A Brief Overview of the Geology of Southwestern NewfoundlandHome
The bedrock that underlies southwestern Newfoundland, from North Branch south to Port aux Basques and then east to Rose Blanche, is not dominated by either one of the 3 fundamental rock types (igneous, metamorphic and sedimentary). Rather the underlying geology draws its character from among them.The oldest rocks in southwestern Newfoundland are those that make up parts of the highest mountains in the area. These are ophilitic rocks, pieces of the ancient ocean floor, which were pushed up during mountain building processes, and which are roughly 500 million years old (Upper Cambrian). These pieces of ancient ocean floor rock were embedded within the mountains, which for the most part are made of granite and roughly 488 million years old (Lower Ordovician).
The rocks in the immediate Port aux Basques area are metamorphic rocks such as gneiss (pronounced "nice"), schist and amphibolite. These rocks haven't been dated to tell their age, however they are thought to be older than the rocks which make up the mountains. Minerals such as garnet, staurolite and kyanite are common in these rocks. Some nice kyanite crystals can be found in the rocks near the tourist chalet at Port aux Basques. The rocks between Port aux Basques and Rose Blanche are much like the rocks in the Port aux Basques area, however there are some areas which also have quite a bit of granite. In fact, some of the finest granite in Newfoundland is found at an abandoned quarry near Petites, which is near Rose Blanche. The granite from this quarry was used to build the main courthouse in St. John's, and pieces of the quarried granite can still be seen on the beach near Petites.
The rocks which underlie the Codroy Valley are the youngest in the area. They are Carboniferous in age, or roughly 325 million years old. For the most part, these rocks are sandstones, siltstones and shales. Small seams of coal can be found in some areas and there is even a small area where the concentration of uranium is high. Limestone is also quite common in some areas of the Codroy Valley, some of which is rich enough to be used for agricultural purposes.
There are 2 major geological faults in southwestern Newfoundland. The Cape Ray Fault is about 1 km wide and crosses the Trans-Canada Highway (TCH) between the entrance to John T Cheeseman Provincial Park and Barachois Brook. This fault extends for about 100kms (60 miles) and eventually crosses the Burgeo Highway.
The largest and most important fault in the area is the Long Range Fault (Cabot Fault) which runs from the bridge crossing the TCH at McDougall's Brook to the northeast coast of Newfoundland at the Baie Verte Peninsula. This fault also runs through Nova Scotia and New Brunswick. The Long Range Fault once marked the boundary between North America and Europe before the two continents separated about 200 million years ago. Neither one of these faults is active.
Many of the oldest rocks in southwestern Newfoundland have elevated gold levels. Hence, they are good source rocks for gold deposits and gold is found in above average crustal abundances in many parts of the region. Galena deposits, large and small, are particularly rich in gold. One large galena deposit in the Cape Ray Fault has been estimated to contain 150,000 ounces of gold.
Links:
Geological Survey of Newfoundland and Labrador