Keno-Lightning project, Yukon

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SRK News | Issue 57Exploration Geology: Keys to success

Simon Craggs, Senior Structural Geology Consultant


In November 2016, Metallic Minerals Corp. commissioned SRK to conduct a desktop and field structural geology analysis of the Keno-Lightning project. This work aimed to define targets for exploration drilling. It included an initial structural interpretation of airborne geophysical data with the aim of developing a litho-tectonic framework for the region, and was followed up by a short program of mapping to ground  truth -interpreted structures.

The Keno-Lightning project is located in the underexplored eastern portion of the historic Keno Hill silver-lead-zinc mining district, within the Selwyn Basin, Yukon. Silver-lead-zinc mineralisation is preferentially hosted in thick, competent quartzite units within the Mississippian Keno Hill Quartzite, and to a lesser extent, in deformed Triassic greenstone units where they occur within broad packages of relatively ductile schist. Three discrete episodes of deformation have been defined in the Keno Hill area: pre-mineralisation fold and thrust belt development (D1); syn-mineralisation sinistral strike-slip to sinistral-normal oblique-slip brittle fault development (D2); and post-mineralisation, Cordillera-parallel, dextral-normal oblique-slip fault development (D3). Silver-lead-zinc mineralisation in the district is controlled by the complex interplay of fault geometry and orientation, secondary thickening of host rocks as a result of early folding and thrusting (D1), and variations in the mechanical properties of the various lithological units.

Understanding the variation in orientation and geometry of D2 faults is critical for exploration targeting within the Keno Hill district. First-order D2 faults occur as laterally extensive east-northeast-trending structures that may be associated with discrete, narrow (less than 0.2 metre wide) mineralised veins. However, thicker, higher grade silver-lead-zinc veins are typically associated with second- and third-order, northeast to north-northeast-trending, D2 faults that splay off, or link between the more laterally extensive first order faults. Veins associated with the second- and third-order structures can reach thicknesses of over 5 metres, and can carry grades well in excess of 1000 gpt silver.

The initial interpretation of airborne magnetic data identified numerous structurally complex zones, where dense networks of second- and third-order D2 faults were present, and where they intersected first-order faults. This interpretation was compared with historic lithological mapping data to refine the targets based on the presence of coexisting structurally complex zones and favourable lithology.

Metallic Minerals used this interpretation, combined with their own mapping efforts, to drive their exploration drilling and trenching program over the summer of 2017. Preliminary results from the defined targets are promising with numerous boreholes intersecting wide (greater than one metre), high-grade mineralisation in two of the primary targets outlined by SRK.

Simon Craggs: scraggs@srk.com

 

SRK North America