Summary:
Muir (2002) interprets the Hemlo deposit to be an atypical, mesozonal-orogenic, disseminated-replacement-stockwork deposit, broadly synchronous with D2 and “middle” stage granitoid plutonism, prior to or synchronous with peak regional metamorphism, and involving magmatic ± metamorphic fluids.
The Hemlo deposit is approximately three kilometres long by two kilometres deep and averages 20 m wide with a very small surface expression.
Mineral Reserves at the Williams Mine are currently grouped into two main areas: the B Zone and C Zone. The A Zone has been mined out. The A and B Zones are geologically the same continuous zone, with the B Zone being the down-plunge westerly extension of the A Zone, which sub-cropped at surface. The B Zone is further divided into the main zone and footwall zone. The C Zone represents multiple sub-parallel lenses of irregular, generally narrow, gold mineralization. The C Zone mineralization is stratigraphically different from the main zone and occurs in two broad geological domains, the porphyritic felsic metavolcanics (Moose Lake porphyry) and the intermediate to felsic volcaniclastic sediment unit. Interlake is the down dip extension of the C Zone.
The B Zone extends to a depth of at least 1,300 m below surface and has a strike length of approximately 1,200 m. Main Zone mineralization occurs at or near the contact with the hanging wall sediments in a strongly feldspathized rock unit. The zone dips at 60° to 70° to the northeast and plunges to the northwest at approximately 45°. The horizontal thickness of the mineralization varies from three metres to 45 m. The maximum thickness of ore is located adjacent to the Golden Giant boundary. Moving west from that property boundary, the mineralization generally declines in width and grade. The western portion of B Zone Mineral Reserves includes two or three mineralized zones within the typical host lithology. Internal waste pillars of at least 10 m horizontal thickness separate these zones. This mineralization represents the fringe of the Hemlo deposit and as such, continuity of grade and thickness becomes increasingly erratic.
The B Zone Footwall (BZFW) zone is a series of lower grade mineralized lenses 20 m to 50 m south of the B Zone main zone. It diverges from the main zone above the 9200 elevation and westward from the former Newmont property boundary which is part of the Hemlo Property following the acquisition in 2014. The BZFW Zone is hosted in a series of structures subparallel to the main B Zone mineralization. Mineralization is hosted within a muscovite schist unit which can be traced from the David Bell Mine in the east part of the Hemlo area, through the Golden Giant Mine, to the western rim of the Williams Pit. Four of the seven FW lenses occur in mineable widths from two metres to nine metres over a strike length of up to 150 m and 125 m vertically. FW mineralization is characterized by rapid pinch-outs (within 20 m), but where present, the mineralization is often high grade (10 g/t Au to 30 g/t Au). Associated minerals are molybdenite, pyrite, realgar, orpiment, arsenopyrite, tourmaline, and green mica.
The C Zone mineralization is approximately 400 m to 600 m west of the B Zone and distinctly different from the B Zone. Several zones or lenses are typical; most of which are thin, low to medium grade mineralization. These extend eastward roughly 700 m from the western boundary of the Williams property and vertically from surface to a depth of at least 1,300 m. The Interlake resource is the down dip extension of the C Zone mineralization.
The C Zone mineralization strikes at approximately 100° azimuth, dips 68° to the North, and plunges at 45° to 60° to the west. The higher-grade cores of the lenses are mined by underground methods where ore body widths are generally less than 10 m. Mineralization in the C Zone generally occurs along contacts between the fragmental units or as lenses that parallel the foliation. Individual lenses display pinch and swell features and large variances in grade can occur within each lens. Pre-existing geologic structures appear to have exerted the strongest controls on mineralization. The influence of later deformational events is not well understood. All of the major rock units are highly deformed with multiple events of deformation. Regional metamorphism is up to amphibolite grade. A muscovite schist, which is a key marker, pinches out at depth, between the porphyry and the fragmental unit.