Rio Tinto Fer et Titane Inc. (RTFT), which is wholly owned by Rio Tinto, operates an open cast titanium dioxide mine at Lac Tio near Havre-Saint-Pierre and, at its metallurgical complex in Sorel-Tracy.
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Summary:
There are six ilmenite deposits in the Lac Allard area. The largest and most important of these is the Lac Tio deposit, which is a magmatic Iron-Titanium-Oxide deposit. The deposits in the Lac Allard region contain ilmenites with similar compositions.
The Allard Lake ilmenite deposits lie in the northeastern part of one of the large Precambrian anorthosite masses and comprise a series of metamorphic and igneous rocks that belong to the Grenville Province. The ore bodies consist of a series of narrow dikes, irregular lenses, or sill-like bodies that appear to be genetically related to the anorthosite rocks in which they occur.
Rocks of the "Grenville Series" are represented by quartzites, quartz-biotite gneiss, quartz-hornblende gneiss, garnetiferous gneiss, and small patches o: amphibolite and garnetiferous graphite schist. These rocks occur abundantly along the Romaine River between the First East branch and the Second East branch. Numerous outcrops are also found on the shores of Forget lake and in the adjoining area to the east.
The most important lithological unit in the Lac Allard region is anorthosite and related rocks.
Anorthosite is the major rock type in the vicinity of Lac Allard. As a rule, it is massive, coarse-grained and contains 95 percent or more plagioclase. In fresh exposure, it varies in color from pale gray to pink to somewhat resinous green when it contains more than 5 percent ferromagnesian minerals. In weathered outcrops, the anorthosite is usually gray to chalky white. The equigranular varieties of anorthosite have grains sizes that range from 3 to 6 mm and is characterized by sporadic coarse plagioclase phenocrysts 2 to 35 cm long. The phenocrysts are similar in composition to plagioclase of the enclosing matrix (Hargraves, 1962).
In thin section, the texture of the anorthosite varies from hypidiomorphic to allotriomorphic granular, and the plagioclase grains (An 40-52) range from 3mm to 12mn in size. Approximately half the 25 thin sections examined by Hargraves (1962) showed evidence of cataclasis as indicated by scattered relics of larger crystals exhibiting undulatory extinctions, bent twin lamellae and fractured margins. The finer-grained material surrounding the deformed fragments and locally constituting the entire rock, is anhedral and displays intricately sutured grain bound aries, suggesting recrystallization of crushed material.
The ilmenite rich anorthosite (oxide rich norite of Hargraves, 1962) is medium-grained seed slightly foliated or gneissic. Tie essential constituents of the rock, in paragenetic order, are plagioclase, pyroxene, apatite and oxide. Despite variation in the relative proportion of these constituents, the mafic fraction rarely constitutes less than 50 percent by weight of the rock. Sulfide, largely pyrite with minor pyrrhotite are constant accessories, and secondary biotite is sporadically distributed.
The Lac Tio deposit
The Lac Tio deposit is made up of three orebodies, the Main deposit, the Northwest deposit, and the Cliff deposit (Perreault, 2003). The Main deposit is an equant tabular sheet, 1,097 m by 1,036 m with an estimated thickness of 110 m inclined about 10° to the east. The Northwest deposit, separated from the Main deposit by a late normal fault, forms a band of massive ilmenite alternat ing with anorthosite that varies from 7 to 60 m in thickness, inclined gently to the east. The Cliff orebody is roughly ellipti cal in plan, about 380 m by 230 m and 60 m thick (Hammond, 1952).
At the Lac Tio mine, hemo-ilmenite is dense, black, and mostly present as coarse-grained, thick, tabular crystals, about 5 to 20 mm in length (Hammond, 1952; Charlier and others, 2010). Anorthositic ore consists of massive lenses of titaniferous magnetite (Fe:Ti ratio greater than 2:1) that are phaneritic ranging from equigranular to porphyritic to reticulated with coarse-grained subhedral to euhedral magnetite in a mesh of fine-grained anhedral ilmenite with no flow structures. Gabbro ore is oxide-enriched conformable bands in gabbro (Fe:Ti ratio less than 2:1) that are typically more fine-grained with porphyritic or reticulated textures.
At the Lac Tio, hemo-ilmenite is hosted by anorthosite; accessory minerals include aluminous spinel, orthopyroxene, and Ti-phlogopite with minor amounts of sulfide (pyrite, pyrrhotite, chalcopyrite, and millerite) (Charlier and others, 2010).