Abstract |
- 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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