Tierra de Oro
The Tierra de Oro property is located in a world class mining district just 50 kms to the south of the famous Candelaria IOCG deposit, owned by Freeport-McMoran with reported reserves and production of 470 Mt at 0.95 % Cu, 0.22 g/t Au, 3.1 g/t Ag.
The property is accessed by well maintained gravel roads and is located 20 km from the Pan American highway, next to the main Chile power grid. With a maximum elevation of only 1,500 meters the region enjoys good climactic conditions for year round exploration.
Based on property evaluations, it is felt that the TDO property has the potential to host economic Au and Cu deposits with a low level of risk associated with mine development. (GeoVision Geosciences Inc., February 2009)
The property geology, consists mainly of intrusive rocks on the west, with volcanics to the east. The north-easterly trending boundary between these two domains is a fault splay related to the Atacama Fault situated some 20 kilometres to the west, apparently with some transcurrent movement; the east side dropped down.
The presumed Cretaceous Sierra Chanchero Intrusive Complex, in the western part of the property, is inhomogeneous and consists predominantly of pale monzonitic rocks with some diorite plugs, and is cut by numerous mostly NE-trending dikes of andesite, diorite and monzonite. Locally capping the intrusive complex are remnants of calcareous marine sediments altered to magnetite-epidote-garnet skarns.
To the east of the intrusive complex, largely covered by the Las Lomitas concessions are gently-dipping pyroclastic volcanics, generally of andesitic composition, with subordinate epiclastics. These volcanics are probably Cretaceous to Eocene in age and include calcareous layers and maroon tuffs with a hematitic matrix.
The western intrusive complex hosts mainly Au-Ag and Cu mineralization, while the eastern volcanic domain is generally host to Cu-Ag mineralization.
CHANCHERO ZONE - Porphyry Target
The Chanchero Zone is a 1500 m by 2800 m area with a multicoindent Geological, Geophysical and Geochemical anomalies covering a large Cu-Au bearing porphyry alteration zone.
During the fall of 2007, PBX completed a 62 line kilometre detailed 3D IP/Resistivity survey centered directly over the Chanchero Zone to target porphyry style Cu-Au mineralization to depths of up to 300m.
The survey outlined a strong IP chargeability anomaly (greater than 55 mV/V) and resistivity-low (less than 100 Ohm-m) The large near surface anomaly is elongated northeast-southwest, 2,800 meters long by 1,700 meters wide, and is open at depth. The anomaly is associated with an overlying gold-copper-moly bearing alteration zone. The anomaly is located at the center of a structurally controlled copper-gold camp and may be the source of the near surface copper and gold mineralization found in the surrounding areas. The intensity and homogeneity of this chargeability response, coupled with the presence of altered iron oxide-rich porphyritic intrusives hosting copper-gold veins at surface, may indicate a large sulphide rich system is present at moderate depth (>250m).
Walker (1996) describes the geology as an argillic quartz-sericite+pyrite altered hornblende diorite to granodiorite with roof pendants of hornblende monzonite. Walker (1996) also describes the zone as a large area of pervasive phyllic to argillic alteration representing the upper parts of a large porphyry Cu-Au system.
The center of the anomaly is coincident with an apparent late less altered unmineralized diorite. This diorite is much more magnetic (~40x10-3 SI) than the surrounding monzonite granites ( less than 5x10-3 SI) which likely explains the magnetic anomaly associated with the Chanchero Zone. The IP/Resistivity data suggests that this late diorite intrusion has a lower chargeability (less than 5 mV/V) and higher resistivity (greater than 500 Ohm-m) to that of the surrounding mineralized phyllic to argillic altered monzonitic granitic to dioritic intrusives. The 3D IP model suggests that this diorite is possibly sheet-like or an intrusive plug with the IP anomaly associated with the mineralized monzonite granitic intrusives extending outwards below the diorite at depths of greater than 100m.
The strongest part of an IP/Resistivity anomaly located in the Chanchero Zone on the TDO property is presently untested and is thought to possibly outline the central core of a large Cu-Au-Mo porphyry system in this area. A 300 m to 500 m deep diamond drill hole program is recommended to test the central part of this strong IP/Resistivity target for potential stockwork Cu-Au-Mo mineralization. More due diligence and exploration work is also required to fully evaluate the bulk tonnage as well as placer Au potential of several of the known high grade Au zone on the western portion of the property.
LAS LOMITAS Cu-Ag ZONE
Tierra de Oro East area is thought to have the potential to host several high grade Cu-Ag deposits near surface as well as the potential for IOCG deposits at depth. A large Cu soil anomaly (2kms x 1.5kms) occurs along the eastern part of the TDO property in close contact with a previously mapped diorite plug. This Cu soil anomaly is presently unexplained and warrants further investigation.
Sampling from small scale open cuts and underground operations returned values ranging between 0.5% Cu and 6 g/t Ag to greater than 1.5% Cu and 40 g/t Ag.
Local skarn alteration and hornfelsing is reported in the vicinity of the ocoita sills and around a diorite intrusive plug located on the eastern part of the property. The Cu-Ag+Co mineralization visible in the historic workings occurs primarily as high grade Cu-oxides and hypergene chalcocite mineralization associated with structurally controlled (locally stratabound) hydrothermal epidote-chlorite-carbonate alteration within andesite volcanics and volcanoclastics. This style of hydrothermal alteration and mineralization shows closer similarities to that of Cu-Ag mineralization found in postorogenic stratiform Red Bed Copper belts where similar structurally controls on high grade Cu-Ag+Co deposits are known to occur (El Desouky, 2008). These high level structurally controlled hydrothermal Cu-Ag deposits are postulated by some to result from the remobilization of sulphide mineralization from a deeper source. This may suggest that the structures hosting the Cu-Ag mineralization observed in the Las Lomitas area may be tapping a deeper Cu-Ag rich source potentially related to a buried stratiform Cu-Ag-Co mineralization where sequences of red bed continental sandstones and conglomerates have been reported in the Las Lomitas area.
The large Cu soil anomaly is considered a highest priority target requiring more detailed mapping and prospecting as well as ground geophysics to determine the potential of this area to host a high grade Cu-Ag deposit as well as an IOCG deposit at depth.
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