Genesis of silver mineralization associated with the Anvil Batholith, Mt Mye Trend, Yukon, Canada

English Abstract:

The Keg Property is located 20km north of the mining town of Faro in south-central Yukon. It lies along the Mount Mye trend, a structural trend predominantly contained within the Cretaceous Anvil Batholith. The Hammer Zone, an epithermal style Ag±Zn-Pb system, is one of the most interesting prospects within the Mount Mye trend; assays of the Hammer Zone have produced silver grades in the thousands of grams per ton. In this study, the mineralization and alteration at the Hammer Zone are evaluated to determine the relationship between deposit and batholith, and to develop a deposit model.

The Hammer Zone prospect comprises three discrete ten to fifteen centimeter, sulfide bearing quartz-carbonate veins emplaced in a granodiorite host rock. The veins run almost N-S and are associated with sericitic, propylitic and argillic alteration. They were emplaced late in the development of the batholith and crosscut many late features such as pegmatites.

Transmitted and reflected light microscopy work, supported by analysis of mineral chemistry using the electron probe micro-analyzer, has yielded a paragenesis. There are two main sulfide events in the Hammer zone veins; (1) a carbonate hosted pyrrhotite stage associated with silver deposition, and (2) a quartz hosted pyrite stage. These are preceded by barren brecciation phases and post-dated by a chlorite- and hematite-forming event. Silver is present in stage 1 principally in sulfide form, although some oxidized forms exist. The silver-bearing mineral is freibergite, although there are also small amounts of Ag-bearing galena and other silver-bearing phases. Stable isotope work has been completed on the carbonate phases, and yielded δ¹³C_PDB values of -9.0‰ to 2.8‰, and δ¹⁸O_SMOW values of -2‰ to 9‰. Stable isotope work is currently ongoing for the vein quartz. Fluid inclusion analysis will constrain the temperature and salinity of the stage (1) carbonate and stage (2) quartz. These temperatures can be used to further understand the δ¹⁸O_SMOW values of the mineralizing fluids and to assess the importance of boiling versus mixing in silver precipitation.