ANATOMY OF HIGHLY-METAMORPHOSED ALTERATION HALOS, IZOK LAKE, NUNAVUT TERRITORY, CANADA

Exploration for volcanic-hosted massive sulfide deposits is challenging in metamorphosed and deformed terrains especially as the shape and mineralogy of hydrothermal alteration halos enveloping mineralization may be cryptic. This pilot study utilizes a two-tiered approach that aims to determine potential indicator mineral associations and mineral compositions characteristic of the metamorphosed equivalents of hydrothermally altered rocks related to massive sulfide deposits.

Initially, pressure-temperature-composition (P-T-X) pseudosection diagrams are calculated using average compositions of altered volcanic rocks from unmetamorphosed massive sulfide deposits. Pseudosections allow key mineral assemblages and mineral compositions to be determined for a range of pressures and temperatures relevant to metamorphic terrains in which exploration for these deposits is common. In addition, calculated T-X diagrams determine the change in mineral assemblages and compositions with particular bulk compositional vectors.

The second phase of the study compares modeled to observed mineral assemblages and compositions identified from the amphibolite-facies grade metamorphosed and intensely deformed Izok Lake Zn-Cu-Pb-Ag deposit, Nunavut. The compositions of key lithologies covering the range of apparent volcanic facies and metamorphosed alteration compositions within the deformed alteration halo have been compared to unmetamorphosed equivalents. Detailed mineral assemblage and textural characterization of the recrystallized volcanic rocks, coupled with mineral and bulk rock compositional data allows reverse modeling of the assemblage and P-T history of the Izok rocks and therefore direct comparison to the forward models developed in the first stage of the project.

This integrated methodology is expected to contribute to our ability to unravel the complex mineral assemblage zoning in metamorphosed deposits, allowing: 1) a given zoning pattern to be related to models for massive sulfide formation, and 2) vectors to ore in deposits from complexly deformed terrains to be effectively and efficiently established. In addition, this method could be applied to greenfield exploration through targeting of specific detrital indicator minerals in glaciated or other heavily eroded environments.