Windy Fork

Windy Fork is an elongate peralkaline pluton located 85 miles south of the town of McGrath in west-central Alaska covering an area of ~55 km2. It is thought to be coeval with the Middle Fork complex located 8 km to the northwest. The pluton intrudes limestones, shales, and volcaniclastics of the Dillinger terrane of the southern Alaska Range which are recrystallised and silicified to varying degrees within the narrow 61 m contact zone. The main body of the pluton is composed almost wholly of riebeckite granite and minor riebeckite-biotite granite, the former containing perthite locally displaying schiller, riebeckite, grey quartz, and accessory pale-violet fluorite, apatite, non-metamict zircon, interstitial calcite, and rare allanite. Located in a crudely defined E-W zone are late-stage intrusive rocks distinguished by iron staining, composed of narrow, podiform, 3-6 m long pegmatite pods, limonitic biotite aplite, fine-grained riebeckite-biotite granite, and rhyolite. This zone exhibits higher radiometric response than the rest of the pluton, thought to be caused by heightened amounts of accessory allanite and monazite. Small-scale dykes crosscut the pluton composed of basalt, andesite porphyry, and aplite, with further dykes either radiating out or situated outside the main body ranging from rhyolite to pyroxenite. One 0.6 m wide agpaitic dyke has been identified bearing REE-poor eudialyte, cutting the main body able to be traced for 9 m. Further minerals identified in glaciofluvial outwash include ilmenite, chevkinite, kainosite, bastnaesite, thorite, and uranothorite. Geochemical data including whole rock major and trace element and CIPW norms, along with a resource estimation can be found in Barker (2016).