Subjacent crustal sources of sulfur and lead in eastern Great Basin metal deposits

The thick (≤8 km), regionally extensive section of Neoproterozoic siliciclastic strata (terrigenous detrital succession, TDS) in the central and eastern Great Basin contains sedimentary pyrite characterized by mostly high δ 34 S values (−11.6 to 40.8‰, >70% exceed 10‰; 51 analyses) derived from reduction of seawater sulfate, and by markedly radiogenic Pb isotopes ( 207 Pb/ 204 Pb >19.2; 15 analyses) acquired from clastic detritus eroded from Precambrian cratonal rocks to the east-southeast. In the overlying Paleozoic section, Pb-Zn-Cu-Ag-Au deposits associated with Jurassic, Cretaceous, and Tertiary granitic intrusions (intrusion-related metal deposits) contain galena and other sulfide minerals with S and Pb isotope compositions similar to those of TDS sedimentary pyrite, consistent with derivation of deposit S and Pb from TDS pyrite. Minor element abundances in TDS pyrite (e.g., Pb, Zn, Cu, Ag, and Au) compared to sedimentary and hydrothermal pyrite elsewhere are not noticeably elevated, implying that enrichment in source minerals is not a precondition for intrusion-related metal deposits. Three mechanisms for transferring components of TDS sedimentary pyrite to intrusion-related metal deposits are qualitatively evaluated. One mechanism involves (1) decomposition of TDS pyrite in thermal aureoles of intruding magmas, and (2) aqueous transport and precipitation in thermal or fluid mixing gradients of isotopically heavy S, radiogenic Pb, and possibly other sedimentary pyrite and detrital mineral components, as sulfide minerals in intrusion-related metal deposits. A second mechanism invokes mixing and S isotope exchange in thermal aureoles of Pb and S exsolved from magma and derived from decomposition of sedimentary pyrite. A third mechanism entails melting of TDS strata or assimilation of TDS strata by crustal or mantle magmas. TDS-derived or assimilated magmas ascend, decompress, and exsolve a mixture of TDS volatiles, including isotopically heavy S and radiogenic Pb from sedimentary pyrite, and volatiles acquired from deeper crustal or mantle sources. In the central and eastern Great Basin, the wide distribution and high density of small to mid-sized vein, replacement, and skarn intrusion-related metal deposits in lower Paleozoic rocks that contain TDS sedimentary pyrite S and Pb reflect (1) prolific Jurassic, Cretaceous, and Tertiary magmatism, (2) a regional, substrate reservoir of S and Pb in permeable and homogeneous siliciclastic strata, and (3) relatively small scale concentration of substrate and magmatic components. Large intrusion-related metal deposits in the central and eastern Great Basin acquired S and most Pb from thicker lithospheric sections.

Lower Paleozoic or Proterozoic basement rocks occur in windows and thrust plates in several areas of the Brooks Range. Uranium-lead radiometric analyses of highly metamorphosed rocks from the Baird Mountains and Ernie Lake area have yielded Proterozoic ages. Structural, stratigraphic, petrologic, and isotopic evidence exists for Proterozoic(?) rocks in the schist belt; around the Chandalar, Arrigetch, and Igikpak plutons; and in the Cosmos Hills window. Fossiliferous, lower Paleozoic, low-grade metasedimentary rocks occur in the Romanzof Mountains, Doonerak window, and Baird Mountains, and may also surround the Chandalar plutons. Locally, the Lower Paleozoic rocks are unconformably overlain by Devonian to Mississippian metasediments and may stratigraphically overlie older higher grade metamorphic rocks. Similarities in the stratigraphic settings and lithologies and in fossil ages and affinities allow correlation of the lower Paleozoic rocks in the southern Brooks Range. Correlation of lower Paleozoic rocks exposed beneath the Endicott allochthon at the Doonerak fenster with coeval rocks in an overlying thrust plate to the south at Snowden Mountain is especially significant. A west-trending thrust fault, which is rooted in lower Paleozoic basement, along the north side of Snowden Mountain is postulated to account for these relationships. Apparently, the Endicott allochthon roots beneath the Snowden Mountain thrust fault. Evidence from conodont samples currently being studied by A. Harris may bear on the extent of the lower Paleozoic rocks in the upper plate of the Snowden Mountain thrust and in the Chandalar area. End_of_Article - Last_Page 661------------

Sources of anthropogenic lead in sediments from an artificial lake in Brasília–central Brazil

Hydrocarbon migration patterns and pathways were studied on the basis of three-dimensional seismic interpretation, drilling, geochemistry, production performance, and other data. Using these findings, the main factors controlling hydrocarbon migration and accumulation in the Lower Paleozoic carbonate rocks of the Tazhong Uplift were discussed. The spatiotemporal relationship between the hydrocarbon kitchens and pathway systems of the Tazhong Uplift and the spatial pattern of pathway systems were considered the main factors causing differences in hydrocarbon enrichment. Results also revealed that the Lower Paleozoic carbonates of the Tazhong Uplift have two hydrocarbon accumulation systems (inside and outside the source rocks). For the accumulation system within the source rocks, hydrocarbon migration and enrichment are vertically differentiated. Middle Cambrian gypsum salt rocks serve as the boundary, above which thrust and strike-slip faults mainly allow vertical transport of hydrocarbons. A multistage superposition pattern of strike-slip faults controls the differences in hydrocarbon enrichment on the periphery of the fault zone. Beneath the gypsum-salt rocks, hydrocarbon migration and enrichment is controlled by the topography of paleostructures and paleogeomorphology. For the hydrocarbon accumulation system outside the source rocks, hydrocarbon migration and enrichment are restricted by the layered pathway system, and the topography of the paleostructures and paleogeomorphology is the key factor controlling hydrocarbon enrichment. The Tazhong No. 1 Fault is the main vertical pathway system in the area underlain by no source rocks, and hydrocarbons are enriched at the periphery of the Middle-Lower Cambrian and No. 1 Fault Zone.

Summary This study implements 2D basin modeling and petroleum system assessment in two Caribbean basins to test new geological models recently proposed. The basin modeling integrates existing and new geochemical data to evaluate the hydrocarbon potential of these basins. The southern Llanos basin contains rocks with two different degrees of thermal maturity. Locally, the hydrocarbon generation for possible Lower Paleozoic source rocks started in the Silurian and by the Permian they had reached transformation ratio of 100%. The petroleum expelled was likely accumulated in pre-existing structures that were later uplifted up to 2200m, inducing destruction of the traps and losses of hydrocarbons. Towards the southern area, Paleozoic rocks are less thermally matured and may preserve higher hydrocarbon potential. Cretaceous/Cenozoic rocks are immature for hydrocarbon generation. Possible Upper Cretaceous source rocks located on buried half-graben structures within the Tobago basin are suggested to have started to expel hydrocarbons in the Oligocene and have reached transformation ratio of 70%. The petroleum expelled during the Oligocene-Eocene, was likely accumulated in deeply-buried thrusts formed during the early development of the Barbados accretionary prism, while later structures were charged by remigration from the older structures and younger hydrocarbons. Paleogene source rocks are starting to generate hydrocarbons.

Organic geochemical properties of the oil produced from the Lower Cretaceous O sandstone on the eastern flank of the Denver basin indicate that this oil has been derived from a different source rock than other Cretaceous oils in the basin. O sandstone oil is characterized by low pristane/phytane ratio, high isoprenoid/n-alkane ratios, high asphaltene content, high sulfur content, and slight predominance of even-carbon numbered n-alkanes in the C25+ fraction. These features are evidence of a Paleozoic source and indicate a carbonate rock is the likely source. Preliminary source rock evaluation and correlation data suggest that calcareous black shales and marls of Middle Pennsylvanian (Desmoinesian) age are the source of the O sandstone oil. This is the first rep rted occurrence of oil from Paleozoic source rocks in a Cretaceous reservoir in the Denver basin. Two important implications for further exploration are evident if vertical migration from Paleozoic source rocks has occurred. First, Paleozoic rocks of Middle Pennsylvanian age or younger are potential exploration objectives where reservoirs and suitable trapping mechanisms are present. Second, future exploration for oil in the O sandstone and upper Paleozoic rocks should consider stratigraphic relationships between possible source and reservoir rocks and possible migration conduits.

The Lower Triassic rocks of the eastern Great Basin provide a record of the last marine deposition in the Cordilleran miogeosyncline. Sections are present in eastern Nevada, particularly in Elko County, and in the northwestern Utah. Most of the eastern Great Basin sections can be divided into (1) a lower shaly limestone, (2) the Meekoceras limestone zone, (3) an upper shaly limestone, and (4) an upper thick-bedded limestone. Thicknesses range from 700 to 3,000 feet. Redbeds are present only in the lower part of the western Utah sections and above the uppermost Triassic limestones near Currie. The Meekoceras zone contains many ammonoids, nautiloids, and conodonts. Pelecypods, gastropods, brachiopods, echinoderms, crinoids, foraminifers, and fish remains occur in beds above the Meekoceras interval. The Triassic rests unconformably on Permian rocks throughout the area of study, but no angular discordance was noted. The uppermost Triassic beds are overlain by Tertiary or Recent material. Age determination for the Triassic sections is based on the fossils of the Meekoceras zone which occurs near the base and represents middle Scythic of the European standard. Correlation with adjacent sections in Idaho, Utah, and western Nevada indicates that equivalents of additional Lower Triassic zones are probably present in the eastern Great Basin. Clastics above marine limestone in the Currie area may be Middle Triassic. Names for stratigraphic units have been established in adjacent areas. The Candelaria, Tobin, China Mountain, and Dixie Valley formations of western Nevada and the Moenkopi, Dinwoody, and Thaynes formations of Utah and Idaho can be correlated with the eastern Great Basin Triassic. Early Triassic seas invaded the northeastern Great Basin from Idaho and transgressed Nevada from east to west. Marine connections with the eugeosynclinal part were probably through California into southern Nevada. As the rate of subsidence varied in the miogeosyncline, marine tongues extended over the more stable craton toward the east. Seas were not uniformly present over western Utah and eastern Nevada and in northeastern Nevada a high area shed coarse detritus into the Lower Triassic sea. Redbeds accumulated in western Utah during early Triassic time; the source for this material was probably the Nye-Lincoln geanticline, which extended from southern California to the vicinity of Ely, Nevada. During the Middle Triassic, this feature was widened and fused to the craton, occupying t e position of the former geosyncline.

Isotopic signatures suggest important contributions from recycled gasoline, road dust and non-exhaust traffic sources for copper, zinc and lead in PM10 in London, United Kingdom

Hydrogeochemical and geostatistical analyses were conducted to evaluate natural and anthropogenic effects using stream water data of Southeastern Korea acquired through the Hydrogeochemical Survey Program of the Korea Institute of Geoscience & Mineral Resources. The results of a variographic analysis of the spatial structure of stream water quality show that the semivarigrams of Ca, Mg, and HCO3 have similar patterns and regional distributions, reflecting the same geogenic source of Paleozoic, Tertiary, and Cretaceous sedimentary rocks. Although Ca and Mg originated from Paleozoic sedimentary rocks, the distribution of Mg is significantly different from that of Ca due to the presence of dolomite in northeastern area of Korea, which enhances the Mg concentration in stream water. Studies of mineralization and acid mine drainage resulting from previous mining activities reveal a high Ba in sedimentary rock from of Kyongsang basin, as well as anomalous concentration of Al, Fe, and SO4 in the Ogcheon and Tabaeksan mineralization areas. Saturation indices of barite determined using average Ba and SO4 concentrations in stream water suggest the existence of barite mineralization deposits in sedimentary rock of Kyongsang Group. Na, Cl, K, NO3, and Cl, exhibit effects of anthropogenic and marine sources in the stream water, with increasing values near residential, agricultural, and coastal areas. Cokriging analyses employing Ca-HCO3, Ca-Sr, Ba-SO4, and Na-Cl also revealed the nature of bedrock geology, mineralization, and anthropogenic and marine sources.

The Huogeqi orefield located on the northern side of Mt. Langshan, Inner Mongolia occurs in the Middle Proterozoic Langshan Group metamorphic rocks, and the orebodies are stratiform. In the past twenty years, many Chinese geologists have conducted researches on the Huogeqi Cu-Pb-Zn deposit, but there has been still a controversy on its origin. Some advocate that the deposit is of sedimentary-metamorphic reworking origin, some hold that it is of sea-floor SEDEX origin, and others have a preference for magmatic superimposition origin. The crux of the controversy is that there is no common understanding about the source of ore-forming materials. In this paper, the Pb isotopic compositions of regional Achaean-Early Proterozoic basement rocks, various types of sedimentary-metamorphic rocks and volcanic rocks in the mining district, Late Proterozoic and Hercynian magmatic rocks are introduced and compared with the ore-lead composition, so as to constrain the source of the ore lead. The result indicates that (1) sulfides in the ores have homogeneous Pb isotopic compositions, showing a narrow variation range. Their 206Pb/204Pb ratios are within a range of 17.027–17.317; 207Pb/204Pb ratios, 15.451–15.786 and 208Pb/204Pb ratios, 36.747–37.669; (2) the Pb isotopic compositions of the regional Achaean-Early Proterozoic basement rocks are characteristic of the old Pb isotopic composition at the early-stage evolution of the Earth, which varies over a wider range, reflecting significant differences in Pb isotopic compositions of the ores. All this indicates that the source of ore lead has no bearing on the basement rocks; (3) the sedimentary-metamorphic rocks in the mining district are characterized by highly variable and more radiogenic Pb isotopic compositions and their Pb isotopic ratios are obviously higher than those of ores, demonstrating that ore lead did not result from metamorphic reworking of these rocks; (4) Pb isotopic compositions of Late Proterozoic diorite-gabbro and Hercynian granite are higher than those of ores. Meanwhile, the Pb isotopic compositions of sulfides in the small-sized strata-penetrating mineralized veinlets formed at later stages are completely consistent with that of sulfides in stratiform-banded ores, suggesting that these veinlets are the product of autochthonous reworking of the stratiform-banded ores during the period of metamorphism and the late magmatic superimposition-mineralization can be excluded; (5) amphibolite, whose protolith is basic volcanic rocks, has the same Pb isotopic compositions as ores, implying that ore lead was derived probably from basic volcanism. So, the source of ore-forming materials for the Huogeqi deposit is like that of the volcanic massive sulfide (VMS) deposits. However, the orebodies do not occur directly within the volcanic rocks, and instead they overlie the volcanic rocks, showing some differences from those typical VMS-type deposits.

The South American Global Geoscience Transect 7 is located in northern Argentina and traverses, from west to east, the Cordillera Frontal, Puna, Sierras de Famatina, Sierras Pampeanas, and Llanura Chaco Pampeana. Cenozoic stratovolcanoes that intrude Lower Paleozoic slates and Upper Paleozoic continental sedimentary rocks constitute the Cordillera Frontal. Upper Precambrian to lower Paleozoic metamorphie and sedimentary rocks intruded by Paleozoic granitoids comprise the Sierras de Famatina and Sierras Pampeanas. Restricted outcrops of Ordovician volcanic rock also appear in the Sierras de Famatina. Upper Paleozoic, Mesozoic, and Cenozoic continental deposits unconformably overlay the lower Paleozoic units. Tilted blocks bounded by lystric reverse faults that have formed in response to subduction of the Nazca plate constitute the main structure of the three ranges. Detailed studies of kinematic; markers from mylonitic belts within Paleozoic igneous and metamorphie basement indicate shortening and overthrusting of the Sierras Pampeanas onto the eastern border of the Sierras de Famatina. Quaternary sediments cover the Llanura Chaco Pampeana that extends to the east of 65° W. Magnetotelluric deep soundings were done from 1980 to 1993, between 65° and 68° W. The results of these soundings suggest a conductive layer (electrical resistivity ∼1 ohmm) at depths ranging from 8 to 25 km. Saline fluids produced where there is a large amount of free water released by metamorphie reactions have been proposed as an explanation for lower-crustal conductive anomalies. Beginning 1987, new gravimetric studies were performed between 63° and 68° W. The Bouguer anomaly map incorporates preexisting and new data (more than 700 gravity observations). The gravity field drops from −0.5 mGal at 64° W in the east to −280 mGal at 68° W and reaches nearly −400 mGal to the west in the Chilean part (˜69° W) at latitude 28° S. This regional low is related to crustal thickening within the Cordillera de los Andes. Active seismicity recorded during 1984-1994 defines part of the Benioff zone at depth.

Compound-specific C- and H-isotope compositions of enclosed organic matter in carbonate rocks: Implications for source identification of sedimentary organic matter and paleoenvironmental reconstruction

The lack of production in the Marfa basin remains an enigma. Although covered with approximately 3,000 ft of thick volcanics, the basin has Paleozoic stratigraphy and lithologies similar to the prolific Delaware basin to the east. In a geologic and geophysical review, we analyzed the overall hydrocarbon potential for this basin. The lower Paleozoic (Cambrian through Devonian) rocks, which are conducive to hydrocarbon generation in other Permian basins, have many undrilled structures, as revealed by seismic mapping, but have also pervasive fresh water and dead oil. Several fault systems are mapped on the surface. We believe that the rocks were uplifted in Late Mississippian and Pennsylvanian time and in certain areas were exposed to meteoric water. Hydrocarbons leaked out along with induction of fresh water into the formations. Recharge areas have been identified from isopach maps. In certain parts, the lower Paleozoic rocks are overmature and offer further obstacles to exploration. During the Early Permian, arkosic sediments were deposited in a rapidly subsiding east-west graben. Tilted to the south, the graben accumulated as much as approximately 9,000 ft of Lower Permian sediments that have occasional hydrocarbon shows. Small stratigraphic traps due to pinchouts, truncations, and facies changes are to be expected in these rocks. Possible reef growths in the Late Permian offer further opportunities for trap development. The rocks were also exposed to meteoric water during nondeposition in the Triassic, Jurassic, and post-Cretaceous periods. However, the subtle Permian traps, being small, could have escaped destruction and freshwater flushing and thus might offer some potential for future exploration. End_of_Article - Last_Page 141------------

The Powder River basin is one of the most actively explored Rocky Mountain basins for hydrocarbons, yet the lower Paleozoic (Cambrian through Mississippian) rocks of this interval remain little studied. As a part of a program studying the evolution of sedimentary basins, approximately 3200 km of cross section, based on more than 50 combined geophysical and lithologic logs, have been constructed covering an area of about 200,000 km/sup 2/. The present-day basin is a Cenozoic structural feature located between the stable interior of the North American craton and the Cordilleran orogenic belt. At various times during the early Paleozoic, the basin area was not distinguishable from either the stable craton, the Williston basin, the Central Montana trough, or the Cordilleran miogeocline. Both deposition and preservation in the basin have been greatly influenced by the relative uplift of the Transcontinental arch. Shows of oil and dead oil in well cuttings confirm that hydrocarbons have migrated through at least parts of the basin's lower Paleozoic carbonate section. These rocks may have been conduits for long-distance migration of hydrocarbons as early as Late Cretaceous, based on (1) the probable timing of thermal maturation of hydrocarbon-source rocks within the basin area and to themore » west, (2) the timing of Laramide structural events, (3) the discontinuous nature of the reservoirs in the overlying, highly productive Pennsylvanian-Permian Minnelusa Formation, and (4) the under-pressuring observed in some Minnelusa oil fields. Vertical migration into the overlying reservoirs could have been through deep fractures within the basin, represented by major lineament systems. Moreover, the lower Paleozoic rocks themselves may also be hydrocarbon reservoirs.« less

Research Article| May 01, 1984 Relationship of late Quaternary fault scarps to subjacent faults, eastern Great Basin, Utah Anthony J. Crone; Anthony J. Crone 1U.S. Geological Survey, Box 25046, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Samuel T. Harding Samuel T. Harding 1U.S. Geological Survey, Box 25046, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information Anthony J. Crone 1U.S. Geological Survey, Box 25046, Denver, Colorado 80225 Samuel T. Harding 1U.S. Geological Survey, Box 25046, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1984) 12 (5): 292–295. https://doi.org/10.1130/0091-7613(1984)12<292:ROLQFS>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Anthony J. Crone, Samuel T. Harding; Relationship of late Quaternary fault scarps to subjacent faults, eastern Great Basin, Utah. Geology 1984;; 12 (5): 292–295. doi: https://doi.org/10.1130/0091-7613(1984)12<292:ROLQFS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract High-resolution seismic reflection profiles in the Sevier Desert basin in western Utah help clarify the relationship between some late Quaternary fault scarps and subjacent faults. A profile crossing the Clear Lake fault confirms that Holocene(?) displacement has occurred on a high-angle normal fault that is directly connected to the Sevier Desert detachment. If detachment faults can act as seismogenic source zones, then the young movement on the normal fault suggests that the Sevier Desert detachment may be unstable and perhaps the source of future earthquakes. A swarm of late Quaternary scarps near the Drum Mountains overlies a network of steep faults in competent rock that have had recurrent movement. Many subsurface faults are not associated with scarps, suggesting that selected faults ruptured during the last episode of surface faulting. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.