Gold Vein Types

 

Gold veins are changeable in character and their formation, and appearance of a perplexing and complicated nature develops some types. Basically, there is a gradual passage from one form to another and the classification is not simple. There is often a sharp distinction between one form of gold deposits and another. In this way, it is common to say that a gold vein is a try fissure, a bedded vein or a segregated vein. In some cases, it is difficult to make a difference. A simple classification considers two types, regular and irregular veins. Regular unstratified gold deposits include true veins, segregated veins and cut veins. Irregular include impregnations, fahlbands, and contact deposits.

Gold veins are collections of minerals, often closely related to the enclosing rock, normally in fissures formed in those rocks after the rocks are consolidated. All veins do not carry gold in the same concentration or minerals and may be just quartz, feldspar or calcite like extremely low gold grade spots traversing limestone rocks. Veins may divide or thin out, and are irregular in shape and structure due to the irregular width of the fissures. The portions or rock in direct contact with the vein are called hanging wall and foot wall. This is only in inclined or flat veins, as a vertical fissure vein may not have roof and floor, but only two walls, east and west or north and south according to the compass. The inclination of a vein to the horizontal is its dip. The horizontal direction of a vein at right angles to its dip is its strike. The latter may usually noted along the surface outcrop, the former either in the working of the mine or where the vein is exposed on the side of the canyon.

Both dip and strike of a vein often vary very much, the former with depth, the latter with extension across the area. A gold vein will not start with a gentle dip and decrease rapidly in steepness with depth. For example, the vein may start with a dip of 20^o and a depth of less than a 30 m, reach 50^o or more. As fissure veins commonly occupy fault fissures, their irregularities in dip and strike correspond to those located under faults. The angle of dip is usually taken from its variation from a horizontal, not a perpendicular line. For example, a dip of 70^o means that is very steep, and one of 15^o is a gentle inclination. A layer of clay known as gougue usually lines one or both walls of a vein between the rock and the gangue or vein. it is derived from the elements of the adjacent rock, decomposed by water and sometimes by friction of the walls of the fissure against one another or against the vein in the process of slipping and faulting, which is usually shown by its smoothed, slickensided, polished or grooved.