Abstract
The Parker phlogopite mine, located near Notre-Dame-du-Laus, Quebec, 74 km north of Ottawa, is well known among mineral collectors for its centimetric euhedral crystals of black spinel. Among the dozens of phlogopite mines active in the early 1900s in the Mont-Laurier–Bancroft corridor in the Central Metasedimentary Belt of the Grenville Province, the Parker mine is exceptional because of the association of forsterite + spinel with phlogopite. Euhedral crystals of these minerals are found “frozen” in a carbonate matrix. The carbonate dike and segregations are associated with spinel-rich dunite that contains accessory diopside, phlogopite, and pargasite, as well as ilmenite and apatite. The interstitial melt crystallized to calcite + dolomite. Hematite appeared as flakes in the melt owing to net loss of hydrogen, and the spinel underwent oxidation-induced exsolution. Our spinel crystal entrapped a domain of carbonate during growth. It also entrapped globules of boundary-layer melt that crystallized to a carbonate + sulfate + phosphate + silicate + oxide assemblage. Such globules, where present in the cumulate, are more pristine than in the coarse crystal of spinel, i.e., less affected by a hydrothermal overprint. We contend that the carbonate melt ultimately formed by the hydrous melting of marble, as supported by oxygen-isotope data on all major minerals. Melting occurred 1140 million years ago, at a time of tectonic relaxation following the Shawinigan compressive stresses.
Highlights
IntroductionProvince [1,2]
In the early 1900s, apatite and phlogopite were recovered from dozens of small mines in theMont-Laurier–Bancroft corridor in the Western Quebec/Eastern Ontario portion of the GrenvilleProvince [1,2]
We have investigated in detail two petrographic thin sections of dunite and of one large spinel crystal (Figure 2b)
Summary
Province [1,2] These minerals are found in a calcite matrix, and an association with ultrabasic rocks, pyroxenite or dunite, is prominent in most of these. Among all these deposits, the Parker mica mine, located near Notre-Dame-du-Laus, Quebec (46◦ 05.5’ N, 75◦ 39.7’ W), is among the rare ones which display strikingly euhedral crystals of black spinel associated with dunite. The isolated crystals of spinel are found in a matrix of white to pinkish calcite, along with euhedral forsterite, phlogopite, and apatite [3]. We have characterized one sample of green rock in detail It consists mostly of an accumulation of magnesian olivine (∼65 vol %) and spinel crystals.
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