1967 - Phanerozoic Orogenic Gold Deposits: Concepts and Models. James Mortensen - University of British Columbia. Dave Craw - University of Otago.
1967 - Phanerozoic Orogenic Gold Deposits: Concepts and Models James Mortensen - University of British Columbia Dave Craw - University of Otago Doug MacKenzie - University of Otago Murray Allan - MDRU, U of British Columbia Robert Chapman - University of Leeds
Most published orogenic gold deposits (OGD) models are based heavily on world-class Precambrian deposits, many of which are interpreted to have a spatial and genetic association with crustal-scale, commonly terrane-bounding, transpressive fault zones. Numerous examples of multi-million ounce Phanerozoic OGDs exist, however, and results of recent studies suggest that many (perhaps most) Phanerozoic OGDs are not directly associated with crustal scale faults, but rather represent a broader range of mineralization styles than is described in published models. We redefine Phanerozoic OGDs into several sub-types within a broad spectrum of deposit styles, which differ in terms of tectonic setting, host rock lithologies, metal sources, vein styles, and possibly grade/tonnage potential. Although the same range of processes was responsible for the formation of most or all of these sub-types, this more refined classification of Phanerozoic OGDs provides an improved framework with which to understand and develop exploration strategies for such targets.
The proposed sub-types, with examples, are as follows: 1. Sierra Nevada Foothills type (Mother Lode Belt, Grass Valley, Alleghany, CA; Bridge River-Bralorne, BC; Juneau, AK) - vein arrays associated with major strike-slip fault zones; includes the only Phanerozoic deposits that closely resemble typical Archean OGDs 2. Otago type (Otago Schist Belt, NZ; Chugach Belt, AK) - dispersed vein arrays hosted by fore-arc clastic sedimentary sequences; metals derived from prograde metamorphism at deeper crustal levels; potential for large tonnage if associated with a substantial structure (e.g., Macraes) 3. Klondike type (Klondike, YT; Wells-Barkerville, BC) - widely distributed vein arrays; typically not associated with major structures; metals commonly locally derived so a strong lithological control on gold localization; locally high grade but mostly small 4. Slate belt type (Victoria, AU; Meguma, NS) – hosted by turbiditic sediments; classic saddle reef and related wing veins; veining can be very extensive and locally very high grade
