Matthew Greco HBSc thesis abstract

The Albany deposit is an igneous-hosted, magmatic-hydrothermal, breccia graphite deposit located near Hearst, Ontario.  The deposit is contained within two intrusive vertical pipe structures known as the east and west pipes.  The deposit is estimated to contain 24 million tonnes of ore with an average grade of 3.98% graphite.  The east and west breccia pipes are texturally distinct and contain different graphite grades (5.60% and 2.85%, respectively).  Higher grades in the east pipe are attributed to intragranular mineralization.   Such mineralization is much less abundant in the west pipe, which dominantly contains the intergranular matrix-hosted mineralization that typifies both pipes.

A quantitative assessment of the morphology of graphite hosting breccia within the deposit is conducted by semi-automated digital image analysis using the program Image-J.  Image J is used to manipulate digital images of breccia drill core segments and produce quantitative date based on morphological attributes of the clasts.  Measured properties include: area% of fragments versus matrix; fragment orientations; fractal roughness dimension; shape descriptors; and, sorting.  Results from this analysis are used to assess the key textural differences between the east and west pipes.  The data is also compared to an existing model for breccia classification in order to hypothesize the genetic origin of the Albany breccia pipes.

Key morphological differences between the east and west pipes indicated by the analysis are shown by data regarding fragment shape and area% fragments versus matrix.  Fragments within west pipe breccia samples exhibit a higher degree of roundness and isotropy on average than those from the east pipe.  Impact erosional processes responsible for this roundness can be attributed to a higher number of fluid pulses and or higher energy brecciation during the formation of the west pipe.  These attributes are characteristic of volume expansion brecciation and fluid assisted brecciation processes.  The relatively angular nature of fragments within the east pipe suggest that it was more strongly influenced by fluid-assisted brecciation during its formation.

The most significant morphological similarities determined by analysis are sorting and orientation.  Samples from both suites exhibited very poor sorting, which is indicative of a very high degree of energy during formation associated with volume expansion brecciation.  Fragment orientation is inconsistent within east pipe breccia and absent in west pipe breccia.  Orientation in hydrothermal breccia results from veining and fragment imbrication.  The inconsistent fragment orientation within the east pipe is likely caused by increased influence of fluid-assisted brecciation processes.

The current genetic model for the Albany deposit suggests that the breccia pipes were emplaced violently within a hypabyssal environment by magmatic-hydrothermal activity and in response to a large scale depressurization event.  The hypothesized classification of the breccia derived from the data suggests that both pipes are volume expansion breccia, with characteristics of fluid assisted and corrosive wear breccia.  Volume expansion breccia is what should be expected given the parameters of the current genetic model, therefore, the evidence from this study supports the existing theory of emplacement for the Albany deposit.