粤北大宝山次英安斑岩中副矿物榍石的初步研究

Preliminary Study on the Accessory Mineral of Sphene in Dacite Porphyry from Dabaoshan,Northern Guangdong Province

榍石是花岗岩,尤其是钙碱性花岗岩中常见的副矿物之一。利用背散射图像和电子探针成分分析对粤北大宝山矿区岩心样品(次英安斑岩)中的榍石进行了系统的矿物学研究。结果表明,研究区榍石可分为岩浆榍石和次生(热液)榍石两类,其中岩浆榍石为自形至半自形,颗粒较大,具环带结构,平均w(Al2O3)=1.24%,w(TiO2)=38.10%,w(F)=0.40%;次生(热液)榍石与绿泥石等蚀变矿物共生,多呈它形,平均w(Al2O3)=2.44%,w(TiO2)=36.02%,w(F)=1.00%。榍石的不同世代、成因、副矿物组合特征等可以揭示花岗岩的形成条件、演化历史,且对判别花岗岩的成因类型具有重要意义。

Sphene is a common accessory mineral in granite, especially in the calcium-alkaline granite. In this paper systematic research has been done on sphene from the Dabaoshan daeite porphyry using EPMA. The results show that these sphenes can be sorted into two types, including magmatic sphene and secondary （hydrothermal） sphene. The former is euhedral to hypidiomorphic with larger grains and zoning structures, and has average contents of Al2O3, TiO2 and F of 1.24%, 38.10% and 0.40% respectively. The latter is xenomorphic and grows with symbiosis with chlorite-alteration minerals, and has average contents of Al2O3, TiO2 and F of 2. 44%, 36.02% and 1.00% respectively. Sphenes with different generation, genesis, combination of accessory minerals can reveal the formation conditions and evolution history of its host rock, and plays an important role in discriminating the genetic type of granite.