Dolomite and jasperoid in the Metaline District, northeastern Washington

The replacement ore bodies of the Metaline zinc-lead district, in northeastern Washington are limited to the greatly disturbed fault block through which the Pend Oreille River flows and are associated with the major faults but are not in them. They are mostly near the top of the Metaline limestone, of Middle Cambrian age, and below black Ordovician slate. The ores are generally in jasperoid and are surrounded by a shell of crystalline dolomite. Outside of the dolomite is a shell of coarse-grained calcite that in places was deposited along solution channels long distances from known ore bodies. Jasperoid, crystalline dolomite, and, to a less extent, coarse-grained calcite are therefore favorable but not infallible signs of the presence of ore nearby. The Metaline limestone was dolomitized regionally before the ore was introduced, and this early dolomitization is independent of the ore.