Preliminary Map 61 describes the geology of the Toodoggone River area (94E) of north central British Columbia. The 1:50 000 scale geology map includes a legend.
The basement to the Early to perhaps Middle Jurassic ‘Toodoggone volcanics’ are the strata of the Permian Asitka Group (?), mainly limestone with minor marble and skarn, and the Late Triassic Takla Group, mainly augite phyric basalt flows and breccias. The Toodoggone volcanics have 8 major units. The lowermost Addoogatcho Creek Formation has 3 divisions: a lower quartz plagioclase porphyry, a middle unit of crystal ash tuff, lapilli tuff and rare agglomerate; and an upper unit of quartz, biotite and hornblende-bearing ash flows. The Moyez Creek volcanics comprise crystal tuffs in thin units with associated sandstone and mudstone; and conglomerate with some granite clasts, greywacke, crystal tuff and epiclastic rocks.
The Lawyers-Metsantan quartzose andesite consists mainly of flows and tuffs. The mafic flow and tuff unit contains pyroxene-biotite-hornblende phyric flows; lapilli, crystal and ash tuff with local sandstone and rare marl layers; porphyritic basalt; and pyroxene phyric basalt flows and tuffs. McClair Creek Formation includes an intrusive dome complex and mainly purple, lavender or grey crowded plagioclase phyric flows. Tuff Peak Formation strata include: flows with sparse orthoclase megacrysts; conglomerate or lahar with sandstone and mudstone interbeds, debris flows and lapilli and crystal tuffs; and biotite-augite-hornblende-plagioclase phyric flows. The Toodoggone crystal ash tuff and flow unit has lower epiclastic red arkosic sandstone, siltstone, conglomerate and slide debris, and an upper unit with mainly plagioclase crystal tuff, lapilli tuff and breccia. The upper ‘Grey Dacite’ unit consists of quartzose plagioclase-bearing ash flows of andesitic and rarely dacitic composition that are locally welded. The youngest strata exposed are Upper Cretaceous rocks of the Tango Formation of the Sustut Group comprise polymictic conglomerate, sandstone, shale, and carbonaceous mudstone.
Intrusive rocks in the area include Lower to Middle Jurassic feldspar and hornblende-feldspar porphyry dikes and plugs, granodiorite to quartz diorite, and quartz monzonite to granodiorite bodies that are partly megacrystic as well as minor syenite. Lower Jurassic dikes, sills and small plugs include pyroxene-plagioclase porphyry, diorite to gabbro, augite-hornblende porphyry, and basalt.
Faults in the area trend mainly northerly and northwesterly. The Jurassic volcanic rocks are within a fault-bounded graben.
Epithermal gold deposits, such as Lawyers and the Baker mine, characterize the Toodoggone camp but there is also potential for gold-bearing copper porphyry deposits.