Some aspects of Archean structure and mineralization

The Michipicoten area of N.-central Ontario, one of numerous volcanic-sedimentary segments distributed across the Canadian Shield, represents an Archean composite favorable in composition, structure, size, and location for elucidation of certain structural and metallogenic problems. Detailed investigations of Michipicoten rocks have led to the following tentative conclusions: 1) undulating sectional fold patterns have resulted from the association of E.-W. primary folds and N.-S. cross folds; 2) younger, pre- or syntectonic granite of metasomatic derivation, conformably emplaced in the volcanic-sedimentary series, is concentrated along present anticlinal axes; 3) volcanic extrusives, subvolcanic intrusives, and associated mineral deposits are of common igneous derivation; 4) syngenetic and epigenetic mineral deposits are distributed along favorable volcanic source horizons, particularly in the vicinity of maximum explosive discharge; 5) Timiskaming-type sedimentary units, which represent contemporaneous erosional products of underlying volcanics, tend to be of local distribution only and are therefore of limited value for purposes of stratigraphic correlation across broad regions. By way of illustration, the conclusions are applied to a generalized, regional interpretation of Archean segments in the Superior-Timiskaming portion of the Shield, extending specifically from Lake Winnipeg on the W. to the Grenville "front" on the E. Major fold axes are located on the basis of established structural plunges, in conjunction with location of regional granite belts. On the basis of predominant mineral deposits, the segments may be grouped into an older Fe-Au province, extending from Red Lake on the W. to Kirkland Lake on the E., and a younger Au-Cu-Zn province extending eastward therefrom to the Grenville "front." It is suggested that mineral provinces reflect contrasting compositions of parental magmas from which mineral deposits and associated volcanics were derived. Geological data and interpretations are presented in order to stimulate thought and study along similar lines in other portions of the Shield.

This record provided courtesy of AGI/GeoRef.