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PHYSICO-CHEMICAL MODELING
OF GOLD-BEARING SULFOARSENIDE SOLUTIONS IN THE GRANITE SYSTEMS
Vilor N.V.*, Kazmin L.A.**
*Institute
of Geochemistry SB RAS, Irkutsk, Russia, vilor@igc.irk.ru,
**Research
Center of Geotechnology FED RAS, Petropavlovsk-Kamchatsky, Russia,
kazmin@igc.irk.ru
Sulfoarsenide
systems form in granite pluton upper intrusive areas. Its
redistribute gold, concluded in early mineral associations, and
concentrate the metal inside of arsenopyrite ore type.
Physico-chemical modeling
on the “Selector” program complex basis is used for the
determination of arsenic important geochemical role for the high
production gold ore formation, which connected with granite massifs.
This calculation method has some difficulties, which are deficit of
the chemical (compound composition) and thermodynamic (thermodynamic
constants) information.
The
thermodynamic base creation (gt
function
calculation is the first of all) for Fe
- As – Na – S – Cl – H –O
system components includes its coordinate procedures for 3 additional
systems: 1) solution + magnetite, 2) solution + pyrite and 3)
solution + arsenopyrite (+lollingite). General system includes the
equilibrium of Fe oxides, sulfides and arsenides with wide pH
interval of chloride solution. Modeling was consisted of the
coordination of these 3 systems.
The
calculated system composition is, mol: arsenopyrite 1, H2S
0.66 ÷ 0.92 x 10-3,
HCl and NaOH 1 x 10-6
÷
0.001, H2O 1 kg. Calculated parameters are t oC
100-300, P - from the saturation water vapor pressure to 300-500
bars. The number of solution particles is 515, gases 105, solid
minerals 47.
Arsenic is in
the solution as thioarsenic acid H3AsS30
(less that 2x10-2
m) with presence As(OH)2HS0
and As(OH)(HS)+
complexes in the acidity interval from 3.53 to 6.36 and H2S
concentration from 0.69 x10-3
to 0.92 x10-3
m. Asenite acid H3AsO3
dominates about 300 0C
under the saturation water vapor pressure. Fe transports as the
hydrosulfide group composition: Fe(HS)+,
Fe(HS)2
0,
Fe(HS)3-
and concentration equal from 5.4x10-4
to 1.9 x10-2
m. The supposed ferrothioarsenites
Fe(1-2)H(0-3)As(1-4)S(1-7)(-1÷+4)are
minor for hydrothermal process used conditions.
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