DESCRIPTIVE MODEL OF CLIMAX Mo DEPOSITS

MODEL 16

By Stephen D. Ludington

APPROXIMATE SYNONYM Granite molybdenite (Mutschler and others, 1981).

DESCRIPTION Stockwork of quartz and molybdenite associated with fluorite in

granite porphyry (see fig. 47).

Figure 47. Cartoon cross section of Climax Mo deposit showing relationship of ore and alteration zoning to porphyry intrusions from Mutschler and others (1981). Cartoon represents a region about 1 km wide.

GENERAL REFERENCE White and others (1981).

GEOLOGICAL ENVIRONMENT

Rock Types Granite-rhyolite with >75 percent SiO2. Rb, Y, Nb are high, Ba, Sr, Zr low. Stocks with radial dikes; small breccias common.

Textures Porphyry with fine- to medium-grained aplitic groundmass.

Age Range Examples are mainly mid-Tertiary.

Depositional Environment Multistage hypabyssal intrusions.

Tectonic Setting(s) Mainly extensional zones in cratons. May be related to subduction, but found far from continental margins in areas of thick crust, and late in the cycles.

Associated Deposit Types Ag-base-metal veins, fluorspar deposits. On the basis of similar geochemistry of associated rhyolite magmas, rhyolite-hosted Sn deposits may be a surface expression. Porphyry tungsten deposits, as at Mount Pleasant, Canada, may be W-rich Climax systems.

DEPOSIT DESCRIPTION

Mineralogy Molybdenite + quartz ± fluorite ± K-feldspar ± pyrite ± wolframite ± cassiterite ± topaz.

Texture/Structure Predominantly in veinlets and fractures; minor disseminations.

Alteration Intense quartz and quartz + K-feldspar veining in ore zone. Upper phyllic and propylitic zones. Halo of rhodochrosite, rhodonite, spessartine garnet. Minor greisen veins below ore body.

Ore Controls Stockwork ore zone draped over small, <1 km2 stocks. Multiple phases of intrusion and mineralization are highly favorable.

Weathering Yellow ferrimolybdite stains.

Geochemical Signature Mo, Sn, W and Rb anomalies close above ore zones. Pb, Zn, F, and U anomalies in wall rocks up to a few kilometers distant. Cu anomaly external to Mount Emmons deposit. In panned concentrates, Sn, W, Mo, and F may be important.

EXAMPLES

Redwell Basin, Winfield, Middle Mtn.

Climax, Henderson,

and Mt. Emmons, USCO (White and others, 1981)

Pine Grove, USUT (Abbott and Williams, 1981)

Mount Hope, USNV (Westra, 1982b)

Big Ben, USMT (Witkind, 1973)