A striking natural metal is placer gold. Placer gold is naturally occurring, impure, large-grained, and irregularly shaped gold nuggets. It is usually composed of a collection of natural gold, quartz, and other minerals. Because it resembles a dog's head, it is called placer gold; if it resembles a horseshoe, it is called horseshoe gold.

 

In the mid-19th century, a carpenter found a 32kg placer gold nugget by the roadside on the west coast of the United States, which triggered the California Gold Rush.

 

A total of more than a thousand placer gold nuggets have been discovered in China. In 1909, a gold miner in Yan Yuan, Sichuan, was unfortunately injured in the foot by a "rock" falling from above while working underground. When he moved the "rock" to the pit, it turned out to be a piece of gold weighing 31kg.

 

However, is prospecting all about luck? Of course not. If you don't have scientific prospecting techniques and rich prospecting experience, and you keep thinking about "a gold nugget falling from the sky", you will hardly find any ore.

 

I. How to find gold mines

 

 

Gold deposits can occur in almost any rock type and in strata of any age, but the Precambrian greenstone belts are the most important. The types of gold mineralization are: greenstone belt type (containing basic and ultrabasic rocks), volcanic type, porphyry type (containing alkaline rocks and granite), turbidite type, black rock series type, sandstone type, river sediment type; according to genetic type, there are quartz vein type, sulfide vein type, fine dissemination type, tectonic altered rock type, iron manganese cap type, laterite type, etc.

 

1. First, attention should be paid to silicified zones, quartz veins, and secondary quartzites. This is because gold mineralization is closely related to silicification; it can be said that there is no gold without silica. Of course, not all siliceous bodies contain gold, but gold-bearing siliceous bodies are mostly smoky gray and have good water color. This is because gold-bearing siliceous bodies contain more or less sulfides, and because the sulfides are very fine, the quartz appears smoky gray. In particular, platy quartz veins (which may contain multiple black bands, such as a mixture of carbonaceous and fine-grained sulfides) are highly gold-bearing. Even in the case of low-sulfide bright gold quartz veins, when gold ore is present, sulfides such as stibnite, bismuthinite, wheel ore, arsenopyrite, and fish-egg-like lead-zinc ore are often present.

 

2. Secondly, attention should be paid to fault structural zones, especially ductile shear zones. Gold mineralization is invariably associated with faults; it can be said that there is no gold without structure. In particular, attention should be paid to ultramylonite, mylonite, micro-sugar-like quartzite, and talc magnesite schist, which are often the locations of rich gold ore bodies. The gold content of giant to large fault zones is often poor, while the adjacent secondary fault zones are often the sites where gold ore bodies are produced.

 

3. Third, attention should be paid to the gold content determination of iron hats, reddish-brown and brownish-yellow residual colluvium, and carbonate solution groove and trough deposits. They can not only themselves become iron hat type and laterite type gold mines, but also indicate the search for primary gold mines.

 

4. Fourth, attention should be paid to finding gold in antimony, mercury, and arsenic mines (especially realgar and orpiment). As far as antimony mines are concerned, they can coexist with gold to form antimony-gold deposits; they can also be separated, but not far apart, hence the saying "not in it, not far from it". Gold can also be found in the periphery of some lead-zinc mines, such as the periphery of the Qingchengzi lead-zinc mine; and the lower part of copper deposits. The alteration zone of copper-nickel sulfide deposits is also a good place to find gold.

 

5. In addition to silicification, alterations related to gold mineralization also include iron dolomite alteration, iron calcite alteration, chromic muscovite alteration, pyrite sericite alteration, albitization, fine-grained pyrite alteration, and low-temperature alteration combinations of arsenic, antimony, mercury, bismuth, and thallium mineralization.

 

6. Pay attention to the fault fracture zones and tectonic alteration zones within basic rocks, ultrabasic rocks, porphyry, alkaline rocks, peralkaline granitic rocks, carbonaceous siliceous mudstones, and impure carbonate rocks.

 

7. Carry out river heavy mineral, gully secondary halo, and various geochemical prospecting work. Using gold to find gold is currently the most important method of gold prospecting.

 

8. Find gold based on indicator elements of gold, such as the elemental combination anomalies of mercury, antimony, bismuth, arsenic, thallium, selenium, lead, zinc, copper, and silver.

 

9. Use geophysical methods to determine the distribution of faults and sulfides to indirectly search for gold mines.

 

II. How to find placer gold

 

There are many methods for prospecting placer gold, and the commonly used methods are five: ① natural heavy mineral method, ② engineering heavy mineral method, ③ investigation of old mines, ④ geological and geomorphological analysis, and ⑤ geophysical and new aerial technology methods.

 

The first three methods are direct prospecting methods that determine the presence or absence of placer gold by sampling and investigation and directly determine whether ore formation has occurred; the latter two methods are indirect prospecting methods that infer the possibility of ore formation by analyzing and evaluating ore-forming conditions, studying the environment, and studying certain characteristics of sediments. Among them, geological and geomorphological surveys are the basis for placer gold prospecting analysis. Usually, the geological and geomorphological analysis provides the basis for determining where to look for placer gold deposits and where and in which parts to arrange sampling projects. The specific methods of placer gold prospecting are introduced below.

 

I. Natural Heavy Mineral Method

 

The natural heavy mineral method is based on the fact that the density (specific gravity) of placer gold particles is very high, and it can be directly selected using a panning dish. This method involves digging pits to sample the surface or shallow layers of loose clastic sediments and panning directly in the field to determine whether placer gold is present. Sampling includes river heavy mineral sampling of water system sediments, outcrop sampling of terrace gravel layers, and residual colluvial heavy mineral sampling of slopes.

 

The first two types of sampling can understand the gold content of water system sediments, the general distribution range of placer gold, and the grade and thickness of gold-bearing layers in terraces. Sampling of residual colluvial layers on slopes is carried out within a small gully mountainous area where placer gold is known to exist, used to trace the source of placer gold, and to delineate the distribution range and narrow down the rock gold prospecting target area by digging shallow pits at certain intervals on the slope and at the foot of the slope and panning according to the results. Among these three sampling methods, the most widely used is the river natural heavy mineral method.

 

River natural heavy mineral sampling work is generally carried out from bottom to top along the upstream of the water system or along the small and medium-sized valleys containing gold. Its advantages are: simple tools (only a shovel and a panning pan), small sampling workload (digging shallow pits 0.3-0.5m deep, sample weight 20-40kg), simple and easy to operate, one person can also do it, and near-surface placer gold information can be obtained quickly. Disadvantages are: Because the samples are taken from the shallow near-surface, it cannot reflect the gold content of the deep gravel layer, and placer gold is usually mainly enriched in the lower part of the gravel layer near the bedrock, so the results of river heavy mineral measurement near the surface generally only have qualitative significance in prospecting.

 

The effect of natural heavy mineral sampling depends on the selection of sampling points and layers. In the plane range, sampling points should be distributed in places conducive to placer gold enrichment, such as where the river suddenly widens, the convex bank of the river bend, the gravel deposition area of the riverbed shoal, near the confluence of the main and tributary rivers, under the rock steps and stone beaches in the riverbed, above the rock crevices, on the side beach or heart beach, in front of large obstacles in the water flow, where the riverbed slope changes from steep to gentle, the "closed mountain" and the accumulation area in front of the "迎门山" in the upper reaches of the river valley, etc. In the vertical profile direction, the bottom of the gravel layer close to the bottom rock is the best. In the gravel rock area, it should be taken in the riverbed sediment below the branch ditch and small valley cutting the gravel rock layer. In mountainous areas with multi-level gully networks, sampling should be prioritized in tributary valleys. When taking samples of terrace sedimentary outcrops, the bottom of the gravel layer or near the bedrock surface should be taken as much as possible. Each sample is 0.2-0.5m long. The sample weight should be at least no less than 20kg or 0.01m3 by volume (approximately equivalent to a standard boat-shaped panning pan full of sand samples). When sampling along the river, the spacing depends on the scale of the gully and does not need to be mechanically fixed.

 

The determination of sampling points should be based on the principle of favorable geological and geomorphological conditions. For a small ditch of three to five kilometers long, sampling can be carried out at intervals of approximately 800m, and for a ditch of about ten kilometers long, sampling can be carried out at intervals of 1600m. When taking residual slope accumulation samples, sampling points are arranged parallel to the contour lines of the mountain slope, with a point spacing of 80-40m. All sampling layers should be taken in gravel layers or clay-containing sandy gravel layers, avoiding pure clay layers. Old tailings should be sampled directly from the near upper surface, with a pit depth of 0.3-0.5m. For various heavy mineral sampling, the weight or volume of the sample should be calculated for grade calculation. Samples are panned in the field and then sent to the laboratory.

 

II. Engineering Heavy Mineral Method

 

This is an effective method to use sand drills or exploration wells to penetrate loose sedimentary layers and systematically sample to understand the gold content of loose sediments and directly determine the grade of gold-bearing layers. Since placer gold and industrial placer gold layers are mainly located at the bottom of loose sedimentary layers, the engineering heavy mineral method can ascertain the deep placer gold enrichment situation and provide direct prospecting information. The basic points of using this method are that the arrangement of sampling engineering points should have sufficient basis and feasibility of construction. Secondly, no matter what kind of sampling process is used, the gold-bearing layer must be penetrated and at least 0.2m deep below the bedrock surface must be controlled. Using sampling engineering for placer gold prospecting must be based on the analysis of geological and geomorphological conditions. According to prospecting markers and clues, favorable locations are selected in the favorable ore-forming sections, and engineering is arranged according to a certain engineering grid density. Favorable locations should be determined according to the enrichment and ore-forming laws of placer gold.

 

III. Investigation of Placer Gold Old Mining Traces and Folk Mining

 

Many placer gold areas often have traces of manual placer gold mining in the upstream or tributary valleys of rivers. They are effective markers for placer gold prospecting. Based on old mining traces, further prospecting around them can often achieve good results. Tailings piles from larger-scale manual old mining areas are often ore bodies with industrial value. In addition, through folk mining surveys, a lot of valuable information can be obtained on the geological characteristics, laws, and prospecting clues of placer gold mineralization in this area, so folk mining surveys of placer gold have important prospecting significance.

 

IV. Geological and Geomorphological Survey

 

This is a basic method for placer gold prospecting, mainly used for the analysis of placer gold mineralization conditions and the prediction of favorable ore-forming sections. In the prospecting stage, it mainly involves river valley route surveys. Among them, geological surveys can use natural outcrop methods, river detritus observation methods, and use rocks from known gold-producing ditches in the area for comparative analogy, while also collecting some natural heavy mineral samples to understand the gold content. Indirectly or directly determine whether there is placer gold supply and the richness of the supply. During the investigation, attention should be paid to understanding the tectonic background of the gully and geological phenomena related to gold mineralization.

Geomorphological observation mainly divides river valley types and various geomorphological units and determines their distribution, understands their scale, genesis, sediment characteristics and gold content, etc., and draws geomorphological Quaternary geological sketches on 1:50000 or 1:25000 scale topographic maps, drawing the boundary lines of the main geomorphological units, providing reference for the arrangement of sampling engineering and the later delineation of ore bodies.

 

V. Some Experiences of Local People in Finding Placer Gold Mines

 

Heilongjiang Province is a major placer gold producing area in China, with a long history of mining, and local people have accumulated rich experience in finding placer gold mines.

 

(1) Determine the prospective section according to geomorphology and placer gold enrichment law

 

1. Look at the "three mountains" and "four non-exposures", namely "seat mountain", "closed mountain", "迎门山", "no mouth in front of the ditch", "no blockage behind the ditch", "no wind in the ditch", and "no bones in the whole ditch". "Seat mountain" is the gold-producing mountain upstream of the river valley. It is characterized by its height ("no blockage") and many "horse tooth stone" veins (quartz). Experience suggests that the greater the possibility of placer gold deposits forming in the river valley if there is a seat mountain.

 

"Closed mountain" refers to the pliers-shaped mountain of the river valley, also known as "closed mouth". "迎门山" is the mountain facing the river at the bend of the river valley, also known as "no mouth" and "no opening". This geomorphology is a favorable marker for placer gold mineralization. In the upper part of the "closed mountain" or in front of the "迎门山" in the river valley, are sections where placer gold is enriched.

 

"No wind" is also known as "no waist". The mountains on both sides of the river valley producing placer gold should be relatively high, and the "wind" seems unable to blow away. "No bones" means that the rocks on the bottom of the riverbed are not exposed, indicating that the river valley is in the accumulation stage.

 

2. "Small ditch out of the mouth", "large ditch has legs", "not big or small in the belly". A small ditch refers to a small valley less than 3km in length. "Small ditch out of the mouth" means that attention should be paid to finding placer gold mines at the outlet of small ditches. When the length is more than 10km, it is a large ditch. "Large ditch has legs" means that if placer gold mines are found in larger river valleys, placer gold mines may also be found in some tributary valleys upstream. Conversely, if there are placer gold mines in tributary valleys, there may also be placer gold mines in the main valley. Medium-sized ditches (3-10km in length) are mainly ore-forming in the valley itself.

 

3. "Gold from the shady slope." According to folk experience in frigid regions, alluvial gold deposits, especially those on terraces, are mostly distributed on the shady side of river valleys. That is, in east-west trending valleys, gold deposits are more abundant on the terraces of the south-facing valley slopes, while they are scarce on the north side. In north-south trending valleys, gold deposits are mostly found on the west side terraces, with few deposits on the east side.

 

(2) River heavy mineral sampling for gold

 

Taking heavy mineral samples along rivers for gold prospecting is one of the most commonly used methods among the folk. The main experiences are:

 

1. Sampling points should be reasonable and representative, usually with a spacing of 200-300m between sampling lines.

 

2. Sampling locations should be selected at the inner side of river bends (where the river changes direction); sections where the river flow velocity slows significantly; in front of large obstacles in the riverbed; and beside the confluence of main and tributary streams.

 

3. Pay attention to the sampling layer. Sampling can only be done when mud (clay), sand, and gravel are all present; if one of them is missing, the effect is not good.

 

4. When sampling on old exploration pits or old tailings piles, the topsoil should be removed first, but do not excavate too much. It is best to find gravel with bedrock fragments for sampling; do not sample from purely water-washed gravel.

 

5. Do not scoop samples from the water.

 

Three, How to find silver mines

 

Independent silver deposits are relatively rare, mainly distributed in the United States, Mexico, and Peru. In China, they are found in Fuwan, Gaoming, Guangdong; Fenghuangshan, Long'an, Guangxi; Xiasa, Batang, Sichuan; and Lemachang, Ludian, Yunnan. According to Antonov's reserve classification, >10,000 tons are super-large silver mines, 10,000 tons to >2,000 tons are large silver mines, 2,000 tons to >500 tons are medium-sized silver mines, and <500 tons are small silver mines.

 

In China, silver deposits with an average grade greater than 150 g/t are classified as independent silver mines. Those greater than 1,000 tons are classified as large silver mines, 1,000 tons to >200 tons as medium-sized silver mines, and <200 tons as small silver mines.

 

Signs of silver mines

 

1. Low-temperature alteration and mineralization zones, such as secondary silicification, pyrite-sericite alteration, barite alteration, albitization, montmorillonitization, silicification, iron carbonate alteration, iron-manganese clay alteration, tectonic alteration, etc.;

 

2. Arsenic-antimony-bismuth-mercury sulfide and sulfosalt mineral zones;

 

3. Iron-manganese oxidation zones;

 

4. Copper, lead, zinc, tin, tungsten, and manganese ore districts and their peripheries;

 

5. Black rock series areas;

 

6. Silver geochemical anomaly areas.

 

Note the following two points:

 

1. When using silver geochemical anomalies to find silver mines, it is necessary to distinguish between artificial large-area silver anomalies caused by artificial rainfall or snowfall to avoid misleading. Because artificial rainfall (snow) uses high-altitude cannons and rockets to launch projectiles from the ground, which explode in the clouds, causing the silver iodide and other catalysts in the projectiles to burn into smoke and spread in the clouds, rapidly cooling and condensing the water vapor in the clouds.

 

2. In addition to searching for syngenetic silver mines in copper, lead, zinc, tin, tungsten, and manganese ore districts, attention should be paid to searching for independent silver deposits with low sulfide content, such as independent silver deposits often found in low-sulfide fault tectonic alteration zones.

 

Four, How to find copper mines

 

The main types of copper deposits are: porphyry copper deposits, copper-nickel sulfide deposits, massive sulfide deposits, stratiform copper deposits (volcanic copper deposits, sandstone-shale-conglomerate copper deposits, carbonate copper deposits), skarn copper deposits, and hydrothermal vein copper deposits.

 

Prospecting signs

 

1. Oxidized copper minerals. Because primary copper minerals, high-copper altered rocks, and ancient copper smelting slag are easily oxidized, they form strikingly visible emerald green malachite (commonly known as verdigris), sky-blue azurite (commonly known as blue verditer), bright red cuprite, ash-grey bornite, and bright blue chalcopyrite, which are good indicators for finding copper mines.

 

2. Characteristic plants. For example, toothbrush grass in the middle and lower reaches of the Yangtze River and a creeping plant with purple flowers and purple-red stems in Yunnan are good copper-finding plants.

 

3. Alteration assemblages. Alteration assemblages such as propylitization-pyrite-sericite alteration-clay alteration-potassic alteration-silicification and bleaching in red beds (volcanic red beds or sandstone-shale red beds) are good indicators for finding copper.

 

3. Volcanic structures, spilite-keratophyre volcanic tuffs, eruption sedimentary rocks (iron-manganese siliceous rocks, iron jasper, layered siliceous rocks), light-colored sandstone (gravelstone) in red beds, skarns, ultrabasic rocks, intermediate-intermediate acidic porphyries, stromatolitic siliceous fine-grained dolomite, and carbonaceous volcanic tuff layers are all excellent targets for copper exploration.

 

4. For porphyry copper deposits, they are generally large-tonnage, low-grade deposits and have always been the main target of exploration. It is particularly worth mentioning that: when searching for porphyry copper deposits, one should consider whether they have open-pit mining conditions, whether they have secondary enrichment zones, and whether they are associated with high gold, silver, and molybdenum elements. If they are inconvenient for open-pit mining and do not have high-grade secondary enrichment zones, and the gold, silver, and molybdenum content is low, then due to their low grade, they become stagnant mines, which are difficult to utilize for the time being. Because they consume a large amount of exploration funds, they can put mining companies in a difficult situation.

 

5. Geochemical anomalies of copper elements and their combined anomalies with molybdenum, gold, silver, lead, zinc, iron, and manganese.

 

6. Geophysical anomalies. Induced polarization (high polarization), resistivity (low resistance), and gravity (high gravity) can directly reflect the existence of copper ore bodies, while magnetic anomalies can delineate volcanic structures, contact zones of intermediate-intermediate acidic rock masses, and ultrabasic rock belts. Low gravity can delineate concealed granitic rock masses.

 

7. Pay attention to ore-forming series prospecting. For example, there are iron ores above and copper ores below (such as iron hats often indicate copper, and copper deposits usually exist below magnetite deposits).

 

8. Note the comprehensive prospecting. Copper deposits often coexist or are associated with the following elements: lead, zinc, tungsten, molybdenum, tin, gold, silver, iron, etc.

 

V. How to find lead-zinc deposits

 

1. Gossan and oxidized ores Because lead-zinc ores often contain pyrite, siderite, ferro-dolomite, ferro-calcite or ferro-franklinite, they are easily decomposed under oxidizing conditions, forming accumulations of limonite, etc. Usually, sampling and testing of the gossan can indicate whether there is a prospecting prospect for lead-zinc ores in the area. If the lead and zinc content in the gossan and oxidation zone is very high, it itself constitutes an oxidized ore of lead and zinc. There are subtle differences in the geochemical behavior of lead and zinc, which allows lead and zinc to separate under oxidizing conditions. Lead oxides include cerussite, galena, anglesite, lead sulfate, and lead sulfate. Because lead sulfate is generally insoluble, it remains dispersed in the oxidation zone, with a shorter migration distance and closer to the primary ore body. Sometimes it can be enriched into ore in residual and colluvial deposits; zinc oxides include smithsonite, hemimorphite, hydrozincite, willemite, etc. Because zinc sulfate is easily soluble, it can migrate a considerable distance, so the distribution range of zinc oxide is wider than that of lead oxide, and it is easy to be leached and enriched into ore. Therefore, zinc oxide ore is often more valuable than lead oxide ore.

 

Lead-zinc oxidized ores can have different shades of coffee color, earthy yellow, charcoal black, white pink, light yellowish green, etc., and occur in massive, earthy, honeycomb, powdery, crusty, bean-shaped, grape-shaped, kidney-shaped, and slag-like forms. For oxidized sandstone-type lead-zinc deposits, it is sometimes difficult to identify them with the naked eye. My experience is that black sesame-like substances in yellowish-brown sand (gravel) rock are indicative.

 

2. Alteration marks Carbonate deposits are often associated with silicified dolomite, and the grayish-white dolomitic rocks surrounded by reddish-pink dolomite are often the location of industrial ore bodies. Sand (gravel) rock deposits often have many pores, grain support, as if they have been soaked in water, or have "bird's eye" structure, "snow top" structure, etc. Near-ore wall rock alteration includes brecciation, silicification, barite, celestite, pyritization, iron carbonate, and fluoritization, etc. Asphalt and black bands are often also markers for finding lead-zinc deposits. Hydrothermal deposits also have skarnization, hornfels, and pyrite sericite alteration.

 

3. Geophysical and geochemical anomalies Generally, lead-zinc deposits have low-resistance, high-polarization geophysical anomalies, but massive sphalerite deposits have high-resistance characteristics, which should be paid close attention to when interpreting geophysical anomalies.

 

4. Fault fracture zones in the fold axis, especially thrust nappe zones or large-scale detachment zones, are often related to large to super-large lead-zinc deposits.

 

5. Germanium, gallium, indium, silver, and other trace element anomalies These element anomalies can not only indicate the search for lead-zinc deposits, but also, under specific conditions, can form symbiotic or associated ores with lead-zinc deposits, greatly increasing the value of ore per ton.

 

VI. How to find tungsten deposits

 

Types of tungsten deposits If classified according to mineral element combinations, there are W-(Sn, Bi, Mo), W-Be, W-(Cu, Pb, Zn, Ag), W-Nb-Ta, W-Au-Sb, W-Li, W-Cu-Fe, W-REE, etc. Industrial types include quartz vein-type wolframite deposits (such as Jubaokeng in Guangdong and Dajishan in Jiangxi), porphyry tungsten deposits (fine vein disseminated type, greisen type) (such as Loushushan in Guangdong and Yangchuling in Jiangxi), explosion breccia-type tungsten deposits (such as Dahutang in Jiangxi), skarn-type scheelite deposits (such as Yaogangxian in Hunan, Xianglushan in Jiangxi, and Xiaoliugou in Gansu), layer-controlled polygenic superimposed type mainly composed of skarn (such as Shizhutuan in Hunan), layer-controlled type (such as Damingshan in Guangxi), and placer type, etc.

 

China's proven tungsten deposits are mainly distributed in the Nanling region, with Gan, Xiang, and Yue being the most important. In recent years, large tungsten deposits have been discovered in the North Qilian-North Mountain region, changing the distribution pattern of China's industrial tungsten deposits. Currently, China's tungsten reserves rank first in the world, more than three times the total reserves (1.3 million tons) of more than 30 countries abroad. However, there are not many rich tungsten deposits in China (WO3 greater than 0.5% or 1%), and most of them are poor and difficult-to-select deposits. Other major tungsten-producing countries are Canada and the United States. Shizhutuan in Chenzhou, Hunan Province, is a "World Non-ferrous Metal Museum", with more than 140 kinds of minerals, among which tungsten reserves account for one-fourth of the current world's total reserves.

Therefore, China has influenced the price of the world tungsten market. Currently, the development of tungsten resources is strictly controlled by the state.

 

Markers for finding tungsten deposits

 

1. Stream sediment heavy mineral survey and soil heavy mineral survey. This is because scheelite and wolframite are not easily oxidized and decomposed during weathering and erosion, but accumulate as heavy minerals at the bottom of soft sediments or soil.

 

2. Crust-mantle mixed-source dykes brought from deep by deep faults can form porphyry-type and breccia pipe-type tungsten deposits; while dykes from crustal sources form vein-type or skarn-type tungsten deposits.

 

3. Tungsten-bearing quartz veins in tungsten ore districts often occur in groups and zones, and often have equidistant characteristics. According to the horizontal and vertical zoning distribution law of tungsten mineralization and the law of hydraulic fracturing fissure occurrence, the existence of concealed veins can be accurately predicted. 4. The inner and outer contact zones of granitic intrusions and the surrounding rocks of the intrusion cap, with greisenization, silicification, potassic alteration, sericitization, fluoritization, and skarnization, are good places to look for tungsten deposits.

 

4. In skarn-porphyry type copper, molybdenum, lead-zinc, rare earth, and niobium-tantalum ore districts and in areas with similar layered skarn distribution, attention should be paid to searching for tungsten deposits.

 

5. Because fine-grained scheelite is easily confused with quartz, but scheelite emits pale blue fluorescence, while quartz does not. Therefore, using fluorescence irradiation is the most effective and rapid method to distinguish quartz from scheelite.

 

6. Pay attention to searching for tungsten-antimony-gold deposits in the antimony-gold formation of slightly metamorphosed rocks, such as the Woxi gold deposit in Hunan.

 

VII. How to find tin deposits

 

Tin ore has a very low grade, with vein ores containing 0.2% tin and placer deposits containing 0.04% tin being considered commercially viable. Tin deposits are generally divided into three major categories: cassiterite-quartz vein type (including pegmatite type, greisen type, and porphyry type), cassiterite-sulfide type (skarn type, carbonate type), and cassiterite oxide type, i.e., placer deposits (in-situ oxidized placer deposits - residual slope deposits and lava funnel placer deposits, and placer deposits transported elsewhere - lakeshore placer deposits, seashore placer deposits, and alluvial placer deposits). Some ultrabasic rocks sometimes also produce tin ore, such as the Jiu Mao tin mine in Guangxi.

China's tin mines are mainly concentrated in Yunnan, Guangxi, Guangdong, Hunan, Inner Mongolia, and Jiangxi, with those in Gejiu, Yunnan, and Nandong, Guangxi, being the most famous.

 

Currently, tin ore is a mineral species under China's controlled mining.

 

Tin Ore Prospecting Indicators

 

1. Granite areas or concealed granite areas;

 

2. Marble, hornfels, skarn, greisen, and greisen areas; 3. Rhyolite, granite, granitic porphyry and their contact zones, and ultrabasic rocks and gabbros in individual tin-rich areas;

 

3. Heavy mineral survey. Because cassiterite has high hardness and is insoluble in common acids and alkalis, it is quite stable under natural weathering conditions, so it often occurs as heavy minerals at the bottom of water system sediments. Samples are taken from weathered soil layers and ditch sediments, washed, and checked for the presence of cassiterite or wood tin. Wood tin is the hydrolysis of Sn4+ salts, which separates out Sn(OH)4 sol and gel, and dehydrates to form a wood-like substance;

 

4. Silicification zones, quartz veins, sulfide quartz veins;

 

5. Fracture zones, iron hats, chocolate soil (soil formed by weathering of tin-bearing skarn and marble);

 

6. Fluorine-rich rocks and altered rocks. Tin easily migrates by forming complexes with fluorine, and when tin precipitates, fluorine remains in the nearby rocks. Therefore, anomalies of fluorine, boron, tin, arsenic, antimony, and copper can indicate tin metallogenic prospective areas and predict the size of tin reserves.

 

VIII. How to Find Tin Ore

 

In terms of host rocks, there are seven types of antimony deposits: carbonate rock type, clastic rock type, slightly metamorphic rock type, marine volcanic rock type, continental volcanic rock type, and residual slope deposits, with the carbonate rock type being the most important.

 

Antimony Ore Prospecting Indicators

 

1. Occurs in low-to-medium temperature hydrothermal metallogenic domains, such as the outer margins of granitic intrusions, sedimentary basins far from plate subduction zones, collision zones, and magmatic belts, or slightly metamorphic belts.

 

2. Common associated minerals are quartz, calcite, orpiment, realgar, cinnabar, and low-temperature arsenopyrite.

 

3. Wall rock alteration is mainly silicification, followed by pyritization, baritization, and carbonatization.

 

4. Oxidized zones composed of stibnite bloom, antimony bloom, antimony ochre, stibnite, red antimony, and limonite, etc. Antimony bloom is colorless or white, sometimes with light gray, light yellow, yellowish brown, or red hues, with an adamantine luster, and a pearly luster on the cleavage surface. Cleavage {110} is perfect, {010} is imperfect, it has a high specific gravity and low hardness, and is crust-like. It is soluble in 10% tartaric acid and hydrochloric acid, and produces a white precipitate when water is added to hydrochloric acid. It turns brown and slowly dissolves in ammonium sulfide solution. It is difficult to dissolve in nitric acid. Yellow antimony bloom is light yellow or brown, with an earthy luster, hardness 4-5, and may exhibit a pseudo-morphism of stibnite crystals (columnar, acicular).

 

5. Gold, silver, arsenic, mercury, antimony, or tungsten geochemical exploration anomaly areas.

 

6. Because stibnite is non-conductive and antimony mineralization is closely related to silicification, it often shows high-resistance anomalies in electrical prospecting.

 

IX. How to Find Vanadium Ore

 

In the currently discovered vanadium-bearing associated ores, due to the low vanadium content, most vanadium minerals are not commercially viable. Currently, the following vanadium-bearing minerals can be mined and utilized.

 

1. Vanadium-titanium magnetite type. Vanadium-titanium magnetite is a typical polymetallic associated ore. China's vanadium-titanium magnetite resources are mainly concentrated in Panzhihua, Sichuan; Chengde, Hebei; Maanshan, Anhui; and Hami, Xinjiang.

 

2. Black shale (coal shale) type. This is found in various southern provinces of China, and the black shale (coal shale) resources are extremely abundant in Zhejiang, Jiangxi, Guangxi, Anhui, Hunan, Hubei, Guizhou, Shaanxi, Gansu, and Shanxi provinces.

 

Prospecting signs

 

(1) Vanadium-titanium magnetite type

 

1. Occurs in basic-ultrabasic intrusions such as gabbro-peridotite. These intrusions are mostly distributed on the margins of ancient continental uplift zones and are controlled by deep faults.

 

2. Good differentiation of basic-ultrabasic intrusions.

 

3. Vanadium, titanium, and rare earth element anomaly areas.

 

4. High magnetic anomaly areas.

 

(2) Black shale (coal shale) type

 

1. Carbonaceous siliceous mudstone series, thin-layered. Often interbedded with manganese ore layers, phosphate nodules, shale (slate), and siliceous layers.

 

2. Comprehensive geochemical anomalies of vanadium, molybdenum, manganese, silver, nickel, uranium, cobalt, and barium. 3. High organic carbon content, can be used as low-grade thermal coal.

 

4. Occurs in marginal sea slope areas.

 

5. Phosphate ore, manganese ore, barite, and coal shale layers are often good prospecting indicators.

 

X. How to Find Zirconium and Hafnium

 

Zirconium and hafnium have similar geochemical properties and are inseparable in nature. Both are essential materials for nuclear reactors, and are often called the "Humha Erjiang" (a pair of powerful generals in Chinese opera) of nuclear reactors. Zirconium deposits are divided into two main categories: primary deposits and placer deposits. Primary deposits can be further divided into early magmatic deposits, late magmatic deposits, and pegmatite deposits. Giant zircon deposits are found in nepheline syenite in southern Norway, but they generally have low industrial value and are rarely mined. Placer deposits include beach placers, lake placers, alluvial placers, and residual slope placers. Among them, beach placers have the highest industrial value and are currently the main target for zirconium mining.

 

Finding Zirconium and Hafnium Indicators

 

1. Radioactive anomaly zones;

 

2. Accumulation zones of weathered and eroded products of alkaline rocks and alkaline pegmatites, such as beaches, lakeshores, and river bends, which are suitable for the enrichment of heavy mineral deposits;

 

3. Heavy mineral anomaly zones.

 

Mining Methods

 

Currently, the method for separating zircon from beach sands near and below sea level is as follows: During mining, bulldozers remove the overburden, and the ore sand is sucked up by a dredge and sent to a wet concentration plant. The concentration plant can be located on a floating dredge. During wet selection, a combination of spiral concentrators, cone concentrators, and washing troughs is used to recover heavy concentrates, while light minerals are removed. Most of the rough concentrates are transported to a selection plant, where heavy selection is used to remove residual light minerals, and the heavy concentrates are dried and dehydrated in a drying kiln. The various separated heavy concentrates are then obtained using electrostatic separation and magnetic separation. This inexpensive method of obtaining rough concentrates allows for the mining of deposits with an average heavy mineral content of less than 3%, and in some cases, deposits with an average content of less than 1% can be mined.

 

XI. How to Find Chromite Deposits

 

China's chromite deposits are typical magmatic deposits associated with ultramafic rocks, with the vast majority belonging to the ophiolite type, occurring in ophiolite belts. The Luobusha chromite deposit in Tibet and the Saltuhai chromite deposit in Xinjiang both belong to this type. In terms of ore-forming age, China's chromite deposits are mainly formed in the Mesozoic and Cenozoic eras.

 

Indicators for Finding Chromite Deposits

 

Chromite is a disadvantaged mineral resource in China, with a serious shortage. The discovered chromite resources are small in scale and low in grade, and most are difficult to utilize, requiring greater efforts from us.

 

Indicators for Finding Chromite Deposits Include:

 

1. Chromite deposits are invariably found in basic-ultrabasic complexes and ultramafic dykes and sills, such as the famous Great Dyke in Zimbabwe. Therefore, the first step is to search for them in ultramafic belts.

 

2. Chromite deposits are either found in dunite-dominated dunite and clinopyroxenite-type rock bodies, where ore bodies are mostly hosted in coarse-grained pegmatitic dunite within the dunite lithofacies, showing a gradual transition with the surrounding rocks. The boundaries of the ore bodies need to be determined by analysis and testing. The ore bodies are complex in shape, mostly lenticular, lens-shaped, vein-like, and irregular massive; or they are found in clinopyroxene-dunite-dominated dunite and clinopyroxene-dunite-type magnesian rock bodies, where ore bodies are mostly hosted in clinopyroxene-dunite lithofacies or in dunite xenoliths near the contact zone between this lithofacies and the dunite lithofacies, often concentrated in groups, belts, and segments. The boundaries between the ore bodies and the surrounding rocks are clear. The ore bodies are mostly irregular pod-like, vein-like, sac-like, and columnar.

 

3. Chromite-bearing rock bodies have a high Cr/Fe ratio and a sponge-like structure.

Magnetic anomalies.

 

4. Bright green chromite-bearing altered minerals such as chromian muscovite.

 

XII. How to Find Mercury Deposits

 

Famous mercury deposits in China include the Wanshan mercury deposit in Guizhou, the Wuchuan mercury deposit, the Danzhai mercury deposit, the Tongren mercury deposit, and the Xinhua mercury deposit in Hunan. China's mercury deposits are mainly carbonate-type (accounting for over 90%), with the Wanshan super-large mercury deposit in Guizhou belonging to this type. The second type is clastic rock-type. Most of the known mercury deposits in China are located in the Middle and Lower Cambrian strata (accounting for over 80% of the reserves), far from magmatic activity areas. Mercury deposits were also formed in the Precambrian, Mesozoic, and Cenozoic eras, but they are not significant.

 

Foreign mercury deposits are mainly distributed in the Tertiary fold belt, occurring in various volcanic rocks, intrusive rocks, and metamorphic rocks (accounting for 87%), and are closely related to magmatic activity. One-third of the global mercury consumption is used in small-scale gold mining production.

 

Indicators for Finding Mercury Deposits

 

China was one of the earliest countries to use cinnabar as an indicator for finding gold deposits. The "Dishi Pian" (chapter on geography) in the "Guan Zi" (book of Guan Zhong) records that "where there is cinnabar above, there is gold below." The indicators for finding mercury deposits include:

 

1. Platform-type carbonate strata distribution areas far from magmatic activity, such as the junction area of Hunan, Guizhou, and Sichuan;

 

2. Cenozoic volcanic and geothermal activity areas;

 

3. The axial parts and flanks of anticlines (complex anticlines), especially fault zones in the axial parts of anticlines;

 

4. The most closely related to mercury mineralization is low-temperature alteration, mainly silicification, dolomitization, and calcification, followed by baritization;

 

5. Realgarization, orpimentation, and stibnite mineralization zones;

 

6. Arsenic, antimony, and mercury anomaly zones;

 

7. Mercury meter anomaly zones.

 

XIII. How to Find Cobalt Deposits

 

The vast majority of cobalt is a by-product of copper, nickel, iron, and gold deposits, with only a small portion forming independent industrial deposits. Independent cobalt deposits are generally divided into three categories: arsenide cobalt deposits, sulfide cobalt deposits, and cobalt-rich earth deposits (such as Jiaodingshan and Penglai). Most cobalt deposits are syngenetic or epigenetic cobalt deposits.

 

Cobalt ores are commonly found in skarn type iron deposits, vanadotitanomagnetite deposits, hydrothermal polymetallic deposits, various types of copper deposits, sedimentary cobalt-manganese deposits, copper-nickel sulfide deposits, nickel silicate deposits, and other types of ore deposits. Although their grades are low, their scale is often large, making them the main source for extracting cobalt. Co-associated cobalt deposits are generally classified into: 1. Magmatic type, copper-nickel sulfide type (e.g., Jinchuan), vanadotitanomagnetite type (e.g., Panzhihua); 2. Hydrothermal type, skarn type (e.g., Tonglushan), porphyry copper deposits (e.g., Yulong, Tongkuangyu), vein-type polymetallic deposits (e.g., Kalanggu lead-zinc mine, Lala iron-copper mine); 3. Sedimentary or sedimentary-metamorphic type (e.g., Zambia, Five-element formation, Dahonglu copper mine); 4. Lateritic cobalt-nickel silicate deposits (Yuanjiang-Mojiang cobalt-nickel mine).

 

Prospecting signs

 

1. Ultramafic rock bodies containing copper-nickel ore and vanadotitanomagnetite, and their oxidation zones, often have cobalt enrichment and mineralization.

 

2. Fractured and crushed zones in black rock series.

 

3. Manganese-bearing soil can form cobalt soil deposits. The ore is black or blue-black, with a colloidal structure, nodular or concentric circular texture, composed of cobalt-, nickel-, and copper-bearing psilomelane, lithiophorite, cryptomelane, and limonite, appearing as flaky, botryoidal, spherical, or coralloid shapes.

 

4. Iron, copper, gold, and individual lead-zinc deposits may form associated cobalt deposits.

 

5. Weathering crusts of old metamorphic rocks, such as the Kunyang Group weathering crust of the Kangdian ancient land axis.

 

Fourteen: How to Find Lithium Ore

 

Industrial types of lithium ore include:

 

1) Granitic pegmatite type: Koktokay lithium-beryllium-niobium-tantalum deposit in Xinjiang, Jiayangcun lithium-beryllium deposit in Sichuan Province (should be Jiajika, not Jiayangcun).

 

2) Alkaline granite type: Yichun 414 tantalum (niobium)-lithium deposit in Jiangxi, etc.

 

3) Salt lake (brine) type: Yiliping lithium deposit in the central Qaidam Basin, Qinghai, etc.

 

Prospecting signs

 

1. Areas with abundant alkaline acidic rocks, including granitic pegmatite and alkaline granite;

 

2. Salt lakes and oilfield brine areas;

 

3. Characteristic lithium-bearing minerals; all lithium-bearing minerals exhibit characteristic red or rose-red colors. Lithium minerals with well-formed crystals and vibrant colors become gemstones.

 

Fifteen: How to Find Aluminum Ore

 

All discovered bauxite deposits are formed under supergene conditions, including weathering-residual type (lateritic bauxite), accumulated type, and sedimentary type bauxite. Lateritic bauxite is formed when aluminum-bearing parent rock, under humid and hot climatic conditions with favorable well-drained topography (such as remnant hills, low mountains, and plateaus), undergoes weathering and decomposition due to the action of water, CO2, and biological factors. Easily soluble substances like K, Na, Ca, Mg, and SiO2 in the parent rock are leached out, while less mobile substances like Al, Fe, and Ti remain in situ, forming lateritic bauxite. Accumulated bauxite is formed when aluminum-bearing rocks, lateritic weathering crusts, or pre-existing lateritic deposits are subjected to mechanical or chemical weathering, erosion, and transport by gravity, water, and natural acids (sulfuric acid, carbonic acid, organic acids), accumulating in mountain depressions, valleys, near-shore lake basins, coastal lagoons, or restricted marine basins. In an aqueous medium, sedimentary bauxite is formed instead.

 

Prospecting Signs of Bauxite

 

1. Similar in appearance to claystone, but compared to claystone, it is denser in lithology and harder (diaspore 6.5-7, boehmite 3.5, gibbsite 2.5-3.5), denser (diaspore 3.2-3.5, boehmite 3.01-3.46, gibbsite 2.3-2.43), and has no plasticity.

 

2. Colors are white, grayish-white, yellowish-white, yellowish-brown, grayish-green, light red, or colorless, and the color is related to the impurities present.

 

3. Vitreous luster, pearly luster on cleavage planes, conchoidal fracture, brittle, white streak.

 

4. Cryptocrystalline massive, scaly, colloidal, radial fibrous, crusty, stalactitic, oolitic, pisolitic, or spherulitic nodules.

 

5. Gibbsite has an earthy odor.

 

6. Often associated with modern or ancient karst surfaces.

 

7. Lateritic bauxite is mainly distributed in tropical and subtropical regions near the equator, associated with modern lateritic weathering crusts. The age is primarily Tertiary, secondarily Mesozoic. The parent rocks for weathering are mainly: 1) Basalt; 2) Granite, diorite, nepheline syenite; 3) Gneiss, schist, phyllite, metamorphic basalt, and granite in ancient metamorphic rocks; 4) Various clastic rocks; 5) Carbonate rocks.

 

8. Sedimentary bauxite often develops in marine carbonate rock areas, occurring within carbonate rock series, with certain stratigraphic horizons. Aluminum-bearing horizons are found from the Devonian to the Cenozoic, but mainly occur in the Carboniferous, Cretaceous, and Tertiary systems. It is also found in Cenozoic continental sedimentary rocks, distributed within ancient weathering crust laterites, with an unconformable contact with the underlying country rock, and a conformable contact with overlying lacustrine claystone and fluvial sandstone.

 

Sixteen: How to Find Magnesium Ore

 

Magnesium ore resources primarily come from seawater, natural salt lake brine, oilfield brine, dolomite, magnesite, brucite, and olivine, etc.

 

Prospecting signs

 

1. Magnesite: Magnesite is similar to calcite, but it does not effervesce with cold hydrochloric acid or reacts very slowly; it effervesces vigorously with heated hydrochloric acid. It is commonly found in regional metamorphic zones of ultramafic rocks and dolomites.

 

2. Dolomite deposits. Marine sedimentary dolomite rock often occurs interbedded with siderite layers and limestone layers. In lacustrine sediments, dolomite coexists with gypsum, anhydrite, halite, sylvite, etc. Dolomite can crystallize directly in hydrothermal solutions, or it can be formed by magnesium-bearing hydrothermal solutions metasomatizing limestone or dolomitic limestone. When heated to 700-900°C, dolomite decomposes into a mixture of carbon dioxide, calcium oxide, and magnesium oxide. It is commonly found in lagoonal carbonate rock depositional areas.

 

XVII. How to Find Manganese Ore

 

The occurrence of manganese ore is traceable. As long as we understand the information and signs of manganese ore occurrence, we can find manganese ore based on these.

 

I. Geological Indicators

 

1. Sedimentary manganese deposits often occur as layers with varying numbers of layers, controlled by specific strata, and are found in manganese-bearing strata of different ages. Manganese-bearing strata are generally marine siliceous-carbonate rocks, and the ore forming the manganese ore layer is mainly manganese carbonate ore (rhodochrosite), followed by manganese oxide ore and manganese silicate ore.

 

2. Residual manganese deposits (manganese cap deposits) are located within the oxidation zone of sedimentary manganese ore layers or manganese-bearing layers, with the exact same stratigraphic position as the primary manganese ore zone, differing only in ore type.

 

3. Eluvial manganese deposits are formed after manganese-bearing rock series of various periods are weathered, and manganese is leached out and then secondarily enriched. The stratigraphic position of eluvial manganese deposits is not very stable.

 

4. Placer manganese deposits are formed when residual or eluvial manganese deposits continue to be weathered, destroying the ore body, and the ore accumulates in situ or elsewhere to form new ore bodies. They generally occur as semi-stratified deposits in Quaternary laterite or brown soil layers. The distribution of the above types of weathered manganese deposits is controlled by specific manganese-bearing horizons.

 

II. Direct Prospecting Indicators

 

1. Outcrops of manganese ore layers are direct prospecting indicators. What is usually found on the surface are layered secondary manganese oxide outcrops. The ore is mainly composed of psilomelane, pyrolusite, and manganite, exhibiting obvious secondary textures and structures, often mixed with siliceous and argillaceous materials, with a loose texture. The boundaries between the top and bottom of the ore layer are relatively clear, and the arrangement of the ore still retains discontinuous bedding, indicating a stable stratigraphic position. Based on these characteristics, it can be determined that these are residual manganese ore outcrops. Such manganese deposits can extend for several to tens of kilometers along the strike and down to near the groundwater table, reaching depths of tens of meters, along the dip. Residual manganese deposits not only have good industrial value but also serve as important indicators for finding sedimentary manganese deposits. In the deeper parts of residual manganese deposits, i.e., below the groundwater table, there are mostly primary sedimentary manganese ore layers or sedimentary metamorphic manganese ore layers, or manganese-bearing layers that currently have no industrial value, such as manganiferous limestone, manganiferous siliceous limestone, manganiferous chert, etc. Sedimentary manganese ore layers are generally composed of carbonate ores such as rhodochrosite, manganoan calcite, and manganite. Sedimentary manganese deposits are large in scale, generally medium to large, but there are more lean ores than rich ores, and lean ores can be utilized after roasting and beneficiation. Rhodochrosite ore is identifiable in the field because it has various colors such as dark and light gray, grayish-green, light brown, and flesh-red, is hard and dense, has a smooth fracture, feels heavy in hand, and often exhibits lineation structures, making it easy to distinguish from other carbonate rocks. If the grade of residual manganese ore exceeds 30%, the primary sedimentary material is mostly manganese ore; if the grade of residual manganese ore is below 30%, the primary sedimentary material is mostly manganese-bearing rock.

 

2. Manganese ore boulders/cobbles. Manganese ore bodies are often covered by topsoil, making their natural outcrops difficult to observe directly. However, after weathering, the ore body is easily broken down, forming manganese blocks and grains of varying sizes, unevenly scattered on the surface or in streams. These manganese blocks and grains are commonly psilomelane and pyrolusite, and are also direct prospecting indicators. In sedimentary rock areas, the discovery of manganese ore boulders indicates the presence of manganese-bearing strata nearby. The discovery of piles of manganese ore boulders or larger manganese ore blocks on hilltops indicates the presence of a weathered manganese deposit nearby. If manganese ore boulders are found at the bottom of a slope or in alluvial deposits, attention should be paid to searching for manganese ore bodies on nearby slopes and cliffs.

 

III. Indirect Prospecting Indicators

 

1. Soil indicators. After weathering, manganese-bearing rock series often form laterite, yellowish-brown soil, or black-brown soil. Not all laterite, yellowish-brown soil, or black-brown soil are indicators for manganese. Only laterite commonly containing rounded manganese grains the size of mung beans or soybeans, or black-brown soil containing manganese ore detritus, can serve as important indicators for finding weathered manganese deposits and indirect indicators for finding sedimentary manganese deposits.

 

2. Lithological indicators. Sedimentary manganese ore layers are difficult to find their outcrops because they are easily weathered or covered by overlying strata. However, the distinct characteristics of the host rocks can be used as prospecting indicators. Rock layers that are harder and stably distributed can serve as prospecting indicators. For example, black shale and tillite in the Sinian manganese deposits; manganiferous lenticular limestone in the Devonian system, interbedded thin-bedded siliceous limestone and siliceous limestone in the Carboniferous system, and manganiferous chert and coal-bearing series in the Permian system can all serve as marker beds.

 

3. Structural indicators. Sedimentary manganese deposits are distributed on the limbs of anticlines and in the cores of synclines; residual manganese deposits are mostly distributed in the shallow parts of the synclinal limbs, i.e., within the oxidation zone above the groundwater table; eluvial manganese is mostly distributed within structural fracture zones, and placer manganese deposits occur in Quaternary laterite layers.

 

4. Geomorphological indicators. Most sedimentary manganese deposits are distributed in low mountain and hilly areas, with a few found in karst peak cluster depressions or dissolution hill depressions. Weathered manganese deposits are distributed above the groundwater table. Residual manganese deposits mostly outcrop on higher slopes or hilltops; eluvial manganese deposits are distributed in structurally complex areas of low mountain and hilly regions, closely related to groundwater activity; placer manganese deposits are distributed in low mountain and hilly areas with gentle slopes, gently inclined hillsides, and relatively flat hilltops, but ore bodies are rare on slopes steeper than twenty degrees, low-lying valleys, and karst peak cluster areas.

 

XVIII. How to Find Molybdenum Ore

 

Molybdenum deposits are widely distributed, but only a very small number of deposits are of mining value. The United States is the most molybdenum-rich country, accounting for more than 60% of the world's total output, followed by Chile and Canada. China's molybdenum deposits are distributed in 28 provinces (regions and municipalities), with Henan being the most abundant, accounting for 30.1% of the country's total reserves, followed by Shaanxi and Jilin. There are many large molybdenum deposits, such as Jinduicheng in Shaanxi, Luanchuan in Henan, Yangjiazhangzi in Liaoning, and Daheishan in Jilin.

 

The most important deposit types are porphyry molybdenum deposits and porphyry-skarn molybdenum deposits. Examples of the former include Jinduicheng in Shaanxi and Dexing in Jiangxi, while examples of the latter include Nannihu molybdenum deposit in Henan; skarn type, carbonate vein, and quartz vein types are secondary; sedimentary molybdenum-uranium-vanadium-nickel deposits have considerable potential value, while pegmatite vein molybdenum deposits have no independent industrial significance. In terms of the formation age of molybdenum deposits, except for a few molybdenum deposits formed in the Late Paleozoic and Cenozoic, the vast majority of molybdenum deposits were formed in the Mesozoic, as products of Yanshanian tectonic magmatic activity.

 

Molybdenum Prospecting Indicators

 

1. Porphyry molybdenum deposits (disseminated vein-type molybdenum deposits): Occur within and around granite and granite porphyry bodies, mineralization is closely related to silicification and potassic alteration, mainly pyrite, molybdenite, and chalcopyrite, ore bodies are layered, lenticular, cylindrical, and giant lenticular in shape, with low grades, and associated with copper, tungsten, silver, rhenium, lead, zinc, cobalt, and sulfur. Identifying potassic-silicified porphyry is crucial for finding porphyry molybdenum deposits, because potassic minerals and minerals formed by magmatic crystallization are difficult to distinguish for those lacking careful observation or experience.

 

2. Skarn-type molybdenum deposits: Occur in the contact zone between granitic rocks and carbonate wall rocks, and along layers in the outer contact zone. Common metallic minerals are pyrite and molybdenite, followed by chalcopyrite, pyrrhotite, wolframite, scheelite, galena, sphalerite, etc. Ore bodies are lenticular, bean-shaped, layered, sac-shaped, cylindrical, vein-like, etc., with relatively high grades, and associated with copper, tungsten, lead, zinc, gold, rhenium, and sulfur.

 

3. Vein-type molybdenum deposits: Occur in fracture zones of various rocks (intrusive rocks, extrusive rocks, metamorphic rocks, sedimentary rocks), often steeply inclined, common pyrite, molybdenite, followed by chalcopyrite, pyrrhotite, wolframite, bornite, galena, sphalerite, etc. Ore bodies are vein-like, multiple vein-like, lenticular, often associated with copper, tungsten, lead, rhenium, sulfur, gold, and silver.

 

4. Sedimentary molybdenum deposit characteristics: Can be divided into sandstone-type molybdenum-copper deposits, sandstone-type molybdenum-uranium deposits, and black shale-type (coal-type, low-grade coal-type, carbonaceous shale) five-element molybdenum deposits. Common minerals include molybdite, chalcocite, pyrite, chalcocite, and uranium-molybdenum minerals, nickel sulfides. Ore bodies are layered, lenticular, bean-shaped, associated with copper, uranium, nickel, vanadium, lead, zinc, cobalt, germanium, selenium, etc.

 

5. Secondary minerals of molybdenum: Powellite, crystals are square plate-shaped, brightly colored, mostly yellow, wax yellow, straw yellow, orange yellow to orange red. Adamantine luster, high density and coexisting with other lead minerals are used for identification. When heated on charcoal with sodium carbonate, it melts into a small lead ball; when tested with phosphorus salt as a bead test, it shows green in reducing flame; in oxidizing flame, it is yellowish-green when hot, and almost colorless when cooled. Molybdite, crystals are fine platy, acicular or tabular, earthy aggregates, honey yellow, pale greenish yellow to colorless, streak grass green, flexible. Molybdomenite, amorphous, cryptocrystalline powder, film-like or crust-like, blue, light to dark blue, streak sky blue. Ferrimolybdite, an amorphous variety of molybdenite, occurs in gel-like, spherical forms, can recrystallize into molybdenite or weather into molybdomenite, often found in black shale-type molybdenum deposits.

 

Nineteen. Let's talk about finding niobium and tantalum

 

Niobium and tantalum are called "fiery diamond" and "corrosion champion" respectively, a pair of "twin brothers".

 

The main types of niobium and tantalum deposits are:

 

1. Granite pegmatite type: Occurs in pegmatites, with coarse grains. Main associated minerals include beryl, spodumene, gangue minerals include quartz, feldspar, garnet, ore minerals include manganotantalite, tantaloniobite, microlite. Examples include: K可可托海 lithium-beryllium-niobium-tantalum deposit in Xinjiang and Xikeng tantalum-niobium deposit in Nanping, Fujian.

 

2. Granite type: Can be further divided into euxenite type (such as Gupo Mountain), columbite type (such as Taimei, Hengfeng), columbite-tantaloniobite type (such as Taimei 521), tantaloniobite-manganotantalite type (such as Laohutou, Shuixi Temple), manganoniobite-microlite type (such as 414, Dajishan). Associated minerals may include monazite, zircon, ilmenite, cassiterite, wolframite, lepidolite, beryl, and xenotime, gangue minerals are quartz and feldspar.

 

3. Sedimentary metamorphic high-temperature metasomatic type: Represented by Bayan Obo, ore minerals include columbite, columbite-rutile, and pyrochlore, associated minerals include magnetite, pseudomorphous hematite, limonite, monazite, and bastnaesite, gangue minerals include aegirine, fluorite, mica, quartz, and feldspar.

 

4. Carbonate pyrochlore type: Represented by Araxá in Brazil, ore mineral is pyrochlore, associated minerals are uranium-thorium minerals and rare earth minerals, gangue minerals are calcite and mica.

 

5. Residual slope-alluvial type: Such as Taishan residual slope-alluvial and alluvial niobium-tantalum sand deposits in Guangdong, and Paitan river alluvial columbite sand deposits in Zengcheng.

 

Prospecting signs

 

1. Alkaline-granitic magmatic activity zones and complexes. Generally related to the late-stage, alkali-rich, volatile-rich peralkaline intrusive small rock bodies and dykes.

 

2. Pegmatite areas. Niobium-tantalum minerals are often found in pegmatites in mixed granite or granite-based areas.

 

3. Lithium, beryllium, tungsten, tin, and rare earth mineral areas can serve as prospecting targets for niobium-tantalum minerals.

 

4. Niobium-tantalum placer deposits can be found along the coasts, lakeshores, and rivers bordering granitic rock areas.

 

5. Most niobium-tantalum minerals contain iron and can coexist with magnetite, so magnetic methods can quickly delineate the mineralization range.

 

6. Niobium-tantalum minerals often contain radioactive elements such as uranium and thorium, so airborne and ground radioactivity surveys are effective methods for prospecting niobium-tantalum minerals.

 

7. Lithium-mica alteration, spodumene alteration, and albitization are prospecting indicators for niobium-tantalum minerals.

 

Twenty. Prospecting for Nickel Ores

 

Nickel deposits are formed by magmatic segregation and weathering crust (laterite) types. Industrial types include copper-nickel sulfide and nickel oxide-nickel silicate types. In addition, nickel is often enriched in black rock formations, forming a five-element deposit with cobalt, silver, bismuth, and uranium.

 

Prospecting indicators for nickel ores include:

 

1. Nickel deposits are distributed in rift and fault trough environments within old cratons or in the transition zones between different tectonic units after the collisional stage.

 

2. The distribution of nickel deposits is controlled by long-active deep faults.

 

3. Nickel deposits occur in mafic-ultramafic rock basins, dykes, and igneous complexes.

 

4. The higher the differentiation degree of mafic-ultramafic rocks, the more favorable it is for the formation of nickel deposits.

 

5. Because pentlandite and other minerals are magnetic, magnetic anomalies can serve as prospecting indicators for nickel deposits.

 

6. Because pentlandite, niccolite, and other minerals have good conductivity, electromagnetic anomalies can serve as prospecting indicators.

 

7. Geochemical anomalies of copper, nickel, cobalt, and arsenic can serve as prospecting indicators.

 

Twenty-one. How to Find Thallium Ores

 

In terms of tectonic location, thallium-rich deposits are concentrated in sedimentary areas and low-temperature metallogenic domains around cratons, namely the Mediterranean-Alpine low-temperature metallogenic domain, the southwestern Guizhou metallogenic domain in China, the Carlin metallogenic domain in North America, and the North Caucasus metallogenic domain in Russia.

 

Prospecting indicators for thallium-rich deposits:

 

1. Mesozoic and Cenozoic sedimentary rocks, volcanic rocks, and modern geothermal activity areas in low-temperature metallogenic domains;

 

2. Anticlinal structures and axial fault zones composed of carbonaceous limestone, marl, siltstone, clay sandstone, carbonaceous dolomite, and volcanic tuff;

 

3. Favorable metallogenic environments are characterized by medium-low temperature, weak acidity, moderate salinity, reducing environment, and high sulfur fugacity;

 

4. Realgar, arsenopyrite, mercury, antimony, some lead-zinc, and Carlin-type gold deposits are the best areas for prospecting thallium-rich deposits. Conversely, thallium anomalies can serve as prospecting indicators for Carlin-type gold and antimony-mercury deposits;

 

5. Low-temperature alteration mineral assemblages and alteration zones;

 

6. Low-temperature, high-sulfur areas.

 

7. The ores of thallium-rich deposits are colorful and eye-catching. Because the red thallium mineral is very similar to cinnabar, it looks like a budding cherry blossom, and the thallium-containing realgar ore can form a beautiful picture of red, yellow, and red-yellow interlaced colors.

 

Twenty-two. How to Find Titanium Ores

 

Prospecting indicators for titanium ores:

 

1. Ultramafic-mafic complexes distributed along ancient blocks, block margins, and deep faults are good places to look for vanadium-titanium magnetite deposits. Examples include the Yanhe-Lijiang platform edge depression, the Kangdian axis, the northern margin of the North China platform, the Mianlue Ning area, the central Tianshan Mountains, Zuoquan Tongyu, Daixian Heishangou, Licheng Xitou, Huairou Xindi, Changping Shangzhuang, Wuyang Zhaoanzhuang, Xingning Xiaolan, Hami Weiya, and Humar in Heilongjiang. The enrichment and mineralization law is: in the late magmatic stage, titanium forms independent minerals or participates in iron oxides as isomorphic substitutions, forming differentiated and intrusive ilmenite deposits and titanomagnetite deposits with industrial value.

 

2. Coastal sediments, residual slope deposits, and river alluvial deposits along mafic-ultramafic rock areas and old metamorphic rock areas are good places to look for ilmenite and rutile placer deposits. They are mainly distributed in the eastern coastal areas of Hainan Island (Province), including Wanning Baoding, Nanqiao, Dongao-Longbao, Hengshan, Kenglong, Qionghai Shaolao, Nangan, Boao, Tanmen, Wenfengling, Wenchang Fuchian, Sangersi, Lingshui Wushi-Gangpo, Wan Zhoupo, Xincun Port, Nanwanling, Sanya Maling, Danzhou Longshan, Xuwen Liuwei, Lufeng Jiazi, Yangjiang Nanshanhai, Wuchuan Wuyang, Xiamen Huangcuo, Zhaoan Gongkou, Hepu Shikang, Baoshan Banqiao, Tengxian Dongsheng, Sanji Rang, Hanchi, Cangwu, Dingnan Chebu, Chishui, Ankang Datong, Yueyang Xinqianghe, Huarong Sablangyan, Xiangyin Wangxiang, Menghai Menghe, Mengwang, Ankang Fujiahe, Yuehe Hengkou, Cenxi Yichanghe, Lingshui Lingshuihe, and Hunchun Hunchunhe.

 

3. Ultramafic to intermediate-mafic regional metamorphic rock areas are good places to look for rutile deposits. Examples include Zaoyang Dafushan, Daixian Nianzigou, Ruian Xianyan, Dahe Xiong Shangou, Xixia County Bamiaozigou, Xinxian Hongxianbian, Yangchong, and Laixi Liujiagzhuang.

 

4. Heavy artificial sand anomalies. Due to the high specific gravity and strong weathering resistance of titanium minerals, they are easily accumulated in the downstream of water systems, sediments or soil layers, and enriched into ore under weathering and erosion conditions. Sometimes, titanium is also concentrated in deposited bauxite and laterite.

 

5. Magnetic anomalies. Often used to find primary titanium ore, because ilmenite and titanomagnetite in primary titanium ore have weak magnetism, and magmatic and metamorphic titanium ores often coexist or are associated with magnetite, which will show stronger magnetism.

 

Twenty-three, How to find uranium ore

 

According to the geological environment, uranium resources can be divided into the following deposit types:

 

1) Unconformity type: Located near large erosion unconformities, mostly formed 1.6-1.8 billion years ago, often containing arsenic, nickel, molybdenum and gold.

 

2) Sandstone type: The uranium minerals contained in the primary ore are pitchblende and uraninite, which are oxidized to form secondary uranium minerals such as barium potassium uranate, vanadyl calcium uranate and calcium silicate uranate, suitable for in-situ leaching.

 

3) Quartz pebble conglomerate type: Only exists in early Proterozoic sedimentary rocks formed under anoxic conditions, such as Rand-type deposits, which are by-products of gold.

 

4) Vein type: Refers to deposits filled in fissures, cracks or breccias.

 

5) Breccia complex type: Formed in the Proterozoic ancient landmass during non-orogenic periods, the surrounding rocks are quartzites and sedimentary rocks rich in volcanic clastic rocks, and uranium mineralization occurs in the strata above the near-granite basement complex, the ore generally occurs in layered and unconformable forms, accompanied by copper, silver and gold.

 

6) Intrusive rock type (porphyry type): Refers to uranium deposits related to intrusive rocks or deep-source rocks, such as white granite and carbonate rocks.

 

7) Phosphate rock type: Refers to phosphate rocks containing low-grade uranium, which are by-products of the phosphate industry.

 

8) Caldera type: Located in calderas, uranium and molybdenum, silver, etc. are enriched in the permeable breccia fillings of volcanic pipes and arcuate fault zones around volcanic pipes.

 

9) Volcanic rock type: Occurs in layered or conical volcanic structures of acidic volcanic rocks, associated with molybdenum and fluorine.

 

10) Calcrete type: Formed in the Quaternary period, shallowly buried, related to calcified sediments, the sedimentary environment is peat, swamp, karst caves and fissures.

 

11) Metasomatic type: Occurs in metasomatic rocks of microcline granite.

 

12) Metamorphic type: Formed in sedimentary metamorphic rocks or volcanic sedimentary rocks.

 

13) Lignite type: Occurs in lignite and clay or sandstone directly adjacent to lignite.

 

14) Black shale type: Five-element formation, the uranium content is very low, and can only be used as a by-product.

 

15) Other types of deposits, such as the Todilto limestone deposit in Grants District, New Mexico, USA.

 

Indicators for finding uranium ore

 

1. Since uranium is radioactive, aerial and ground radioactivity surveys can be used to find uranium deposits.

 

2. Use the colorful secondary minerals of uranium to search, such as autunite, torbernite, uranophane, tyuyamunite, and carnotite.

 

3. Use the discoloration of symbiotic gangue minerals to find uranium ore. Radioactivity can turn fluorite purple, quartz into smoky quartz, diamonds green, and topaz blue. Uranium in zircon can produce pleochroic halos in biotite. Irradiation of radioactive rays can make some minerals emit fluorescence and phosphorescence.

 

4. Use characteristic wall rock alteration to search. Alteration assemblages related to uranium mineralization include: silicification, reddening, sericitization, chloritization and carbonatization. Reddening can turn potassium feldspar, plagioclase, chlorite, and even quartz and calcite red, which is due to the oxidation of divalent iron in iron-bearing minerals to trivalent iron by radioactive action. Microgranular hematite often appears in these minerals, mainly distributed along cleavage and irregular cracks.

 

5. Uranium and thorium geochemical anomalies; red basins around granite basement, sandstone, black rock series, coal-bearing and phosphorus-bearing strata, alkali metasomatic zones, and volcanic red bed zones.