Ellisite, Tl₃ AsS₃, a new mineral from the Carlin gold deposit, Nevada, and associated sulfide and sulfosalt minerals

Ellisite, Tl₃AsS₃, occurs with lorandite, getchellite, christite, realgar, and native arsenic as dispersed grains, and with realgar, lorandite, christite, and getchellite in small discontinuous patches, in mineralized laminated carbonaceous dolomite beds in the Carlin gold deposit, Nevada. The mineral is named for Dr. A. J. Ellis of the Chemistry Division, D.S.I.R., New Zealand. Ellisite is opaque, and the color is dark gray, streak is light brown with a tinge of orange, and luster on fresh surfaces is metallic but less bright than that of stibnite. The mineral is trigonal, hexagonal parameters a = 12.324(2), с = 9.647(2)A; cell volume = 1269.0(4)A³, Z = 7. The d values (A) of the strongest X-ray diffraction lines and their relative intensities are: 2.669 (100), 3.214 (53), 5.333 (37), 2.327 (28), and 3.559 (20). Ellisite shows excellent to good rhombohedral cleavage and hackly fracture. Vickers hardness measured with a 50-g load varied from 36.4−44.0 and averaged 39.3 kg mm ⁻², and with a 25-g load varied from 41.0−51.5 and averaged 45.9 kg mm⁻² (Mohs hardness, about 2). Density of synthetic Tl₃AsS₃ is 7.10(5) (meas) and 7.18 g cm⁻³ (calc). In reflected light the mineral is light gray with a distinct purple tint (light purplish-gray), very weakly bireflectant, ranging from light purplish-gray to light pinkish-gray, and anisotropic, with polarization colors blue-purple, red-purple, and brownish-orange; the mineral has a deep red to deep orange-red internal reflection. Reflectances (R) in air are: 650nm = 28.3, 589nm = 28.9, 546nm = 29.7, 470nm = 31.7. Electron microprobe analyses gave TI 78.2, As 9.6, S 12.3, sum 100.1 weight percent. Most abundant trace elements, determined by emission spectrographic analysis, are Sb (500 ppm) and Fe (200 ppm).

Disseminated assemblages include; the gold-pyrite-quartz in the ore bodies; the thallium-arsenic assemblage of ellisite-christite-lorandite-getchellite-realgar-native arsenic-quartz; the mercury assemblage of galkhaite-cinnabar-quartz; and the carlinite-pyrite-hydro-carbon-quartz assemblage. Vein mineral assemblages which crosscut rocks, ores, and disseminated zones include christite-lorandite-orpiment-realgar-barite-quartz, weissbergite-stib-nite-quartz, and frankdicksonite-quartz. Veins are distinct and separate from each other and postdate the ore and zones of disseminated sulfides. Gold ore bodies formed from solutions at temperatures between 160-180°C, but many minerals in late veins formed at temperatures above 200°C. Most of the disseminated sulfide and sulfosalt minerals probably formed during the late stages of the more moderate temperature event and the vein minerals were deposited from hotter fluids (200-300°C) in response to supersaturation caused by falling temperatures and pressures of the fluids during ascent.