MP 5: GAC Hutchison Medallist Lecture Tour 2004-05

Structural thinking: a key to mineral deposit studies in deformed terrain
by Shoufa Lin.

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Abstract

Structural geology has played and will continue to play a key role in mineral deposit studies and mineral exploration in deformed terrain. Many mineral deposits are structurally controlled, both at the regional and deposit scales. The ore bodies and/or the host rocks are often deformed, whether the deposits were originally structurally controlled or not. Structural study is necessary for understanding the current geometry and the kinematic history, for restoring the geometry and thus the spatial relationships among different lithological units/structures at different stages of the geological history (in particular at the time of mineralization), and for understanding the relationships among various geological events (e.g. alteration/mineralization, deformation, sedimentation, metamorphism, magmatism, etc.). All these will help to understand the genesis of the deposits concerned and identify favourable locations for mineralization. In this talk, these general points are discussed using examples from various parts of Canada. Special attention is paid to two gold deposits in the Archean Superior Province: the Henderson Island deposit in Manitoba and the Hemlo deposit in Ontario. At the Henderson Island deposit, mineralization occurred very late in the deformation history and after peak metamorphism, and gold-bearing quartz veins was controlled by a late brittle-ductile shear zone that cuts at a high angle across the main structural trend in the hosting greenstone belt. In addition, there is evidence that gold mineralization post-dated the emplacement of the hosting quartz veins, possibly by as much as 30 m.y. At the Hemlo deposit, mineralization occurred relatively early in the deformation history and before peak metamorphism. The deposit is spatially associated with, and probably controlled by a shear zone that is parallel to the dominant structural trend in the hosting greenstone belt. Both the ore body and the host rocks are strongly deformed by multiple generations of deformation. A better understanding of the structural and stratigraphic setting and timing relationships leads to the suggestion that the deposit is shear zone-controlled with a magmatic source for mineralization fluids. It is emphasized that the key to the success of a project in a deformed terrain is a multidisciplinary approach spear-headed by structural geology.

CD-ROM Disc (2005)
Geological Association of Canada; ISBN-13: 978-1-897095-27-0; ISSN: 1706-936X

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