ÒMADOCITEÓ
HereÕs a rock from Ontario having a mineral
combination you don't see very often. This sample is from a metamorphosed
mafic dike that intrudes tremolite-talc schists hosted in dolomitic
marble. The metamorphism has converted the original mafic igneous
minerals into a mixture dominated by tourmaline (black) and pyrite (brassy
gold). Some of the small bright white patches are talc.
Tourmaline-pyrite metamorphic rocks lack a formal name, so the term ÒmadociteÓ
has been used by some geologists. Published mineral analysis indicates
that ÒmadociteÓ contains tourmaline, pyrite, tremolite, and some phlogopite
mica.
Age of metamorphism - probably ~1.24 billion years, during the Mesoproterozoic.
Subsequent metamorphism occurred at ~1.1 billion years, during assembly of the
Rodinia supercontinent.
Initial metamorphic agent - probably emplacement of the nearby Deloro Granite.
Locality:
Canada Talc Limited mine at Madoc, south-central Hastings County, southeastern
Ontario, southeastern Canada.
ÒMadociteÓ (field of view ~2.7 cm across) from
the Precambrian of Ontario.
Most info. from:
Dunn (1998) - Formation of dolomite-hosted massive
talc at Madoc, Ontario. Geological Society of America Abstracts with
Programs 30(7): 229-230.