Study On Expansion And Collapse Mechanism Of Water-sensitive Tuff In Nibao And Zaofanshan Mining Areas In Southwestern Guizhou

Southwest Guizhou is an important gold ore concentration area in China.It is an important part of the"Golden Triangle"of Yunnan,Guizhou and Guangxi.It is known as"Jinzhou".There are some super large and large gold deposits such as Shuiyindong gold deposit,Nibao gold deposit,Lannigou Gold Deposit,Yata gold deposit and other small and medium-sized gold ore groups.The main gold deposits in this area are Linka type gold deposits,one of which is characterized by a large number of tuffs in the ore bearing strata.Tuff is a kind of special soft rock,which generally has the properties of water swelling,disintegration,even argillization and decomposition.These special properties have brought huge problems to mineral exploration and mining,such as drilling,roadway excavation and other projects involving tuff,if handled improperly,it will bring huge economic losses,even casualties.In this paper,the typical tuffs of Nibao gold mine and zaofanshan gold mine in Southwest Guizhou Province are selected as the research objects.Based on the summary and analysis of the existing relevant geological data,field survey,systematic rock and mineral testing,and analysis of the test phenomena and data,the material composition,microscopic appearance,pore characteristics,hydrochemistry,weathering mechanism and collapse prevention of tuffs are carried out In this paper,the main factors of water swelling and collapse of tuff in this area are analyzed and summarized.The main achievements and understandings are as follows:(1)The chemical elements of tuff in Nibao and zaofanshan gold deposits consist of O,Si,Al,K and Fe.The total content of O,s and K is more than 95%.The main mineral components are quartz,mica and pyrite according to the XRD test data.The samples with low weathering degree contain a small amount of feldspar.Through the analysis of the production of tuff,the mica minerals are mainly volcanic glassy devitrification in the water environment,and then obtained through the weathering and the mutual transformation between minerals.The main mineral that leads to the decomposition of tuff is mica,which is similar to clay mineral and can be converted into illite by combining with water.The low sulfur of iron ore is easily oxidized to form soluble salt solution,and the sulfuric acid formed in the oxidation process also promotes the decomposition of mica minerals.(2)SEM technology was used to observe the micro morphology of tuff in Southwest Guizhou Province.It was found that there are a lot of pores and micro lamellae structure in the tuff.By using EDS to analyze the composition of the structural elements of the micro lamellae,the main elements are o,Si,Al and a small amount of S.combined with the analysis results of the material composition of tuff,the mica minerals are the main minerals of the micro lamellae.Through the observation of the micro morphology of the tuff after the dry and wet cycles,the micro layer structure of tuff is obviously curled and the internal pores become larger.The capillary phenomenon of pores in tuff and the hydrophilic mica mineral with micro lamellar structure accelerate the speed of water entering into the rock;through the low-temperature nitrogen adsorption experiment and high-temperature mercury injection experiment on tuff samples,the pore size distribution characteristics and specific surface area and other pore characterization parameters are obtained.The experiment proves that the pore size in tuff is mainly mesoporous,and the macropore is auxiliary There are a few micropores and a large number of micropores and mesopores,which increase the specific surface area of tuff,and then accelerate the interaction between water and tuff.(3)Through a series of chemical tests,the results show that the inorganic salt ions which have inhibition effect on tuff expansion and disintegration in water are mainly cations.The smaller the ion radius,the higher the valence state and the higher the concentration,the better the effect of inhibiting tuff disintegration is.The Na⁺,K⁺,Si O_4,^2-Cl^-,Br^-which have better effect also have certain inhibition effect.The tuff is in a strong oxidation state in the natural environment.The anti collapse test is carried out by using the above ions.The solution of Na Cl and k₂Si O₃ added with antioxidant has a good anti collapse effect on the tuff.