The Broken Hill Ore Deposit is located underneath Broken Hill in western New South Wales, Australia, and is the namesake for the town. It is arguably the world's richest and largest zinc-lead ore deposit.
The Broken Hill Ore Deposit is located underneath Broken Hill in western New South Wales, Australia, and is the namesake for the town. It is arguably the world's richest and largest zinc-lead ore deposit.
Charles Sturt made a pencil sketch of the area in 1844 and noted iron ore along an isolated hill. In 1866 the Mount Gipps sheep station named their paddock, which embraced the lode outcrop, Broken Hill. However, the hill was thought to be mullock. On 5 September 1883, a Mount Gipps boundary rider named Charles Rasp staked a claim on the outcrop because it looked like tin oxide as described in his prospecting guide book. With six others he staked the entire outcrop. In 1884, the syndicate reorganized as the Broken Hill Mining Company. Horn silver was discovered in 1885 and the Broken Hill Proprietary Company Limited was organized. [1]
Charles Rasp discovered the gossan or weathered sulfide outcrop of massive lead-zinc sulfides on a feature known as Broken Hill. Rasp reported finding massive galena, sphalerite, cerussite and other oxide minerals, but was most concerned with the galena, a primary source of lead. His reports, believed exaggerated at the time, of masses of lead in the desert, soon proved true and sparked a 'lead rush' similar to gold rushes.
Broken Hill was exploited initially by small prospectors working the gossan for easily won galena, and soon dozens of shafts were sunk. Ore was carted to South Australia by camel trains, wagons and pack mules. A major secondary source of income became apparent, with extremely high silver grades recovered, including native silver, and other rare silver minerals present in abundance.
Open-pit mining of silver oxide ores was the norm from 1885 to 1898, with local smelting. From 1898 until 1915, the leadzinc-silver sulfide minerals were developed with the concentrates treated overseas. Starting in 1915, the concentrates were treated entirely in Australia. The central part of the lode was depleted by 1940 and production was concentrated in the north and south ends. Properties in the 1950s included North Broken Hill Limited, Broken Hill South Limited, The Zinc Corporation Limited, and New Broken Hill Consolidated Limited. Through 1946, 63.8 million tons of ore have produced 8.6 million tons of lead, 5.2 million tons of zinc, 538 million ounces of silver, and 165,000 ounces of gold. [1]
Mining has gradually moved away from the initial small prospectors, in line with the experience in all other major mineral fields, toward gradual consolidation of claims and tenure, an increase in tenure and mine size and efficiencies in operations resulting in smaller workforces. This has accelerated in the last part of the 20th century via the formation of the Broken Hill Proprietary Company and its exit from Broken Hill, toward only two operators at present, utilising highly efficient bulk underground mechanised mining.
Broken Hill South Limited ceased operations in 1972 and its leases were acquired by Minerals Mining & Metallurgy (MMM). Underground mining stopped in 1976 and open pit mining is concentrated in the Blackwood Open Cut, which commenced in 1973, and the Kintore Open Cut. Stope fill, plus remnant supergene silver and sulphide ore characterize the ore reserve. [2]
Pasminco took over the leases of Zinc Corporation and New Broken Hill Consolidated. Their main shafts included ZC, NBHC and Southern Cross. These ZC Mines Leases lie south of the MMM Mining Leases along the Broken Hill "line of lode". [3]
By the early 1950s the Broken Hill area had suffered a major drought of over eight years which was close to shutting down the mining operation. Due to the acute water shortage problem, the mine owners set in motion what became at by that time the largest use of a train for a massive water lift. Over a period of several months, special tanker car trains transported over 250 million gallons of water 40 miles by train which was pumped from the Darling River near Horse Lake, west to the small Mount Gipps rail siding where the water was transferred to large storage tanks that were built for the purpose. From the Mount Gipps storage tanks the water flows down hill through a large pipe to the Stephens Creek Reservoir, Broken Hill's main water storage facility. From Stephens Reservoir the water makes another downhill journey by a large pipe to the Broken Hills mining operation. [4]
According to Gustafson, "The Broken Hill lodes are massive lead-zinc sulphide replacement orebodies forming (before erosion) a long continuous, irregular flat, curving pencil of ore roughly 2,000-3,000 high and 300 feet thick. In longitudinal section, the deposit describes a broad arc, flat in its middle (highest) portion, and pitching downward at each end...continuously mineralized for a horizontal distance of more than 3 miles." Sphalerite and galena are the main metallic minerals. [1] The simplified geology of the Broken Hill ore body is a series of boomerang-shaped, highly sheared and disrupted ribbon-like and poddy massive sulfide lenses which outcropped in the central section (the old "Broken Hills" gossan hills) and plunge steeply north and moderately south.
The Broken Hill ore body is hosted within the gneisses of the Willyama Supergroup, a mesoproterozoic sequence of sillimanite gneisses. The original sediments consisted of alternating clays, sandy clays, sands, granitic sills, gabbro sills, and pegmatite sheets. Deformation, folding, and metamorphism converted the sediments into gneiss, the granitic rocks in augen, and the gabbro into amphibolites and hornblende schists. [1]
The ore consists of massive, recrystallised sphalerite-rich, galena-sphalerite and galena-rich sulfide lenses in folded horizons, known as No. 2 Lens Formation and No.3 Lens Formation. Both have distinctive metal ratios and gangue minerals. The ore boundaries are parallel to the bedding planes. According to Gustafson, "There is evidence that the ore has been introduced into an old, already folded, rock and has replaced certain favourable layers of that rock, particle by particle, with large tonnages of garnet, rhodonite, fluorite, marmatite (and wurtzite), galena, and other minerals that constitute the orebodies." The Potosi-Footwall Gneiss is found on both sides of the main lode. [1] The ore often consists up to 100% lead-zinc sulfides, with little or no pyrite, chalcopyrite or gangue sulfides.
The footwall to the mineralization is a psammopelite gneiss, consisting of feldspar, quartz, garnet, biotite and amphibole, with a pelite gneiss on the hanging wall. The footwall gneiss contains anomalous mineral chemistries including a rare lead-rich feldspar and manganese-rich garnet chemistries. Ore is predominantly hosted at this stratigraphic break, but much of the ore body is structurally remobilised or offset into both the hangingwall and footwall, and the geometry of the ore deposit is particularly complex on the local scale.
The genesis of the Broken Hill ore body is of great historical importance to geologists, particularly in Australia, as it is an iconic ore body and one of the most studied in the world, with over 1,500 papers published to date. It is also of great current importance, as conceptions of the genesis of this enigmatic ore deposit and its structural and stratigraphic setting drives exploration for repetitions of the ore deposit along strike, and in finding analogues elsewhere in the world.
The genesis of Broken Hill is also of interest as it is of enduring controversy and conjecture, with the jury still mostly out on the matter although consensus has been reached on several key facets of the genetic processes which resulted in Broken Hill's formation. The interpretations presented below are the most palatable middle view of a range of opinions.
Broken Hill is widely considered to be a sedimentary exhalative (SEDEX) deposit which has been extensively reworked and modified by metamorphism and shearing. [5] Key evidence for this overarching theory includes the association of silver, lead and zinc, which is found in many other SEDEX deposits worldwide and the position of the bulk of mineralization at a key stratigraphic contact between psammite and psammopelite gneisses. But there is mounting evidence that the situation at Broken Hill is much more complex. [6] [7] [8]
The Potosi Gneiss, and the manganiferous garnet horizon, are considered key indicators of original bedding orientation (S0) and are thus key exploration targets, as there is a proven association of anomalous lead and zinc within the gneissic stratigraphy with these horizons on a regional basis.
The Broken Hill ore deposit is hosted within the Proterozoic gneisses of the Broken Hill Block, adjacent to the Curnamona Craton in South Australia. The terrane in which Broken Hill is hosted has undergone a series of several metamorphic deformations at amphibolite facies. [9] This has resulted in the 'squeezing' of the lead and zinc sulfides into the current basic boomerang shape, and resulted in the separation of the ore body into zinc-rich and lead-rich lodes and domains.
The lodes themselves show various structural facies, and show variable responses to shearing, though mostly in a ductile fashion. Many lodes, particularly the lead lodes, have sharp contacts with gneissic host rocks, indicating they have become structurally relocated during peak metamorphism. Similarly, it is conjectured that the current position of the zinc and lead lodes at Broken Hill may not necessarily be related to their original position along the bedding planes (S0), or vertically within the stratigraphic section.
It has taken some considerable effort to 'see through' the overwhelming structural overprint of metamorphism to infer the SEDEX classification.
The lower part of the Willyama Supergroup has undergone intense sodium alteration, particularly the Broken Hill Block and subdomain. This has resulted in pervasive albite alteration particularly in the Olary domain adjacent to Broken Hill.
The influence of high-temperature metamorphic fluids on the ore deposit cannot be discounted, although it is considered less central to genetic factors than previous theories of hydrothermal origins for the deposits. The current consensus view is that metasomatic overprints are present as a result of the focusing of flow through the zones of weakness around the massive sulfides, which are ductile failure loci in themselves.
Metasomatic effects include re-equilibrating isotopic systematics of the lead-zinc sulfides and wall-rocks, and introduction of rare elements into the sulfide bodies to form one of the most diverse mineralogical assemblages in the Earth's crust, with 1500 or more mineral species recognized at Broken Hill, including several dozen not reported elsewhere.
The association of the Broken Hill line of lode with a horizon of manganiferous garnets is considered to be partly a function of a potential protolith of exhalative manganiferous chert, metamorphically upgraded to a garnetiferous gneiss, and perhaps some reconstitution of that protolith by metasomatism associated with the nearby massive sulfides.
Broken Hill is the type locality for a class of ore deposits known as Broken Hill Type, or BHT, ore deposits. [6] This is a classification grouping of similar deposits for use in ore genesis theories and mineral exploration methodologies. [10]
The key criteria for BHT ore deposits are; [11]
Sphalerite is a sulfide mineral with the chemical formula (Zn,Fe)S. It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in sedimentary exhalative, Mississippi-Valley type, and volcanogenic massive sulfide deposits. It is found in association with galena, chalcopyrite, pyrite, calcite, dolomite, quartz, rhodochrosite, and fluorite.
The Rammelsberg is a mountain, 635 metres (2,083 ft) high, on the northern edge of the Harz range, south of the historic town of Goslar in the North German state of Lower Saxony. The mountain is the location of an important silver, copper, and lead mine. When it closed in 1988, it had been the only mine still working continuously for over 1,000 years. Because of its long history of mining and testimony to the advancement and exchange of technology over many centuries, the visitor mine of Rammelsberg was inscribed as a UNESCO World Heritage Site in 1992.
Galena, also called 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.
In geology, a lode is a deposit of metalliferous ore that fills or is embedded in a fracture in a rock formation or a vein of ore that is deposited or embedded between layers of rock. The current meaning dates from the 17th century, being an expansion of an earlier sense of a "channel, watercourse" in Late Middle English, which in turn is from the 11th-century meaning of lode as a "course, way".
Volcanogenic massive sulfide ore deposits, also known as VMS ore deposits, are a type of metal sulfide ore deposit, mainly copper-zinc which are associated with and created by volcanic-associated hydrothermal events in submarine environments.
The Southeast Missouri Lead District, commonly called the Lead Belt, is a lead mining district in the southeastern part of Missouri. Counties in the Lead Belt include Saint Francois, Crawford, Dent, Iron, Madison, Reynolds, and Washington. This mining district is the most important and critical lead producer in the United States.
Various theories of ore genesis explain how the various types of mineral deposits form within Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined.
Sedimentary exhalative deposits are zinc-lead deposits originally interpreted to have been formed by discharge of metal-bearing basinal fluids onto the seafloor resulting in the precipitation of mainly stratiform ore, often with thin laminations of sulphide minerals. SEDEX deposits are hosted largely by clastic rocks deposited in intracontinental rifts or failed rift basins and passive continental margins. Since these ore deposits frequently form massive sulfide lenses, they are also named sediment-hosted massive sulfide (SHMS) deposits, as opposed to volcanic-hosted massive sulfide (VHMS) deposits. The sedimentary appearance of the thin laminations led to early interpretations that the deposits formed exclusively or mainly by exhalative processes onto the seafloor, hence the term SEDEX. However, recent study of numerous deposits indicates that shallow subsurface replacement is also an important process, in several deposits the predominant one, with only local if any exhalations onto the seafloor. For this reason, some authors prefer the term "Clastic-dominated zinc-lead deposits". As used today, therefore, the term SEDEX is not to be taken to mean that hydrothermal fluids actually vented into the overlying water column, although this may have occurred in some cases.
Kambalda type komatiitic nickel ore deposits are a class of magmatic iron-nickel-copper-platinum-group element ore deposit in which the physical processes of komatiite volcanology serve to deposit, concentrate and enrich a Fe-Ni-Cu-(PGE) sulfide melt within the lava flow environment of an erupting komatiite volcano.
Seafloor massive sulfide deposits or SMS deposits, are modern equivalents of ancient volcanogenic massive sulfide ore deposits or VMS deposits. The term has been coined by mineral explorers to differentiate the modern deposit from the ancient.
Carbonate-hosted lead-zinc ore deposits are important and highly valuable concentrations of lead and zinc sulfide ores hosted within carbonate formations and which share a common genetic origin.
The Admiralty mining district is a mining area in the U.S. state of Alaska which consists of Admiralty Island. Silver and base metals are mined, with gold recovered as a by-product.
The Bathurst Mining Camp is a mining district in northeast New Brunswick, Canada, centred in the Nepisiguit River valley, and near to Bathurst. The camp hosts 45 known volcanogenic massive sulfide (VMS) deposits typical of the Appalachian Mountains. Some of the ore is smelted at the Belledune facility of Xstrata. Although the primary commodity is zinc, the massive-sulphide ore body produces lead, zinc, copper, silver, gold, bismuth, antimony and cadmium.
The Iberian Pyrite Belt is a vast geographical area with particular geological features that stretches along much of the south of the Iberian Peninsula, from Portugal to Spain. It is about 250 km long and 30–50 km wide, running northwest to southeast from Alcácer do Sal (Portugal) to Sevilla (Spain). The mining activity in this region goes back thousands of years.
The le Puy Mine is an ancient lead mine in the northwestern Massif Central, France. The mine produced mainly silver-bearing galena.
Rampura Agucha is a zinc and lead mine located on a massive sulfide deposit in the Bhilwara district of Rajasthan, India. Rampura Agucha is located 220 km (140 mi) from Jaipur. It is north of Bhilwara, and northwest of Shahpura. Rampura Agucha is 10 km (6.2 mi) southeast of Gulabpura on NH 79. The mine is owned by Hindustan Zinc Limited (HZL), and has the world's largest deposits of zinc and lead.
In ore deposit geology, hypogene processes occur deep below the Earth's surface, and tend to form deposits of primary minerals, as opposed to supergene processes that occur at or near the surface, and tend to form secondary minerals.
Hydrothermal mineral deposits are accumulations of valuable minerals which formed from hot waters circulating in Earth's crust through fractures. They eventually create metallic-rich fluids concentrated in a selected volume of rock, which become supersaturated and then precipitate ore minerals. In some occurrences, minerals can be extracted for a profit by mining. Discovery of mineral deposits consumes considerable time and resources and only about one in every one thousand prospects explored by companies are eventually developed into a mine. A mineral deposit is any geologically significant concentration of an economically useful rock or mineral present in a specified area. The presence of a known but unexploited mineral deposit implies a lack of evidence for profitable extraction.
Massive sulfide deposits are ore deposits that have significant stratiform ore bodies consisting mainly of sulfide minerals. Most massive sulfide ore deposits have other portions that are not massive, including stringer or feeder zones beneath the massive parts that mostly consist of crosscutting veins and veinlets of sulfides in a matrix of pervasively altered host rock and gangue.
