碳酸盐岩石成因类型的判别分析和白云鄂博“白云岩”的成因讨论

DISCRIMINANT ANALYSIS OF GENETIC TYPE OF CARBONATE ROCK AND DISCUSSION ON GENETIC DOLOMITITE IN BAI YINOBO REGION

本文根据对世界上20多个国家和我国21个省碳酸盐岩石化学全分析数据的统计和换算结果,发现岩浆碳酸岩与沉积碳酸盐岩之间常量元素的一般含量无显著不同,但采用两组或逐步判别分析的方法,仍能将岩浆碳酸岩与沉积碳酸盐岩很好的区分开。判别效率可达90％以上。将这一方法应用到白云”鄂博矿区的“白云岩”和灰岩,90％以上的“白云岩”样品判为岩浆碳酸岩,灰岩的样品全部判为沉积碳酸盐岩,与它们的地质产状和地球化学特征一致。

The writer collected 769 data on bulk analysis of carbonate rock and carbonatite from more than 20 country in the world and 21 provinces of china.Results of statistics and calculation indicated that content ranges of main elements between sedimentary carbonate rock and carbonatite are similar.The carbonatite can be distinguished from sedimentary carbonate rock by discriminant anaalysis.The carbonatite is P2O5-rich and usually content of P2O5 is more than0.2% .The number of data, P2O5> 0.2% , is 86% of all carbonatite data. But sedimentary carbonate rock is P2O5-poor.The number of data, P2O5>0.2% only makes up 12% in all this rock s data.Therefor, content of P2O5 is one important standard for discriminanting genetic type of carbonate rock. When eleven variables are adopted in two set discriminant analysis, discriminanting efficiency of various genetic type of calcareous carbonate rocks, dolomitic carbonate rocks and ferruginous carbonate rock is 93.5%, 90.7% and 89.8% separetaly.When P2O5, Na2O, A12O3, MnO, CaO, K2O and Fe2O3 are used as discriminating variables in discriminant analysis of step by step, discriminanting effect of calcareous carbonate rock is the best and discriminanting efficiency is 94. 5%. While FeO, Fe2O3, Al2O3 and P2O5 are adopted in discriminant analysis for dolomitic carbonate fock, process of calculation is more simple and discriminanting efficiency reached 96% . Using CaO. P2O5 MgO, SiO2, Fe2O3 and Al2O3 for discriminant analysis of ferruginous carbonate rocks, discriminanting efficiency comes up 98. 5% . Generally, discriminanting effect of sedimentary carbonate rocks (near 100%) is better than carbonatite (more than 85% ) , i.e. sedimentary carbonate rock generally isn ' t distinguished.Results of discriminant analysis of limestone and dolomitite from Baiyinobo region indicat that 17 samples of limestone are all distinguished sedimentary carbonate rock, but 3 samples in 57 samples of dolomitite are distinguished sedimentary carbonate rock, making up 5.3% of collecting data, other samples are distinguished carbonatite.The conclusion is in accord with its geological occurrence, geochemical and isotopic composition characteristics