By VK and Lev Eppelbaum
‘Vestnik Kavkaza’ has recently told its readers about the fundamental monograph by Israeli researchers Lev Eppelbaum and Boris Khesin, ‘Geophysical Studies in the Caucasus’ (2012, Springer). Some specialists became interested in the topic, so we’ve decided to publish yet more material about the authors and their book.
In 1982 Lev V. Eppelbaum was awarded a scholarly degree in geophysics in the Baku Oil and Chemistry Institute (Azerbaijan) and in 1989 he was awarded another degree by the Southern Department of the Baku Geophysics Institute and the Tbilisi Geophysics Institute (Georgia). In 1982-1983 while working with the Southern Department of the Baku Nonferrous and Precious Metals Institute he applied a complex of geophysical surface and underground methods on ore deposits. In the period from 1983 to 1990 he was employed by the gravimagnetic prospecting department of the Southern Department of the Baku Geophysics Institute. In 1991-1993 he conducted his post-doctorate research in Tel-Aviv University’s Geophysics department. In 1993 he became a senior research officer and senior lector in this department, and in 2005 he became an associated professor.
Lev Eppelbaum authored more than 280 publications, including 4 monographs, 98 papers and 40 proceedings. His most important work are the books ‘Interpretation of Geophysical Fields in Complicated Environments’ (1996, Kluwer Acad. Publ., Ser.: Modern Approaches in Geophysics) and ‘Geophysical Studies in the Caucasus’ (2012, Springer). Eppelbaum in cooperation with B. Hessin invented a system of interpretation of potential and quasi-potential geophysical fields in complex conditions (oblique polarization, uneven landscape and hostile environment). This system was successfully applied on multiple occasions in resolving practical problems on the Caucasus and the Eastern Mediterranean.
Prof. Eppelbaum gives the lecture courses ‘Potential geophysical fields’, ‘Applied geophysics’ and ‘Archaeological geophysics’ in the Tel-Aviv University.
Lev Eppelbaum is a member of the following professional associations: Society of Exploration Geophysicists, Euroscience, International Society for Archaeological Prospection, EARSeL SIG (remote sensing and archaeology), American Geophysical Union, European Association of Exploration Geophysicists, Society of Mediterranean Geologists and Geophysicists, EuroScience, Geoinformatics (Japan), Israel Geological Society and Prehistoric Society of Israel.
He is also a reviewer in more than 20 international scientific magazines: “Acta Geophysica”, “Advances in Geosciences”, “Applied Geophysics”, “Archaeological Prospection”, “Archaeometery”, “Earth and Planetary Science Letters”, “Earth Sciences Research Journal”, “Geophysical Prospecting”, “Geophysical Research Letters”, “Geophysical Journal International”, “Geophysics”, “HIAT Journal of Science and Engineering”, Journal of Asian Earth Sciences, “Journal of Geophysics and Engineering”, “Journal of Natural Hazards”, “Near Surface Geophysics”, “New Journal of Physics”, “Journal of Stratigraphy and Sedimentology”, “Marine Geophysical Researches”, “Planetary and Space Science”, “Sensors”, “The Open Mineral Processing Journal”, “Exploration Geophysics”, “Central European Journal of Geosciences”, and “Scientific Israel”. Eppelbaum is also deputy editor-in-chief of the “Geophysical Instrumentation, Methods and Data System” magazine, a member of the editorial board of “Positioning”, “Open Mineralogical Processing Journal”, “Open Petroleum Engineering Journal”, “LatinMag Letters”, “Stratigraphy and Sedimentology” magazines and a an associate editor of the “Advances in Geosciences” and “Jour. of Geophysics and Engineering”.
Eppelbaum was elected as the section head and organization committee member for 10 international conferences. He is a member of the ‘Earth’s revolution’ international commission and of the ‘WebmedCentral Ecology’ consultation committee.
Prof. Eppelbaum consults a number of Israeli as well as foreign organizations on matters of applies geophysics. His biography is published by “Who’s Who in America”, “Who’s Who of Professionals”, “Who’s Who in the World”, “Dictionary of International Biograph” (Cambridge), “American Biographical Institute”, as well as in some other publications. In 1998 prof. Eppelbaum was nominated for the State Award of Israel, and in 2011 – for the Christiaan Huygens medal of the European Geophysical Society.
Five years ago German Springer publishing house published a fundamental research by two Israeli scientists Lev Eppelbaum and Boris Khesin ‘Geophysical Studies in the Caucasus’. A considerable part of their scientific interests and experience is connected to the geophysical research and prospecting of minerals in Azerbaijan and neighboring regions. Therefore a lot of examples of the implementation of the system of interpretation of the potential and quasi-potential geophysical fields in complex conditions created by the authors are related to Azeri territory.
At the same time, the range of problems addressed in this book is not confined to Azerbaijan but covers the whole territory of the Greater and Lesser Caucasus, the Kurinsk depression and some other nearby regions. After Eppelbaum and Khesin moved to Israel they carried on their Caucasian studies, as this region is truly interesting from many points of view (more than 15 articles in international scientific magazines on the implementation of geophysical methods in the Caucasus preceded the monograph).
Another suggestion made by the authors of the book is increasing the Katexskoe polymetallic ore deposit reserve by applying 3D gravitational field modelling, which proved to be a very efficient method of geological prospecting. The authors have already applied the method to the gold deposit in Kyzylbulakh in 1993.
VK publishes an extract from Lev Eppelbaum and B. Khesin's “Advanced 3D modelling of gravity field unmasks reserves of a pyrite-polymetallic deposit: a case study from the Greater Caucasus”, published in ‘First Break’, the magazine of the European Association of Geoscientists and Engineers (EAGE).
Analysis of the application of gravity prospecting for ore deposits (e.g. Davis et al. 1957; Frasheri et al. 1997; Hansen, 2001; Hearst & Morris, 2001; Jorgensen, 2000; Khesin et al. 1993; Kleinkopf et al. 1970; Leaman, 1991; Nabighian & Asten, 2002; Parasnis, 1997; Yarosh & Polyakov, 1963) indicates that this method plays a significant role for ore body localization. An important prerequisite for its efficiency is the enhanced density contrast between ore targets and surrounding media. At the same time, detailed gravity survey in mountainous regions, where ore deposits mainly occur, is complicated by a lot of different factors. The typical ore deposit is usually found in a deformed structural environment characterized by the presence of a great variety of tectonic structures and geological bodies with different physical properties. Influence of surrounding terrain relief is also a basic disturbing factor. All these aspects make the clear definition of gravity anomalies difficult to discern and interpret (Jorgensen, 2000; Khesin et al. 1996; Steinhouser et al. 1990).
A lot of papers have discussed 3D modelling of gravity field. From the recent publications we can note Boulanger & Chouteau (2001); Chakravarthi & Sundararajan (2004); Furness (2000); Gallardo-Delgado et al. (2003); Holstein, H. (2003); Mauriello & Patella (2001); Zhang et al. (2004). The authors of this paper have successfully applied 3D gravity-magnetic modelling of gravity and magnetic fields in a few ore deposits of the Greater and Lesser Caucasus. For the first time the effectiveness of computing of rugged terrain relief effect during the process of 3D physical-geological modelling was demonstrated by integrated geophysical investigation of Kyzylbulakh gold-pyrite deposit (Mekhmana ore field, Lesser Caucasus) (Khesin et al. 1993). The most illustrative example of gravity field analysis displaying a geophysical examination of Katekh ore deposit (Belokan- Zakataly ore field, northern Azerbaijan) is presented below.
Geological background Katekh pyrite-polymetallic deposit is located at the southern slope of the Greater Caucasus (northern Azerbaijan) in an area of severe rugged topography (Figure 1). According to the data of the Azerbaijangeologiya Association, a geological section of the area is characterized mainly by interstratifications of sandy-clays associations of the Upper Aalenian. Two sub-parallel stratified sheet-like bodies represent the Katekh deposit. Tectonic faults control the space dislocation of all known economically recoverable ore bodies. The main morphological type of ore bodies in this deposit is lenticular shape. However, a combination of latitude and longitude faults complicates this type so much that they acquire the form of steam-chest beds. The Katekh deposit has been investigated by mining and drilling to a depth of 500 m. However, some experts note that due to extremely complicated tectonics, these operations have failed to completely delineate the ore bodies.
The following types of texture ores were identified in Katekh deposit: (1) massive, (2) veiny-clastic and (3) spottydisseminated. Main ore minerals of the Katekh deposit are pyrite, sphalerite, chalcopyrite and galena. Secondary ore minerals are presented by hepatic pyrite, wurtzite, arsenopyrite and melnikovite; rare minerals are silver and gold (Mekhtiev et al. 1976; Zaitseva et al. 1988).
3D gravity-magnetic software The GSFC (Geological Space Field Calculation) program was developed for solving specific 3D gravity and magnetic prospecting problems under complex geological conditions (Khesin et al. 1996). This program has been designed for computing the field of Δg (Bouguer, free-air or observed value anomalies), ΔZ, ΔX, ΔY, ΔT, as well as second derivatives of the gravitational potential under conditions of rugged relief and inclined magnetization. The geological space can be approximated by (1) three-dimensional, (2) semi-infinite bodies and (3) those infinite along the strike closed, LH non-closed, RH on-closed and open. Geological bodies are approximated by horizontal polygonal prisms.
The program has the following main advantages besides those already mentioned: (1) Simultaneous computing of gravity and magnetic fields; (2) Description of the terrain relief by irregularly placed characteristic points; (3) Computation of the effect of the earth-air boundary by the method of selection directly in the process of interpretation; (4) Modelling of the selected profiles flowing over rugged relief or at various arbitrary levels (using characteristic points); (5) Simultaneous modelling of several profiles; (6) Description of a large number of geological bodies and fragments.
The basic algorithm realized in the GSFC program is the solution of the direct 3D problem of gravity and magnetic prospecting for horizontal polygonal prism limited in the strike direction. In the developed algorithm integration over a volume is realized on the surface limiting the anomalous body.
Detailed description of analytical expressions of the first and second derivatives of gravity potential of the approximation model of the horizontal polygonal prism and their connection with magnetic field is presented in Khesin et al. (1996).
Results of 3D gravity field modeling A 3D combined modelling of the field ΔgBouguer (gravity field in the Bouguer reduction) and magnetic field ΔZ (vertical component of the total magnetic field) was performed using the following scheme. A detailed physical-geological model of the Katekh deposit with a length of 800 m and depth of 400 m was constructed by using generalized data (Mekhtiev et al., 1977) and Zaitseva et al., 1988). Then, all-available data for the area with density (Gadjiev et al., 1984) and magnetic susceptibility (Ismail-Zade et al., 1983) were utilized.
For the enhanced calculation of surrounding terrain topography, a digital terrain relief model was created. The SW-NE regional topography trend in the area of the Katekh deposit occurrence required the selection of a rectangular digital terrain relief model (DTRM) 20 km long and 600 m wide (our geological profile with a length of 800 m was located in the geometrical centre of the DTRM). As a whole, 1000 characteristic points were used to describe the DTRM (with the points focused in the centre of the DTRM and more rarely on the margins).
Results of a first iteration of gravity and magnetic fields modelling are shown in Figure 4. The plots of ΔZ and ΔUSP (self-potential anomalies) oscillate about zero and could not provide useful information about the buried targets. This can be explained by the peculiarities of mineralogical composition of ores in the Katekh deposit. Practical absence of magnetic mineral pyrrhotite causes the ores to be almost nonmagneticin nature. On other hand, a fairly large lead content impedes the normal course of oxidation-reduction reaction necessary for triggering intense SP anomalies. Thus, we can conclude that the essential geophysical information may be derived only from the curve ΔgBouguer.
From the analysis of the observed and computed gravity fields, it follows that the initial physical-geological model has some deficit of anomalous masses. 3D modeling of the gravity field was performed using about 25 sequential iterations with the results obtained in Figure 5. Two ore bodies of massive composition (not reflected in the previous geological constructions) were singled out in the southwestern and northeastern segments of the deposit. It should be noted that the conclusion concerning the presence of a hidden ore object in the southwestern portion of the profile was in concordance with the results of independent investigations involving underground geothermal observations and a ground geochemical survey. A temperature anomaly of 0.50 to 0.80 C was recorded in adit 8 during the underground geothermal investigations between 250-300 m. The surface zone containing a substantial amount of lead and zinc was revealed in the 150-200 m vicinity (according to Ginzburg et al. (1981) and data of Azerbaijangeologiya Association).
Conclusion
We can conclude that a gravity field analysis can play a significant role in detailed investigation of pyrite-polimetallic deposits. Instead of magnetic and self-potential methods whose application is based on the presence of magnetic minerals in ore and the course of oxidation-reduction reactions, an essential difference in dense properties between the pyritepolimetallic ores and the host medium (which practically always exists) provides the necessary prerequisite for gravity field employment. Combing available geological and petrophysical data with such a powerful tool as 3D modelling of gravity field allowed a reconsideration of the reserves of pyrite-polymetallic in the deposit Katekh were located under conditions of severe rugged relief and complex tectonics at the southern slope of the Greater Caucasus.
