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  U N I V E R S I D A D D E C O N C E P C I Ó N DEPARTAMENTO DE CIENCIAS DE LA TIERRA 10° CONGRESO GEOLÓGICO CHILENO 2003 Geologic Characteristics and Exploration Significance of Gold-Rich Porphyry Copper Deposits in the El Salvador Region, Northern Chile Sergio L. Rivera, Tomás Vila, and Jorge Osorio CODELCO- CHILE. Huérfanos 1270, Santiago, Chile ([email protected]) The  porphyry copper systems of the El Salvador region, represented mainly by El Salvador, Potrerillos, Exploradora, Sierra Jardín and Coya, are located in the southern portion of the Late Eocene – Early Oligocene Porphyry Copper Belt of northern Chile. They have distinctively higher gold (>0.1 to 0.5 g/t) and lower molybdenum grades (<10 ppm) than those systems located in the northernmost part of the belt. The El Salvador and Potrerillos deposits each contain resources >300 Mt at >0.5% Cu and up to 0.1-0.2 g/t Au. The Exploradora Cu- Au porphyry  prospect contains geologic resources of ~100 Mt at 0.3% Cu and 0.2 g/t Au, with an upper, gold-enriched, leached capping zone averaging ~0.5 g/t. The Sierra Jardín and Coya prospects show the lowest Cu contents and Au grades in the 0.1 to 0.5-g/t range. The deposits are related to discrete magmatic pulses empl aced in different lithotectonic environme nts, including the  borders of Paleocene, caldera-like volcanic structures (El Salvador and Sierra Jardín; 45-40 Ma), dilational jogs (Exploradora), and reverse and transfer faults (Potreril los and Coya, respectively) with ages between 37 and 31 Ma. Host rocks are mainly volcanic and marine sedimentary rocks of Jurassic-Lower Cretaceous age. The salient geological feat ures of these deposits are: mi nor differentiation of sever al, sintectonic intrusive pulses; intense superposition (telescoping) of intrusion and alteration-mineralisation phases; development of early, magnetite-rich, potassic alteration-mineralisation events; moderately- to weakly-developed sericitic alteration; and late stages of “collapsed” advanced argillic alteration along with post-mineral phreatomagmatic activity, characterized by pebble-dykes and/or diatreme breccias. The range in the composition of productive porphyries, between granodiorit e and tonalite; their broadly similar age; their various structural s ettings; and the differenc es in Cu/Au rat ios and Mo contents even at the cluste r scale, suggest that the metal budget in each case may have been controlled by specific cooling conditions. Moreover, the abundance of gold-rich porphyries (as opposed to their gold-poor counterparts) discovered during the past ten years in the Chilean Andes, implies that the geologic conditions for the formation of gold-rich porphyry copper systems have been far more favorable than previously considered. Several key characteristics of gold-rich porphyry copper deposits of the El Salvador region can be used as exploration guidelines and open new ground for prospecting. Additional discoveries will certainly help to fill metallogenic gaps in the previously defined porphyry belts of northern Chile. Todas las contribuciones fueron proporcionados directa mente por los autores y su contenido es de su e xclusiva responsabilidad.  

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  • U N I V E R S I D A D D E C O N C E P C I N

    DEPARTAMENTO DE CIENCIAS DE LA TIERRA 10 CONGRESO GEOLGICO CHILENO 2003

    Geologic Characteristics and Exploration Significance of Gold-Rich Porphyry Copper Deposits in the El Salvador Region, Northern Chile

    Sergio L. Rivera, Toms Vila, and Jorge Osorio CODELCO-CHILE. Hurfanos 1270, Santiago, Chile ([email protected])

    The porphyry copper systems of the El Salvador region, represented mainly by El Salvador, Potrerillos, Exploradora, Sierra Jardn and Coya, are located in the southern portion of the Late Eocene Early Oligocene Porphyry Copper Belt of northern Chile. They have distinctively higher gold (>0.1 to 0.5 g/t) and lower molybdenum grades (300 Mt at >0.5% Cu and up to 0.1-0.2 g/t Au. The Exploradora Cu-Au porphyry prospect contains geologic resources of ~100 Mt at 0.3% Cu and 0.2 g/t Au, with an upper, gold-enriched, leached capping zone averaging ~0.5 g/t. The Sierra Jardn and Coya prospects show the lowest Cu contents and Au grades in the 0.1 to 0.5-g/t range. The deposits are related to discrete magmatic pulses emplaced in different lithotectonic environments, including the borders of Paleocene, caldera-like volcanic structures (El Salvador and Sierra Jardn; 45-40 Ma), dilational jogs (Exploradora), and reverse and transfer faults (Potrerillos and Coya, respectively) with ages between 37 and 31 Ma. Host rocks are mainly volcanic and marine sedimentary rocks of Jurassic-Lower Cretaceous age. The salient geological features of these deposits are: minor differentiation of several, sintectonic intrusive pulses; intense superposition (telescoping) of intrusion and alteration-mineralisation phases; development of early, magnetite-rich, potassic alteration-mineralisation events; moderately- to weakly-developed sericitic alteration; and late stages of collapsed advanced argillic alteration along with post-mineral phreatomagmatic activity, characterized by pebble-dykes and/or diatreme breccias. The range in the composition of productive porphyries, between granodiorite and tonalite; their broadly similar age; their various structural settings; and the differences in Cu/Au ratios and Mo contents even at the cluster scale, suggest that the metal budget in each case may have been controlled by specific cooling conditions. Moreover, the abundance of gold-rich porphyries (as opposed to their gold-poor counterparts) discovered during the past ten years in the Chilean Andes, implies that the geologic conditions for the formation of gold-rich porphyry copper systems have been far more favorable than previously considered. Several key characteristics of gold-rich porphyry copper deposits of the El Salvador region can be used as exploration guidelines and open new ground for prospecting. Additional discoveries will certainly help to fill metallogenic gaps in the previously defined porphyry belts of northern Chile.

    Todas las contribuciones fueron proporcionados directamente por los autores y su contenido es de su exclusiva responsabilidad.


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