The rocks in the area are part of the Yukon-Tanana Terrane of the northern Cordillera; they consist largely of late Paleozoic to Devonian medium- to high-grade metamorphic rocks that have been intruded by Cretaceous and Tertiary granitic stocks and batholiths (Baknes, 2008; Wilson and others, 1998). The metamorphic rocks are structurally complex with an older, middle to early Paleozoic and/or late Proterozoic unit that consists of gneiss, schist, quartzite, and amphibolite, and a younger, Mississippian and/or Devonian unit that consists largely of augen gneiss that locally forms domal structures. The metamorphic rocks are intruded by 55 Ma to 107 Ma, granitic plutons. The structure of the area is complex and difficult to determine because of poor exposure but several major thrust fault have been identified as well as a series of northeast-trending, northwest-dipping high-angle faults.
The dominant mineralization in the area and the target of most of the exploration are deposits related to Cretaceous intrusions, several classic examples being the Fort Knox Mine (FB115) near Fairbanks and the nearby Pogo Mine (BD033). These deposits are characterized by an association with moderately reduced, I- and S- type granitic intrusions and a lithophile, gold-bismuth-tungsten-arsenic-tellurium-molybdenum(-tin-copper-lead-antimony) suite of elements. The deposits vary from low-sulfide, sheeted or stockwork deposits in the intrusions to replacement deposits, veins, and stockworks in the country rock. The mineralization at the nearby Pogo deposit is the model used in exploring this and other prospect in the area. The mineralization at Pogo consists of thick gently-dipping quartz veins that grade laterally into pegmatite dikes related to 107 Ma syenite and monzonite intrusions. The quartz veins contain about 3 percent sulfides, mainly arsenopyrite, pyrite, pyrrhotite, loellingite, chalcopyrite, bismuthinite, native bismuth and native gold. The veins are associated with biotite alteration overprinted by sericite-dolomite-chlorite(-quartz) alteration, that extends into the country rock for several meters.
Soon after the recognition of nearby Pogo as a major and economically attractive deposit in 1998, Rimfire Minerals Corporation in conjunction with several joint-venture partners began work in the area and identified this deposit. In 2008, they entered into a joint venture with Rubicon Minerals Corporation and commissioned a thorough technical report on their properties in the Goodpaster District (Baknes, 2008), which is the source of most of the information on this prospect.The geochemical anomalies and mineralization at the Southeast Surf prospect are mainly in Devonian to Mississippian augen gneiss near a granitic stock. Few lineaments can be identified but they appears to trend consistently north and northeast. Two areas of mineralization have been identified at the surface. The Spur showing covers an area about 200 by 250 meters where numerous samples of granitic float contain vuggy quartz stockworks. The mineralized granite is altered to quartz, sericite, and dolomite, and some samples are intensely silicified. The quartz stockworks contain pyrite, arsenopyrite and traces of stibnite. Four samples contained 1,020 parts per billion (ppb) gold, 0.2 to 3.2 parts per million (ppm) silver, 1,385 to 6,730 ppm arsenic, less than 2 to 2 ppm bismuth, 2 to 32 ppm copper, and 6 to 970 ppm lead. At the Ol' Timer showing, strongly sericitized augen gneiss with quartz stockworks can be traced for 50 meters in talus. The quartz contains arsenopyrite, pyrite, and traces of stibnite. A sample contained 1,020 ppb gold, less than 0.2 ppm silver, 1,950 ppm arsenic, less than 2 ppm bismuth, 8 ppm antimony, 98 ppm antimony, and 20 ppm lead. No holes have been drilled at the Southeast Surf prospect.