Kuskokwim basin
Tags: andesite basalt dyke granite granodiorite granodiorite porphyry lower cretaceous monzonite rhyolite sill upper cretaceous
Description:
The Kuskokwim basin is predominately underlain by the Upper Cretaceous Kuskokwim Group, a back-arc continental margin basin fill assemblage that formed in response to a change in the angle of convergence between the Kula oceanic plate and the Cretaceous North American continental margin. Sediments primarily consist of a coarse- to fine-grained turbidite comprising sandstone, siltstone, and shale with minor conglomerate.
Late Cretaceous and Early Tertiary volcano-plutonic complexes intrude and overlie the Kuskokwim Group sedimentary rocks. Volcanic components of these complexes consist of intermediate tuffs and flows. Subaerial volcanic tuffs, flows, and domes are regionally extensive and dominantly andesitic, locally include dacite, rhyolite, and basalt. Associated plutons are calc-alkaline in composition, ranging from monzonite to granodiorite. Felsic to intermediate hypabyssal granite to granodiorite porphyry dikes, sills, and plugs are also widely distributed and often intruded into northeast-striking extensional faults. Volumetrically minor Upper Cretaceous intermediate to mafic intrusive bodies are also common.
The centre of the Kuskokwim basin lies between two continental-scale, dextral slip-fault zones: the Denali-Farewell Fault system to the south and the Iditarod-Nixon Fork Fault system to the north. Fold-and-thrust-style deformation formed the earliest structures in response to subduction-related compression shortly after deposition of the Kuskokwim sediments. Eastward-trending folds and thrust faults are common in the central Kuskokwim basin, including the Donlin Creek area. Younger north–northeast-trending folds are dominant near the Iditarod-Nixon Fork Fault and Denali-Farewell Fault but also formed throughout the region in response to basin-scale dextral movement. Most of the folds predate emplacement of the volcano-plutonic complexes. Pre-, syn-, and post-(?) intrusion, northeast-striking normal and oblique slip faults formed during subsequent late compressional and extensional events and focused intrusive igneous rocks and hydrothermal systems across the basin.
Regional Geology of Central Kuskokwim Area:
Deposits
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Name: Donlin
Phase: Development
Mine Type: Pit
Intro:
USA, Alaska. The Donlin deposits are situated approximately 280 miles (450 km) west of Anchorage and 155 miles (250 km) northeast of Bethel up the Kuskokwim River. The closest village is the community of Crooked Creek, approximately 12 miles (20 km) to the south, on the Kuskokwim River.
The Donlin gold deposits lie in the central Kuskokwim basin of southwestern Alaska, and is a northeast-trending basin that subsided between a series of amalgamated terranes. Rocktypes within the basin include Mesozoic marine volcanic rocks, Palaeozoic clastic and carbonate rocks, and Proterozoic metamorphic rocks.
Mineralizations
No mineralizations available.
Placers
No placers available.