Iron Industry (2) Dune Boggle

By IonMars

August 10, 2014

If it were possible to ride like a cowboy on the Mars Reconnaissance Orbiter and look down at Mars’ surface through the lens of the High Resolution Imaging Science Experiment (HiRise)1 what scenes might be revealed? One strange panorama would certainly be the dark dunes of Mars. 

Most of the photos sent back to Earth through the various NASA probes and landers are strikingly Earth-like. When we see the boulder-strewn grounds at the site of the Pathfinder lander, one might think “oh yeah, I saw that scene when I drove through Utah.” Or when viewing the hillsides near Mount Sharp, one might expect the Rover Curiosity to drive over the next ridge and reveal the buildings of Denver. But looking down at the dark dunes of Mars can only place you in a sci-fi movie, like the adjacent view.

 

2Are these giant slugs crawling across the surface?  No, these dunes are composed of dark basaltic sand and were formed in response to fall and winter westerly winds.2The secondary dunes are commonly seen on terrestrial dunes of this size. 

Anyone who has read the 1965 novel “Dune” by Frank Herbert will recognize that giant sand worms are lurking under a thin sand cover. Everyone else will accept that these are curved barchan (crescent shaped) dunes and a straight seif (longitudinal) dune that lie in the north polar region of Mars3.

 This image was taken at the fringes around the polar icecaps where dark spots appear and disappear over the course of a Martian year.4The dark spots occur in the middle of a dune field during a Martian “summer” and are believed to be basalt dune material showing through a frosty white coating of CO2 and perhaps H2O.

We are interested in basalt and dark dunes because the iron ore magnetite (also known as lodestone) is also dark in color and is a likely component of some of the dark dunes.  We can imagine the mining of fine-grained, powdery dark sand that would be easy to prepare for the blast furnace. The mineral magnetite, like hematite, is a very high-grade iron ore. When purified it contains 72 percent iron as compared to 70 percent for hematite. Magnetite, however, does require more steps in processing to achieve purity, as compared to hematite “blueberries.”  

MagnetometerA field survey will be required to locate the fine-grained magnetite dunes on the ground surface. A field survey will require a field instrument, a magnetometer. First invented by Carl Gauss in 1833, this device is used to measure magnetic field strength in units of gauss5 (of course). Modern instruments, however, record the magnetic field strength in units of Tesla (T). The objective of a Mars magnetic iron ore exploration survey using magnetometers will be to map out the locations of the magnetite-rich dunes.

 

 

Man Taking a Reading at a Base StationTwo field technicians in dune-adapted Mars Utility Vehicles (MUVs) will conduct the survey (See the article “Mars Village Vehicles.”). These vehicles will not be traveling over well-prepared ground like the roads in a Mars village; rather, they will be driving over unexplored sandy slopes and drifts.  The wheels will be designed especially for this terrain and may be similar to the wheels of the moon buggy driven by Apollo astronauts or the wheels of the NASA space exploration vehicle (surface version). The MUV arms will manipulate the instruments and other tools to be employed in the survey.

The first step is to establish a base station. On Earth, the company PetroSeis (Malaysia) has performed numerous geomagnetic surveys for magnetite that led to successful iron ore mining operations.6 The field technicians of PetroSeis employ a Geometrics G856-AX magnetometer7 at a base station to determine the Earth’s diurnal (solar) magnetic field variations at that location. This instrument model is expressly designed for a base station and the data are automatically downloaded to a mapping program where the base measurements enable the raw field data to be corrected for diurnal and heading variations.

Field Readings The next step is to record the field readings along survey lines that were predetermined by a survey plan. For this purpose, PetroSeis technicians employ a more sensitive instrument, the Overhausser GSM-19G magnetometer.8 Produced by GEM Systems; this device enables highly accurate measurements to be recorded regardless of ambient temperature, location or instrument orientation. It is called a “walking” survey magnetometer that can collect nearly continuous data along a survey line. On Earth, a technician carries this magnetometer in a backpack, whereas on Mars he/she will carry a comparable instrument inside an MUV.

 


The graph below demonstrates how accurate survey data enhances the detection of a magnetic anomaly. The data display a series of readings near 50000 nT followed by a spike to 65000 nT.

  Chart

Locating magnetic anomalies on the ground, however, will not be enough. We want to be sure that the iron ore is located on the ground surface and not buried in hard rock mixed with other minerals. We also want the magnetite to be in the form of small loose particles that do not require extensive beneficiation to separate them from other sandy grains. The regolith of Mars were blown around the planet for four billion years, enough time for any particle to experience more friction with the ground surface and with other particles.  Such particles have become more fine-grained than beach sand particles on Earth. Some of the them have become so powdery fine that they remain entrained in the Martian atmosphere foe years despite Mars’ miniscule atmosphere. The particles are so fine that we can be certain that each grain is an individual mineral and is not agglomerated with other minerals. In other words, fine-grained magnetite particles are already beneficiated by Mother Mars; a situation that Mars pioneers can exploit to gather an easy-to-use iron ore for the blast furnace. 

To help ensure that the magnetite is in the form of loose particles; colony planners will direct the field survey toward a region where moving sand dunes have been detected. Scientists on Earth have used a time series of dune observations, using dune-observing Mars satellites such as HiRise, to identify dunes that have shifted location. If a dune can shift location under the influence of a mild force exerted by a thin atmosphere, it must ne very fine-grained. Many such dunes have been found; we would like to find some located close to a Mars village. 

Once a magnetic anomaly has been located, a field technician will carry out a test of the regolith at the site of the anomaly.  He/she will jab the ground with a remote manipulator to see if is loose or compact. (Don’t worry; no one has rushed to patent this procedure.) Field technicians will also take samples to be tested in the Mars village laboratory, probably a 3-squqre-meter workbench. Analyses of the samples will determine the size distribution of particles and verify the presence of magnetite. Sample testing, magnetic field maps, and ground observations will enable a mining plan can be formulated.

Magnetic field survey display  The design of a mining plan will depend on the location, depth and extent of the magnetite ore. The plan will involve a base camp where the ore is separated from other regolith particles and where miners will live. The locations of ore-containing dunes will determine the location of the camp and whether it will be entirely mobile or semi-permanent. In the beginning of this cottage industry, the mining base camp will be mobile because experience will be required to determine how the camp shouldl operate in the future and what additional equipment and housing will be required.

A dune-based camp will be similar to the base camp described in the previous section concerning the mining of blueberries. It will contain a regolith screening machine and dry separation device. The first step of dry screening will look similar to the dry screening of hematite spherules, but dune regolith will be processed  a larger volume because the percentage of pure magnetite in dune regolith will be less than the concentration of hematite in blueberry-laden regolith. A device that can process a larger volume is the Pitbull 2300, the same two-screen machine that was exemplified in the previous segment. The difference is that each of three outputs from this machine will have its own conveyor. In the previous operation one front-end loader was employed to deliver input to the screener, pick up the screened-out waste, collect the output from the first screen, and collect the output from the second screen. The front-end loader became a limiting factor that reduced the output compared to the machine’s rated capacity.

Magnetic field survey display

 

The main objective of this screening operation will be to limit the particles delivered to the separator to those sizes that it can accommodate without clogging. The inputs sent to the separator will be the material coming from the second screen (hidden in this image) and delivered via the conveyor on the left side of the machine. This material will consist of small particles and fines.

The large size waste clumps separated out at the top screen will drop onto the center conveyor directly across from the hopper. This conveyor will dump its waste load onto a pile, into a portable bin, or directly into the box of a dump truck.

The intermediate sized material will be deposited onto the conveyor on the right side of the machine. This size of material can be employed for a secondary purpose, namely, to serve as aggregate for a roadbed. The dune area where mining will take place is comprised of sandy, fluffy regolith unsuitable to support a vehicle.  Such terrain can be improved by laying down a layer of aggregate rock over the soft regolith until a solid roadbed is established. Then a layer of fine-grained regolith can be laid over the roadbed and tamped (See the article “Pioneering Road Building). Such improved roads will speed up mining operations and contribute to expanding the capacity of this new industry. 

Inducted roll magnetic seperatorNext, the screened dune regolith will be loaded into a dry magnetic separator. One company that produces this type of machine is Master Magnets, LTD (UK). This company manufactures an induced roll magnetic separator9 for the extraction of small magnetic particles from a processing stream of mixed minerals. It purifies these minerals for the ceramic and mineral processing industries. 

Master Magnetics uses a schematic diagram to illustrate how magnetic separation works on their drum rolls (see diagram below). The material to be treated is fed from a hopper or vibratory feeder onto a high intensity magnetic roll at a controlled rate. Non-magnetic material is thrown off the face of the roll in a normal trajectory, due to momentum. The magnetic material attaches itself onto the roll face, or is deflected towards the roll, and is discharged off the roll at a point of lower magnetic intensity, aided by a brush. A splitter plate is interposed between the two product streams. This particular machine is intended for a high-flow operation where a small amount of magnetic material is to be removed from a product stream and it may not apply to the beneficiation of iron ore.

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Shibang Machinery Company, however, manufactures dry magnetic separation machines that are expressly designed for the separation of magnetite ore from gangue (waste material). The company produces a wide range of sizes with processing capabilities ranging from 1 to 220 T/h. One model that is suitable for shipment to Mars is Model CTS(N,B)-66, which can process ore at a rate of 8 to 15 T/h and carries a weight of only 750 kg. It should easily meet all the requirements of a cottage iron industry during the early stages of colonization.  

Here is the specification list:

Model:                                             CTS(N,B)-69

Roller diameter:                              600 mm

Roller length:                                   900 mm

Average magnetic intensity:         170 mT

Processing capability:                   8-15 T/h        

Roller rotary speed:                       40 rpm

Drive power                                    1.1 Kw

Weight:                                            830 kg


Note that this machine employs a low intensity magnetic field because it is used to treat a strong magnetic ore.  Strong magnetic ores include magnetite, pyrrhotite, and maghemite.2 In order to separate minerals on Mars the electric motor on this machine must be converted to a methane-fuelled motor of equal capacity. Electricity will not be available at a remote location outside a Mars village for a considerable time to come. 

 

Are Magnetic Dunes Dangerous?

Return once again to the weird dune formations that can be observed by the HiRise camera.  A person can imagine a field technician conducting a magnetic survey in an MUV and carrying a field magnetometer. Suddenly the magnetic reading soars and the technician peers ahead to the following vista. He sees what look like giant stalagmites in the middle of the dune field. The hair on the back of his head rises up in imitation of the stalagmites. He jams the MUV into reverse gear, guns the motor, and races back to base camp. What could be so frightening? 

Matian dune field stalagmites.
The second picture below is a close-up of iron filings on a bar magnet where some of the filings strand straight up. The stalagmites look like a high school physics class experiment, except on a giant scale! What could create such tall structures - a giant bar magnet? A mass of magnetite the size of a soccer field? The size of a city? If the magnetic force is great enough to stack minerals into a giant column, what could it do to a vehicle containing metal parts?  To metal instruments? To a human being containing iron hemoglobin? 

The concerns of this author are his alone. No scientist has proffered this hypothesis as the best explanation for the observed phenomena, which remains to be solved. In the meantime, let us proceed with caution!

References

 

  1. NASA/JPL (Undated) “High Resolution Imaging Science Experiment” Retrieved 8-2-2014 from http://mars.jpl.nasa.gov/mro/mission/instruments/hirise/
  2. N. Atkinson (11-1-2010) “the Dark Dunes of Mars;” Universe Today, Retrieved 8-2-2010 from http://www.universetoday.com/77146/the-dark-dunes-of-mars/
  3. N. Viscarra (2010) NASA Earth Observing System Data and Information System, “Unearthly Dunes.” Retrieved 8-2-2014 From https://earthdata.nasa.gov/featured-stories/featured-research/unearthly-dunes
  4. Federation of American Scientists (Updated 2006) “The Remote Imaging Tutorial Section 19 The Solar System and Planetary Exploration,” Retrieved 8-2-2014 from http://fas.org/irp/imint/docs/rst/Sect19/Sect19_11.html
  5. “Magnetometers” (Undated) Wikipedia, Retrieved 8-3-2014 from http://en.wikipedia.org/wiki/Magnetometer#Scalar_magnetometers
  6.  “Magnetic Iron Ore Exploration” (Undated) PetroSeis, Retrieved 8-2-2014 from http://www.petroseis.asia/Land_Magnetic.html
  7. Geometrics (Undated)  “G-856 Magnetometer,’’ Retrieved 8-3-2014 from http://www.geometrics.com/geometrics-products/geometrics-magnetometers/g-856-magnetometer/
  8. GEM Systems,(Undated) “Rugged Overhauser Magnetometer” Retrieved 8-3-2014 from http://www.gemsys.ca/products/rugged-overhauser-magnetometer/
  9. Master Magnets, LTD. (Undated) “Induced Roll Separators,” Retrieved 8-2-2014 from http://www.mastermagnets.com/product/induced-roll-separators/
  10. Shanghai Shibang Manufacturing Company (Undated) “Magnetic Separation Machine,” Retrieved 8-2-2014 from http://shsbjq.en.china.cn/selling-leads/detail,1066171160,Magnetic-Separation-Machine-for-basalt-production-line.html