Summary:
Property Geology
The Springpole Gold Project has been extensively studied during past programs and the findings of those studies will not be covered in detail here; however, they are adequately covered in the technical reports of Zabev (2004) and Armstrong et al..., (2006).
Trachyte Porphyry Intrusion
A polyphase alkali, trachyte intrusion displaying autolithic breccia textures lies at the heart of the Springpole Gold Project. The intrusion is comprised of a system of multiple phases of trachyte believed to be part of the roof zone of a larger syenite intrusion, as fragments displaying phaneritic textures were observed from deeper drill cores in the southeast portion of the Portage zone. Early intrusive phases consist of megacrystic feldspar phenocrysts, up to 5 cm long, of albite and orthoclase feldspar in an aphanitic groundmass. Successive phases show progressively finer grained porphyritic texture while the final intrusive phases are aphanitic.
Confederation Age Volcanic and Siliciclastic Rocks
The country rocks pre-date the alkali intrusion and are composed of a complex sequence of altered and metamorphosed intermediate andesitic volcanic and associated volcaniclastic rocks, siliciclastic sedimentary rocks, chemical sediments including banded iron formation (BIF), and coarse pebble conglomerates. Devaney (2001a) indicates that the sediments are likely of the Confederation assemblage dating at around 2,740 Ma, representing the proximal portions of a mixed volcanic-sedimentary basin.
“Timiskaming-type” Conglomerates
Barron (1996) states pebble conglomerate outcrops between Springpole Lake and Birch Lake contain clasts of the trachyte porphyry, suggesting that the “Timiskaming-type” conglomerates postdate the intrusion. Devaney (2001a) suggests these arcuate form conglomerates represent late orogenic, deformed, dextral sense strike-slip (pull-apart) basins of “Timiskaming-type”, late Archean, post Confederation assemblage age rocks.
Structure
Deformation has added complexity to the apparent geometry of, and the potential of, the Springpole gold deposit. Gravity and magnetic surveys carried out across the Project demonstrate that several phases of deformation are evident. Banded iron formations describe north-northwest facing tight to isoclinal antiforms and synforms and are illustrated on the geological map produced during the summer 2005 mapping program (Armstrong et al..., 2006) and are evident as strong magnetic anomalies on the aeromagnetic surveys conducted by Fugro.
Alteration
All rocks on the Project exhibit pervasive alteration that consists of multiple overprinted phases. Distinguishing between the individual phases will take considerable study on a microscopic scale. The country rocks and alkali intrusive rocks exhibit pervasive green-schist facies metamorphism and alteration, probably the result of burial. This manifests as chlorite, calcite, and pyrite in the intermediate volcanic rocks, pyritization of the banded iron formation, and sericite-pyrite alteration within the alkali intrusive associated rocks.
Porphyry-style Mineralization
The main intrusive complex appears to contain many of the characteristics of alkaline, porphyry-style mineralization associated with diatreme breccias (e.g., Cripple Creek, Colorado). Direct comparison with drill core from the two sites shows a number of consistent textures and styles of mineralization. A recent observation made from drilling, combined with the airborne magnetic survey, shows that potentially economic gold mineralization is coincident with an unexplained geophysical anomaly. This style of mineralization is characterized by the Portage zone and portions of the East Extension zone where mineralization is hosted by diatreme breccia in aphanitic trachyte. It is suspected that ductile shearing and brittle faulting have played a significant role in redistributing structurally controlled blocks of the mineralized rock. Still to be identified is a form of porphyry style alteration zoning consisting of an outer zone of phyllic (sericite) dominant alteration with narrow zones of advanced argillic alteration characterized by illite and kaolinite, and a core zone of intense potassic alteration characterized by biotite and K-feldspar.
Lode Gold Mineralization
The intrusion of the trachyte complex into the volcanic pile, as well as the chemical and siliciclastic sedimentary rocks in a near-surface environment, produced mesothermal to epithermal style lode vein mineralization. The difference between mesothermal and epithermal mineralization regimes is the temperature and pressure of the mineralizing fluids.
Higher temperature (mesothermal) fluids would have existed within the emplaced intrusive, associated with the diatreme breccias, and in the immediately adjacent wall rock/country rocks. In the porphyry intrusive, and at the contact between intrusive and wall rock in the East Extension zone, and localized within the Main zone, mesothermal style quartz-biotite-calcite-sulphide veins with occasional tourmaline are observed with occasional coarse, visible gold.
Gold Remobilization During Metamorphism
As evidenced from the high degree of deformation, both ductile and brittle—in the form of isoclinal folding, ductile shear zones with protomylonite and blastomylonite textures, and brittle fault textures — the Springpole deposit has been subjected to alteration and metamorphism. These processes alone have remobilized gold in epithermal quartz veins that were the principal motivation for exploration at the Springpole Gold Project in the late 1980s and early 1990s, when shear zone hosted gold deposits were the targets of choice in the Red Lake area.
Deposit types
Mineralization at the Springpole Gold Project is dominated by large tonnage, low grade, disseminated porphyry-style or epithermal-style gold mineralization associated with the emplacement of an alkali trachyte intrusion. Textures observed in the extensive repository of drill core appear to confirm that the disseminated gold-silver-sulphide mineralization, the mesothermal to epithermal lode vein gold mineralization, and the banded iron-formation hosted gold mineralization are all the result of the emplacement of multiple phases of trachyte porphyry and associated diatreme breccias, hydrothermal breccias, dikes and sills.
The initial exploration on the property was conducted on the assumption the mineralization was a typical example of Archean mesothermal, sulphide-hosted lode gold type. While this model has not been completely ruled out, it has been replaced in favor of a high-level emplacement porphyry model. Barron’s thesis (1996) work presented strong evidence that the gold and associated fluorite mineralization at Springpole are genetically related to the high-level emplacement of a large, alkaline porphyry intrusive and breccia pipe complex.
Barron considered the Springpole Complex to be the end product of magmatic fractionation processes and of fluids that evolved from magmatic to hydrothermal in the high level, sub-volcanic porphyry environment. These processes produced a low-grade gold-porphyry-epithermal type deposit and associated high-grade veins and breccia pipes.