A conceptual model of the copper–porphyry ore formation based on joint analysis of deep 3D geophysical models: Sorskoe complex (Russia) case study     

Viacheslav V. Spichak  Alexandra G. Goidina 《Acta Geophysica》2017,65(6):1133-1144

Joint analysis of deep three-dimensional models of the electrical resistivity, seismic velocity, and density of the complex hosting the Sorskoe Cu–Mo deposit (Russia) is carried out aimed at finding geophysical markers characterizing the areas of ore generation, transportation and deposition. The three-dimensional lithology model of the study area is built based on the empirical relationship between the silica content of the rocks and seismic velocities. It is in agreement with geological and geochemical studies provided in this area earlier and could be used as a basis for forecasting locations of the copper–molybdenum ore deposits at depth. A conceptual model of the copper–porphyry complex explaining the mechanisms of ore generation, transportation from the lower to the upper crust and deposition in the upper crust is suggested. In particular, it is supposed that post-magmatic supercritical gas–water ore-bearing fluids are upwelling through the plastic crust due to the sliding of the fluid films along the cleavage planes of the foliated rocks while at the depths of the brittle upper crust this mechanism could be changed by volumetric fluid transportation along the network of large pores and cracks.  相似文献   

Intertidal spring dynamics and coastal nutrient loading revealed through geophysics,drone surveys,and in-situ monitoring     

Alexandra C. Oliver  Rob C. Jamieson  Kathryn A. Smith  Julia A. Cantelon  Barret L. Kurylyk 《水文研究》2024,38(5):e15144

Coastal eutrophication poses an increasing risk to ecosystem health due to enhanced nutrient loading to the global coastline. Submarine groundwater discharge (SGD) represents a significant pathway for nitrate-nitrogen (NO₃-N) transport to the coast, but diffusive SGD transport is difficult to monitor directly, given the low flux rates and expansive discharge areas. In contrast, focused SGD from intertidal springs can potentially be sampled and directly gauged, providing unique insight into SGD and associated contaminant transport. Basin Head is a coastal lagoon in Prince Edward Island, Canada that is a federally protected ecosystem. Nitrate-nitrogen is conveyed from agricultural fields in the contributing watershed to the eutrophic lagoon via intertidal groundwater springs and groundwater-dominated tributaries. We used several field methods to characterize groundwater discharge, nutrient loading, and in-channel mixing associated with intertidal springs. The tributaries and intertidal springs were gauged and sampled to estimate a representative summer nitrate load to the lagoon. Our analysis revealed that NO₃-N export to the lagoon through tributaries and springs throughout summer 2023 was on average 401 kg N/month, with the combined spring loading comparable in magnitude to the combined tributary loading. We collected thermal infrared and visual imagery using drone surveys and found spatial overlap between cold-water plumes from the spring discharge and macroalgae blooms, indicating the local thermal and ecosystem impacts of the focused SGD. We also mapped the electrical resistivity (salinity) distribution in the water column around one large spring with electromagnetic geophysics at different tidal stages to reveal the three-dimensional spring plume dynamics. Results showed that the fresher spring water floated above the saline lagoon water with the brackish plume oriented in the direction of the tidal current. Collectively, our multi-pronged field investigations help elucidate the hydrologic, thermal, and nutrient dynamics of intertidal springs and the cascading ecosystem impacts.  相似文献   

Editorial statement     

A. Navrotsky 《Physics and Chemistry of Minerals》1987,14(4):293-293

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Analysis of the incommensurately modulated OS phase of SiO2 tridymite     

Alexandra K. A. Pryde  Volker Heine 《Physics and Chemistry of Minerals》1998,25(8):603-610

The structure, symmetry and origin of the incommensurately modulated OS phase of tridymite (SiO₂) and its lock-in to the OP three-fold superlattice structure are discussed in a computational study. The structure of the OS phase (which has not been determined experimentally) is deduced as the only geometrically possible structure derived from the parent OC phase by rotation and translation of the SiO₄ tetrahedra without significant distortion of these units. It can be visualised conveniently in terms of the McConnell formalism of two component difference structures C₁ and C₂ whose space group symmetries are derived. The results are in accordance with the known lock-in structure at wave vector Q= a ^*. In the latter, the ±C₁ regions expand and the structure can square up in a very general way to take advantage of the lost symmetries (lost compared with the OC phase). Received: 4 August 1997 / Revised, accepted 24 November 1997  相似文献   

Thermodynamics of element partitioning: (1) Systematics of transition metals in crystalline and molten silicates and (2) Defect chemistry and “the Henry's law problem”     

Alexandra Navrotsky 《Geochimica et cosmochimica acta》1978,42(6):887-902

The distribution of Mg, Mn, Fe, Co and Ni among olivine, orthopyroxene, calcic clinopyroxene and liquid can be described by exchange reactions of the form: M (phase A) + Mg (phase B) = M (phase B) + Mg (phase A). The thermochemical data predict the observed partitioning within the limits of error of both sets of data when assumptions of ideal solid solution are used, except for Mn-Mg exchange. Because ΔS and ΔV for these exchange reactions are generally small, K_D varies relatively little with temperature and pressure, although individual ion distribution coefficients (D values) are more sensitive to these variables and to changing liquid composition.Trace elements present at the ppm level can enter crystals in normal lattice sites, can participate in point defect equilibria and can enter various defect sites present metastably in the crystal as a result of its P,T history. Metastable defect equilibria, in which the number of sites (grain boundaries, surfaces, intergrowths, etc.) is fixed, can lead to enhanced trace element solubility in the crystal at very low concentrations and thus to apparent deviations from Henry's law.  相似文献   

Capitalising the farm family entrepreneur: negotiating private equity partnerships in Australia     

Alexandra Langford 《The Australian geographer》2019,50(4):473-491

ABSTRACT

Research on the financialisation of land and agribusiness has highlighted major shifts in agri-food systems globally. Yet these accounts tend to focus on the activities of financial actors, and few take seriously the role of farmers in negotiating investments in land and agribusiness. Farmers in the global North may be well placed to benefit from partnerships with financial investors, although little is known about the way that such partnerships are formed. Australian studies of farmer agency have been productive in examining farm family entrepreneurs and globally engaged farmers who work beyond the farm gate to organise supply chains. This paper adds to these studies by providing insights about a capitalising farm family entrepreneur, who successfully negotiated and entered into a direct equity partnership with a large foreign pension fund. Several observations are significant: the exceptional skill, time and expense required to negotiate these partnerships; the role of consultants and non-human actors in structuring them; and the spatially- and temporally divergent farm development practices that are enabled by a shift from debt to equity financing. These observations are indicative of a new adaptive strategy of family farmers to shifting financial landscapes and of emergent family, corporate, and financial farm hybridity.  相似文献   

Slow growth and early sexual maturity: Bane and boon for the red coral Corallium rubrum     

Ivo Gallmetzer  Alexandra Haselmair  Branko Velimirov 《Estuarine, Coastal and Shelf Science》2010

This study investigates the size, age and growth of Corallium rubrum which is a key species of the only large reef-like structure in the Mediterranean Sea, the coralligéne. Two populations were studied in the Ligurian Sea at a depth between 36 and 42 m. Basal diameter, colony height and numbers of branches of 230 colonies were measured, and age and growth rates were assessed from 25 colonies. Mean growth rate was 0.2 mm yr⁻¹ of basal diameter growth, corresponding to a mean annual total branch length increase of 5 mm. These results point to a coral growth much slower than assumed in many earlier studies. Additionally, age and size at first reproduction were analysed. Male colonies were shown to become sexually mature at a minimum age of six years (1.2 mm of basal diameter), while female colonies reached maturity when at least 10 years old (2 mm of basal diameter). We further discuss the implications of slow growth and early sexual maturity for red coral management and conservation.  相似文献   

Diamond precipitation from ascending reduced fluids in the Kaapvaal lithosphere: Thermodynamic constraints     

Jan Marten Huizenga  Alexandra Crossingham  Fanus Viljoen 《Comptes Rendus Geoscience》2012,344(2):67-76

Previous research has shown that the Kaapvaal lithospheric mantle is generally reduced and characterised by a decreasing redox state with increasing depth. As a consequence, C-O-H fluids in the Kaapvaal lithospheric mantle are dominated by H₂O, CH₄, and C₂H₆. Thermodynamic calculations demonstrate that diamond precipitation from such a fluid during ascend is possible as it is exposed to a more oxidised environment and both CH₄ and C₂H₆ are oxidised. However, the calculations also demonstrate that the diamond precipitation potential from such a fluid decreases when: (1) the mantle is either more reduced or oxidised compared to the Kaapvaal mantle, or (2) the change in temperature with pressure is smaller compared to that of the Kaapvaal mantle. Therefore, the presence of reduced mantle fluid species and a generally decreasing oxygen fugacity with increasing depth do not necessarily warrant diamond precipitation from a rising reduced fluid.  相似文献   

Paleoproterozoic mafic dyke swarms of the Belomorian Province,eastern Fennoscandian Shield     

Alexandra Stepanova  Vladimir Stepanov 《Precambrian Research》2010

Paleoproterozoic mafic igneous rocks (2450–1970 Ma) are exposed in the form of layered intrusions, dykes, and volcanic rocks in the Karelian, Kola and Murmansk provinces and in the form of dykes and small intrusions in the Belomorian Province, Eastern Fennoscandian Shield. The age and sequence of mafic dyke emplacement during the Paleoproterozoic are very similar in these regions. Further comparisons of geochemical characteristics of mafic dyke swarms in the Belomorian Province and neighboring cratons show considerable similarities.  相似文献   

The Hubble Deep Field North SCUBA Super-map – III. Optical and near-infrared properties of submillimetre galaxies     

Alexandra Pope  Colin Borys  Douglas Scott  Christopher Conselice  Mark Dickinson  Bahram Mobasher 《Monthly notices of the Royal Astronomical Society》2005,358(1):149-167

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