geology of sulphide-facies iron-formations and associated rocks in the lower steel river-little steel lake area, terrace bay, ontario
abstract
the lower steel river - little steel lake area is located
about 25 km east of terrace bay, ontario. seventeen
iron-formations were investigated within this metamorphosed
archean volcanic and sedimentary terrain, which represents a
portion of the abitibi - wawa subprovince of the superior
structural province.
sulphide-facies iron-formations are the dominant chemical
sedimentary rocks in the schreiber - terrace bay area, and
represent deposition during quiescent periods in clastic
accumulation and in volcanic activity. the iron-formations
commonly mark contacts between the volcanic and sedimentary
rocks. they are interbedded with carbonaceous slates at the
base of sedimentary successions and overlain by de
turbidites. this suggests chemical sedimentation on a
subaqueous basinal plain slightly distal to an outer fan.
sulphide-facies iron-formations consist of a mixture of
chemical and clastic components, and while highly variable,
the iron-formations in the study area contain three commonly
recognizable units: 1) pyritic-carbonaceous slate; 2)
disseminated, massive, laminated and nodular pyrite; and 3)
chert or siliceous sedimentary rock. sedimentary textures
and structures combined with trace element abundances and
geochemical evidence support the mixing of clastic and
chemical components, and a hydrothermal source for the iron.
exhalative discharge probably occurred episodically as
moderate- to low-temperature solutions percolated through
near-surface pillowed volcanics and, once vented, deposited
a blanket of chemical sediment. vent-proximal deposits
include massive and layered pyrite; the domal and colloform
varieties support the existence of organic mats. the
presence of carbon is interpreted as a relic of the organic
activity. pyritic-carbonaceous slates consisting of
alternating chemical and clastic components represent
vent-distal deposits. radial structures within pyrite
nodules provide evidence of diagenetic transformation and
tectonic deformation.
structural evidence suggests that the study area was
affected by a complex folding event related to one
deformational episode, probably preceded by syn-sedimentary
slumping in some areas. the competency differences between
sedimentary and volcanic rocks, combined with the
fine-grained nature of the sedimentary rocks (de turbidites
and iron-formation ) at major volcanic-sedimentary contacts,
focussed deformation and dike emplacement in the contact
areas.
collections
- retrospective theses [1604]