The Nanjan prospect area is underlain by an assemblage of undivided Mesozoic or Paleozoic metamorphosed sedimentary, volcanic, and intrusive rocks; and by a stock and dikes of Cretaceous granodiorite and quartz diorite (Berg and others, 1988, p. 21, 22). The undivided assemblage was regionally metamorphosed to amphibolite grade in middle or Late Cretaceous Cretaceous time, and locally remetamorphosed to hornblende hornfels near the contacts of some of the granodiorite and quartz diorite plutons. The prospect is situated on a prominent high-angle fault of unknown displacement that strikes north-northwest, along the valley of the unnamed creek that adjoins the property (Maas and others, 1995, fig. 70).
The Nanjan prospect consists of sparse nodules of pyrite and molybdenite in a quartz fissure vein that reportedly lies near the contact of hornblende granite and altered limestone (Maas and others, 1995, p. 268). The vein strikes between N40W and N20E and dips generally to the west. The vein is up to 8 feet thick, but probably averages less than 3 feet thick; it is exposed intermittently along strike for at least 1300 feet. Most of the molybdenite is associated with fault gouge that bounds the vein. The vein apparently is younger than most or all of the middle or Late Cretaceous regional metamorphism, but older than an episode of local(?) faulting.Molybdenite mineralization was discovered at the Nanjan property in about 1935, Workings in the 1930s included trenches, opencuts, test pits, and shafts, but little of the work was evident in 1992 (Maas and others, 1995). Samples collected by Maas and others (1995, p. 269) along the Nanjan vein revealed low precious- and base-metal values. The highest molybdenum analysis was 0.25% Mo in a selected sample, and 0.20% Mo across a 4-foot-wide section of the vein.