core are from the same rock stratigraphic interval between the Curly bed and Wavy bed tuffs. This interval includes the Mahogany zone, which is the thickest and richest oil-shale unit with the greatest economic potential for extraction of oil. One core is from Naval Oil Shale Reserve No. 2, another is from Federal Prototype Oil Shale Lease Tract Ua, and the third is from an area nominated for a possible federal oil-shale in situ tract. Dolomite and quartz are generally the most abundant minerals; calcite, albite, and K-feldspar are less abundant. Minor minerals in varied amounts include illite, analcime, aragonite, and smectite. Smectite is abundant in one core and has not previously been recognized in the Mahogany zone. The presence of this mineral is important, inasmuch as it will increase retorting energy requirements. Saline minerals were not detected.
Utah↗
Research is needed to inform environmental management of hydrothermally inactive and extinct polymetallic sulfide (PMS) deposits
Polymetallic sulfide (PMS) deposits produced at hydrothermal vents in the deep sea are of potential interest to miners. Hydrothermally active sulfide ecosystems are valued for the extraordinary chemosynthetic communities that they support. Many countries, including Canada, Portugal, and the United States, protect vent ecosystems in their Exclusive Economic Zones. When hydrothermal activity ceases temporarily (dormancy) or permanently (extinction), the habitat and associated ecosystem change dramatically. Until recently, so-called “inactive sulfide” habitats, either dormant or extinct, received little attention from biologists. However, the need for environmental management of deep-sea mining places new imperatives for building scientific understanding of the structure and function of inactive PMS deposits. This paper calls for actions of the scientific community and the emergent seabed mining industry to i) undertake fundamental ecological descriptions and study of ecosystem functions and services associated with hydrothermally inactive PMS deposits, ii) evaluate potential environmental risks to ecosystems of inactive PMS deposits through research, and iii) identify environmental management needs that may enable mining of inactive PMS deposits. Mining of some extinct PMS deposits may have reduced environmental risk compared to other seabed mining activities, but this must be validated through scientific research on a case-by-case basis.
Marine Policy↗