夕卡岩矿床中共生单斜辉石-石榴石酸度计及夕卡岩矿床的酸度相

THE ACIDOMETER OF PARAGENETIC CLINOPYROXENEGARNET IN SKARN DEPOSITS AND ACIDITY FACIES OF SKARN DEPOSITS

基于对我国夕卡岩矿床的地质研究,应用固溶体热力学模型,对夕卡岩矿床中共生单斜辉石-石榴石矿物对进行分析,建立了共生单斜辉石-石榴石矿物酸度计,以此可以较好地估计夕卡岩形成的介质条件。经对我国各类金属矿化夕卡岩形成酸度的研究表明:不同矿化类型、不同产出条件的夕卡岩具有不同的形成酸度条件和含矿流体的酸度变化趋势。在此基础上,佐以共生矿物氧逸度的研究,可以建立夕卡岩矿床的氧逸度-酸度相。反映出金属矿化与夕卡岩间具有密切的成因联系。

The acidometer of the mineral couple of clinopyroxene-garnet is set up according to the studies of the skarn deposits and using thermodynamic models of the solid solution. The acidometer is givin by the formula (4) and (13) (in the paper).It may estimate acidities in the process of the formation of skarns. The studies on major types of mineralized skarn in China suggest that various type of mineralizations and skarns occurring in different geological environments have different conditions of the acidities. The acidities increase approximately along the following sequence: Fe, Cu, Fe-Sn→Mo, W→Sn. pH ranges from 3.5 to 7.5. According to the study of oxygen fugacities of the paragenetic minerals, it is possible to establish the following facies of the oxygen fugacity-acidity of skarn: high oxygen fugacity-low acidity facies, including Fe, Cu, Fe-Sn-bearing skarns; the medium oxygen fugacity-normal (medium) acidity facies, including Mo(W)-bearing skarns; the low oxygen fugacity-high acidity facies, including mainly Sn-bearing skarns and secondly W-bearing skarns. These facies may indicate the genetic relationship between mineralization and skarn.The oxygen fugacities and acidities in the process of formation of the ore-bearing skarns have the character of long-continued and multi-stage evolution, which is an obvious indicator-for distinguishing them from the barren skarns. These characteristics may serve as important criteria for the evaluation of ore potentiality of the skarns.