Niou Gold Deposit Structural Framework, Goren Belt, West African Craton

Abstract

Niou gold deposit is open-pit mine located in the southwestern portion of Goren segment within Boromo greenstone belt, one of Burkina Faso Birimian greenstone belts that hosts world-class gold deposits. The Goren segment, Borom-Goren belt northeastern part, is one of Burkina Faso birimian formations. This area was affected by multiple deformations and hydrothermal events in Paleoproterozoic. The structural and stratigraphic complexity of the sector requires detailed mapping to constrain the primary controls gold mineralization. Open pit mapping at 1:100 scale, combined with macroscopic logging of drill core representing 6 holes and field mapping, allowed identification of several lithotypes, including: metaandesite, metabasalte and metadiorite, metagabbro dykes, quartz veins with sulfides, chlorite, biotite, quartz carbonate veins. Airborne geophysical imagery interpretation combined with field measurements reveals two sub-meridional (NNW-SSE) shear zones parallel in deposit southern part, which bend to E-W in the eastern portion, where they accommodate mineralized quartz veins, underlying by penetrative foliations and crenulation cleavage. Structural analysis reveals two main deformation phases: 1) an early phase D 1Ni responsible for penetration foliation S 1Ni dipping to NE or SW, and 2) a shortening event associated with localized shear zones producing crenulation cleavage with NW and SE vergence and NNE-SSW S 2Ni schistosity. Dominant hydrothermal alteration styles include carbonation, chloritization, silicification and sulfidation underlying biotite. These combined geological, structural and textural observations indicate that gold deposition at Niou was controlled by the interplay between progressive deformation, lithological contrasts, and multiple episodes of hydrothermal fluid flow, like many other deposits described in the Birimian of West Africa.