Veins

Although partially obscured by spray paint applied by the miners, this mining face underground shows a very confused pattern of thin quartz ± feldspar veins and veinlets distributed throughout the dark amphibole-rich country rock. In this picture you are facing NE. Turning slightly to your left gives you the view below.

Here the granitic veins are thicker (the upper one is roughly 10 cm thick) with very sharp margins that show evidence of being chilled (whiter, finer-grained outer 2-5mm) against the cooler country rock. The upper two veins are younger than the lower thicker one being intruded along a slightly steeper set of fractures.

Here a 30 cm thick vein (same generation as the 2 younger ones above?) has been fractured nearly perpendicular to its long dimension. These fractures could be called tension gashes having formed in the brittle granitic rock during movement following the dikes solidification. The tension gashes are filled by quartz and show relatively minor reaction haloes in the dike rock.

Here a tension fracture across the same granitic vein shown above has been filled by coarse-grained quartz which has a very wide, non-symmetrical alteration halo around it. The halo is characterized mineralogically by the addition of feldspar to the granitic rock and the destruction of the minor amounts of mafic minerals originally present.