Mineral chemistry characteristic and enlightenment to diamond prospecting of spinelite in kimberlite from Shizhuang area Henan Province

Kimberlite in Shizhuang area of southern Henan Province lies in the south of North China plate and in the north of Luanchuan-Minggang deep-large fault zone.Indicative minerals of diamond, such as spinel, are found in Kimberley rocks.The indicative minerals of spinel and other diamonds have been obtained from kimberlite in Shizhuang area by artificial heavy sand identification.The chemical composition of spinel was studied by means of electron microprobe analysis in this paper.The results show that the spinel group minerals in kimberlite in Shizhuang area are mainly composed of magnesia chromite(MgCr₂O₄)-chromite(FeCr₂O₄)-magnesia spinel(MgAl₂O₄)-spinel(FeAl₂O₄), in which magnesia chromite(Fe, Mg)Cr₂O₄ is dominant.The content of Cr₂O₃ and Al₂O₃ in chromite varies widely, MgO content is high(5.57%~15.8%), TiO₂ content is low, and there exists a chromite with low titanium, rich magnesium and high aluminum content(S5 type).Among the cations of chromite, Mg²⁺ > Fe²⁺, while Cr³⁺ and Al³⁺, Mg²⁺ and Fe²⁺ have experienced extensive substitution.A preliminary analysis shows that chromite in kimberlite in Shizhuang area is mantle xenocryst, while in situ mantle is peridotite.The chemical characteristics of spinel minerals show that the kimberlite in Shizhuang area has the capability of carrying diamond, which is of great significance for the exploration of kimberlite type diamond deposits.