Precious and structural metals on asteroids

Metals and metallic elements in silicate/oxide form are abundant in asteroid materials and are often touted as a valuable space resource that can be returned to Earth or used in space. However, the data that come along with these claims are decades old, incomplete, and of questionable quality. Here, we draw on newer measurements and statistics from the vast meteorite collection to assess the concentrations of many elements in likely asteroid materials compared to terrestrial ore deposits. A cursory comparison of 83 elements identifies a promising group that are examined in more detail: the platinum group metals (PGMs) Rh, Ru, Pd, Os, Ir, Pt, and the base metals Fe, Mg, Al, and Si. PGMs are found to deviate from chondritic ratios with respect to Ir at higher Ir values, such that maximum PGM contents in asteroids likely do not reach as high as previously thought. However, there may be other strategies to form a PGM-rich concentrate, for example separating out refractory metal nuggets from more primitive undifferentiated asteroids. In addition to precious metals, the base metals Fe, Mg, Al, and Si can be chemically reduced and used to support in-space manufacturing, particularly for large space structures and solar panels. In all cases, the path from raw asteroid material to refined products can be organized using the concept of flowsheets from terrestrial mining, where mineral processing/beneficiation is of first-order importance.