Area Geology

Geology-Intro

1
2
3
4
5
6

last update: 15 April  2017

Introduction

There are some (older)  interesting papers on the Geology in Chandos Township (now called “The Township of North Kawartha”).  Most of this early interest arose because of the mining and prospecting potential in the area.  There have been successful mines both north and south of Chandos Township, but nothing in the immediate areas was ever found to be economically viable.

from Shaw, p. 2:   geology-of-chandos-twp-r011
“In spite of active prospecting for many years, no economically important deposits have been found in Chandos township.  The earliest prospecting was for iron; a small magnetite showing near the south boundary has been known for over 50 years.  More recently there has been extensive prospecting for radioactive deposits.  Of the several showings that have been trenched, blasted, and drilled during the past 10 years, none has warranted development work.  The geology of the town ship differs in several ways from that of the radioactive mineral belt to the north; proximity to the Bancroft region gives no assurance that radioactive deposits should also be found in Chandos township.  Sporadic sulphide showings that occur in the township are chiefly pyrite.  An old copper prospect exists in lot 32, concession 11, close to the southeast corner of the township.  No other base-metal prospects have been reported.”

Apsley-Gneiss

1
2
3
4
5
6

The Apsley Gneiss

The Apsley Gneiss can be found at Wolfe Hill (shown in this old postcard) on Cty Rd 504 just east of Apsley.   It is an interesting rock formation that shows how the rock was at one point deformed and metamorphosed under great heat and pressure during the Grenville Orogeny.

wofe-hill-apsley-gneiss

Here are some pictures of the actual gneiss where it outcrops on Cty Rd 504.

East  end of outcrop-

apsley-gneiss-north-end-sept-23-2016

middle portion-

apsley-gneiss-south-end-sept-23-2016

West end of outcrop-

apsley-gneiss-middle-sept-23-2016

Some scientific background on this outcrop is given here.

This paper is difficult to read without a strong geological foundation, being even more dense than the gneiss itself; however some of the general description is informative.

Loon-Lake-Pluton

1
2
3
4
5
6

The Loon Lake Pluton

Chandos Lake, prior to 1937,  was called Loon Lake, and much of South Bay is actually sitting on the Loon Lake Pluton.

A pluton is basically igneous molten rock (magma) that intrudes through the earth’s crust, but doesn’t quite get to the earth’s surface before it solidifies.  Think of an underground volcano.   This pluton is younger rock than the Canadian Shield, because it intruded after the shield was formed.  The Loon Lake Pluton’s age is estimated at 1065 +/- 13 Ma.(loon-lake-plutone82-086 p.1045).

Over time, because of erosion and glaciation, portions of the pluton become exposed. Below is a suspected exposed portion of the Loon Lake Pluton, on the east side of South Bay, about 100 feet inland.

kids-and-plutonic-rock-img_2948

The geology is quite varied in this region, and has been well studied, as evidenced by the maps in the following papers….The Chandos Township Geology paper is the easier read.

Zebra-Mussels

1
2
3
4
5
6

Zebra Mussels, Calcium, and Geology

There are  2 types of rocks:  igneous and sedimentary.  The igneous rock mostly shows up as calcium poor, silicate rich  granite, but there are other forms that are richer in calcium, and less silicate.  The Loon lake Pluton, is mostly granitic with little calcium.  However, the entire area is underlain with marbles and other calcium rich  materials. The low level of calcium in the  Loon Lake Pluton may be a  moderating factor in the inability of Zebra mussels to have gained a foothold in Chandos Lake.  Calcium enters the lake through leachate runoff mainly from the catchment area soils, and from the weathering of area rocks; as well, there is an atmospheric source component.

Recently these molluscs have been found in Wollaston Lake. (see:  zebra mussels in Wollaston Lake)    The calcium levels in Wollaston are in the order of 28 mg/L, where as in  Chandos the level is around 21 mg/L. Part of the geology influencing Wollaston Lake is  metasedimentary marble (marble being a metamorphosed limestone, which is high in calcium).

Other factors, besides calcium levels, also influence the ability of Zebra Mussels to become established, such as magnesium, pH, and lake environment (littoral zone, rocks, depth, etc). So it is difficult to state an absolute calcium threshold for Zebra Mussels; however, few lakes below 25mg/L  have these creatures in the full adult form.

See the map at EDDS Zebra Mussel mapping distribution  for an idea of where Zebra mussels have been found. As of 2016, Zebra veligers have been noted at Catchacoma, Paudash and Jack Lake, but no adults, likely because the calcium levels are insufficient for them to advance to maturation.

The level of calcium in Chandos hopefully is just low enough to withstand an invasion, but one doesn’t want it too low, as the calcium carbonates act as a buffer towards acidification from acid rain.  We seem to be right on the edge of having them or not, but given the experience of similar lakes, zebra mussels may still be in our future.

An intriguing fact is that the calcium levels in the Canadian Shield lakes have been in decline over the last several years.  Fortunately, the levels in Chandos are sufficiently high to support various other organisms such as water fleas, snails, and crayfish, which have a fairly low threshold of about 1.5mg/L.  click here: calcium-in-ontarios-inland-lakes-information-sheet , and here: calcium-decline-threat-dr-norman-yan

It is interesting to see how much calcium concentrations differ from lake to lake. See: calcium-2008-12

The-Gut

1
2
3
4
5
6

The Gut Conservation area

The Gut is a waterfall/gorge on the Crowe River, just down the Lasswade Road.  The fissure is about 230 metres long, and over 30 metres high. It is always worth a visit, both for reasons of natural beauty and for its unique geological features.    See:  Crowe Valley Conservation Authority

Reputedly, the strange rock formations are a basalt lava ridge.

https://upload.wikimedia.org/wikipedia/commons/d/d1/Precambrian_basalt_lava_ridge_at_%27The_Gut%27%2C_Apsley%2C_Ontario%2C_Canada.JPG

Photo by Dan Delong  see: the Gut, Apsley Crowe River 

 

 Photos by GRA 2016