Journal of the Virtual Explorer

Based on the electron probe analysis from 18 chlorite samples, the crystal chemical formula have been calculated and then ploting them on the genesis figure, they can be divided into following type: the main type is brunsvigite, the others are prochlorite, chamosite and diabantite. The typical characteristics of chlorites in the Caijiaying deposit are iron rich higher than the general hydrothermal poly metal deposits.

The analytic results of IR spectrum for chlorites listed in Table 2). Two stronger dilation vibration zone of OH^- located at near 3556～3538cm^-1 and 3427～3390cm^-1, at the same time, dilation vibration zone of Si－O－Si(Al) is a very stronger single peak with lower and mostly at near 990cm^-1. According to the classification by Menka (Ying Y P, 1982), the chlorites in Caijiaying deposit can be classified as two types, and most of them are thuringite, the others are ripidolite. The other OH^- dilation vibrated frequency locates between 3430～3390cm^-1; a few samples are ripidolite whose librated zone of OH^- locates at 3560cm^-1, 3425cm^-1 and bend librated at near 655cm^-1.

The results of differential analysis of chlorites in the deposit listed in Table 3. Most of chlorites have two decalescence valley, located at the range 500～600^oC and 600～700 ^oC or 700～800 ^oC. Based on the classification principle on the structural decompose by Werner Smyktar Kloss, the chlorites in the ore field are maily ripidolite, brunsvigite and some chlorite with deaquation and prochlorite. All those characteristics are consistent with the conclusion that chlorite often belong to brunsvigite in the Pb-Zn deposit (Ye D N, 1984).

According to the data of x-ray diffraction analysis on chlorites, the d(001), d(002),d(060) can be obtained, on the basis of these information, the atom numbers of Fe²⁺, Fe³⁺, Mg²⁺ and Si⁴⁺ in chlorites can be calculated and then plotting the results on the figure provided by Brown B E,1962, the poly type of chlorites in Caijiaying deposit are I_ba, I_bb and II_bb (Table 4).

Sericite is one of the main wall rock alterations in Caijiaying deposit. The experiments was finished at electron probe room of geology department, Beijing University, the results of two main ore belts and stratum are listed in Table 5, it shows that the K₂O is very high, so they can be named as potassium mica. The metal oxide amounts are follows: w SiO₂ (wt%) 43.20%－52.69%, w (K₂O) 6.49%－10.63%, w (MgO) 0.98%-2.39%, w (FeO) 1.56%－8.77%, w (Al₂03) 30.47%－37.41% and minor Na₂O, MnO₂, TiO₂. Accepted chemical computation method (Xiao P, 2001), the potassium mica chemical formula are calculated and results listed in Table 6.

In order to discuss the composition variation of potassium mica, we researched from several aspects:

(i) Genesis diagram

Put the data of x(Al^IV), x(Fe³⁺)/x(Fe³⁺+Al^IV) and x from Table 6 on the genesis diagram, all the potash mica fell in the hompgeneity multiple facial hydrothermal area of 1 Md, lM, 2M, 2M₁, 2M₂, 3T. This demonstrates that potassium mica is hydrothermal genesis.

Figure 2. Characteristics of crystal chemistry of dioctahedron sericites in different genesis

I～III. Diagenesis – initial epigenesis 1 Md-1 M polyphase of sedimentary mica; I. Al illite area; II. evaporation of illite; III₁ glauconite; IV. 1M₂ M₁ polyphase of mica in deep epigenesis belt ;V. metamorphic belt of mica; Ⅵ.1 Md, 1M, 2M₁, 2M₂ and 3T polyphase hydrothermal mica; VII. 1 pictoamesite area（after A T Kososyvier and B.A. Deliz,1975）

(ii) The relation of K and Na in potassium

The K ion number of potassium mica in Caijiaying ore body changes between 0.54 and 0.89, but Na ion number is 0. Though the K ion number of potassium mica in the stratum of Datongying Formation is 0.71 which is near to the ore body, the Na is 0.08 which is different from the ore body. The reason is that Na is carried out in the rock when hydrothermal alteration occurred.

(iii) The relation of Mg and Si in potassium mica

The Mg ion number of potassium mica in Caijiaying ore body changes between 0.12 and 0.23, all Si ion number are higher than 3.00 and range from 3.18 to 3.41, they belong to silicon poly mica. But the Mg ion number in stratum is lower and Si ion number equal to 2.99 which similar to silicon poly mica.

(iv) The Al occupy position in potassium mica

The Al^IV and Al^VI in the tetrahedron position of the potassium mica in the ore body are 0.64-0.82 and 1.38-1.84, but the numbers that of stratum is 1.01 and 1.84 respectively. The reason may be that Al^VI was carried out during hydrothermal alteration.

(v) The relation among Al, Fe, Mg in octahedron position

Plotting the Al, Fe and Mg atom numbers in octahedron position of potassium mica on the Al-Fe-Mg diagram, w(FeO),w(MgO) of sample No. 3 are the highest, 4.03% and 8.77% respectively, Fe, Mg atom numbers are 0.43 and 0.22. It demonstrates there is positive relation between Mg and Fe in octahedron position of potassium mica, w(Mg) and w(Fe) are higher, so the Al^VI is lower. The other samples locate in a small area. All these characteristics show that w(A1), w(Mg) and w(Fe) are similar in potassium mica.

The nine samples of potassium mica in the deposit have been analyzed at differential analysis room of geology department, Beijing University. The structural decompose of potassium mica range from 615–860^oC and most of them at 620-750^oC. Based on the classification principle on the structural decompose, the potassium mica in the ore field are mainly 1M, 1M-2M₁ and 2M₁ poly type. The species of potassium mica can be named as sericite, hydromuscovite, hydromuscovite-sericite. The weight loss amount of potassium mica is different from 5% to 9.25%, these results are consistent with the fugitive constituent analyzed by electron probe analysis from 3.46% to 7.42%.

Ten samples of potassium mica in the deposit have been analyzed by x-ray diffraction. The experiment was finished at X-ray room of geology department, Beijing University. The crystal indexes of potassium mica are calculated and compare with the standard data by Ye D N (1984). There are different d(060) in different poly type potassium mica, the d(060) of dioctahedral and trioctahedral are 0.1480－0.1510 nm and 0.1530－0.1557 nm respectively. There are poly type of potassium mica 1M, 1M + 2M₁, 2M₁, 2M₁ + 3T in the Caijiaying deposit (Table 7) and this result consistent with differential analysis. At the same time, there are some relation between the poly type of potassium mica and depth which they locate, and 1M poly type can be seen at 1432.6 m reflecting that the depth is shallow. But the 2M₁ poly type formed at deep, 1361－1153.0 m, 1M +2M, poly type formed at 1361 and 1302 m.