Irina Korsakova, MSc

The Bidgood deposit is located 7 km east of Kirkland Lake, Ontario, and is part of the world-class Kirkland Lake-Larder Lake gold camp (>47 Moz) situated in the southern Abitibi greenstone belt of the Superior Province. Gold deposits in the camp are associated with faults and shear zones, such as the Larder Lake-Cadillac deformation zone, and are predominantly classified as orogenic (e.g., Kerr Addison-Chesterville, Omega, Cheminis) and, less commonly, intrusion-related (e.g. Upper Beaver deposit).  The Bidgood deposit is hosted within intrusive units that cut across sedimentary and volcanic rocks of the Timiskaming assemblage, representing the youngest Archean supracrustal assemblage in the Abitibi greenstone belt. Due to the complex deformational history of the area and the presence of several intrusive units at Bidgood, the style and origin of the gold mineralization remain poorly understood. Furthermore, constraints on the composition and genesis of the intrusive host lithologies are lacking. This complicates the interpretation of Bidgood into a deposit type. This study therefore aims to identify the lithostratigraphic, geochemical, and alteration controls on mineralization at the Bidgood deposit, using field mapping, detailed core logging, petrographic descriptions, and whole rock geochemistry. 

Sedimentary and volcaniclastic units at Bidgood include siltstone, greywacke, conglomerate, and trachytic tuff units of the Timiskaming assemblage (≤2679 – ≤2669 Ma). They are intruded by diorite, feldspar and quartz-feldspar porphyries, with diorite as the oldest unit. Thin syenite and bimodal quartz-feldspar porphyry dikes appear to be the youngest intrusive units. The diorite shows evidence of at least two stages of alteration: an early assemblage of chlorite-epidote-calcite-magnetite is overprinted by a sericite-ankerite-pyrite+/-quartz assemblage. The latter is weak to strong, pervasive and selectively pervasive (appearing as vein envelopes). This alteration type is also prominent in sedimentary rocks of the Timiskaming assemblage and later intrusive feldspar porphyry and quartz-feldspar porphyry.  

Gold mineralized zones are mainly hosted by diorite and feldspar porphyries altered to sericite-ankerite+/-quartz and closely associated with pyrite within mm-thick veins of quartz+/-molybdenite, calcite, and pyrite only stringers. Visible gold is present in the pyrite-calcite vein, occurring as specks less than 1 mm in size.

Although it is too early to propose a deposit model for Bidgood, it likely formed as either an intrusion-related or orogenic deposit, both present in the camp. Ongoing and future work includes the alteration mineralogy and geochemistry of the intrusive units, and the age of the host rocks and mineralization will be determined using U-Pb zircon and Re-Os molybdenite dating, respectively, to identify the most applicable deposit model.