David J. Gliddon HBSc thesis abstract

Thesis Title: 
The Mineralogy and Genesis of the Archean Hemlo Barite Occurrences in Northern Ontario
David J.

A baritic horizon occurring within the Arechean supracrustal rocks of the Hemlo area, northern Ontario, exhibits characteristics that suggest a syngenetic origin is likely.  The baritic unit outcrops in five locations situated five to thirteen kilometers east of the town of Marathon, and appears to parallel the regional stratigraphy.  It occurs between pyroclastic plus pillowed mafic metavolcanics to the south and siliceous metasediments plus intermediate to felsic pyroclastic metavolcanics to the north.  The barite is massive, thinly laminated to wispy laminated and is generally interlaminated with recrystallized quartz, albite, pyrite and carbonaceous material, forming a unit one to three meters thick.  The contacts with adjacent rock layers appear conformable.  Rock lithologies associated with the baritic unit include pyritiferous graphitic schists and DE turbiditic argillaceous siltstones (starved basin-type sediments), argillaceous siltstones with green mica (rip-up?) clasts, green mica schists, biotite-hornblende schists, sericite-carbonate schists, mafic metavolcanic fragmentals and flows, a very thin tuffaceous unit and quartz-feldspar porphyry sills.  Although these rock units have likely been structurally transposed relative to one another, their presence at all the barite occurrences suggest that they were formed in special association with the barite.

In comparing the characteristics of the Hemlo baritic horizon with those of other documented modern to Archean syngenetic and epigenetic barite occurrences throughout the world, it becomes evident that the Hemlo occurrences more closely resemble syngenetic than epigenetic deposits.  Characteristics in common with other syngenetic occurrences include: regional and local conformity of the baritic unit with associated lithologies; lateral continuity of the barite horizon (possibly eight kilometers); associated deep water/starved basin-type sedimentary units; the thinly laminated to wispy laminated character of the barite.