Gold-bearing arsenian pyrite and marcasite and arsenopyrite from Carlin Trend gold deposits and laboratory synthesis

Abstract

Invisible gold in natural and synthetic arsenian pyrite and marcasite correlates with anomalous As content and Fe deficiency, and high contents of invisible gold in most natural and all synthetic arsenopyrite correlate with excess As and Fe deficiency. As-rich, Fe-deficient arsenopyrite synthesized hydrothermally contains up to 3.0 wt% Au uniformly distributed in growth zones of light backscattered electron contrast. At the Deep Star gold deposit, Carlin Trend, Nevada, the sulfide compositions apparently span the full range of metastability from FeSz to near FeAsS (40 at% S); arsenian pyrite contains up to 0.37 wt% Au, but arsenopyrite has excess S and is relatively Au poor. Observed minimum Fe contents are 29.1 at% in arsenian pyrite and marcasite from the Deep Star deposit and 31.3 at% in synthetic arsenopyrite. We suggest that invisible gold in arsenian pyrite and marcasite and arsenopyrite from sediment-hosted gold deposits represents Au removed from ore fluids by chemisorption at As-rich, Fe-deficient surface sites and incorporated into the solids in metastable solid solution. However, the oxidation state of invisible gold (Aua, AU1+) remains uncertain because the chemisorption process is intrinsically nonsystematic in terms of crystal-chemical parameters and does not result in definitive atomic substitution trends.

The Three Generations of Gold in the Palai-Islica Epithermal Deposit, Southeastern Spain

“…All the Au values obtained by EPMA in the different types of pyrite are similar (mean 0.02 wt%) and well below the detection limit for Au in pyrite (0.32 wt%, or 0.05% in the case of high-acquisition-time analyses), but they are useful as an indicator that the content of "invisible" gold is low compared to the values of 100 to 1300 ppm found in the literature (Cook & Chryssoulis 1990, Arehart et al 1993, Fleet & Mumin 1997, Cabri et al 1998, Asadi et al 1999, Kojonen & Johanson 1999, Ashley et al 2000. Moreover, in the Palai-Islica pyrite, there is no correlation between As and Au (Fig.…”

Fumarolic Activity, Acid-Sulfate Alteration, and High Sulfidation Epithermal Precious Metal Mineralization in the Crater of Kawah Ijen Volcano, Java, Indonesia

“…The As-Au coupled substitution is well-documented (e.g. Cabri et al, 1989;Cook and Chryssoulis, 1990;Fleet et al, 1993;Fleet and Mumin, 1997); Arsenic and Au replace S and Fe, respectively. In the Au-Cu association, Au must enter the pyrite structure as Au ).…”

Petrographic and microprobe study of nephrites from Lower Silesia (SW Poland)

“…Opaque min er als from Z³oty Stok neph rite, follow ing Fleet and Mumin (1997), are clas si fied as löllingite (Fig. 6), al though the com po si tion var ies from nearly pure löllingite to löllingite with a no tice able marcasite ad mix ture, which has the same struc ture (O'Day, 2006).…”