Located in Humboldt County, Nevada, USA, with easy access.

Folded sedimentary rocks of early Paleozoic age, a small intrusive igneous body of uncertain age, Tertiary volcanic rocks, and Tertiary and Quaternary gravels occur in the district.

The sedimentary rocks consist of feldspathic graywacke and feldspathic quartzite, feldspathic pebble conglomerate, shale, and calcareous shale of the Harmony formation. The Harmony formation has been tentatively assigned a Mississippian age by Ferguson and others (2) , but recent work in the Os­ good Mountains quadrangle by the authors ( 3) indicates that the formation is at least in part Late Cambrian.

These sedimentary rocks have been strongly folded into a series of recum­ bent folds. The major folds arc all overturned to the west, but some smaller folds are overturned to the east.

The Harmony formation has been intruded by a small granodiorite stock, which has produced an irregular contact-metamorphic aureole extending for a maximum distance of about 500 feet. Shale and calcareous shale have been converted to hornfels, and the sandstone and grit beds show local silicification and induration.

Basaltic andesite of Tertiary age overlies the Harmony formation with an angular unconformity. The basaltic andesite is evidently younger than the granodiorite rock because the basaltic andesite shows no effect of the meta­ morphism that accompanied the igneous intrusion or the hydrothermal altera­ tion believed to be a late stage of the intrusive activity.

Unconsolidated gravels of two different ages are found within the area. The oldest gravel occurs as isolated patches-too small to be shown on the geologic map-resting on the Harmony formation and overlain in places by basaltic andesite. It consists of well-rounded pebbles, cobbles, and boulders of Harmony conglomerate and graywacke ; and clean, fine-grained quartzite, unlike any rock that is exposed in the area. The gravel represents channel fillings of a pre-basaltic andesite drainage system. These gravels have been extensively prospected for placer gold, but no values in gold have as yet been reported. The younger gravels occur in the bottoms of the canyons, on the alluvial fans, and as slope wash on the sides of the canyons. They consist of rounded pebbles, cobbles, and boulders of basaltic andesite, granodiorite, and rocks derived from the Harmony formation.

-Economic Geology, Nov. 1955, authored by Ronald Willden and Preston E. Hotz

Significant amounts of gold, scheelite, and cinnabar are present in a placer deposit in the Dutch Flat mining district, on the west slope of the southern end of the Hot Springs Range, Humbolt County, Nev. ( Fig. 1). The district is about 18 miles northeast of Winnemucca and 14 miles north of Golconda and consists of 20 lode claims and 160 acres of placer gravels wholly owned by Dulcia Flat Mines, Inc. The claims are explored by 10 small mines with an aggregate of 4.000 feet of underground workings, and in addition many shallow prospect pits and short adits.

Placer gold was discovered in the area by F. G. Wendell in 1893 (7), and most of the mines and prospects are probably the result of subsequent search for lode deposits. Cinnabar was probably noted in the early placer operations, but it was not discovered in place until 1939. The present Dutch Flat mine was developed on this cinnabar showing. The original discovery of scheelite is unknown, but scheelite was recovered along with cinnabar and gold in the operation of a small washing plant in 1952.

The only published production figures available for the district are those given by Vanderburg (7) and Smith and Vanderburg (6) for placer gold production, and those given by Bailey and Phoenix ( 1) for lode quicksilver. Gold production in the first year after discovery amounted to about $75,000 ; and Vanderburg states that the total placer gold production in the district has been worth about $200,000, nearly all of which was recovered by working with rockers ( 7). According to Bailey and Phoenix ( 1), the Dutch Flat mine produced 70 flasks of mercury to the end of 1942. Mercury production since the end of 1942 has amounted to Jess than 2 flasks a year from the Dutch Flat mine.'

-Economic Geology, Nov. 1955, authored by Ronald Willden and Preston E. Hotz