RT Journal Article
T1 Gold behavior in supergene profiles under changing redox conditions : the example of the Las Cruces Deposit, Iberian Pyrite Belt
A1 Yesares Ortiz, María Dolores
A1 Aiglsperger, Thomas
A1 Sáez Ramos, Reinaldo
A1 Ruiz de Almodóvar Sel, Gabriel
A1 Nieto Liñán, José Miguel
A1 Proenza, Joaquín A.
A1 Gómez, Carmelo
A1 Escobar, Juan Manuel
AB The Las Cruces deposit is in the eastern end of the Iberian Pyrite Belt (SW Spain). It is currently beingmined by Cobre Las Cruces S.A. The main operation is focused on the supergene Cu-enriched zone (initialreserves of 17.6 Mt @ 6.2% Cu). An Au-Ag-Pb–rich gossan resource (3.6 Mt @ 3.3% Pb, 2.5 g/t Au, and56.3 g/t Ag) occurs in the upper part of the deposit. The Au grade ranges from 0.01 ppm to >100 ppm, andoccurs as three different Au ore types: (1) Au mineralization in the upper part of the gossan linked to Fe-oxideslithofacies, (2) Au concentration in the lower part of the gossan associated with leached black shales, and (3) Auore in the cementation zone related to subvertical fractures.A hydroseparation device has been used to obtain heavy mineral concentrates from selected samples ofdifferent ore types. Reflected-light microscopy, scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS), and electron probe microanalysis (EPMA) were used to study the separated Au particles. Significantdifferences between the defined ore types include the Au-bearing lithologies, mineral associations, texturalfeatures, particle sizes, morphologies, and fineness. Au-rich minerals include native Au, Au-Ag electrum, andAu-Ag-Hg amalgams. Gold-bearing mineral associations include Pb-oxihalides, Fe-oxides, galena, pyrite, cinnabar,and Ag-sulfosalts.The Au enrichment mechanism in the supergene profile involves (1) dissolution of Au from the primary sulfidesas chloride-rich ionic complexes during the weathering of the deposit under subaerial exposure; dissolvedAu is transported downward through the supergene profile under acidic and oxidized conditions; (2) destabilizationof the Au complexes by Fe-controlled redox reactions; as a consequence, coarse-grained, high-finenessAu particles precipitated in association with Fe-oxyhydroxides. This resulted in secondary concentration in theupper gossan; and (3) after deposition of cover sediments took place a progressive change in the system conditionsresulting in a later Au remobilization as hydroxidehalide, hydroxide, thiosulfate, and bisulfide complexes inthe lowermost gossan and cementation zone. The main pathways for migration of enriched fluids to the cementationzone are secondary permeability zones linked to Alpine reactivated faults. Deposition of Au seems to berelated to fluid interaction with reductant lithologies, including black shales and the primary sulfides.
PB Society of Economic Geologists
SN 0361-0128
SN 1554-0774 (electrónico)
YR 2015
FD 2015
LK http://hdl.handle.net/10272/12204
UL http://hdl.handle.net/10272/12204
LA eng
NO Yesares Ortiz, M.D., Aiglsperger, T., Sáez Ramos, R., Ruiz de Almodovar Sel, G., Nieto Liñán, J.M., Proenza, J., Gómez, C., Escobar, J.M.: "Gold behavior in supergene profiles under changing redox conditions : the example of the Las Cruces Deposit, Iberian Pyrite Belt". Vol. 110(8), págs. 2109-2126, (2015). DOI: 10.2113/econgeo.110.8.2109
NO This research is a contribution to projects P-S Anoxia (CGL2011-30011) and Metodica (CGL2010-21956-C02-02), which are supported by the Spanish government. The authors thank Cobre Las Cruces S.A. for the field assistance and the ongoing collaboration. We are also grateful to Joel Brugger, Steve Hill, and Tim Baker for their constructive suggestions to improve the manuscript.
DS Repositorio Institucional de la Universidad de Huelva
RD 30 may 2026