G. Southam et Tj. Beveridge, THE OCCURRENCE OF SULFUR AND PHOSPHORUS WITHIN BACTERIALLY DERIVED CRYSTALLINE AND PSEUDOCRYSTALLINE OCTAHEDRAL GOLD FORMED IN-VITRO, Geochimica et cosmochimica acta, 60(22), 1996, pp. 4369-4376
A temperature study (4 degrees C, room temperature, 60 degrees C and 9
0 degrees C) employing a bacterial in vitro model (Southam and Beverid
ge, 1994) revealed a role for S and P in octahedral Au formation. Ioni
c Au immobilized by Bacillus subtilis 168 was first precipitated as co
lloidal Au. During diagenesis, these colloids were transformed into sp
herical pseudocrystalline gold particles composed of 74.56 +/- 2.60 at
% Au, 8.56 +/- 1.71 at% S, and 13.94 +/- 1.48 at% P. These minerals th
en aggregated as roughly shaped noncrystalline octahedral Au which was
subsequently transformed into crystalline octahedral Au containing 85
.37 +/- 0.16 at% Au (the maximum detected), 0.77 +/- 1.33 at% S, and 1
0.27 +/- 0.88 at% P. The strong P signals (13.39 +/- 2.01 average at%)
obtained from the Au minerals examined by energy dispersive X-ray spe
ctroscopy suggest that organic phosphate compounds also play a role in
the in vitro development of octahedral Au, possibly as bacteria-Au-co
mplexing agents. Increasing the time to 4 weeks at room temperature or
the temperature to either 60 degrees C or 90 degrees C enhanced forma
tion of the crystalline octahedral gold. This crystalline octahedral A
u generated an electron diffraction pattern consistent with synthetic
Au.