Petrogenesis of the Precambrian Rocks in the Hanson Lake Area, East-Central Saskatchewan
Precambrian rocks in the Hanson Lake area occur in two main groups. The first (Lower Group) consists of quartz dioritic rocks, migmatites, and agmatites which occur in two large anticlinal complexes. These rocks are overlain by and concordant with a complicated sequence of supracrustal rocks which comprise the second group (Upper Group). The basal part of the Upper Group is basaltic and the rest is made up of basaltic, andesitic, dacitic, and rhyolitic fragmental metavolcanic rocks, dacitic metalavas, calc-silicate rocks, and graywacke-type metasediments. Other rocks in the area include several bodies of intrusive granite, one of which has a mass of magnetite - amphibole - epidote ! rock associated with it, a body of metapyroxenite, and a number of apparently intrusive amphobolite bodies. Both beryliferous and non-beryliferous pegmatites are abundant and occur mainly within the rocks of the Lower Group. An interpretation of the petrogenesis, consistent with the available petrographic, structural, and chemical evidence (46 new chemical analyses are presented), suggests that the Upper and Lower Groups were originally parts of a conformable supracrustal sequence. The lower parts of the sequence (Lower Group) were migmatized, partially melted, and mobilized during a complicated orogenic cycle. Le prkcambrien de la rigion de Hanson Lake peut se diviser en deux groupes. Le premier (Groupe InfCrieur) comprend des diorites quartziques, des migmatites et des agmatites qui affleurent dans deux grands anticlinaux. Ces roches sont recouvertes de facon concordante par une sCquence complexe de roches supracrustales qui correspond au second groupe (Le Groupe Supkrieur). La base est basaltique, et le reste est fait de m6tavolcanites, andksitiques, dacitiques et rhyolitiques, de mktadacites, de roches calc-silicatees et de mCtasCdiments de type graywacke. En outre, on trouve dans la rkgion plusieurs granites, B l'un desquel est associCe une roche B magnitite, amphibole et Cpidote, un amas de mCtapyroxenolite, et un certain nombre d'amas d'amphibolites apparemment d'origine intrusive. Dans le Groupe Infkrieur on trouve des pegmatites avec ou sans beryl. Une interprktation de la pCtrogCnkse, conforme aux donnkes ~Ctrographiques, structurales et chimiques (46 analyses inkdites) suggkre que le Groupe SupCrieur et le Groupe Infkrieur faisaient partie d'une sCrie supracrustale continue. La partie infkrieure (Groupe Infkrieur) aurait Ctk migmatisee, partiellement fondue et mobilisCe au cours d'un cycle oroginique complexe.