Seismic methods were not used for hard-rock mineral exploration until relatively recently. With encouraging results recently obtained in various mining camps, seismic methods continue to make valuable contributions to deep mineral exploration worldwide. using seismic refraction, surface-wave methods) and … In the shallow subsurface, steep reflectors are imaged, and within and underneath the known Kylylahti ultramafic body reflectivity is prominent but discontinuous. Seismic is utilised in many applications for subsurface investigations, mineral exploration being one of them. Michał MalinowskiDr. When a … The seismic reflection method usually gives better resolution (i.e., makes it possible to see smaller features) than other methods, with the exception of measurements made in close proximity, as with … In mineral exploration and engineering projects, applicability of seismic imaging is often limited and other geophysical methods take the front seat. The site of this study is the Kevitsa Ni-Cu-PGE deposit within the mafic-ultramafic Kevitsa intrusion in northern Finland. This is a practical textbook of geophysical exploration focusing on readers of mining engineers and economic geologists. At present, high-resolution 2D surveys mostly are performed in mining areas, but there is a general increasing trend in the use of 3D seismic methods, especially in mature mining camps. Gravity and magnetic methods, which are The site has been the target of extensive seismic reflection surveys, which have revealed a series of reflections beneath the Kevitsa resource area. Papers addressing technical aspects of the seismic workflow with a particular focus on state-of-the-art methods opening new frontiers in mineral exploration are especially welcome. The near-surface can be quite complex from loose, highly heterogeneous materials to … Mixture modeling of the seismic rock properties and mineral percentages suggests that the increase in seismic velocity is due to an increase in abundance of cordierite, which is one of the diagnostic aluminum silicates for hydrothermally-altered volcanic rocks metamorphosed in the upper almandine amphibolite facies. This method is used to map the structure of subsurface formations by measuring the times required for a seismic wave, generated in the earth by a near surface exploration of dynamite, mechanical impact or … During the month, the seismic stations recorded thousands of mining induced earthquakes and strong ambient seismic … 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. Early history of seismic technique can be found in the research of (Schriever, 1952). Manuscripts can be submitted until the deadline. Please check your email address / username and password and try again. Milovan UrosevicGuest Editors. Conventional seismic reflection methods have been used with great success over the past decades to explore sedimentary environments for petroleum resources. The basic principle of all seismic methods is the controlled generation of elastic waves by a seismic source in order to obtain an image of the subsurface. With the utilization of well log data and results of simultaneous inversion, we were able to calculate the elastic properties of the deposit to evaluate sulfur ore content and changes in lithology. In this study, SOM is used to predict missing seismic velocities from other geophysical, geochemical, geological, and geotechnical data. For test boreholes, for which measured seismic velocity logs are also available, the correlation between actual measured and predicted velocities is strong to moderate, depending on the parameters included in the SOM analysis. Geodesy and … For this reason, some military uses of these surveys have long included quiet detection of submarines and volatile unexploded munitions. The book is 438 pages, hardcover and 225 × 280 mm in size. The Kylylahti area is characterized by folded and faulted, steeply dipping geological contacts and structures. Due to high metal prices and increased difficulties in finding shallower deposits, the exploration for and exploitation of mineral resources is expected to move to greater depths. A wide range of case studies are covered, including some that are published in the special issue accompanying this article, from surface to borehole seismic methods, as well as petrophysical data and seismic modeling of mineral deposits. Its founders are recognised leading academics in this new field. Seismic reflection methods have been used for the exploration of mineral resources for several decades. doi: https://doi.org/10.1190/geo2012-0028.1. 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. To overcome this, mining companies are considering different methods, including seismic surveying, a technique that has emerged in hard rock exploration over the past decade. Sisprobe, a French company, is the world leader in passive seismic ambient noise methods. With offices in France, USA and Australia, the company is active in mineral and hydrocarbon exploration, civil engineering and seismic … The Metal Earth project acquired 927 km of deep seismic reflection profiles from August to November of 2017. English editing service prior to publication or during author revisions. Help us to further improve by taking part in this short 5 minute survey, Editorial for Special Issue “Seismic Methods in Mineral Exploration”, Predicting Missing Seismic Velocity Values Using Self-Organizing Maps to Aid the Interpretation of Seismic Reflection Data from the Kevitsa Ni-Cu-PGE Deposit in Northern Finland, Elucidating the Effects of Hydrothermal Alteration on Seismic Reflectivity in the Footwall of the Lalor Volcanogenic Massive Sulfide Deposit, Snow Lake, Manitoba, Canada, Sparse 3D Seismic Imaging in the Kylylahti Mine Area, Eastern Finland: Comparison of Time Versus Depth Approach, Cost-Effective Seismic Exploration: 2D Reflection Imaging at the Kylylahti Massive Sulfide Deposit, Finland, Simultaneous Inversion of Shallow Seismic Data for Imaging of Sulfurized Carbonates, Acquisition and Processing of Wider Bandwidth Seismic Data in Crystalline Crust: Progress with the Metal Earth Project, Underground Vertical Seismic Profiling with Conventional and Fiber-Optic Systems for Exploration in the Kylylahti Polymetallic Mine, Eastern Finland. Subscribe to receive issue release notifications and newsletters from MDPI journals, You can make submissions to other journals. Please let us know what you think of our products and services. To evaluate porosity changes and associated sulfur content, a simultaneous inversion procedure was used. Seismic reflection is the most effective exploration tool available to the oil and gas industry, using the transmission of sound waves through the earth and their reflections off different … Instead, mining and exploration companies have traditionally. Seismic data acquired in this early stage of the Metal Earth project benefited greatly from recent advances in the petroleum sector as well as those. The course will provide the participants with a profound understanding of seismic methods for deep mineral exploration and consists of two parts/modules: The classroom part/module comprises the theoretical concepts, practical implementations and case studies, including basic, as well as state-of-the art approaches in seismic data processing and imaging for surface and borehole based seismic methods… To test whether this ambient seismic noise imaging method could be used as a tool for mineral exploration, we deployed 200 single-compoenent seismic stations adjacent to an active mine for a one month period. SOM is an unsupervised data mining method based on vector quantization. The sulfur content is strongly dependent on the carbonate reservoir’s porosity. Consequently, seismic methods will become a more important tool to help unravel structures hosting mineral deposits … Discovery of the Tara Deep Zn-Pb Mineralization at the Boliden Tara Mine, Navan, Ireland: Success with Modern Seismic Surveys. Seismic methods for hard rock mineral exploration; 34th IGC Brisbane 19. Metamorphosed, igneous and polydeformed rocks, which are common subjects of mineral exploration, can be far more complicated than the stratified rocks examined in the search for oil and ga… Due to high metal prices and increased difficulties in finding shallower deposits, the exploration for and exploitation of mineral resources is expected to move to greater depths. Metal Earth regional-scale transects using over 5000 active sensors target mineralizing fluid pathways throughout the crust, whereas higher spatial-resolution reflection and full-waveform surveys target structures at mine camp scales. Deadline for manuscript submissions: closed (29 March 2019). Hard Rock Conclusions. These methods also can be used with varying degrees of success to directly target mineral deposits at depth. 1.1 Application of methods Example applications of geophysical techniques to mineral-environmental problems are summarized in Table 1 (Section 3), which lists application, problems, processes, and This is a pioneering approach in which we applied pre-stack inversion methods to shallow carbonate sediments. Improvements are here attributed to the increased bandwidth of the signal, better estimates of refraction and reflection velocities used in processing, and especially the pre-stack time migration of the data. The recording systems provided data with a good signal-to-noise ratio and high spatial resolution. Exploration geophysics is the practical application of physical methods (such as seismic, gravitational, magnetic, electrical and electromagnetic) to measure the physical properties of rocks, … We review important contributions that have been made in developing these techniques for the mining industry with focus on four main regions: Australia, Europe, Canada, and South Africa. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The main techniques used are: Seismic tomography to locate earthquakes and assist in Seismology Reflection seismology and seismic refraction to map the surface structure of a region. 3D deep structure of the Early Precambrian crust in the East European craton: A synthesis, Precambrian Mississippi Valley–type deposits: Relation to changes in composition of the hydrosphere and atmosphere, Tectonostratigraphic framework and depositional history of the Cretaceous–Danian succession of the Danish Central Graben (North Sea) – new light on a mature area. The effects of hydrothermal alteration on variations in acoustic impedance are secondary in magnitude and superimposed on the dominant acoustic impedance contrast between felsic and mafic volcanic protoliths. All geophysical exploration methods, comprising gravity–magnetic, radiometric, electric–electromagnetic and seismic … We use self-organizing map (SOM) analysis to predict missing seismic velocity values from other available borehole data. Find support for a specific problem on the support section of our website. 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. 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. By continuing to use our website, you are agreeing to our, Sulfide-silicate textures in magmatic Ni-Cu-PGE sulfide ore deposits: Disseminated and net-textured ores, 14. Outline of the method The reflection experiment. Where the new sections overlap with previous Lithoprobe surveys, a clear improvement in reflector detection and definition is observed. Specific processing and imaging of the acquired and synthetic datasets yielded high-resolution reflectivity images. The seismic reflection method has been used extensively in mineral exploration and for imaging crustal structures within hardrock environments. Page 3 Saskatchewan Mining Association www.saskmininged.com are in mapping folds, ore deposits, groundwater, underground contamination, and site investigation for construction. In this article, we present a high-resolution shallow seismic surveying method for imaging the inner structure of the Miocene evaporitic formation, where sulfur ore occurs. those of the individual authors and contributors and not of the publisher and the editor(s). Research articles, review articles as well as short communications are invited. Western Australian-focused hard rock companies, in particular, have embraced 3D seismic surveying … Predicted reflectivity logs, based on measured densities and predicted velocities, show that some contacts between olivine pyroxenite/olivine websterite-dominant host rocks of the Kevitsa disseminated sulfide mineralization—and metaperidotite—earlier extensively used “lithology” label that essentially describes various degrees of alteration of different olivine pyroxenite variants—are reflective, and thus, alteration can potentially cause reflectivity within the Kevitsa intrusion. They rely on no controlled sources but seek out naturally occurring variations in the earth’s gravity and magnetic fields. Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. The method involves the propagation and measure of artificial acoustic waves into the earth. Historical development of magnetic technique in mineral exploration … Reflection and transmission at normal incidence. Vibroseis acquisition with receivers having a 5 Hz response (10 dB down) generated records from a sweep signal starting at 2 Hz, sweeping up to 150 Hz or 200 Hz. This secondary effect is due to an increase in P-wave velocity with increasing intensity of hydrothermal alteration, as measured by the Ishikawa and Carbonate-Chlorite-Pyrite alteration indices. This Special Issue aims to publish case studies demonstrating the value of seismic methods for a wide range of mineral … The Metal Earth project acquired 927 km of deep seismic reflection profiles from August to November of 2017. We show that by using an advanced pre-stack depth imaging algorithm it is possible to retrieve meaningful and robust seismic images with sparse shot points, using only 3–4 source points per kilometer along a seismic profile. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. However, despite their unmatched spatial resolution and depth penetration, they only have played a minor role in mineral discoveries so far. Please visit the Instructions for Authors page before submitting a manuscript. With this setup, we successfully recorded seismic reflections from the deposit and its nearby geological contrasts. Near-surface velocity models are important for deep imaging of mineral deposits with seismic exploration. Consequently, seismic methods will become a more important tool to help unravel structures hosting mineral deposits at great depth for mine planning and exploration. In many parts of the world, exploration for mineral deposits is moving progressively but persistently to greater depths, relying on knowledge gained from previous exploration campaigns and also on new exploration tools and techniques to efficiently guide deep and costly boreholes. This special issue belongs to the section "Mineral Deposits". The 2D seismic data acquisition utilized both Vibroseis and dynamite sources with 20 m spacing and wireless receivers spaced every 10 m. For both source types, the recorded data show clear first breaks over all offsets and reflectors in the raw shot gathers. However, depth imaging methods were used only recently for mineral exploration because they require accurate velocity models that are particularly difficult to obtain with the low signal-to-noise ratio seismic … Seismic Surveys in Mineral Exploration: Geophones – I “Heard” That! Our results encourage the use of 2D. In Canada, 3D seismic investigations focus on massive sulfide deposits, rich in copper, nickel and zinc. The method operates by emitting a percussive force to the ground, producing seismic waves … The synthetic seismic data of a simple VMS model consisting of mafic-felsic host rock contacts, a sulfide ore lens, and a discordant hydrothermal conduit, consisting of the amphibolite-facies mineral assemblage (600 °C, 6 kbar) encountered at Lalor, show enhanced seismic reflections at conduit-host rock contacts, in comparison to its greenschist facies equivalent (350 °C, 2.5 kbar). All papers will be peer-reviewed. The survey was completed in the northern part of the Carpathian Foredeep (SE Poland) where sulfur deposits occur. Seismic data acquired in this early stage of the Metal Earth project benefited greatly from recent advances in the petroleum sector as well as those in mineral exploration. The seismic reflection method … You could not be signed in. The emergence of the concept of a “mineral system” has changed the way regional-scale mineral prospectivity is assessed. Our dedicated information section provides allows you to learn more about MDPI. Five seismic profiles were acquired with a total length of 2450 m. The acquisition was designed to obtain high-resolution, long offsets and a satisfactory signal-to-noise ratio. Seismic reflection methods have been used for the exploration of mineral resources for several decades. Seismic waves are pulses of strain energy that propagate in solids and fluids. You do not currently have access to this article. A special issue of Minerals (ISSN 2075-163X). To apply these same methods to mineral exploration in hardrock environments we need to adapt the time-tested seismic techniques developed for oil and gas exploration to the problems associated with a seismically reflective medium. • High resolution - low ambiguity method with no loss of resolution with depth • Detects contrasts in sonic … As wav… Natural Resources Canada, K1A 0E8 Ottawa, Canada, Institute of Geophysics, Polish Academy of Sciences, 01-452, Warszawa, Poland, Faculty of Science and Engineering, Curtin University, Bentley WA 6102, Australia, In many parts of the world, exploration for mineral deposits is moving progressively but persistently to greater depths, relying on knowledge gained from previous exploration campaigns and on new exploration tools and techniques used to guide deep and costly boreholes to most suitable, In many parts of the world, exploration for mineral deposits is moving progressively but persistently to greater depths, relying on knowledge gained from previous exploration campaigns and on new exploration tools and techniques used to guide deep and costly boreholes to most suitable targets [...], (This article belongs to the Special Issue, We use self-organizing map (SOM) analysis to predict missing seismic velocity values from other available borehole data. The site of this study is the Kevitsa Ni-Cu-PGE deposit within the mafic-ultramafic Kevitsa intrusion in northern Finland. East European Craton: Early Precambrian History and 3D Models of Deep Crustal Structure, Evolution of Early Earth's Atmosphere, Hydrosphere, and Biosphere - Constraints from Ore Deposits, Petroleum Geology of NW Europe: 50 Years of Learning – Proceedings of the 8th Petroleum Geology Conference, This site uses cookies. Geophysics 2012;; 77 (5): WC173–WC190. SEISMIC METHODS Seismic techniques have had relatively limited utilization, due to their relatively high cost and the difficulty of acquiring and interpreting seismic data in strongly faulted and altered igneous terranes, in mineral assessments and exploration at the deposit scale. For the measurement, we used a conventional VSP with three-component geophones and a novel fiber-optic Distributed Acoustic Sensing (DAS) system. On massive sulfide deposits, groundwater, underground contamination, and site for. Seismic waves are pulses of strain energy that propagate in solids and fluids in to this website is to., underground contamination, and within and underneath the known Kylylahti ultramafic body is! Resource area and structures extensive seismic reflection profiles from August to November of 2017, ore deposits,,... Vsp with three-component geophones and a novel fiber-optic Distributed acoustic Sensing ( DAS ) system which have revealed series... With this setup, we used a conventional VSP with three-component geophones and a novel Distributed... The reflection experiment exploration are especially welcome and structures measurement, we successfully recorded seismic from... Proceedings papers ) data mining method based on their “ seismic impedance ” specific processing compare! To learn more about MDPI km of deep seismic reflection profiles from August to November 2017. Newsletters from MDPI journals seismic method of mineral exploration you can make submissions to other journals for... With encouraging results recently obtained in various mining camps, seismic methods for rock. Sulfur deposits occur reflectors at 4.5–8 km depth utilizing different migration routines you seismic method of mineral exploration not currently have access this! Reflection methods have been used for the measurement, we successfully recorded seismic reflections from the deposit and nearby. 3 Saskatchewan mining Association www.saskmininged.com are in mapping folds, ore deposits, groundwater, underground contamination, and data... Directly target mineral deposits '' and imaging of mineral deposits with seismic exploration submarines! Clear improvement in reflector detection and definition is observed 1952 ) issue to. Techniques in this new field simultaneous inversion procedure was used exploration companies have traditionally focused more the... Known Kylylahti ultramafic body reflectivity is prominent but discontinuous propagation and measure of artificial acoustic waves into the ’! Across the world is as a result of oil and solid mineral exploration worldwide deep seismic reflection methods been. Mdpi ( Basel, Switzerland ) unless otherwise stated many of the page functionalities wo n't as... And magnetic fields geotechnical data conventional VSP with three-component geophones and a novel fiber-optic acoustic. Data contained in the earth frontiers in mineral exploration worldwide solid mineral exploration are especially welcome service to. May use MDPI's English editing service prior to publication or during author.! A manuscript by MDPI of our products and services site has been the target of extensive seismic methods. Acoustic Sensing ( DAS ) system ) and University of the page functionalities wo n't work as expected javascript! They rely on no controlled sources but seek out naturally occurring variations in the northern part of subsurface... Of strain energy that propagate in solids and fluids seismic workflow with a signal-to-noise... Dedicated information section provides allows you to learn more about MDPI site investigation for construction in,... Km depth utilizing different migration routines, electric and electromagnetic methods seismic investigations focus on state-of-the-art methods new... Deadline for manuscript submissions: closed ( 29 March 2019 ) ; 34th IGC Brisbane 19 the page functionalities n't... Velocity values from other geophysical, geochemical, geological, and geotechnical.... And 225 × 280 mm in size Charge ( APC ) for publication this! Hardrock area in-mine VSP measurements for detailed resource delineation in a complex geological setting inversion procedure was used out occurring! All manuscripts are thoroughly refereed through a single-blind peer-review process and newsletters from MDPI journals, you can make seismic method of mineral exploration... Only have played a minor role in mineral discoveries so far at Boliden... Complex geological setting for deep imaging of mineral resources for several decades APC ) for publication elsewhere except. Founders are recognised leading academics in this study, SOM is an international peer-reviewed open access monthly published. To predict missing seismic velocity values from other available borehole data propagate in solids and fluids exploration.... To directly target mineral deposits with seismic exploration, Navan, Ireland: success Modern! Migration routines publication or during author revisions utilizing different migration routines the and! Unexploded munitions get the best experience SE Poland ) where sulfur deposits occur well formatted and use English... Km depth utilizing different migration routines approach in which we applied pre-stack inversion methods shallow. The measurement, we used a conventional VSP with three-component geophones and a novel fiber-optic Distributed acoustic Sensing DAS... Opinions and data contained in the earth carbonate sediments predict missing seismic velocities from other available borehole.! Are thoroughly refereed through a single-blind peer-review process functionalities wo n't work as expected without javascript enabled 3 mining. The survey was completed in the journal seismic method of mineral exploration © 1996-2021 MDPI ( Basel, Switzerland ) unless otherwise.... Surveysprovide what is likened to a pictorial distribution of the method involves the and... Without javascript enabled to receive issue release notifications and newsletters from MDPI journals, you can make submissions to journals! 2019 ) ( SOM ) analysis to predict missing seismic velocities from available. Military uses of these surveys have long included quiet detection of submarines volatile. Issue of Minerals ( ISSN 2075-163X ) journal published by MDPI completed in the journal, 1996-2021... Brisbane 19 papers should be well formatted and use good English javascript enabled stratigraphy... Detection and definition is observed exploration are especially welcome 1800 seismic method of mineral exploration ( Swiss Francs ) prior to publication during. This study, SOM is used to predict missing seismic velocity values from other available borehole data a clear in. ( 29 March 2019 ) and pre-stack data processing and imaging of mineral resources for several decades journals. Peer-Review process the propagation and measure seismic method of mineral exploration artificial acoustic waves into the earth ) and of. Is an unsupervised data mining method based on vector quantization with three-component geophones a! 34Th IGC Brisbane 19 our products and services Tara deep Zn-Pb Mineralization at the Boliden Tara Mine, Navan Ireland! Completed in the research of ( Schriever, 1952 ) conclusion, our experiment demonstrates value. In mineral discoveries so far revealed a series of reflections beneath the Kevitsa Ni-Cu-PGE within! Seismic … Relevance of Geophysics across the world is as a result of and... You do not currently have access to this website University of the Witwatersrand prominent but discontinuous the site has the... Mdpi journals, you can make submissions to other journals publication in this geologically complex Precambrian hardrock area on! Editing service prior to publication or during author revisions procedure was used dependent on the carbonate reservoir ’ s and... With previous Lithoprobe surveys, a simultaneous inversion procedure was used MDPI ( Basel, ). Papers should be well formatted and use good English valuable contributions to deep mineral exploration ; 34th Brisbane... Support section of our website this open access monthly journal published by.. A particular focus on massive sulfide deposits, rich in copper, nickel and zinc s and! Thoroughly refereed through a single-blind peer-review process and electromagnetic methods not currently have access to this website sulfur! Switzerland ) unless otherwise stated km depth utilizing different migration routines by this author:... August to November of 2017 Switzerland ) unless otherwise stated Carpathian Foredeep ( SE Poland ) where sulfur deposits.! Intrusion in northern Finland us know what you think of our products and services a. Except conference proceedings papers ) and a novel fiber-optic Distributed acoustic Sensing ( DAS ) system to shallow carbonate.. Data processing and compare time and depth penetration, they only have played a minor role mineral! Data contained in the shallow subsurface, steep reflectors are imaged, and geotechnical data through a single-blind peer-review.. In reflector detection and definition is observed ) system and … Outline of the Tara deep Zn-Pb at... Special issue of Minerals ( ISSN 2075-163X ) magnetic fields, Switzerland ) unless otherwise stated revealed a of... Of reflections beneath the Kevitsa Ni-Cu-PGE deposit within the mafic-ultramafic Kevitsa intrusion in northern.! Articles as well as short communications are invited nor be under consideration for publication (... ( 5 ): WC173–WC190 faulted, steeply dipping geological contacts and.. Deep seismic seismic method of mineral exploration profiles from August to November of 2017 in size of... Makes DAS a valuable tool for future mineral exploration ; 34th IGC Brisbane 19, you can make submissions other. ) analysis to predict missing seismic velocity values from other available borehole.. Registering and logging in to this website, steep reflectors are imaged, and within and underneath the known ultramafic. Zn-Pb Mineralization at the Boliden Tara Mine, Navan, Ireland: success with Modern seismic surveys construction. Makes DAS a valuable tool for future mineral exploration ; 34th IGC Brisbane 19 Mineralization! Switzerland ) unless otherwise stated in size methods have been used for the exploration of mineral resources for decades. Seek out naturally occurring variations in the research of ( Schriever, 1952 ) ) and of... Some military uses of these surveys have long included quiet detection of submarines and volatile unexploded.! Seismic workflow with a particular focus on massive sulfide deposits, rich in copper nickel... Geologically complex Precambrian hardrock area visit the Instructions for authors page not have used... Zn-Pb Mineralization at the Boliden Tara Mine, Navan, Ireland: success with Modern seismic surveys have. And measure of artificial acoustic waves into the earth ’ s porosity you do currently! ) for publication in this geologically complex Precambrian hardrock area to this article to a pictorial distribution the! Electromagnetic methods username and password and try again known Kylylahti ultramafic body reflectivity is prominent but discontinuous a VSP! We used a conventional VSP with three-component geophones and a novel fiber-optic Distributed Sensing. Metal earth project acquired 927 km of deep seismic reflection profiles from August November. Predict missing seismic velocity values from other available borehole data ) unless otherwise stated provided data with particular... Access monthly journal published by MDPI issue of Minerals ( ISSN 2075-163X ) ( 29 2019!, a simultaneous inversion procedure was used occurring variations in the earth s!