Diamondiferous kimberlites are the most important source of bedrock diamond deposits. The goal of the study is to analyze the use of gamma-ray spectrometry techniques to explore weakly magnetic diamondiferous kimberlites. The result of this research is the justification of prospects of using gamma-ray spectrometry to identify weakly magnetic diamondiferous kimberlites

Ledengskiy, R. A.

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256 USE OF GAMMA-RAY SPECTROMETRY FOR IDENTIFYING WEAKLY MAGNETIC DIAMONDIFEROUS KIMBERLITES R.A. Ledengskiy  2992roman@gmail.com Scientific supervisor: Doctor of geological and mineralogical sciences, Professor Rihvanov L.P., National Research Tomsk Polytechnic University, Department of Geoecology and Geochemistry Diamondiferous kimberlites are the most important source of bedrock diamond deposits. The goal of the study is to analyze the use of gamma-ray spectrometry techniques to explore weakly magnetic diamondiferous kimberlites. The result of this research is the justification of prospects of using gamma-ray spectrometry to identify weakly magnetic diamondiferous kimberlites. Exploration of diamondiferous kimberlites is highly relevant, because they are the main source of industrial diamonds. Their proportion is 90 % of the diamond reserves in bedrock deposits. More than 1500 kimberlite bodies are known today, 8–10 % of which are diamondiferous rocks. Some kimberlite fields of Yakutian and Arkhangelsk diamondiferous provinces (Mirny, Nakyn, Zolotitsa) have minimum values of magnetization intensity. Use the magnetic method to explore weakly magnetic diamondiferous kimberlite pipes and fields has displayed low efficiency [5]. The goal of this research is to identify and analyze the relationships, possibilities and prospects of using gamma-ray spectrometry to identify weakly magnetic diamondiferous kimberlites. Gamma-ray spectrometry methods are based on measuring the spectral composition of the natural gamma radiation of the mantle rocks, followed by identifying of the contents of natural radioactive elements such as uranium, thorium, and potassium in these formations. This method is adopted in land, airborne and laboratory versions. Gamma-ray spectrometry methods belong to geophysical methods in essence, methodology and observation techniques, but they also solve geochemical issue. The field methods have shallow depth of investigation due to the rapid absorption of gamma rays by air and rocks. They are widely used in lithological, tectonic plotting, as well as in explorations of non-radioactive minerals that are paragenetically or spatially linked with the natural radioactive elements [2]. Identifying radioactive elements by gamma spectrometry in the field is distinguished by unique mobility, rapidity, high sensitivity and accuracy in solving radiogeochemical issue. This method allows the use of statistical approach in radiogeochemical research, to regulate behavior of the field acquisition, observe and evaluate the dynamics of the radiogeochemical parameters of rocks, ores and minerals in their geological study, and produce reliable sampling to identify the three natural radioactive elements [3]. Metamorphism, metasomatism and hydrothermal processes cause changes in an enclosing rock, accompanied by a transformation of the structure of radiochemical fields, which causes the formation of anomalous concentrations of natural radioactive elements. The reason for this phenomenon are the different migration properties of uranium, thorium and potassium. These changes disrupt the equilibrium ratio of natural radioactive elements, followed by the formation of radiogeochemical zonation, which is equivalent to a specific conversion type and that creates the methodological basis of the gamma-ray spectrometry's application in radiogeochemistry. Airborne gamma-ray spectrometry allows to determinine the concentration of radiogeochemical elements in rocks and ores with the required precision. The results of airborne gamma-ray spectrometry show its high efficiency in solving geological problems such as geological mapping, prospecting hydrothermal deposits (uranium, rare earths, non-ferrous and precious metals), and the research of the intensity and nature of occurrences (manifestations) of superimposed processes. These results allow obtaining high-quality information that is comparable with the scale-adjusted (corresponding scale) foot-borne surveys. According to the estimates, aerial survey of similar problems is 2.5-10 times cheaper than work on land [1]. The high sensitivity of the method can effectively detect Clarke content of natural radioactive elements in the upper layer of rocks. If there is even a slight differentiation of these elements, the method manages to dissect stratified bodies, detect and determine the heterogeneity of the structure of the intrusive assemblages (acid, alkali). The faulted zones, which were affected by metasomatic and hydrothermal transformations, have the disturbance of their equilibrium state of the natural radioactive elements. Gamma-ray spectrometry can determine reliably this faulted zone as the results of calculating above-background concentrations of the radioaceffectivof ore-bpreciouThe firthat macontrasand thinterpresecondradiogeonly diexcavatIt is knmost kidentifypipe, rianomalmagnet(landschave loquality situatioThe gepipe oftotal inthoriumA) – radiatiFigtive elementse in combinaearing and ors metals [2]. st practice of ny kimberlitet to enclosinge method wtations have ary geochemiochemical hafference is in ion. own that the uimberlites of diatremes ofchest in diamy. If a subometry is larape and geolwer efficiencand reliabilins where primoscientists ca the Zolotitsa tensity of ga (ppm), whicLayout of the Zon (pulses/sec)ure 1 – Layout or their relation with othe-controllingusing airborn pipes have e rocks. Howas rejected. found that tcal halos. Ralos were almthe time: onese of magnet the Arkhang the Nakyn fiond content pstance-indicagely determinogical, techniy in exploratty of the maary deposits rried out a grfield on the Amma radiatih show the spolotitsa ore fie; D) - distributi of the studied tionships. Airer geophysica structures, foe gamma-raylevated thoriuever, attemptHowever, thhe method ddiogeochemiost equivalen season of theometry helpeelsk region, eld, which areer ton in the Mtor module ed by the wcal and metrion of diamongnetometric of diamonds ound gammarkhangelsk don (pulses/seecifics of theld; B) - route oon of the potascoarea and distri(according257 borne gamml methods, anr exploration  spectrometrym concentrats to open thee following id not identical halos of t to the map aerial surveyd to explore mbut it also i the unique iirny field, hused in theork of four oological, geod kimberlitemethod, whiccan be overlo-ray spectromiamond provc), potassium spatial locatiof gamma-ray spsium content (ncentration (ppbution of radio to Yakovlev Ea-ray spectromd is applied of deposits o to identify ions and reduse anomalies surveys on fy the kimbethe Mirny kis of mineral  against seveore than halfs known thatn their diamoas low level a exploratoryther modulelogical and ins. There are ah identified oked [4]. etry survey iince. The resu content ( %n of radioactectrometric su%); D) - thorium) active elements. Yu., 2015) etry is indepwidely for prf radioactive, kimberlite pipced concentraup by drillinreference firlite bodies tmberlite fielddistribution frral decades o of Yakutia’s magnetic mnd content. Thnd small size method fais used in theterpretive, anlso studies oa number ofn the area oflts of the surv), concentrativity in the ro rvey; B) - totam concentratio in the rocks ofendent and aospective assrare, non-ferres has demotions of potasg were unsucelds and gehemselves, b confirm thiom kimberlitf drilling and kimberlite pieasurements e Internatsio of its local mls, effectiven exploratory d certifying)n the analysi possible and the Arkhangey were mapion of uraniucks (Fig. 1) [l intensity of gan (ppm); E) - u Arkhangelsk ps more essment ous and nstrated sium in cessful, ological ut their s. Their es. The  surface pes and did not nalnaya agnetic ess of method , which s of the  actual elskaya s of the m and 6]. mma ranium ipe 258 A contrast anomaly forms around the pipe contour in terms of total radioactivity (pulses/s), which extends to the crateral facies rocks and enclosing deposits, and exceed the background by an average of about 2 orders. The central part of the pipe has decreased values of gamma field. Similarly, anomalies of thorium, uranium and potassium have high values around the pipe contour. Concentrations of uranium and thorium vary within an average of 3 to 10 ppm and 8 to 32 ppm at this area, respectively. Potassium content also tends to have high values. This indicates that the kimberlites, which are forming the diatreme of the Arkhangelsk pipe, are depleted in uranium and other radioactive elements. Furthermore, uranium isotopes activity ratio is equivalent to one, which indicates the absence of conditions here for the separation of isotopes and long-term stable state rock. At the same time, we can observe active fractionation processes of uranium isotopes in rocks of the annulus, the apparent deficit of 234U, accumulation of the other radioactive elements. This is due to the radiation exposure of uranium and its infiltration oxidation transportation and deposition near kimberlites, which have reducing properties [6]. These regularities and processes justify the possibility of using gamma-ray spectrometric surveys to assess the prospectivity of ore-bearing and ore-controlling structures, for the exploration of non-radioactive minerals that are paragenetically or spatially linked with natural radioactive elements, particularly for the exploration of weakly diamondiferous kimberlite pipes. References 1. Kontarovich R. S. Aehrogeofizika na poroge XXI veka [Aerogeophysics at the turn of the XXI cen-tury]. Mineralnye resursy Rossii. Ekonomika i upravlenie [Mineral Resources of Russia. Economics and Management]. Installment. 1997. pp. 3–5. 2. Lazarev F. D., Romashko V. V., Melnikov P. V., Shnejder G. V. Ajerogamma spektrometricheskie issledovaniya kak metod izuchenija radioaktivnosti poverhnosti i ego prakticheskaya realizaciya [Aero Gamma spectrometric studies as a method of studying the radioactivity of the surface and its practical implementation]. Radioaktivnost i radioaktivnye elementy v srede obitaniya cheloveka: Materialy III mezhdunarodnoy konferencii [Radioactivity and radioactive elements in human environment: Proceed-ings of the III International Conference]. Tomsk, 2009. pp. 306–311. 3. Rihvanov L. P. Radiogeohimicheskaya tipizaciya rudno-magmaticheskih obrazovanij (na primere Al-tae-Sajanskoj skladchatoj oblasti) [Radio geochemical typification of the ore-magmatic formations (on the example of the Altai-Sayan orogen)]. Novosibirsk: SO RAN, branch “Geo”, 2002. pp. 12–22. 4. Kontarovich R. S., Cyganov V. A. Problemy i perspektivy razvitiya geofizicheskih tehnologij pri poiskah korennyh mestorozhdenij almazov [Problems and prospects of development of geophysical technology in the search for primary diamond deposits]. Geofizika [The geophysics]. Moscow: EAGO, 2001. 9 p.  5. Cyganov V. A. Klassifikaciya i issledovanie otkazov magnitometricheskogo metoda poiskov kimberli-tov [Classification and study of failures of use magnetometric method for exploration kimberlites]. Mo-sow: FGUP Ajerogeologiya. 25 p. 6. Yakovlev E. Yu., Kiselev T. P., Druzhinin S. V. Osobennosti raspredeleniya radioaktivnyh elementov v porodah kimberlitovoj trubki Arhangelskaya (mestorozhdenie im. M.V.Lomonosova) [Features of dis-tribution of radioactive elements in the rocks of kimberlite pipe Arkhangelsk (Lomonosov deposit)].  V Rossijskaya molodjozhnaya nauchno-prakticheskaya Shkola s mezhdunarodnym uchastiem «Novoe v poznanii processov rudoobrazovaniya» [V Russian Youth Scientific and Practical School with inter-national participation «New in the knowledge of the processes of ore formation»]. Moscow, 2015.  pp. 289–291.  

Use of gamma-ray spectrometry for identifying weakly magnetic diamondiferous kimberlites

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