Scenarios for the Marine Mining of Heavy Minerals


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With the increased understanding of the occurrence of heavy minerals offshore, the need for efficient marine mining systems is emerging. This marine environment demands a dredge mining solution as dry truck & shovel operations are no longer possible.

For the marine mining of heavy minerals, multiple scenarios can be developed. They can differ both in the mining systems used and in the sequence and location of process steps required. The selection of the dredge mining equipment is generally a function of the required depth of excavation, the soil conditions and the target production. In a marine environment, the climate and sea conditions also need to be accounted for. Examples of dredge mining equipment include wheel suction dredgers, applicable in shallow depths for medium to loose sandy deposits and high productions. Wheel dredgers however have limited tolerance for wave conditions, so will likely find applications in sheltered bay or harbour locations. Trailing suction hopper dredgers are applicable in deeper waters for loose sand deposits and high productions. They have a higher tolerance for wave conditions and can therefore be successfully applied offshore.

Given the relatively low grades of heavy minerals found in the deposits, it is preferable to perform a first concentration step as quickly as possible after the mining to create a concentrate. In conventional, inland dredge mining operations this is done at the floating primary concentrating plant. Spiral concentrators are the equipment generally used for this process. In a marine environment, application of spirals on a floating platform will be strongly dependent on the sea state conditions. Wave induced motions of the floating platform will disrupt the concentration process of the spirals. This limits the application of the spirals to steady platform.

Combining the optimal dredge mining equipment with the optimal processing solution is a complex process. Both aspects cannot be regarded individually and have to be seen as an integrated process where capacities and process characteristics have to matched to find the optimal integrated marine mining solution. As example a case will be presented for the mining of heavy minerals approx. 30 km off the coast of Western Australia. Multiple scenarios for this case were produced. These include the use of a stationary suction dredger that fills barges that were tugged to a port facility where a process facility was located. An alternative scenario would use a trailing suction hopper dredger to mine the ore, sail to port and dump the material in water near the quay, where a small second dredger would re-handle to ore and directly feed a process installation onshore. Selection of the optimal scenario requires careful and detailed evaluation of all applicable variables.

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  • Offshore gold mining started in early 1900s. Gold and tin were the key elements dredge mined. Gold provinces offshore included Tierra del Fuego (CL/AR), majority of gold fields were alluvials inshore. Key offshore developments took place on South-East Asian tin belt, focused around Indonesia.
  • Important aspect of deep sea mining is an answer to the question what can be found offshore. Not all minerals occur in deposits on the seafloor. The geologic processes that form the deposits are different from the ones that formed the deposits on the continents and as a results the deposits found on the seafloor are unique and different from the ones on the continent.In this figure I’ve shown the most commonly occurring types of deposit, moving from shallow to deeper waters. Offshore placers are deposits of valuable minerals that are transported by the river or wave-action and laid down in shallow offshore waters. The diamonds, gold, tin or heavy minerals are eroded on the continent and washed offshore. Water depths range from the beach and dunes down depths to about 300m. Significant occurrence are known in the world. Known example is Nome in Alaska, where Discovery Channel’s Gold Divers is situated. More industrial mining takes place in Indonesia where tin is mined offshore, I’ll give an example in a few minutes. Diamonds are also mined off the coast of South Africa and Namibia, I’ll give an example of that as well shortly. Next deposit down are phosphorites. This a type of phosphate deposits formed in 300-500m of water depth. Phosphate is a raw material for fertilizer, market dominated by exports from Marocco. In several places in the world projects are in an early phase of development, including New Zealand and Namibia. The deposit occur rather frequently around the continental shelf margins, including near Mexico, Chile and Brasil.Crust is a name for a deposit of manganese and cobalt, occurring on the slopes of seamount, primarily in the West Pacific. Although promising in metal content and volume, extraction will be difficult as the crust is a hard layer rock inter-grown with the host rock underneath it. Another difficulty is the remote location of the occurrences near the Marshall Islands and Micronesia. They occur in depths of 1500-3000m Seafloor Massive Sulphides are deposits formed by black smokers. The smokers are plumes of hot water driven by volcanic activity. The hot water contains base and precious metals, like copper, gold, zinc, silver and lead. When in contact with cold water the metals precipitate as sulphides. This makes them very comparable to base metal ores found on land. Given their high grades, quite a lot of interest exists in the deposits. They occur in water depths from 1500-2000m Nodules, also known as manganese nodules, are formed in the deep ocean between 4000-6000m. They are polymetalic and consist of mangenese, iron, nickel and copper. The nodules size from gravel to potatos, but can be sucked or scooped up as they lay in the clay of the deep sea floor. Current interest is not only in the base metals, but also in the rare earth elements the nodules contain traces of. Bottom of the figure gives an overview of legislation offshore, with the EEZ extenidng to 200 nm, and depending on the shelf upto 320 nm. The area outside that is governed by the united nations body, named the International Seabed Authority. It does not directly related with the indicated minerals, as crust and SMS occur frequently within EEZs, even nodules do.
  • The photo demonstrates a typical example: the mining of heavy minerals using to IHC mining dredgers. In the dune area of South Africa, these tools mine titanium-dioxide and zircon minerals. The Titanium dioxide is used as feedstock for pigment, the white colouring of your toothpaste or wall paint. Zircon is used in the ceramics industry. The dredgers pump the sand to a floating processing plant that makes a first separation step and deposits the tailings, the sand back. The majority of the HM are produced in this way and IHC is market leader in the supply of this equipment.
  • At price, but might provide future solutions
  • Scenarios for the Marine Mining of Heavy Minerals

    1. 1. Scenarios for the Marine Mining of Heavy Minerals Heavy Mineral Conference 2013 Visakhapatnam, India 27-29 November 2013 Bart Hogeweg Andrina Drost Rogier Kalis IHC Mining B.V. The Netherlands
    2. 2. 3 IHC Merwede Overview IHC Merwede facts & figures: • Financial turnover in 2012: EUR 0.9 billion • Staff in 2012: 3,200 • 5 Shipyards in The Netherlands, 1 in China; Singapore & Batam with Jaya Shipbuilding & Engineering •World wide services and manufacturing locations
    3. 3. 4 Outline • • • • • Introduction Marine mining technology Mineral processing in marine environments Marine mining scenarios Conclusions
    4. 4. Introduction / Mining / Processing / Scenarios 5 Mining of the seafloor has been ongoing for a long time • Offshore gold and tin mining started in early 1900s
    5. 5. Introduction / Mining / Processing / Scenarios 6 Current marine mining activities are still based around historic areas… • PT Timah operates offshore Indonesia with large integrated bucket ladder dredgers • In water depths to 50 m • Recently, IHC and PT Timah converted one of the dredgers to a hydraulic wheel dredger, extending water depth to 70 m Source: PT Timah
    6. 6. Introduction / Mining / Processing / Scenarios 7 …but also moved into new areas • De Beers Marine operates a mining vessel with a crawler offshore Namibia • Diamonds are mined from water depths to 150 m Source: De Beers Marine
    7. 7. Introduction / Mining / Processing / Scenarios 8 Heavy minerals are found offshore in relatively shallow water depths Offshore placers: Diamonds, gold, tin, heavy minerals (Ti-Zr) Phosphates Crust (Mn, Co) Seafloor Massive Sulphides (Cu, Au, Zn) Nodules (Mn, Ni, Cu) Source: GRID-UNEP
    8. 8. Introduction / Mining / Processing / Scenarios 9 Heavy minerals are very suitable for dredge mining • Richards Bay Minerals is world largest heavy minerals mining operation, using mining dredgers in multiple ponds
    9. 9. Introduction / Mining / Processing / Scenarios 10 How can we build a pond on the other side of the shore line?
    10. 10. Introduction / Mining / Processing / Scenarios 11 Different concepts can be used for marine mining • Stationary • Cutter/wheel suction dredger • Bucket ladder dredger • Trailing • Trailing suction hopper dredger
    11. 11. Introduction / Mining / Processing / Scenarios 12 Moving offshore brings in factors like wind, waves, currents etc. • Cutter suction dredgers are fixed to ground by spud  wave action limits operation • Trailing suction hopper dredgers don’t have this limitation
    12. 12. Introduction / Mining / Processing / Scenarios 13 Wind and waves also have a large impact on the separation of heavy minerals • Sea state and resulting vessel motions have impact on performance of separation equipment • Vessel movements inhibit proper operation of spiral concentrators
    13. 13. Introduction / Mining / Processing / Scenarios 14 Technology can provide solutions, but they come at a price • Increase size of the platform to create more stability • Motion compensation Source: Husky Energy Source: Barge Master
    14. 14. Introduction / Mining / Processing / Scenarios 15 Combining mining and mineral processing results in different mining scenarios • Integrated platform combining mining and mineral processing functions • De-coupled functions
    15. 15. Introduction / Mining / Processing / Scenarios 16 An integrated solution provides distinct benefits, but has limited application in sea state • Single unit • Direct tailing repositioning, no tailing transportation required • Well suited for mining of thicker layers of material • Limited sea state, as processing is integrated onboard the dredge
    16. 16. Introduction / Mining / Processing / Scenarios 17 Separated functions provide more flexibility • Opportunity to use trailing suction hopper dredgers • Operating cycle: process is discontinuous Transport Dredging Dumping Transport Pumping ashore Rain-bowing
    17. 17. Introduction / Mining / Processing / Scenarios 18 Choices in mining cycle can create a variation of scenarios • Similar to the operating cycle of the TSHD, a mining cycle can be setup • For each step in cycle, different options exist Transport tailings • TSHD Mining • CSD • WSD • Floating • Onshore Process plant Concentrate Transport ore • TSHD • Barge Source: Van Oord
    18. 18. Introduction / Mining / Processing / Scenarios 19 Various scenarios are usually possible. Logistics determine the optimal scenario Example 1 Example 2 Example 3
    19. 19. Introduction / Mining / Processing / Scenarios 20 Finding the optimal requires thorough analysis • Multiple technology solutions for marine mining are available • Factors as proximity to shore, wind and wave conditions have a large impact on both the mining and mineral processing options for a mining scenario • Mining scenarios are a combination of mining, processing and transportation methods selected on a project-to-project basis • The optimal mining scenario is driven by logistics