Site Evaluation:
The Sampling Program

Even though local information on power, water, work force, roads, transportation, topographic relief, geologic factors, etc., continues to be collected and evaluated, the cornerstone of site investigation is the sampling program. While the immediate purpose of the sampling program is to delineate enough ore reserves to guarantee an economic mine, the quality of the program affects decisions made during the entire life of the mine. Geologic sampling takes many forms, but the most common tool by far is the core drill. Cores are taken at an interval small enough to sample accurately both ore reserves and any geologic formations that can affect mining operations. The depth and area of the core sampling program must represent the volume to be mined. While a minimum number of samples is required for a decision to start operations, sampling continues throughout the life of the mine.

Site Evaluation:
The Ore Body Model

Ore body models are by far the major analytical tool used in the evaluation, design, and planning process. The importance of building as accurate a model as possible cannot be overstressed.

The model itself is a mathematical representation of relevant subsurface and surface features: ore grades, amount of waste, geologic formations affecting mining, etc. This math model is derived from the data collected during the sampling program. Thus, sampling and modeling are related and concurrent processes. The model can be constructed in a variety of ways, from simple linear interpolation between samples (called "data points") to sophisticated variance-reduction geostatistical models. A modeling method may be selected because it worked well in the past. More than one model may be constructed, using one model to check the other. Regardless of the modeling method chosen, the influential factor in generating an accurate model is sampling interval and procedure.

The model allows the mine designer to plan the optimal mine, determine its profitability, and compare it to another property. The entire mining and milling operationJs computer simulated over the life of the mine: different mining methods are tried; mill feed variation is calculated; production schedules are determined; sensitivity analyses are performed to determine the most important parameters for cost-effective operation. Over the life of the operation, data are collected and added to the model, and the model is continually updated and reanalyzed.

Design and Construction

The final model is no longer just a model of the ore body but a model of the entire project. Since the model determined economic viability, it is also the basis for mine design and production planning. The many design details are added, and the design is finished. As the design is completed, equipment and materials are ordered and construction begins. Design and planning continue throughout the entire mine life.

Implications for Nonterrestrial Resources

Presuming that the approach to developing nonterrestrial resources will parallel that for developing mineral resources on Earth, we can speculate on some of the problems associated with developing lunar and asteroidal resources. Even in the terrestrial case, the mine design and construction process is very complex. Much of the complexity results from the many unknowns in the process, which must be estimated from the data or in some cases guessed. As mineral sources, the Moon and the asteroids increase these unknowns by an order of magnitude.

 The baseline for our study group was a small lunar mine and oxygen extraction facility. The facility would produce liquid oxygen (LOX) by electrostatically separating ilmenite from mined lunar soil and then reducing it to oxygen, iron, and titanium dioxide by a hydrogen reduction process. The production of 100 metric tons of lunar oxygen for delivery to low Earth orbit (LEO) implies production of an additional 300 metric tons for use in the Moon-LEO leg of the transportation system (200 to take 200 from the Moon to LEO; 100 of that 200 to bring hydrogen back to the Moon). This production requires that 40 000 metric tons of material be mined to supply the LOX feedstock. The mine and extraction facility would operate only during the lunar day (that is, 14 Earth days in operation, 14 off) throughout the year. Our study group considered only the problems that would be encountered in identifying the mining site, delineating the ore at the site, and building and operating the lunar mine, not those associated with the extraction facility or the technology.


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[NASA] [Ames Research Center]
WebWork: Al Globus, Bryan Yager, and Tugrul Sezen
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