Geochemical and paragenetic studies have demonstrated the existence of upside-down zoning in the Frood orebody. The zones are, from top to bottom, disseminated blebs of sulfide in quartz diorite, massive and breccia ore, becoming richer in copper and arsenic with depth, and a siliceous zone with volatile substances (Pb, Zn, Sn, Bi, As, Te, carbonates, and H 2 O). The inverted zoning is attributed to the structural position of the orebody below the norite heat source. An appendix evaluates the implications of new experimental evidence for very low solubility of sulfides in silicate melts, and discusses alternative ways of deriving sulfide liquids.

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