Enrichment of metal elements by media rich in organic matter

The enrichment of metal elements by organic-rich media is a complex process, which mainly includes the following four functions: ① Complexation and chelation of metal ions by organic matter are related to the content of organic carbon, the composition and structure of organic matter and the chemical properties of complexing elements; ② Adsorption of metal elements by colloid formed by mixing organic matter with clay; ③ The wrapping and carrying effect of organic matter such as peat and sapropelic mud on metal element particles; (4) The secondary silica colloid generated in soil and river sediments can encapsulate metal ions and compounds in a low-temperature and weak-acid environment rich in organic matter.

(1) Relationship between Organic Carbon Content and Sample Size

The content of organic carbon in sediments and soil of organic-rich rivers in forest swamp area has a certain relationship with the sample size. Generally speaking, the content of organic carbon in a sample often increases in proportion to the particle size of the sample (Table 3-2), and the enrichment of metal elements that increases in proportion with the increase of organic carbon content in the sample is related to the complexing and chelating of metal ions by organic compounds in the same sample.

From the data in Table 3-2, it can be found that: ① In the water system sediments of Mordaoga (gold mine) and Delpur (lead-zinc-silver mine), the complexing and chelation of organic compounds to metal ions obviously enriched four elements, namely Cu, Hg, Au and Ag, and they increased synchronously with the content of organic carbon as the particle size of the samples became finer, at the same time, as, Zn and Mn were also shown in Mordaoga mining area. (2) The contents of Au, Ag, Zn and Ni in the valley sediments of Dongan Gold Mine also increased synchronously with the organic carbon content, while other elements did not. ③ The metal enrichment formed by organic carbon adsorption is limited, and generally only high background and low value anomalies are formed.

(2) The influence of peat on gold

Peat can wrap and carry gold-bearing mineral particles, but the element enrichment formed by this wrapping and carrying has no obvious regularity, but sometimes it can form high-value anomalies of Au (Table 3-3).

(3) The influence of secondary silica gel on gold

In Mordaoga, Niuernao, Delpur and other mining areas, silicate phase is the absolute dominant form of gold in peat and humus samples, which can form high-value anomalies of Au (Table 3-4), indicating that the encapsulation effect of secondary silicate colloid on Au is very obvious in forest swamp landscape areas.

(4) The difference of adsorption and enrichment of metal elements by organic matter.

For elements with different chemical properties, the adsorption and enrichment of metal elements by organic matter show great differences. In Tianhexing porphyry copper mine area of Changbai Mountain, the comparison of element contents between peat and stream sediments at the same point shows that organic matter has a strong adsorption effect on Hg, Cd, Ag, Cu and Bi, and the enrichment degree can reach 2 ~ 6 times. Lead, zinc, manganese, cobalt, nickel, tungsten, molybdenum and other elements are also enriched to some extent. However, elements such As K, Na and As are not enriched, but are lower than those in river sediments (Table 3-5). At the same time, the coefficient of variation of more than half of the elements in peat decreased, indicating that peat has obvious characteristics of element enrichment and abnormal reduction.

Table 3-2 Relationship between Organic Carbon Content and Metal Elements in Medium

Content unit (wB): gold, silver and mercury are10-9; Organic carbon is10-2; The other elements are 10-6.

Table 3-3 Phase Analysis Results of Gold Elements in Peat with Different Particle Sizes

Element content unit (wB):Au is10-9; Organic carbon is 10-2.

Table 3-4 Phase Analysis Results of Gold in Peat (a) and Humus Soil (b)

Note: the gold element content (wB) is 10-9.

Table 3-5 Comparison of Statistical Parameters of Peat and River Sediments in Tianhexing Area

Note: 1— Peat (sample number = 31); 2 —— stream sediments at the same point as peat (sample number = 31); 3— River sediments in the whole area (sample number =229). Material content unit (wB):K2O and Na2O are 10-2, Ag is 10-9, and other elements are 10-6.