Aurihydrargyrumite, a Natural Au6Hg5 Phase from Japan

Abstract

Aurihydrargyrumite, a natural Au6Hg5 phase, was found in Iyoki, Uchiko, Ehime Prefecture, Shikoku Island, Japan. Aurihydrargyrumite with a metallic silver luster occurs as a submicron- to 2 μm-thick layer on the outermost surface of the placer gold. A prismatic face may be formed by {001} and {100} or {110}. The streak is also silver white and its Mohs hardness value is ca. 2.5. Its tenacity is ductile and malleable, and its density, as calculated based on the empirical formula and powder unit-cell data, is 16.86 g·cm−3. The empirical formula of aurihydrargyrumite, on the basis of 11 Au + Hg, is Au5.95Hg5.05. Aurihydrargyrumite is hexagonal, P63/mcm, with the lattice parameters a = 6.9960(10) Å, c = 10.154(2) Å and V = 430.40(15) Å3, which is identical with the synthetic Au6Hg5 phase. The seven strongest lines in the powder X-ray diffraction (XRD) pattern [d in Å(I/I0)(hkl)] were 2.877(29)(112), 2.434(42)(113), 2.337(100)(104), 2.234(87)(211), 1.401(39)(314), 1.301(41)(404), and 1.225(65)(217). Aurihydrargyrumite forms through the weathering of mercury-bearing placer gold by involvement of self-electrorefining. This new mineral has been approved by the IMA-CNMNC (2017-003) and it is named for its composition, being a natural amalgam of gold (Latin: aurum) and mercury (Latin: hydrargyrum).

Minakawaite and platinum–group minerals in the placer from the clinopyroxenite area in serpentinite mélange of Kurosegawa belt, Kumamoto Prefecture, Japan

“…Many PGM deposits have since been developed as placer deposits only in Hokkaido (Suzuki, 1950). Although we have confirmed the occurrence of the PGM placer from Oda River in Ehime Prefecture (Nishio-Hamane et al, 2018), PGM placers from outside Hokkai-do are quite rare (Suzuki, 1950). Hokkaido PGM mainly occurs as the alloy of the iridium-subgroup platinumgroup elements (IPGE: Ru, Os, and Ir), and new minerals rutheniridosmine (Ir,Os,Ru) and native ruthenium (Ru) were found as placers (Aoyama, 1936;Urashima et al, 1974;Harris and Cabri, 1991).…”

Structural and chemical study of weishanite, (Au,Ag,Hg), from the Keystone mine, Colorado, USA.

“…Finally, an interesting note concerns the possible ordering of atoms in Au–Ag–Hg compounds. Moschellandsbergite (Ag 2 Hg 3 ; Berman and Harcourt, 1938), luanheite (Ag 3 Hg; Dianxin et al , 1984), and the recent aurihydrargyrumite (Au 6 Hg 5 ; Nishio-Hamane and Minakawa, 2017), exhibit unit-cell values indicating ordered superstructures of the ideal cubic cell of ~4 Å. In particular, in synthetic Ag 2 Hg 3 (Fairhurst and Cohen, 1972), Ag and Hg occupy distinct positions.…”

Gold particles from Kamchatka: A brief look at gold biogeochemical cycling in a distinct environment

“…Some placer gold particles can contain trace levels of mercury, which is indicative of their primary origin (Reith et al , 2010). Additionally, aurihydrargyrumite (Au 6 Hg 5 ) has been detected on the surface of some placer gold particles (Nishio-Hamane et al , 2018). It has been suggested that, in natural environments, the formation of this gold–mercury phase is analogous to how gold-enriched rims develop on particles.…”

“…It has been suggested that, in natural environments, the formation of this gold–mercury phase is analogous to how gold-enriched rims develop on particles. Briefly, gold and mercury are dissolved from the particle surface but are immediately re-precipitated back onto the surface via self-electrorefining and forming aurihydrargyrumite (Nishio-Hamane et al , 2018). Therefore, it is possible that some mercury-bearing placer particles from Kamchatka could contain coatings of aurihydrargyrumite.…”