The Lac des Iles graphite mine (LDI) is operated by Graphite Nordique Inc., a wholly-owned subsidiary of Northern Graphite Corp. The mining title is fully registered to Graphite Nordique Inc.
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Summary:
Graphite mineralization at the Quarry is hosted in a strongly folded marble unit within a paragneiss host rock, and mineralization is characteristic of flake graphite. Internal waste units of paragneiss and intrusive rocks have been identified within the marble. The fold hinge line is oriented approximately north-south and the hinge plane dips to the east at approximately 40° to 50° to nearly horizontal towards the south end of the deposit. Unconsolidated Pleistocene deposits are widespread in the area and overlay the deposit.
The mineralization consists of large graphite flakes and is commonly associated with regular banding of paragneiss, conforming to beds. The protolith is thought to comprise a clayey-carbonate sandstone. A change in the depositional environment resulted in the precipitation of a carbonate platform rich in organic matter with variable carbon content. A subsequent event of terrigenoussedimentation deposited sandstone with clay horizons on top of the carbonaceous carbonate platform.
High pressures and temperatures associated with the Grenville orogeny transformed the sedimentary protoliths to biotite gneiss, graphitic limestone marbles, and garnet gneiss that outcrop at the Quarry. The graphite mineralization is thought to be associated with the transformation of organic matter during metamorphism together with the contribution of deep fluids rich in CO2 resulting in graphitic limestone marbles. Slow cooling of the mineralized material has produced crystalline large flake graphite.
Graphite mineralization is associated with limestone marbles. The marbles are zoned with respect to calcite content: the core is characterized by a higher calcite content (“soft ore”) that becomes more silicious (“hard ore”) with the introduction of diopside towards its margin. The calcite zonation is thought to reflect the chemical composition of the protolith. The change in calcite content is gradational within the marble, and the contact between the marble and surrounding paragneiss is sharp.
The protolith was disrupted by various intrusive events. Felsic to mafic intrusions have been identified locally, as well as differentiated pegmatites. Intrusions, which range from <0.1 m to several metres in thickness, are emplaced along zones of weakness (shears, formational contacts) and often disrupt the contact between the graphitic mineralization within the marble with surrounding paragneiss.
The sedimentary protoliths, together with the intrusions, have undergone at least three phases of ductile tectonics. The first phase of east-west compression folded the sedimentary package to form an “S” fold. A second phase of compression distorted, flattened, and locally boudinaged the rocks with a general dip to the east. A final, third phase of north-south compression resulted in a north-south undulation of the sequence along this axis. This undulating folding influences the depth at which the graphic mineralization occurs across the deposit. Folding is seen on all scales, from less than one metre to hundreds of metres.
The sequence also underwent several phases of brittle deformation. There are north-south normal faults dipping to the west and a second set of sinistral east-west faults that has displaced some of the graphitic mineralization observed in the main mineralized zone.
The thickness of the marble units varies from an average of approximate five metres to 10 m and higher at the fold noses. Since marble is particularly ductile during the compression phase, the local thickness can vary greatly.
In the context of exploration on the deposit at the Quarry, the north-south axis of mineralization serves as a general guide, with east-west faulting shifting mineralization. This offset is observed within the open pit. The complex folding dictatesthe depth and thickness of the mineralization. The thickness of graphitic mineralization is greatest within the fold hinges and thins out and can be absent within the fold limbs. The mafic and felsic intrusions, together with pegmatites disrupt the stratabound mineralization and the boundary between ore and waste, which is typically quite sharp, is mixed and traditional.
Syngenetic graphite deposits, such as at the Quarry, are usually stratabound, with tabular, lenticular, or irregular mineralized bodies. Graphite mineralization results from the progressive transformations that the carbonaceous matter undergoes through prograde metamorphism, or graphitization (Kwiecinska and Petersen 2004). The changes induced by metamorphism on the carbonaceous matter include both structural and chemical modifications which begin during the earlier stages of diagenesis and greatly affect the impurities and final product grade, which can vary from 75% C to 97% C (Luque et al., 2014).