Katri Vaittinen

Boliden (Sweden)

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Crustal conductors in a complex accretionary orogen in Fennoscandia

Annakaisa Korja Katri Vaittinen Muhamed Abdel Zaher Markku Pirttijärvi Annakaisa Korja

Accretionary wedge

Source

Cite

Citations (0)

Underground Vertical Seismic Profiling with Conventional and Fiber-Optic Systems for Exploration in the Kylylahti Polymetallic Mine, Eastern Finland

Minerals (2018)

Marko Riedel C. Cosma N. Enescu Emilia Koivisto Kari Komminaho

Seismic reflection methods have been used for the exploration of mineral resources for several decades. However, despite their unmatched spatial resolution and depth penetration, they only have played a minor role in mineral discoveries so far. Instead, mining and exploration companies have traditionally focused more on the use of potential field, electric and electromagnetic methods. In this context, we present a case study of an underground Vertical Seismic Profiling (VSP) experiment, which was designed to image a (semi-)massive sulfide deposit located in the Kylylahti polymetallic mine in eastern Finland. For the measurement, we used a conventional VSP with three-component geophones and a novel fiber-optic Distributed Acoustic Sensing (DAS) system. Both systems were deployed in boreholes located nearby the target sulfide deposit, and used in combination with an active seismic source that was fired from within the underground tunnels. With this setup, we successfully recorded seismic reflections from the deposit and its nearby geological contrasts. The recording systems provided data with a good signal-to-noise ratio and high spatial resolution. In addition to the measurements, we generated a realistic synthetic dataset based on a detailed geological model derived from extensive drilling data and petrophysical laboratory analysis. Specific processing and imaging of the acquired and synthetic datasets yielded high-resolution reflectivity images. Joint analysis of these images and cross-validation with lithological logging data from 135 nearby boreholes led to successful interpretation of key geological contacts including the target sulfide mineralization. In conclusion, our experiment demonstrates the value of in-mine VSP measurements for detailed resource delineation in a complex geological setting. In particular, we emphasize the potential benefit of using fiber-optic DAS systems, which provide reflection data at sufficient quality with less logistical effort and a higher acquisition rate. This amounts to a lower total acquisition cost, which makes DAS a valuable tool for future mineral exploration activities.

Geophone

Vertical seismic profile

Distributed Acoustic Sensing

Petrophysics

Mineral exploration

10.3390/min8110538

Cite

Citations (28)

3-D imaging of the Central Lapland Greenstone Belt using magnetotelluric and seismic data

EGU General Assembly Conference Abstracts (2012)

I. Lahti T. Korja Maxim Smirnov Katri Vaittinen E. Sandgren

Magnetotellurics

Greenstone belt

Source

Cite

Citations (4)

COGITO-MIN seismic reflection study in Polvijärvi: Insight into the first results

Gardar Gislason Suvi Heinonen M. Malinowski Emilia Koivisto Ł. Sito

Cogito ergo sum

Reflection

Cite

Citations (0)

Delineating structures controlling sandstone‐hosted base‐metal deposits using high‐resolution multicomponent seismic and radio‐magnetotelluric methods: a case study from Northern Sweden

Geophysical Prospecting (2015)

Alireza Malehmir Shunguo Wang Jarkko Lamminen Bojan Brodic Mehrdad Bastani

ABSTRACT Over the past few decades seismic methods have increasingly been used for the exploration of mineral, geothermal, and groundwater resources. Nevertheless, there have only been a few cases demonstrating the advantages of multicomponent seismic data for these purposes. To illustrate some of the benefits of three‐component data, a test seismic survey, using 60 digital three‐component sensors spaced between 2 m and 4 m and assembled in a 160 m‐long prototype landstreamer, was carried out over shallow basement structures underlying mineralized horizons and over a magnetic lineament of unknown origin. Two different types of seismic sources, i.e., explosives and a sledgehammer, were used to survey an approximately 4 km‐long seismic profile. Radio‐magnetotelluric measurements were also carried out to provide constraints on the interpretation of the seismic data over a portion of the profile where explosive sources were used. Good quality seismic data were recorded on all three components, particularly when explosives were used as the seismic source. The vertical component data from the explosive sources image the top of the crystalline basement and its undulated/faulted surface at a depth of about 50 m–60 m. Supported by the radio‐magnetotelluric results, however, shallower reflections are observed in the horizontal component data, one of them steeply dipping and associated with the magnetic lineament. The vertical component sledgehammer data also clearly image the crystalline basement and its undulations, but significant shear‐wave signals are not present on the horizontal components. This study demonstrates that multicomponent seismic data can particularly be useful for providing information on shallow structures and in aiding mineral exploration where structural control on the mineralization is expected.

Magnetotellurics

Lineament

Basement

Geophone

Vertical seismic profile

10.1111/1365-2478.12238

Cite

Citations (29)

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

Surveys in Geophysics (2017)

Thomas Kalscheuer Niklas Juhojuntti Katri Vaittinen

A combination of magnetotelluric (MT) measurements on the surface and in boreholes (without metal casing) can be expected to enhance resolution and reduce the ambiguity in models of electrical resistivity derived from MT surface measurements alone. In order to quantify potential improvement in inversion models and to aid design of electromagnetic (EM) borehole sensors, we considered two synthetic 2D models containing ore bodies down to 3000 m depth (the first with two dipping conductors in resistive crystalline host rock and the second with three mineralisation zones in a sedimentary succession exhibiting only moderate resistivity contrasts). We computed 2D inversion models from the forward responses based on combinations of surface impedance measurements and borehole measurements such as (1) skin-effect transfer functions relating horizontal magnetic fields at depth to those on the surface, (2) vertical magnetic transfer functions relating vertical magnetic fields at depth to horizontal magnetic fields on the surface and (3) vertical electric transfer functions relating vertical electric fields at depth to horizontal magnetic fields on the surface. Whereas skin-effect transfer functions are sensitive to the resistivity of the background medium and 2D anomalies, the vertical magnetic and electric field transfer functions have the disadvantage that they are comparatively insensitive to the resistivity of the layered background medium. This insensitivity introduces convergence problems in the inversion of data from structures with strong 2D resistivity contrasts. Hence, we adjusted the inversion approach to a three-step procedure, where (1) an initial inversion model is computed from surface impedance measurements, (2) this inversion model from surface impedances is used as the initial model for a joint inversion of surface impedances and skin-effect transfer functions and (3) the joint inversion model derived from the surface impedances and skin-effect transfer functions is used as the initial model for the inversion of the surface impedances, skin-effect transfer functions and vertical magnetic and electric transfer functions. For both synthetic examples, the inversion models resulting from surface and borehole measurements have higher similarity to the true models than models computed exclusively from surface measurements. However, the most prominent improvements were obtained for the first example, in which a deep small-sized ore body is more easily distinguished from a shallow main ore body penetrated by a borehole and the extent of the shadow zone (a conductive artefact) underneath the main conductor is strongly reduced. Formal model error and resolution analysis demonstrated that predominantly the skin-effect transfer functions improve model resolution at depth below the sensors and at distance of $$\sim $$ 300–1000 m laterally off a borehole, whereas the vertical electric and magnetic transfer functions improve resolution along the borehole and in its immediate vicinity. Furthermore, we studied the signal levels at depth and provided specifications of borehole magnetic and electric field sensors to be developed in a future project. Our results suggest that three-component SQUID and fluxgate magnetometers should be developed to facilitate borehole MT measurements at signal frequencies above and below 1 Hz, respectively.

Magnetotellurics

Resistive touchscreen

Overburden

10.1007/s10712-017-9454-y

Cite

Citations (35)

High-resolution Multicomponent Hardrock Seismic Imaging of Mineral Deposits and their Host Rock Structures

Proceedings (2014)

Alireza Malehmir Shunguo Wang Jarkko Lamminen Mehrdad Bastani Christopher Juhlin

Although applied in the past, there are only a few cases demonstrating the advantages of multicomponent seismic data for mineral exploration. To illustrate this, a test survey using sixty 3C-digital sensors, spaced between 2 to 4 m and assembled in a 160 m long landstreamer, was carried out to provide information on shallow structures hosting mineralization and also a magnetic lineament with an unknown origin. The survey, totally about 1.3 km long, was complemented by Radio MagnetoTelluric (RMT) measurements. Although an explosive source was used to generate the seismic signal, the seismic data show good quality for all the three components. Supported by the RMT results, clear reflections are observed in the horizontal component data at about 25 m depth, one of them steeply dipping, likely associated with the magnetic lineament. Field static corrections were well estimated thanks to the close shot and receiver spacing and the broadband frequency content of the data. This study demonstrates that multicomponent seismic data can be useful for providing information on shallow structures and linking them to the surface geology. The vertical component data, however, show deeper penetration and better image the crystalline basement and its undulated/faulted surface at about 50 m depth.

Lineament

Magnetotellurics

10.3997/2214-4609.20140509

Cite

Citations (0)

Decomposition analysis of the BEAR magnetotelluric data: implications for the upper mantle conductivity in the Fennoscandian Shield

Geophysical Journal International (2005)

I. Lahti Annakaisa Korja P. Kaikkonen Katri Vaittinen

Long-period magnetotelluric (MT) and geomagnetic depth sounding data (GDS) have been acquired on the Fennoscandian Shield under the framework of the Baltic Electromagnetic Array Research (BEAR) project. The field campaign was carried out in the summer of 1998 when variations of the natural electromagnetic field were recorded simultaneously at 46 MT and 20 GDS stations. The key targets of the project are to investigate the electrical properties of the upper mantle and to determine the depth to the lithosphere—asthenosphere boundary in the Fennoscandian craton. A challenging task emerges from the fact that numerous highly conductive crustal bodies and local conductivity contrasts generate galvanic and inductive distortions to the calculated transfer functions in the research area. We present here a systematic decomposition and dimensionality analysis of the BEAR data and use the results of this analysis to verify regions for which 1-D inversion is justified. We argue that most of the BEAR data represent regional 2-D and 3-D structures with local galvanic distortion. The decomposition of the long-period (T > 3000 s) MT impedance tensors yield a set of smoothly varying regional strike directions. Yet strike angles vary significantly in the scale of the BEAR array and have abrupt regional changes in some areas. The spatial behaviour of strike angles cannot be connected with large-scale geological units. Moreover, strong variation of strike azimuths over the BEAR array convincingly shows that the strike angles cannot be associated with present day plate motion or mantle convection, because that would require a consistent strike azimuth over the whole array. Observed long-period strike angles indicate mainly upper mantle 2-D and 3-D structures or frozen in anisotropy induced by several Palaeoproterozoic and Archaean events. The dimensionality analysis of the BEAR data shows that in the northeastern part of the array the regional structure is approximately 1-D. 1-D inversion of selected data from the western Lapland-Kola Domain reveals a conducting layer in the middle crust. An increase of conductivity is required also at depths greater than 170 km providing a minimum estimate of the lithosphere thickness beneath the target area. Partial melts or dissolved water in olivine are most plausible sources for increased conductivity at such depths.

Magnetotellurics

10.1111/j.1365-246x.2005.02744.x

Cite

Citations (34)

High-resolution magnetotelluric studies of the Archaean-Proterozoic border zone in the Fennoscandian Shield, Finland

Geophysical Journal International (2012)

Katri Vaittinen T. Korja P. Kaikkonen I. Lahti Maxim Smirnov

The Archaean-Proterozoic collisional zone is a complex mixture of the Archaean complexes [e.g. Iisalmi Complex (IC)], Proterozoic supracrustal belts [e.g. Kainuu Belt (KB) and Savo Belt (SB)] and oceanic arc lithologies in the central Fennoscandian Shield. The zone was formed in the Savo orogeny when the Keitele microcontinent collided with the Archaean Karelian craton in the Palaeoproterozoic time. The crustal architecture of this palaeosuture is studied using new broad-band magnetotelluric data from 104 sites. 2-D conductivity models across the border zone between the Palaeoproterozoic Svecofennian Domain and the Archaean Karelian province are constrained using the recent, partly collocated reflection seismic data from the Finnish Reflection Experiment (FIRE). Dimensionality analyses, in particular the Q-function analysis, show that magnetotelluric data represent reasonably well regional 2-D structure at periods <100 s, which is the longest period used in this study. Strike determinations gave a stable strike of N15W. For the inversions, the data are projected into three parallel profiles with an azimuth of N75E. The determinant inversion is selected as the most suitable method for the data set. Especially the phase data are useable only from the determinant since one of the polarizations have the out-of-quadrant phase at several sites. The interpreted final, geological more appropriate models, where smoother thick conductive areas are replaced by thinner layers, are constructed from the results of the unconstrained smooth inversions with the help of forward modelling, synthetic and prior model inversions and reflection seismic models. The two major sets of crustal conductors are identified. They have an opposite dip and together they form a bowl-shaped conductor. In the west, the eastward dipping SB conductors are located at the bottom of the formation underlain by the Keitele microcontinent. The SB conductors extend to the east possibly cutting the westward dipping conductors of the KB. The conductive KB is flanked above and below by the resistive Archaean IC/Rautavaara and Eastern Finland Complexes and represents the remnants of a basin that was squeezed between two Archaean blocks in the collision. The crustal conductors revealed by the inversion extend to the surface, where they can be associated with the near-surface conductors mapped by airborne electromagnetic surveys. Geological mapping has shown that the near-surface conductors are caused by graphite and/or sulphide-bearing metasedimentary rocks. Thus the deep conductors related with the Proterozoic KB and SB were formed on the surface and transported into the upper and middle crustal levels in the Savo orogeny. The crust in the Karelian Craton is highly resistive having only minor resistivity variations in our research area. Also the Archaean lower crust is resistive on the contrary to the conductive lower crust of the Proterozoic SB and the Keitele microcontinent.

Magnetotellurics

Lithology

10.1111/j.1365-246x.2011.05300.x

Cite

Citations (15)

Distributed Acoustic Sensing versus Conventional VSP Imaging of the Kylylahti Polymetallic Deposit

Marko Riedel C. Cosma N. Enescu Emilia Koivisto Kari Komminaho

Summary This work presents a high-resolution seismic imaging study of a target sulphide mineralization located in the Kylylahti polymetallic mine, Eastern Finland. For this purpose, in-mine VSP measurements were carried out, using two different technologies: a conventional three-component VSP and a fibre-optic Distributed Acoustic Sensing (DAS) system. The two acquisition systems were placed in existing exploration boreholes adjacent to the deposit and successfully recorded reflections from the target and its host rocks. Subsequent application of a target-specific VSP processing and imaging workflow to the conventional and DAS data provided high-resolution reflectivity images from both systems. To support geological interpretation, a 3D seismic forward modelling study was conducted using a geological model created from exploration drilling data and laboratory petrophysical measurements. Cross-validation of the acquired VSP data with the synthetic seismograms and extensive logging data enabled identification of the target reflection as well as interpretation of several new geological contrasts. Between the two VSP methods, the conventional system exhibits slightly superior signal-to-noise ratio and bandwidth. However, the DAS system also provides images of satisfactory quality at much less acquisition time and logistical effort. Thus, DAS offers a powerful and particularly cost-effective exploration technology suitable for detailed delineation of mineral resources.

Petrophysics

Distributed Acoustic Sensing

Vertical seismic profile

Geophysical Imaging

Seismic vibrator

10.3997/2214-4609.201802744

Cite

Citations (2)