Osmium isotope ratios for two types of plati- num group mineral (PGM) nuggets of eluvial (residual) origin, associated with the Freetown Layered Gabbro Complex, were determined in-situ using an ion micro- probe. The values for erlichmanite nuggets are ~ 1.08. Those for PGM inclusions in Pt-Fe alloy nuggets are higher, ranging from 1.2 to 2.1. Ratios of 187Os/186Os vary between the nuggets, but they are consistent within individual nuggets. The data suggest early formation of the erlichmanite nuggets, prior to a postulated substan- tial contribution of crustal Os. The Pt- Fe alloy nuggets, on the other hand, were formed later in a residual melt which was contaminated by crustal Os due to the assimi- lation (< 10%) or the gaseous/fluid transport of Os from Archaean host rocks into the magma. The lack of sys- tematic mineralogical and chemical changes of the Com- plex and extensive granulitization in the adjacent host rocks and xenoliths may favor the latter process. The lack of high Ia7Os/ZS6Os ratios, consistent ~87Os/ 186Os values within individual nuggets and their textures and mineralogy suggest that the studied PGM nuggets were not formed during lateritization or in low-tempera- ture depositional environments.