The Richardson District is characterized by gentle slopes and broad, alluvium-filled valleys (Prindle and Katz, 1913). The area is unglaciated and largely overlain by windblown silt, sand, and loess, locally up to 50 meters thick (Foster and others, 1979). The rocks consist of three structure-bounded units (Weber and others, 1978; Swainbank and others, 1984; Noyes and others, 2006; Freeman, 2011). There is a core that consists mainly of biotite-hornblende-feldspar-quartz gneiss and lesser amphibolite, quartzite, marble and calc-silicate hornfels. The core is bounded on the north and south by amphibolite-grade pelitic schist. The contacts between the units are probably low-angle faults; north-trending vertical faults occur widely. Weber and others (1978) assign the pre-metamorphic age of the rocks to the Precambrian or Paleozoic. They were metamorphosed in the Middle to Late Devonian and recrystallized in the Early Cretaceous (Dusel-Bacon and others, 2004; Freeman, 2011). The metamorphic rocks are intruded by 90 Ma, felsic to intermediate dikes and plugs, notable the quartz-feldspar porphyry dike at the nearby Democrat Mine (BD014).
The Junction prospect was discovered in 1991 by searching for the source of anomalous stream sediment and panned concentrate samples collected during a regional geochemical study done by the Tri-Valley Corporation and TSNIGRI of the Russian Ministry of Geology (Vartanyan, 1992; Freeman, 2011). Half of the samples from streams draining the north side of the Junction prospect had visible gold. The concentrates also had high contents of pyrite, ilmenite, tourmaline, magnetite, and biotite.The country rocks at the prospect consist of quartz-muscovite schist and quartz-feldspar-biotite schist cut by east-trending, steeply-dipping, quartz-feldspar porphyry dikes 100 to 250 meters thick, similar to those at the nearby Democrat Mine (BD014). The mineralization consists of closely-spaced quartz and quartz-pyrite veinlets in the dike. Talus boulders up to 0.3 meter in diameter consist of druzy to coarsely-crystalline quartz with fine-grained silver-lead-bismuth minerals. Weak to intense, greisen-like, quartz-muscovite-sericite alteration is notable in and at the margin of the quartz-feldspar-porphyry dike but does not extend far into the country rock. Twenty-eight samples contained from less than 5 to 307 parts per billion gold, from l 0.2 to 41.1 parts per million (ppm) silver, 14 to 710 ppm arsenic, less than 5 to 76 ppm bismuth, 9 to 4,500 ppm lead, less than 5 to 54 ppm antimony, and 3 to 171 ppm zinc.