Molybdenite in matrix (Henderson Orebody, Red Mountain Complex, Oligocene; Henderson Mine, Colorado, USA) 3

Molybdenite in matrix from the Oligocene of Colorado, USA.

A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 6100 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.

The sulfide minerals contain one or more sulfide anions (S-2). The sulfides are usually considered together with the arsenide minerals, the sulfarsenide minerals, and the telluride minerals. Many sulfides are economically significant, as they occur commonly in ores. The metals that combine with S-2 are mainly Fe, Cu, Ni, Ag, etc. Most sulfides have a metallic luster, are moderately soft, and are noticeably heavy for their size. These minerals will not form in the presence of free oxygen. Under an oxygen-rich atmosphere, sulfide minerals tend to chemically weather to various oxide and hydroxide minerals.

Molybdenite is a molybdenum sulfide mineral (MoS2). It has hexagonal crystals, metallic luster, a silvery-gray color, and a dark gray streak. It is fairly soft (H=2) and has one cleavage plane. Molybdenite is especially distinctive in being flexible - thin scales or plates of molybdenite will easily bend but won't snap back into shape as biotite or muscovite mica do.

Molybdenite is nearly identical to graphite (C) in its physical characteristics (see: www.flickr.com/photos/jsjgeology/sets/72157650963514503). Graphite is a principally a metamorphic mineral. Molybdenite is usually an igneous mineral, occurring in hydrothermal veins and pegmatites. It also occurs in some contact metamorphic rocks (skarns - www.flickr.com/photos/jsjgeology/sets/72157646562268189).

The molybdenite-bearing specimen seen here is from the Henderson Mine in the Colorado Mineral Belt. The Henderson Mine targets a significant molybdenum ore body in an Oligocene-aged, subvolcanic, felsic intrusive complex. Molybdenite in the host rocks occurs in veins, veinlets, and as small, disseminated masses.

Geologic unit: Henderson Orebody, Urad-Henderson Porphyry Molybdenum Deposit, Red Mountain Complex (Red Mountain Intrusive Center / Red Mountain Intrusive Suite), Oligocene, ~27-30 Ma

Locality: Henderson Mine, Dailey-Jones Pass Mining District, west of Empire, northwestern Clear Creek County, Front Range of the Rocky Mountains, north-central Colorado, USA (~39° 45' 30.79" North latitude, 105° 50' 24.21" West longitude) (see: www.mindat.org/loc-6086.html)
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Site-specific info. from:
Wallace et al. (1978) - Geology of the Urad and Henderson Molybdenite Deposits, Clear Creek County, Colorado, with a section on a comparison of these deposits with those at Climax, Colorado. Economic Geology 73: 325-368.

Shannon et al. (2004) - Surface and underground geology of the world-class Henderson molybdenum porphyry mine, Colorado. Geological Society of America Field Guide 5: 207-218.

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Taken on: December 18, 2024

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Oligocene

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Sets appears in: • Colorado Rocks, Minerals, Fossils • Oligocene Rocks & Fossils more » • Minerals - Sulfides (Molybdenite) « less

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