Summary:
This PhD thesis presents a study about the origin of the metals in porphyry
Cu-Au deposits. New data is given from Skouries deposit and is coupled with
existing one from Skouries, Elatsite, Mamut and Ok Tedi deposits. The precious
metals (Au, Pd, Pt) are found in ultramafic to mafic magmatic rocks and come
from the partial melt of the asthenospheric mantle wedge or the lower crust,
that gives basaltic magma. Precious metals are incorporated into the sulfur
segment of this magma and under oxidizing conditions are liberated, to be
carried by hydrothermal solutions. The enrichment of metalliferous rocks in
uncompetitive elements (Ba, Sr, Pb, U, Th, LREE: La, Ce, Nd) is a result of
fragment crystallization (mainly), but also of crustal material incorporation.
Moreover a recovery method for Au, Pd and Pt is implemented on chalcopyrite
concentrates. These concentrates are representative of the whole metalliferous
rocks in the porphyry Cu-Au deposits: Skouries, Elatsite, Mamut and Ok Tedi.
The recovery method includes two stages: a) oxidizing roasting of the
concentrates in 915 oC for 2 h and b) oxidizing leaching of the roasted and
grained concentrates in 70 oC for 24 h. The leaching is carried out in a
spherical reactor, that contains an aquatic solution of 500 ml HCl 6 M and H2O2
0,03 M, under continuous stirring. The recovery percentages are greater than
85%. The sustainability of mining and processing in Skouries deposit is being
researched through a techno-economical analysis, based on data from Behre
Dolbear and Kvaerner Metals feasibility studies. These data in combination with
the recovery percentages and the metal prices, are being used for the Net
Present Value (N.P.V.) calculation. The simultaneous recovery of Pd and Pt, as
by-products, besides Cu and Au that remain the main products, contributes
importantly in an N.P.V. increase (about 31 mil. U.S. $). This improves
Skouries deposit’s economic attractiveness.
