A large part of southern Nova Scotia is made up of granites (South Mountain Bath

Question

A large part of southern Nova Scotia is made up of granites (South Mountain Batholith) (375-380 million years old) exposed at surface. What plate tectonic and gcological conditions were necessary to produce this large volume of granite? How could these rocks become exposed at surface? In the study area given in Maps 1, 2 and 3 there are two types of uranium deposits present. What are the types of uranium deposits and how did they form? Could there be a genetic relationship between these types of deposits? If so explain the relationship. (Give references to support your answer) A company has hired you to undertake an environmental radioactivity assessment on the study area near Windsor, Nova Scotia (see maps 1, 2, 3 and 4). The company wants to build a large resort in the study area. The company has hired you assess the radioactive environmental risks in the area. What are the risks? If the resort has to depend on drilled wells to provide water, what might be some of the problems they might encounter?(Hint see map 4) Given that you must locate a site in this area, what procedures would you undertake to assess the risks and recommend a location? What are the remedial steps that you would recommend at the resort during construction or after it is built? (Give references where applicable)

Explanation / Answer

Plate tectonics and geological condition of large granite rocks of scotia

In Nova Scotia it tends to form knolls and high ground areas characterize by a hummocky, boulder-strewn outside; thin, acid soils; and great areas of exposed bedrock. Water can go through the body of granite only along the joints (fractures), which may be more than a few meters apart. Most rainfall is therefore held on the uneven surface in frequent unified bogs, low lakes and streams. Granite is found throughout mainland Nova Scotia and Cape Breton in plutons of a variety of sizes and represents about 20–25 per cent of the bedrock crossways the region. The largest pluton is the South Mountain Batholith, which is the leading characteristic in the landscape of southwestern Nova Scotia. It extend in an arc from Yarmouth to Halifax and outcrop over an area of 10 000 km.

A hot magma which forms at a depth of 20–40 km in the earth’s crust may rise also by forcing a path along lines of weakness or by contravention off and incorporate overlying rocks. There are no signs of strain within the sedimentary rocks nearby the South Mountain Batholiths, which might point to forced passage, but several signs analytic of ascent by amalgamation of blocks from the overlying strata (called country rock).

The contact with the nearby Meguma country rock is usually steep, and in several places, blocks of sediment, some with clear sedimentary banding, are included into the granite mass. These blocks, or xenoliths, were slowly assimilated by the hot magma and can be establish in a variety of degrees of alteration in several locality near the limits of the granite; for instance, at Portuguese Cove.

Types of uranium deposits

Divided herein into two types:

(1) carbon-pyrite quartz sandstone type hosted by the Horton Bluff Formation and

(2) Hematite arkosic sandstone type hosted by the Cheverie Formation.

1) Carbon-Pyrite Quartz Sandstone Type

This deposit type is hosted by the “glass sand unit” of Bell (1929) which occurs near the top of the Horton Bluff Formation (map 3). This unit is the Hurd Creek Member of the Horton Bluff Formation in the terminology of Martel and Gibling (1996). The unit is dominated by coarse- to fine-grained quartz-rich sandstone. The porosity of the sandstone ranges from 9–15% with permeability between 5 and 250 mD (millidarcys). The most common bedforms are low-angle for-sets and shallow trough cross-stratification. Multilateral, multistoried channel sequences form sandstone sheets up to 30 m thick. The bases of the individual channels commonly consist of coarse pebbly quartz sandstone that has abundant plant detritus as lag material. Though, where it does occur it exists as K-feldspar that has been intensely kaolinized. Thin interbeds of grey cross-laminated siltstone and shale occur within the sandstone bodies and the sand bodies are underlain and over-lain by lacustrine grey shale and siltstone. The environment of deposition for the unit is interpreted to be in distributary channels in a lacustrine delta setting (Martel and Gibling 1996). Ryan et al. (2005) suggested that the quartz-rich nature of the sandstone is the result of a monomineralic source area rather than a unique environment of deposition. These authors postulated that the “glass sand unit” is made up of detritus derived from the upper levels of the pre-Carboniferous paleosaprolite in which the intensity of weathering resulted in only kaolinite and quartz remaining.

2) Hematite Arkosic Sandstone Type

Uranium occurrences in the Cheverie Formation are restricted to the lower sequence of thick arkosic sandstone, silt-stone, and pebbly conglomerate. The arkosic sandstone is best described as granite wash, with feldspar representing up to 25% of the rock. The sandstone occurs as multilateral, multistoried channel sand sheet bodies up to 20 m thick. The coarse-grained sandstone generally exhibits only crude fining-upward cycles and the sandstone to siltstone/shale ratio is approximately 8 to 1 in the Three Mile Plains area. The most common bed forms in the sandstone are large scale (up to 10 m wide) trough cross-beds. The sandstone is variably micaceous with flakes of both biotite and muscovite. Carbonaceous plant material is present but much less abundant than in the sandstone of older Horton Group strata. The overbank siltstone and mudrock are generally red or green, although minor grey beds occur. The green and grey fine-grained beds are commonly mottled with red. Rip-up clasts of the fine-grained overbank strata, up to 5 cm in diameter, are commonly incorporated into the arkosic sandstone. The lower sandstone-dominated portion of the Cheverie Formation has been interpreted as a lower alluvial fan-braided stream deposit

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