| Title | Structure of the Kamchatka's Largest Nizhne (Lower)-Koshelevsky Vapour-Dominated Geothermal Deposit: New Geology and Geophysics Data |
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| Authors | Ilyas F. ABKADYROV, Sergey N. RYCHAGOV, Yury Yu. BUKATOV, Sergey O. FEOFILAKTOV, Ivan A. NUZHDAYEV |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | volcanic massif, vapour-dominated geothermal deposit, thermal anomaly, subvolcanic intrusion, deep-seated fault, boiling region, water-confining stratum, ascending fluid, geophysical methods |
| Abstract | The development of geothermal power industry in Russia's Kamchatka in the 70-80's induced the assessment of geothermal resources of the Koshelevsky volcanic massif (South Kamchatka). The massif consists of five adjoining quaternary stratovolcanoes and occupies a complex geodynamic position: It is confined to junction of the volcanic belts and located at the interface of the Kamchatkan and Kurile geological structures. In the central part of the massif, in the volcano crater, the Verkhne (Upper)-Koshelevsky steam jets are located and the Nizhne (Lower)-Koshelevsky thermal anomaly is located on the western slope in the deep-cut ravine of the Gremutchiy (Rattling) Stream. The total heat efflux is 75 GW/s (Vakin et al., 1976). Exploration drilling in the area of the Nizhne-Koshelevsky thermal anomaly revealed a more than 1.5-km-deep zone of superheated (dry) steam. A subintrusive body of diorites – diorite porphyries surrounded by a brecciated mantle and overlaid by a stratum of volcanogenic-sedimentary rocks. Dimensionally, the steam zone is inclined to the apical part of the multi-phase subintrusion. It is hypothesized that a lava-extrusive complex of andesidacites in the near-surface part of the section is an upper water-confining stratum for the modern hydrothermal system. The electric power capacity of the Nizhne-Koshelevsky vapour-dominated geothermal deposit is estimated at 90 MW (Pisareva, 1987), while forecast resources of the whole massif are 300 ÌW. In recent years, the South-Kamchatka-Kuril surveying company of Institute of Volcanology and Seismology FED RAS has additionally conducted integrated exploration in order to specify the deep-seated structure of the Nizhne-Koshelevsky geothermal deposit and for understanding of the nature of the geological structures that govern the steam zone. Based on microseismic sensing, low-speed regions corresponding to decompressed rocks have been identified: a cup-shaped 250-300-meter-deep zone located directly under the thermal anomaly; a 100-meter-thick 5-km-deep subvertical zone related thereof. The first zone corresponds to the hypergenesis zone of the geothermal system and composed of argillaceous rocks saturated with a gas-steam mixture. Most likely, the second zone is a fracture-breccia structure in the form of a subvertical channel through which a heat-conducting medium ascends to the surface. This channel is confined to the previously identified deep-seated fault and dips in the interior of the subintrusive body. High-precision gravimetry identified not only the thermal anomaly but also another zone of reduced density rocks linked to it. We interpret this zone as an ore-forming paleo-hydrothermal system composed of argillizated rocks and quaternary quartzites. A magnetometer survey helped to define more precise boundaries of the Nizhne-Koshelevsky thermal anomaly, thickness and stretch of the lava-extrusive rock unit (the upper water-confining stratum). Electrical exploration helped to define the position of local channels through which the gas-hydrothermal heat-conducting medium is discharged in the upper part of the geothermal deposit. It is planned to continue geological-geophysical activities because of the great importance of the Koshelevsky volcanic massif for the scientific-technical research and the heat and power supply to Kamchatka Krai. This work has been carried out with a financial support from the Russian Foundation for Fundamental Research (Project 13-05-00262) and Far-Eastern Division of the Russian Academy of Science. |