International Journal of Astronomy and Astrophysics, 2011, 1, 98-104 doi:10.4236/ijaa.2011.12014 Published Online June 2011 (http://www.scirp.org/journal/ijaa) Concerning Diamond and Gold-Bearing Astropipes of Mongolia Dorj Dorjnamjaa1, D. M. Voinkov2, L. S. Kondratov2, D. Selenge1, G. Altanshagai1, B. Enkhbaatar1 1Paleontological Center, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia 2VNIIgeosystem, Warsaw Highway, Moscow, Russia E-mail: [email protected] Received March 15, 2011; revised April 19, 2011; accepted May 16, 2011 Abstract In this paper we present summation of thirteen year’s investigation of the all diamond-bearing structures of Mongolia. Four gold and diamond-bearing astropipe structures of exemplified by the Agit Khangay, Khuree Mandal, Bayan Khuree and Tsenkher astropipes of Mongolia. Detailed geological and gas-geochemical in- vestigation of the diamond and gold-astropipe structures show that diamond genesis is an expression of col- lision of the lithospheric mantle with the explosion process initiated in an impact collapse meteor crater. Keywords: Astropipe, Diamond, Impact Crater, Spherules Meteoritic Iron, Shatter Cones, Pyrope 1. Introduction like melt formation within the mantle. 2) An additional factor of petrological and geochemi- Dorjnamjaa et al. [1-5] have established for the first time cal diversity of impact-generated formation is considered the presence of diamond and gold-bearing ring-shaped to be the compositional inhomogeneity of magma gen- impact structures called “astropipes” in Mongolia at Agit eration zones of the mantle at the expense of inclusions Khangay, Khuree Mandal, Bayan Khuree, and Tsenkher of eclogite-like paragenesis, enhancing the intensity of (Figure 1). The term ‘astropipes’ is a neologism in Earth mica kimberlite formation comparing with baric standard science and these structures are unique in certain aspects. and their corresponding diamond contents. This term was proposed for this type of newly recognized 3) Evolution of impact-diamond-generated magma- meteorite crater as compared with an “astrobleme” [2,3,6]. tism had been proceeding from more deep-seated (> 100 Many meteorites are large enough to create impact km) levels to lees deep-seated (< 100 km) ones, and craters. The Mongolian astropipes are genuine ‘meteorite magma generation zones in the considered astropipe re- crater’ structures but they also contain kimberlite (man- gions, that was likely to trace a displacement of litho- sphere plate under a hot spot within the Paleoasian ocean tle-derived) diamonds and gold. Within the terrestrial structures.We must recognize that the mantle substruc- planets this process is considered as a rare phenomenon ture is revealed close to terrestrial surface within the that occurs especially in the evolution of both the at- Mongolian astropipe structures. True, the proposed mo- mosphere and mantle. Our preliminary investigation of del of impact-diamond-generation composition, although petrological and geochemical databases of diamondifer- approximating rather closely to reality, calls in many ous kimberlite-like “agizite” or impact-related rocks from respects for refinements according to isotope geochemi- astropipe structures has resulted in the creation of a pet- cal and mineralogical data, also geophysical log. The rologic model of kimberlite-like formation, one that pursuance of fundamental investigations of discovered logically combines a large variety of petrographic, min- astropipe structures with the complex mastering of in- eralogical and geological features. formation on mantle inclusions, mineralogical, structural The main positions of this model are as follows: petrography, geochemistry and petrochemistry is quite 1) Geochemical composition of impact-diamond gen- possible. erated rocks a sequence of their bedding within the as- The Mongolian astropipe structures recognized to date tropipes and diamond contents are interralated and de- include: termined by depths of impact-generated or kimberlite- Agit Khangay (10 km in diameter, 47˚38'N; 96˚05'E), Copyright © 2011 SciRes. IJAA D. DORJNAMJAA ET AL. 99 Figure 1. Location of the Mongolian diamond-bearing astropipe structures; Type I, studied in 1997-2009: 1, Agit Khangay (47˚38'N; 96˚05'E) 2, Khuree Mandal (46˚28'N; 98˚25'E); 3, Bayan Khuree (44˚06'N; 109˚36'E); 4, Tsenkher. (43˚36'N; 98˚21'E); Type II, insufficiently studied diamond-bearing structures: 5, possible astropipe structure “Flying Saucer” (49˚25' N; 92˚05'E). Khuree Mandal (D = 11 km, 46˚28'N; 98˚25'E); Tsenk- ple 17/03) have been compared with that of an analogous her (D = 7,3 km, 98˚21'N; 43˚36'E), and Bayan Khuree form in volcanic rocks of modern (Volcano Gorelii, (D = 1 km; 44˚06'N; 109˚36'E) impact-magmatic pipes Kamchatka) and ancient (Maikhant-sample 25 - 04, and have been distinguished in Mongolia (Figure 1). These Zuun Busluur-sample 36/04 from Dariganga plateau, astropipes are well-protected from erosion and active Mongolia) volcano eruptions as well as kimberlite pipes denudation, and characterized by both good natural ex- (Victory-1, Shandong province, China). As a result our posures and a diversity of different impact-derived, data with marked specifications of gas composition shocked metamorphic, and magmatogenic rocks and (HCGaf is adsorbed form of the hydrocarbonic gas) of the minerals. astropipe rocks indicate their similarity to the composi- tion of the kimberlite pipe gases (Figures 2 and 3). 2. New Methodology In this study, all the minerals were investigated using thin sections, X-ray spectral and structural microanalyses, The scrutiny of adsorbed gases in rocks of diamondifer- and scanning electron microscopy [2]. ous provinces is a new nontraditional prospecting me- thod to determine gas concentration and composition of 3. Results the samples (fraction 0.1 - 0.25 mm) by gas chromatho- graphy. This is accomplished by heating the sample in a 3.1 Khuree Mandal Astropipe Structure reactor of special design up to a temperature of 200˚C in an argon environment. The method has been substanti- The Khuree Mandal astropipe structure (Figure 1.2), 220 ated by experimental investigation and its practical ap- km N-NW of Bayankhongor city in central Mongolia is plication verified for the study of numerous geological within the Upper Paleozoic volcanic intramontane Buut- objects-kimberlite pipes, astropipe impactites, volcano sagaan depression with a diameter of 11 km and has a structures and etc. [1-3]. similar geomorphological position as the Agit Khangay The adsorbed gases in the Mongolian astropipe impac- astropipe crater. As shown in Figure 4, the principal mor- tites (Agit Khangay-sample 32/99, Khuree Mandal sam- phostructural elements of the astropipe ring are: Inner Copyright © 2011 SciRes. IJAA 100 D. DORJNAMJAA ET AL. CnH2/ CnH2n+2 PH legend CH4 C2H6 C2H4 C3H8 C3H6 C4H10 C4H8 C5H12 Figure 2. Contrast curves of adsorbed form of the hydrocarbonic gas (HCGaf) components (see Legend). 1.1 cm3/kg phostructures (Figure 4), which are represented by vari- HCGaf 100% 1.0 ous ore-bearing and mineral formation complexes. Suevite-like rocks (fluidizate) and volcanic breccia from 90 H 0.9 (C various parts of the crater and central hilly rise are charac- n H 80 2 0.8 n) terized by the presence of olivine, coesite, moissanite, 70 0.7 khondrite, picroilmenite, pyrope, phlogopite, orthite, and 60 0.6 gold (from 0.13 to 6.33 - 32 g/t) closely associated with mantle- and impact-derived fine diamonds (Figure 6; 0.1 - 50 0.5 0.5 to 2.5 mm in size). Special pressure and temperature 40 0.4 conditions are necessary to account for the coexistence of 30 0.3 phlogopite, pyrope, picroilmenite, gold and other accom- 20 panying accessory minerals with the diamonds. It is rea- af 0.2 4 HCG 10 CH sonable to assume that the Khuree Mandal astropipe 0.1 structure is closely related to diamond-bearing rocks and is 5 0 0 analogous to the diamond-bearing lamproites of the ‘Ar- 1234567 gail’ pipe of Australia [2]. So-called shatter cones that Figure 3. Comparison of concentrations and composition of were produced when the shock wave traversed the Per- HCGaf in volcanic rocks from eruptions with rocks from mian volcanogenic rocks were first described by us in astropipies and kimberlite. connection with the Khuree Mandal and Tsenkher astro- pipe structures (Figures 5 and 10). Meanwhile, shatter (small) diamond-gold-bearing pediment plain (I); Inner cones are known from many meteorite craters on the Earth ring-shaped rise or Inner tectonomagmatic bar (Central as being typical of impact craters [1]. hilly rise-II); Central ring depression (III); Outward cir- cular bar (IV); Inner ore-bearing crater mould (V). The 3.2. Agit Khangay Astropipe Structure astropipe relief morphostructures have an inversion nature with respect to the non-meteoritic country structures. The The Agit Khangay astropipe structure (Figure 1.1) in main difference is characterized by radial-ring mor- western Mongolia was formed within a Permian granite Copyright © 2011 SciRes. IJAA D. DORJNAMJAA ET AL. 101 Figure 4. Geological map and cross-section of the Khuree Mandal astropipe structure; 1-Cenozoic: coarse-fragmental rocks composing terraces (conglomerate, gritstone with diamonds, tektite glass, cosmic spherules); 2-Diluvial and diluvial-proluvial deposits with gold, moissanite; 3-Allogenic lavabreccia boulder, gravel, sandstone, loamy sand with gold mineralization, me- teoric matter; 4-Mesozoic: mural palingenetic granite with fluidizate-like loamy sand volcanic breccia and plural acute-angle xenoliths;