Mars may containores that would be very useful topotential colonists.[1][2] The abundance of volcanic features together with widespread cratering are strong evidence for a variety of ores.[3] While nothing may be found on Mars that would justify the high cost of transport to Earth, the more ores that future colonists can obtain from Mars, the easier it would be to build colonies there.[4]
Ore deposits are produced with the help of large amounts of heat. On Mars, heat can come from molten rock moving under the ground and from crater impacts. Liquid rock under the ground is calledmagma. When magma sits in underground chambers, slowly cooling over thousands of years, heavier elements sink. These elements, includingcopper,chromium,iron, andnickel become concentrated at the bottom.[5] When magma is hot, many elements are free to move. As cooling proceeds, the elements bind with each other to form chemical compounds orminerals. Because some elements do not bond easily to form minerals, they exist freely after nearly all the other elements have bonded into compounds or minerals. The remaining elements are called incompatible elements.[6] Some of them are quite useful to humans. Some examples includeniobium, a metal used in producingsuperconductors and specialtysteels,lanthanum andneodymium, andeuropium for television monitors and energy-efficientLED light bulbs.[7] After the mass of magma has cooled and has mostly frozen or crystallized into a solid, a small amount of liquid rock remains. This liquid bears important substances such aslead,silver,tin,bismuth, andantimony.[8] Sometimes minerals in the magma chamber are so hot that they occupy a gaseous state. Others are mixed with water andsulfur in aqueous solutions. The gases and mineral-rich solutions eventually work their way into cracks and become useful mineralveins. Ore minerals, including the incompatible elements, remain dissolved in the hot solution, thencrystallize out when the solution cools.[9] Deposits created by means of these hot solutions are called hydrothermal deposits. Some of the world's most significant deposits ofgold, silver, lead,mercury,zinc, andtungsten started out this way.[10][11][12] Nearly all the mines in the northern Black Hills of South Dakota came to be because of hot water deposits of minerals.[13] Cracks often form when a mass ofmagma cools because magma contracts and hardens when it cools. Cracks occur both in the frozen magma mass and in the surrounding rocks, so ore is deposited in any kind of the rock that happens to be nearby, but the ore minerals first had to be concentrated by way of a molten mass of magma.[14]
Research carried out at Louisiana State University found different types of volcanic materials around volcanoes inElysium Mons. This showed that Mars can have a magma evolution. This leads to the possibility of finding useful minerals for a future human population on Mars."[15][16]
The presence of many hugevolcanoes on Mars shows that large areas were very hot in the past.Olympus Mons is the largest volcano in theSolar System;Ceraunius Tholus, one of its smaller volcanoes, nears the height of Earth'sMount Everest.
There is strong evidence for much more widespread sources of heat in the form ofdikes, which indicate that magma traveled under the ground. Dikes take the shape of walls and cut across rock layers.[17] In some cases, dikes on Mars have become exposed byerosion.
Large areas of Mars contain troughs, called fossa, which are classified asgrabens by geologists. They stretch thousands of miles out from volcanoes.[18] It is believed that dikes helped with the formation of grabens.[19][20][21] Many, maybe most, of the grabens had dikes under them. One would expect dikes and other igneous intrusions on Mars because geologists believe that the amount of liquid rock that moved under the ground is more than what we see on the top in the form of volcanoes and lava flows.[22]
On Earth, vast volcanic landscapes are calledlarge igneous provinces (LIPs); such places are sources of nickel, copper,titanium, iron, platinum,palladium, andchromium.[4][23] Mars'sTharsis region, which contains a group of giant volcanoes, is considered to be a LIP.
Besides heat generated by molten rock, Mars has had much heat produced whenasteroids impacted its surface making giantcraters. The area around a large impact may take hundreds of thousands of years to cool.[4]
During that time, ice in the ground will melt, heat, dissolve minerals, then deposit them in cracks or faults that were produced with the impact. Studies on the earth have documented that cracks are produced and that secondary minerals veins are filled in the cracks.[24][25][26][27] Images from satellites orbiting Mars have detected cracks near impact craters.[28] Areas of aqueous and low-grade thermal alteration have been found by the Opportunity Rover on the rim ofEndeavour crater.[29] These are found near joints and fractures that allowed deep fluid circulation which caused chemical and thermal alteration of the rocks. So, the area around martian craters may contain a variety of minerals that were produced as an indirect result of an impact.[30]
Heat from impacts results from several processes. Immediately after an impact, there is a rebound off the floor which causes hotter rocks to be uplifted to the surface. However, most of the heat comes from the kinetic energy that is produced during the impact. This enormous heat creates several useful products that may start forming early and then continue for some time. These are called "epigenetic deposits." Circulation of hot mineral-rich fluids in the fractures from the impact cause hydrothermalism. Important examples are the Cu-Nisulfides at theSudbury Igneous Complex inCanada. For a number of years, these ores from the Sudbury area had a value of $2 billion each year. The Sudbury formation has provided us with ores ofzinc,copper,gold, andlead.[25][31]
Strong evidence for hydrothermalism was reported by a team of researchers studyingAuki Crater. This crater contains ridges that may have been produced after fractures formed with an impact. Using instruments on theMars Reconnaissance Orbiter they found the mineralsSmectite,Silica,Zeolite,Serpentine,Carbonate, and Chlorite that are common in impact-induced hydrothermal systems on Earth.[32][33][34][35][36][37] There is other evidence of post-impact hydrothermal systems on Mars from other scientists who studied other Martian craters.[38][39][40]
The surface of Mars contains abundant evidence of a wetter climate in the past along with ice frozen in the ground today; therefore it is quite possible that hydrothermal systems could be set up from impact heat.NASA'sMars Odyssey actually measured the distribution of ice from orbit with agamma ray spectrometer.[41] So, in the past, much water could have been available to circulate in cracks and deposit new minerals. This process, calledhydrothermal alteration has been found in a meteorite from Mars. Research, published in February 2011, detailed the discovery of clay minerals, serpentine, and carbonate in the veins of aNakhlite martian meteorite.[42][43] ThePhoenix lander, whose rocket engine blast actually exposed a layer of ice, watched ice melt (the ice disappeared by sublimation).[44][45]
Because 30% of the roughly 180 impact craters on Earth contain minerals or oil and gas, it seems that the cratering promotes the development of natural resources[46] Some of the ores produced from impact-related effects on Earth include ores ofiron,uranium,gold,copper, andnickel. It is estimated that the value of materials mined from impact structures is 5 billion dollars/year just for North America.[25]
It has for some time been accepted by the scientific community that a group ofmeteorites came from Mars. As such, they represent actual samples of the planet and have been analyzed on Earth by the best equipment available. In these meteorites, calledSNCs, many important elements have been detected.Magnesium,aluminium,titanium, iron, and chromium are relatively common in them. In addition,lithium,cobalt, nickel, copper, zinc, niobium,molybdenum, lanthanum, europium, tungsten, and gold have been found in trace amounts. It is quite possible that in some places these materials may be concentrated enough to be mined economically.[47]
The Mars landersViking I,Viking II,Pathfinder,Opportunity rover, andSpirit rover identified aluminium, iron,magnesium, and titanium in the Martian soil.[48]Opportunity found small structures, named "blueberries" which were found to be rich inhematite, a major ore of iron.[49] These blueberries could easily be gathered up and reduced to metallic iron that could be used to make steel.
In addition, bothSpirit andOpportunity rovers found nickel-ironmeteorites sitting on the surface of Mars.[50][51] These could also be used to producesteel.[52]
In December 2011,Opportunity rover discovered a vein ofgypsum sticking out of the soil. Tests confirmed that it contained calcium, sulfur, and water. The mineral gypsum is the best match for the data. It likely formed from mineral-rich water moving through a crack in the rock. The vein, called "Homestake," is in Mars' Meridiani plain. Homestake is in a zone where the sulfate-rich sedimentary bedrock of the plains meets older, volcanic bedrock exposed at the rim ofEndeavour crater.[53]
Dark sand dunes are common on the surface of Mars. Their dark tone is due to the volcanic rock called basalt. The basalt dunes are believed to contain the mineralschromite,magnetite, andilmenite.[54] Since the wind has gathered them together, they do not even have to be mined, merely scooped up.[55] These minerals could supply future colonists with chromium, iron, and titanium.
Theoretically, ore resources exist on Mars.[55] Moreover, sensitive equipment can predict where to look for them, such as around craters and near volcanic regions. As more images are gathered, more information will be gathered which will help to better map the locations of smaller structures, such as dikes, that indicate intrusive (under the surface) igneous activity. Later, flying uncrewed craft with gravity and magnetic measuring devices will be able to determine the exact locations of mineral deposits.
