Archean volcanic studies in the Timmins-Kirkland Lake-Noranda region of Ontario and Quebec
Authors: Goodwin A M 
Published: October 2014

Archean volcanic rocks have been systematically studied and sampled under stratigraphic control along 50 suitably-spaced section lines in the 6000 sq mi Timmins-Kirkland Lake-Noranda region of southwestern Abitibi Subprovince in Superior Province of the Canadian
Shield. One thousand and seventy-six volcanic units, mainly lava flows but including some pyroclastic units, were carefully chip-sampled. Each sample was chemically analyzed for 13 major and 13 minor elements leading to normative classification by series and class according to the IrvineBaragar
system.
The region comprises seven geographic areas. Together with adjoining terrain the rocks have been divided into 12 stratigraphic groups of which 9 are volcanic. The resulting lithologic and chemical data provide weighted mean compositions in terms of chemical components and volcanic class and series
by section, geographic area, stratigraphic group and region. These results, which are presented in tabular form, constitute the main contributions of this study.
The volcanic rocks are arranged in mafic to felsic sequences or rhythms, each forming an individual volcanic pile or volcano. Certain lower mafic horizons may form a substratum common to several adjoining volcanoes. Individual piles feature the following three-part construction: l) predominant
tholeiitic basalt flows in lower stratigraphic horizons, 2) predominant calc-alkaline andesitic flows and fragmentals in middle horizons and 3) intermediate to felsic volcanic rocks at the top. A repetition of this rhythmical arrangement in time and space has resulted in a complicated lensoid
disposition of numerous partly coalescing and overlapping volcanic piles as illustrated in a series of regional lithologic and chemical distribution maps. For these reasons and in the absence of intervolcano marker horizons, precise stratigraphic correlations are difficult if not impossible to make
at this stage. However the data do provide a basis for tentative regional correlations.
Pre-Timiskaming stratigraphic correlations are based on general relationships to the Blake River Group, a large diversified volcanic pile that occupies the north-central and eastern parts of the region. The following mainly pre-Blake River volcanic groups, within the expanded region as specified
above, are recognized: Redstone, Deloro, Tisdale, Godfrey, Munro, Malartic and Skead. Highway No. 11 basalts overlie Timiskarning sedimentary and volcanic rocks. The Blake River Group comprises the four following conformable subgroups in ascending, eaststepping succession: Bowman Mg-tholeiites,
Garrison Fe-tholeiites, Misema calc-alkaline volcanic rocks and Noranda mixed tholeiite-calc-alkaline volcanic rocks. Maximum felsic volcanic concentration in the region occurs in the Noranda Subgroup. An additional major felsic concentration forms the upper part of the Godfrey pile 20 mi west of
Timmins. Both Noranda and Godfrey felsic concentrations lie in volcanic subsidence structures.
Principal mineral deposits in the region are located in or near felsic volcanic concentrations including trachytic rocks situated at Noranda, Kirkland Lake and Timmins, respectively. Although possibly related to gross igneous differentiation processes in general, the localization of individual ore
deposits may reflect undisclosed processes of metal . mobilization from host rocks to favourable lithologic, stratigraphic and structural sites under appropriate thermotectonic stimulations.
The remarkable profusion of independent to semi-dependent volcanic piles in such a comparatively small region points to the original presence of numerous close-spaced possible fissurecontrolled vents tapping subjacent high level magma chambers themselves fed by widespread common mantle-derived
igneous material. The compositional tholeiite to calc-alkaline transitions probably reflect changing oxygen fugacity levels in response to periodic hydrous introductions as a function of stratigraphic height in growing volcanic piles. the exact nature of the controls, whether related to seawater
introduction, plate motion or other mechanism, remains speculative. Felsic volcanic development, also a function of stratigraphic height, may have been under similar controls with the added possibility of contamination by sialic crust. The main development of high potash or trachytic volcanic rocks
is clearly related to the narrow linear late-stage Timiskaming graben or semigraben. Further detailed studies are required to determine petrogenetic and tectonic controls in development of these and other similar Archean volcanic assemblages.