The diamond potential of kimberlites is generally determined using indicator minerals (i.e., xenocrysts), entrained by the parent magma while ascending through the sub-continental lithospheric mantle (SCLM). It is becoming increasingly apparent that olivine can also be used to understand mantle sampling depth, using the Al-in-olivine thermometer, and to constrain the extent of diamond-destructive metasomatism in the SCLM. To further current understanding of vertical sampling and diamond preservation in the SCLM, we present geochemical results for kimberlitic olivine of the Koidu mine (Sierra Leone). We combine our olivine data with pressure-temperature estimates from available olivine diamond inclusions, clinopyroxene xenocrysts, and eclogite xenoliths to visualise the vertical distribution of lithologies in the SCLM beneath Koidu. In agreement with the absence of peridotitic olivine and low abundance of olivine diamond inclusions in the lower SCLM, megacrysts appear to dominate the material sampled from the lowermost lithosphere. At shallower levels a distinct eclogite-dominated region is observed (160-180 km) whereas the SCLM at depths of 110-150 km is heterogeneous comprising depleted harzburgite/dunite, lherzolite, and eclogite. Diamonds are predominantly eclogitic with pressure-temperature estimates for diamondiferous eclogites of 150-190 km within the eclogite-dominated region. The near absence of diamonds sampled from near the lithosphere-asthenosphere boundary is attributed to diamond destruction by extensive infiltration of proto-kimberlite melts leading to metasomatism of the eclogite and peridotite substrate and megacrysts formation. Widespread metasomatism of the deepest reaches of the SCLM sampled by kimberlites elsewhere suggests that Koidu does not represent an isolated case and the extent of diamond-destructive metasomatism can be constrained using olivine xenocrysts.

金伯利岩的钻石潜力通常是通过母岩浆在上升穿过次大陆岩石圈地幔 (SCLM) 时夹带的指示矿物（即异晶）来确定的。越来越明显的是，橄榄石还可以使用橄榄石中铝温度计来了解地幔采样深度，并限制 SCLM 中金刚石破坏性交代作用的程度。为了进一步了解目前 SCLM 中的垂直取样和钻石保存，我们提供了 Koidu 矿（塞拉利昂）金伯利岩橄榄石的地球化学结果。我们将橄榄石数据与现有橄榄石钻石包裹体、单斜辉石捕虏晶和榴辉岩捕虏体的压力-温度估计值相结合，以可视化 Koidu 下方 SCLM 中岩性的垂直分布。与下部 SCLM 中不存在橄榄岩橄榄石和低丰度橄榄石金刚石包裹体相一致，巨晶体似乎在最下部岩石圈采样的材料中占主导地位。在较浅层观察到明显的以榴辉岩为主的区域（160-180 公里），而在 110-150 公里深度的 SCLM 是非均质的，包括贫化方辉橄榄岩/纯辉岩、二辉橄榄岩和榴辉岩。钻石主要是榴辉岩，对榴辉岩为主的区域内 150-190 公里处的含钻石榴辉岩进行压力-温度估计。岩石圈-软流圈边界附近几乎没有采集到钻石，这是由于原金伯利岩熔体的广泛渗透导致了榴辉岩和橄榄岩基质的交代作用以及巨晶的形成而导致的钻石破坏。 其他地方金伯利岩采样的 SCLM 最深处广泛的交代作用表明，Koidu 并不代表一个孤立的案例，并且可以使用橄榄石异晶来限制对钻石破坏的交代作用的程度。