The thesis map area is located in northeastern Ontario in and west of the Adams Mine site. The Adams Mine produces iron ore and is situated 15 km southeast of the town of Kirkland Lake. Kirkland Lake is the largest population centre in the Kirkland Lake-Larder Lake gold camp. The Adams Mine lies south of this camp.
The thesis map area is underlain by volcanics (most of which are komatiitic), clastic, chemical and pelitic sediments and various intrusives (peridotite sills, layered peridotite-gabbro and gabbro sills, discordant gabbro bodies, alkali-rich dykes and diabase dykes. The syenitic Lebel Stock forms the northern boundary of the map area.
The map area lies entirely within the Larder Lake Group which forms the lower part of the second major volcanic cycle (cycle II) in the Archean aged Abitibi greenstone belt. The Kinojevis and Blake River Groups overlie the Larder Lake Group north of Kirkland Lake and are also part of cycle II. The Skead Group constitutes the upper most part of cycle I. The top of this group marks the southern boundary of the map area.
The fold axis of the Lebel Syncline passes through the northern half of the map area. This fold is isoclinal and has no plunge. The fold axis and the stratigraphy are broadly conformable to the shape of the Lebel Stock. Tight folds with north-south trending axial surface traces and a drag fold occur on the south limb of the Lebel Syncline.
The Lebel Syncline and these second-order folds are believed to pre-date Intrusion of the Lebel Stock. The stock may have modified the trend of the Lebel Syncline fold axis so that it and the strata parallel the stock's shape.
Five faults with unknown but apparently little displacement were recognized. Faulting is not prominent in the map area.
The northern half of the map area has been metamorphosed to the hornblende hornfels facies. This occurred during contact metamorphism following intrusion of the Lebel Stock. Greenschist facies mineralogy is present in the southern half of the map area and developed during an earlier regional metamorphic event.
There are eight volcanic sequences on the south limb of the Lebel Syncline. Seven of these are komatiitic. There are three komatiitic sequences on the north limb. Komatiitic sequences are characterized by volcanic flows which show decreases in MgO contents stratigraphically upwards. Komatiites occur at the base of each sequence and are overlain by one or more of high MgO komatiitic basalt, high MgO komatiitic andesite, low MgO komatiitic basalt, low MgO komatiitic andesite, low komatiitic dacite, high A12O3 komatiitic basalt, andesite and dacite and high Fe2O3, Α12Ο3 komatiitic basalt.
. Most low MgO komatiitic basalts and andesites on the south limb of the Lebel Syncline have anomously high Cr (>1000 ppm) and Ni (>200 ppm) contents when compared to similar lithologies in other Archean terranes. The high Cr abundances are linked to high chromite contents.
Sequences with Cr and Ni-rich volcanics do not contain high A12O3 komatiitic volcanics; the latter have low Cr (approximately 400 ppm) and Ni (approximately 80 ppm) contents. High Fe2O3, Α12Ο3 komatiitic basalt occurs in sequences with high A12O3 komatiitic basalts. High Α120β and high Fe203, Al203 komatiitic basalts are not found in other Archean terranes. Cr and Ni-rich komatiitic volcanics are found in Destor Township in Quebec (within the Abitibi greenstone belt). They are not otherwise found.
Sequence 1 basalts are regarded as tholeiitic or calc-alkalic. There are no ultramafic or high MgO flows in this sequence and lithological variation with stratigraphic height is not observed.
The high Cr and Ni contents in the komatiitic basalts and andesites are explained by rapid cooling in a magma chamber. This process stops or reduces olivine and chromite crystallization in the magma as it reaches a MgO content of 12 % to 15 %. The residual magma is thus enriched in Cr and Ni. The production of high komatiitic volcanics can also be explained by rapid cooling in a magma chamber. This process lowers the temperature of plagioclase crystallization resulting in A12O3 enrichment in the magma.
Many of the sedimentary rocks in the map area are deposits from submarine debris flows and turbidity currents. The flow mechanism is not known for massive sandstones. The presence of conglomerates (debris flow deposits) suggests a proximal depositional environment, using a submarine fan model. The source area is comprised of sedimentary, volcanic and plutonic lithologies.
Peridotite sills are believed to syn-volcanic with komatiitic volcanism. Peridotite-gabbro and gabbro sills are likely syn-volcanic with tholeiitic volcanism now preserved in the Kinojevis Group north of Kirkland Lake. The discordant gabbro Intrusions are believed to be syn- volcanic with calc-alkalic volcanism now preserved in the Blake River Group north of Kirkland Lake. Lateral equivalents to both groups may have once overlain the Larder Lake Group but have since been eroded. This is consistent with the fact that higher metamorphic grades prevail south of the Larder Lake Break.
The sills and discordant gabbros were emplaced prior to regional metamorphism. The Lebel Stock, syenite, biotite lamphrophyre, feldspar porphyry and diabase dykes were emplaced following deformation and greenschist metamorphism.
The alkali-rich intrusions are likely contemporaneous with Archean trachytic volcanism now preserved in the Timiskaming Group. / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/29264 |
| Date | January 1986 |
| Creators | McRoberts, Gordon David |
| Contributors | Crocket, James H., Geology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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