Examples of typical mineral deposits

Greenville Nickel Mine is located in the tropical area of North Queensland, Australia, with south latitude 19, east longitude 145 and west of townsville 175km.

(1) Geological background

The most important structural unit in Greenville area is the Broken River Fault Zone (Fletcher et al., 1975). This is a 200km long NE-trending structural belt, which is the contact boundary between the Precambrian metamorphic strata in Georgetown in the west and the Paleozoic sedimentary rocks in the Broken River Basin in the east. On the one hand, fault zone promotes the development of permeability zone in alteration zone; On the other hand, it becomes the main channel for discharging altered dissolved substances. The fault zone plays an important role in the formation of the deposit. The contour plane at the bottom of the ore body shows that these fault zones control the distribution of graben and their strike is parallel to the regional tectonic direction. In addition, nickel mineralization is still developed in some deep faults.

Three ultrabasic rock complexes are exposed in Greenville area, namely Precambrian Sandul Wood serpentine of Georgetown Formation, Devonian Peulegeli complex and Greer klick complex deposited in Broken River Rift. The Geli complex in Pule is closely related to the formation of lateritic nickel deposits.

Serpentine peridotite in Plegley complex constitutes the basement of Greenville ore body. The rock mass covers an area of about 5.5km2 and occurs in the crust of gabbro in the form of crystal nucleus. Minerals are evenly distributed, and there are no signs of bedding or zoning in the rocks. Serpentine is dark green to gray with fine and soft particles. The rocks are almost entirely composed of serpentine minerals, followed by a small amount of chlorite and olivine, mainly disseminated authigenic particles.

The average chemical composition of fresh serpentine is SiO237. 1%, TiO 2 < 0.02%, Al2O30.63%, Cr2O30.39%, Fe2O36.7%, FeO0.47%, MnO 0.1%and MgO39.2%. Showing a high nickel content.

(2) Greenville orebody

The laterite remains are distributed in the whole area (Fletcher et al., 1975), covering all types of basement rocks. Starting from the new rock, it gradually transits from the zone with different properties to the soil zone on the surface, forming a mature weathering profile with chemical and mineralogical characteristics. This profile is widely distributed in the area about 1/3 above the serpentine in Greenville. Some remaining areas have been partially or completely eroded. It is speculated that 5.5km2 of serpentine in the whole area was once covered by nickel-bearing laterite, but only 3.3km2 remained due to erosion. Figure 12-3 shows the surface geological conditions of the deposit and the mineralization distribution profile reaching industrial grade.

Greenville deposit has a typical laterite profile, which is generally divided into four zones from bottom to top. The lowest layer is the weathered serpentine belt directly covering the bedrock, and the top is the limonite belt, bean red soil belt and soil belt in turn (Chen et al., 1993).

1. Serpentine laterite belt

From fresh rock to weathered serpentine, the rock density decreased from 2.7t/m3 to 1.4t/m3. However, the mineral structure and rock structure of the basement parent rock have been preserved. Microscopically, rocks are composed of porous reticulated serpentine minerals, which are distributed around clay minerals, and magnesite and goethite veinlets develop along cracks. In the upper part of the belt, the weathered serpentine is strongly altered, the iron is more abundant, and the primary structure of the parent rock gradually disappears. The bottom of weathered serpentine is gray-green or olive-gray, with yellow and brown increasing upward, and the transition from brown to limonite belt is mainly yellow and brown. In the weathered serpentine belt, the enrichment of nickel is as high as 10 times that of the parent rock, and generally reaches the highest value at the edge of the belt. The serpentine laterite belt is 10m thick, in which the seam is 5m thick.

2. Limonite laterite zone

The laterite area of limonite is characterized by the lack of parent rock structure and mineral combination. It is mainly composed of goethite, which is generally massive and brownish yellow. Rock is often cut by vertical voids and tubular bodies that extend upward to the upper bean belt. The enrichment of nickel in this zone is usually lower than that in the weathered serpentine zone, but the enrichment of cobalt reaches a peak, which is 25 times higher than that in the original rock and the content reaches 0.5%. Cr2O3 and MnO are also abundant.

3. Bean red soil region

This area contains iron nodules, some of which are dispersed in the soil, some of which are glued into strips, or exposed to the ground to form iron shells. Its color is reddish brown to brown, and the transition between the lower part and the underlying limonite laterite belt gradually turns yellow brown. Tuberculosis is pea-shaped, oolitic or irregular plate. The size and content of nodules usually increase upwards, reaching 4.5 cm at the top of the area. From the bottom to the top, the contents of nickel and cobalt decrease, and at the top, they drop to the background value, while the content of A 12O3 increases obviously.

4. Soil belt

A thin layer of reddish-brown loose residual soil is developed on most sediments. The depth of reddish-brown soil and clay layer in low-lying areas in central China can reach 10m, with an average of 3m.

Figure 12-3 Geological map and profile of serpentine body in Greenville

(III) Ore type and distribution

Ores can be divided into three types: weathered serpentine, limonite and siliceous.

1. Weathered serpentine ore

Weathered serpentine ore accounts for almost half of the ore reserves. This kind of ore is mainly silicate minerals, with nickel grade 1.5% ~ 1.7%, low cobalt grade (0.05%), low iron (15% ~ 20%), high magnesium (15%) and silicon 30. Weathered serpentine minerals occur in the central area under bean laterite and limonite laterite, and are exposed on the surface of the north and south edges of the ore body, with an average thickness of 5m.

2. Limonite

Limonite accounts for 1/4 of the ore reserves, mainly oxidized minerals, and the nickel content is generally lower than the average level (1.2% ~ 1.4%). Cobalt is mainly concentrated in this kind of ore, with an average of 0.25%, and most of it is more than 0.5%. High iron content (40% ~ 50%), low magnesium content (1% ~ 5%) and low silicon content (15% ~ 20%). Limonite mainly occurs in low-lying areas in the middle of the deposit, with an average thickness of 3 m.

3. Siliceous ore

Siliceous ore accounts for 25% of ore reserves. According to the structure, it can be divided into block type and shell type. The massive siliceous ore appears irregularly in the upper part of weathered serpentine, or in horizontal strips or blocks to explain limonite laterite. The massive siliceous ore is distributed in the whole ore body in lenticular or strip shape, and the width can reach tens of meters. Nickel content is generally low (3.2% ~ 1.2%), cobalt is lower than the average (0.05% ~ 0.08%), iron is low (15% ~ 20%), magnesium content changes greatly, and silicon dioxide content is very high (50% ~ 60%). Shell-shaped minerals usually have a strong fracture zone, and its width varies greatly, from 10cm to more than 5 m. Shell-shaped minerals are generally distributed in linear bands throughout the ore body. The ore consists of thin-walled chalcedony shell with a width of 10 ~ 50 cm, and the shell is filled or partially filled with strongly altered serpentine or limonite. The crust contains ores with the highest nickel content (up to 6%), cobalt content is generally higher than the average (0. 15% ~ 0.20%), iron content is low (15%), magnesium content is low (5% ~ 10%), and silicon content is high (40%).

(iv) Genesis of the deposit

The enrichment of nickel begins with olivine crystal absorbing metal from magma, and then olivine containing nickel condenses into olivine magma. During Devonian, the tectonic activity along the fracture zone led to the intrusion of Peuler ultramafic rock mass. Ultramafic rocks contain about 0.2% nickel. Serpentine fossilization turns these rocks and minerals into hydrous silicates, and then tectonic uplift blocks and erosion expose these rocks to tertiary surface and climatic environment. After the chemical balance formed by these minerals under the deep underground geological conditions is destroyed, it is broken under the physical and chemical action of the near-surface environment. The new conditions are favorable for laterization. Metals released from the decomposition of serpentine minerals enter the laterite system according to their relative solubility, and nickel is enriched to form Greenville ore body.

The main factors for the enrichment of Greenville laterite nickel deposit may be:

(1) serpentine is widely distributed, with 0.2% nickel, uniform mineralization and high degree of fragmentation.

(2) On the one hand, the cyclic rainfall causes the change of groundwater level, which makes the rock in an alternating state of saturation and aeration, which is helpful for oxidation; On the other hand, acidic water periodically moves vertically downward through the oxidized rock layer, which causes the redistribution of metals due to dripping and precipitation.

(3) The steep groundwater level gradient and lateral water movement cause the migration of soluble elements.

(4) Appropriate temperature for effective reaction.

(5) Exploration history

Nickel-bearing laterite in Greenville was discovered during the regional geological mapping jointly conducted by Australian Bureau of Mineral Resources and Greenville Geological Survey in 1957. At that time, the iron-bearing zone in the upper part of Greenville laterite was explored and it was found that the abundance of nickel in it exceeded 1%. 1966, the northern metal exploration company of Australia took nickel mine as one of the exploration projects, and Greenville was listed as the key prospecting target area. Compared with the nickel mine area in New Caledonia, the possibility of nickel-rich silicate belt under iron cap is put forward. Geologists of the company confirmed the existence of nickel ore belt through field verification. Geologists took a sample from an outcrop in this area, and after testing, the grade of nickel exceeded 3%. Subsequently, more than 5000 meters of drilling, exploration wells and a large number of trench samples were carried out. 1969 The ore reserve is 40 million tons, with an average of Ni 1.57% and Co0. 12%. 1990, the resource reserve is 8 million tons, Ni 1.357%, Co0. 1 1%.

Two. Nickel mines in New Caledonia

(1) Geological background

New Caledonia is an island country located in the northeast of Oceania, with a length of 400km in the northwest and 48km in the northeast, with an area of1.9000 km2. The island is an island arc gradually formed after Mesozoic due to the subduction of the Pacific plate to the Australian plate. The strata in this area are mainly Cenozoic ophiolite suite, volcanic rocks and clastic sediments. 75% of the island is ultramafic-mafic rock series. Nickel mines are produced in countless places, concentrated on the east and west coasts. More importantly, Nepoui and Poum on the west coast, Poro, Kouaoua and Thio on the east coast, and nickel mines near Noumé a, the capital. The total amount of nickel resources exceeds 45 million tons.

Nickel mines in New Caledonia were discovered in 1864. New Caledonia was the most important nickel mine producing area in the world before sudbury nickel mine was developed and utilized. At present, due to the massive exploitation of nickel sulfide, laterite nickel ore has been relegated to a secondary position in the world, but the nickel output of New Caledonia still ranks fourth in the world.

Most nickel mines in New Caledonia are laterite nickel mines developed on ultramafic rocks. The types of bedrock rocks are mainly dunite and gabbro peridotite, which mostly intrude into Cretaceous and older sedimentary rocks, and the age is Paleogene. Serpentinization of rocks is widespread, which is mainly the result of hydration of ultramafic minerals in rocks during rock emplacement, and has nothing to do with modern topography and weathering.

(II) Lateritization profile

Serpentine exposed in New Caledonia has undergone intense weathering since Paleogene, forming a red soil profile similar to that in other tropical regions. Nickel deposits have an ideal laterite profile (Chen et al., 1993), which can be divided into five zones from top to bottom (Figure 12-4). The downward and lateral flow of ore-bearing solution in the adjacent area increases the content of nickel, and the migration and enrichment of nickel are shown in Figure 12-5.

(1) Iron cap belt: After a long period of intense weathering, a large number of silicon, magnesium, alkali and alkaline earth substances are lost, and the remaining substances are mainly iron oxides, which are bonded into hard shells to form iron caps or iron nodules.

(2) Bean-shaped red soil zone or iron nodule zone: composed of soft dark red red red soil and dispersed bean-shaped or spherical iron oxide. The main component of laterite is powdered limonite, lacking clay minerals, and the content of nickel and cobalt is close to the background value.

(3) Limonite laterite zone: it is composed of soft and porous iron oxide and a small amount of clay minerals, and the ore grade is low.

(4) Serpentine zone: mainly serpentine weathered sapropelic soil, composed of sphalerite and montmorillonite, containing residual core of original rock. Serpentine zone is the main ore-bearing stratum, nickel occurs in sphalerite, and montmorillonite (or montmorillonite) is magnesium-iron isomorphic. From the weathered serpentine belt upward, the nickel content gradually decreases and the cobalt content gradually increases.

(5) Bedrock zone: it is mainly composed of fresh serpentine, and there are often a large number of secondary nickel silicate veinlets in the fracture development area of the nearly weathered serpentine zone, with less ore content.

(III) Ore type

There are two kinds of ores mined by laterite nickel mine in New Caledonia (Hu Pinmei,1980; Chen et al., 1993): one is nickel silicate ore, which consists of a large number of green nickel-bearing serpentine varieties-silicomagnesite and a small amount of nickel-bearing saponite. The ore is dark green, apple green to gray, soft sapropelic, and mainly occurs in the lower part of weathering zone. The Si-Mg-Ni ore is filled in the cracks of serpentine in the form of veinlets, or condensed in the pores of parent rock in the form of fine particles, and its thickness can reach several meters. Nickel silicate ores can be divided into two subtypes. When nickel replaces iron in silicate, the ore contains high magnesium and is green (or green ore). Where nickel replaces magnesium in silicate, the iron oxide content remaining in the ore is high and brown (or "chocolate" ore). Green ore occurs in the lower part of weathered serpentine belt and cracks in bedrock; "Chocolate" minerals are distributed in the upper part of sapropelic zone and the lower part of lateritic zone. The other is nickel oxide ore, which is produced in limonite laterite zone. Many limonite laterite zones are rich in cobalt, forming a kind of nickel-cobalt bearing soil ore, with the highest cobalt content of 10%, which is of great industrial value. The common gangue minerals in laterite are talc, sepiolite and a small amount of chalcedony.

Figure 12-4 Profile of Laterite Nickel Deposit in New Caledonia

Figure 12-5 Migration and Enrichment Map of Nickel in New Caledonia Nickel Deposit

Nickel mines in New Caledonia are mainly nickel silicate, with an average nickel content of about 1% ~ 3.5%, and the highest nickel content can reach 10%, which is the region with the highest grade of laterite nickel ore in the world. Nickel is enriched in the lower part of laterite profile, forming a nearly horizontal ore body. The best ores generally appear on the gentle slopes of the mountains and the saddle of the mountain mouth extending from the main ridge. There are few nickel mines in alpine plains, which may be because the erosion rate of mountains is too fast and the rocks cannot be fully oxidized. In plain areas, nickel-bearing rocks are not easy to decompose and oxidize because of the high groundwater level and thick deposits on the surface.

Laterite nickel ore is mainly related to serpentine, and there is little chance of mineralization of non-serpentine ultramafic rocks. This may be because serpentine has poor permeability compared with other unaltered ultramafic rocks, which can prevent the circulation and downward migration of ore-bearing water and create favorable conditions for nickel enrichment.

refer to

Paul Golightly J. 1983。 Laterite nickel deposit, metal mineralization theory and prospecting method. Beijing Institute of Metallurgical Geology, Ministry of Metallurgical Industry.

Cao Yisheng. 2007. Progress and development prospect forecast of international nickel mine industry. World nonferrous metals, 8: 34 ~ 39.

Chen, Wu, Fu Debin, et al. Nickel deposit. Beijing: Geological Publishing House, 1 ~ 199.

Hu Pinmei. 1980. Overview of nickel resources in the world. Iron and steel, 15 (1): 65 ~ 70.

Xiao zhenmin. 2002. Development of laterite nickel ore in the world and application of high pressure acid leaching technology. China mining industry, 56 ~ 59.

The Ministry of Metallurgy went to the Philippine Porphyry Copper Mine Geological Survey Mission. 1980. Formation and prospecting of lateritic nickel deposits in the Philippines. Geology and exploration, 1: 16 ~ 29.

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Fletcher K., Couper J. 1975. Greenwall nickel laterite mine in North Queensland. Economic Geology of Australia and Papua New Guinea, 995~ 100 1.

Kula C.M. 2000, Understanding Mineral Deposits. Dordrecht: Kluwer Academic Press, 37~40.