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

Hydrothermal alteration on the Hank property, northwestern British Columbia, 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 (185±3 Ma) potassiumfeldspar megacrystic porphyry which intrudes the stratified rocks. Alteration on the property forms two sub-parallel northeast trending zones (Upper and Lower alteration zones) which are capped by broad tabular zones at higher elevations (Felsite Hill and Rojo Grande). The lower alteration zone (LAZ) strikes northeasterly and dips steeply to the southeast cutting the stratigraphy on the property and is characterized by intense illite-dominant alteration. The pit area of the Upper alteration zone (UAZ) is semiconformable to stratigraphy, strikes northeast and dips moderately to the southeast. The pit area of the UAZ is hosted within volcaniclastic breccias with footwall and hanging wall 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. This transition from illite/smectite to kaolinite-dominant alteration is marked by a zone of intense, multiphase silicification dipping gently to the south. Alteration mineralogy on the Hank property is characteristic of a near-surface, lowsulphidation epithermal environment dominated by illite alteration at depth and illite/smectite and kaolinite alteration at higher elevations. The overall morphology of these alteration zones suggests that the LAZ is a conduit for hydrothermal fluids which cuts stratigraphy. The UAZ, and the Flats Zone (FZ) are semiconformable to stratigraphy, indicating lateral movement of hydrothermal fluids along a permeable horizon outward from the central conduit. The silicified zone, which lies above the UAZ, may indicate a zone of increased permeability or the presence of a paleo-water table or aquifer. Above the silicified zone, tabular zones of kaolinite-dominant alteration reflect the upper parts of an epithermal environment, derived from acidic, vapour condensate above the paleo-water table. Illite/smectite alteration within the potassium-feldspar megacrystic porphyry suggests that it intruded during the final stages of hydrothermal activity and may be the causative intrusion. Alteration and mineralization on the Hank property represents one extreme of a continuum of mineralization styles throughout the Iskut River area including porphyry, vein and exhalative examples, all co-temporal with Middle Jurassic intrusions.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat