Procrustean science: Indigenous siderophiles in the lunar highlands, according to Delano and Ringwood

The best estimate of indigenous lunar siderophiles comes from 29 pristine lunar rocks, characterized by low siderophile abundances, plutonic textures, and high age. Delano and Ringwood's blanket rejection of these rocks, on the contention that they are impact melts, is not justified by the petrologic evidence. Contrary to their claims, gold in highland breccias is largely meteoritic and is unaffected by fumarolic volcanism, as shown by its correlation with Ir and noncorrelation with fumarolic Tl (r = 0.896 and 0.272). Delano and Ringwood's approach, involving substraction of an H-condrite meteoritic component from highland breccias, ignores the variation of Ir/Au ratios in modern and ancient meteorites, and hence leads to spurious excesses of Au, Ni, and volatiles, and in some cases to physically meaningless, negative residuals. Their 'excess volatiles' in highland crust relative to mare basalts disappear when the highland composition is based on pristine lunar rocks rather than undercorrected breccias. Contrary to claims by Delano and Ringwood, the Ni/Co trend in Apollo 16 samples cannot be explained by an indigenous component rich in Ni (150-200 ppm) and Co (30-45 ppm); mixing lines show that much lower Ni and Co contents are required (e.g. approximately 7 ppm each). (Auth.)