Marmora Mine, Ontario Canada

  • Type: Man Made Structure
  • Diameter: 840 X 365 metres and 215 metres deep
  • Location: South of Algonquin Park, Ontario, Canada N 44° 28.6’ W 77° 39.5’
  • Marmora pit-mine is a pluton* in the southwestern Grenville Province

*Pluton: A large igneous intrusion formed at great depth in the crust. Any body of igneous rock that solidified below the earth’s surface.

Illustrated left to right, MARMORA MINE – Mt MORIAH – LAKE SKOOTAMATTA – may be part of a approximately 1085 Ma suite of syenite intrusions (plutons) that stretch from Madoc in Ontario to Mount Laurier in Quebec*** (Easton, personal communication). – Google image.
Marmora pit-mine from GOZooM.
Marmora Mine 840 X 365 metres and 215 metres deep (1700 feet X 1200 feet and 700 feet deep).
Over time, underground streams and rainfall have slowly filled two thirds of the mine with water. So much so that it is now officially classified as a lake.

Marmoraton Mine

In 1948, a government airborne survey employing the brand new science of geophysics discovered a vast ore body of iron that lay beneath 120 feet of solid limestone overburden near the town of Marmora. in 1953, stripping began to remove 70 million tons of waste rock and expose one of southern Ontario’s richest iron deposits. Before it closed in 1979, the Marmoraton mine had produced 1.3 million tons of iron ore for the Bethlehem steel mills in New York. Today, the water-filled pit covers 75 acres and reaches depths of more than 600 feet, qualifying it as an artificial lake!

Elzevir Terrane Syenites

The alkalic rocks of the Elzevir Terrane typically occur as large (10 to 40 km2), round plutonic bodies. A northeast trending group of syenites, the Gawley Creek Syenite in the south, followed by the Mount Moriah and Skootamatta Syenites are situated to the east and northeast of the Blue Mountain Syenite.

The Gawley Creek, Mount Moriah, Skootamatta and Mount St. Patrick Syenites may be part of a approximately 1085 Ma suite of syenite intrusions that stretch from Madoc in Ontario to Mount Laurier in Quebec*** (Easton, personal communication). The equivalent plutons have recently been studied in detail by Corriveau (personal communication). These bodies are younger than the peak of Grenville metamorphism, having distinct pluton shapes and little affected by Grenville tectonism (Easton, personal communication) unlike the syenites of the Bancroft Terrane. These bodies are therefore attractive targets since they are relatively uniform, massive, coarse grained homogeneous bodies.

**SYENITE: is a plutonic rock defined as an igneous, intrusive rock composed of at least 65% alkali feldspar, and less than 5% quartz. Plagioclase and mafic minerals make up the remaining mineralogy. A leucocratic syenite can contain up to 30% mafic minerals, and a mesocratic syenite will contain more than 30% mafic minerals (e.g., mesocratic nepheline syenite of the Callander Bay Complex). The term alkali syenite is often used to describe a rock where alkali feldspars constitute 90% or more of the rock, and plagioclase compositions are Ano-40, where plagioclase is present. Syenites such as the Otto Stock, Lebel Stock, McElroy Stock of the Superior Province and the Gawley Creek, Mount Moriah, Skootamatta, Burns Lake and Mount St. Patrick Syenites of the Grenville Province containing neither quartz nor nepheline is considered saturated. Oversaturated rocks contain modal quartz, incompatible with the presence of nepheline and therefore representing less attractive targets since AhOa content is limited. Undersaturated rocks contain modal nepheline, and these bodies, where they contain less than 10% mafic minerals, represent more prospective A12O3 and CaO+NazO+KzO targets (Dolan et al, 1991).

***The SYENITE intrusions that stretch from Madoc, Ontario to Mount Laurier, Quebec include: Skootamatta Lake, Mount Moriah and the Sainte-Véronique structure.
Area Highlights

This conservation reserve, located in ecological Site District 5E-11, is the most dramatic landscape feature in south central Hasting County, rising hundreds of feet above the surrounding land. Mount Moriah is also an intact natural ecosystem. The soils are thin, supporting juniper and blueberries. There are vast areas of open rock barrens, extensive granite barrens, steep bedrock slopes, small cliffs and outcrops. Where forests exist, they are often scrubby Red Oak and Aspen. There are some larger stands of trembling aspen, white pine, sugar maple and white spruce. This diverse topography has trapped water in many shallow ponds, bogs and flooded areas.

Prior to 2008, all younger granitoid intrusions (1065 to 1090 million-years-old) within the Central Metasedimentary Belt were considered to be part of the ultrapotassic Kensington–Skootamatta suite (see references in Easton 2008), even though some of these intrusions consist mainly of granite rather than diorite to monzonite. A renewed look at the data on these intrusions by Easton (2008) indicates that there are actually 2 types of late felsic intrusions within the Central Metasedimentary Belt. The slightly older, alkalic plutons of the classic Kensington–Skootamatta suite and the slightly younger, anorogenic granites of the Catchacoma intrusive suite. The former have limited uranium potential, whereas the later have potential for Rössing-style granite-hosted uranium mineralization.

Plutons of the ultrapotassic Kensington–Skootamatta suite are alkalic, shoshonitic to ultrapotassic, and generally have low to moderate silica contents (45 to 60 weight %). They are characterized by TiO2 >0.8 and P2O5 >0.21 (Corriveau 1990). They are typically associated with intense aeromagnetic highs, and generally have low to moderate eU and eTh contents on detailed airborne gamma ray spectrometric maps of the area. Monzonite to syenite plutons of the Kensington–Skootamatta suite in Ontario have U/Pb zircon age determinations ranging from 1077 to 1090 Ma, but most ages cluster around 1088 Ma (Easton et al, 2009).

Horizontal Paleozoic limestone beds lie on top of vertically inclined meso-Proterozoic crystalline limestone beds (marbles). This geological feature is called an angular unconformity. Two complete cycles of “decay and restoration of land upon the globe” has occurred here (located 6 km north of the pit-mine). Marc Forget

Three ancient ocean basins occur here, spanning 1.5+ billion years of earth’s history.

A Paleozoic basin (limestone, shale, sandstone) lies over top of a meso-Proterozoic back-arc basin (volcanics, marbles, wackes, arenites & quartzites and their corresponding conglomerates) lies over top of a late paleo-Proterozoic basin with similar sedimentary rocks as the back-arc and make it very problematic to correlate the strata.

Marmora was once a tropical island surrounded by huge explosive stratovolcanos (a classic island arc), including a forearc and backarc. The backarc, forearc and shelf was tectonically folded and imbricated onto the continental margin to create a Rockies like mountain chain from Labrador to Texas. It eroded and was submersed during the Paleozoic and is now above sea level (for the time being). These rocks have gone through two major orogenies.

Soil Geochemical & Lithogeochemical Survey Of the Harlowe Shear Zone M. Forget, 2012.


Corriveau, L. 1990. Proterozoic subduction and terrane amalgamation in the southwestern Grenville Province, Canada:evidence from ultrapotassic to shoshonitic plutonism; Geology, v.18, p.614-617.

Davidson, A., van Breemen, O., Late Grenvillian granit plutons in the Central metasedimentary belt, grenville Province, southeastern Ontario. Radiogenic age and isotopic studies: report 13, Geological Survey of Canada, 2000.

M.L. Dolan, D.H. Hains and D.R. Ash, High-Alumina Rocks in Ontario: Resources and Process Technology. Mines and Minerals Division, Ministry of Northern Development and Mines, 1991.

Easton, M., Sangster, P., LeBaron, P., Rössing-style (Granite-Hosted) Uranium Mineralization in the Central Metasedimentary Belt of the Grenville Province, 2009.