DESCRIPTIVE MODEL OF SILICA-CARBONATE Hg

MODEL 27c

By James J. Rytuba

APPROXIMATE SYNONYM New Almaden type.

DESCRIPTION Cinnabar at contact of serpentine and siltstone-graywacke above subduction-related thrust.

GENERAL REFERENCE Bailey (1964).

GEOLOGICAL ENVIRONMENT

Rock Types Serpentine, siltstone-graywacke.

Age Range Tertiary.

Depositional Environment Serpentinized intrusive rocks (sills and dikes) into siltstone, and graywacke and siltstone, fractures in altered serpentine.

Tectonic Setting(s) Deposits occur in accreted terrane above subduction-related thrust fault.

Associated Deposit Types Stibnite veins.

DEPOSIT DESCRIPTION

Mineralogy Cinnabar, native Hg, other minor sulfides: pyrite, stibnite, chalcopyrite, sphalerite, galena, and bornite.

Texture/Structure Replacement and minor veins.

Alteration Replacement of serpentine by quartz and dolomite and minor hydrocarbons to form "silica-carbonate" rock.

Ore Controls Contact of serpentine with siltstone especially where contact forms antiform. Ore primarily in silica-carbonate rock.

Geochemical Signature Unknown, probably Hg + Sb + Cu + Zn.

EXAMPLES

New Almaden, USCA (Bailey, 1964)