MOLYBDENUM AND TUNGSTEN DEPOSITS IN SOUTHERN NEWFOUNDLAND: GRANOPHILE MINERALIZATION LINKED TO NEOACADIAN MAGMATISM

Middle to late Devonian (385-374 Ma) granitoid plutons in southern Newfoundland are compositionally evolved, and are linked to diverse granophile mineralization, including Mo, W, Sn, F, Pb-Zn-Ag, Ba and possibly U. This paper reviews what is known about Mo and W mineralization, and draws attention to the potential of correlative suites elsewhere.

Molybdenum mineralization in the district falls into two main types. Disseminated but locally high-grade mineralization of "endocontact" type is exemplified by prospects in the ca. 378 Ma Ackley Granite, that are hosted by evolved alaskitic phases at or near the roof of the pluton. There is also evidence for "exocontact" Mo mineralization in country rocks several km from contacts, where similar granites may lurk in the subsurface. Exocontact Mo-Cu mineralization within sheeted quartz vein systems is exemplified by a developing prospect near Grey River, which may have potential as a bulk-tonnage, low-grade porphyry-style deposit. The immediate host rocks are syntectonic megacrystic granites of probable Silurian age, but mineralization is likely connected to younger leucogranite dykes that contain disseminated syngenetic Mo. These are believed to be offshoots from a buried Devonian (?) Pluton. Tungsten mineralization is also known in the Grey River area, where two mineralized quartz veins within a more extensive swarm define a small, high-grade wolframite deposit. The genetic relationship between the W-bearing veins and nearby Mo mineralization is not known, but a common link to a buried pluton is suspected. Similar models may apply to other Mo-W bearing sheeted vein systems in south-central Newfoundland. Skarn-type mineralization is uncommon, but scheelite-bearing calcsilicate rocks in central Newfoundland may be of this type, and are perhaps linked to nearby plutonic suites.

Southern Newfoundland demonstrates that late-stage, evolved, plutonic rocks associated with the NeoAcadian event have metallogenic promise, and provide interesting avenues for applied geoscience research. These specialized plutons are one small part of a wider European and north American magmatic province that may merit more detailed exploration assessment for Mo, W and other granophile commodities.