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Stratigraphic, lithofacies, paleogeographic conditions for prospecting conditions

Release date:2018-09-28  source:中南选矿网  Browse times:918
Stratigraphy, lithofacies, paleogeographic conditions
In order to predict and find various deposits formed by the external ore-forming process, it is very important to conduct in-depth study and analysis of the layers, lithofacies and paleogeographic conditions of the survey area.
(1) Stratigraphic and mineralization relationship
The stratum is a sediment with certain facies characteristics in a certain period of time. The formation of many sedimentary deposits is related to the formation (Table 2-3-2). The stratum is mainly reflected in the control of the metallogenic age and the distribution of ore-forming space. Therefore, in the prediction and search of the relevant deposits, it should be noted that in certain specific ages, the ore prospecting is carried out according to the horizon. Over the years, China's mineral exploration experience has shown that most of the deposits are controlled by a certain stratum or a set of strata. For example, iron, manganese, aluminum, phosphorus, coal, and salt deposits all have certain enrichment times and stratigraphic horizons. More than 50% of the world's iron ore reserves are concentrated in the Precambrian. Manganese reserves are also concentrated in the Precambrian and Permian. The most important bauxite deposits are concentrated in the Carboniferous. Coal is mainly concentrated in the Carboniferous, Erdi, Triassic, Miluo, and Tertiary. Therefore, according to stratigraphic prediction, sedimentary minerals are found, and in practice, mineral exploration is carried out along a certain stratum. At present, mineral exploration is extremely important.
(2) Relationship between lithofacies and mineralization
Lithofacies are products of the results of sedimentary differentiation under certain deposition conditions. From the existing data, many important sedimentary deposits are controlled by specific lithofacies, and there are certain phase transition laws, forming a unique sedimentary deposit zoning, which not only reflects the genetic characteristics, but also points out the spatial distribution law. For example, various sedimentary iron ore can have four different mineral facies belts (Fig. 2-3-9); sedimentary manganese ore also has similar phase transition characteristics, and Af Bieheqin divides manganese ore into three facies (Figure 2 3-10). The above phase change zoning is extremely important in mineral exploration. When a phase band is first discovered, the direction and location of the other phase bands should be considered, and sometimes the discovery may not be industrially significant, but it can lead to more significant discoveries.

Figure 2-3-9 Schematic diagram of sedimentary iron ore transformation


Figure 2-3-10 Schematic diagram of sedimentary nucleation phase transition


Table 2-3-2 metallogenic age of China's sedimentary deposits

The same mineral species is characterized by a phase change of the deposit zone, and between different minerals is the ore-forming sequence law. As described above, a group of mineralization such as iron and manganese forms a shallow coastal area in a warm and humid climate. The distribution is from the coast to the shallow sea, followed by the deposition of iron-manganese-phosphorus. These rules should be fully observed in mineral exploration.

(3) Paleogeography and mineralization relationship

Paleogeography refers to the natural geography of sea, land, water system distribution, topography and climate in a geological period. It marks the external environment in which matter is deposited. The analysis of paleogeography is based on the study of lithofacies. From the distribution and changes of different rock groups, the distribution of land and sea, the change of seawater depth, the direction of seawater retreat, the salinity of seawater, the paleoclimatic change and the source of sediments are analyzed.

The main features of paleogeography for sedimentary minerals control are:

(1) important sedimentary deposits are mostly distributed in the middle zone between the sedimentary zone and the denuded zone (ancient land margin, coastal sea, shallow sea, lagoon, delta, etc.). For example, the Xuanlong iron ore in the lower part of the Sinian in northern China is distributed in the southern margin of Inner Mongolia (Fig. 2-3-11 (b)); the Ningxiang iron ore in the southern Devonian of China is produced at the edge of the ancient land of Jiangnan (Figure 2 3-11 (a)).


Figure 2-3-11 Relationship between sedimentary iron deposits and paleogeography in northern China (Xuanlong) and southern China

(a) Distribution of Ningxiang-type iron ore and Devonian paleogeographic map; (b) Schematic diagram of ancient location of Xuanlong Iron Mine

(2) The formation of sedimentary deposits is closely related to climate. According to climatic conditions, it mainly divides into two categories: temperature, humidity and drought. The former is represented by mineralization sequences such as Fe, Mn, P, A1 and coal. The various salt mines are representative of drought weather. There are also some transition types of minerals in between.

(3) The crustal movement also controls the formation of ore. Two different sequences of transgression and retreat are caused by the movement of the earth's crust due to crustal movement. At the transgression stage, Fe, Mn, P and other deposits are formed, which are mostly distributed in the bottom of the transgressive rock series; while the sea retreat stage forms Cu, salt and other deposits; A1, coal is a common transition product; in the stable stage, there are limestone and diatomaceous earth. The formation of non-metallic deposits.

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