Exploration and Mining

Exploration and mining now and then

Historical Exploration

Native copper found in small surface outcrops was known to some of the oldest civilisations in the world, with a history of use that is at least 10 000 years old. A period called the copper age, is defined by historians as a phase of the bronze age in which the addition of tin to copper, to form bronze during smelting, remained unknown. Copper discoveries and exploration was limited to the finding of surface outcrops. Famous copper discoveries in the middle age, were often done by local farmers or hunters, who kept their discovery secret until negotiating their reward from mineral prospectors. In Norway, copper and other metals have always been resources belonging to the government. In a letter from the Danish king in 1644, he encouraged the population to look for metals and minerals, but threatened with punishment for not reporting possible discoveries. Copper mining started in Røros in 1644 and in Løkken in 1654, after rumours of copper discoveries some years before. As the interest for geological resources increased with the discoveries of metals and minerals, geological research commenced, with regional mapping and theories about ore forming processes.

The depletion of rich, near surface copper deposits, forced prospectors to look for other indicators than just shiny outcrops. The area below depleted ores, caught geologists attention, when their knowledge, technology and increased copper prizes, opened new possibilities. Between the two world wars, geophysical ore body exploration intensified around the world. Structures in depth could be indicated by measuring the gravimetric field or shooting seismic waves. Metals in the subsurface could be indicated by measuring the magnetic field or the electric conductivity above an area of interest. As the industrial revolution provided the combustion engine and better steel, diamond drilling became more and more common in the 20th century. Diamond drill cores can provide valuable information from the subsurface about copper grade, lithology and rock strength.

Exploration Today

Exploration for base metals, including copper, happens all over the world, both in established mining regions and in under-explored areas. In the period 1995 to 2004 Copper was the second most explored commodity after gold, predominately in south America, the US and Canada. Exploration is commonly divided into phases associated with a given uncertainty and financing. At first, areas are targeted, securing mineral rights for exploration based on regional geology, outcrop observations or rumours. Field geologists then look for traces of copper by rock and soil sampling. A suspicion of copper below surface, may be strengthened by inducing a current in the ground, measuring conductivity and induced polarisation, to see if there are anomalies caused by high copper content. If these low cost methods prove copper anomalies, the will for financing a drilling program increase and exploration can progress to a phase of higher certainty. A drill rig may use a diamond drill bit for core sampling or reverse circulation drilling for sampling drill cuttings.

Core samples and other samples, and the density of them intersecting a deposit, is the basis for geostatistical resource estimations of copper grade and tonnage. A sparsely sampled resource may only be classified as "inferred". A sampling density sufficient to prove continuation may lead to an "indicated" resource and denser sampling classify the resource to be "measured", which is one of the criteria’s before investors are willing to invest in a mine start. Exploration continues during mining production also, to verify the un-mined parts of the deposit with a higher certainty.

Mining Before and Now

Early evidence of prehistoric copper mining, prove that humans exploited native copper with primitive hand tools from surface outcrops. Mine openings however, were labour intensive to make with only hand tools and fire-setting, and therefore limited in size. The discovery of “the copper man” in Chilenian mine site Chuquicamata, dated to year 550 A.D, prove some of the prehistoric mining activities. The copper man mummy was identified as an indigenous miner who got trapped in a mine shaft by fall of rock. Excavation of drifts and stopes by fire-setting was practiced at Røros and Løkken copper mines in Norway, until replaced by gunpowder in the late 1600’s. The invention of dynamite and electricity in the middle of 1800’s, improved the efficiency of mining. Drilling was done by air driven hand drills and rail wagons replaced horses for hauling the ore. Even with the improvements in technology, mining was still limited to underground mining of narrow veins and lenses of copper rich ores.

Modern copper mining of low grade porphyry copper ores, with extraction rates in the order of 100 000 tons per day, springs out of a development which started in the early 1900’s. At Bingham Canyon in Utah, USA and in Chuquicamata, Chile, mining engineers developed a new technique for processing low grade copper ore, as part of their plan to start large scale open pit mining of the huge resources. Steam shovels from the Panama canal were part of the equipment used in Chuquicamata. With the high copper demand, several huge open pit porphyry copper mines opened during early 1900’s and after the world war. Mostly in south America and the U.S, but also in Peru and Indonesia. The idea behind these large open pit mines, is to increase production capacity as much as possible, by large wheal going machines exploiting from multiple areas of the pit, making the overall mining cost per tone remain low. This allows mining to progress very deep in open pit’s before an underground mining pays off. If the porphyry copper deposits are situated deeper down, block caving method is used, making large volumes of rock cave into a system of draw bells in the bottom, where ore can be loaded safely in haulage tunnels. Example of large scale underground block caving is El Teniente in Chile.

Even though Copper is a regionalized resource, dominated by open pit mining in south and north America, there are also a large number of smaller mines, extracting copper ore by various methods depending on the geometry of the deposit. Deep, flat lying deposits like the Kupherschiefer in Poland are usually mined by room and pillar method, whereas steeply dipping deposits found in the Zambian copper belt, are mined by sublevel stoping or sublevel caving. For rich underground ores, stopes are backfilled for support, allowing pillars to be recovered afterwards. Most of the modern underground copper mines operating today, use mechanized wheel going equipment and sophisticated technology for monitoring stability.

 

 

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