Summary:
The James Bay Niobium Deposit is hosted by the Carbonatite Complex and occurs in the northern portion of the KSZ of the Superior Province. Numerous alkalic and carbonatite intrusions occur along this structure, which extends from the east shore of Lake Superior northeast to James Bay. Rocks in the general area of the Property are characterized by granulite facies rank gneisses and a pervasive north- to northeast-trending fault pattern.
The Carbonatite Complex is overlain by approximately 10 m of overburden and 20 m of Lower Devonian rocks of the Sextant Formation consisting of poorly bedded sandstone, mudstone, siltstone, and loosely cemented conglomerate.
The Carbonatite Complex appears to be a dyke-like body with a long axis striking north. The enclosing gneisses are described as mylonitic or augen gneisses.
The principal niobium-bearing mineral is pyrochlore, but niobium also occurs, to a much lesser extent, in the mineral columbite.
According to Stockford (1972), the main pyrochlore-bearing phases of the Carbonatite Complex include lineated dolomitic carbonatite, calcite-dolomite carbonatite breccia, massive calcite-dolomite carbonatite, and “crushed” dolomitic carbonatite.
Significant pyrochlore mineralization occurs only in sodium and magnesium-rich phases of the carbonatite. The highest-grade mineralization occurs in a mixed dolomite-calcite host. The pure dolomitic host produces intermediate grades and pure calcite is normally low in grade or barren.
The columbite occurs along the eastern side of the complex over a strike length of 120 m in the crushed dolomitic carbonatite. The columbite is totally or partially pseudomorphic after pyrochlore. The columbite may occur in the core or the rim of the crystal, or it may completely replace the pyrochlore. The columbite does not appear to be restricted to any one rock unit, however, it does appear to be related to fracturing and hematitic alteration.
Pale green fluor-variety of apatite is universally present in all rock units within the carbonatite-pyroxenite complex. Usually, the highest-grade bands of pyrochlore-bearing carbonatite also contain abnormally high quantities of apatite, while the converse is not true.
Deposit Types
Carbonatite-associated deposits such as James Bay include a variety of mineral deposits that occur both within and in close spatial association with carbonatites and related alkalic silicate rocks. Carbonatite-associated deposits are mined for rare-earth elements (“REEs”), niobium, iron, copper, apatite, vermiculite, and fluorite. By-products include barite, zircon, or baddeleyite, tantalum, uranium, platinum group elements, silver, and gold.
Carbonatites may consist of a number of intrusive phases with different textural and mineralogical characteristics. Early phases typically consist mainly of calcite, do not contain peralkaline pyroxenes or amphiboles, and contain associated apatite + magnetite ± pyrochlore mineralization. Later phases, which may contain dolomite, ankerite and siderite, in addition to calcite, are commonly enriched in pyrochlore.