Gold Vein Deposits

 

Gold may be present in long, narrow patches, veins, strings, large crystalline masses or in scattered crystals. The gangue matter is usually in the majority in a vein and the ore thinly sparingly and irregularly distributed in it. In some cases when a gold vein is 3 m or more meters wide, it is not to be supposed that 3 m of solid ore is meant, but that this is the width of the gangue between walls. The orebody may be only a few inches wide. The streak or main body of ore called pay streak has a tendency to keep near one wall or the other, or at times to cross from wall to wall.

Basically, in gold veins, flakes or wires of free or native gold occur in the decomposed gangue and sometimes in the pure undecomposed quartz. Silver is found in much the same way, but more specimens than as continuous orebodies. Isolated patches of rare, or valuable minerals such as Ruby silver, horn silver or silver glance occur locally in parts of the vein, sometimes coating stalactites or crystals of a vugh or cavity lined with quartz or other crystals. According to some geologist, an assay from such picked specimens would give a very unfair average of a precious metal prospect.

Some gold vein deposits are characterized by low sulphization and the mineralogy consists of quartz, pyrite, galena, sphalerite and lesser chalcopyrite. In some places, sulphides are accompanied by calcite and some silver minerals.  It has been noted that the veins may be in part transitional between quartz-sulphide gold and carbonate-base metal gold, but also distinguished from each of these, by differing mineralogy and geological environment.  Base metal grades are variable, appearing higher grades in more dilational ore structures whose main characteristic, the presence of gold bearing minerals. Some vein deposits presence high content of silver and gold such as 100-180 g/t of silver and 0.5-1.0 g/t of gold. Polymetallic operations in Peru and Mexico present this distinctive characteristic that makes attractive the development of the project.

There are locally in different polymetallic deposits with precious metals differences in the value of certain minerals and ores. For example, a coarse galena is generally poor in silver; while fine grained galena is usually reach in silver. The opposite case is possible, but no common.