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Geochemistry and potassium-argon ages of plutonic rocks in the Battle Mountain mining district, Lander County, Nevada

1973; United States Government Publishing Office; Linguagem: Inglês

10.3133/pp798a

2330-7102

Ted G. Theodore, Miles L. Silberman, D.W. Blake,

Geochemistry and Elemental Analysis

The Battle Mountain mining district is in Lander County, north-central Nevada, at the northwest end of the Eureka-Battle Mountain mineral belt.The district is underlain predominantly by lower to upper Paleozoic sedimentary rocks, which occur in three major thrust plates and an interjacent autochthonous tectonic block.These rocks were intruded by a single Cretaceous (87million years) pluton and subsequently by a large number of stocks and dikes in the Tertiary from 41 to 38 m.y.ago.Many of the intrusive rocks are inferred to have originally been granodiorites, now hydrothermally altered in varying degrees to more potassic K-feldspar-white mica-(biotite) assemblages.The altered plutons are chemically equivalent to quartz monzonites.These silicate alteration assemblages are commonly associated with economic sulfide deposits in the southern part of the district.In addition, increases in concentrations of Cu, Ag, Mo, and Rb in the intrusion at Copper Canyon during alteration followed increases of K20.At Copper Canyon, biotite K-Ar ages for an altered granodiorite associated with the nearby porphyry copper deposit average 38.22±0.23 m.y.The age of metallization in the porphyry copper deposit is 37.2o±O.Os m.y., as measured by wholerock K-Ar determinations.Hypogene sulfide veins that cut the intrusion establish the post-magmatic nature of most metallization.However, the measured 1-m.y.time interval between crystallization of coarse primary biotite and metallization may be a maximum value, resulting from the much finer grain size of the hydrothermal assemblage rather than from an actual age difference.During cooling of the ore, its retentivity of argon was probably less than that of the coarse primary biotites.