Geology and lithological and structural conditions of brecciated rocks localization of the central part of the Ukrainian Shield (as an example of the Hruzske field of pipe-like bodies)

Abstract

The main purpose of the article — is using the complex of structural-tectonic, geological-geophysical and lithologic-structural investigations, to describe in general the brecciated formations and pipe-like bodies of their localization as a precondition for solving the diamond-bearing problems of the Raihorodska suite (Paleocene) by the example of the Hruzske field of explosive structures in the central part of the Ukrainian Shield. Structural-tectonic, geophysical and morphostructural analyzes of the Precambrian basement surface have been used for diagnostics and outlining of local isometric pipe structures. Petrographic composition of the Hruzske field rocks was studied in core samples from wells No. 4087 (structure Hruzka-Pivdenna), 4040, 4043 and 4045 (structure Lisova-Skhidna), drilled by GPE-37 SE «Kirovheolohiia». Lithologic-stratigraphic and micropaleontological methods were used to determine the age of brecciated rocks. The morphology of bodies, some specific petrographic peculiarities of brecciated rocks of the Hruzske field are characterized by the complex of lithologic-structural features, as well as conclusions regarding their belonging to the endogenous (magmatogenic) group of diamond-bearing formations are made. Brecciated rocks of the Raihorodska suite are attributed to the clay-fine-clastic breccias, which are clearly confined to the lows in the Precambrian basement of the Shield central part and fill the depressions like the diatremes. Their explosive nature is substantiated; the Cretaceous-Palaeogene age of formation is confirmed; the rocks are compared with «sandy» tuffs of the Argyle lamproite pipe in Western Australia and volcanoclastic kimberlites of the Fort a la Corne area in Canada. It has been shown for the first time that the depressions in the Precambrian basement of the Ukrainian Shield central part are pipe-shaped bodies of the stockwork-maars type with a clearly expressed non-eroded craterous part. At a depth, they pass into the system of un-oriented joints, which played the role of incurrent canals for a mobile alkaline-ultrabasic magma, rich in volatile components. According to the structural-material characteristics, these specific brecciated formations of the Raihorodska suite are attributed to the products of rapid brecciation during the fluidizate-explosive processes of the maar volcanism development. Based on the performed researches it is possible to estimate the prospects of pipe-like bodies in relation to the search for industrial diamonds deposits on the Shield, to distinguish local structures, perspective on manifestations of explosive processes and related endogenous (kimberlite-lamproite) diamond content.