Intrusion-Related Gold Deposits

Under construction

Trench with visible twofold-split vein as part of an IRGS, Portugal. On the left-hand side the vein consists mainly of quartz and patchy arsenopyrite, on the right-hand side mainly of weathered arsenopyrite and minor quartz. In this outcrop the vein exhibits 17.61 g/t Au over 61 meters. Encircled hammer for scale.

Auriferous quartz-sulphide veins (intrusion-related gold system, IRGS) in granitic complex, Portugal. This area has been explored and exploited for gold since at least Roman times (200 BC to 400 AD), more recently in the 1930’s to the 1950’s and again
in the 1970’s to the 1990’s and to the present. 
Gold grades and content of gold in vein systems is dependent upon the amount of 
arsenopyrite in the veins. High grades of gold (up to 25 g/t Au) are always found with arsenopyrite rich material. The veins vary in width from +/- 5 cm to up to 3 m. This vein returns by underground sampling 5.75 g/t Au over an average width of 0.79 m for a strike length of 220.2 m.