There are many methods of prospecting for placer gold, and there are 5 commonly used methods: ①natural heavy sand method, ②engineered heavy sand method, ③old mining survey, ④geological and geomorphological analysis
1. Natural heavy sand method
The natural heavy sand method is based on the high density (specific gravity) of the placer gold particles, which can be directly selected by the elutriation tray. The samples are digging at the surface or not deep in the loose debris deposits, and then elutriating in the field directly determines whether there is any Placer gold exists in a way.
Sampling includes heavy sand sampling from river sediments, outcrop sampling of terrace gravel deposits, and heavy sand sampling from residual slope deposits on mountain slopes.
♦Sampling of river heavy sand from river sediments and outcrop sampling of terraced gravel layers can be used to understand the gold-bearing nature of river sediments, the general distribution range of placer gold, and the grade and thickness of terrace gold-bearing layers.
♦The sampling in the residual slope layer of the hillside is used to trace the source of the placer gold in the Xiaogou mountain area known to have placer gold. The sampling and panning of shallow pits are excavated at certain intervals on the hillside and the foot of the slope, and delineated according to the gold results. Distribution range, narrow the rock gold prospecting target area.
2. Engineering heavy sand method
It is an effective method to use sand drills or exploratory 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 mainly occur at the bottom of loose sedimentary layers, the engineering heavy sand method can ascertain the deep placer gold enrichment and provide direct prospecting information.
♦The basic point of adopting this method is that the layout of sampling project points must have a sufficient basis and have construction feasibility, and secondly, no matter what kind of main sampling process, it must penetrate the gold-bearing layer and control the depth of at least 0.2m below the bedrock surface. The use of sampling engineering for placer gold prospecting must be based on the analysis of geological and geomorphic conditions, and according to the prospecting signs and clues, the favorable positions in the favorable ore-forming zone shall be selected, and the engineering shall be arranged according to a certain engineering network. Favorable positions should be determined according to the rules of placer gold enrichment and mineralization.
3. Old placer gold mining and civilian mining investigation
In many placer gold areas, there are common old placer gold manual mining traces in the upper reaches of rivers or in the branch ditch and valleys, which are effective signs of placer gold prospecting. According to the old excavations, further development of peripheral prospecting can often achieve good results. Large-scale tailings piles in old manual mining areas are often ore bodies of industrial value. In addition, through civilian mining surveys, a lot of valuable information about the geological characteristics, rules and prospecting clues of the placer gold mineralization in this area can be obtained, so the local placer mining investigation has important prospecting significance.
4. Geological and geomorphological survey
It is the basic method of placer gold prospecting, which is mainly used for the analysis of placer gold metallogenic conditions and the prediction of favorable mineralization areas. In the prospecting stage, the investigation of the valley route is mainly carried out. The geological survey can use the natural outcrop method and the river debris observation method, using the known gold-producing ditch rocks in the area as a comparison and analogy, while taking some natural heavy sand samples to understand the gold-bearing properties. Indirectly or directly determine whether there is a placer gold supply and the degree of richness or poorness of the supply. During the investigation, attention should be paid to understanding the structural background of the valley and the geological phenomena related to gold mineralization.
A sampling of heavy sand from rivers to find gold
Taking heavy sand samples along the river for placer gold prospecting is one of the most commonly used methods. The main experience is
1. The sampling points should be reasonable and representative. Usually, the sampling line spacing should be 200-300m.
2. The sampling location should choose the inner part of the river to change the flow direction (turn); the area where the river flow rate is significantly slower; the front of the big obstacle in the river bed; the side where the main tributary merges.
3. Pay attention to the sampling level. It can only be taken when there are mud (clay), sand and gravel. The lack of one of the three is not effective.
4. When sampling in old exploration pits or sand piles of old mining tailings, the topsoil part should be stripped first, but do not excavate too much. It is best to find gravel with broken pieces of bedrock for sampling. It is not possible to take the pure water-washed gravel.
5. Can’t get samples in water.
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