Graduate Thesis Or Dissertation

 

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  • The Lateral Lake Area is located 30 km northeast of Dryden in Echo and Webb Townships in the District of Kenora in northwestern Ontario. The area has been the focus of molybdenum exploration since 1906. Most exploration and development has been centered on the Pidgeon Prospect in Echo Township. Although, to date, no production has occurred, active exploration is continuing on the prospect. The Lateral Lake Stock is an elongate, diapiric, granodioritic pluton that intrudes a series of mafic metavolcanic and metasedi mentary rocks of the amphibolite grade of regional metamorphism. The emplacement of the stock occurred during the period of regional metamorphism which affected the supracrustal rocks. This period is known as the Kenoran Orogeny in the Superior Province of the Canadian Precambrian Shield, and is dated at 2480 m.y. The con formability of textural and structural features in the stock and the supracrustal rocks suggest that their formation occurred con currently with the intrusion of the stock into the supracrustal rocks. The stock was emplaced at a relatively deep crustal level as inferred by the contact relationships between the pluton and the supracrustal rocks. Recrystallization has affected most of the stock to some extent, although it is best-developed at the margins, and in the western part of the pluton, which is considered to be the deepest, exposed level of the intrusion. A period of potassic metasomatism followed, and partly overlapped, the period of regional metamorphism. The effects of potassium metasomatism are present throughout the stock. However, they are most intense along the eastern contact of the pluton in Echo Township, and in a small area along the southern contact of the stock in Webb Township. Both areas are characterized by microcline-rich pegmatites and sills of aplite, and represent the upper levels or cupolas of the stock. Molybdenite mineralization is directly associated with the zones of intense potassic metasomatism. Most molybdenite was deposited along the selvages of, and in the wall rock adjacent to quartz and quartz-microcline pegmatite veins and dikes. The highest cancentratations of molybdenite occur where these veins intrude sills of aplite, although granodiorite is also a favourable host. Minor amounts of molybdenite were deposited along late chlorite and epidote- bearing fractures, and calcite-bearing fractures. Pyrite is present in subequal amounts as molybdenite. Minor amounts of pyrrhotite, chalcopyrite, bismuthinite, and native bismuth are associated with the more abundant sulphides. Zonation of sulphides is not apparent, although pyrite is more widely distributed than molybdenite. Potassic, phyllic, and propylitic types of hydrothermal alteration are associated with the molybdenite mineralization. They are confined mostly to the wall rock adjacent to the veins, Zonation of alteration mineral assemblages is not well-defined; however, zonation patterns are similar to those encountered in porphyry ore systems. Sulphide and alteration mineralization are almost entirely confined to the Lateral Lake Stock. However, trace amounts of molybdenite, and evidence of potassic alteration are present in the metavolcanic rocks east of the stock, which suggests that a weak hydrothermal system developed above the pluton. In addition to molybdenite mineralization, a complex pegmatite, which contains lithium, cesium, and tantalum is present within the metavolcanic rocks south of the stock in Webb Township. Its relationship to the stock is unknown.
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