Mount Moriah, Ontario Canada
- Type: Syenite/Pluton
- Diameter: ~5.5 Km
- Location: South of Algonquin Park, Ontario, Canada N 44° 42.3’ W 77° 26.1’
- Mount Moriah 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.
MOUNT MORIAH SYENITE**
The Mount Moriah Syenite lies mainly in Grimsthorpe Township, although the south margin of the body extends into Elzevir Township. The body is accessible by dirt road from Cooper, 17 km north from Madoc. The body covers an area of approximately 25 km2 .
The Mount Moriah Syenite is a circular intrusion, situated near the south end of the Elzevir Terrane, in the Grenville Province. This body is similar to the Gawley Creek syenite (Hewitt 1968) but again, details of the geology are not provided. The rocks are pink coarse-grained syenite (Hewitt 1968). The general geology is outlined by Brown and Thivierge (1979).
The Mount Moriah Syenite consists of two phases. An earlier augite hornblende syenite comprises the bulk of the body, covering a subcircular area of approximately 20 km2 . A later phase occurs at the south end of the body as an arcuate unit, separated from the main mass by a narrow sliver of volcanic rocks. The main mass consists of potassic feldspar (perthitic orthoclase and microperthitic microcline), lesser plagioclase (albite), augite, and 5 to 10% hornblende and biotite (Easton, personal communication).
The rock is coarse grained, with large irregularly shaped feldspars, surrounding the other minerals. Grain boundaries are typically sutured. Hornblende, biotiteand minor magnetite occur as primary grains, and as alteration products of augite. Accessory minerals include apatite, zircon, allanite, magnetite, epidote and calcite. Quartz is locally present in very small amounts (less than 2%) and occurs interstitially as very fine grains. Some of the apatite and zircon grains form inclusions in the feldspars, calcite occurs along fractures and some of the feldspar is epidotized.
The smaller mass to the south has a lower mafic content, with a colour index of only five. This syenite is medium grained and consists essentially of perthitic microcline, with approximately lO% albite plagioclase, minor biotite and quartz. The microcline occurs as large, irregularly shaped grains. Grain boundaries of all the minerals are variably sutured except for the plagioclase which occurs as euhedral to subhedral grains. Accessory minerals include zircon, apatite, allanite, magnetite and hematite. As within the main mass, zircon and apatite occur as inclusions within the feldspars. Magnetite and hematite occur interstitially and along grain boundaries. Quartz monzonite and granite occur as pods and lenses with the southern unit and as narrow (usually l to 2 m wide) dikes throughout the Mount Moriah Syenite. Microcline, orthoclase, albite, quartz (up to 15% in the granite) and biotite in varying proportions, make up the mineralogy of these units (Dolan et al, 1991).
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).
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).
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