TOODOGGONE REGIONAL GEOLOGY

Regional Geology

The Toodoggone District lies within the eastern margin of the Intermontane Tectonic Belt, which consists of four unique Terranes. The project area lays within the Stikinia and, in part the Quesnellia Terranes. The Stikinia and Quesnellia Terranes consist mainly of island-arc volcanic, plutonic and sedimentary rocks of late Triassic to early Jurassic age with a Lower Permian aged basement represented by the Asitka Group (Diakow and Metcalfe, 1997). To the east, older metamorphosed Precambrian and younger strata (clastic and chemical sedimentary rocks) of the Cassiar Terrane (Omineca Belt) are separated from the Intermontane Belt by a regional system of trans-current faults (Diakow, Panteleyev and Schroeter, 1993).

The Toodoggone District consists of a series of northwest trending volcanic belts some 90 kilometres long and 40 kilometres wide. The stratigraphy is fairly monoclinal with generally northwest striking, shallowly west-dipping upright stratigraphy and therefore youngs to the west. The large-scale northwest trending faults generally parallel the long axis of the district and illustrate the basic fabric of the accreting terrains and its internal evolution. The northwest trend is common to the stratigraphy, plutonism and major mineralizing events and therefore implies major crustal activity along this trend. Overlying younger stratigraphic intervals, such as the Sustut Group of conglomerates and sediments, covered the earlier mineralized and altered Jurassic volcanics and plutons, therefore protecting them from deeper erosion and glaciation. This resulted in the preservation of complete mineralized and altered sequences ranging from the causative copper-gold porphyry systems up through the undeformed stratigraphy, which hosts the upwardly evolving low-to-high sulphidation epithermal systems with their attendant clayrich alteration caps still intact.
 
Stratigraphy 

Lithologies in the Toodoggone area are Permian to Cretaceous in age, comprised from oldest to youngest as follows: Asitka Group, Stuhini Group, Toodoggone Formation and Sustut Group (Diakow and Metcalfe, 1997). Lower Permian aged rocks of the Asitka Group consist of andesite, dacite and rhyolite volcanic rocks with locally prominent sections of inter-bedded marine sedimentary rocks consisting of limestone and chert at the top of the section. These rocks may reflect a submergent island arc sequence.
 
Upper Triassic rocks of Stuhini Group (also referred to as Takla Group) unconformably overlie the Asitka Group. Stuhini Group rocks are more widespread and characterized by clinopyroxene-bearing basalt, andesite, and associated epiclastic rocks, and locally appear similar to Paleozoic rocks. These rocks may reflect an emergent submarine to sub-aerial island arc sequence. Locally, Lower Jurassic Toodoggone Formation (Hazelton Group) volcanic fragmental rocks of dacite-andesite composition lie in non-erosional, gently dipping unconformity with Stuhini Group rocks. Minor basalt lava flows and rare rhyolite flows and breccia occur in the Toodoggone Formation (Diakow, personal communication, 2004). The Upper Cretaceous Sustut Group consists of conglomerates, sandstones and siltstones with minor felsic tuff and occurs in unconformable contact with Takla (Stuhini) and Hazelton Group rocks. 

Intrusive Rocks 

The early-middle Jurassic Black Lake Intrusive suite of calc-alkaline plutons is apparently coeval with the Toodoggone Formation volcanic rocks and with the development of an elongated volcano-tectonic depression that is richly endowed with numerous precious and base metal occurrences (Diakow and Metcalfe, 1997). The composite Black Lake Intrusive suite is generally medium grained and grades from granodiorite to quartz monzonite. This intrusive suite includes the Black Lake Pluton (granodiorite to quartz monzonite), Jock Creek Pluton (quartz monzonite, diorite), Giegerich and Duncan Lake plutons (hornblende-biotite granodiorite, monzonite, quartz monzonite, quartz diorite) and the Sovereign pluton (quartz-hornblende-biotitegranodiorite to tonalite). Dykes and dyke swarms of quartz monzonite are locally proximal to and associated with copper-gold mineralization as at the Brenda occurrence and with epithermal or transitional precious metal vein occurrences as at Northwest Breccia. These dyke sets usually follow the northwest trending structural breaks that trace several of the mineralizing events within the Toodoggone Camp. Dykes and sills of trachyandesite to latite and minor basalt cut previous lithologies. Late Triassic Alaskatype ultramafic intrusions are regionally mapped east of Kemess North with other possible occurrences southwest of the Mex prospect (Cascadero Copper) and on the Pil prospect to the northwest. Mapping by Stealth and the BCGS in 2004 outlined a new plutonic body of mainly quartz monzonite. Its upper contact dips shallowly westward beneath the overlying Triassic to Jurassic stratigraphy and extends from the Findlay River area in the southeast part of Nub Mountain, north to the north end of the Kevin claims. Exposures are visible all along the northeast trending section of Jock Creek, hence the local nomenclature of the Jock Creek Pluton, which is part of the Black Lake Plutonic suite. 

Structure 

A system of high-angle normal and possibly contraction faults that trend from 120o to 150 o occur locally with secondary faults trending from 20o to 40 o and 60 o to 80 o. These structures may impart primary control of high-level co-magmatic plutons and deposition of the coeval Toodoggone Formation rocks.
 
Regional-scale northwest trending structures include the Saunders, Wrich, Black and Pil faults that cut the Toodoggone District and occur over distances of more than 80 kilometres. Parallel faults also display dip-slip movement, locally placing Stuhini Group in contact with Toodoggone Formation rocks as at Kemess North (Diakow, 1997) and Asitka Group rocks adjacent to intrusive plutons.
 
North-easterly trending high-angle faults cut and displace northwest trending structures, tilting and rotating monoclinal strata (Diakow, 1986). The presence of high-level epithermal mineralization at Goat, Wrich Hill and the Electrum prospects (Cascadero Copper) at substantially lower elevations to the north, may suggest a post-mineral, north side down displacement along a northeast trending fault system in the Finlay River valley (Blann, 2001). North trending, right-lateral strike-slip faults are prominent along the eastern margin of the Giegerich Pluton and are Cretaceous and early Tertiary in age. These faults may cut Toodoggone aged and older rocks.

last updated: Jul 31, 2008