Orogenic gold mineralization in the structurally-complex Lupa Terrane, South West Tanzania: New insights into regional- to deposit-scale structural controls derived from integrated structural mapping, geophysical analysis and 3D modelling
Tect was approached in late 2018 by Shanta Gold to conduct a thorough review of the structural geology and gold mineralization of New Luika Gold Mine and the surrounding exploration licenses, with the purpose of guiding and focusing brownfields and greenfield exploration efforts.
The Lupa Goldfield and encompassing Paleoproterozoic Lupa Terrane in southwestern Tanzania is known for its high prospectivity. It hosts several gold deposits, ranging from 150 – 4000 kt at 1.5 – 5 g/t Au, and numerous artisanal gold mines. Shanta Gold’s New Luika Mine is currently the largest open and underground mine within the Lupa Goldfield. It comprises at least 10 different deposits, over an area of 18 km2, with a combined resource of 3,645 kt at 4.4 g/t Au (2016). However, despite the conspicuous prospectivity of the region, comparative recent discoveries or extensions to known high-grade (> 4g/t) deposits have been elusive.
The Lupa Terrane predominantly comprises a suite of Archaean granitiods (2.74 Ga) intruded by Palaeoprotrozoic granites and gabbro-diorites (1.96 Ga), that reflect re-working of the southern margin of the Tanzania Craton during protracted deformation of the Ubendian Orogeny (2.1 – 1.88 Ga). Relatively late-tectonic auriferous quartz veins account for economic mineralization (1.88) Ga within narrow, mostly ductile, mylonitic shear zones developed under greenschist facies conditions. From a regional- to deposit-scale, mylonite zones are generally continuous and interconnected, representing an extensive, structurally-controlled fluid conduit system. However, away from known deposits, along these mylonite zones, surface exploration and drilling have historically produced mixed results.
To advance the understanding on the structural controls of mineralization and to increase the success rate of drilling, Tect conducted a regional- to deposit-scale structural analysis that integrated regional aeromagnetic and radiometric surveys, pit and field structural mapping, drillhole data and soil geochemistry data over New Luika Mine and surrounding areas. This resulted in a structural fabric map and its analysis in QGIS, and 3D structural modelling in Leapfrog. Regional- to deposit-scale, fault-fill, auriferous vein-systems and associated mylonite fabrics were structurally and kinematically characterized and delineated. The result is the identification of a 1st-order or regional network of wide, incipient to intensely-strained “shear zone corridors” that act as mineralized fluid conduits across several tens of kilometres. These corridors host well-developed, deposit-scale 2nd – 3rd order mineralized mylonite zone, with grades up to 5 g/t Au. In turn, these contain zones of increased dilation and structural complexity wherein grade is further enhanced to >6g/t Au, thereby comprising distinct ore-shoots.
This structural interpretation and mineralization model has significantly added to the resource at New Luika Gold Mine, which has significantly increased the LOM. Moreover, it has also provided a framework for expanding regional exploration in the Lupa Goldfield and resulted in a high-quality CP report in Shanta’s Singida Prospect, which was completed with Pivot Mining. This re-emphasizes the value of careful structural analysis in these structurally convoluted terranes. Tect remains actively involved in collaboration with Shanta Gold Geoscientists, processing new exploration data, assisting with forward exploration planning and providing guidance on targeting.
(In preparation) Deciphering Paleoproterozoic orogenic gold mineralization in the Lupa Terrane, South West Tanzania: New insights into regional- to deposit-scale structural controls derived from integrated structural mapping, geophysical analysis and 3D modelling of New Luika Gold Mine by Corné Koegelenberg, Jonathan Gloyn-Jones, Ian Basson, Paul Mbuya, Alfred Kulwa, Shineni Ramadhani and Dustan Daud, aimed at the Ore Geology Reviews, or similar.