Northumberland Mine, Northumberland Mining District, Toquima Range, Nye County, Nevada, USAi

Regional Level Types
Northumberland Mine	Mine
Northumberland Mining District	Mining District
Toquima Range	Mountain Range
Nye County	County
Nevada	State
USA	Country

This mine has been operated intermittently since 1866 for silver, gold and barite.
Structure: Major thrust sheets have affected the rocks. A Jurassic granodioritic stock has domed the country rocks. Silicified horizons of the Pogonip group rocks have been extensively fractured and microfractured.

Alteration: silicification, sericitization, jasperoid, argillization

Tectonics: Northumberland caldera ring fracture zone

Commodity: Ore Materials: ruby silver, cerargyrite, arsenopyrite, free gold, scorodite Gangue Materials: quartz, jasperoid,sericite, barite

Deposit: There are 3 main veins at the deposit: Lady Cummings, Northumberland, and Detroit veins. Disseminated gold mineralization occurs largely in a carbonaceous shale bed near contact of granitic intrusive. Ore is present in both upper and lower plate rocks along thrust fault. Siltstone and limestone have been considerably replaced by jasperoid, which is locally hydrothermally brecciated. Late-stage veinlets contain coarse barite crystals. Ore is strongly altered, iron-oxide-stained, thin-bedded carbonaceous shale. On the west side of the canyon are highly altered, fractured volcanic rocks. Gold occurs in microfracture fillings of quartz and barite in silicified horizons of the Ordovician Pogonip Group associated with the margins of a monzonite intrusive. Disseminated gold mineralization occurs largely in a carbonaceous shale bed near the contact with a granitic intrusive. Ore is present in both upper and lower plate rocks along a thrust fault. Siltstone and limestone have been considerably replaced by jasperoid, which is locally hydrothermally brecciated. Late stage veinlets contain coarse barite crystals.

Deposit type: Carbonate-hosted Au-Ag

Development: The silver deposits were discovered in 1866 and the Monitor-Blue Bell ore was treated at a 10-stamp mill at a spring in West Northumberland Canyon, now marked by stone ruins. Sporadic silver mining continued until 1891. Gold was discovered just east of the old silver workings in 1936 and the Northumberland Mining Co was operating from 1939 until 1942 when the gold mine was closed. Gold exploration was resumed in the 1960s by Homestake , Idaho Mining Co., and others in the 1970s resulting in the mining of the low-grade gold deposit in 1981, first by Amoco (later Cyprus Minerals), with mining continuing off and on to the present at the rate of 3000 tpd heap leached ore. Standard Oil Co. spun off Cyprus in 1985. Newmont drilled seven widely spaced holes on the property in 1989 to test targets in Tertiary volcanic tuffs and encountered shallow oxide gold mineralization. In 2003, the NewWest Resources Group's Nevada Western Gold Corporation announced that Newmont Mining Corporation had signed a joint venture agreement for the exploration and development of its Northumberland project. Newmont would be pursuing its exploration program at Northumberland and was embarking on a drilling program in 2004.

Geology: Disseminated gold mineralization occurs largely in a carbonaceous shale bed near the contact with a granitic intrusive. Ore is present in both upper and lower plate rocks along a thrust fault. Siltstone and limestone have been considerably replaced by jasperoid, which is locally hydrothermally brecciated. Late stage veinlets contain coarse barite crystals.

Ore(s): Ore is in and adjacent to a thrust fault separating lower plate Roberts Mtn Fm from upper plate Vinini Fm. Calcareous argillite bed is intruded by felsitic porphyry dikes.

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Link to USGS MRDS:	10310362

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References