STUDIES ON THE PROBLEM OF DEEP-SEA POLYMETALLIC SULFIDES (DPS) IN THE AXIAL ZONE OF THE MID-ATLANTIC RIDGE
The first information about the presence of hydrothermal activity in the rift valley of the Mid-Atlantic Ridge (MAR) was obtained in the 1970s by French and American researchers. In the early 1980s, they also discovered large hydrothermal fields with ore sulphides "TAG" (26°08´ N) and "MARK" (23°22̍´ N).
Domestic research on the problem of deep-sea polymetallic sulphides in the axial zone of the Mid-Atlantic Ridge began in 1985, while the leading role in these studies belonged and now belongs to JSC PMGE and FSBI VNIIOkeangeologiya. In addition to these organizations, occasional studies are conducted by a number of organizations of the Russian Academy of Sciences.
In the course of regional recognnaissance works of scale 1: 1,000,000 (bathymetric, hydromagnetic, hydrophysical and hydrochemical studies, and geological sampling of bedrock and sediments), conducted mainly by PMGE, a large segment of the axial zone of the MAR was studied (10 ° 40- 26 ° 30 N). In the course of these studies, conducted along the axial zone of the ridge, 16 promising areas with an area from 200 to 1200 sq. Km were determined.
Since 1991, PMGE has been using a specially equipped research vessel "Professor Logachev" to search for DPS in the Ocean.
R/V "Professor Logachev" , a specialized scientific research vessel equipped for
carrying out exploration work on the DPS.
Between 1993 and 2017, about 20 cruises were carried out on the R/V "Professor Logachev" within the boundaries of the sections of MAR axis zone, promising to detect DPS. During this period, large areas of the Mid-Atlantic Ridge axial zone were covered by works of various scales. And most importantly, the geologists of PMGE managed to open and survey 12 large ore objects within the Mid-Atlantic Ridge. These discoveries made Russia one of the world's most recognized leaders in the study of sulphide ores in the Ocean.
The first major discovery was made in 1994, when the "Logachev" ore node was discovered. Then, the Ashadze ore cluster was discovered in 2003, the Krasnov ore field in 2004, the Semenov ore cluster in 2007, the Zenit Victoria ore field was discovered, and the Puy-de-Vall ore field specificated in 2008; in 2010 the "Petersburg" ore field, in 2011 the Irinovskoe ore field, in 2012 the ore fields "Surprise" and "Jubilee", in 2014 the ore field "Hilly", in 2015 the ore field node "Victory" were discovered.
The forecast resources (Р2 + Р3) for all ore objects are currently 101.7 million tons of ore mass. During the works of 2017-2020 they will be likely to increase to 110 - 120 million tons.
Ore sample on board.
This success is based on a huge amount of regional and experimental work done on the R/V "Professor Logachev", which resulted in the development of an optimal method for searching for hydrothermal sulphide ores on the Ocean floor - that is, the complex of the most effective methods, combined with a certain sequence and stage-by-stage progress of works.
The signing of a 15-year contract for the exploration of polymetallic sulphides by the Ministry of Natural Resources and Environment of the Russian Federation and the International Sea-Bed Authority of the United Nations-ISA, held in Moscow on October 29, 2012, opened a new stage in the domestic DPS research.
The Russian exploration area (REA), within which our country obtained the exclusive right to conduct exploration work on the DPS, is located in the central part of the Atlantic Ocean, in the axial zone of the Mid-Atlantic Ridge, in the latitude interval between 12° 48'36 "and 20° 54'36 "N).
The area includes 100 blocks : size 10 × 10 km, not more than 100 sq. km. each. The exploration work plan, which is an integral part of the Contract, provides for geological exploration in three stages:
- Stage 1, 2013-2018, duration 6 years;
- Stage 2, 2019-2023, duration 5 years;
- Stage 3, 2024-2027, duration 4 years.
Officially, according to the exploration plan, the main tasks are:
- identification of priority prospect areas for more detailed exploration (stage 1);
- identification of specific ore objects and assessment of potential resources of their constituent ores (stage 2);
- exploration of industrially significant ore objects with calculation of the reserves of their constituent ores and final designation of the mining area (stage 3).
At present, JSC PMGE is carrying out a complex of geological prospecting works to assess the prospects of 100 blocks of the Russian exploration area (stage 1).
Russian Exploration District
The following instrument-methodical complex is used for the work:
1. Hydroacoustic profiling by the hardware complex MAK-1M-SP, including sonar - 120 kHz (swath 500 m), acoustic profilograph (frequency 4 kHz, depth up to 125 m), redox potential sensor, towed streamer with six sensors for NF (natural electric field) measuring.
Descent of the side-scanning sonar MAK-1M with a NF streamer.
The side-scan sonar localization is performed with the simultaneous measurement of the natural electric field (NF) with an inter-profile distance of 500-600 m), which makes it possible to obtain sonograms of the bottom within the work area, on the basis of which it is possible to establish zones of tectonic disturbances, often associated with ore objects, to establish the distribution at the bottom of igneous rocks and, the key point, to reveal the anomalies of the natural electric field, directly indicating the location of the ore object.
With the help of the MAK-1M-NEF complex, 7 ore objects of 12 were discovered.
Mosaic sonograms of side-scanning sonar.
2. Hydrophysical sounding of the water layer is carried out to identify abnormal structures of oceanic waters associated with hydrothermal activity and for geoecological monitoring. The work is carried out by the SBE 911 plus hydrophysical probe (measured parameters: pressure, electrical conductivity, temperature, transparency - light transmission). The probe can also use Eh and pH sensors, a dissolved oxygen sensor and a flux sensor.
Modern hydro-therms are discharged directly into the bottom water layer, forming a mixture of thermal spring with sea water. This mixture is warmer than sea water, and, accordingly, less dense, so the so-called hydrothermal plume - an ascending stream of warmer water - is formed. Having risen to a certain horizon of the water column, where its density becomes equal with the density of the surrounding water, the plume spreads in the horizontal direction. An increase in temperature, a change in salinity, an increase in turbidity in the bottom layer of seawater recorded by the hydrophysical probe denote the proximity of discharging of modern hydro-therms ("black smokers"). With the help of this method, an active hydrothermal ore occurrence was discovered in 2003. After geological testing it was called "Ashadze".
Hydrophysical probe SBE 911 plus
The results of hydrophysical sounding with sampling by SBE 32 Carousel equipped with 12 5-liter bathometers are also used for environmental monitoring of the aquatic medium.
3. Geological sampling using box samplers and rock dredges.
Geological sampling with a rock dredge (rectangular cross section 120 x 70 cm, accumulator 2 m long, mass of material taken up to 500 kg) allows the selection of bedrock. In addition to the goals of geological mapping, the selection of bedrock is also carried out to identify wallrock alterations, which are a good prospecting indication. The prospecting efficiency of geological sampling by rock dredge was confirmed in the discovery of the Zenit-Viktoria ore field in 2008. Initial information which attracted attention to this site was the presence of wallrock alterations in basalts, revealed during geological testing on a sparse grid. Further detailed sampling made it possible to discover the ores themselves.
Geological sampling with a box corer (BC-1.5 with a square section of 40 x 40 cm and a length of a sampling part of 1.5 m) makes it possible to identify the indicators of the near mineralisation in bottom sediments by mineralogical associations ,or to lift metalliferous bottom sediments. With the help of this sampler the "Krasnov" ore field was discovered in 2004 by R/V "Professor Logachev".
Bottom sampling with a telegrab allows to obtain large-volume samples of sulphide ores on identified ore objects. The installation of a telegrab on the bottom and sampling are preceded by the television screening of the selection site in the position-profile mode using the thruster. A technological sample is also taken from the large-volume sample of sulphide ores to perform laboratory work on the material and technological examination of DPS ores for metallurgical processing.
The telegrab DG-1.
The telegrab DG-1 (hydrostatic bottom dredger) with a bucket capacity of 0.4 m3, a capture area of 1.5 m2, a hydrostatic drive powered by autonomous accumulator batteries (AAB) is equipped with a television module based on the LCL-217HS color digital camera with a sensitivity of 0.5 Lx.
During the reconstruction of the R/V "Professor Logachev" under the contract with OOO "GIKO", DG-1 telegrab was modernized. DG-1M is a bottom grab with hydraulic drive, power 380 V from the ship, remote control panel, cable driver.ia cable. In addition, the telegrab "Preussag" was repaired and practically re-created. It was called GK-6T: sample volume is 1 m3, capture area 4 m2, weight 3.5 t, hydraulic drive, remote control with a control panel.
Testing GK-6T telegrab
A sample of sulphide ore
4. Television profiling serves for geological mapping, identifying biodiversity in ecological researches and applies for visual search of ore bodies in promising areas of the ocean floor, where serious signs of hydrothermal activity were revealed: indicator minerals, NEF anomalies, wallrock alteration, etc. The prospective area is examined in detail with the help of an underwater television set (module) towed above the bottom surface. At the same time, there is a direct visual control of the broadcast picture with the fixation of important information in the logbook, and the recording of the entire video material on electronic media for further analysis. The Near bottom television studies allow visual recognition, delineation and identification of the morphology of the ore bodies of the DPS, as well as ecological monitoring of the bottom biota. To carry out this type of research, a towed television underwater vehicle (TUV) "Abyssal" was used at stage 1 of the work. To ensure this type of work in PMGE, two unified television modules were developed and manufactured, which can be used both as parts of TUV and on the DG-1 tele grab, based on the LCL-217HS color digital camera with a sensitivity of 0.5 Lx. Registration of video information on the TUV was carried out on a single-channel mobile digital video recorder EDSR-100M, which included a hard disk with a capacity of 550 Gbyte. The recording was conducted in the HIGH quality mode, with a recording rate of 25 fps. The resolution of the recording is 720х480. All 12 PPP-DPS objects were examined using this TUV
After the reconstruction of R/V "Professor Logachev" in 2015-2017, BTA "Sperre AS" (produced in Norway, 2015), equipped with 2 LED lights, a color video camera and an altimeter will be used for the television profiling.
Fragments of underwater television shooting.
Tests of BTA "Sperre AS" from board of the R/V "Professor Logachev"
5. Remotely Operated Underwater Vehicle (ROV). According to Stage 2 of PPP-DPS exploration plan "Identification of specific ore objects and assessment of potential resources of the constituent ores", as per 2019, detailed works will be carried out at ore objects. For this purpose, it will be necessary to use remotely operated unmanned underwater vehicles (ROUV). During the reconstruction period, the R/V "Professor Logachev" received a new ROUV Sub-fighter 30k OFFSHORE (Norway)
ROUV Sub-fighter 30k OFFSHORE
Central control station.
HydroLek manipulator with 7 degrees of freedom and sampling up to 10 kg weight, azimuth search sonar Kongsberg MS1000 with a range of 100 m, 4 lamps and video cameras with a resolution of 1920 * 1080 are installed on the ROUV.
At Stage 2, the ROUV will perform two main types of work: video and photographic shooting of the bottom and collecting ore samples and biological material. Additional types of work are possible, such as setting / removing experimental installations (devices), conducting measurements (for example, temperature, etc.).
6. Underwater navigation. For the planned positioning of underwater vehicles, R/V "Professor Logachev" is equipped with the underwater navigation system "HiPap 101" (manufacturer Kongsberg (Norway)) with the super-short or long base mode of operation, bottom beacon-responders and positional accuracy 0.2% of the depth.
7. Bathymetric survey. To proceed to the solution of the tasks of Stage 2, it will also be necessary to perform an area-based bathymetric survey of the bottom on scale of 1:50 000 using a multi-beam echo sounder.
The echosounder ATLAS Hydrosweep MD / 30 1̊ х 1̊ (Germany) - 320 beams, frequency of the emitted signal 24 kHz - 30 kHz was installed on the R/V "Professor Logachev" during the reconstruction.
A bathymetric survey scheme and an antenna of multibeam echo sounder
ATLAS Hydrosweep MD / 30
8. Environmental research will be carried out at all stages of work in the Russian exploration area with the goal of creating a database on the initial state of the ecosystem in accordance with the requirements of the International Seabed Authority (ISA). To carry out this research, the entire scientific and technical equipment installed on the R/V "Professor Logachev" is used.
9. Engineering-geological studies on the Russian exploration area are carried out at all stages of work to assess the engineering-geological conditions of occurrence of identified ore objects. On board the R/V "Professor Logachev", the physicomechanical properties of hydrothermal formations, host rocks and bottom sediments raised by sampling tools during geological testing of ore objects are determined.
To carry out geological, engineering-geological and ecological research, three container laboratories were installed on the vessel during the reconstruction: ecological laboratory, engineering-geological laboratory and sample preparation laboratory.
10. Exploratory drilling at ore objects. To assess the depth of occurrence of DPS ore bodies, an underwater drilling machine is needed to drill in the ocean floor the exploratory core wells with a depth of 15 meters or more. During 2014 - 2016, a working model of TK-15 drilling machine was designed and created with a planned drilling depth of up to 15 meters. The weight of the machine is about 5 tons, the height is 5 m, the power supply from the ship's board along the load-carrying cable (3-phase, 20 kW). The TK-15 tests in November 2015 in the Atlantic and in November 2016 in the Baltic Sea showed working capacity of the model and put forward a number of design requirements for the creation of a working drilling machine for purpose of its operation on R / V "Professor Logachev" .
Test of TK-15 in the Baltic Sea.
At present, the continuation of TK-15 drilling machine construction is entrusted to OOO GIKO, which has production capacities for this. With adequate funding, these works can be brought to the creation of a domestic deep-sea drilling machine at the RRR-DPS ore sites.
During the reconstruction period of R/V "Professor Logachev" some equipment units were replaced with new ones: parking diesel generators, main engine generators, bow thruster, a new more powerful crane for 12 tons, desalination plants, transit winch with reels, conditioning system, modern navigational aids, communication and alarm facilities, ADMS was upgraded. The galley, scientific laboratories and cabins were also refurnished.
Currently, with R/V "Professor Logachev" which is the main ship of the Ministry of Natural Resources of the Russian Federation on DPS problem, modern geological exploration equipment and methodical complex, experienced PMGE staff, JSС PMGE is ready to solve the most important state and geopolitical tasks in the field of prospecting and reconnaissance of minerals in the Ocean and on the shelf.