Summary:
Regional Geology
The Holloway and Holt mines lie within the Southern Abitibi Greenstone Belt (SAGB) of the Superior Province in north-eastern Ontario. The 40 km long, mostly contiguous HoltHolloway property package is a grouping of strategically located claims straddling the Porcupine-Destor Fault Zone (“PDF”) midway along its 260 km length.
Local Geology
The deformation history of the area is defined by five events. The earliest episode of regional D1 deformation (compression and extension) predated the Porcupine angular unconformity at 2,690 Ma. The D2 event (compression and extension) post-dated the Porcupine assemblage and resulted in localized folding and thrusting and early southside up, dip-slip, ductile deformation on regional deformation zones. Broadly synchronous with the syntectonic opening of the Timiskaming basins in dilatational jogs was D3 folding that resulted in significant left lateral slip movement along the PDF. The D4 folding event created synclines within the Timiskaming assemblage rocks and rightlateral strike-slip displacement along the PDF. The D4-D5 event represents the final stage of transpressional deformation along the PDF. Gold mineralization in the HoltHolloway area is interpreted to be early D3 in age. Lightning Zone replacement mineralization is cut by an inter-mineral dike with an age of 2672 ± 1.9Ma, which is overprinted by a later auriferous quartz-carbonate veining event. The bulk of the gold in the Timmins area was related to late D3 events.
Holt Property Geology
The Holt Mine Complex is situated on the eastern portion of the PDF. Interpretations are made through diamond drilling and underground mapping within the mine complex. As a mafic volcanic deposit, the lithology is mainly Fe-tholeiitic basalts with minor intrusive syenites, which may be up to 2m thick. Syenites cross cut the main mineralized trend potential as conjugate faults. Mineralization is present mainly on the hanging wall side of the Ghostmount Fault. The lower portion of Zone 4 shows a steeper change in dip showing possible rolling of the zone through a fold or offset fault.
DEPOSIT TYPE
At Holt-Holloway, the deposit is a mafic volcanic hosted where the gold mineralization is quite unlike the classical Superior province auriferous quartz vein systems resulting from deformed, extensional fracture arrays. Rather, it is associated with disseminated sulphides in altered rock, sometimes described as replacement mineralization. Mineralization typically consists of moderately to steeply dipping tabular zones of disseminated pyrite (generally less than 5 per cent per volume) and gold in intensely altered tholeiitic basalt, with variably developed microveinlet stockworks. The ore is gold rich (Au:Ag is greater than 5) and contains concentrations of arsenic. The mineralized zones occur in a variety of geological settings reflecting a variety of controls on the localization of the mineralization: along low-strain lithological contacts (Lightning, Blacktop and Lightning Deep zones at Holloway), along brittle and/or ductile faults (McDermott, Worvest and Mattawasaga zones), and as shallowly dipping discordant zones (Tousignant, South Zone and Zone 4) of which the South Zone (Holt) is spatially coincident with an array of shallowly dipping syenitic dykes.
Mineralized zones are coincident with zones of intense albite-ankerite alteration of the host basalt, which, in turn, are partly fringed by sericite alteration haloes at Holloway and fringed by broader zones of calcite alteration. Disseminated specular hematite can be present within or outboard of mineralized zones.
Gold mineralization at the Holt and Holloway Mines is associated with replacement carbonate-pyrite-albite-quartz alteration that overprints mafic volcanic rocks in, and adjacent to, D3-D4 high strain zones. The overprinting of multiple mineralization phases in the same area suggests that mineralization was long lived and spanned syn-tectonic deformation during exploitation of the same fluid channel ways.
Holt
At the Holt Mine, mineralized zones that have been historically mined are hosted by the McDermott shear zone, a 10 m to 50 m wide south-southeast dipping carbonate-sericitechlorite ± albite altered ductile D3-D4 shear zone, which is hosted by otherwise massive, and generally low strain mafic volcanic rocks. The McDermott shear zone has been traced laterally for approximately 10 km along strike, joining the PDF corridor to the northeast. It has been traced by drilling at least eight kilometres west of the Holt Mine headframe. The shear zone may be localized along an older D2 thrust plane that has structurally emplaced lenses of fine-grained clastic sedimentary units along it. Principal mineralized zones that have been mined to date along the structure include the South, C-104, McDermott, Worvest/Three Star, Mattawasaga, and C-97 zones, which occur over a strike length of three kilometres and have been mined to depths of over one kilometre below surface.
More recently, the C-103, Zone 4 and Zone 6 gold mineralization has been identified along these geologic structures and are host to the bulk of the existing gold mineralization. All but the South Zone and Zone 4 occur in steeply south dipping sections of the shear zone. The South Zone and Zone 4 occur where the shear zone rolls to moderate to shallow southerly dips (Rhys, 2005a). Prominent within the Holt Mine geology are two northeast to east-northeast trending brittle faults: the Ghostmount and the McKenna. Although once interpreted as mineralization controlling structures, they offset mineralization and are in fact the youngest structural elements in the region (Rhys, 2005a).
Mineralization frequently occurs within the upper (hanging-wall/south) portions of the McDermott shear zone, often in areas where the structure defined by its carbonatesericite-quartz altered high strain zone widens from a thickness of generally less than 10 m to locally greater than 50 m wide. The widening may in part be controlled by the interaction of the shear zone with lenses of carbonaceous sedimentary rocks in its footwall. Mineralization occurs in massive to banded quartz-carbonate-pyrite-albite alteration that occurs within the McDermott shear zone and may extend a short distance into adjacent, unfoliated, massive mafic volcanics. Diffuse quartz veinlet networks and matrix are commonly developed, locally imparting breccia textures in sheared rocks. The apparent overprinting of foliation by alteration, and rotation of shear zone fabrics in breccia fragments, collectively suggest that mineralization overprints portions of the McDermott shear zone, and that it formed during or after most shear zone fabric development. An early phase of hematite-bearing carbonate-albite-quartz alteration is often preserved as lenses and domains within and adjacent to the Holt Mine mineralized zones (Rhys, 2005a).
Zones 4, 6 and C-103 at the Holt Mine have a well- established higher grade gold zone (i.e. greater than 3 g/t Au) related to a zone of more intense alteration, including sericite, chlorite, hematite and silicification, and elevated concentrations of sulphides within an overall lower grade envelope. This higher grade zone, typically three to five metres thick, is almost exclusively located along the hanging wall of the deposit, against the Ghostmount fault or any associated fault splay. The zones typically extend over 100 m along strike and 100 m down dip.