Mercury deposits of western California: an overview

Abstract

Summary. Mercury deposits in western California are near a thrust fault that separates two groups of Mesozoic rocks. The Franciscan Assemblage, a metamorphosed melange with serpentine and graywacke, is structurally overlain by the Great Valley Sequence, a sedimentary series resting on oceanic crust. These Mesozoic rocks are partly covered by volcanic and sedimentary rocks of Cenozoic age. Cinnabar with silica minerals, dolomite, native mercury, and bituminous matter occurs around the fractured margins of serpentine bodies and around hot springs that emanate from the Franciscan Assemblage. Fluid inclusions and hot springs suggest that cinnabar precipitated from CO2-H20 fluids with < 2 wt% chlorine at T < 250 °C. Prograde metamorphism of Mesozoic sediments expulsed mercury-bearing fluids that migrated up serpentine-related fractures and exhaled onto the surface.

Mercury (Hg) mineral evolution: A mineralogical record of supercontinent assembly, changing ocean geochemistry, and the emerging terrestrial biosphere

“…Most notably, mindat.org records more than 300 separate mercury mines, prospects, dumps, placers, and other localized Hg mineral sites associated with the Pliocene to Recent (5.3 to 0 Ma) hydrothermal systems of west-central California. This important mining district, including the New Almadén mine in Santa Clara County and the New Idria mine in San Benito County (two of the world's largest mercury producers), represents a single mineralized province with ages restricted to the last 5.3 million years (Bailey 1962;White 1981;Studemeister 1984;Varekamp and Buseck 1984;Barnes 1997;Smith et al 2008). Similarly, hundreds of separate localities in southwest Alaska (Szumigala 1996), central Arizona (Eastoe et al 1990), west Texas (Thompson 1954Henry et al 1997), and southwest Utah (Cunningham et al 1982), as well as clusters of localities in many countries, represent individual mineralized districts.…”

A Paleozoic mercury mineralisation event in South China: In situ U-Pb dating and chemical compositions of calcite from the Jianyan Hg deposit

“…Representative examples include the Wanshan Hg, Huayuan Pb-Zn, and Dazhuyuan Ba-F deposits (Figure 1; Wang et al, 2010;Hu et al, 2017;Zou et al, 2022). These deposits are poorly dated because of the simple mineral paragenesis comprising sulphides associated with calcite/dolomite, barite, fluorite, and rare quartz, and because of the low contents of radiogenic elements (Studemeister, 1984;Luo et al, 2020). Reported ages include a Rb-Sr age of 431±24 Ma for sphalerite from the Aozigang Pb-Zn deposit (Cao et al, 2015), Sm-Nd age of 364±24 Ma for calcite from the Luanyantang Hg deposit (Wang and Wen, 2015), and Rb-Sr age of 492±37 Ma for fluid inclusions hosted in quartz from the Pingqiu Au deposit (Hu et al, 2007).…”

Fluid inclusion study of the Horní Luby cinnabar deposit, Saxothuringian Zone, Bohemian Massif: clues for the metamorphic remobilization of mercury

“…Akçay et al 2006;Martín-Izard et al 2009) and ii) epithermal deposits like the silica-carbonate deposits formed during hydrothermal alteration and replacement of serpentinite bodies (< 5.3 Ma in age; New Almadén and New Idria in California, USA; e.g. Studemeister 1984;Smith et al 2008), as well as numerous hot-spring mercury deposits worldwide (e.g. White 1981; Hampton et al 2004).…”