江西浒坑钨矿含矿韧性剪切带及其40Ar-39Ar年代学约束

摘要

Hukeng tungsten deposit is a large scale quartzs-veins-type tungsten deposit which locates at the Wugong Mountain in the west of Jiangxi Province. Besides the massive structure,the banded structure occurs widely in the ore-bearing quartz veins. Detailed field work and microscope research reveal that these banded quartz veins are actually ductile shear zones showing the characteristics of penetrative shear foliation,stretching lineation,shear lens and fractionated strip. The rock of the shear zone is quartz mylonite which is rich in plastic microstructure. The survey and statistic of micro-shearing direction-pointing structures indicate that the moving direction of both EW and NW-trending ductile shear zones are sinistral normal slipping,and near horizontal one,normal slipping. 40Ar-39Ar dating of new-generated sericites from mylonite in the NW-trending shear zone yields a plateau age of 140.3±1.0 Ma and an isochron age at 139.6±2.4 Ma respectively.But the plateau ages of EW-trending shear zone are complicated,as the high-temperature stage plateau age may be affected by muscovite remnant phenocryst which is formed in mineralization stage.The medium-temperature stage total gas age and apparent age are more close to the age of plateau age of sample HK121.It is concluded that the age of ductile shearing is about 140 Ma,indicating that ductile shearing deformation occurs after petrogenesis and mineralization.The banded quartz veins are formed by the ductile shearing of massive quartz veins.The formation mechanism of the ductile shearing may be related to sidelong intrusion of the later supplementary magma,but more reasonable model will be approved by further study and data.%江西省浒坑钨矿是一个大型石英脉黑钨矿矿床,含矿石英脉除了块状石英脉以外,还大量发育条带状石英脉.本文针对条带状石英脉进行了专门研究,认为条带状石英脉实质上是韧性剪切带,以透入性发育的剪切面理和拉伸线理、剪切透镜体、剪切分异条带普遍发育为特色.剪切带岩石以石英质糜棱岩为主,具有丰富的塑性变形显微构造特征.显微剪切指向构造统计表明,东西向和北西向脉组的运动方式均以左旋正滑为主,近水平脉组则以正滑为主.北西向韧性剪切带的新生绢云母40Ar-39Ar坪年龄为140.3±1.0 Ma,相应的等时线年龄为139.6±2.4 Ma;而东西向韧性剪切带绢云母40Ar-39Ar坪年龄则比较复杂,高温阶段年龄可能受到成矿期白云母残斑的影响,中温阶段的表观年龄和总气体年龄更接近前一样品的坪年龄.据此认为韧性剪切变形的年龄为140 Ma左右,韧性变形发生在成岩和成矿之后.条带状石英脉系块状石英脉韧性剪切改造而成,推测其形成主要与晚期补充岩体的斜向上侵作用有关,但更为合理的模式需要更多资料的进一步证实.