Detailed mapping and reevaluation of biostratigraphic data provide new insights into the regional stratigraphic significance of the Ordovician Comus Formation at its type locality at Iron Point, Edna Mountain, Humboldt County, Nevada. Mapping of the internal stratigraphy of the Comus Formation yielded six new subunits and a previously unrecognized formation that is potentially correlative to the Middle Ordovician Eureka Quartzite. The age designation of the Comus Formation was reexamined, using the most current understanding of Ordovician graptolite biostratigraphy. The species of graptolites found in the Comus strata at Iron Point are Late Ordovician, in contrast to the Middle Ordovician age assignment in previous studies. Structural analyses using the new detailed mapping revealed six deformational events at Iron Point. The first fold set, F 1 , is west-vergent and likely correlative to mid-Pennsylvanian folds observed nearby at Edna Mountain. The second fold set, F 2 , records north–south contraction and is likely correlative to Early Permian folds observed at Edna Mountain. The King fault is a normal fault that strikes north and dips east. It truncates the F 1 and F 2 fold sets and has not been active since the Early Permian. The Silver Coin thrust strikes east, places the Ordovician Vinini Formation over the Comus Formation, truncates the King fault, and is not affected by the F 1 and F 2 fold sets. Timing of the Silver Coin thrust is unknown, but it is likely post-Early Permian based on crosscutting relationships. The West fault strikes southeast and dips southwest. It truncates the Silver Coin thrust on the west, and the fault surface records several phases of motion. Finally, Iron Point is bounded on the east side by the Pumpernickel fault, a normal fault that strikes north and dips east. The movement on this structure is likely related to Miocene to Recent Basin and Range faulting. Several key findings resulted from this detailed study of the Ordovician rocks at Iron Point. (1) Based on detailed mapping of the internal stratigraphy of the Comus Formation at Iron Point, it is here interpreted to be correlative with the autochthonous Late Ordovician Hanson Creek Formation rather than the well-known “Comus Formation” that hosts Carlin-style gold mineralization in the Osgood Mountains to the north. (2) The Comus Formation at Iron Point is autochthonous, and the Roberts Mountains thrust is not present at Iron Point, either at the surface or in the subsurface. (3) The stratigraphic mismatch between Iron Point and Edna Mountain requires a fault with significant lateral offset between the two areas; its current expression could be the West fault. (4) West- and southwest-vergent structures at Iron Point and Edna Mountain are rotated counterclockwise relative to northwest-vergent structures at Carlin Canyon and elsewhere in northern Nevada. This relationship is consistent with large-scale sinistral slip along the continental margin to the west.

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Abstract HU0.0: I80 EXIT 194 GOLCONDA. At the top of the off ramp, turn north (left). Proceed 0.1 mi to the stop sign at the junction with SR789. County mileposts begin here. Turn east (right) on SR789. Steam from active hot springs can sometimes be seen on the north and northeast sides of the town of Golconda. The springs range from 109° to 165°F, are anomalously radioactive, and are actively depositing travertine ( Garside and Schilling, 1979 ). Metals in the spring waters include As (0.02 ppm), Cu (0.05 ppm), Li (0.36 ppm), Mn (0.10 ppm), and Hg (0.0001 ppm). The gravel road to the south at the Interstate off ramp leads to the Adelaide mining district. The district was discovered in 1866 and has intermittently produced small amounts of gold, silver, lead, zinc, copper, tungsten, and manganese. Total gold production has been approximately 40,000 oz. About 25,000 oz of gold were recovered during 1897–1910 from the Adelaide mine (copper-gold skarn), and about 10,000 oz were produced during the 1930–1940s and 1990–1991 at the Adelaide Crown mine (quartz-adularia veins). The ore occurred in three banded cryptocrystalline to chal-cedonic quartz veins, the Crown, the Recovery, and the Margharita. These veins averaged 30 ft in width. The remainder of the gold was recovered from placers mostly in the very early days. The original Adelaide mine was once owned by President Herbert Hoover. Franco-Nevada Mining Corporation is the major property owner in the district (Pete Maciulaites, pers. commun., 2000).

Abstract The Golconda Group was deposited during the early to middle Chesterian, a time of transition in the Mississippian from when conditions favored ooid formation (Valmeyeran) to when conditions were unfavorable (late Chesterian). As a result, the Golconda is one of the youngest Chesterian carbonate units in the Illinois basin containing abundant ooids. Oolitic limestone is common along the western, southern, and eastern margins of the basin. Elsewhere, oolitic deposits are more sporadic and thin. The presence of a positive area (i.e., the Ozark dome) in Missouri induced conditions appropriate to ooid formation in the southwestern part of the basin. Antecedent topography formed by bioaccumulation also favored oolite deposition. Terrigenous influx and storm activity tended to discourage ooid formation. Although there are similarities between Valmeyeran and Chesterian oolite characteristics, notable differences exist.

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