Overview of Results from the Greenstone ... - Geology Ontario
Overview of Results from the Greenstone ... - Geology Ontario
Overview of Results from the Greenstone ... - Geology Ontario
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area (ca. 2700–2696 Ma: Péloquin and Piercey 2005), but are similar to o<strong>the</strong>r late tectonic TTG plutons<br />
in <strong>the</strong> sou<strong>the</strong>astern Abitibi greenstone belt (e.g., Clarice Lake, Lac Dufault; Corfu and Noble 1992;<br />
Mortensen 1993). The Clifford stock and equivalent rocks have very distinctive lithogeochemical<br />
signatures typical <strong>of</strong> high-Al TTG suites, and have very distinctively low Y (0.4), Al 2 O 3 /Yb (>10), and La/Yb (>10) ratios, as compared to <strong>the</strong> older<br />
Blake River Group rocks; <strong>the</strong>se features can be used to geochemically discriminate felsic magmatism<br />
associated with <strong>the</strong> Blake River Group <strong>from</strong> younger TTG-related magmatism associated with <strong>the</strong><br />
Clifford stock and o<strong>the</strong>r TTG magmatism (ca. 2690 Ma).<br />
Mineralization in Clifford Township consists <strong>of</strong> an older VMS-related style <strong>of</strong> mineralization, and a<br />
younger, overprinting porphyry copper-molybdenum-gold (Cu-Mo-Au) style <strong>of</strong> mineralization. The VMSrelated<br />
mineralization consists <strong>of</strong> epidote-quartz-pyrite-chlorite assemblages, typical <strong>of</strong> semi-conformablestyle<br />
alteration associated with permeable zones (e.g., amygdules, pillow margins and interpillow regions) in<br />
<strong>the</strong> volcanic rocks <strong>of</strong> <strong>the</strong> Blake River Group. There are also some zones <strong>of</strong> higher temperature chloritequartz-chalcopyrite-pyrite<br />
assemblages typical <strong>of</strong> pipe-like alteration. The younger porphyry Cu-Mo-Au<br />
style mineralization occurs as a series <strong>of</strong> breccia pipes and stockwork vein systems. This latter style <strong>of</strong><br />
mineralization is associated with a complex array <strong>of</strong> veinlet and vein-styles <strong>of</strong> alteration that is quite<br />
distinctive <strong>from</strong> VMS mineralization. The fact that this mineralization is hosted in <strong>the</strong> Clifford stock and<br />
associated dikes that are circa 2690 million years old suggests that this mineralization represents a distinctly<br />
younger magmatic-hydro<strong>the</strong>rmal event, distinctive <strong>from</strong> <strong>the</strong> early VMS-related event.<br />
METAMORPHIC SUBPROJECT<br />
The Metamorphic Subproject <strong>of</strong> <strong>the</strong> <strong>Greenstone</strong> Architecture Project, Discover Abitibi Initiative, is<br />
designed to address a significant gap in knowledge <strong>of</strong> <strong>the</strong> geological setting <strong>of</strong> gold deposits and <strong>of</strong> <strong>the</strong><br />
application <strong>of</strong> metamorphic data and concepts to gold exploration in <strong>the</strong> Timmins–Kirkland Lake area.<br />
There are three reasons why this gap should be filled. First, some metamorphic zone boundaries may be<br />
<strong>the</strong>mselves valid gold exploration targets (Hall 1998, using data <strong>from</strong> Mikucki and Roberts 2004;<br />
Thompson 2002, 2003, 2005). Second, metamorphic data and <strong>the</strong> concepts developed to explain <strong>the</strong><br />
origin <strong>of</strong> metamorphic rocks impose constraints on <strong>the</strong> geological setting <strong>of</strong> gold deposits and <strong>the</strong><br />
mineralization and alteration <strong>the</strong>rein. Third, this project provides a basis for comparison <strong>of</strong> <strong>the</strong><br />
metamorphic settings <strong>of</strong> <strong>the</strong> Timmins and Kirkland Lake gold camps with each o<strong>the</strong>r and with <strong>the</strong> less<br />
productive adjacent parts <strong>of</strong> <strong>the</strong> greenstone belt. Map-scale variations <strong>of</strong> metamorphic grade combined<br />
with textures and mineral assemblages are <strong>the</strong> basis for analysis and interpretation <strong>of</strong> <strong>the</strong> spatial and<br />
temporal relationships between metamorphism and magmatism, deformation, alteration, and gold<br />
mineralization. The resulting metamorphic framework (Thompson 2005) advances knowledge <strong>of</strong> known<br />
gold deposits and helps to define new exploration targets.<br />
Subdivision <strong>of</strong> <strong>the</strong> greenschist zone using <strong>the</strong> appearance <strong>of</strong> biotite in metamorphosed<br />
quartz<strong>of</strong>eldspathic and aluminous rocks and <strong>the</strong> appearance <strong>of</strong> amphibole in metamorphosed ultramafic<br />
rocks (Table 7) reveals a striking spatial relationship between <strong>the</strong> metamorphic zone boundary and a<br />
significant number <strong>of</strong> past and presently producing gold mines (Figure 27). Higher priority targets are<br />
defined by <strong>the</strong> coincidence <strong>of</strong> metamorphic anomalies defined by <strong>the</strong> boundary with major structural<br />
features, particular rock compositions, and moderate to intense deformation and/or alteration. For<br />
example, in Tully, Prosser, and Wark townships, a lenticular zone <strong>of</strong> upper greenschist grade rocks<br />
surrounded by lower greenschist zone rocks is associated with a nor<strong>the</strong>ast-trending fault zone, a small<br />
alkalic pluton and, at <strong>the</strong> nor<strong>the</strong>ast end, numerous gold occurrences. On a smaller scale, <strong>the</strong> linear array<br />
<strong>of</strong> metamorphic “hot” spots located between two branches <strong>of</strong> <strong>the</strong> Destor–Porcupine fault in Whitney<br />
Township may be significant. A more detailed examination <strong>of</strong> <strong>the</strong> relationship between a metamorphic<br />
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