Pyrite is a semiconductor mineral. When there is a temperature difference between its two ends, it will generate a thermoelectric thermal potential. This phenomenon is called thermoelectric effect or electrothermal property. This electromotive force is called thermoelectromotive force. It is generally believed that the generation of this electromotive force is related to the local excess of anions and cations formed by the isomorphous substitution of heterovalent elements in pyrite. When impurity elements enter the internal lattice of pyrite and enable it to donate electrons, When , excess valence electrons will be produced. This impurity element is called a donor impurity element. Pyrite with donor impurities is called N-type conductor pyrite. N-type semiconductors are electronically conductive. When the impurity elements entering the pyrite crystal lattice cause the electricity price to be insufficient, excess holes appear in the crystal lattice, which can easily accept external electrons. This impurity element is called an acceptor impurity (element). Pyrite with acceptor impurity elements is called P-type pyrite, and P-type semiconductors conduct holes. If the thermoelectric coefficient, that is, the electric heating rate, is α, then +α belongs to P type and -α belongs to N type. It is not difficult to see that the conductivity (N or P) and thermoelectric coefficient (±α, ±μV/℃) of pyrite mainly depend on the type and concentration of homogeneous isomorphic impurity elements and the type of crystal structure defects. Common donor elements in pyrite are Co2+, Ni2+, Cu2+, Zn2+, etc. in isomorphous states. As (Te, Sb) that replaces sulfur in pyrite is the most common acceptor element. Since As has one less valence electron than S2, each As atom entering the pyrite lattice will increase the amount of pyrite. A hole. The 3d electrons of Co are 1 more than Fe, and the 3d electrons of Ni are 2 more than Fe. Their entry into the pyrite lattice will increase pyrite by 1 or 2 electrons respectively, so the following formula can be derived:

A=As content/As atomic weight - (Co content/Co atomic weight + 2Ni content/Ni atomic weight)

The A value can roughly reflect the hole or electron content in pyrite. When A is a positive value, there are more holes than electrons in pyrite, and pyrite is hole conductive; when A is a negative value, it reflects that there are more electrons than holes in pyrite, and it is electronic conductivity ( Yang Guojie et al., 1992). The conductivity type of pyrite is also related to the S and Fe content in the pyrite crystal. Generally speaking, when there is more Fe and less S in the pyrite, the pyrite thermoelectric coefficient is negative (electron type); when there is more S and less Fe, the conductivity of pyrite is negative (electronic type). , the thermoelectric coefficient of pyrite is positive (hole type).

Research shows that when As, Sb, Co, Ni, etc. enter the pyrite lattice as isomorphs, they are obviously affected by temperature. High temperatures are conducive to Co and Ni replacing Fe in pyrite; As and Sb are unstable in the pyrite structure, and low temperature is conducive to As and Sb entering pyrite to replace sulfur. Therefore, pyrite formed at high temperature is N-type, pyrite formed at low temperature is P-type, and pyrite formed at medium temperature is N-P mixed type. Therefore, when the thermoelectricity of most pyrite is P-type or N-P mixed type, the ore-forming temperature is relatively low, generally around 200℃±; when its thermoelectricity is N-type or N-P mixed-type, the ore-forming temperature is higher, greater than 250℃ (Yang Guojie et al., 1992).

In the Xiaoqinling-Xionger Mountain area, the thermoelectric properties of pyrite in different types of gold mines have their own characteristics (Table 3-16).

Table 3-16 Thermoelectric coefficient (μV/℃) of pyrite in gold mines in Xiongershan area

The main conductivity types of pyrite in Xiaoqinling quartz vein-type gold deposits It is N type. For example, among the 104 pieces of pyrite in Dongchuang No. 507 vein, 100 pieces of pyrite have electronic type (N type), 4 pieces are mixed type (P-N type), and the thermoelectric coefficient of pyrite is - 157.4μV/℃ (Wang Guanglan et al., 1998). More than 700 pyrite grains in Tonggou No. 303 vein were measured, and only 6 grains were of cavity type (P type), and the rest were all N type, accounting for 99.2%. The thermoelectric coefficient of pyrite is (-132.6~-197.5) μV/℃, all of which are N-type (Xue Liangwei et al., 1996). The pyrite in Wenyu S505 vein and Yangzhaiyu S60 vein is electronic type (N-type) regardless of mineralization stage or output level. The maximum thermoelectric coefficient of pyrite in S505 vein is -33.0 μV/℃, and the minimum is -313.4 μV/℃, generally between (-131~-170) μV/℃. The maximum thermoelectric coefficient of pyrite in the main mineralization stage of S60 vein is -122 μV/℃, and the minimum is -258 μV/℃, generally (-150～-213) μV/℃ (Li Shimei et al., 1996). The pyrites in veins 304 and 305 are all electronic type (N type). This characteristic of the pyrite in the gold-bearing quartz veins in Xiaoqinling reflects its relatively high formation temperature and the Co and Ni content in the pyrite. It is consistent that the w(Co)/w(Ni) ratio is mostly greater than 1.

The thermoelectric coefficients and conductivity types of pyrite in the gold deposits dominated by altered rock type and blasting breccia type in the Xiong'ershan area vary (Table 3-15). The A value of the blasted breccia-type Qiyugou gold mine pyrite is -872~-786, the thermoelectric coefficient is (-140.4~-479.28) μV/℃, and the conductivity is N type; Dianfang gold mine yellow The thermoelectric coefficient of iron ore is (-248~+492) μV/℃, and the conductivity is N-type and N-P type.

Among the altered rock-type gold deposits, the A value of the Beiling gold mine is 14729. P-type pyrite is mainly formed in the main mineralization stage, and N-P type pyrite is mainly formed in the late mineralization stage. The A value of the Shanggong gold mine is 14238. N-type pyrite appears in the early mineralization stage, and P-type and N-P-type pyrite form in the main mineralization stage. The Qianhe gold deposit is mainly N-type pyrite, and N-P mixed-type pyrite appears locally. This feature is related to the metallogenic temperature of pyrite. The metallogenic temperature of explosion breccia gold deposits is high, while the metallogenic temperature of altered rock gold deposits is relatively low. However, Qianhe altered rock-type gold deposits are mainly N-type due to their relatively high mineralization temperature.