THE GEOLOGY AND GEOCHEMISTRY OF THE ARCHEAN FLAVRIAN PLUTON, NORANDA, QUEBEC

The composite Flavrian pluton is the west part of an intrusive complex which is emplaced in and is partially coeval with Blake River Group volcanic rocks in Noranda. The pluton's intrusive sequence is summarized as follows: an extensive diorite sill, volumetrically minor porphyritic rhyolite, the polyphase albite granite, Eldrich diorite dikes, the Lac Flavrian plagiogranite, the St. Jude plagiogranite and breccia, and late diorite. The plagiogranites were coeval with the Lac Dufault granodiorite to the east. (delta)D and (delta)('18)O results indicate that the landmass above the Flavrian emerged above sealevel prior to the emplacement of the plagiogranites. A significant component of metamorphic fluid, in addition to subordinate seawater, was associated with the later stages of alteration and metal concentration.;Seawater alteration of diorite, tonalite, and andesite overlying the albite granite caused pervasive albitization, Cu-Zn leaching, a lightening of (delta)('18)O(,wr) to +2.9 (+OR-) 1.5%, and other chemical changes. The albite granite intruded these altered rocks, and was itself (delta)('18)O-depleted and pervasively altered to albite-quartz-epidote-chlorite by seawater wihch had evolved to somewhat higher Ca:Na ratios. The dehydration of low-(delta)D, Fe-rich chlorites in the aureole contributed to (delta)D depletion of the evolved seawater to calculated values of -42%.;The early diorite recrystallized within the albite granite aureole to form widespread tonalitic rocks. These rocks are essentially ferroactinolitic hornblende-plagioclase (Ab(,90))-quartz. Heterogeneous tonalite occurs along the granite contact; its upper margin with massive tonalite is an assimilative front marked by a P(,2)O(,5) peak of 0.39%, a steep Zr-Y gradient, and the commencement of a decrease in CaO, MgO, and FeO toward the granite. The low, erratic Cr content of the albite granite is largely a consequence of tonalite incorporation.;In contrast, the alteration of the Lac Flavrian and that associated with Au occurrences in the pluton were mediated largely by meteoric water with (delta)('18)O = -1.7 to -2.8, (delta)D = -19. The Au occurrences formed at 180 to 210 C; peripheral alteration minerals include Fe-rich epidote (X(,pi) (TURNEQ) 0.34). CO(,2)-enriched metamorphic fluids with (delta)('18)O (TURNEQ) +6 were associated with the alteration of the St. Jude plagiogranite and breccia. Seawater, implicated in some coeval alteration, must have underlain the meteoric reservoir beneath the emergent area.