Geology; alteration and mineralization on the Hank property, northwestern British Columbia: A near-surface, low-sulfidation epithermal system

摘要

Hydrothermal alteration on the Hank property is hosted by andesitic to basaltic volcaniclastic breccias, flows and sills of the Upper Triassic Stuhini Group; Lower Jurassic sedimentary rocks; and, a hypabyssal, Middle Jurassic potassium-feldspar megacrystic porphyry which intrudes the stratified rocks. Alteration forms two sub-parallel, northeast-trending zones which are capped by broad tabular zones at higher elevations. The lower alteration zone (LAZ) is characterized by intense illite-dominant alteration. The pit area of the Upper alteration zone (UAZ) is semi-conformable to stratigraphy. The pit area of the UAZ is within volcaniclastic breccias with footwall and hangingwall defined by flows or sills. Alteration is characterized by illite/smectite which grades into illite/smectite + kaolinite-dominant alteration near the top of the zone. Above the UAZ, alteration comprises kaolinite-dominant alteration containing minor natroalunite within the volcanic and overlying sedimentary sequences. The transition from illite/smectite to kaolinite-dominant alteration is marked by a zone of intense, multiphase silicification, which is characteristic of a near-surface, low-sulphidation epithermal environment dominated by illite alteration at depth and illite/smectite and kaolinite alteration at higher elevations.