Petrology, Geochemistry and Structure of the Late Intrusives of the Jaffray-Melick Area, North Western Ontario.

Abstract

<p> Crosscutting all of the major lithologies of the Jaffray-Melick area are numerous sharply discordant late synkinematic and post kinematic minor intrusions. In terms of field relationships, petrography and geochemistry, these intrusions may be subdivided into four main Groups: Group 1 Undeformed suite of microgranites, layered pegmatitic-microgranitic mixed intrusives and granite pegmatites. </p> <p> Group 2 Deformed suite of microgranites, mixed intrusives and pegmatites very similar to the above Group 1. </p> <p> Group 3 Deformed microgranodioritic to microgranitic intrusives temporally associated with the Group 2 suite. </p> <p> Group 4 Deformed microgranodioritic intrusions which are chemicaly and morphologicaly distinct from the above 3 Groups. </p> <p> The form of the intrusives is usually dike like, as they commonly intrude along preformed joint surfaces. Analysis of the orientation of these surfaces for the undeformed Group 1 dikes combined with observations on dike distribution suggests that the emplacement of the dikes was controlled by structures developed by intrusion of the elliptical Dalles body. </p> <p> Comparison of the geochemical data on the late intrusives with analyses of one phase of the Dalles intrusion, suggests that the source melt for the Groups 1-3 dikes was a residual phase of the large Dalles body. The chemical differences between these groups, which are not large, could have developed due to polybaric fractionation of the residual phase induced by rapid pressure loss associated with the emplacement of the dikes. </p> <p> Once expelled from source area, the undersaturated, granitic melt became strongly enriched in volatiles due to a process of along dike accretional crystallization. In this way the pegmatite intimately associated with the microgranites was formed. </p> <p> Fig. 1 Groups 1 and 2 dikes on outcrop. </p>