Click here to skip to the content

Overview

Minerals and Mining

Colour image of globe showing changing position of continents 475 million years agoOrdovician Period rocks are found in south, central and northern New Brunswick. The sedimentary rocks occur primarily in a band through northeast New Brunswick in the Kedgwick – Grand Falls area, in pockets between Bathurst and Woodstock, between Moncton and Fredericton and in the Saint John area. Igneous rocks, both extrusive (volcanic) and intrusive (plutonic) are found between Bathurst and Woodstock.

In the Late Cambrian and Early Ordovician 500 to 443 million years ago, sediments were eroded from the margin of the Gondwanan and Laurentian continents and the microcontinents of Avalonia and Ganderia. Mud and sand were deposited on the continental shelf and on the deep ocean floor. Sedimentary rocks formed from these sediments are now exposed in the Miramichi highlands between Bathurst and Woodstock. Black shales from the deeper ocean are found in Saint John and contain graptolite fossils, the remains of animals that floated as colonies in the sea. Trilobites and brachiopods lived on the shallow seabed.

Colour graphic of a hot spot forming within an ocean plateDuring the Early to Late Ordovician a rift basin opened in the continental crust behind the Popelogan volcanic island arc. As the continental crust pulled apart, volcanic eruptions produced lava and ash. Basaltic lavas emerged from a “hot spot” beneath the ocean floor. It is in these deeper ocean environments where many of New Brunswick’s mineral resources were formed. Undersea volcanoes spewed sulphide minerals rich in metals onto the seafloor. Referred to as VMS (volcanogenic massive sulphide) deposits they are rich in copper, zinc and lead minerals.

As the Iapetus Ocean continued to close, bringing the Brookville (Ganderia) and Caledonia (Avalon) terranes closer to ancient North America, more volcanic islands formed above the subduction zones. While the underlying crust of the Iapetus Ocean was destroyed, the Popelogan volcanic arc crumpled against the continental crust. Remnants of the Popelogan Arc are exposed at Eel River and near the Popelogan River.

 

Colour graphic showing three stages of crust subduction

Near Belledune rocks of the Fournier Group include an ‘ophiolite’ sequence, where part of the ocean crust was obducted, rather than subducted. Instead of the ocean crust sinking back into the mantle, a piece of denser crust was pushed up and over the lighter crust.

Near Belledune rocks of the Fournier Group include an ‘ophiolite’ sequence, where part of the ocean crust was obducted, rather than subducted. Instead of the ocean crust sinking back into the mantle, a piece denser crust was pushed up and over the lighter crust. The obducted group of rocks is exposed at the surface. Ophiolites are part of the ocean crust and consist mostly of the rock types peridotite, gabbro, and sills, dikes and pillow basalt. The Fournier Group of rocks includes the Devereaux Formation made up of the rock types gabbro, basalt, plagiogranite, and diabase that forms ‘sheeted dyke complexes’. These are common structures in the ocean crust. A dike is where the igneous rock is injected into the crust from the underlying molten source. Each injection represents a step in seafloor spreading. They eventually pile up like sheets standing side-by-side.

 

Colour graphic showing layers of the earth's crust and mantle on the ocean floor

Ophiolites are part of the ocean crust and consist mostly of the rocks types peridotite, gabbro, diabase sills, dikes and pillow basalt.

By the Late Ordovician, the Iapetus Ocean was nearly closed and the terranes were beginning to collide with ancient North America (Laurentia). Limestones were deposited in the ocean off the coast of the Popelogan Volcanic Island Arc after it attached to Laurentia. These limestones are seen at Grand Falls in the gorge formed by the Saint John River.