Ore Deposits, Zoning of

the regular spatial change in the chemical and mineral composition of ores, leading to the formation of ore zones with predominance of certain metals.

A distinction is made between primary zoning, which is caused by the processes of formation of mineral deposits, secondary zoning, which arises in connection with the trans-formation of ore bodies near the surface of the earth upon their oxidation, and among zoning of ore provinces, which is caused by the regular formation of definite groups of ore de-posits that arise successively in the process of development of the earth’s crust; zoning of ore fields, which is determined by the alternation of deposits of ores of various metals in passing from one area of an ore field to another; and zoning of ore bodies, which is characterized by regular change in the mineral and metal composition of the ores within them.

The change in the ore composition can occur along the length, width, and depth of the bodies. Change with respect to depth is called vertical zoning, in which two varieties are distinguished: stage (pulsation) zoning, which results from the successive discontinuous entry into the ore cavity of portions of ore-forming material of various composition, forming at different vertical levels zones with contrasting mineral composition, and facies zoning, which forms in cases of successive deposition of various mineral complexes as ore-forming substances advance from the interior of the earth to the surface and is characterized by continuous change of mineral complexes on the margins of the ore bodies, with the formation of zones of like composition.