福建丁家山铅锌矿区磁黄铁矿成因矿物学特征研究

GENETIC MINERALOGICAL STUDY OF PYRRHOTITE IN THE DINGJIASHAN Pn-Zn ORE DISTRICT,FUJIAN PROVINCE

通过野外观察、光学显微镜、矿物场填图、X射线衍射、微区成分分析等手段,针对福建丁家山铅锌矿区磁黄铁矿的成因矿物学特征进行研究。结果表明,丁家山铅锌矿区磁黄铁矿具沿北东向断层串珠状排布,揭示明显的热液成矿特征;矿区内有4类产出形态各异的磁黄铁矿,多为单斜、六方混合相磁黄铁矿,其中单斜磁黄铁矿为六方磁黄铁矿的固溶体分离产物,指示矿区成矿为缓慢的降温过程;六方磁黄铁矿结晶温度在322℃～304℃之间,与同成矿期石英包裹体均一测温结果完全符合。六方磁黄铁矿-黄铁矿-闪锌矿成矿压力计计算结果集中在0.2GPa～0.3GPa之间,与该区燕山期花岗岩成岩压力完全一致。由此认为丁家山铅锌矿为燕山期花岗岩与中-新元古代马面山岩群龙北溪组上段经区域变质的富钙质岩发生接触交代作用而形成的矽卡岩型矿床。

Pyrrhotite from Dingjiashan Pn-Zn ore district is investigated by means of optical microscope, X-Ray diffraction, micro-area chemical analysis, field observation and mineralogical mapping. The result suggests that pyrrhotite from this ore district generally crosscut the strata, and the enrichment centers of pyrrhotite distribute along NE-trending fault, indicating that the oreforming minerals are derived from hydrothermal fluid. Most of pyrrhotite is characteristic of mixed phase of both monoclinic and hexagonal. Monoclinic pyrrhotite is the products of solid solution separation, showing that the ore-forming experienced a moderate cooling process. The crystallization temperature range of hexagonal pyrrhotite is 322 ℃ -304 ℃, consistent with the inclusion homogenization temperature of contemporaneous quartz. Geobarometer of hexagonal pyrrhotite-pyrite-sphalerite paragenesis reveals a confining pressure of 0.2 GPa-0.3 GPa, consistent with the forming pressures of ore-forming-related Yanshanian granite. It is considered that the ore-forming process of Dingjiashan Pn-Zn ore district is resulted from the contact metasomatism between Yanshanian granite and the regional metamorphosed calcareous rock of mesoproterozoicneoproterozoic Mamianshan Formation.