Papers by Alessandro Sandrin
Geological Survey of Denmark and Greenland Bulletin, May 27, 2020
Play analysis has been widely used in hydrocarbon exploration for decades with great success. In ... more Play analysis has been widely used in hydrocarbon exploration for decades with great success. In recent years, progress has also been made to describe reservoir properties of very low permeability reservoirs. However, comparatively little research has been conducted into play analysis for such reservoirs, which may lead to misleading estimates of their hydrocarbon potential. Here, the concept of a semi-conventional play is defined and characterised as having a reservoir of such low permeability that a hydrocarbon column can form down-dip of an effective dry trap. A new exploration approach is proposed for such plays using the Chalk Group Play in the Danish North Sea as an example. It is suggested that together with the usual risk elements, a more detailed analysis of 'charge' is necessary, paying particular attention to identifying possible hydrocarbon entry-points, palaeostructures and the maximum distance from these entry-points that the hydrocarbons may have reached since they first entered the reservoir. The application of this novel approach for semi-conventional plays in mature basins could help unlock further resources in proximity of existing fields, and reduce the risk of failure in frontier exploration.
Ore Geology Reviews, 2007
In the last decades Fe-oxide Cu-Au (IOCG) deposits attracted the interest of exploration geologis... more In the last decades Fe-oxide Cu-Au (IOCG) deposits attracted the interest of exploration geologists and geophysicists. General geophysical descriptions of IOCG deposits have been published in the recent past, but there is still a lack of detailed geophysical investigations. We present a petrophysical study of rock samples from exploration borehole TJ71305, which intersects the Cuprospect in the Tjårrojåkka IOCG mineralised area, northern Sweden. Furthermore geophysical data are compiled and analysed to tentatively define a geophysical signature, at local scale, for this type of deposit. The study area is dominated by intrusive and volcanic rocks of Middle Proterozoic age, the latter hosting the Cu and Fe occurrences. The Fe occurrences are clearly defined from both aeromagnetic and ground magnetic data, and are also indicated by gravity, geoelectric and electromagnetic data. Enrichment in ferromagnetic minerals in the area is suggested by the high values of magnetic susceptibility commonly obtained for different rock types; magnetite and Ti-magnetite are the dominant magnetic minerals. Haematite with variable contents of Ti was detected and it is probably a result of oxidation of magnetite in alteration zones. In Tjårrojåkka a clear spatial relationship is noted between Cu occurrences and high K/Th ratios. This ratio is calculated from airborne radiometric data and is an expression of enrichment in potassium, due to alteration. The Cu-prospect is also indicated by high gravity and magnetic anomalies, by clear positive anomalies in induced polarisation data and by negative anomalies for the imaginary part of ground electromagnetic (Slingram) data. However, high-density/high-susceptibility/low-resistivity (Ti)-magnetite is associated with the Cu-prospect and this may lead to misinterpretation of potential field, electromagnetic and geoelectric data.
Ore Geology Reviews, Jul 1, 2006
Ore Geology Reviews aims to familiarize all earth scientists with recent advances in a number of ... more Ore Geology Reviews aims to familiarize all earth scientists with recent advances in a number of interconnected disciplines related to the study of, and search for, ore deposits. The reviews range from brief to longer contributions, but the journal preferentially publishes manuscripts that fill the niche between the commonly shorter journal articles and the comprehensive book coverages, and thus has a special appeal to many authors and readers. Ore Geology Reviews covers topics related to ore geology in its broadest sense. The following exemplifies the range of subject matter that can be described and discussed in the journal: Metalliferous and non-metalliferous (industrial mineral) ore geology of all types; land-based and oceanic studies; economic geology per se; mineral economics; pollution studies related to exploration and mining; ore and gangue mineralogy, petrography, petrology, petrogenesis; host-rock studies; metallogeny and minerogenesis (e.g. metallotectonics); specific deposits, districts, and belts; local to regional, detailed to general or reconnaissance studies, on any scale; pure and applied studies, i.e. theoretical and practical data; methodology of any kind: laboratory-based and field-oriented; geological (including stratigraphic, structural, remote-sensing); mathematical (e.g. computer geology); geochemical, geophysical and philosophical; research and exploration techniques. Benefits to authors We also provide many author benefits, such as free PDFs, a liberal copyright policy, special discounts on Elsevier publications and much more. Please click here for more information on our author services.
A tectonophysical study has been performed on the Tjarrojakka Cu-Fe mineralisations, WSW of the c... more A tectonophysical study has been performed on the Tjarrojakka Cu-Fe mineralisations, WSW of the city of Kiruna, northern Sweden. The bedrock is characterized by intermediate to mafic meta-volcanite ...
The Tjarrojakka area in northern Sweden hosts a number of Fe-oxide Cu-Au (IOCG) occurrences.The m... more The Tjarrojakka area in northern Sweden hosts a number of Fe-oxide Cu-Au (IOCG) occurrences.The major Cu-prospect in the area has been studied by magnetic and electron microprobe analyses of four s ...
In the last decade the importance of Fe-oxide Cu-Au deposits has been increasing constantly and a... more In the last decade the importance of Fe-oxide Cu-Au deposits has been increasing constantly and a relevant effort was put on the creation of efficient exploration models. Among the other discipline ...
Proceedings, Jun 4, 2012
Polygonal faults have been mapped in several basins worldwide within fine-grained sedimentary sec... more Polygonal faults have been mapped in several basins worldwide within fine-grained sedimentary sections. In a few cases, such features have been noticed also for chalk rocks at both outcrop and seismic scale. In this paper we present a case history of polygonal faults in the Late Cretaceous chalk units at the Tyra Field, Danish North Sea. The use of 3D seismic data has allowed producing images of the polygonal faults of excellent quality. Seismic data show polygonal faults within the Tor Formation (Maastrichtian Age) that do not extend into the overlying Ekofisk Formation reservoir of Danian age. In the case of the Tyra Field, the possible changes in porosity/lithology, hence permeability, associated with the polygonal faults, do not reach the Ekofisk Formation reservoir, but may have acted as preferential pathways for vertically migrating hydrocarbons. The present study illustrates the morphology of the polygonal faults, addressing also their spatial relationship with major Cretaceous faults and gravitational mass movements in the area.
In the last decades Fe-Oxide Cu-Au deposits have been discovered and developed in Australia, Sout... more In the last decades Fe-Oxide Cu-Au deposits have been discovered and developed in Australia, South America and Canada. This class of mineral deposits is also present in northern Sweden and thus rep ...
A geophysical-petrophysical study has been performed in an area WSW of the city of Kiruna, northe... more A geophysical-petrophysical study has been performed in an area WSW of the city of Kiruna, northern Sweden. Particular attention has been dedicated to the Tjarrojakka iron oxide copper gold (IOCG) ...
The Tjarrojakka area in northern Sweden hosts a number of Fe-oxide Cu-Au (IOCG) occurrences.The m... more The Tjarrojakka area in northern Sweden hosts a number of Fe-oxide Cu-Au (IOCG) occurrences.The major Cu-prospect in the area has been studied by magnetic and electron microprobe analyses of four s ...
A tectonophysical study has been performed on the Tjarrojakka Cu-Fe mineralisations, WSW of the c... more A tectonophysical study has been performed on the Tjarrojakka Cu-Fe mineralisations, WSW of the city of Kiruna, northern Sweden. The bedrock is characterized by intermediate to mafic meta-volcanite ...
82nd EAGE Annual Conference & Exhibition, 2021
Summary In the last years the discipline of Urban Mining has been established, and the existing l... more Summary In the last years the discipline of Urban Mining has been established, and the existing landfills may be now considered as a source of valuable commodities. For the estimation of the presence and amount of recyclable materials, a thorough exploration approach is strongly recommended. Non-invasive investigation methods are obviously preferred, due to the potentially high environmental impact of invasive methods in case of accidents. In this paper it is presented a case history from a landfill in Denmark. A set of geophysical surveys was performed to determine the presence of metals within the waste, and possibly define their location and depth. The integration of magnetic, geoelectric, and seismic data seem to be able to provide a reliable assessment of the presence of magnetic metals at around 8 m depth in the westernmost part of the landfill. More detailed exploration methods and modelling techniques will be required for a quantitative evaluation of the valuable volumes in place
GEUS Bulletin, 2020
The Isortoq Giant Dykes in the Proterozoic Gardar Province, South Greenland, includes Isortoq Sou... more The Isortoq Giant Dykes in the Proterozoic Gardar Province, South Greenland, includes Isortoq South giant dyke and Isortoq North giant dyke. The fine-grained Fe-Ti-V deposit hosted by the Isortoq South giant dyke, referred to as the Isortoq Fe-Ti-V deposit, is considered a good test site for the use of magnetic susceptibility for the mapping of ore grades. Here, we test this and show that the Fe, Ti and V distribution is controlled by titanomagnetite disseminated throughout fine-grained troctolite. The deposit displays a clear correlation between magnetic susceptibility and Fe, Ti and V grades in bulk samples of consecutive 2 m sections from 11 drill cores, totalling 2671 m in length. We observe that Fe, Ti and V are almost entirely hosted in titanomagnetite, which controls the magnetic susceptibility. Field measurements of the magnetic susceptibility can thus be considered as a reliable exploration tool for this type of mineralisation. We further consider the origins of the deposit...
GEUS Bulletin, 2020
Geophysical methods have been widely used in recent decades to investigate and monitor landfill s... more Geophysical methods have been widely used in recent decades to investigate and monitor landfill sites for environmental purposes. With the advent of the circular economy, waste contained in old landfills may be considered a resource that can be developed. Since the content of old landfills is largely unknown, the occurrence and quantity of valuable materials must be investigated before embarking on any development activity. Two landfills on Sjælland, Denmark (located at Hvalsø and Avedøre) were selected for a pilot study to characterise their content. At both locations, a set of geophysical surveys is underway. Here, we present the data obtained from magnetic and 2D seismic refraction surveys. Magnetic data show various anomalies that can be interpreted as caused by iron-rich waste. At both sites, the landfill material results in generally low P-wave velocity (<400 m/s), lower than those obtained for Quaternary sediments at Avedøre. The seismic velocities appear to increase in th...
GEUS Bulletin, 2020
Play analysis has been widely used in hydrocarbon exploration for decades with great success. In ... more Play analysis has been widely used in hydrocarbon exploration for decades with great success. In recent years, progress has also been made to describe reservoir properties of very low permeability reservoirs. However, comparatively little research has been done into play analysis for such reservoirs, which may lead to misleading estimates of their hydrocarbon potential. Here, the concept of a semi-conventional play is defined and characterised as having a reservoir of such low permeability that a hydrocarbon column can form down-dip of an effective dry trap. A new exploration approach is proposed for such plays, using the Chalk Group Play in the Danish North Sea as an example. It is suggested that together with the usual risk elements, a more detailed analysis of ‘charge’ is necessary, paying particular attention to identifying possible hydrocarbon entry points, palaeostructures and the maximum distance from these entry points that the hydrocarbons may have reached since they first ...
Physical properties of rocks and geophysical data as tools for targeting Fe-oxide Cu-Au mineralis... more Physical properties of rocks and geophysical data as tools for targeting Fe-oxide Cu-Au mineralisations in northern Sweden
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Papers by Alessandro Sandrin