STRUCTURAL CONTROLS ON GOLD MINERALIZATION AT THE ROCK CREEK DEPOSIT, NOME, ALASKA: IMPLICATIONS FOR MIDDLE CRETACEOUS LODE EMPLACEMENT ON THE SOUTHWEST SEWARD PENINSULA

Gold mineralization at the Rock Creek deposit near Nome, Alaska is hosted by ~110 Ma mesothermal low-sulfide quartz-carbonate veins infilling extension fractures and brittle shear zones. Three quartz-dominated vein sets are associated with gold mineralization. Sub-horizontal veins define an early, volumetrically minor set. Vertical, northeast striking extension veins define a dominant sheeted complex. These veins strike parallel to the trend of striations on coeval low-angle faults, evidence that the veins formed during local northeast-southwest contraction. Late-stage extension veins strike ENE to east and appear coincident with emplacement of vertical northeast striking shear veins associated with the Albion Shear Zone, a 50 meter wide fault zone with dextral slip. A series of post-mineralization, northwest striking normal faults down-drop the Rock Creek deposit to the northeast.

Auriferous northeast striking sheeted veins are not restricted to Rock Creek, but also occur at multiple prospects throughout the Nome Mining District, suggesting that structural controls on lode gold formation were regional in nature. A new model involving regional northeast-southwest contraction is proposed to explain lode emplacement at Rock Creek and throughout the southwest Seward Peninsula. In this model two orthogonal sets of mineralized extension veins and faults, one northeast striking (including Rock Creek and Mt. Distin) and the other northwest striking (including Big Hurrah), are kinematically related to flexural slip folding of Nome Complex rocks during northeast to east vergent folding and thrusting during the middle Cretaceous (100-115 Ma).