Structural Evolution and Helium Potential
of the Rukwa Rift, Tanzania

Abstract

The Rukwa Rift is regarded as example of active continental rifting with complex
structure patterns associated with significant helium occurrences. Gas composition
data in the Rukwa Rift Basin indicate high radiogenic helium content ~ 10% which is
far above the economic threshold of 0.3%. Unlocking helium resources is critical as
the current global society faces a significant shortage of helium supply.
An integrated study of geological, geochemical and structural evidence such as 2-D
seismic data, Digital Elevation Model (DEM) and wells data from the Rukwa Rift
Basin has been used to define the evolution and timing of structural patterns within
two structural domains: Domains A (north) and B (south). These structural domains
are separated by the Saza Shear Zone (SSZ) which controls the oblique divergent
effects of the Rukwa Rift. We demonstrate how these structures control the
distribution of potential helium traps and reservoirs quality, average porosity and
permeability ranges (c. 26-30% and 272.7- 660.6 mD) respectively. Most of sites with
high helium concentrations occur along deep-rooted fault systems which suggest the
possibility of such faults being the main migration conduits of helium from the
Precambrian basement rocks.
The Rukwa Rift has high heat flow ~64-99 mW/m2 and a high probability of helium
charge from the surrounding crustal rocks in the region with flux capability of ∽22 x
10-6 mol 4He/m2 yr. We argue that it is not the extreme thermal conditions which
matters for the release of radiogenic helium as long as they are above closure
temperature for common helium-retentive minerals. Generally, these findings
provide both qualitative and quantitative insight into assessment of helium resource
potential.