Stephen West HBSc thesis abstract
The two breccia pipes that comprise the Albany graphite deposit, located near Hearst, Ontario are examples of fluid-derived, igneous-hosted graphite. Both the East and West pipes have been have been subjected to post-emplacement alteration at levels near the unconformity with the overlying Paleozoic carbonate rocks of the Gravel River Basin, and as a result have undergone various types of alteration. Carbonate and hematite alteration affect the supergene zone, while sericite alteration affects the known vertical extent of the deposit. Post-emplacement intrusions at depth within both pipes result in additional carbonate and hematite alteration zones within the graphite breccia.
The transitional trend in limestones/dolostones from continuous veins to isolated anhedral masses which underlain Paleozoic carbonate rock is attributed marine transgression of the Ordovician oceans. Sericitization is present in both pipes for the entire sampling depth and is controlled by the potassium feldspars. The degree of sericite alteration decrease with depth from the supergene zone into the breccia. Hematite alteration of the feldspars within the supergene zone correlates nicely with sericite alteration.
A combination of core logging, optical microscopy, x-ray diffraction, and whole-rock geochemistry have been used to document and determine the origin of this shallow level alteration of the Albany graphite deposit. The alteration styles are similar for both pipes but there are key in differences for each. The spatial relationship among the three style is complex. At least two of the three alteration types noted above, are present at depth of within the deposit, often with all three overlapping.
The presence of each alteration type will have an impact on metallurgical beneficiation of the ore based on extent and degree of alteration. By delineating the zones and distinguishing between supergene alteration and alteration occurring at depth within the breccias, processing techniques can be varied as each complicating zone is encountered.