Formation of poikilitic chromite in the basal dunite series of the 2.44 Ga Näränkävaara layered intrusion

Abstract

Poikilitic chromite has been described only from komatiitic cumulates with >Fo91–92. Its formation is thought to be related to high temperatures inhibiting chromite nucleation. Here, we describe poikilitic chromites found in the olivine adcumulate (Fo<91) basal dunite series of the Näränkävaara intrusion, and suggest a formation mechanism for poikilitic chromite in intrusive settings whereby low oxygen fugacity in the parental magma inhibits chromite nucleation. Results of this and other recent studies from the Näränkävaara intrusion are summarized, and implications for massive sulfide exploration in Fennoscandian 2.44 Ga intrusions are presented.