Gralheira Gold Mine

Application

Targeting deep extensions in vein systems

The Gralheira deposit lies some 700m (2,300 feet) north of the Jales mine in Northern Portugal and is contained within an extensive mineralized shear zone that extends for some 3,000m (9,800 feet). Romans mined both the Jales and Gralheira deposits; at Gralheira, the Romans mined along a strike length of 2,000m (6,500 feet). The main gold mineralization at Jales is hosted within a system of sub parallel veinlets and veins ranging from 0.5m to 1.5m in width. The Jales was mined to a depth of around 620m (2,000 feet) and is known to be a mesothermal system. Geological theory tells us that mesothermal veins can have great depth extension. The vein system at Gralheira is also mesothermal. Previous drilling has tested the depth extent of the surface veins in the range of 150 to 300 metres. St Elias Mines was intent on proving the system continued to depth and required a means for drill targeting.

Purpose

The intent of the Titan 24 survey was to provide deep information that would directly enhance the exploration efforts in the vicinity of the mine, particularly providing drill targets that could be related to satellite ore bodies. By mapping the resistivity and chargeability of the subsurface to assist the geologic understanding away from previously drilled environments, a focused program could reduce overall drilling costs by eliminating low potential ground from exploration drilling.

Challenges

Old mine workings, cultural noise, small targets, and deep complex environment.

Survey

The Titan survey was executed on 5 lines, each line was 2.4 km in length and line spacing was roughly 200 metres. The survey was carried out in December and results were made available early in the new year.

Results

The Titan 24 survey identified over fifteen major chargeability high and resistivity low anomalies that are consistent with vein-gold mineralized zones and lie buried between depths of 100-750m. Anomalies are oriented along 5 linear trends (A-E) that extend across the property. Zone A corresponds to the main Gralheira vein system. It is mapped from surface to depths between 500-750m as an IP high feature. It shows potential deep extensions along L100W in particular, L700W and possibly 250E. Deeper ore shoots are implied between 400E and 300W along the baseline. Additional secondary veins are indicated north of the main Gralheira system. Typical Titan 24 data sections for chargeability, resistivity and deep MT resistivity are shown below for one of the lines.

Titan applications for gold exploration

• Deep structural mapping, shears, faults etc.
• Disseminated sulphide distribution (surface to depths of 500m and more)