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Project Topic
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University of Helsinki, Geological Survey of Finland, Institute of Geophysics, Polish Academy of Sciences, Boliden, Vibrometric and Geopartner, research institutions and industry partners from Finland and Poland, are collaborating on an applied research project on cost-effective, novel geophysical mineral exploration techniques, with particular emphasis on seismic imaging. One of the main challenges of mineral exploration, as also stated on the ERA-MIN research agenda, is finding and characterizing deeper-seated resources to satisfy the growing worldwide demand for raw materials. Seismic imaging is particularly attractive for deep mineral exploration because of superior depth penetration and resolution when compared to other geophysical imaging techniques. This research initiative joins the forces of research institutions and industry, and aims at comprehensive methodological advances in the use of seismic imaging for mineral exploration in Europe and beyond. We acknowledge also the need for well-integrated geophysical and geological approaches, and aim at developing joint analyses of different data. The overall goal is to develop integrated geophysical-geological approaches for building realistic 3D geological models, delineation of known deposits and identifying new reliable drilling targets, with further impact on reducing the cost of drilling, and as such fitting the objectives of the ERA-MIN network. All the partners in our proposal have their unique expertise in different aspects of the project, and the core of the project is knowledge transfer between the partners. We consider this project a first step in a future of collaborations. Specific attention will be paid to communicating acquired knowledge also to a broader audience.
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Project Results
(after finalisation)
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The
overall aim of COGITO MIN was to develop cost effective geophysical
mineral exploration techniques, with new advances in particular in data
acquisition, processing and interpretation of passive and active source surface
and borehole seismic data Koivisto et al 2016 2018 In 2016 COGITO MIN
acquired an extensive seismic dataset in the Kylylahti sulphide mine and
exploration area in Finland The COGITO MIN experiments included i a 3 D
passive seismic survey in which 1000 receivers in a 3 5 x 3 km grid were left to
record ambient noise sources for 30 days Chamarczuk et al 2018 2019 ),),(
two approximately 6 km long high resolution seismic reflection 2 D profiles
Heinonen et al 2019 ),),( a sparse active source 3 D seismic reflection survey
utilizing the passive seismic grid and a “ distribution of Vibroseis and
explosive sources (Singh et al 2019 and ( a multi azimuth walk away three
component Vertical Seismic Profiling ( survey in three boreholes starting
from the mine tunnels, with one borehole instrumented also with fibre optic
Distributed Acoustic Sensing ( technology (Riedel et al 2018 in
collaboration with Silixa The experiments were designed with different stages
of the exploration workflow in mind from mapping of the ore host rocks at
larger scale to high resolution near mine and in mine exploration Seismic
surveys were supported by petrophysical measurements Luhta 2019 that
provide constraints for interpretation of the dataset
Project COGITO
MIN
COst effective Geophysical Imaging Techniques for supporting Ongoing MINeral exploration in Europe
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High
resolution 2D reflection profiles confirmed the depth extent of the Outokumpu assemblage rocks that
host the mineralizations in the Kylylahti area. These rocks manifest themselves in form of increased piecewise
reflectivity, which provides interesting targets for further investigations ( Heinonen et al. 2018). A specialized
pre stack depth imaging ( Hlousek et al. 2015) was tested in co operation with TU Bergakademie Freiberg. This
so called Fresnel Volume Migration outperformed a more traditional time imaging approach, especially in
imaging shallow steeply dipping contacts. Heinonen et al (2019) demonstrated that seismic reflection profiling
combined with this type of depth imaging can be a powerful tool even when source access is limited,
encouraging more frequent, cost effective seismic mineral exploration efforts also in greenfield areas. Sparse
and irregular active source 3D survey provided new details about the architecture of the Kylylahti area, in
particular about the spatial extent of the Outokumpu assemblage rocks. Similar to 2D imaging, a significant
uplift in imaging was brought by the pre stack depth imaging (Singh et al. 2019). The results show that a sparse
3D active source survey is a viable, cost effective option when a full active source 3D survey is not possible.
VSP results, involving development of a VSP imaging scheme corroborated by detailed forward modelling and
interpretation workflow, led to successful interpretation of key geological contacts including the target
sulphide mineralization (Riedel et al. 2018). The results demonstrate the value of tailored in mine VSP
measurements for in mine exploration and resource delineation in a complex geological setting, especially
when coupled with the fiber optic DAS technology which provides reflection data of sufficient quality with less
logistical efforts. To our knowledge this was the first time that DAS technology was tested in a crystalline rock
mining environment. The VSP data acquisition and processing workflows can be readily applied to new sites
and are offered as a commercial service by Vibrometric .
Within COGITO
MIN project, also a new software was tested by Geopartner for joint inversion of 2D gravity
and audio magnetotelluric (AMT) data. The tests provided new information for developing the software.
However, in the Kylylahti type geological environment a 3D magnetotelluric survey would be more applicable.
The COGITO
MIN seismic data successfully delineate the main geological contacts in the Kylylahti area. The
COGITO MIN dataset is jointly interpreted with other geological and geophysical data, e.g. AMT data and
earlier 2D reflection seismic profiles from the area, to construct a 3D model of the main geological contacts.
Tests are being run to parameterize and integrate seismic data into an exploration workflow.
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