Talk
Critical Minerals Geology and Exploration

Unravelling the Effects of Deformation on Clastic-Dominated Zn-Pb deposits: A Case Study of the Howard’s Pass XY deposits

Online pre-recorded
(Student abstract)

Author(s)

D.K. Kamal (Presenting)
University of British Columbia
K.A.H. Hickey
University of British Columbia
M.A. Reynolds
Northwest Territories Geological Survey, GNWT

Clastic-dominated (CD) sulfide deposits are a major source of critical metals (Zn, In, Ge, etc.) that are needed for the global transition to a green energy economy. These deposits typically form in extensional basins located near the edge of intact continental lithosphere and are prone to crustal shortening in later orogenic events. As a consequence, CD deposits commonly undergo ductile deformation and metamorphism as the host basins are incorporated into developing fold-and-thrust mountain belts. Basin structures may reactivate and concentrate deformation into different structural domains. Such deformation can have significant effects on the spatial distribution of ore and its associated sulfide mineralogy and gangue.

The CD Zn-Pb deposits of the Howard’s Pass district represent one of the world’s largest undeveloped massive sulfide districts. Sulfide deposition occurred during the Silurian and the deposits were deformed during the Cretaceous Cordilleran Orogeny. The Zn-Pb deposits have been incorporated into a series of upright to steeply inclined WNW striking, gently plunging folds in a 40 km corridor along the border of the Yukon and the Northwest Territories. Owing to the structural complexity of deposits, multiple models have been proposed for their evolution. A recent model proposes that the deposits are hosted in a regional shear zone where transposition of bedding and thrust faulting has resulted in previously interpreted stratigraphic boundaries being tectonic in origin.

This study aims to test this hypothesis and is focused on the XY group of deposits of the Howard’s Pass district. Lithostratigraphic and structural mapping indicate one main phase of folding, F1, is responsible for the gross geometry of the deposits. The XY cluster is located on the southern limb of a macroscopic syncline. A regionally developed, steeply NE dipping, cleavage, S1, is axial planar to F1 folds. The S1 fabric manifests as a slaty cleavage comprising pervasive dissolution seams. The mineralization at XY is hosted in the Duo Lake Formation. In mineralized strata, S1 forms sulfide-rich dissolution seams with local remobilization of sphalerite, galena, and pyrite. The seams are axial planar to microfolds and transition to a stylolitic dissolution foliation in intervening layers of non-mineralized carbonaceous mudstone. A later kink fabric, S2, crenulates S0 and S1 at the microscopic and mesoscopic scale and shows a sinistral sense of asymmetry. A series of WNW and NNE striking faults exhibit normal dip-slip movement and overprint F1 folds. Lithofacies adjacent to these faults preserve no evidence that they were active at the time of sedimentation or controlled the upwelling of metalliferous fluids that formed the XY deposits.

Results from this study indicate that the geometry of the XY deposits is primarily controlled by folding and contacts between units are dominantly stratigraphic in origin. S1 and S2 are the only foliations observed. No shear zone fabrics were identified and there is no evidence for strong transposition of bedding. Ongoing work will integrate modern geochemical and microanalytical techniques to evaluate the scales at which sulfides are remobilized and assess the impacts of remobilization on the economic viability of orebodies in deformed CD deposits.