Kabwe or Kabwe-Ka Mukuba means 'ore' or 'smelting' but the European/Australian prospectors named it Broken Hill after a similar mine in Broken Hill, New South Wales, Australia.
Broken Hill Man was found in this area of the mine. GC8M3B0
The oldest mine in Zambia, the Kabwe mine site occupies approximately 3 km² and is located to the south of Kabwe and east of the Great North Road in Zambia. The Kabwe mine was discovered during 1902 and began operations in 1904, reaching full-scale production in 1906. It officially closed down on 3 June 1994 as it was no longer economic to mine. The site was placed under care and maintenance by the ZCCM. Until its closure in 1994 it held a key position of national economic importance. During its lifetime the mine produced:
Zinc (Zn) 1,800,000 tons. Lead (Pb) 800,000 tons. Vanadium Oxide (V2O) 7,816 tons. Silver (Ag) 80,000kg. Cadmium (Cd) 235,000kg.
Over the years the mine complex expanded to include open cast and underground workings, mineral processing, smelting and refining facilities. By 1994, the Lead-Zinc ore was exhausted but it is estimated that the mineral-rich tailings, slag, and waste left onsite during the mining years which are still in place, contain 356,843t of zinc and 351,386t of lead
This carbonate-hosted Lead-Zinc deposit consists of four main epigenetic (meaning formed later than the surrounding or underlying rock formation), pipe-like orebodies, structurally controlled along NE–SW faults. Sphalerite, galena, pyrite, minor chalcopyrite, and accessory Ge-sulphides of briartite and renierite constitute the primary ore mineral assemblage. Cores of massive sulphide orebodies are surrounded by oxide zones of silicate ore (willemite) and mineralized jasperoid that consists largely of quartz, willemite, cerussite, smithsonite, goethite and hematite, as well as numerous other secondary minerals, including vanadates, phosphates and carbonates of Zn, Pb, V, and Cu.
Since the mine’s closure, the local economy has declined significantly. This has lead to people scavenging off the dangerous slag heaps to find lead for resale. Tunnels are dug by hand to reach the brown layers of slag, which the miners believe have a higher lead content. Almost a century of lead smelting and mining in a government-owned mine, the Zambia Consolidated Copper Mines (ZCCM), has left the once-thriving city of Kabwe, with over 300,000 inhabitants, heavily polluted affecting the high-density townships of Chowa and Kasanda, located to the north-east and north-west of the mining area respectively. Lead poisoning is of huge concern to the locals. In affected townships, the lead in soils is about 10 times the US safety limit and far higher in some hotspots e.g at the only medical clinic in Chowa where it is measured frequently over 10,000 parts per million (ppm), the limit in the US is 400ppm.
The difficulty for local people is townships like Malalulu is that the lead is blown in as dust and lays on the surface. Vegetables grown underground are okay to eat (apparently), once they are washed, maize too once washed. Low pools of surface water are dangerous, while water from wells is safe.
A large project conducted by the World Bank and the Nordic Development Fund commenced in 2005 for the environmental rehabilitation of the mine area. This is still ongoing, with an Environmental Impact Assessment underway. In 1994, much of the site area was sold to private investors, while ZCCM have the overall responsibility for rehabilitation of the sites. Since 2008 BMR has steadily acquired the land, they now own all the surface rights of the 705 hectares. Currently, Jubilee Metals Group and BMR Group are jointly developing tailings reprocessing facilities at the Kabwe mine to recover lead and zinc from these tailings deposits one site. BMR completed a definitive feasibility study (DFS) of the wash plant tailings in September 2013. Construction of the zinc recovery circuit at Kabwe started in the second quarter of 2018, while commissioning is anticipated by mid-2019.
The mine is estimated to contain JORC-compliant measured mineral resources of 304,771m³ of wash plant tailings. The tailings, slag and waste contain an estimated 61,147t of zinc and 41,345t of lead grading 10.66% Zn and 7.21% Pb. The processing plant will include separate zinc, lead and vanadium recovery circuits. Zinc is proposed to be recovered first, followed by further processing of the discard of the zinc circuit in the lead recovery circuit. An estimated 10,800 tonnes per month (tpm) is proposed to be processed in the initial stage, which will be further increased to 25,000tpm in the second and final phase.
Geological History
The oldest rocks in Zambia are part of the crystalline Precambrian basement complex, formed beginning in the Proterozoic eon of the Precambrian. They outcrop in the east and as the structurally complex Lufubu System in the Copperbelt. The granite, gneiss, migmatite, schist, amphibolite, charnockite, granulite, khondalite, phyllite, limestone and metaquartzite basement rocks date to the Paleoprpterozoic.
Due to extensive metamorphism and deformation, they were altered from older rocks, possibly from earlier in the Archean, but heat and pressure has destroyed evidence of earlier condition, obscuring the geologic history of the region.
Additionally, the basement rocks are intruded by other granites, syenite, dolerite, grabbo, rhyolite, andesite, metavolcanic and ultrabasic rocks. Although primarily exposed in the north and east, dome outcrops of basement rock exist at other locations in the country.
Stratigraphy & Geologic History of Zambia
A one-billion-year Proterozoic unconformity separates the basement rock from the conglomerate, quartzite, schists, iron-rich sandstones and mudstones of the Muva Supergroup. The supergroup is intruded by carbonite, dolerite, granite, granite porphyry, lamprophyre, norite, pegmatite and other igneous rock types. A rhyolite porphyritic belt, formed at the same time as the Muva Supergroup extends along the eastern bank of the Luapula River, between Lake Tanganyika and lake Mweru.
In the Neoproterozoic, the Katanga Supergroup deposited conglomerate, shale, argillite, quartzite, arkose, greywacke, dolomite and aeolian sandstones unconformably atop both the Muva Supergroup and Precambrian basement rocks.
Paleozoic
The deposition of the Katanga Supergroup continued into the Cambrian, in parallel with the rapid expansion of multi-cellular life. Geologists divide the supergroup into the Roan Group, Mwasha Group and Kundelungu Group in the Copperbelt, and simply into upper and lower units elsewhere. The Roan Group hosts much of the copper in the Copperbelt as chalcopyrite, chalcocite, bornite, malachite and azurite, in shale, sandstone, dolomite and quartzite associated with the margins of the Kafue syncline.
The Kundelungu Group dolomites, limestones and carbonaceous shales unconformably overly the Mwasha Group shale, argillite and interbedded quartzites. The lower unit of the Kundelungu Group is a conglomerate formed from glacial sediments, potentially related to the Hirnantian glaciation in the Ordovician, as Zambia, within the supercontinent Gondwana drifted close to the South Pole.
In the mid-Paleozoic, a large rift valley formed across southern Gondwana, spanning much of what is now southern Africa and southern South America. The Karoo Supergroup, the most widespread stratigraphic unit in southern Africa, deposited in the rift. In Zambia, the Karoo Supergroup is represented by outcrops in major rift block valleys, in the east and south, such as the Luangwa, Lukusashi, Lunsemfwa, Rufunsa and mid-Zambezi rivers. Because glaciations continued throughout much of the Paleozoic, into the Permian, in Gondwana, the bottom sequence of Karoo Supergroup rocks is a tillite that appears to be glacially produced. Ascending units includes sandstones and the Gwembe Coal Formation, mudstones and additional sandstones.
Mesozoic-Cenozoic (251 mya-present)
Deposition of the Karoo Supergroup continued into the Mesozoic, with the sequence capped by basalt lava flows from the Jurassic. Today, the basalt is exposed on the walls of Batoka Gorge, below Victoria Falls.
The Karoo Supergroup is overlain by Late Jurassic and Cretaceous sandstones and mudstone, and intruded by carbonite and kimberlite.
During the past 66 million years of the Cenozoic, the Kalahari Desert underwent a major expansion during a long lasting dry period. In the Neogene through the Pleistocene, this climate change deposited moderately consolidated sandstones and windblown sands as the Kalahari Group in the Western Province and other parts of northwest, south and central Zambia. Pleistocene and Holocene alluvial deposits line the major rivers, as well as the Bangweulu Swamps and Kafue Flats.
Minerals mined in Kabwe
Copper is one of the few metals that can occur in nature in a directly usable metallic form, native copper. This led to very early human use in several regions, from c.8000 BC. Thousands of years later, it was the first metal to be smelted from sulphide ores, c.5000 BC, the first metal to be cast into a shape in a mould, c.4000 BC and the first metal to be purposefully alloyed with another metal, tin, to create bronze, c.3500 BC. Common throughout the world, copper is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. It is widely used in electronics industry especially for use in wires, in plumbing, as a building material and as a constituent of various metal alloys, such as sterling silver, cupronickel and coins, and also in jewellery. It is a soft, orange-red metal.
Copper (Cu) is often found in the sedimentary layer, where sand and mud are compressed until they form a layer of sedimentary rock on the surface of the earth. Copper ore gets trapped in oxidized zones within these types of rocks; in hydrothermal veins; in the cavities of basalt that have been in contact with hydrothermal solutions; and as pore fillings and replacements in conglomerates that have been in contact with hydrothermal solutions. Copper is typically extracted from oxide and sulphide ores that contain between 0.5 and 2.0% copper. Currently, about 80% of global copper production is extracted from sulphide sources.
The great majority of zinc deposits contain the lead mineral, galena, and both the lead and zinc minerals are mined together.
Zinc (Zn) and lead (Pb) minerals often occur together because, as elements, they have similar chemical behaviour and combine with sulphur as primary minerals. People have used zinc-bearing mineral compounds for more than 2,500 years. Sediment-hosted Pb-Zn deposits can be divided into two major subtypes. The first subtype is clastic-dominated lead-zinc (CD Pb-Zn) ores, which are hosted in shale, sandstone, siltstone, or mixed clastic rocks, or occur as carbonate replacement, within a CD sedimentary rock sequence.
Lead has a bad reputation for its poisoning capabilities, some of which may have been exaggerated by fear. It cannot be absorbed by the skin or breathing, but it is harmful if it touches food or drink. It was at one time used in paint, pencils and eating utensils.
Galena/lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals.
Sphalerite is a zinc sulphide mineral with a chemical composition of (Zn,Fe)S. It is found in metamorphic, igneous, and sedimentary rocks in many parts of the world. Sphalerite is the most commonly encountered zinc mineral and the world's most important ore of zinc.
Pyrite/iron pyrite is an iron sulphide with the chemical formula FeS₂. Pyrite is considered the most common form of sulphide minerals. Pyrite's metallic lustre and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname fool’s gold.
Chalcopyrite is a copper iron sulphide mineral that crystallizes in the tetragonal system. It has the chemical formula CuFeS2. It has a brassy to golden yellow colour. It is often confused with pyrite and gold since all three of these minerals have a yellowish colour and a metallic luster. Chalcopyrite has a distinctive black streak with green flecks in it. Pyrite has a black streak and gold has a yellow streak.
Slag is the glass-like by-product left over after a desired metal has been separated from its raw ore. Slag is usually a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulphides and elemental metals.
In order to log this earthcache please send answers via 'messages' to the following questions.
1 What is the earliest era in which rocks in Zambia may have been formed?
2 Lead and Zinc were mined extensively in Kabwe mine. Name two other minerals mined.
3 What colour are the tailings that you see around GZ.
4 There are some smaller stones at the foot of the tailings. a) Is this Marble/Limestone/Granite/Slate? b) Describe the colour and texture.
5 The global price of copper has declined. Give one reason why this may have happened, in your opinion (some independent research required).
6 Can you make an educated guess as to why Broken Hill Man was found close to the listed coordinates?
7 a) Do you thing the adjacent road is Red Sandveld or Kalahari Sands? b) Explain your reasoning.
8 In order to prove you were at the location, please email the first letter on the sign on the wall behind you at GZ.