The Journal of geology, 1991-05, Vol.99 (3), p.395-414
1991
Volltextzugriff (PDF)
Details
- Autor(en) / Beteiligte
- Titel
- Magmatic Oxidation in the Syenitic Murdock Creek Intrusion, Kirkland Lake, Ontario: Evidence from the Ferromagnesian Silicates
- Ist Teil von
- The Journal of geology, 1991-05, Vol.99 (3), p.395-414
- Ort / Verlag
- University of Chicago Press
- Erscheinungsjahr
- 1991
- Quelle
- Alma/SFX Local Collection
- Beschreibungen/Notizen
- The syenitic Murdock Creek intrusion, of late Archean age, lies within one of the major lode gold camps of the world, at Kirkland Lake, Ontario. There is a strong spatial association between syenitic intrusions, gold mineralization, and carbonatization. Hydrothermal fluids that carried the gold had an unusually high oxygen fugacity ($f_{o_{2}}$). Notwithstanding a wide range in rock compositions within the intrusion (from clino-pyroxenite to alkali-feldspar syenite), clinopyroxene and biotite have consistently low Fe/(Fe + Mg) and high$Fe^{3+}/(Fe^{2+} + Fe^{3+})$ratios. These compositional features indicate a deficiency of$Fe^{2+}$in the magma during crystallization. Together with the presence of abundant, early-formed magnetite and titanite, this is interpreted to result from an intrinsically high magmatic$f_{o_{2}}$that remained constant during pluton evolution ($f_{o_{2}} \approx 10^{-12} bars$). Mineral compositions, proportions of crystallizing mineral phases, and textural features indicate that the pluton formed from a single pulse of already-evolved syenitic magma that fractionally crystallized in situ under low water pressure at mid-crustal depths. The intrinsically oxidized nature of the pluton implies an oxidized source region such as metasomatized upper mantle where partial melting occurred.$CO_{2}$-rich fluid or melt was the likely agent for metasomatism. Dissolution and transport of gold is favored by high$f_{o_{2}}$in the fluid phase. The high$f_{o_{2}}$of the syenitic magma suggests a common genetic link between magma generation,$CO_{2}$represented by "carbonatization, and gold-bearing fluids.