Entity

Time filter

Source Type

Teekkarikyla, Finland

Ruotoistenmaki T.,Geological Survey of Finland
Journal of African Earth Sciences | Year: 2014

During the years 2008-2012, the geology of most of Uganda was studied within the framework of the Sustainable Management of Mineral Resources Project (SMMRP). During the project, comprehensive airborne magnetic and radiometric surveys were flown over the entire country and geological, petrophysical, geochemical sampling, geological field studies and detailed geophysical field profiles were undertaken in selected sub-areas. This report concentrates on the geophysical properties of three major geophysical structures in the area considered during the project: the Pan-African (0.6-0.7. Ga) Aswa shear zone and Nagasongola discontinuity (suture), and the 1.36. Ga Uganda-Tanzania semi-circular 'ring dyke' complex.The geophysical profiles across the Aswa shear indicate that the fault zone dips steeply, at about 60° to NE. The structure represents a magnetic, gravimetric (density), radiometric and topographic discontinuity, all diminishing from SW to NE across the zone. The zone is also characterized by complex radiometric anomalies. A schematic reconstruction of the evolution of the Aswa shear zone on the magnetic map suggests a nearly 60. km sinistral horizontal component of displacement along the zone. The Nakasongola zone is another distinct magnetic, gravimetric and radiometric discontinuity, interpreted to represent a collision (suture) zone, where the northern, low-magnetic block has been thrust over the southern, denser and more magnetic block. Modeling of gravity and magnetic data are consistent with a geometry in which the southern, magnetic and high-density block dips gently to great depth beneath the northern block. Bedrock exposures in both the Aswa shear zone and Nagasongola zone areas indicate a very protracted and complex history of tectonic processes commencing in the Archaean-Paleoproterozoic era and culminating in Pan-African orogenies. Both, the Aswa shear zone and Nagasongola discontinuity are cut by continuous younger dykes that show no signs of disruption, indicating that these deformation zones are presently relatively inactive. Thus, the dating of these dykes can constrain estimates of minimum activation ages of the structures that they transect.The semicircular ring dyke complex in SW Uganda, which continues southwards across Lake Victoria to NW Tanzania, is most clearly visible in magnetic anomaly maps as curved anomalies with a diameter of about 450-650. km. Magnetic profile interpretations across the dykes in Tanzania and Uganda indicate that the dykes dip at about 30-40° towards the geometric center of the concentric rings, implying a cone shaped geometry for the dykes in three dimensions. Minimal offsets in anomalies cut by dykes indicate that the dykes were not intruded within fault zones associated with major dislocations, rather that they were emplaced within extensional fractures due to uplift above a mantle plume below the conical dyke complex.The present study, based on the results of the SMMRP, gives valuable, but still preliminary new information concerning large scale tectonic processes operating in the bedrock of Uganda. The structures described here can all be potentially related to hydrothermal events and enrichment of elements of economic interest. © 2014 Elsevier Ltd. Source


Kietavainen R.,Geological Survey of Finland | Purkamo L.,VTT Technical Research Center of Finland
Frontiers in Microbiology | Year: 2015

The emerging interest in using stable bedrock formations for industrial purposes, e.g., nuclear waste disposal, has increased the need for understanding microbiological and geochemical processes in deep crystalline rock environments, including the carbon cycle. Considering the origin and evolution of life on Earth, these environments may also serve as windows to the past. Various geological, chemical, and biological processes can influence the deep carbon cycle. Conditions of CH4 formation, available substrates and time scales can be drastically different from surface environments. This paper reviews the origin, source, and cycling of methane in deep terrestrial crystalline bedrock with an emphasis on microbiology. In addition to potential formation pathways of CH4, microbial consumption of CH4 is also discussed. Recent studies on the origin of CH4 in continental bedrock environments have shown that the traditional separation of biotic and abiotic CH4 by the isotopic composition can be misleading in substrate-limited environments, such as the deep crystalline bedrock. Despite of similarities between Precambrian continental sites in Fennoscandia, South Africa and North America, where deep methane cycling has been studied, common physicochemical properties which could explain the variation in the amount of CH4 and presence or absence of CH4 cycling microbes were not found. However, based on their preferred carbon metabolism, methanogenic microbes appeared to have similar spatial distribution among the different sites. © 2015 Kietäväinen and Purkamo. Source


Vallius H.,Geological Survey of Finland
Marine Pollution Bulletin | Year: 2014

The Baltic Sea has received considerable loads of pollutants due to industrialization in Eastern Europe. Concern for the Baltic's ecological health eventually led to legislation and voluntary measures to limit pollution during the last decades of the 20th century. Heavy metal concentrations in open sea surface sediments reflected these steps to limit contaminant loads almost immediately, suggesting the possibility that the trend would continue in the ensuing years. Recent seafloor samples reveal that the declines have persisted over the past two decades. Currently, almost all heavy metal species have declined in surface sediments to levels approaching the safe limits for humans and the environment. Cadmium and mercury however remain at relatively high concentrations in many areas. Arsenic concentrations, which occur at safe levels within the Gulf of Finland persist at unacceptably high levels in surface sediments of the Bothnian Bay, and thus pose a potential threat to marine life in the area. © 2013 Elsevier Ltd. Source


Tuusjarvi M.,Geological Survey of Finland
Resources, Conservation and Recycling | Year: 2013

This article considers the environmental impacts and the governance framework of the domestic and international supply of iron, zinc, copper and nickel concentrates smelted and refined in Finland. The metals industry in the country is heavily dependent on imported concentrates, and the research is thus focused on defining the level of impacts related to mining and mineral processing abroad, and the change in the impacts between 2000 and 2010. The estimations of environmental impacts are based on waste minerals and CO 2eq emissions, and the quality of governance in the set of indicators measuring different aspects of governance. The total amount of waste minerals and CO2eq emissions related to metal concentrates decreased over the ten-year period. At the same time, the quality of governance improved in all concentrate groups except nickel. Ore grade, mine type and transportation distance appear to be the most influential factors on environmental impacts. The results suggest that the country of origin can have a noticeable effect on the environmental impacts and the quality of governance of the mining and processing of metal concentrates. © 2013 Elsevier B.V. All rights reserved. Source


Vallius H.,Geological Survey of Finland
Marine Pollution Bulletin | Year: 2015

The Gulf of Finland is a shallow sea where a multitude of activities compete of space. Many of the activities include reworking of the sea floor. The gulf is known to have been rather largely contaminated by heavy metals during the last century, and although indications of recovery have been reported, it is crucial to know the levels of sea floor sediment contamination before any decisions of activities are taken by the authorities. In order to predict sediment toxicity the sediment concentrations acquired during a study from 2001 to 2004 are compared to Canadian sediment quality guidelines (SQG: s), which reveal that in the majority of the subsamples the metals and arsenic exceed the threshold levels of the used SQG: s, some exceed also the probable effect level. As, Cd, Hg, and especially Zn concentrations occur at unacceptably high levels in the coastal Gulf of Finland sediments. © 2015 Elsevier Ltd. Source

Discover hidden collaborations