西藏玉龙斑岩铜矿含矿斑岩体钾长石斑晶的有序度及成因探讨

Degrees of ordering and origin of K-feldspar phenocrysts in a mineralized porphyry of the Yulong porphyry copper deposit,Tibet.

通过对玉龙含矿斑岩体中钾长石斑晶的X射线衍射及红外光谱分析,其有序度分别为0．457～0．597(X射线衍射)及0．64～0．72(红外光谱),三斜度分别为0．675～0．775(X射线衍射)及0．16～0．44(红外光谱),结构参数为0．278～0．813。这些数据表明钾长石斑晶为中微斜长石,测定的结构温度为370℃～442℃。此外,还从热力学、晶体结构诸方面探讨微斜长石的成因,认为三斜微斜长石与单斜正长石之间的转变在地质历史中很可能是一个不可逆的过程,由微斜长石加热可以转变为正长石,但正长石冷却不会自发地转变为微斜长石,因此由微斜长石结构测得的温度应为钾长石形成时的最高温度,从而得出玉龙含矿斑岩体中钾长石(中微斜长石)斑晶不是岩浆结晶的产物,而是热液作用的产物。

X-ray powder diffraction and infrared spectrum analyses of K-feldspar phenocrysts from a mineralized porphyry at Yulong provide degrees of ordering of 0.457 - 0. 597 （ X-ray diffraction） and 0.64 - 0.72 （ infrared spectrometry ） and triclinities of 0.675 - 0.775 （X-ray diffraction） and 0. 11 - 0.44 （infrared spectrometry） respectively, as well as structural parameters of 0.78 -0. 813. These data suggest that K-feldspar pheuocrysts are andesine-microcline with structural temperatures of 370 - 442℃. Furthermore, the orion of the microcline is discussed from the thermodynamics and crystal structure. The authors think that the transformation between triclinic microcline and monoclinic orthoclase is most likely to be an irreversible process in the geologic history. Microcline may be transformed into orthoclase by heating, while orthoclase cannot be spontaneously transformed into microcline on cooling. Therefore the structural temperatures obtained by microcline measurements should be the highest temperatures at which k-feldspar forms. Thus it is concluded the k-feldspar phenocrysts in the Yulong mineralized porphyry is not the product of magroatic crystallization but the product of hydrothermal activity.