This is the most amazing conglomerate IÕve ever seen.  This is the Timiskaming Conglomerate of Ontario, Canada.  ItÕs a polymict conglomerate, which means it consists of pebbles of many different lithologies (rock types).  Apart from the striking colors and shapes, this polymict conglomerate is especially spectacular for the presence of pebbles of rare rock types.  The sample shown below includes pebbles of the rare ultramafic extrusive igneous rock komatiite.  The komatiite pebbles are easily recognizable based on their spinifex texture (long, needle-shaped crystals).  ThereÕs also has a small clast of banded iron formation.


The Timiskaming Conglomerate is a fluvial to alluvial fan deposit.  Its clasts are a wonderful variety of Archean rock types, including intrusive igneous rocks (diorites, anorthosites), extrusive igneous rocks (basalts, komatiites, dacites, rhyolites), sedimentary rocks (graywackes, siltstones, cherts), and other clasts such as vein quartz and even pyrite pebbles (Gray & Hutchinson, 2001).


The komatiite pebbles shown in the photos below are consistent with eastern OntarioÕs Pyke Hill Komatiite (2.703 to 2.715 billion years).


Unit & Age: Timiskaming Conglomerate, upper Neoarchean, <2.674 billion years.


Locality: Kirkland Lake, northeastern Timiskaming District, eastern Ontario, southeastern Canada.


Polymict conglomerate (above & below; 6.0 cm across) having pebbles of komatiite and banded iron formation (see labels below) from the Timiskaming Conglomerate (Neoarchean, <2.674 billion years) at Kirkland Lake, Ontario, Canada.



Polymict conglomerate (5.7 cm across) having komatiite pebble (lower right) from the Timiskaming Conglomerate (Neoarchean, <2.674 billion years) at Kirkland Lake, Ontario, Canada.



Reference Cited:


Gray, M.D. & R.W. Hutchinson.  2001.  New evidence for multiple periods of gold emplacement in the Porcupine Mining District, Timmins area, Ontario, Canada.  Economic Geology 96: 453-475.




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