Summary:
Kilbourne Mineralization
Graphite mineralization at Kilbourne, and elsewhere within the Grenville Province, likely resulted from the metamorphism of organic-rich sediments deposited contemporaneously with the host rocks, with tectonic burial providing the necessary pressure-temperature conditions for graphitization. This syndepositional source of carbon has resulted in stratiform graphite mineralization. In the nomenclature of the Balmat-Edwards District, the mineralized horizon is the Upper Marble Unit 2.
Unit 2 is currently divided into three sub-units, with transitional zones between each. The names assigned are based on their current relative positioning. The overall thickness of the unit varies substantially both along strike, and along dip. With the thinnest Unit 2 intercepts totaling 25 ft, and the thickest intercepts totaling 312 ft. These fluctuations are interpreted to be the result of the ductile behavior of the rocks during metamorphism, a behavior documented frequently in the units hosting the Company’s zinc mineralization.
A) The Upper Graphitic Schist (UGS) is a granulite composed of quartz-biotite/phlogopitegraphite-sillimanite-pyrite-pyrrhotite with rare garnet. The unit has a dark grey color, with discrete blebs of sillimanite often altered to clay. Graphite is generally coarser grained than in the lower mineralized unit and makes up an estimated 1.5%–3% Cg of the lithology. Grades as high as 13.5% Cg have been returned in assay. The average thickness of the Upper Unit is 57.1 ft.
The transitional zone leading into the middle unit is marked by an increase in clay/chlorite altered/replaced sillimanite, and garnets. A stronger fabric is also documented. Graphite remains present but is often at a lower percentage than in the upper mineralized unit. There is often a band of higher-grade graphite mineralization near the lower contact with the middle zone.
B) The Phlogopitic Garnet Schist (PGS) is a visually distinguishable phlogopite/biotite schist with a strong wavy fabric and pegmatitic boudins/inclusions. The sub-unit is dominated by a dark ferromagnesian mica with quartz-sillimanite-garnet-graphite with less common pyrite/pyrrhotite. Graphite mineralization is present, often coarser grained than the upper and lower units, but is sparsely disseminated, contributing to <1% of rock groundmass. The average thickness of the Middle Unit is 61 ft.
The transitional zone between the middle and lower units is similar in appearance and composition to the transitional zone between the upper and middle units, marked by a weaker fabric, higher Cg, and discrete clay/chlorite altered/replaced sillimanite.
C) The Lower Graphitic Schist (LGS) is a dark grey to black, massive granulite. The constituent minerals are likely ferromagnesian mica and quarts, with fine grained graphite and possibly fine-grained sulfide, contributing to the dark color of the rock. Graphite grades range from 1.5%–3% Cg, with samples as high as 11.3% Cg recorded. The average thickness of the Lower Unit is 29 ft.
Unit 2, as defined by drilling, has an approximate strike length of 32,800 ft and extends to a vertical depth of 3,450 ft below surface.
In all of the Kilbourne sub-units, iron sulfides (pyrite>pyrrhotite) are present. Trace sphalerite has also been documented in veinlets and rarely as disseminated mineralization.