Geology

Geology of the Porcupine Area
Map indication geology of Ontario

Geology of Ontario – Click to enlarge

The name Porcupine came from an island in Porcupine Lake, which resembled a porcupine from a distance. Porcupine Lake was the main hub of activity after the initial gold discovery in 1909 and is located east of the Timmins downtown core between the outlying villages of Porcupine and South Porcupine. The Porcupine gold camp is characterized by an extremely diverse bedrock geology, whose rocks span an age range of about 3 billion years.

The Timmins District encompasses a large portion of the Canadian Shield which in itself is subdivided into geological provinces. The Superior Province, which is the oldest, largest and which consists of rocks of Achaean age (i.e. greater than 2.5 billion years old) dominates the local geological terrain.

In general, the Superior Province consists of east-west trending alternating belts of predominantly volcanic, sedimentary and gneissic rocks, representing the accreted remains of ancient continents and ocean basins. The Superior Province is accordingly further subdivided into a number of subprovinces, depicted on the figure below and described according to their lithologies, structures, and metamorphic grade character.

Geology of Abitibi

Geology of Abitibi – click to enlarge

The Abitibi/Wawa Subprovince rocks underlie most of the Porcupine area. These are lithologically diverse metavolcanic rocks with a wide variety of intrusive suites and lessor amounts of chemical and clastic metasedimentary rocks. Individual greenstone belts within the subprovinces are intruded, deformed and truncated by intervening felsic batholiths. The Quetico/Opatica Subprovince rocks outcrop between Abitibi/Wawa subprovince and Phanerozoic rocks of the Moose River Basin.

Felsic Volcanic Breccia

Felsic Volcanic Breccia

The rocks are predominantly clastic sediments and metamorphosed schists and gneisses of sedimentary origin. Such rocks comprise the greystone belts of the province. The majority of Ontario’s metallic mineral wealth (e.g. gold, copper, zinc, etc.) is obtained from the rocks of the Abitibi/Wawa subprovince of the Superior Province, as are various industrial minerals and building stone.

In the northern portion of the Porcupine area, Paleozoic and Mesozoic sediments of the Hudson Bay and Moose River basins comprise the bedrock geology, punctuated by Proterozoic rocks of the Sutton Inlier. Paleozoic rocks of the Moose River Basin unconformably overlie Achaean rocks of the Superior structural province. The contact between Phanerozoic and Achaean rocks is faulted producing an Arctic watershed draining into Hudson Bay as rapids, cataracts and waterfalls from the higher southern Achaean bedrock surface to the Paleozoic lowlands.

Erosion throughout geologic time has resulted in peneplanation of the Archean rocks, hence the topography throughout the area is subdued. Glaciation during the Pleistocene has resulted in widespread drift cover of unconsolidated Quaternary sediments. Extensive till sheets, glaciolaustrine clays and glaciofluvial deposits blanket much of the bedrock. Many outcrops are glacially striated, permitting reconstruction of the latest glacial history. The bedrock surface continues to rebound since Pleistocene times and moderate earth tremors with shallow epicentres and low magnitudes are occasionally felt throughout the Porcupine area.

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