Classification of Ores and Concentrates
The following c l a s s i f i c a t i o n of mineral products is commonly used in the mining industry, and the definitions given w i l l apply throughout t h i s c i r c u l a r .
Ore is a mineral or mineral aggregate t h a t can be mined and marketed a t a p r o f i t . At l e a s t one mineral (a naturally occurring chemical element or assemblage of elements) is valuable; the valueless minerals make up the gangue or waste.
A base-metal ore t h a t contains valuable amounts of two or more metals (i.e., copper, lead, and zinc) is termed a complex ore. Ores are further classed by the type of contained valuable minerals. The five most important such types of minerals occurring i n base-metal ores are native (metal in free or metallic s t a t e ) , s u l f i d e (metal combined with s u l f u r ) , oxide (metal combined with oxygen), carbonate (metal combined with carbon and oxygen), and s i l i c a t e (metal combined with s i l i c o n and oxygen). Ores containing a combinat i o n of oxide, carbonate, and s i l i c a t e minerals are camonly grouped as oxidized ores. The term mixed is used t o describe ores containing both sulfideand oxide-group minerals. Ores can be c l a s s i f i e d further as milling or directsmelting ores. A milling ore can be treated and separated into one or more concentrates containing the bulk of the valuable minerals and some gangue and a t a i l i n g consisting chiefly of gangue minerals and any unrecwered residue of valuable minerals. Normally t h i s residue cannot be recovered economically.
As a means of categorizing s t a t i s t i c s for production of gold, s i l v e r , copper, lead, and zinc by class of ore and m a t e r i a l t r e a t e d , a c l a s s i f i c a t i o n of ores and concentrates of gold, s i l v e r , copper, lead, and zinc, based on smelter terminology, smelter settlement contracts, and metal recovery, was devised and adopted by the Bureau of Mines in 1905. This c l a s s i f i c a t i o n , with
modifications to cover lpwering of economic ore grades and improvements in metallurgy,has been used continuously in the s t a t i s t i c a l tables published by the Bureau of Mines in the Minerals Yearbook and other reports. Concentrates are classified under the same rules as ores. The term “ores” i s often used in a collective sense that includes both ore as mined and ore products (concentrates).
It covers a l l mined products that are sold to smelters or equivalent plants for the valuable metals contained. The current basis of ore classification i s as follows:
Copper ores include smelting ores that contain 2.5 percent or more recoverable copper and ores and tailings concentrated or leached chiefly for their copper content, irrespective of the precious metal content. Ores leached in place or ores for which the tonnage cannot be calculated are excluded; slags smelted for their copper content are included.
Lead ores are those that contain 5 percent or more recoverable lead, irrespective of the precious metal content; and ores, tailings,
or slags that are treated chiefly for their lead content. Zinc conwutrating ores include those from which a marketable zinc concentrate is made, irrespective of precious metal content. Virtually no zinc ore i s now smelted directly except slags, which, when fumed, are classified as smelting ore and may contain as l i t t l e as 5 percent recoverable zinc.
The cmplex ores are combinations of those enumerated above; they w i l l be designated by the names of their constituent base metals in alphabetical order, irrespective of the predominance of value.
Gold, gold-silver, and silver ores with the base-metal content too small to be classified in accordance with the abwe are ‘dry’ ores, regardless of method or treatment. Dry ores, chiefly, siliceous, are valuable for t h e i r s i l v e r and gold contents and, in sane instances, for their fluxing properties. Dry gold ores are defined as those in which the gold value equals or exceeds three-fourths of the combined gold and silver values; dry silver ores are those in which the silver value equals or exceeds three-fourths of the combined gold and silver values. In dry gold-silver ores both the gold and silver values equal or exceed one-fourth of the cmbined gold and silver values.