“Space, the final frontier” as they say on Star Trek. How compelling. Several recent films have invoked the mining of precious metals on asteroids. It is an exciting notion, but one must be grounded in reality when investing hard-earned dollars. In the movie Alien (1979), a spacecraft brings several million tons of ore back to Earth to be processed. Those contemplating a real-life asteroid mining scenario have recently formed a couple of start-up companies that are actively pursuing this goal. Those major investors are wealthy individuals who are no doubt very intelligent and highly successful entrepreneurs. If television reflected real life, those start-ups would be in good shape. Organizations commonly save money by not hiring a competent mineral resource geologist to advise them on geological matters. How hard can it be to hit a rock with a hammer, swagger about regally in khaki pants with a roll of maps under your arm, or draw diagrams in the dirt with a stick? After all, that is what television geologists do. I know a few people who are quite wealthy and have seen them chase romantic, exciting projects similar to asteroid mining that are ultimately found to be unrealistic. For the uber-rich, this is no more than an exciting and trendy venture that might end in failure without substantially altering their net worth. For the hoi polloi, however, such investment can result in financial hardship and possibly poverty, especially if an exit strategy for their investment is not readily available.
Devil In The Details
The notion that mining companies merely scoop up metals from the surface of the ground when they are found is inaccurate. The occurrence of any mineral must be defined in three dimensions, which means that once drill targets are established by preliminary surface work, they must be tested by drilling to evaluate the third dimension of the mineralization. The reason for this is to establish continuity, grade, and tonnage of a resource so that ultimately a relatively complete value of that mineral existing in a given area can be determined. The drilling is also necessary to separate waste rock from valuable rock. Most ore deposits are irregular in shape and contain blocks of internal waste rock within the valuable rock. This costly and time-consuming work is necessary before a rational production decision can be made. Ultimately, it determines whether or not a mineral resource is economic to mine. Even on earth, where variables and costs are well-known, it takes many years and hundreds of drill holes completed at great expense to determine the feasibility of mining a given mineral resource. All of this work done prior to mining would be dreadfully expensive in outer space. There is no technology in sight that would permit us to bypass the tedious preliminary work that is presently necessary to define an ore deposit.
Although current costs for interstellar transport of a given amount of material will likely decrease greatly in the future, it is unlikely that it will decrease many thousand-fold, the amount required to make the venture profitable, until some incredible new technology comes along. That technology is not yet in sight. If it has not yet even been envisioned, it may never even happen, at least in our lifetimes. If very low-cost space travel becomes reality in 50 or 100 years, most of the current investors will be pushing up daisies by then. And, 50 or 100 years is a long time for many negative things to happen when a company’s only cash flow comes from equity sales, assuming their only profits come from future asteroid mining. From a geological standpoint, there are some insurmountable problems with the asteroid mining scenario. Mostly, these have to do with the lack of gravity, the absence of weathering, and the lack of water. Those three items play a major part in the formation of ore deposits. The main problems regarding asteroid mining are elucidated below:
1) If a large nickel-iron asteroid could be located and successfully boarded, it should be recognized that nickel and iron are much cheaper to mine and process on earth. Even if the nickel-iron asteroid contained valuable Platinum Group Elements (PGE), the concentration of those PGE in the nickel-iron matrix is very limited. Valuable PGE deposits mined here on earth often have an average of less than 30 grams of PGE per ton of rock. This limitation is predominantly due to Laws of Thermodynamics that are probably very nearly the same over much of the universe.
2) The PGE are probably disseminated throughout the nickel-iron matrix and cannot just be picked up off the surface like nuggets. Nuggets are an Earth phenomenon resulting from intense weathering and mechanical concentration by water. The hypothetical ore mentioned above that contains 30 grams per ton PGE would have a unit value of about $1,000 per ton given the prevailing PGE prices. The cost to move one ton of rock to the earth for processing would be, to be very conservative, several thousand times more than the value of the PGE.
3) On earth, nickel-iron ore that contains valuable PGE is concentrated through flotation, a process that requires gravity. Since asteroids have negligible gravity, the flotation process would not work, meaning that ore would have to be transported to earth for processing. Even with gravity, the venture should be considered an unwinnable battle just due to the cost factor since a great deal of processing equipment would have to be moved to the asteroid. An attempt at mechanical magnetic separation of nickel-iron ore from the surrounding rock would only produce a concentrate with slightly elevated PGE contents because most of the nickel-iron rock is magnetic. That concentrate would be 99% nickel-iron, which is mined cheaply here on earth, thus rendered relatively uneconomic in space.
The recent excitement about asteroid mining also ignores several important geologic facts. Ore deposits on the earth are enriched many fold in metal content through three different processes. It is highly unlikely that any of these three processes are at work on an asteroid. Without the processes described below, ore deposits on asteroids will likely be much less concentrated than those found right here on earth, assuming of course that the Laws of Thermodynamics are relatively constant across the universe.
First, weathering and oxidation are important factors in metal enrichment. They tend to mobilize and concentrate metals through both physical and chemical action when surface water moves laterally and vertically through fractures or pores in the rocks. Second, gravity also helps enrich ore deposits through selective layering or sorting of heavier metals and downward movement of mineral-rich water. Third, movement of super-heated waters containing dissolved metals, ascending through Earth's crust, creates metal concentrations where temperature and pressure gradients become steep, resulting in a lower solubility of metals in those hot waters. The metals are then precipitated. Without these three processes in operation, rich deposits of metallic ore will probably not form on asteroids. The idea that you can simply board an asteroid and scrape up platinum and gold nuggets is absurd.