U–Pb, Pb–Pb, and K–Ar isotopic study and petrography of uraniferous phosphate-bearing rocks in the Thelon Formation, Dubawnt Group, Northwest Territories, Canada

1989 ◽  
Vol 26 (5) ◽  
pp. 867-880 ◽  
Author(s):  
A. R. Miller ◽  
G. L. Cumming ◽  
D. Krstic
Keyword(s):  
Northwest Territories ◽  
Tectonic Setting ◽  
Uranium Mineralization ◽  
Isotopic Study ◽  
Thelon Basin ◽  
Wide Range ◽  
Minimum Age ◽  
Basal Conglomerate

The Thelon Formation, uppermost unit of the Dubawnt Group, overlies a regionally extensive paleoweathered zone developed on a wide range of lithochronological units including formations in the lower Dubawnt Group. Authigenic uraniferous phosphate minerals, fluorapatite and goyazite, cementing Thelon conglomerate–sandstone and filling fractures in the underlying paleoweathered zone, were dated in an attempt to better constrain the age of Thelon sedimentation and diagenesis. The oldest age, 1720 ± 6 Ma, derived from phosphate-cemented sediments, is interpreted as a minimum age for diagenesis and therefore brackets initial Thelon sedimentation between emplacement of fluorite-bearing granites at 1753 Ma and authigenic phosphate cementation at 1720 Ma. Additional ages of 1685 ± 4 and 1647 Ma are interpreted as remobilization or subsequent cementation events. K–Ar ages on illite, 1386 ± 37 and 1266 ± 31 Ma, from the paleoweathered zone and basal conglomerate, respectively, are significantly younger than ages derived from coexisting phosphate. These K–Ar ages record hydrothermal events that may be related to processes associated with unconformity-type uranium mineralization at approximately 1400–1300 Ma.Ages from the Thelon Basin permit geochronologic correlations with the Athabasca and Hornby basins, long correlated on the basis of similarities in sedimentation, stratigraphy, and tectonic setting.

Sources of sulphur for the Proterozoic Kiggavik uranium deposit, Nunavut, Canada

2020 ◽  
Vol 57 (11) ◽  
pp. 1312-1323
Author(s):  
Brandi M. Shabaga ◽  
Mostafa Fayek ◽  
David Quirt ◽  
Patrick Ledru
Keyword(s):  
Low Temperature ◽  
Secondary Ion Mass Spectrometry ◽  
Uranium Mineralization ◽  
Uranium Deposits ◽  
Athabasca Basin ◽  
Thelon Basin ◽  
Mass Independent Fractionation ◽  
Hydrothermal Processes ◽  
Wide Range ◽  
Secondary Ion

The Thelon Basin is temporally and spatially related to the Athabasca Basin in Saskatchewan, Canada, which hosts the highest-grade unconformity-related uranium deposits in the world. Several uranium deposits occur within the Aberdeen sub-basin of the Thelon Basin, and it has been suggested that they may also be unconformity-related deposits. However, the genesis of the deposits is still debated and the age of the uranium mineralization event remains loosely constrained. In this study, we use secondary ion mass spectrometry to measure three sulphur (S) isotopes in pyrite from the Kiggavik deposit to constrain the sources of sulphur. We use this information to determine whether these sulphides, if dated by the Re–Os method, would provide a better constraint on the timing of uranium mineralization. The Kiggavik deposit comprises three zones (Main, Centre, and East) that formed from ∼200 °C fluids at ∼1600 Ma. Non-hydrothermal pyrite and galena from all three zones have a wide range of δ34S values, from −41.2‰ to +37.4‰. The Δ33S values (>0‰) indicate recycling of mass independent fractionation sulphur, suggesting that pyrite from the Kiggavik deposit derived sulphur from the Neoarchean metagraywacke host rock. The preservation of these anomalous Δ33S values suggests that the pyrite formed from low-temperature processes rather than hydrothermal processes. Low-temperature, high-latitude fluids may have been involved in the formation of the pyrite because some of these sulphides are also associated with uranium minerals that are devoid of Pb and contain corroded calcite. Based on these data, Re–Os geochronology of these sulphides would not yield an age that would constrain the timing of hydrothermal uranium mineralization.

The petrological and geochemical study of granitoid rocks from Mashhad area, Iran: Evidence for the Late Triassic Collisional Belt Northeast of Iran

2021 ◽  
Author(s):  
Banafsheh Vahdati ◽  
Seyed Ahmad Mazaheri
Keyword(s):  
Subduction Zones ◽  
Tectonic Setting ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Late Triassic ◽  
Common Belief ◽  
Thrust Tectonics ◽  
Wide Range ◽  
Lree Enrichment ◽  
Granitoid Rocks

<p>Mashhad granitoid complex is part of the northern slope of the Binalood Structural Zone (BSZ), Northeast of Iran, which is composed of granitoids and metamorphic rocks. This research presents new petrological and geochemical whole-rock major and trace elements analyses in order to determine the origin of granitoid rocks from Mashhad area. Field and petrographic observations indicate that these granitoid rocks have a wide range of lithological compositions and they are categorized into intermediate to felsic intrusive rocks (SiO<sub>2</sub>: 57.62-74.39 Wt.%). Qartzdiorite, tonalite, granodiorite and monzogranite are common granitoids with intrusive pegmatite and aplitic dikes and veins intruding them. Based on geochemical analyses, the granitoid rocks are calc-alkaline in nature and they are mostly peraluminous. On geochemical variation diagrams (major and minor oxides versus silica) Na<sub>2</sub>O and K<sub>2</sub>O show a positive correlation with silica while Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub>, CaO, Fe<sub>2</sub>O<sub>3</sub>, and MgO show a negative trend. Therefore fractional crystallization played a considerable role in the evolution of Mashhad granitoids. Based on the spider diagrams, there are enrichments in LILE and depletion in HFSE. Low degrees of melting or crustal contamination may be responsible for LILE enrichment. Elements such as Pb, Sm, Dy and Rb are enriched, while Ba, Sr, Nd, Zr, P, Ti and Yb (in monzogranites) are all depleted. LREE enrichment and HREE depletion are observed in all samples on the Chondrite-normalized REE diagram. Similar trends may be evidence for the granitoids to have the same origin. Besides, LREE enrichment relative to HREE in some samples can indicate the presence of garnet in their source rock. Negative anomalies of Eu and Yb are observed in monzogranites. Our results show that Mashhad granitoid rocks are orogenic related and tectonic discrimination diagrams mostly indicate its syn-to-post collisional tectonic setting. No negative Nb anomaly compared with MORB seems to be an indication of non-subduction zone related magma formation. According to the theory of thrust tectonics of the Binalood region, the oceanic lithosphere of the Palo-Tethys has subducted under the Turan microplate. Since the Mashhad granitoid outcrops are settled on the Iranian plate, this is far from common belief that these granitoid rocks are related to the subduction zones and the continental arcs. The western Mashhad granitoids show more mafic characteristics and are possibly crystallized from a magma with sedimentary and igneous origin. Thus, Western granitoid outcrops in Mashhad are probably hybrid type and other granitoid rocks, S and SE Mashhad are S-type. Evidences suggest that these continental collision granitoid rocks are associated with the late stages of the collision between the Iranian and the Turan microplates during the Paleo-Tethys Ocean closure which occurred in the Late Triassic.</p>

Implications of source overcharge for prospect assessment

2015 ◽  
Vol 3 (2) ◽  
pp. T93-T107
Author(s):  
Richard S. Bishop
Keyword(s):  
Oil And Gas ◽  
Tectonic Setting ◽  
Field Studies ◽  
Fundamental Aspect ◽  
Statistical Distributions ◽  
Free Gas ◽  
Wide Range ◽  
Fault Leakage ◽  
Discrete Values ◽  
Gas Leaks

A fundamental aspect of prospect evaluation is whether the trap volume or the charge volume limits the volume of trapped hydrocarbons. Traps filled to a leak point are full traps, although I rarely describe them as such. I commonly say “full to spill” but rarely do I hear “full to a leak point.” Why not? A summary of literature from fault leakage, seeps, field studies, and theoretical source-yield calculations illustrates the implication that source overcharge (i.e., the charge exceeding the trap volume) occurs in basins that vary widely in age and tectonic setting. Perhaps surprisingly, this is true for oil and gas fields and for a wide range of source rock quality from rich to lean. The most obvious implication from source overcharge is that the volume of trapped hydrocarbons is limited by the absolute volume of the trap. Less obvious is the recognition that if oil and free gas are available to a trap, gas will displace the oil. Thus, if there are no gas leaks, the trap will contain only gas. If there is preferential leakage of gas, then the trap may contain a gas cap and an oil leg. Furthermore, the occurrence of oils saturated with gas likely indicates selective leakage of free gas. Hydrocarbon contacts (whether oil-water, gas-oil, or gas-water) are interpreted to define the leak or spill point or seal capacity. Thus, instead of using continuous statistical distributions to describe all elements of traps, some elements such as area are more appropriately described as discrete values and a full assessment may be a combination of discrete plus continuous statistical distributions. Overcharge may also lead to different interpretations of risk. Interpreting the trap volume, particularly with leak points, leads to the notion that risk evaluation might consider the number and quality of potential leak points.

Polyphase tectonothermal events recorded in metamorphic basement rocks from the northern Altyn Tagh, southeastern Tarim Craton

2020 ◽  
Author(s):  
Zhongmei Wang ◽  
Chunming Han ◽  
Wenjiao Xiao ◽  
Patrick Asamoah Sakyi
Keyword(s):  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Mineral Chemistry ◽  
Metasedimentary Rocks ◽  
Exposed Rock ◽  
Altyn Tagh ◽  
Argillaceous Rocks ◽  
Southeastern Margin ◽  
Minimum Age ◽  
Tarim Craton

<p>  Paleoproterozoic is a pivotal time for understanding the geochronological framework of the Tarim Craton. Located on the southeastern margin of the Tarim Craton, the northern Altyn Tagh is the main exposed region for Paleoproterozoic magmatic-metamorphic rocks. These rocks are diverse, diachronous and modified by multiple magmatic and/or metamorphic events. In this study, we performed systematic analyses on the amphibolite, felsic gneisses, and metasedimentary rocks in the Aketashitage area, southeastern Tarim Craton, including petrography, mineral chemistry, and whole-rock geochemistry, as well as in-situ zircon U-Pb ages and Hf isotopes, to examine the Paleoproterozoic magmatic-metamorphic events in the northern Altyn Tagh. Geochemically, the amphibolite and felsic gneisses in the Aketashitage area seemingly represent the typical bimodal associations of mafic and acidic volcanic rocks. In addition, the felsic gneisses are characterized by high Sr and low Y contents, with high Sr/Y and La<sub>N</sub>/Yb<sub>N</sub> ratios, and indistinctive Eu anomalies, closely resembling high-SiO<sub>2</sub> adakites derived from subducted basaltic slab-melt. The palimpsest textures and geochemical features of the Aketashitage metasedimentary rocks suggest that their protoliths are argillaceous rocks. The amphibolite has a metamorphic age of 1.96 Ga, and the felsic gneisses yield crystallization ages of 2.54-2.52 Ga. For the metasedimentary rocks, the major age peaks of 2.72 Ga, 2.05 Ga and 1.97 Ga are consistent with the magmatic and/or metamorphic events in the study area. The minimum age peak suggests that the depositional age is no earlier than 1.97 Ga. The geochemical and geochronological evidences documented by the exposed rock associations in the Aketashitage area suggest a subduction-related tectonic setting in the Paleoproterozoic. Our new data combined with the previous studies indicate that the Paleoproterozoic magmatism and metamorphism in the northern Altyn Tagh area are nearly synchronous, and both are likely related to oceanic subduction.</p>

Characteristics of nest trees and nest hollows used by the forest red-tailed black cockatoo (Calyptorhynchus banksii naso) in south-west Western Australia: comments on Johnstone et al. (2013)

2015 ◽  
Vol 21 (2) ◽  
pp. 133
Author(s):  
K. R. Whitford ◽  
D. Wiseman ◽  
W. L. McCaw ◽  
F. J. Bradshaw
Keyword(s):  
Western Australia ◽  
Timber Harvesting ◽  
Substantial Contribution ◽  
Partial Cutting ◽  
Eucalyptus Marginata ◽  
South West ◽  
Size And Age Structure ◽  
Wide Range ◽  
Minimum Age ◽  
Management Context

Johnstone et al. (2013) (Pacific Conservation Biology 19, 122–141) make a substantial contribution to the knowledge of the forest red-tailed black cockatoo (Calyptorhynchus banksii naso) (FRTBC), presenting data on nest hollows and nest tree attributes. They discuss the threats to the current and future breeding hollows and conclude that ‘we are facing a major crisis in southern forests’. Although there are sound reasons for concern over the conservation of cockatoo species, the imminence of a crisis is not established by the data presented. We provide spatial and management context and present data relevant to discussion of threats to FRTBC hollows in south-west Western Australia. The primary strategy for providing habitat across the publicly owned forests is reservation, which formally excludes timber harvesting from more than 50% (1.3 million ha) of the forest, informally protects a further 11%, and protects habitat trees within harvested areas. Timber harvesting in these forests generally involves partial cutting, which retains trees of a wide range of size and age classes. A realistic minimum age for trees bearing hollows used by FRTBC in the jarrah (Eucalyptus marginata) forest is ~120–150 years (trees diameters of 50–60 cm), well below the 209 years highlighted by Johnstone et al. (2013). Most nest hollows occur in intermediate-sized trees. Clustering of FRTBC nest trees was not demonstrated in their data but is worthy of further investigation. Improved estimates of nest tree availability and loss would provide perspective on the threats to FRTBC, as would knowledge of population size and age structure of the FRTBC. The protection of known nest trees and control of feral competitors, where possible, would benefit FRTBC.

Amino Acid Geochemistry of Fossil Bones from the Rancho La Brea Asphalt Deposit, California

1982 ◽  
Vol 18 (2) ◽  
pp. 174-183 ◽  
Author(s):  
Mark A. S. McMenamin ◽  
David J. Blunt ◽  
Keith A. Kvenvolden ◽  
Scott E. Miller ◽  
Leslie F. Marcus ◽  
...  
Keyword(s):  
Amino Acids ◽  
Los Angeles ◽  
Aspartic Acid ◽  
Equivalent Age ◽  
Aspartic Acid Racemization ◽  
Wide Range ◽  
Fossil Bones ◽  
Minimum Age ◽  
Rancho La Brea ◽  
Age Estimates

AbstractLow aspartic acid d:l ratios and modern collagenlike concentration values indicate that amino acids in bones from the Rancho La Brea asphalt deposit, Los Angeles, California are better preserved than amino acids in bones of equivalent age that have not been preserved in asphalt. Amino acids were recovered from 10 Rancho La Brea bone samples which range in age from less than 200 to greater than 36,000 yr. The calibrated rates of aspartic acid racemization range from 2.1 to 5.0 × 10−6yr−1. Although this wide range of rate constants decreases the level of confidence for age estimates, use of the larger rate constant of 5.0 × 10−6yr−1provides minimum age estimates which fit the known stratigraphic and chronologic records of the Rancho La Brea deposits.

Provenance of Paleozoic sedimentary rocks in the Canadian Cordilleran miogeocline: a Nd isotopic study

1997 ◽  
Vol 34 (12) ◽  
pp. 1603-1618 ◽  
Author(s):  
Carmala N. Garzione ◽  
P. Jonathan Patchett ◽  
Gerald M. Ross ◽  
JoAnne Nelson
Keyword(s):  
British Columbia ◽  
Northwest Territories ◽  
Middle Devonian ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Canadian Shield ◽  
Isotopic Study ◽  
Middle Ordovician ◽  
Southern Alberta ◽  
T Values

Nd isotopes and trace elements in sedimentary rocks of the Yukon, the Northwest Territories, and northern British Columbia are used to examine the source of sediments in the Canadian Cordilleran miogeocline. Previous Nd isotope studies in southern Alberta demonstrated that strata of Neoproterozoic to Late Ordovician age were derived from Archean and Proterozoic Canadian Shield sources, whereas by the Late Devonian, a shift of 6 εNd units to younger crustal sources (εNd (T) = −6 to −9) had occurred. In this study, we found that the shift to younger crustal Nd isotopic signatures in the Yukon and Northwest Territories occurred much earlier than in southern Alberta. Cambrian and older strata have εNd(T) values of −10.0 to −21.1, consistent with derivation from Canadian Shield sources. Lower Ordovician through Permian strata in the Yukon and Northwest Territories, including the Innuitian-derived Imperial Assemblage, have εNd(T) values of −5 to −11.4. In northern British Columbia, the shift to a younger source reflects a wider range of εNd(T) values, from -−8.7 to −14.6 in Middle Ordovician through Middle Devonian strata, suggesting continued input from Canadian Shield sources. By the Middle Devonian, a complete shift to younger crustal signatures (εNd(T) = −5.9 to −10.5) had occurred in northern British Columbia. Several sources for the more juvenile sediments include (1) a mixture of locally erupted volcanic rocks with Canadian Shield sources, (2) a Grenville source, and (3) an Innuitian source. We propose that Ordovician to Lower Devonian strata were derived from a mixture of locally erupted, juvenile volcanics and pre-Cambrian Canadian Shield sources, and post-Middle Devonian strata were sourced from the Innuitian orogen in the Canadian Arctic.

Hydrogeology, sequence stratigraphy and diagenesis in the Paleoproterozoic western Thelon Basin: Influences on unconformity-related uranium mineralization

2011 ◽  
Vol 187 (3-4) ◽  
pp. 293-312 ◽  
Author(s):  
Steve R. Beyer ◽  
Eric E. Hiatt ◽  
Kurt Kyser ◽  
Robert W. Dalrymple ◽  
Chris Pettman
Keyword(s):  
Sequence Stratigraphy ◽  
Uranium Mineralization ◽  
Thelon Basin
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