Fibrous diamond growth zones can contain abundant high density fluid inclusions (HDFs) and these provide the most direct information on the source and composition of diamond-forming fluids. Four different fluid end-members have been defined; silicic, low-Mg carbonatitic, high-Mg carbonatitic, and saline. Continuous arrays exist between the silicic and low-Mg carbonatitic end-member and between the saline and high-Mg carbonatitic end-member. Different processes have been proposed to explain the two major element compositional arrays, but the origin of and relation between the various fluid end-members is still uncertain. In this study we provide new constraints on the evolution and origin of these diamond-forming fluids by combining noble gas systematics with δ13C, N concentrations, and fluid inclusion compositions.