Sm–Nd fluorite dating of Proterozoic low-sulfidation epithermal Au–Ag deposits and U–Pb zircon dating of host rocks at Mallery Lake, Nunavut, Canada

2003 ◽  
Vol 40 (12) ◽  
pp. 1789-1804 ◽  
Author(s):  
William A Turner ◽  
Larry M Heaman ◽  
Robert A Creaser
Keyword(s):  
Linear Trend ◽  
Lake Basin ◽  
Age Difference ◽  
Lake Area ◽  
Epithermal Deposits ◽  
Intimate Association ◽  
Baker Lake ◽  
End Members ◽  
Host Rocks ◽  
Low Sulfidation

The Mallery Lake area contains precious metal-bearing quartz–chalcedony stockworks that are pristine examples of ancient low-sulfidation epithermal deposits. Fluorite extracted from these epithermal deposits define a Sm–Nd errorchron age of 1434 ± 23 Ma mean square of weighted deviates (MSWD) = 4.8. This date is interpreted to have age significance because (1) a simple linear trend does not exist between the 143Nd/144Nd ratios of the fluorite with respect to their 1/Nd concentrations as would be expected for mixing of two geochemical end members; (2) microthermometric studies indicate that the fluorite analysed in this study has an intimate association with a single high-salinity, calcic brinal fluid; and (3) the age determined from seven fluorite samples extracted from a single outcrop location yielded an identical age result (1434 ± 60 Ma; MSWD = 5.5) compared to the fluorite composite. Rhyodacites of the Pitz Formation and syenites from the Nueltin suite (intrusive equivalent to the rhyodacites) are the youngest volcanic–plutonic rocks that are observed in outcrop in the Mallery Lake area, and they were dated by U–Pb zircon analysis at 1760 ± 43 Ma and 1755.4 ± 1.8 Ma, respectively. The ~320 million year age difference between the epithermal deposits and the hosting rhyodacitic flows suggests that the epithermal stockworks may have formed by a regional hydrothermal event unrelated to this earlier Paleoproterozoic volcanic activity. Uranium deposits in the Thelon and Athabasca basins, to the northwest and south of the Baker Lake Basin, were determined to have similar ore emplacement ages with no evident heat source.

scholarly journals Effects of Climate and Land Use/Land Cover Changes on Water Yield Services in the Dongjiang Lake Basin

2021 ◽  
Vol 10 (7) ◽  
pp. 466
Author(s):  
Wenbo Mo ◽  
Yunlin Zhao ◽  
Nan Yang ◽  
Zhenggang Xu ◽  
Weiping Zhao ◽  
...  
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Water Resource Management ◽  
Water Source ◽  
Water Yield ◽  
Lake Basin ◽  
Lake Area ◽  
Land Use Land Cover ◽  
Lulc Changes ◽  
Regional Water

Spatial and quantitative assessments of water yield services in watershed ecosystems are necessary for water resource management and improved water ecological protection. In this study, we used the InVEST model to estimate regional water yield in the Dongjiang Lake Basin in China. Moreover, we designed six scenarios to explore the impacts of climate and land use/land cover (LULC) changes on regional water yield and quantitatively determined the dominant mechanisms of water yield services. The results are expected to provide an important theoretical reference for future spatial planning and improvements of ecological service functions at the water source site. We found that (1) under the time series analysis, the water yield changes of the Dongjiang Lake Basin showed an initial decrease followed by an increase. Spatially, water yield also decreased from the lake area to the surrounding region. (2) Climate change exerted a more significant impact on water yield changes, contributing more than 98.26% to the water yield variability in the basin. In contrast, LULC had a much smaller influence, contributing only 1.74 %. (3) The spatial distribution pattern of water yield services in the watershed was more vulnerable to LULC changes. In particular, the expansion of built-up land is expected to increase the depth of regional water yield and alter its distribution, but it also increases the risk of waterlogging. Therefore, future development in the basin must consider the protection of ecological spaces and maintain the stability of the regional water yield function.

scholarly journals A Photometric Study of Regolith Intimate Mixing with Ice-Like Impurity

2021 ◽  
Author(s):  
Dwaipayan Deb ◽  
Pavan Chakraborty
Keyword(s):  
Solar System ◽  
Linear Trend ◽  
Geological Processes ◽  
Solar System Objects ◽  
Shadowing Effect ◽  
Mixing Proportion ◽  
In Situ Observations ◽  
End Members ◽  
Reflectance Data

Abstract Surfaces of solid solar system objects are covered by layers of particulate materials called regolith originated from their surface bedrock. They preserve important information about surface geological processes. Often regolith is composed of more than one type of particle in terms of composition, maturity, size, etc. Experiments and theoretical works are being carried out to constrain the result of mixing and extract the abundance of compositional end-members from regolith spectra. In this work we have studied, photometric light scattering from simulated surfaces made of two different materials – one is highly bright quartz particles ≈ 80µm and the other moderately bright sandstone particles ≈ 250µm. The samples were mixed with varying proportions and investigated at normal illumination conditions to avoid the shadowing effect. Said combinations may resemble ice mixed regolith on various solar system objects and therefore important for in situ observations. We find that the combinations show a linear trend in the corresponding reflectance data in terms of their mixing proportion and some interesting facts come out when compared to previous studies.

scholarly journals Uranium geology in the central Baker Lake Basin, District of Keewatin

1979 ◽  
Author(s):  
A R Miller
Keyword(s):  
Lake Basin ◽  
Baker Lake

Exemples de mélange de magmas en contexte plutonique: les enclaves des tonalites–granodiorites du massif de Bono (Sardaigne septentrionale)

1989 ◽  
Vol 26 (6) ◽  
pp. 1264-1281 ◽  
Author(s):  
C. Cocirta ◽  
J. B. Orsini ◽  
C. Coulon
Keyword(s):  
Geochemical Data ◽  
Mixing Process ◽  
Calc Alkaline ◽  
Specific Group ◽  
Mineralogical Analysis ◽  
Magmatic Origin ◽  
Interaction Mechanisms ◽  
Compositional Variations ◽  
End Members ◽  
Host Rocks

In calc-alkaline orogenic plutons, the dark xenoliths and their host rocks must be considered the expression of partial mixing of magma.Three associations of this type have been investigated and are illustrated by the Bono pluton (northern Sardinia)— a composite pluton including three intrusives of different nature (tonalitic to granodioritic) and containing a very large number of basaltic xenoliths of magmatic origin. Detailed mineralogical analysis of the two end members in each association, coupled with geochemical data, has determined the major petrogenetic mechanisms intervening in the mixing process in a plutonic setting: temperature equilibration, mechanical exchanges of crystals, chemical exchanges, etc. The most important result of this article, however, is to show that each intrusion is related to a specific group of xenoliths that is characterized by constant FeOt/MgO. The latter reflects the different composition of basaltic components, and it is concluded that each intrusive event is associated with a unique mixing episode. As in volcanic settings, the mixing process may have initiated the intrusion.The extreme compositional variations in the magmatic xenoliths, recognized in several series of orogenic plutons, is explained here by different initial basaltic end members and by variation in the intensity of the interaction mechanisms. [Journal Translation]

Perovskite, loparite and Ba-Fe hollandite from the Schryburt Lake carbonatite complex, northwestern Ontario, Canada

1994 ◽  
Vol 58 (390) ◽  
pp. 49-57 ◽  
Author(s):  
R. Garth Platt
Keyword(s):  
Fluid Phase ◽  
Ultramafic Rocks ◽  
Subsequent Reaction ◽  
Carbonatite Complex ◽  
Silicate System ◽  
Northwestern Ontario ◽  
Intimate Association ◽  
Free Mica ◽  
Host Rocks ◽  
Light Rare Earth Elements

AbstractWithin a suite of felsic-free, mica-rich alkaline ultramafic rocks of the Schryburt Lake carbonatite complex of northwestern Ontario, loparite and Ba-Fe hollandite occur in intimate association with perovskite. The host rocks have variable modal proportions of Mg-olivine, phlogopite, magnetite, ilmenite, apatite and carbonate (generally calcite) with minor Mg-salite. Thus, they correspond to ultramafic lamprophyres (i.e. aillikites), in the sense of Rock (1990) or the lamprophyric facies of the melilitite clan, in the sense of Mitchell (1993).Perovskite is the principal titanate phase, forming both euhedral and anhedral grains, the latter showing evidence of marginal resorption. It exhibits complex zonal patterns due principally to variations in the light rare earth elements, Na and Nb. In the nomenclature suggested, they may be termed perovskite and cerian perovskite. Loparite forms as small euhedral overgrowths on corroded perovskite cores. Chemically they are essentially solid solutions of loparite, lueshite and perovskite. Consequently, they may be termed calcian-loparite, calcian niobian loparite, niobian calcian loparite, loparite and niobian loparite. Titanates of the hollandite group are rare accessory minerals whose composition closely approach that of the septatitanate BaFe2+Ti7O16.The complex zoning of the perovskite grains has been attributed to the periodic introduction of carbonatite-derived fluids enriched in REE, Na and Nb into the silicate system during perovskite crystallization. Subsequent reaction of the early perovskite with F-bearing fluids leads to a localized environment enriched in Ti, Na, Nb and REE derived from both the fluid phase and the unstable perovskite. Loparite subsequently crystallizes from these micro-chemical environments.

scholarly journals Mapping of Major Land-Use Changes in the Kolleru Lake Freshwater Ecosystem by Using Landsat Satellite Images in Google Earth Engine

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2493 ◽  
Author(s):  
Meena Kumari Kolli ◽  
Christian Opp ◽  
Daniel Karthe ◽  
Michael Groll
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Land Use Changes ◽  
Google Earth ◽  
Nutrient Concentrations ◽  
Freshwater Ecosystem ◽  
Lake Ecosystem ◽  
Lake Basin ◽  
Lake Area ◽  
Google Earth Engine

India’s largest freshwater ecosystem of the Kolleru Lake has experienced severe threats by land-use changes, including the construction of illegal fishponds around the lake area over the past five decades. Despite efforts to protect and restore the lake and its riparian zones, environmental pressures have increased over time. The present study provides a synthesis of human activities through major land-use changes around Kolleru Lake both before and after restoration measures. For this purpose, archives of all Landsat imageries from the last three decades were used to detect land cover changes. Using the Google Earth Engine cloud platform, three different land-use scenarios were classified for the year before restoration (1999), for 2008 immediately after the restoration, and for 2018, i.e., the current situation of the lake one decade afterward. Additionally, the NDVI (Normalized Difference Vegetation Index) and NDWI (Normalized Difference Water Index) indices were used to identify land cover dynamics. The results show that the restoration was successful; consequently, after a decade, the lake was transformed into the previous state of restoration (i.e., 1999 situation). In 1999, 29.7% of the Kolleru Lake ecosystem was occupied by fishponds, and, after a decade of sustainable restoration, 27.7% of the area was fishponds, almost reaching the extent of the 1999 situation. On the one hand, aquaculture is one of the most promising sources of income, but there is also limited awareness of its negative environmental impacts among local residents. On the other hand, political commitment to protect the lake is weak, and integrated approaches considering all stakeholders are lacking. Nevertheless, alterations of land and water use, increasing nutrient concentrations, and sediment inputs from the lake basin have reached a level at which they threaten the biodiversity and functionality of India’s largest wetland ecosystem to the degree that immediate action is necessary to prevent irreversible degradation.

scholarly journals Modelling water yield with the InVEST model in a data scarce region of northwest China

2020 ◽  
Vol 20 (3) ◽  
pp. 1035-1045 ◽  
Author(s):  
Xu Yang ◽  
Ruishan Chen ◽  
Michael E. Meadows ◽  
Guangxing Ji ◽  
Jianhua Xu
Keyword(s):  
Temporal Dynamics ◽  
Northwest China ◽  
Reanalysis Data ◽  
Water Yield ◽  
Lake Basin ◽  
Lake Area ◽  
Bosten Lake ◽  
Invest Model ◽  
Unused Land ◽  
Integrated Valuation

Abstract The Bosten Lake basin is an important arid region of northwest China, and has exhibited a declining trend in both lake area and level of water during recent decades. Reliable information on water yield, an important attribute of available water resources in a region, is vital to assess the potential for socio-economic development. The Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model is applied here to simulate water yield in the Bosten Lake basin. The spatial and temporal dynamics of water yield, and the response of water yield to land use and precipitation change, are analysed for the period 1985 to 2015. The results show that, overall, water yield increased during 1985–2015, and that the magnitude of change was greater in the eastern part of the region. The water yield capacity, positively correlated with precipitation, is highest under grassland vegetation and lowest in cultivated and unused land. The paper demonstrates that statistical downscaling and climate reanalysis data can be used in the InVEST model to improve the accuracy of simulated water yield in data scarce regions.

Thermoluminescence of Uranium Host Rocks in Ambrosia Lake Area: ABSTRACT

AAPG Bulletin ◽  
1979 ◽  
Vol 63 ◽  
Author(s):  
D. L. Hayslip, G. E. Fuller, P. W.
Keyword(s):  
Lake Area ◽  
Host Rocks
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