The majority of the property covers a NW-SE trending metamorphosed volcanosedimentary package of rocks. The Ecstall Belt represents a mid-Devonian volcanic arc that likely developed in a similar setting to the Finlayson Lake District in the Yukon Territory. The geologic history of the property began with mid-Devonian volcanism and syn-volcanic intrusive activity with subsequent sedimentation. This was followed by several phases of intrusive activity and deformation ranging in age from Jurassic to Eocene.
The stratified rocks of the belt can be divided into four principal units: metavolcanics rocks, metasedimentary rocks, quartzite and layered gneiss. The metavolcanics unit consists of mafic and intermediate composition metavolcanics rocks, interlayered with lesser felsic metavolcanics and metasedimentary rocks.
Metavolcanic rocks are intruded by two large, elongate, mid-Devonian plutons called the Big Falls tonalite. The metavolcanics package and its coeval subvolcanic stocks areoverlain by a regionally extensive package of metasedimentary rocks, consisting of a lower metapelitic unit and an upper quartzite unit. These strata are overlain in turnalong the eastern margin of the Ecstall belt by a mafic gneiss. The protolith for this black and white banded gneiss is interpreted as a mafic volcanic package of lateDevonian age.
The metavolcanics unit is heterogeneous. Biotite schist, hornblende-biotite schist and semi-schist comprise 70% of the unit. Interlayered with these lithologies are lenses of pyrite-quartz-sericite schist up to 100 metres thick, as well as amphibolite, quartzite, metasiltstone and calcareous muscovite-biotite schist layers. These smaller lenses may extend along strike for several kilometres. Mafic metavolcanics rocks are preserved as strongly deformed pillow lavas and fragmental basalts, and as intensely foliated mafic schists or amphibolites. Subtle fragmental textures are preserved in some amphibolite outcrops. The lithologic heterogeneity observed in the unit suggests a highly dynamic depositional environment. Discontinuous carbonate lenses appear to be primary and are indicative of a subaqueous environment.
Felsic volcanics within the belt are the primary host to mineralization. They occur as heterogenous units composed of pyritic quartz-sericite schist interlayered with 10-20 meter thick bands of muscovite-bearing quartzite and hornblende-biotite schist. Quartz-muscovite schist is a medium to coarse- grained rock with significant sulphides, containingon average 5% to 15% pyrite. These rocks also locally display relict clastic or fragmental volcanic textures. Primary compositional layering, on a 1 to 10 centimetre scale, is defined by alternating quartz and phyllosilicate layers. Pyrite seams or layers, up to 4 millimetres thick, are concordant with compositional layering and characterize the lithology. Pyritic quartz-sericite schists are interpreted as metamorphosed felsic volcanic flows, tuf fs and fragmental rocks associated with subaqueous extrusion.
The volcanic succession is overlain regionally by a metasiltstone unit of medium to dark grey to black metapelite to metasiltstone to metaquartzite that is locally pyritic. The black metapelite unit is overlain regionally by an extensive unit of quartzite (metasandstone). The quartzite unit consists predominantly of muscovite-bearing quartzite, but also includes minor units of metasiltsone.
At least four plutonic events post-date the middle to upper Devonian stratigraphic succession. An extensive suite of small, weakly deformed diorite stocks are scatteredthroughout the central Ecstall belt. One stock has yielded an Early Mississippian age, which may indicate the age for all these plugs. In addition to Paleozoic intrusions, two elongate plutonic bodies of Early Jurassic age, the Johnston Lake and the Foch Lake tonalites, intrude the eastern part of the belt. The two bounding plutons, the mid-Cretaceous Ecstall on the west and the Paleocene Quottoon on the east, have associated dikes, sills and small stocks which cut the Ecstall belt rocks.
The stratigraphic sequence has been isoclinally folded. Strata are exposed as a mirror-image sequence along the two margins of the belt. The two plutons of Big Falls tonalite are likely repetitions of the same subvolcanic pluton duplicated by folding.
Rocks of the central Ecstall belt are highly deformed and characterized by north-striking, steeply dipping to vertical foliation defined by near-parallel compositional layering and cleavage.
Two metamorphic episodes have been documented; a peak regional prograde metamorphic event (M1) and a much later regional retrograde metamorphic event (M2). Peak metamorphic grades vary from lower amphibolite facies in the south-west part of the belt to granulite facies in the northeast part of the belt. In the central part of the Ecstall Belt, biotite, muscovite, garnet and kyanite are consistent with upper amphibolite facies metamorphism.