Large and super-large orogenic golden deposits: Geodynamics, structure, genetic consequences

Research subject. Large and super-large orogenic gold deposits are widely distributed across all continents. This work was aimed at characterizing 24 giant facilities with reserves and resources of more than 500 tons of metal.Materials and methods. The work was based on the authors’ long-term fieldwork research into large and super-large gold deposits in Central Asia and the North-East of the Russian Arctic. In addition, an extensive bibliographic analysis of publications devoted to the largest gold deposits in the world was carried out.Results. A structural analysis showed that the formation of these deposits underwent two main stages. The early – subduction stage – was characterized by the development of gentle disturbances, such as thrusts, thrust nappies, viscous discontinuities and crushing zones, while the structural paragenesis included isocline lying folds and cleavage of the axial surface. The second stage – collision-transpression – began with the deformation of the previously formed structure into open and compressed folds with steep axial surfaces; as a result of further compression, a series of longitudinal discontinuous disturbances developed. An oblique collision of interacting plates lead to the development of shear transpression structural paragenesis, in which oblique cracks predominate. It is established that, in orogenic gold deposits, different stages were characterized by ore-controlling and ore-bearing structures. The binding of ore-bearing disturbances to different stages enabled isolation of deposits of various types that differ in structural and morphological features. The main characteristics of the identified types of deposits are provided. The formation of these deposits occurred during convergent processes, with the ore-controlling structures being a surface manifestation of the movement of block terrains along the surface of the detachment.Results. It is concluded that the surface of the detachment is not only a tectonic zone, but also a channel that provides a link between various deep levels of the subduction zone, from where ore-bearing hydrothermal fluids emerge.

Geodynamic conditions of oil and gas accumulation in the fore-Urals and fore-Novaya Zemlya belt

A brief tectonic and geological overview of the fore-Urals and fore-Novaya Zemlya belt of oil and gas accumulation and the results of studying of the conditions for hydrocarbon deposits formation in uplift-thrust structures of its eastern side are presented. It is shown that the early stages of the belt formation are associated with Paleozoic subduction and obduction processes occurring in the transition zone between the Paleo-European continent and Uralian paleo-ocean located eastward (in modern coordinates) the continent. The intensive thrust-folded dislocations of the western verergency are fixed into the eastern side of the fore-Urals and fore-Novaya Zemlya belt of oil and gas accumulation. We associate their formation with the continental collision that occurred during the closure of the Uralian paleo-ocean at the Latest Paleozoic, and in the most northern segments of the belt, probably, at the Earliest Mesozoic. The structural paragenesis of the eastern side of the fore-Urals and fore-Novaya Zemlya belt of oil and gas accumulation includes uplift-thrusts and thrusts, as well as various scaled structural units formed under the conditions of the latitude compression.

GEODYNAMICS

In the article the first results of researches of joints and slickensides from outcroppings in the valley of the Sukil River are given. In 37 points of the flysh deposits of thrusts: Orivska, Skolivska and Parashka about 1100 intentions of joints and 90 intentions of slickensides are executed in the different deposits strata: from the Upper Cretaceous to Oligocene formations. By the complex (method of structural paragenesis and kinematics one) analysis of these mesostructures, with the use of the modern computer providing (StereoNett, Win-Tensor and other) the reconstruction of main parameters was carried out. Deformation regimes and orientations of main axes of the old and young stress fields which occur in Paleogene-Neogene time to and during and after fold formation in this area of Ukrainian Carpathians was specified.