A History of Tailings1

A HISTORY OF MINERAL CONCENTRATION: A HISTORY OF TAILINGS1 by Timothy c. Richmond2 Abstract: The extraction of mineral values from the earth for beneficial use has been a human activity- since long before recorded history. Methodologies were little changed until the late 19th century. The nearly simultaneous developments of a method to produce steel of a uniform carbon content and the means to generate electrical power gave man the ability to process huge volumes of ores of ever decreasing purity. The tailings or waste products of mineral processing were traditionally discharged into adjacent streams, lakes, the sea or in piles on dry land. Their confinement apparently began in the early 20th century as a means for possible future mineral recovery, for the recycling of water in arid regions and/or in response to growing concerns for water pollution control. Additional Key Words: Mineral Beneficiation " ... for since Nature usually creates metals in an impure state, mixed with earth, stones, and solidified juices, it is necessary to separate most of these impurities from the ores as far as can be, and therefore I will now describe the methods by which the ores are sorted, broken with hammers, burnt, crushed with stamps, ground into powder, sifted, washed ..•. " Agricola, 1550 Introduction identifying mining wastes. It is frequently used mistakenly The term "tailings" is to identify all mineral wastes often misapplied when including the piles of waste rock located at the mouth of 1Presented at the 1.991. National mine shafts and adi ts, over- American. Society for Surface burden materials removed in Mining and Reclamation Meeting surface mining, wastes from in Durango, co, May 1.4-17, 1.991 concentrating activities and sometimes the wastes from 2Timothy c. Richmond, Project smelting operations. For the Officer, Abandoned Mine Land purpose of this discussion, the Program, Wyoming Department of following definitions shall Environmental Quality Cheyenne, apply: WY 82002 Page 369 Tailings: Tailings are the improvement after mining but finely ground gangue or host before smelting and which rock materials from which the includes the milling process. desired mineral values have been extracted during the Mining, concentrating and concentration process. smelting of ores for their Tailings may contain the metals have been a part of residues of reagent materials human activity since before that were added to enhance recorded history. The mineral mineral separation (Young 197 6, processing methods remained PEDCO 1984) . Tailings will basically unchanged from usually have the same ancient times until the latter mineralization as the host part of the 19th century. rock. "Chat" is a term used in certain regions of the United The disposal of mineral states for tailings. Waste wastes did not present much of materials derived from the a problem to human health and processing of coal, including welfare until the first part of the terms "refuse, 11 "slack," the twentieth century. and "gob" are often incorrectly However, as the modern mining referred to as tailings {Thrush industry continues to satisfy 19 68) • the increasing demands for metal and other mineral Slag: Slag is the impurities products, mine wastes and and reject material formed tailings will also expand in during the smelting or refining ever increasing proportions. of ores or mineral concentrates About 362,872,000 metric tons by pyrometallurgical methods of tailings were generated {Thrush 1968). Slag is the annually in the United States generally accepted term in the alone in the early 1970's (Dean United states for wastes et al 1974). A decade later, produced from the smelting it had increased to 598,771,900 process, but may occasionally metric tons, exclusive of be used to define any or all of uranium mining (PEDCO 1984). the mineral industry waste products. Early Methodologies Beneficiation: Beneficiation is There is little doubt that the upgrading of ore by sizing, the first discoveries of gold, removal of impurities or silver and copper were found in otherwise improving the quality their free. or native state as of the ore {Thrush 1968). nuggets lying on the surface of Beneficiation can apply to any the ground or in pools of water ore grade improvement from in streams and rivers. Such sorting in the mine through finds were opportunistic, but concentration prior to early man quickly learned where smelting. to look for these metals. It was soon discovered that by concentration: Concentration is digging and washing sands and the separation and accumulation gravels in certain streams, or of economic mineral values from from their banks, gold nuggets gangue {Thrush 1968). would be found. Where water Concentration is generally was not available, the earth limited to ore quality could be winnowed or tossed Page 370 into the air from an animal hammered or pried free to be hide or perhaps a woven fabric, carried to the surface. and the lighter materials would Particles of the host rock were be carried away by the wind in often attached to the metals much the same manner that chaff and had to be broken free and was separated from kernels of discarded. grain. This was the beginning of what is commonly termed Somewhere along the way, placer mining, forms of which ancient man learned that some are in common use today. It is of the mineral forms of metals a method that many consider could be refined to an almost among the most ancient methods pure state by the use of fire of separating metal from waste and heat. The discovery of (Young 1976). smelting by fire made additional ores useful, mainly Placering, with the most the oxide and carbonate ores of rudimentary pans, or the more copper. Smelting also provided sophisticated sluices, strakes, the ability to separate silver rockers and jigs, then as now, from lead, to refine gold by is the mechanical separation by removing the often naturally gravity of native or free metal alloyed silver and to mix tin and heavy metallic salts from with copper to make bronze. naturally crushed rock (Young 1976). These methods are most The desirability of removing often associated with gold the largest possible amount of recovery. The waste products gangue or earthy matter from of early pl.acering, tailings if the valuable metal before you will, were carried away to smelting had been recognized be deposited elsewhere with for thousands of years and was little or no apparent regularly practiced by ancient consequence.• peoples (Aitchison 1960). The earliest apparent indications The next step in the of mineral concentration are recovery of metals was the found as inscriptions on discovery that these metals, Egyptian monuments dating from along with tin and lead, could the IV Dynasty (about 4000 BC) . be found in their native state Other monuments dating from the in outcrops of rock, but first XII Dynasty (2400 BC) had to be broken loose. This specifically suggest the was the beginning of mining in working of gold ore (Hoover and the sense that it is commonly Hoover in Agricola 1912). perceived; the excavation of Written accounts of ancient metal-bearing rock, initially mineral concentration as surface expressions and then techniques are limited, most tunneling underground. The descriptions tracing back to tools of excavation were stone, the lost works of horn, bone, and in time, bronze Agatharchides, a Greek and iron. A fire, the primary geographer of the second loosening agent, would be built century, BC, who described against the metal-bearing face Egyptian mining and and the rock heated. Then concentration methods (Hoover water would be dashed against and Hoover in Agricola 1912). the hot rock causing it to The process involved breaking fracture. The pieces were then mine-run rock into smaller Page 371 pieces using stone mortars and lashed to a forked stick that stone or iron pestles. The in turn was supported by small pieces, "the size of a another forked stick that acted vetch, " were then taken to a as a fulcrum. A flat rock with mill where they were further a slight depression served as a ground "as fine as meal. 11 This mortar. The ore was placed on finely ground powder was spread the mortar and crushed by over . a broad board or rough repeatedly raising and dropping stone slab, somewhat inclined the stone (Young 1976). or sloping, where it was washed by pouring water over the The arrastra was a common powdered rock. The material tool of the ancients. It was would be worked by hand over widely used in the Americas by the board or slab, the water the Spanish Conquistadors washing away the earthy during the sixteenth century, material and the gold, being and it found continued heavier, was retained (Hoover widespread use in the western and Hoover in Agricola 1912, Americas into the twentieth Poss 1975). century. The arrastra also employed stones lashed to a The famous ancient Greek pole. However, the pole was silver mines at Mount Laurion attached to a center pivot in a were extensively worked before tub made of very hard rock 500 BC, but it is unclear when spaced closely together to form the ores were first a tight, smooth floor. Men or concentrated before being animals would push on one end smelted. At some time before of the pole and the stones the Third Century, BC, an lashed to the other would extensive system of milling and finely crush or grind the ore concentration had been placed in the tub by an developed. One estimate abrasive action. The finely suggests that the Mount Laurion ground ore was recovered· for area produced more than further processing of the metal 6,350,000 metric tons of reject values. The arrastra was (tailings) over the several simple to build and could be centuries of its activity operated as either a wet or dry (Hoover and Hoover in Agricola grinder or as a separator.

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