Keno-Lightning is located within Neoproterozoic to late Paleozoic slope-to-basin facies strata of the epicratonic Selwyn Basin. Selwyn Basin strata are characterized by off-shelf deep water clastic rocks (shale, chert, basinal limestone), and are bound by the Mackenzie Platform, to the northeast and truncated by the Tintina fault to the southwest.
Northeast directed compression during the Jurassic and early Cretaceous resulted in thrust faulting, the development of open to tight similar folds within relatively incompetent Selwyn Basin strata (compared to the bounding carbonate platforms), and greenschist facies metamorphism. Widespread granitic magmatism during the early to mid-Cretaceous led to the formation of at least five main intrusive suites between 112 and 90 Ma and a younger suite at 65 Ma. Strike-slip faulting along the Tintina Fault zone during the late Cretaceous and early Tertiary displaced the western margin of the Selwyn Basin at least 450 km west into what is now Alaska.
The Keno-Lightning project is underlain by highly deformed rocks of Mississippian Keno Hill Quartzite and dominantly clastic metasedimentary rocks of the Devono-Mississippian Earn Group, with lesser Mississippian felsic volcanic schist, all of which are intruded by Triassic dolerites and Cretaceous aplite dykes and sills. Deformation of the host rocks, which is characterized by intense foliation, appears to be related to displacement along the Tombstone thrust fault, located northeast of the property. North- to northeast- and northwest-trending faults are evident throughout the area.
Locally, stratigraphy within the Keno mining camp has been divided into three units; the Upper Schist, Central Quartzite and Lower Schist. The Upper Schist comprises graphitic schist and phyllite, thin bedded quartzite, quartz-mica schist, calcareous schist and minor limestone, and quartz-sericite metavolcanic schist. The Central Quartzite contains thick and thin-bedded quartzite, massive quartzite, minor graphitic phyllite, schist and calcareous schist. This unit is up to 700m in thickness and hosts many of the principal silver deposits of the camp. It is most prevalent at Homestake, with narrower bands underlying the Silver Basin, Caribou, Faith and Duncan areas. The Lower Schist includes graphitic schist and phyllite, argillite, thin-bedded quartzite, calcareous schist, slate and sericite schist and two bands of thick and thin-bedded quartzite with lesser phyllite and graphitic schist. Stratigraphy principally strikes east-west and dips 20° to 30° south. Metamorphosed diorite and gabbro sills and lenses are conformable with stratigraphy.
Two stages of vein mineralization have been recognized in the district. The first stage deposited quartz, pyrite and some arsenopyrite with trace gold and some sulphosalts in the vein faults. A second stage deposited siderite, galena, sphalerite, pyrite, freibergite and pyrargyrite, more typical in the central part of the Keno mining camp
Silver mineralization in the Keno district is representative of clastic metasediment hosted silver-lead-zinc enriched polymetallic vein deposits, examples of which include the Coeur d’Alene district of Idaho and the Freiberg district of Germany. Typically, mineralization is expressed as quartz-carbonate (siderite±ankerite, calcite)-sulfide (sphalerite, galena, pyrite, tetrahedrite-tennantite, chalcopyrite, arsenopyrite, stibnite) veins, with silver minerals most commonly hosted as inclusions in galena. Wall-rock alteration, which generally consists of sericitization, silicification and pyritization, is typically of limited extent (< 1 m). Regional faults, fault sets and fractures are an important ore control, although veins are typically associated with second order structures and postdate deformation and metamorphism. Significant deposits are restricted to competent lithologies.
Within the Keno Hill district, silver mineralization is hosted by two sets of vein faults; longitudinal veins, which strike between 035° and 080° and transverse veins, which strike between 000° and 035°. Both sets dip between 50° and 80° to the southwest. Longitudinal veins were the main producers of silver in the Keno camp, and have significant strike extent, whereas transverse veins represent dilational zones between en-echelon longitudinal faults and are generally limited in strike but locally contain very high grades.
Gold mineralization is hosted within quartz-arsenopyrite veins in quartzite and schist and is interpreted to be associated with the emplacement of Cretaceous-age Tombstone suite granitoid intrusions. This style of mineralization is characteristic of intrusion related gold systems (IRGS) and is found elsewhere in the Tintina gold belt.