Volcanogenic massive sulphide targeting in the Noranda Camp: Using a 3D implicit modelling platform for deeper exploration through the integration of structural and geochemical vectors.

Abstract

The Noranda camp is a world-class region for volcanogenic massive sulphide (VMS) deposits hosted in the 2704-2695 Ma volcanic Blake River assemblage, Abitibi greenstone belt. Of the ~20 VMS deposits (past production ~225 Mt ore) in the Noranda camp, the most recent discovery of the West Ansil deposit in 2005 was attributed to the integration of multidisciplinary data (geological mapping, drilling data, geochemical data and geophysical surveys), in a 3D modelling platform (GoCAD). Although there has been limited success since the discovery of West Ansil (depth from the surface: 270 m), continued exploration has shown some potential at greater depth, such as the showing at 1300 m depth in the Ribago area evident by drill logs and core samples. VMS deposits in the study area occur less than 750 m below the surface, with the exception of Ansil, which occurs at a depth of 1260 m below the surface. This research focuses on the potential for new deeper discoveries of VMS mineralization along known synvolcanic structures to help guide camp-scale exploration. A new implicit (interpolant-based) 3D geological model was built from an updated 2017 drill hole database combined with primary lithological interpretation from the 2005 3D GoCAD geological model in Seequent’s Leapfrog® Geo®. The 3D geological model is coupled with a 3D representation of geochemical alteration signatures, mass-balance calculations, and normative minerals. Compared to existing models, the new model has a depth of 2.5 km compared to the previous 1.5 km and provides geochemical vectors that consider structural trends resulting from synvolcanic faults, which are the inferred pathways for hydrothermal fluids. Structural trends guide the 3D interpolation of alteration models and extend to greater depths, highlighting metal-bearing hydrothermal fluid pathways. The proposed VMS targets were developed using 3D block model integration of the 3D geological model and all the developed 3D numeric models of alteration. Using queries, the block model highlights the proximal alteration zones associated with VMS deposits at the intersection of known synvolcanic faults and exhalite horizons in the area. In addition, the targets were developed considering the possibility of multiple stacked sulphide lenses deeper in the stratigraphy and the effect of zone refining was evaluated. The developed queries yielded two potential targets in the Noranda South camp and seven potential targets in the Noranda Main camp. The Main camp targets are associated with the Beecham, Lewis, and Corbet exhalite along synvolcanic faults associated with high values of alteration and the gains/losses of major elements. Despite the sparse structural data, alterationmodelling results of the South camp targets show VMS-style alteration extending southwest of the Beauchastel fault, with high values of normative alteration index and gains in Fe and Mg concentrated in the Powell andesite of the Powell block. Most of the potential targets occur at a depth range between 400-800 m, with the exception of three targets (MCT-3, MCT5, and MCT7) that occur below 1,000 m depth. In addition, most of the drilling in the area did not extend deeper than the developed targets, as in the case of one potential target associated with Beecham exhalite. The target shows substantial alteration near the Beecham breccia horizon, but none of the drill holes in the area intersects the horizon. The new 3D model and exploration targets presented here highlight the potential for VMS discoveries at greater depth if specific key structural trends are integrated with 3D alteration models. The potential targets are deeper than existing drill holes in the area (historical and new). The new 3D implicit geological model has improved on Noranda's previous 3D explicit geological model, mainly as the exhalite horizons have been updated using new contact points derived from recent and historical drill holes. The new 3D model can be dynamically updated as exploration progresses and new data becomes available. In addition, structural trends control the flow of rising hydrothermal fluids and are a key input to highlight deeper prospects.