ABSTRACT

Strontium isotope ratios in whole fibrous diamonds from Zaire do not correlate with Rb/Sr ratios, but with La/Ba and La/Nd ratios. Diamonds with lower La/Ba and higher La/Nd gave higher ⁸⁷Sr/⁸⁶Sr. Leaching experiments on crushed diamonds gave lower La/Ba and higher La/Nd for water leachate and higher La/Ba and lower La/Nd for acid leachate, and more importantly, the former has higher ⁸⁷Sr/⁸⁶Sr ratios than the latter, which is in accord with the experiments of whole diamonds. The two leachates are considered to be from water-rich fluid and carbonates, respectively. It is likely that the diamonds have formed in the environment where water-rich fluid and carbonate-rich fluid or melt were mixing and that the mixing may have triggered kimberlitic magmatism.