Fieldwork was conducted in the active north crater of Oldoinyo Lengai volcano, Tanzania. Gases, aqueous fumarole condensates, and freshly erupted natrocarbonatite lavas were collected from several hornitoes associated with the same eruptive center and are considered to represent genetically related products of the same shallow magma chamber. Apparent trace-metal mineral-mineral partition coefficients were derived for the major carbonate phases, gregoryite and nyerereite, and several accessory phases within the fresh lava samples. Trace metals display an affinity for the accessory minerals. Textural information suggests that fluorite and coexisting sylvite are also present interstitially as quenched immiscible salt melts, and that any trace metals present may be scavenged from the carbonatite by the immiscible separation of these salt phases. Gas condensate analyses from the fumaroles associated with the eruption reveal further partitioning of trace elements into the vapor phase. Chalcophile elements show particularly high volatility, and this implies either gas release prior to sulfide formation or the decomposition of sulfides prior to eruption. The strong partitioning of metals into the halogenide and vapor phases has broad implications for the mobility of trace elements in the mantle source, the genesis of exotic mineralization associated with other carbonatites, and the ability of fumarole condensates to carry a direct chemical signature from their parent magma.