Timing and origin of gold mineralization in the Neoproterozoic Xixano Complex, Mozambique Belt, northeastern Mozambique: Case study of the Nanlia and Makorongo prospects

The metallogeny of gold in northeastern Mozambique is still debated, with the main point of contention being the timing of mineralization with respect to regional tectonism, metamorphism, and magmatism. In this study, we applied Re–Os sulfide geochronology to constrain the age of gold mineralization in the Nanlia and Makorongo prospects hosted by the Xixano Complex, in the southern part of the Mozambique Belt. In addition, chemical analyses of host rocks and sulfides complement the discussion on the genesis of mineralization. Single-mineral Re–Os model ages of pyrite and pyrrhotite in quartz veins constrain the occurrence of gold mineralization in the Nanlia and Makorongo prospects between ca. 580 and ca. 560 Ma. This mineralization age interval postdated the timing of peak metamorphism of the host rocks established at ca. 631–607 Ma and is contemporaneous with the metamorphism of basement rocks between ca. 607 and ca. 564 Ma, during the thrusting of tectonic nappes in the last stage of the Pan-African orogeny. In addition, the strike of the veins in the Nanlia and Makorongo prospects is parallel to the local orientation of the thrust fault that separated the overlying rocks from the basement rocks and the dominant S1 foliation of the host rocks. These geochronological and structural data indicate a close relationship between auriferous veins in the study area and the Pan-African thrust fault associated with the emplacement of the tectonic nappes. We propose a metamorphic model for the gold mineralization in the Nanlia and Makorongo prospects, in which the mineralizing fluids were sourced mainly from dehydration of basement rocks, as a result of prograde metamorphism triggered by the juxtaposition of the Neoproterozoic tectonic nappes, including the Xixano Complex, during the last stage of the Pan-African orogeny. The mineralizing fluids ascended through the Pan-African thrust faults and structures to the overlying rocks, where the gold was deposited along the S1 foliation.